Method for manufacturing optical modulator, and optical modulator

Abstract

The present invention makes it easier to ensure that the relation between a second cladding layer and an optical waveguide material layer is as designed. This method for manufacturing an optical modulator (1) comprises a first substrate forming step and a bonding step. In the first substrate forming step, a first substrate (100) is formed. The first substrate (100) includes: a second cladding layer (7) having a planar main surface (701); and a support substrate (10). The first substrate (100) has a planar main surface (111). In the bonding step, a second substrate (200) is prepared, the second substrate (200) having a first main surface (211) and a planar second main surface (212), and in which an optical waveguide material that serves as the basis of an optical waveguide material layer (20) including an optical waveguide (2) is exposed on the second main surface (212), the main surface (111) of the first substrate (100) and the second main surface (212) of the second substrate (200) are arranged to face one another, and then the first substrate (100) and the second substrate (200) are bonded together.

Description

Method for manufacturing an optical modulator, and an optical modulator

[0001] The present invention generally relates to a method for manufacturing an optical modulator and an optical modulator, and more particularly to a method for manufacturing an optical modulator equipped with an optical waveguide and an optical modulator equipped with an optical waveguide.

[0002] Non-patent document 1 describes an optical modulator comprising an optical waveguide material layer having a first main surface and a second main surface and including an optical waveguide formed on the first main surface side, a signal electrode and a ground electrode arranged on both sides in the width direction of the optical waveguide on the first main surface of the optical waveguide material layer, and SiO covering the optical waveguide. ２ layer (SiO ２ Clad) and SiO ２ The present invention discloses an electro-optic modulator comprising a high dielectric constant material layer (high dielectric constant cladding) covering the layer.

[0003] Non-patent document 1 states that in an optical modulator equipped with a high dielectric constant cladding, SiO ２ It has been reported that compared to optical modulators with cladding only, the electric field strength within the optical waveguide is higher, and the figure of merit of the optical modulator, Vπ·L, is reduced.

[0004] Nuo Chen et al., High-efficiency electro-optic modulator on thin-film lithium niobate with high-permittivity cladding, Laser Photonics Rev. 2023, 17, 2200927

[0005] In the optical modulator disclosed in Non-Patent Document 1, a high-dielectric cladding (second cladding layer) is formed such that it covers a structure having an uneven shape that includes a signal electrode, an optical waveguide, and a ground electrode. However, the relationship between the second cladding layer and the optical waveguide material layer may not be as designed.

[0006] The object of the present invention is to provide a method for manufacturing an optical modulator and an optical modulator, in which the relationship between the second cladding layer and the optical waveguide material layer is more likely to be as designed.

[0007] A method for manufacturing an optical modulator according to one aspect of the present invention is a method for manufacturing an optical modulator comprising an optical waveguide material layer, a first electrode, a second electrode, a first cladding layer, a second cladding layer, and a support substrate. The optical waveguide material layer has a first main surface and a second main surface. The optical waveguide material layer includes an optical waveguide. The first electrode is spaced in the width direction from a first end in the width direction of the optical waveguide and is arranged along the optical propagation direction of the optical waveguide. The second electrode is spaced in the width direction from a second end in the width direction of the optical waveguide and is arranged along the optical propagation direction of the optical waveguide. A voltage is applied between the second electrode and the first electrode. The first cladding layer overlaps the optical waveguide in a plan view from the thickness direction of the optical waveguide material layer and is located on the second main surface of the optical waveguide material layer between the first electrode and the second electrode. The second cladding layer overlaps at least the first and second electrodes in a plan view from the thickness direction of the optical waveguide material layer and is located on the second main surface side of the optical waveguide material layer. The support substrate supports the second cladding layer. The refractive index of the first cladding layer is smaller than the refractive index of the optical waveguide. The dielectric constant of the second cladding layer is larger than the dielectric constant of the first cladding layer. The method for manufacturing the optical modulator comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate having a planar main surface is formed, including the second cladding layer having a planar main surface and the support substrate. In the bonding step, a second substrate is prepared having a first main surface and a planar second main surface, with the optical waveguide material that will become the optical waveguide material layer containing the optical waveguide exposed on the second main surface, and the first substrate and the second substrate are bonded together with the main surface of the first substrate and the second main surface of the second substrate facing each other.

[0008] An optical modulator according to one aspect of the present invention is an optical modulator manufactured by the above-described method for manufacturing an optical modulator.

[0009] An optical modulator according to one aspect of the present invention comprises an optical waveguide material layer, a first electrode, a second electrode, a first cladding layer, a second cladding layer, a support substrate, and a third cladding layer. The optical waveguide material layer has a first main surface and a second main surface. The optical waveguide material layer includes an optical waveguide formed on the first main surface side of the optical waveguide material layer. The first electrode is spaced in the width direction from a first end in the width direction of the optical waveguide and is arranged along the optical propagation direction of the optical waveguide. The second electrode is spaced in the width direction from a second end in the width direction of the optical waveguide and is arranged along the optical propagation direction of the optical waveguide, and a voltage is applied between it and the first electrode. The first cladding layer overlaps the optical waveguide in a plan view from the thickness direction of the optical waveguide material layer and is located on the second main surface of the optical waveguide material layer between the first electrode and the second electrode. The second cladding layer overlaps at least the first and second electrodes in a plan view of the optical waveguide material layer from the thickness direction and is located on the second main surface side of the optical waveguide material layer. The second cladding layer has a planar main surface. The support substrate supports the first and second cladding layers. The third cladding layer is in contact with the optical waveguide and has a refractive index smaller than that of the optical waveguide. The second main surface of the optical waveguide material layer is planar. The refractive index of the first cladding layer is smaller than that of the optical waveguide. The dielectric constant of the second cladding layer is greater than that of the first cladding layer and greater than that of the third cladding layer.

[0010] The method for manufacturing an optical modulator and the optical modulator of the present invention make it easier for the relationship between the second cladding layer and the optical waveguide material layer to be as designed.

[0011] Figure 1 is a partially broken perspective view showing an optical modulator according to Embodiment 1. Figure 2 is a partially broken plan view of the same optical modulator. Figure 3 is a cross-sectional view of the same optical modulator taken along line III-III in Figure 2. Figure 4 is a plan view of the main part of the same optical modulator. Figure 5 is a schematic diagram of the electric field lines generated in the same optical modulator. Figure 6 is an explanatory diagram for explaining the first to fourth steps in the manufacturing method of the same optical modulator. Figure 7 is an explanatory diagram for explaining the fifth to eighth steps in the manufacturing method of the same optical modulator. Figure 8 is a graph showing the relationship between the normalized slit width and the normalized Vπ・L. Figure 9 is a cross-sectional view of the main part of an optical modulator according to Modification 1 of Embodiment 1. Figure 10 is a distribution diagram showing the distribution of electric field lines generated in the same optical modulator. Figure 11 is a graph showing the relationship between the thickness of the second cladding layer and the normalized Vπ・L. Figure 12 is an explanatory diagram for explaining the sixth to eighth steps in the manufacturing method of an optical modulator according to Embodiment 2. Figure 13 is an explanatory diagram illustrating the sixth and seventh steps in the manufacturing method of an optical modulator according to Embodiment 3. Figure 14 is a partially broken perspective view showing an optical modulator according to Embodiment 4. Figure 15 is a cross-sectional view of the main part of the same optical modulator. Figure 16 is an explanatory diagram illustrating the first to fourth steps in the manufacturing method of the same optical modulator. Figure 17 is an explanatory diagram illustrating the fifth to eighth steps in the manufacturing method of the same optical modulator. Figure 18 is a partially broken cross-sectional view of an optical modulator according to a modified example of Embodiment 4. Figure 19 is an explanatory diagram illustrating the sixth to eighth steps in the manufacturing method of an optical modulator according to Embodiment 5. Figure 20 is an explanatory diagram illustrating the sixth and seventh steps in the manufacturing method of an optical modulator according to Embodiment 6. Figure 21 is a partially broken cross-sectional view of an optical modulator according to Embodiment 7. Figure 22 is an explanatory diagram illustrating the first to fourth steps in the manufacturing method of the same optical modulator. Figure 23 is an explanatory diagram illustrating the fifth to eighth steps in the manufacturing method of the same optical modulator. Figure 24 is a graph showing the relationship between the ratio of the relative permittivity of the second cladding layer to the relative permittivity of the first cladding layer and the normalized Vπ・L in the optical modulator described above. Figure 25 is a partially broken cross-sectional view of the optical modulator according to Modification 1 of Embodiment 7.Figure 26 is a graph showing the relationship between t0 / t1 and the normalized Vπ・L, where t1 is the thickness of the first portion of the second cladding layer that is in contact with the optical waveguide material layer, and t0 is the thickness of the second portion of the optical waveguide material layer that overlaps with the optical waveguide in the thickness direction of the optical waveguide material layer. Figure 27 is a partially broken cross-sectional view of an optical modulator according to a modification 2 of Embodiment 7. Figure 28 is a graph showing the relationship between W2 / W1 and the normalized Vπ・L, where W1 is the width of the second portion of the second cladding layer in a direction parallel to the width direction of the optical waveguide, W2 is the width of the thinned portion in a direction parallel to the width direction of the optical waveguide, and the ratio of the thickness of the thinned portion to the thickness of the first portion of the second cladding layer is a parameter. Figure 29 is a partially broken cross-sectional view of an optical modulator according to a modification 3 of Embodiment 7. Figure 30 is a partially broken cross-sectional view of an optical modulator according to a modification 4 of Embodiment 7. Figure 31 is an explanatory diagram for explaining the 6th to 8th steps in the manufacturing method of an optical modulator according to Embodiment 8. Figure 32 is an explanatory diagram illustrating the sixth and seventh steps in the manufacturing method of an optical modulator according to Embodiment 9. Figure 33 is a partially broken cross-sectional view of an optical modulator according to Embodiment 10. Figure 34 is a partially broken cross-sectional view of an optical modulator according to a modified example of Embodiment 10. Figure 35 is a partially broken cross-sectional view of an optical modulator according to Embodiment 11. Figure 36 is a partially broken cross-sectional view of an optical modulator according to Embodiment 12. Figure 37 shows a partially broken cross-sectional view of an optical modulator according to Embodiment 13. Figure 38 is a partially broken cross-sectional view of an optical modulator according to Embodiment 14. Figure 39 is an explanatory diagram illustrating the first to third steps in the manufacturing method of the optical modulator described above. Figure 40 is an explanatory diagram illustrating the fourth to sixth steps in the manufacturing method of the optical modulator described above. Figure 41 is an explanatory diagram illustrating the seventh to ninth steps in the manufacturing method of the optical modulator described above. Figure 42 is a partially broken cross-sectional view of an optical modulator according to Embodiment 15. Figure 43 is an explanatory diagram illustrating the first to fourth steps in the manufacturing method of an optical modulator according to Embodiment 16. Figure 44 is an explanatory diagram illustrating the fifth and sixth steps in the same manufacturing method of an optical modulator. Figure 45 is an explanatory diagram illustrating the first to fourth steps in the manufacturing method of an optical modulator according to Embodiment 17.Figure 46 is an explanatory diagram illustrating the fifth to seventh steps in the manufacturing method of the optical modulator described above. Figure 47 is an explanatory diagram illustrating the first to fourth steps in the manufacturing method of the optical modulator according to Embodiment 18. Figure 48 is an explanatory diagram illustrating the first to third steps in the manufacturing method of the optical modulator according to Embodiment 19. Figure 49 is an explanatory diagram illustrating the first to fourth steps in the manufacturing method of the optical modulator according to Embodiment 20. Figure 50 is an explanatory diagram illustrating the fifth to seventh steps in the manufacturing method of the optical modulator according to Embodiment 21. Figure 51 is a partially broken plan view of the optical modulator according to Embodiment 22. Figure 52 shows the optical modulator described above and is a cross-sectional view taken along the line XXXXXII-XXXXXII in Figure 51. Figure 53 shows the optical modulator described above and is a cross-sectional view taken along the line XXXXXIII-XXXXXIII in Figure 51. Figure 54 is a partially broken plan view of the optical modulator according to Embodiment 23. Figure 55 shows the optical modulator described above and is a cross-sectional view taken along the line XXXXXV-XXXXXV in Figure 54. Figure 56 shows the optical modulator described above, and is a cross-sectional view taken along the line XXXXXVI-XXXXXVI of Figure 54. Figure 57 is a partially broken plan view of the optical modulator according to Embodiment 24. Figure 58 shows the optical modulator described above, and is a cross-sectional view taken along the line XXXXXVIII-XXXXXVIII of Figure 57. Figure 59 shows the optical modulator described above, and is a cross-sectional view taken along the line XXXXXIX-XXXXXIX of Figure 57. Figure 60 shows the optical modulator described above, and is a cross-sectional view taken along the line XXXXXX-XXXXXX of Figure 57. Figure 61 is a partially broken plan view of the optical modulator according to Embodiment 25. Figure 62 shows the optical modulator described above, and is a cross-sectional view taken along the line XXXXXXII-XXXXXXII of Figure 61. Figure 63 shows the optical modulator described above, and is a cross-sectional view taken along the line XXXXXXIII-XXXXXXIII of Figure 61. Figure 64 shows the optical modulator described above, and is a cross-sectional view taken along the line XXXXXXIV-XXXXXXIV of Figure 61.

[0012] Embodiments 1 to 25 will be described below with reference to the drawings. The drawings referenced in Embodiments 1 to 25 below are schematic diagrams, and the size and thickness of the components shown in the drawings do not necessarily reflect the actual dimensions, nor do the ratios of size and thickness between components necessarily reflect the actual dimensional ratios. Furthermore, each drawing defines and represents a Cartesian coordinate system with three mutually orthogonal axes: the X, Y, and Z axes. The X, Y, and Z axes are all virtual axes, and the arrows indicating "X," "Y," and "Z" in the drawings are merely for illustrative purposes and do not represent actual objects.

[0013] (Embodiment 1) An optical modulator 1 according to Embodiment 1 will be described with reference to Figures 1 to 5, and a method for manufacturing the optical modulator 1 will be described with reference to Figures 6 and 7.

[0014] (1) Configuration of the optical modulator As shown in Figure 1, the optical modulator 1 comprises an optical waveguide material layer 20, two first electrodes 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, a support substrate 10, and a third cladding layer 3. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes two optical waveguides 2 formed on the first main surface 201 side. The two first electrodes 4 correspond one-to-one with the two optical waveguides 2. Each of the two first electrodes 4 is spaced in the width direction from the first end 21 in the width direction (direction parallel to the X axis) of the corresponding optical waveguide 2 and is arranged along the optical propagation direction (direction parallel to the Y axis) of the optical waveguide 2. The second electrode 5 is spaced in the width direction away from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The first cladding layer 6 overlaps the two optical waveguides 2 in a plan view from the thickness direction of the optical waveguide material layer 20 (plan view from the Z-axis direction) and is in contact with the second main surface 202 of the optical waveguide material layer 20 between each of the two first electrodes 4 and the second electrode 5. The second cladding layer 7 overlaps at least two of the first electrodes 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is in contact with the second main surface 202 of the optical waveguide material layer 20. The support substrate 10 supports the first cladding layer 6 and the second cladding layer 7. The third cladding layer 3 is in contact with the two optical waveguides 2. The refractive index of the third cladding layer 3 is smaller than the refractive index of each of the two optical waveguides 2. The refractive index of the first cladding layer 6 is smaller than the refractive index of each of the two optical waveguides 2. The dielectric constant of the second cladding layer 7 is larger than that of the first cladding layer 6 and larger than that of the third cladding layer 3. The refractive index of the second cladding layer 7 is smaller than that of the optical waveguide material layer 20.

[0015] In the following explanation, for the sake of clarity, when distinguishing between the two optical waveguides 2, the optical waveguide 2 on the left in Figure 1 may be referred to as the first optical waveguide 2, and the optical waveguide 2 on the right may be referred to as the second optical waveguide 2. Similarly, when distinguishing between the two first electrodes 4, the first electrode 4 on the left in Figure 1 may be referred to as the first signal electrode 4, and the first electrode 4 on the right may be referred to as the second signal electrode 4. In the optical modulator 1, in a plan view from the Z-axis direction, the first signal electrode 4, the first optical waveguide 2, the second electrode 5, the second optical waveguide 2, and the second signal electrode 4 are arranged in the order of first signal electrode 4, first optical waveguide 2, second electrode 5, second optical waveguide 2, and second signal electrode 4.

[0016] Furthermore, the optical modulator 1 further comprises a low dielectric constant layer 9. In the optical modulator 1, the optical waveguide material layer 20, which includes two optical waveguides 2, is supported on the support substrate 10 via a second cladding layer 7 and a low dielectric constant layer 9. In addition, as shown in Figure 4, the optical modulator 1 further includes, in addition to the two optical waveguides 2, a Y-shaped input optical waveguide 25 connected to the first end of the two optical waveguides 2 in the optical propagation direction, and a Y-shaped output optical waveguide 26 connected to the second end of the two optical waveguides 2 in the optical propagation direction. Note that the third cladding layer 3 is omitted from the illustration in Figure 4.

[0017] In the optical modulator 1, the first electrode 4 and the second electrode 5, which are positioned on both sides in the width direction of the optical waveguide 2, are two electrodes for controlling the light guiding the optical waveguide 2 located between the first electrode 4 and the second electrode 5. In the optical modulator 1 of this embodiment, the first electrode 4 is the signal electrode and the second electrode 5 is the ground electrode. In the optical modulator 1, a first voltage signal consisting of a digital signal is supplied from an external control device (not shown) to the first electrode 4 and the second electrode 5 on both sides of the first optical waveguide 2. In addition, in the optical modulator 1, a second voltage signal consisting of a digital signal is supplied from the control device to the first electrode 4 and the second electrode 5 on both sides of the second optical waveguide 2. If V0 is the voltage applied when there is no phase difference between the light passing through the first optical waveguide 2 and the light passing through the second optical waveguide 2, and V1 is the voltage when the phase difference is 180 degrees, then Vπ is Vπ = V1 - V0. In the optical modulator 1, if L (see Figure 4) is the length of the first electrode 4 and the second electrode 5 in the direction along the optical propagation direction of the optical waveguide 2, then the smaller the value of Vπ・L, the more it becomes possible to improve performance while miniaturizing the device.

[0018] (1.1) Support Substrate As shown in Figure 3, the support substrate 10 has a main surface 101. The support substrate 10 is rectangular in shape when viewed from the thickness direction of the support substrate 10, but is not limited to a rectangular shape; for example, it may be square. The support substrate 10 is, for example, a semiconductor substrate. The semiconductor substrate is, for example, a silicon substrate. The silicon substrate constituting the semiconductor substrate may be a silicon substrate doped with impurities, or an undoped silicon substrate. The semiconductor substrate is not limited to a silicon substrate; it may be an SOI (Silicon On Insulator) substrate or a CSOI (Cavity-SOI) substrate. Furthermore, the semiconductor substrate is not limited to a silicon substrate; for example, it may be a germanium substrate or a compound semiconductor substrate (for example, a GaAs substrate). Furthermore, the support substrate 10 is not limited to a semiconductor substrate; for example, it may be a sapphire substrate, a glass substrate, or a quartz substrate.

[0019] (1.2) Low dielectric constant layer The low dielectric constant layer 9 (see FIGS. 1 and 3) has a dielectric constant smaller than that of each of the two optical waveguides 2. As shown in FIG. 3, the low dielectric constant layer 9 is disposed on the main surface 101 of the support substrate 10. The low dielectric constant layer 9 is disposed, for example, so as to cover the entire main surface 101 of the support substrate 10.

[0020] The refractive index of the low dielectric constant layer 9 is smaller than that of each of the two optical waveguides 2. The material of the low dielectric constant layer 9 is, for example, SiO ２ . The material of the low dielectric constant layer 9 is SiO ２ and is not limited to this, and may be oxides such as Al ２ O ３ , LaAlO ３ , LaYO ３ , ZnO, HfO ２ , MgO, Y ２ O ３ etc., or polymers such as BCB (benzocyclobutene), PI (polyimide).

[0021] (1.3) First optical waveguide, second optical waveguide, input optical waveguide, output optical waveguide and optical waveguide material layer As shown in FIG. 1, in the present embodiment, each of the two optical waveguides 2 is a ridge type optical waveguide. In each of the two optical waveguides 2, the width W0 (see FIG. 2) of the optical waveguide 2 is larger than the thickness of the optical waveguide 2 (thickness in the direction along the Z axis). As shown in FIG. 4, each of the two optical waveguides 2 is long in the width direction (direction parallel to the X axis) with the short side direction. In the optical modulator 1 of the present embodiment, in a cross-sectional view orthogonal to the optical propagation direction of the two optical waveguides 2, the two optical waveguides 2 are symmetrically arranged around the second electrode 5. As shown in FIG. 4, in the present embodiment, the input optical waveguide 25, the second electrode 5, and the output optical waveguide 26 are arranged in this order: the input optical waveguide 25, the second electrode 5, and the output optical waveguide 26. Each of the input optical waveguide 25 and the output optical waveguide 26 is a ridge type optical waveguide.

[0022] As shown in Figure 3, the optical waveguide material layer 20 has a first main surface 201 and a second main surface 202 opposite to the first main surface 201. In the optical waveguide material layer 20, two optical waveguides 2 are formed on the side of the first main surface 201, while the second main surface 202 is planar. In the optical waveguide material layer 20, no convex structures such as optical waveguides 2 are formed on the second main surface 202, so the second main surface 202 is flatter than the first main surface 201. The second main surface 202 of the optical waveguide material layer 20 is in contact with the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7.

[0023] The material of the optical waveguide material layer 20 is, for example, lithium niobate (LiNbO ３ In this embodiment, the optical waveguide material layer 20 is a lithium niobate substrate. The material of the optical waveguide material layer 20 is not limited to lithium niobate, but can also be LiTaO ３ (Lithium tantalate), PLT (lead lanthanum titanate), PZT (lead titanium zirconate), PLZT (lead lanthanum zirconate titanate), KNbO ３ (Potassium niobate), BaTiO ３ (Barium titanate), KTN (Potassium niobate tantalate), SrTiO ３ (Strontium titanate), Bi ４ Ti ３ O １２ The material may be selected from the group consisting of bismuth titanate and electro-optic polymers (EO polymers).

[0024] (1.4) Two First and Second Electrodes In this embodiment, as shown in Figure 1, the two first electrodes 4 and the second electrode 5 are arranged on the first main surface 201 of the optical waveguide material layer 20. The two first electrodes 4 and the second electrode 5 are formed in predetermined patterns on the first main surface 201 of the optical waveguide material layer 20. In the optical modulator 1 of this embodiment, in a cross-sectional view perpendicular to the optical propagation direction of the two optical waveguides 2, the two first electrodes 4 are arranged symmetrically with respect to the second electrode 5. Each of the two first electrodes 4 and the second electrode 5 is elongated with the width direction of the optical waveguide 2 as its shorter side. In the optical propagation direction of the optical waveguide 2 (direction parallel to the Y-axis), the lengths of the two first electrodes 4 and the second electrode 5 are the same. "The lengths of the two first electrodes 4 and the second electrode 5 are the same" means that the lengths of each of the two electrodes (the two first electrodes 4 and the second electrode 5) do not necessarily have to be exactly the same as the length of the remaining electrode, but rather the lengths of the two electrodes do not necessarily have to be within the range of 90% to 110% of the length of the remaining electrode. In this embodiment, the thicknesses of the two first electrodes 4 and the second electrode 5 are the same. "The thicknesses of the two first electrodes 4 and the second electrode 5 are the same" means that the thicknesses of each of the two electrodes (the two first electrodes 4 and the second electrode 5) do not necessarily have to be exactly the same as the thickness of the remaining electrode, but rather the thicknesses of the two electrodes do not necessarily have to be within the range of 90% to 110% of the thickness of the remaining electrode. In this embodiment, the thickness of each of the two first electrodes 4 and the second electrode 5 is greater than the thickness of each of the two optical waveguides 2.

[0025] The two first electrodes 4 and the second electrode 5 are electrically conductive. The materials of the two first electrodes 4 and the second electrode 5 are, for example, aluminum, copper, platinum, gold, silver, titanium, nickel, chromium, molybdenum, tungsten, tantalum, magnesium, iron, or alloys mainly composed of any of these metals. The two first electrodes 4 and the second electrode 5 may also have a structure in which multiple metal films made of these metals or alloys are laminated.

[0026] (1.5) First cladding layer In this embodiment, as shown in Figure 1, the first cladding layer 6 overlaps the two optical waveguides 2 in a plan view from the thickness direction of the optical waveguide material layer 20, and is in contact with the second main surface 202 of the optical waveguide material layer 20 between each of the two first electrodes 4 and the second electrode 5.

[0027] The refractive index of the first cladding layer 6 is smaller than the refractive index of each of the two optical waveguides 2. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide material layer 20. The first cladding layer 6 is a low dielectric constant region having a dielectric constant smaller than that of the two optical waveguide material layers 20. The material of the first cladding layer 6 is, for example, SiO ２ The material of the first cladding layer 6 is SiO ２ Not limited to Al ２ O ３ , LaAlO ３ LaYO ３ ZnO, HfO ２ , MgO, Y ２ O ３ These may be oxides, polymers such as BCB (benzocyclobutene) and PI (polyimide).

[0028] (1.6) Second Cladding Layer In this embodiment, as shown in Figure 1, the second cladding layer 7 is arranged in contact with the second main surface 202 of the optical waveguide material layer 20. The second cladding layer 7 overlaps at least two first electrodes 4 and second electrodes 5 in a plan view from the thickness direction of the optical waveguide material layer 20. The second cladding layer 7 faces the two first electrodes 4 and second electrodes 5 via the optical waveguide material layer 20. The dielectric constant of the second cladding layer 7 is greater than that of the optical waveguide 2. The second cladding layer 7 is a high dielectric constant layer having a higher dielectric constant than the optical waveguide material layer 20 and the first cladding layer 6.

[0029] The material of the second cladding layer 7 is SrTiO ３ (Strontium titanate), BaTiO ３ (Barium titanate), PbLaTiO ３ (Lead lanthanum titanate), PZT (Lead titanium zirconate), PLZT (Lead titanium lanthanum zirconate), LiNbO ３ (Lithium niobate), LiTaO ３(Lithium tantalate), KNbO ３ (Potassium niobate), PbTiO ３ (Lead titanate), PKNO (lead potassium niobate), PMN (lead magnesium niobate), Bi ４ Ti ３ O １２ (Bismuth titanate), BST (Barium strontium titanate), KLN (Potassium lanthanum niobate), Al ２ O ３ , LaAlO ３ LaYO ３ ZnO, HfO ２ , MgO, Y ２ O ３ , TiO ２ Ta ２ O ５ The material is selected from the group consisting of SiN and ALN. The material of the second cladding layer 7 may be any material having a higher dielectric constant than the materials of the third cladding layer 3, the first cladding layer 6, and the low dielectric constant layer 9.

[0030] The second cladding layer 7 has two slits 72 that overlap each of the two optical waveguides 2 in the thickness direction of the optical waveguide material layer 20. The two slits 72 penetrate the second cladding layer 7 in the thickness direction of the optical waveguide material layer 20. In the optical modulator 1 of this embodiment, as shown in Figure 3, the width W1 of the slits 72 in the second cladding layer 7 is wider than the width W0 of the optical waveguide 2 (first optical waveguide 2). The width W1 of the slits 72 is the width of the slits 72 in the width direction of the optical waveguide 2. In the optical modulator 1 of this embodiment, as shown in Figure 1, the first cladding layer 6 is located inside each of the two slits 72 in the second cladding layer 7. In this embodiment, as shown in Figure 3, the planar main surface 701 of the second cladding layer 7 and the planar main surface 601 of the first cladding layer 6 are in contact with the planar second main surface 202 of the optical waveguide material layer 20. The second cladding layer 7 has a surface 702 opposite to the main surface 701.

[0031] As shown in Figures 1 and 3, the second cladding layer 7 has a portion 74 that overlaps with the first electrode 4 in the direction along the thickness direction of the optical waveguide material layer 20, and a portion 75 that overlaps with the second electrode 5 in the direction along the thickness direction of the optical waveguide material layer 20.

[0032] (1.7) Third Cladding Layer As shown in Figures 1 and 3, the third cladding layer 3 is arranged on the first main surface 201 of the optical waveguide material layer 20 so as to cover the two optical waveguides 2. The third cladding layer 3 is in contact with the first main surface 201 of the optical waveguide material layer 20 and the two first electrodes and the second electrode 5. In this embodiment, the third cladding layer 3 covers the region on the first main surface 201 of the optical waveguide material layer 20 that is not in contact with either of the two first electrodes 4 and the second electrode 5, as well as the two first electrodes 4 and the second electrode 5.

[0033] The refractive index of the third cladding layer 3 is smaller than the refractive index of each of the two optical waveguides 2. The refractive index of the third cladding layer 3 is smaller than the refractive index of the optical waveguide material layer 20. The third cladding layer 3 is a low dielectric constant region having a dielectric constant smaller than the dielectric constant of each of the two optical waveguides 2. The material of the third cladding layer 3 is, for example, SiO ２ The material of the third cladding layer 3 is SiO ２ Not limited to Al ２ O ３ , LaAlO ３ LaYO ３ ZnO, HfO ２ , MgO, Y ２ O ３ These may be oxides, polymers such as BCB (benzocyclobutene) and PI (polyimide). In this embodiment, the material of the third cladding layer 3 is the same as the material of the first cladding layer 6, but the material of the third cladding layer 3 may be different from the material of the first cladding layer 6.

[0034] (2) Electric field during operation of the optical modulator In the optical modulator 1 of this embodiment, when a voltage is applied between the first electrode 4 and the second electrode 5, as shown in Figure 5, the electric field lines passing through the second cladding layer 7 (electric field line e1 in Figure 5) bend and enter the optical waveguide 2 more easily, making it possible to increase the electric field strength in the optical waveguide 2. In the example in Figure 5, the electric field line e1 reaches the second electrode 5 from the first electrode 4 through the optical waveguide material layer 20, the second cladding layer 7, the optical waveguide material layer 20, the optical waveguide 2, the optical waveguide material layer 20 and the second cladding layer 7. As electric field line e1, there is also an electric field line that reaches the second electrode 5 from the first electrode 4 through the optical waveguide material layer 20, the second cladding layer 7, the optical waveguide material layer 20, the third cladding layer 3, the optical waveguide 2, the third cladding layer 3, the optical waveguide material layer 20 and the second cladding layer 7.

[0035] (3) Method for manufacturing an optical modulator The method for manufacturing the optical modulator 1 according to Embodiment 1 will be described below with reference to Figures 6 and 7.

[0036] In the manufacturing method of the optical modulator 1 according to Embodiment 1, for example, steps 1 to 8 are performed sequentially.

[0037] In the first step, a support substrate 10 is prepared, and a low dielectric constant layer 9 is formed on the main surface 101 of the support substrate 10 to obtain a substrate S1 with the structure shown in Figure 6(a). As a method for forming the low dielectric constant layer 9, for example, the CVD (Chemical Vapor Deposition) method can be used. Note that the support substrate 10 is a silicon substrate and the material of the low dielectric constant layer 9 is SiO ２ In this case, for example, a CVD method or a thermal oxidation method can be used as a method for forming the low dielectric constant layer 9.

[0038] In the second step, a substrate S2 having the structure shown in Figure 6(b) is obtained by forming a second cladding material layer 70 on the low dielectric constant layer 9. The second cladding material layer 70 is the base layer for the second cladding layer 7. The material of the second cladding material layer 70 is the same as the material of the second cladding layer 7. As a method for forming the second cladding material layer 70, for example, sputtering, vapor deposition, or CVD can be employed.

[0039] In the third step, the second cladding material layer 70 is patterned to form the second cladding layer 7, thereby obtaining a substrate S3 with the structure shown in Figure 6(c). In the third step, the second cladding layer 7 is formed by creating slits 72 in the second cladding material layer 70 using, for example, photolithography and etching techniques. As the etching technique, for example, dry etching or wet etching techniques can be employed.

[0040] In the fourth step, a substrate S4 having the structure shown in Figure 6(d) is obtained by forming a first cladding material layer 60 that covers the low dielectric constant layer 9 and the second cladding layer 7. The first cladding material layer 60 is the base layer for the first cladding layer 6. The material of the first cladding material layer 60 is the same as the material of the first cladding layer 6. The material of the first cladding material layer 60 is the same as the material of the low dielectric constant layer 9, but it may be different from the material of the low dielectric constant layer 9. As a method for forming the first cladding material layer 60, for example, the CVD method can be used. The main surface 600 of the first cladding material layer 60 formed in the fourth step has an uneven shape due to the shape of the substrate of the first cladding material layer 60.

[0041] In the fifth step, the outermost surface of the substrate S4 is flattened from the main surface 600 side of the first cladding material layer 60 to form the first cladding layer 6 and expose the second cladding layer 7, thereby obtaining a substrate S5 with the structure shown in Figure 7(a). The first cladding layer 6 is a part of the first cladding material layer 60. In the fifth step, the first cladding material layer 60 is subjected to CMP (Chemical Mechanical Polishing) from the main surface 600 side of the first cladding material layer 60 to obtain a substrate S5 with the structure shown in Figure 7(a). In the substrate S5, the main surface (outermost surface) composed of the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7 is planar. In the substrate S5, the main surface 701 of the second cladding layer 7 and the main surface 601 of the first cladding layer 6 are flush. In the fifth step, instead of CMPing the first cladding material layer 60, the first cladding material layer 60 may be etched back to form the first cladding layer 6 and expose the second cladding layer 7. The substrate S5 includes the first cladding layer 6, the second cladding layer 7 having a greater dielectric constant than the first cladding layer 6, and the support substrate 10 supporting the first cladding layer 6 and the second cladding layer 7, and the outermost surface, including the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer, is planarized. In this embodiment, the substrate S5 constitutes the first substrate 100. The first substrate 100 has a planar main surface 111 including the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer. In this embodiment, the first substrate formation step for forming the first substrate 100 includes the first to fifth steps.

[0042] In the sixth step, a second substrate 200 is prepared, and the first substrate 100 and the second substrate 200 are joined to obtain a substrate S6 having the structure shown in Figure 7(b). The second substrate 200 has a first main surface 211 and a second main surface 212. The optical waveguide material is exposed on the second main surface 212 of the second substrate 200. In the sixth step, the main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are faced towards each other, and then the first substrate 100 and the second substrate 200 are joined. As a joining method for joining the first substrate 100 and the second substrate 200, for example, a direct joining method is employed, and as a direct joining method, for example, a room temperature joining method can be employed. The joining temperature in the direct joining method is not limited to room temperature (for example, 20°C to 27°C), but may also be a temperature higher than room temperature (for example, 50°C to 100°C). In this embodiment, the sixth step constitutes the bonding step. Also in this embodiment, the second substrate 200 is an optical waveguide material substrate formed of an optical waveguide material. "Optical waveguide material" means the material of the optical waveguide 2, and "optical waveguide material substrate" is the substrate that forms the basis of the optical waveguide material layer 20. For example, the material of the optical waveguide 2 is lithium niobate (LiNbO ３ In this case, the optical waveguide material substrate is a lithium niobate substrate that is thicker than the optical waveguide material layer 20.

[0043] In the seventh step, the second substrate 200 is thinned by grinding or the like to obtain a substrate S7 with the structure shown in Figure 7(c).

[0044] In the eighth step, the thinned second substrate 200 is processed to form an optical waveguide material layer 20 containing two optical waveguides 2, then two first electrodes 4 and a second electrode 5 are formed on the first main surface 201 of the optical waveguide material layer 20, and then a third cladding layer 3 is formed to obtain a substrate S8 with the structure shown in Figure 7(d).

[0045] In the manufacturing method of the optical modulator 1 of this embodiment, the support substrate 10 prepared in the first step is a wafer (for example, a silicon wafer), and the substrates S1 to S8 are wafers having different structures from each other. In the manufacturing method of the optical modulator 1 of this embodiment, by performing each of the steps from the first to the eighth step, a wafer containing multiple optical modulators 1 can be obtained as the substrate S8. In the manufacturing method of the optical modulator 1 of this embodiment, after the eighth step, multiple optical modulators 1 can be obtained by cutting the substrate S8 with, for example, a dicing saw or a laser dicing device.

[0046] (4) Performance of the optical modulator Figure 8 is a graph showing the relationship between W1 / W0 and the normalized Vπ・L. In Figure 8, the horizontal axis is W1 / W0 and the vertical axis is {(Vπ・L) / (Vπ・L0)} × 100. In Figure 8, Vπ・L0 is the value of Vπ・L for the comparative example in which the second cladding layer (high dielectric constant layer) is not provided on the second main surface of the optical waveguide material layer, and the second cladding layer is provided on the first main surface of the optical waveguide material layer. Therefore, the vertical axis of Figure 8 is Vπ・L normalized with the value of Vπ・L0 for the comparative example set to 100.

[0047] As can be seen from Figure 8, when W1 / W0 is greater than 0.4 and less than 2.4, it is possible to reduce Vπ・L compared to the comparative example. Furthermore, when W1 / W0 is between 0.6 and 1.7, it is possible to reduce Vπ・L by 10% or more.

[0048] Furthermore, as can be seen from Figure 8, when W1 / W0 is 1, Vπ・L can be reduced compared to when W1 / W0 is different from 1. More specifically, as shown in Figure 9, in the relationship between the slit 72 and the optical waveguide 2 that overlap in the thickness direction of the optical waveguide material layer 20, when the width W1 of the slit 72 is the same as the width W0 of the optical waveguide 2, Vπ・L can be reduced compared to when the width W1 of the slit 72 is different from the width W0 of the optical waveguide 2.

[0049] When W1 / W0 is set to 1, as shown in Figure 10, the electric field lines passing through the second cladding layer 7 between the first electrode 4 and the second electrode 5 bend and enter the optical waveguide 2 more easily, thereby increasing the electric field strength of the optical waveguide 2 and reducing Vπ・L.

[0050] Furthermore, in a cross-sectional view perpendicular to the optical propagation direction of the optical waveguide 2, as shown in Figure 9, when the thickness of the second cladding layer 7 is t1, it is preferable that the thickness t1 is 0.11 μm or more.

[0051] Figure 11 is a graph showing the relationship between the thickness t1 of the second cladding layer 7 and the normalized Vπ・L in an example where the width W1 of the slit 72 is the same as the width W0 of the optical waveguide 2. In Figure 11, the horizontal axis is the thickness t1, and the vertical axis is {(Vπ・L) / (Vπ・L0)} × 100. Vπ・L0 is the value of Vπ・L when t1 = 0. Therefore, the vertical axis of Figure 11 is Vπ・L normalized by setting the value of Vπ・L0 to 100 when there is no second cladding layer (high dielectric constant layer) and the first cladding layer (low dielectric constant layer) is in contact with the entire second main surface of the optical waveguide material layer.

[0052] From Figure 11, it can be seen that when W1 = W0, if the thickness t1 of the second cladding layer 7 is 0.11 μm or more, Vπ・L can be reduced by 10% or more.

[0053] (5) The method for manufacturing the optical modulator 1 according to the first embodiment is a method for manufacturing the optical modulator 1 comprising an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 side of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator 1 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate 100 is formed which includes a second cladding layer 7 having a planar main surface 701 and a support substrate 10 and has a planar main surface 111. In the bonding process, a second substrate 200 is prepared, having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate 100 and the second substrate 200 are bonded together.

[0054] According to the above configuration, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed. More specifically, according to the above configuration, after forming a first substrate 100 having a planar main surface 111 including the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7, a second substrate 200 is prepared with the optical waveguide material exposed on a planar second main surface 212, and the first substrate 100 and the second substrate 200 are joined together with the main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 facing each other, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed, and it is easier to bring the second cladding layer 7 and the optical waveguide material layer 20 into contact. Furthermore, the optical modulator 1 according to Embodiment 1 can employ the above-described method for manufacturing the optical modulator 1, so the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed. Furthermore, in the manufacturing method of the optical modulator 1 according to Embodiment 1, the first substrate 100 further includes a first cladding layer 6, and the first cladding layer 6 is supported by a support substrate 10. The main surface 111 of the first substrate 100 includes the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7. The second substrate 200 is an optical waveguide material substrate 200 formed of an optical waveguide material. After the bonding process, an optical waveguide material layer 20 including an optical waveguide 2 is formed by processing the optical waveguide material substrate 200. According to this manufacturing method, the optical waveguide 2 can be formed after the bonding process.

[0055] Furthermore, in the manufacturing method of the optical modulator 1 according to Embodiment 1, the second cladding layer 7 has a slit 72 formed in the thickness direction of the optical waveguide material layer 20 that overlaps with the optical waveguide 2. The slit 72 penetrates the second cladding layer 7 in the thickness direction of the optical waveguide material layer 20. The first cladding layer 6 is located inside the slit 72 of the second cladding layer 7.

[0056] According to the above configuration, when a voltage is applied between the first electrode 4 and the second electrode 5 on both sides of the optical waveguide 2 in the optical modulator 1, the electric field concentration in the region overlapping the optical waveguide 2 in the second cladding layer 7 can be mitigated, the electric field strength in the optical waveguide 2 can be increased, and Vπ・L can be reduced.

[0057] Furthermore, in the manufacturing method of the optical modulator 1 according to Embodiment 1, the thickness t1 of the second cladding layer 7 is 0.11 μm or more.

[0058] With the above configuration, it is possible to reduce the Vπ·L of the optical modulator 1 by 10% or more.

[0059] (Embodiment 2) The configuration of the optical modulator 1 according to Embodiment 2 is the same as the configuration of the optical modulator 1 according to Embodiment 1 shown in Figures 1 to 4, so the explanation will be omitted.

[0060] The method for manufacturing the optical modulator 1 according to Embodiment 2 will be described below with reference to Figures 6, 7, and 12. In the method for manufacturing the optical modulator 1 of this embodiment, the first to fifth steps for forming the first substrate 100 (see Figure 7(a)) are the same as the method for manufacturing the optical modulator 1 of Embodiment 1 (see Figures 6(a), 6(b), 6(c), 6(d), and 7(a)), so the explanation will be omitted.

[0061] In the method for manufacturing the optical modulator 1 according to Embodiment 2, the configuration of the first substrate 100 is the same as the configuration of the first substrate 100 in the method for manufacturing the optical modulator 1 according to Embodiment 1, and as shown in Figure 12(a), the configuration of the second substrate 200 differs from the configuration of the second substrate 200 used in the method for manufacturing the optical modulator 1 according to Embodiment 1 (see Figure 7(b)). The second substrate 200 prepared in this embodiment includes a second support substrate 230 which is different from the first support substrate 10 which is the support substrate 10, and an optical waveguide material thin film 220 which is laminated on the second support substrate 230 and formed of an optical waveguide material.

[0062] In this embodiment, after the fifth step, in the sixth step, a second substrate 200 having a second support substrate 230 and an optical waveguide material thin film 220 which will become the optical waveguide material layer 20 is joined to the first substrate 100 to obtain a substrate S16 with the structure shown in Figure 12(a). The material of the optical waveguide material thin film 220 is the same as the material of the optical waveguide material layer 20. In the second substrate 200 of this embodiment, the main surface of the second support substrate 230 that is not in contact with the optical waveguide material thin film 220 constitutes the first main surface 211 of the second substrate 200, and the main surface of the optical waveguide material thin film 220 that is not in contact with the second support substrate 230 constitutes the planar second main surface 212 of the second substrate 200.

[0063] In this embodiment, in the seventh step following the sixth step, the second support substrate 230 is removed from the substrate S16 to obtain a substrate S7 having the structure shown in Figure 12(b).

[0064] In this embodiment, in the eighth step, the optical waveguide material thin film 220 of the substrate S7 is processed to form an optical waveguide material layer 20 containing two optical waveguides 2, then two first electrodes 4 and a second electrode 5 are formed on the first main surface 201 of the optical waveguide material layer 20, and then a third cladding layer 3 is formed to obtain a substrate S8 with the structure shown in Figure 12(c).

[0065] In the manufacturing method of the optical modulator 1 of this embodiment, the support substrate 10 prepared in the first step is a wafer (for example, a silicon wafer), and the substrates S1 to S5, S16, S7, and S8 are wafers having different structures from each other. In the manufacturing method of the optical modulator 1 of this embodiment, by performing each of the steps from the first to the eighth step, a wafer containing multiple optical modulators 1 can be obtained as the substrate S8. In the manufacturing method of the optical modulator 1 of this embodiment, after the eighth step, multiple optical modulators 1 can be obtained by cutting the substrate S8 with, for example, a dicing saw or a laser dicing device.

[0066] The manufacturing method for the optical modulator 1 according to Embodiment 2 is a method for manufacturing the optical modulator 1 comprising an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 side of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator 1 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate 100 is formed which includes a second cladding layer 7 having a planar main surface 701 and a support substrate 10 and has a planar main surface 111. In the joining process, a second substrate 200 is prepared having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate 100 and the second substrate 200 are joined together. According to the manufacturing method of the optical modulator 1 of Embodiment 2, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed. Furthermore, since the optical modulator 1 of Embodiment 2 can employ the above-described manufacturing method of the optical modulator 1, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0067] Furthermore, in the manufacturing method of the optical modulator 1 according to Embodiment 2, the first substrate 100 further includes a first cladding layer 6, and the first cladding layer 6 is supported by a support substrate 10. The main surface 111 of the first substrate 100 includes the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7. The second substrate 200 has a second support substrate 230 which is different from the first support substrate 10 which is the support substrate 10, and an optical waveguide material thin film 220 which is laminated on the second support substrate 230 and becomes the basis of the optical waveguide material layer 20. After the bonding process, the second support substrate 230 is removed and the optical waveguide material thin film 220 is processed to form the optical waveguide material layer 20 which includes the optical waveguide 2. According to this manufacturing method, the optical waveguide 2 can be formed after the bonding process.

[0068] (Embodiment 3) The configuration of the optical modulator 1 according to Embodiment 3 is the same as the configuration of the optical modulator 1 according to Embodiment 1 shown in Figures 1 to 4, so the explanation will be omitted.

[0069] The method for manufacturing the optical modulator 1 according to Embodiment 3 will be described below with reference to Figures 6, 7, and 13. In the method for manufacturing the optical modulator 1 of this embodiment, the first to fifth steps for forming the first substrate 100 (see Figure 7(a)) are the same as the method for manufacturing the optical modulator 1 of Embodiment 1 (see Figures 6(a), 6(b), 6(c), 6(d), and 7(a)), so the explanation will be omitted.

[0070] In the manufacturing method of the optical modulator 1 according to Embodiment 3, the configuration of the first substrate 100 is the same as the configuration of the first substrate 100 in the manufacturing method of the optical modulator 1 according to Embodiment 1, and as shown in Figure 13(a), the configuration of the second substrate 200 differs from the configuration of the second substrate 200 used in the manufacturing method of the optical modulator 1 according to Embodiment 1 (see Figure 7(b)). The second substrate 200 prepared in this embodiment includes an optical waveguide material layer 20 containing an optical waveguide 2, two first electrodes 4 (only one first electrode 4 is shown in Figure 13(a)) and a second electrode 5, a third cladding layer 3, and a second support substrate 230 which is different from the first support substrate 10 which is a support substrate.

[0071] In this embodiment, after the fifth step, in the sixth step, the main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are placed facing each other as shown in Figure 13(a), and then the first substrate 100 and the second substrate 200 are joined to obtain a substrate S26 with the structure shown in Figure 13(b). In the second substrate 200 of this embodiment, the main surface of the second support substrate 230 that is not in contact with the third cladding layer 3 constitutes the first main surface 211 of the second substrate 200, and the second main surface 202 of the optical waveguide material layer 20 constitutes the planar second main surface 212 of the second substrate 200.

[0072] In this embodiment, in the seventh step following the sixth step, the second support substrate 230 is removed from the substrate S26 to obtain a substrate S8 having the structure shown in Figure 13(c).

[0073] In the manufacturing method of the optical modulator 1 of this embodiment, the support substrate 10 prepared in the first step is a wafer (for example, a silicon wafer), and the substrates S1 to S5, S26, and S8 are wafers having different structures from each other. In the manufacturing method of the optical modulator 1 of this embodiment, by performing each of the steps from the first to the seventh step, a wafer containing multiple optical modulators 1 can be obtained as the substrate S8. In the manufacturing method of the optical modulator 1 of this embodiment, after the seventh step, multiple optical modulators 1 can be obtained by cutting the substrate S8 with, for example, a dicing saw or a laser dicing device.

[0074] The manufacturing method for the optical modulator 1 according to Embodiment 3 is a method for manufacturing the optical modulator 1 comprising an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 side of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator 1 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate 100 is formed which includes a second cladding layer 7 having a planar main surface 701 and a support substrate 10 and has a planar main surface 111. In the joining process, a second substrate 200 is prepared, having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate 100 and the second substrate 200 are joined together. According to the manufacturing method of the optical modulator 1 of Embodiment 3, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed. Furthermore, since the optical modulator 1 of Embodiment 3 can employ the above-described manufacturing method of the optical modulator 1, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0075] Furthermore, in the manufacturing method of the optical modulator 1 according to Embodiment 3, the first substrate 100 further includes a first cladding layer 6, and the first cladding layer 6 is supported by a support substrate 10. The main surface 111 of the first substrate 100 includes the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7. The second substrate 200 has an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a third cladding layer 3, and a second support substrate 230 which is different from the first support substrate 10, which is the support substrate 10. The optical waveguide material layer 20 includes an optical waveguide 2. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2, and a voltage is applied between it and the first electrode 4. The third cladding layer 3 is in contact with the optical waveguide 2 and has a refractive index smaller than that of the optical waveguide 2. The second support substrate 230 overlaps the third cladding layer 3. After the bonding process, the second support substrate 230 is removed. According to this manufacturing method, the optical waveguide 2 can be formed before the bonding process.

[0076] (Embodiment 4) The optical modulator 1A according to Embodiment 4 will be described with reference to Figures 14 and 15, and the method for manufacturing the optical modulator 1A will be described with reference to Figures 16 and 17. With respect to the optical modulator 1A according to Embodiment 4, components that are the same as those in the optical modulator 1 according to Embodiment 1 (see Figures 1 to 4) are denoted by the same reference numerals and their description is omitted.

[0077] (1) Configuration of the optical modulator In the optical modulator 1A according to Embodiment 4, the two slits 72 formed in the second cladding layer 7 do not penetrate the second cladding layer 7 in the thickness direction of the optical waveguide material layer 20. The two first cladding layers 6 correspond to the two slits 72. Each of the two first cladding layers 6 is located inside the corresponding slit 72. In the second cladding layer 7 of this embodiment, the thickness of the portion 712 (hereinafter also referred to as the second portion 712) that overlaps with the optical waveguide 2 in the thickness direction of the optical waveguide material layer 20 and is separated from the second main surface 202 of the optical waveguide material layer 20 is thinner than the thickness of the portion 711 (hereinafter also referred to as the first portion 711) that is in contact with the second main surface 202 of the optical waveguide material layer 20.

[0078] The first cladding layer 6 is interposed between the second main surface 202 of the optical waveguide material layer 20 and the second portion 712 of the second cladding layer 7 in the thickness direction of the optical waveguide material layer 20. The first cladding layer 6 is in contact with the second main surface 202 of the optical waveguide material layer 20. In this embodiment, the thickness of the first cladding layer 6 is thinner than the thickness of the first portion 711 of the second cladding layer 7 that is in contact with the second main surface 202 of the optical waveguide material layer 20.

[0079] (2) Method for manufacturing an optical modulator The method for manufacturing the optical modulator 1A according to Embodiment 4 will be described below with reference to Figures 16 and 17.

[0080] In the manufacturing method of the optical modulator 1A according to Embodiment 4, for example, steps 1 to 8 are performed sequentially. Regarding the manufacturing method of the optical modulator 1A according to Embodiment 4, steps similar to those in the manufacturing method of the optical modulator 1 according to Embodiment 1 will be omitted from explanation as appropriate.

[0081] In the first step, a support substrate 10 is prepared, and a low dielectric constant layer 9 is formed on the main surface 101 of the support substrate 10 to obtain a substrate S1 with the structure shown in Figure 16(a).

[0082] In the second step, a substrate S2 having the structure shown in Figure 16(b) is obtained by forming a second cladding material layer 70 on the low dielectric constant layer 9. The second cladding material layer 70 is the base layer for the second cladding layer 7.

[0083] In the third step, the second cladding material layer 70 is patterned to form the second cladding layer 7, thereby obtaining a substrate S3 with the structure shown in Figure 16(c). In the third step, the second cladding layer 7 is formed by creating slits 72 (in the illustrated example, slits 72 that do not penetrate the second cladding material layer 70) in the second cladding material layer 70 using, for example, photolithography and etching techniques. As the etching technique, for example, dry etching or wet etching techniques can be employed.

[0084] In the fourth step, a substrate S4 having the structure shown in Figure 16(d) is obtained by forming a first cladding material layer 60 that covers the second cladding layer 7. The first cladding material layer 60 is the base layer for the first cladding layer 6. The main surface 600 of the first cladding material layer 60 formed in the fourth step has an uneven shape resulting from the shape of the second cladding layer 7, which is the base shape of the first cladding material layer 60.

[0085] In the fifth step, the outermost surface of the substrate S4 is planarized from the main surface 600 side of the first cladding material layer 60 to form the first cladding layer 6 and expose the second cladding layer 7, thereby obtaining a substrate S5 with the structure shown in Figure 17(a). The first cladding layer 6 is a part of the first cladding material layer 60. In the substrate S5, the main surface (outermost surface) composed of the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7 is planar. The substrate S5 includes the first cladding layer 6, the second cladding layer 7 having a larger dielectric constant than the first cladding layer 6, and a support substrate 10 supporting the first cladding layer 6 and the second cladding layer 7, and the outermost surface including the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer is planarized. In this embodiment, the substrate S5 constitutes the first substrate 100. The first substrate 100 has a planar main surface 111 that includes the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer. In this embodiment, the first substrate forming step for forming the first substrate 100 includes steps 1 to 5.

[0086] In the sixth step, a second substrate 200 is prepared, and the first substrate 100 and the second substrate 200 are joined to obtain a substrate S6 having the structure shown in Figure 17(b). The second substrate 200 has a first main surface 211 and a second main surface 212. The optical waveguide material is exposed on the second main surface 212 of the second substrate 200. In the sixth step, the main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are faced towards each other, and then the first substrate 100 and the second substrate 200 are joined. In this embodiment, the sixth step constitutes the joining process. In this embodiment, the second substrate 200 is an optical waveguide material substrate formed from an optical waveguide material.

[0087] In the seventh step, the second substrate 200 is thinned by grinding or the like to obtain a substrate S7 with the structure shown in Figure 17(c).

[0088] In the eighth step, the thinned second substrate 200 is processed to form an optical waveguide material layer 20 containing two optical waveguides 2 (only one optical waveguide 2 is shown in Figure 17). Then, two first electrodes 4 (only one first electrode 4 is shown in Figure 17) and a second electrode 5 are formed on the first main surface 201 of the optical waveguide material layer 20. After that, a third cladding layer 3 is formed to obtain a substrate S8 with the structure shown in Figure 17(d).

[0089] In the manufacturing method of the optical modulator 1A of this embodiment, the support substrate 10 prepared in the first step is a wafer (for example, a silicon wafer), and the substrates S1 to S8 are wafers having different structures from each other. In the manufacturing method of the optical modulator 1A of this embodiment, by performing each of the steps from the first to the eighth step, a wafer containing multiple optical modulators 1A can be obtained as the substrate S8. In the manufacturing method of the optical modulator 1A of this embodiment, after the eighth step, multiple optical modulators 1A can be obtained by cutting the substrate S8 with, for example, a dicing saw or a laser dicing device.

[0090] (3) The method for manufacturing an optical modulator 1A according to the 4th embodiment is a method for manufacturing an optical modulator 1A comprising an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the side of the second main surface 202 of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator 1A comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate 100 is formed which includes a second cladding layer 7 having a planar main surface 701 and a support substrate 10 and has a planar main surface 111. In the joining process, a second substrate 200 is prepared, having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate 100 and the second substrate 200 are joined together. According to the manufacturing method of the optical modulator 1A of Embodiment 4, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed. Furthermore, since the optical modulator 1A of Embodiment 4 can employ the above-described manufacturing method of the optical modulator 1A, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0091] Furthermore, in the manufacturing method of the optical modulator 1A according to Embodiment 4, the first substrate 100 further includes a first cladding layer 6, and the first cladding layer 6 is supported by a support substrate 10. The main surface 111 of the first substrate 100 includes the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7. The second substrate 200 is an optical waveguide material substrate 200 formed of an optical waveguide material. After the bonding process, an optical waveguide material layer 20 including an optical waveguide 2 is formed by processing the optical waveguide material substrate 200. According to this manufacturing method, the optical waveguide 2 can be formed after the bonding process.

[0092] (4) Modification of Embodiment 4 The optical modulator 1A according to the modification of Embodiment 4 will be described with reference to Figure 18. With respect to the optical modulator 1A according to the modification of Embodiment 4, components that are the same as those in the optical modulator 1A according to Embodiment 4 (see Figures 14 and 15) are denoted by the same reference numerals and their description is omitted.

[0093] The optical modulator 1A according to a modified embodiment of Embodiment 4 differs from the optical modulator 1A according to Embodiment 4 in that, in a direction parallel to the width direction of the optical waveguide 2, the width of the optical waveguide 2, the width of the first cladding layer 6, and the width of the second portion 712 of the second cladding layer 7 are the same.

[0094] The method for manufacturing the optical modulator 1A according to a modified example of Embodiment 4 is the same as the method for manufacturing the optical modulator 1A according to Embodiment 4.

[0095] (Embodiment 5) The configuration of the optical modulator 1A according to Embodiment 5 is the same as the configuration of the optical modulator 1A according to Embodiment 4 shown in Figures 14 and 15, so the explanation will be omitted.

[0096] The method for manufacturing the optical modulator 1A according to Embodiment 5 will be described below with reference to Figures 16, 17, and 19. In the method for manufacturing the optical modulator 1A of this embodiment, the first to fifth steps, which involve forming the first substrate 100 (see Figure 17(a)), are the same as the method for manufacturing the optical modulator 1A according to Embodiment 4 (see Figures 16(a), 16(b), 16(c), 16(d), and 17(a)), so the explanation will be omitted.

[0097] In the manufacturing method of the optical modulator 1A according to Embodiment 5, the configuration of the first substrate 100 is the same as the configuration of the first substrate 100 in the manufacturing method of the optical modulator 1A according to Embodiment 4, and as shown in Figure 19(a), the configuration of the second substrate 200 differs from the configuration of the second substrate 200 used in the manufacturing method of the optical modulator 1A according to Embodiment 4 (see Figure 17(b)). The second substrate 200 prepared in this embodiment has a second support substrate 230 which is different from the first support substrate 10 which is the support substrate 10, and an optical waveguide material thin film 220 which is laminated on the second support substrate 230 and formed of an optical waveguide material.

[0098] In this embodiment, after the fifth step, in the sixth step, a second substrate 200 having a second support substrate 230 and an optical waveguide material thin film 220 which will become the optical waveguide material layer 20 is joined to the first substrate 100 to obtain a substrate S36 with the structure shown in Figure 19(a). The material of the optical waveguide material thin film 220 is the same as the material of the optical waveguide material layer 20. In the second substrate 200 of this embodiment, the main surface of the second support substrate 230 that is not in contact with the optical waveguide material thin film 220 constitutes the first main surface 211 of the second substrate 200, and the main surface of the optical waveguide material thin film 220 that is not in contact with the second support substrate 230 constitutes the planar second main surface 212 of the second substrate 200.

[0099] In this embodiment, in the seventh step following the sixth step, the second support substrate 230 is removed from the substrate S36 to obtain a substrate S7 having the structure shown in Figure 19(b).

[0100] In this embodiment, in the eighth step, the optical waveguide material thin film 220 of the substrate S7 is processed to form an optical waveguide material layer 20 containing two optical waveguides 2 (only one optical waveguide 2 is shown in Figure 19(c)), then two first electrodes 4 (only one first electrode 4 is shown in Figure 19(c)) and a second electrode 5 are formed on the first main surface 201 of the optical waveguide material layer 20, and then a third cladding layer 3 is formed to obtain a substrate S8 with the structure shown in Figure 19(c).

[0101] In the manufacturing method of the optical modulator 1A of this embodiment, the support substrate 10 prepared in the first step is a wafer (for example, a silicon wafer), and the substrates S1 to S5, S36, S7, and S8 are wafers having different structures from each other. In the manufacturing method of the optical modulator 1A of this embodiment, by performing each of the steps from the first to the eighth step, a wafer containing multiple optical modulators 1A can be obtained as the substrate S8. In the manufacturing method of the optical modulator 1A of this embodiment, after the eighth step, multiple optical modulators 1A can be obtained by cutting the substrate S8 with, for example, a dicing saw or a laser dicing device.

[0102] The manufacturing method for the optical modulator 1A according to Embodiment 5 comprises an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 side of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator 1A according to Embodiment 5 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate 100 is formed which includes a second cladding layer 7 having a planar main surface 701 and a support substrate 10 and has a planar main surface 111. In the joining process, a second substrate 200 is prepared, having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate 100 and the second substrate 200 are joined together. According to the manufacturing method of the optical modulator 1A of Embodiment 5, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed. Furthermore, since the optical modulator 1A of Embodiment 5 can employ the above-described manufacturing method of the optical modulator 1A, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0103] Furthermore, in the manufacturing method of the optical modulator 1A according to Embodiment 5, the first substrate 100 further includes a first cladding layer 6, and the first cladding layer 6 is supported by a support substrate 10. The main surface 111 of the first substrate 100 includes the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7. The second substrate 200 has a second support substrate 230 which is different from the first support substrate 10 which is the support substrate 10, and an optical waveguide material thin film 220 which is laminated on the second support substrate 230 and becomes the basis of the optical waveguide material layer 20. After the bonding process, the second support substrate 230 is removed and the optical waveguide material thin film 220 is processed to form the optical waveguide material layer 20 including the optical waveguide 2. According to this manufacturing method, the optical waveguide 2 can be formed after the bonding process.

[0104] (Embodiment 6) The configuration of the optical modulator 1A according to Embodiment 6 is the same as the configuration of the optical modulator 1A according to Embodiment 4 shown in Figures 14 and 15, so the explanation will be omitted.

[0105] The method for manufacturing the optical modulator 1A according to Embodiment 6 will be described below with reference to Figures 16, 17, and 20. In the method for manufacturing the optical modulator 1A of this embodiment, the first to fifth steps, which involve forming the first substrate 100 (see Figure 17(a)), are the same as the method for manufacturing the optical modulator 1A according to Embodiment 4 (see Figures 16(a), 16(b), 16(c), 16(d), and 17(a)), so the explanation will be omitted.

[0106] In the manufacturing method of the optical modulator 1A according to Embodiment 6, the configuration of the first substrate 100 is the same as the configuration of the first substrate 100 in the manufacturing method of the optical modulator 1A according to Embodiment 4, and as shown in Figure 20(a), the configuration of the second substrate 200 differs from the configuration of the second substrate 200 used in the manufacturing method of the optical modulator 1A according to Embodiment 4 (see Figure 17(b)). The second substrate 200 prepared in this embodiment includes an optical waveguide material layer 20 containing two optical waveguides 2 (only one optical waveguide 2 is shown in Figure 20(a)), two first electrodes 4 (only one first electrode 4 is shown in Figure 20(a)) and a second electrode 5, a third cladding layer 3, and a second support substrate 230 which is different from the first support substrate 10, which is the support substrate 10.

[0107] In this embodiment, after the fifth step, in the sixth step, the main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are placed facing each other as shown in Figure 20(a), and then the first substrate 100 and the second substrate 200 are joined to obtain a substrate S46 with the structure shown in Figure 20(b). In the second substrate 200 of this embodiment, the main surface of the second support substrate 230 that is not in contact with the third cladding layer 3 constitutes the first main surface 211 of the second substrate 200, and the second main surface 202 of the optical waveguide material layer 20 constitutes the planar second main surface 212 of the second substrate 200.

[0108] In this embodiment, in the seventh step following the sixth step, the second support substrate 230 is removed from the substrate S46 to obtain a substrate S8 having the structure shown in Figure 20(c).

[0109] In the manufacturing method of the optical modulator 1A of this embodiment, the support substrate 10 prepared in the first step is a wafer (for example, a silicon wafer), and the substrates S1 to S5, S46, and S8 are wafers having different structures from each other. In the manufacturing method of the optical modulator 1A of this embodiment, by performing each of the steps from the first to the seventh step, a wafer containing multiple optical modulators 1A can be obtained as the substrate S8. In the manufacturing method of the optical modulator 1A of this embodiment, after the seventh step, multiple optical modulators 1A can be obtained by cutting the substrate S8 with, for example, a dicing saw or a laser dicing device.

[0110] The manufacturing method for the optical modulator 1A according to Embodiment 6 comprises an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 side of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator 1A according to Embodiment 6 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate 100 is formed which includes a second cladding layer 7 having a planar main surface 701 and a support substrate 10 and has a planar main surface 111. In the joining process, a second substrate 200 is prepared, having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate 100 and the second substrate 200 are joined together. According to the manufacturing method of the optical modulator 1A of Embodiment 6, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed. Furthermore, since the optical modulator 1A of Embodiment 6 can employ the above-described manufacturing method of the optical modulator 1A, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0111] Furthermore, in the manufacturing method of the optical modulator 1A according to Embodiment 6, the first substrate 100 further includes a first cladding layer 6, and the first cladding layer 6 is supported by a support substrate 10. The main surface 111 of the first substrate 100 includes the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7. The second substrate 200 has an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a third cladding layer 3, and a second support substrate 230 which is different from the first support substrate 10, which is the support substrate 10. The optical waveguide material layer 20 includes an optical waveguide 2. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2, and a voltage is applied between it and the first electrode 4. The third cladding layer 3 is in contact with the optical waveguide 2 and has a refractive index smaller than that of the optical waveguide 2. The second support substrate 230 overlaps the third cladding layer 3. After the bonding process, the second support substrate 230 is removed. According to this manufacturing method, the optical waveguide 2 can be formed before the bonding process.

[0112] (Embodiment 7) The optical modulator 1B according to Embodiment 7 will be described with reference to Figure 21, and the method for manufacturing the optical modulator 1B will be described with reference to Figures 22 and 23. With respect to the optical modulator 1B according to Embodiment 7, components that are the same as those in the optical modulator 1A according to Embodiment 4 (see Figures 14 and 15) are denoted by the same reference numerals and their description is omitted. Note that in Figure 21, the illustration of one of the two optical waveguides 2 (see Figure 14) described in Embodiment 4 is omitted, and the illustration of one of the two first electrodes 4 (see Figure 14) is omitted.

[0113] (1) Configuration of the optical modulator The optical modulator 1B according to this embodiment differs from the optical modulator 1A according to Embodiment 4 in that the low dielectric constant layer 9 has a recess 92 that overlaps the optical waveguide 2 in the thickness direction of the optical waveguide material layer 20, and the second cladding layer 7 has a portion 73 that is located inside the recess 92.

[0114] The recesses 92 of the low dielectric constant layer 9 are formed on the main surface 91 of the low dielectric constant layer 9. In this embodiment, the depth of the recesses 92 is less than or equal to the thickness t1 of the portion 711 in the second cladding layer 7 that is in contact with the second main surface 202 of the optical waveguide material layer 20.

[0115] The portion 73 of the second cladding layer 7 located inside the recess 92 overlaps the optical waveguide 2 in the thickness direction of the optical waveguide material layer 20. The portion 73 of the second cladding layer 7 located inside the recess 92 is separated from the second main surface 202 of the optical waveguide material layer 20 in the thickness direction of the optical waveguide material layer 20. In this embodiment, the first cladding layer 6 is interposed between the second main surface 202 of the optical waveguide material layer 20 and the portion 73 of the second cladding layer 7 located inside the recess 92 in the thickness direction of the optical waveguide material layer 20.

[0116] (2) Method for manufacturing the optical modulator The method for manufacturing the optical modulator 1B according to Embodiment 7 will be described below with reference to Figures 22 and 23.

[0117] In the manufacturing method of the optical modulator 1B according to Embodiment 7, for example, steps 1 to 8 are performed sequentially. Regarding the manufacturing method of the optical modulator 1B according to Embodiment 7, steps similar to those in the manufacturing method of the optical modulator 1A according to Embodiment 4 will be omitted from explanation as appropriate.

[0118] In the first step, a support substrate 10 is prepared, and a low dielectric constant layer 9 is formed on the main surface 101 of the support substrate 10 to obtain a substrate S51 with the structure shown in Figure 22(a). As a method for forming the low dielectric constant layer 9, for example, the CVD method can be used. Note that the support substrate 10 is a silicon substrate and the material of the low dielectric constant layer 9 is SiO ２ In this case, for example, a CVD method or a thermal oxidation method can be used as a method for forming the low dielectric constant layer 9.

[0119] In the second step, a substrate S52 having the structure shown in Figure 22(b) is obtained by forming recesses 92 on the main surface 91 of the low dielectric constant layer 9. In the second step, for example, photolithography and etching techniques are used to form the recesses 92 in the low dielectric constant layer 9. As the etching technique, for example, dry etching or wet etching techniques can be employed.

[0120] In the third step, a substrate S53 having the structure shown in Figure 22(c) is obtained by forming a second cladding layer 7 on the low dielectric constant layer 9. For example, sputtering, vapor deposition, or CVD can be used as the method for forming the second cladding layer 7. The second cladding layer 7 formed in the third step has an uneven shape due to the shape of the low dielectric constant layer 9 which is the base shape of the second cladding layer 7.

[0121] In the fourth step, a substrate S54 with the structure shown in Figure 22(d) is obtained by forming a first cladding material layer 60 that covers the second cladding layer 7. The first cladding material layer 60 is the base layer for the first cladding layer 6. The main surface 600 of the first cladding material layer 60 formed in the fourth step has an uneven shape resulting from the shape of the second cladding layer 7, which is the base shape of the first cladding material layer 60.

[0122] In the fifth step, the outermost surface of the substrate S54 is planarized from the main surface 600 side of the first cladding material layer 60 to form the first cladding layer 6 and expose the second cladding layer 7, thereby obtaining a substrate S55 with the structure shown in Figure 23(a). The first cladding layer 6 is a part of the first cladding material layer 60. In the substrate S55, the main surface (outermost surface) composed of the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7 is planar. The substrate S55 includes the first cladding layer 6, the second cladding layer 7 having a larger dielectric constant than the first cladding layer 6, and a support substrate 10 supporting the first cladding layer 6 and the second cladding layer 7, and the outermost surface including the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer is planarized. In this embodiment, the substrate S55 constitutes the first substrate 100. The first substrate 100 has a planar main surface 111 that includes the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer.

[0123] In the sixth step, a second substrate 200 is prepared, and the first substrate 100 and the second substrate 200 are joined to obtain a substrate S56 having the structure shown in Figure 23(b). The second substrate 200 has a first main surface 211 and a second main surface 212. The optical waveguide material is exposed on the second main surface 212 of the second substrate 200. In the sixth step, the main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are faced towards each other, and then the first substrate 100 and the second substrate 200 are joined. In this embodiment, the sixth step constitutes the joining process. In this embodiment, the second substrate 200 is an optical waveguide material substrate formed from an optical waveguide material.

[0124] In the seventh step, the second substrate 200 is thinned by grinding or the like to obtain a substrate S57 with the structure shown in Figure 23(c).

[0125] In the eighth step, the thinned second substrate 200 is processed to form an optical waveguide material layer 20 containing two optical waveguides 2. Then, two first electrodes 4 and a second electrode 5 are formed on the first main surface 201 of the optical waveguide material layer 20. After that, a third cladding layer 3 is formed to obtain a substrate S58 with the structure shown in Figure 23(d).

[0126] In the manufacturing method of the optical modulator 1B of this embodiment, the support substrate 10 prepared in the first step is a wafer (for example, a silicon wafer), and the substrates S51 to S58 are wafers having different structures from each other. In the manufacturing method of the optical modulator 1B of this embodiment, by performing each of the steps from the first to the eighth step, a wafer containing multiple optical modulators 1B can be obtained as the substrate S58. In the manufacturing method of the optical modulator 1B of this embodiment, after the eighth step, multiple optical modulators 1B can be obtained by cutting the substrate S58 with, for example, a dicing saw or a laser dicing device.

[0127] (3) The optical modulator performance diagram 24 is a graph showing the relationship between ε2 / ε1 and the normalized Vπ・L, where ε2 is the relative permittivity of the second cladding layer 7, and ε1 is the relative permittivity of the first cladding layer 6, the third cladding layer 3, and the low permittivity layer 9, respectively. In Figure 24, the horizontal axis is ε2 / ε1 and the vertical axis is {(Vπ・L) / (Vπ・L0)} × 100. Vπ・L0 is the value of Vπ・L when the relative permittivity of the second cladding layer is the same as that of the first cladding layer and ε2 / ε1 = 1. From Figure 24, it can be seen that Vπ・L can be reduced by making ε2 / ε1 greater than 1 and less than 500. Therefore, it is preferable that ε2 / ε1 be greater than 1 and less than 500. Furthermore, Figure 24 shows that if ε2 / ε1 is in the range of 3.5 to 300, Vπ・L can be reduced by 10% or more, and if ε2 / ε1 is in the range of 11 to 120, Vπ・L can be reduced by 20% or more. Therefore, in the optical modulator 1B of this embodiment, the relative permittivity of the second cladding layer 7 is preferably greater than 1 times and less than 500 times the relative permittivity of the first cladding layer 6, more preferably between 3.5 and 300 times, and desirablely between 11 and 120 times.

[0128] (4) The method for manufacturing the optical modulator 1B according to the effect embodiment 7 comprises an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 side of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator 1B according to Embodiment 7 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate 100 is formed which includes a second cladding layer 7 having a planar main surface 701 and a support substrate 10 and has a planar main surface 111. In the joining process, a second substrate 200 is prepared, having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate 100 and the second substrate 200 are joined together. According to the manufacturing method of the optical modulator 1B of Embodiment 7, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed. Furthermore, since the optical modulator 1B of Embodiment 7 can employ the above-described manufacturing method of the optical modulator 1B, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0129] Furthermore, in the manufacturing method of the optical modulator 1B according to Embodiment 7, the first substrate 100 further includes a first cladding layer 6, and the first cladding layer 6 is supported by a support substrate 10. The main surface 111 of the first substrate 100 includes the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7. The second substrate 200 is an optical waveguide material substrate 200 formed of an optical waveguide material. After the bonding process, an optical waveguide material layer 20 including an optical waveguide 2 is formed by processing the optical waveguide material substrate 200. According to this manufacturing method, the optical waveguide 2 can be formed after the bonding process.

[0130] Furthermore, in the optical modulator 1B according to Embodiment 7, the relative permittivity of the material of the second cladding layer 7 is greater than the relative permittivity of the material of the optical waveguide material layer 20.

[0131] With the above configuration, it becomes possible to reduce the Vπ·L of the optical modulator 1B.

[0132] (5) Modified Examples (5.1) Modified Example 1 Hereinafter, the optical modulator 1B according to Modified Example 1 will be described with reference to Figure 25. With respect to the optical modulator 1B according to Modified Example 1, components that are the same as those in the optical modulator 1B according to Embodiment 7 will be given the same reference numerals and their description will be omitted. The manufacturing method of the optical modulator 1B according to Modified Example 1 is the same as the manufacturing method of the optical modulator 1B according to Embodiment 7, so the description will be omitted.

[0133] In the optical modulator 1B according to Modification 1, as shown in Figure 25, the thickness t1 of the first portion 711 in contact with the optical waveguide material layer 20 in the second cladding layer 7 is different from the thickness t0 of the second portion 712 that is separated from the optical waveguide material layer 20 in the thickness direction of the optical waveguide material layer 20. In this embodiment, in the thickness direction of the optical waveguide material layer 20, a part of the second portion 712 of the second cladding layer 7 overlaps with the optical waveguide 2. In the second cladding layer 7 of this embodiment, the thickness t0 of the second portion 712 is thinner than the thickness t1 of the first portion 711.

[0134] Figure 26 is a graph showing the relationship between t0 / t1 and the normalized Vπ・L, where t1 is the thickness of the first portion 711 in contact with the optical waveguide material layer 20 in the second cladding layer 7, and t0 is the thickness of the second portion 712 that overlaps the optical waveguide 2 in the thickness direction of the optical waveguide material layer 20. In Figure 26, the horizontal axis is t0 / t1, and the vertical axis is {(Vπ・L) / (Vπ・L0)} × 100. In Figure 26, Vπ・L0 is the value of Vπ・L when t0 / t1 = 1. As shown in Figure 26, in the optical modulator 1B according to Modification 1, from the viewpoint of reducing Vπ·L, when the thickness of the first portion 711 in contact with the optical waveguide material layer 20 in the second cladding layer 7 is t1, and the thickness of the second portion 712 overlapping the optical waveguide 2 in the thickness direction of the optical waveguide material layer 20 is t0, it is preferable that t0 / t1 is 0 or more and 0.4 or less.

[0135] In the optical modulator 1B according to Modification 1, when the thickness of the first portion 711 in the second cladding layer 7 that is in contact with the optical waveguide material layer 20 is t1, and the thickness of the second portion 712 that overlaps with the optical waveguide 2 in the thickness direction of the optical waveguide material layer 20 and is thinner than the first portion 711 is t0, then t0 / t1 is 0 or more and 0.4 or less.

[0136] With the above configuration, it becomes possible to reduce the Vπ·L of the optical modulator 1B.

[0137] (5.2) Modification 2 Hereinafter, the optical modulator 1B according to Modification 2 will be described with reference to Figure 27. With respect to the optical modulator 1B according to Modification 2, components that are the same as those in the optical modulator 1B according to Embodiment 7 will be given the same reference numerals and their description will be omitted. The manufacturing method of the optical modulator 1B according to Modification 2 is substantially the same as the manufacturing method of the optical modulator 1B according to Embodiment 7, so the description will be omitted.

[0138] The optical modulator 1B according to the modified example 2 differs from the optical modulator 1B according to embodiment 7 (see Figure 25) in that, as shown in Figure 27, a part of the second portion 712 of the second cladding layer 7 that is separated from the optical waveguide material layer 20 in the thickness direction of the optical waveguide material layer 20 is thinned. In this embodiment, when the thickness of the first portion 711 of the second cladding layer 7 that is in contact with the second main surface 202 of the optical waveguide material layer 20 and does not overlap with the recess 92 (groove) of the low dielectric constant layer 9 in the thickness direction of the optical waveguide material layer 20 is t1, the thickness of the unthinned portion 7121 of the second portion 712 of the second cladding layer 7 is t1, and the thickness of the thinned portion 7122 of the second portion 712 is t0.

[0139] Figure 28 is a graph showing the relationship between W2 / W1 and the normalized Vπ・L, where W1 is the width of the second portion 712 in the width direction of the optical waveguide 2, W2 is the width of the thinned portion 7122 in a direction parallel to the width direction of the optical waveguide 2, and t0 / t1 is a parameter. In Figure 28, the horizontal axis is W2 / W1 and the vertical axis is {(Vπ・L) / (Vπ・L0)} × 100. In Figure 28, Vπ・L0 is the value of Vπ・L for the optical modulator 1B of Embodiment 7, where the thickness of the second portion 712 is t1. Therefore, the vertical axis in Figure 28 is Vπ・L normalized with the value of Vπ・L0 for the optical modulator 1B of Embodiment 7 set to 100. In Figure 28, the data for the case t0 / t1=0 is t0=0, and is the data of the normalized Vπ・L for the optical modulator 1B of Modification 3 shown in Figure 29. In the modified optical modulator 1B shown in Figure 30 (modified example 4), the width W1 of the second portion 712 and the width W2 of the thinned portion 7122 of the second portion 712 are the same in the direction parallel to the width direction of the optical waveguide 2, and the thickness t0 of the thinned portion 7122 is thinner than the thickness t1 of the second cladding layer 7.

[0140] Figure 28 shows that the optical modulator 1B according to Modification 2 can reduce Vπ·L by 10% or more when 0 ≤ t0 / t1 ≤ 0.4 and W2 / W1 is between 0.28 and 0.89. Also, Figure 28 shows that the optical modulator 1B according to Modification 3 can reduce Vπ·L compared to the optical modulator 1B according to Modification 2. Also, Figure 28 shows that the optical modulator 1B according to Modification 4 can reduce Vπ·L compared to the optical modulator 1B of Embodiment 7.

[0141] In the manufacturing method of the optical modulator 1B according to the modified example 2, when the width of the second portion 712 of the second cladding layer 7 in the width direction of the optical waveguide 2 is W0 and the width of the slit 72 in the width direction of the optical waveguide 2 is W1, W1 / W0 is 0.28 or more and 0.89 or less.

[0142] With the above configuration, the Vπ·L of the optical modulator 1B can be reduced by 10% or more.

[0143] (Embodiment 8) The configuration of the optical modulator 1B according to Embodiment 8 is the same as the configuration of the optical modulator 1B according to Embodiment 7 shown in Figure 21, so the explanation will be omitted.

[0144] The method for manufacturing the optical modulator 1B according to Embodiment 8 will be described below with reference to Figures 22, 23, and 31. In the method for manufacturing the optical modulator 1B of this embodiment, the first to fifth steps for forming the first substrate 100 (see Figure 23(a)) are the same as the method for manufacturing the optical modulator 1B according to Embodiment 7 (see Figures 22(a), 22(b), 22(c), 22(d), and 23(a)), so the explanation will be omitted.

[0145] In the manufacturing method of the optical modulator 1B according to Embodiment 8, the configuration of the first substrate 100 is the same as the configuration of the first substrate 100 in the manufacturing method of the optical modulator 1B according to Embodiment 7 (see Figure 23(a)), and as shown in Figure 31(a), the configuration of the second substrate 200 differs from the configuration of the second substrate 200 used in the manufacturing method of the optical modulator 1B according to Embodiment 7 (see Figure 23(b)). The second substrate 200 prepared in this embodiment has a second support substrate 230 which is different from the first support substrate 10 which is the support substrate 10, and an optical waveguide material thin film 220 which is laminated on the second support substrate 230 and formed of an optical waveguide material.

[0146] In this embodiment, after the fifth step, in the sixth step, a second substrate 200 having a second support substrate 230 and an optical waveguide material thin film 220 which will become the optical waveguide material layer 20 is joined to the first substrate 100 to obtain a substrate S66 with the structure shown in Figure 31(a). The material of the optical waveguide material thin film 220 is the same as the material of the optical waveguide material layer 20. In the second substrate 200 of this embodiment, the main surface of the second support substrate 230 that is not in contact with the optical waveguide material thin film 220 constitutes the first main surface 211 of the second substrate 200, and the main surface of the optical waveguide material thin film 220 that is not in contact with the second support substrate 230 constitutes the planar second main surface 212 of the second substrate 200.

[0147] In this embodiment, in the seventh step following the sixth step, the second support substrate 230 is removed from the substrate S66 to obtain a substrate S67 having the structure shown in Figure 31(b).

[0148] In this embodiment, in the eighth step, the optical waveguide material thin film 220 of the substrate S67 is processed to form an optical waveguide material layer 20 containing two optical waveguides 2, then two first electrodes 4 and a second electrode 5 are formed on the first main surface 201 of the optical waveguide material layer 20, and then a third cladding layer 3 is formed to obtain a substrate S68 with the structure shown in Figure 31(c).

[0149] In the manufacturing method of the optical modulator 1B of this embodiment, the support substrate 10 prepared in the first step is a wafer (for example, a silicon wafer), and the substrates S1 to S5 and S66 to S68 are wafers having different structures from each other. In the manufacturing method of the optical modulator 1B of this embodiment, by performing each of the steps from the first to the eighth step, a wafer containing multiple optical modulators 1B can be obtained as the substrate S68. In the manufacturing method of the optical modulator 1B of this embodiment, after the eighth step, multiple optical modulators 1B can be obtained by cutting the substrate S68 with, for example, a dicing saw or a laser dicing device.

[0150] The manufacturing method for the optical modulator 1B according to Embodiment 8 comprises an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 side of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator 1B according to Embodiment 8 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate 100 is formed which includes a second cladding layer 7 having a planar main surface 701 and a support substrate 10 and has a planar main surface 111. In the joining process, a second substrate 200 is prepared having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate 100 and the second substrate 200 are joined together. According to the manufacturing method of the optical modulator 1B of Embodiment 8, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed. Furthermore, since the optical modulator 1B of Embodiment 8 can employ the above-described manufacturing method of the optical modulator 1B, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0151] Furthermore, in the manufacturing method of the optical modulator 1B according to Embodiment 8, the first substrate 100 further includes a first cladding layer 6, and the first cladding layer 6 is supported by a support substrate 10. The main surface 111 of the first substrate 100 includes the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7. The second substrate 200 has a second support substrate 230 which is different from the first support substrate 10 which is the support substrate 10, and an optical waveguide material thin film 220 which is laminated on the second support substrate 230 and becomes the basis of the optical waveguide material layer 20. After the bonding process, the second support substrate 230 is removed and the optical waveguide material thin film 220 is processed to form the optical waveguide material layer 20 which includes the optical waveguide 2. According to this manufacturing method, the optical waveguide 2 can be formed after the bonding process.

[0152] (Embodiment 9) The configuration of the optical modulator 1B according to Embodiment 9 is the same as the configuration of the optical modulator 1B according to Embodiment 7 shown in Figure 21, so the explanation will be omitted.

[0153] The method for manufacturing the optical modulator 1B according to Embodiment 9 will be described below with reference to Figures 22, 23, and 32. In the method for manufacturing the optical modulator 1B of this embodiment, the first to fifth steps for forming the first substrate 100 (see Figure 23(a)) are the same as the method for manufacturing the optical modulator 1B according to Embodiment 7 (see Figures 22(a), 22(b), 22(c), 22(d), and 23(a)), so the explanation will be omitted.

[0154] In the manufacturing method of the optical modulator 1B according to Embodiment 9, the configuration of the first substrate 100 is the same as the configuration of the first substrate 100 in the manufacturing method of the optical modulator 1B according to Embodiment 7 (see Figure 23(a)), and as shown in Figure 32(a), the configuration of the second substrate 200 differs from the configuration of the second substrate 200 used in the manufacturing method of the optical modulator 1B according to Embodiment 7 (see Figure 23(b)). The second substrate 200 prepared in this embodiment includes an optical waveguide material layer 20 containing an optical waveguide 2, two first electrodes 4 (only one first electrode 4 is shown in Figure 32(a)) and a second electrode 5, a third cladding layer 3, and a second support substrate 230 which is different from the first support substrate 10, which is the support substrate 10.

[0155] In this embodiment, after the fifth step, in the sixth step, the main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are placed facing each other as shown in Figure 32(a), and then the first substrate 100 and the second substrate 200 are joined to obtain a substrate S46 with the structure shown in Figure 32(b). In the second substrate 200 of this embodiment, the main surface of the second support substrate 230 that is not in contact with the third cladding layer 3 constitutes the first main surface 211 of the second substrate 200, and the second main surface 202 of the optical waveguide material layer 20 constitutes the planar second main surface 212 of the second substrate 200.

[0156] In this embodiment, in the seventh step following the sixth step, the second support substrate 230 is removed from the substrate S46 to obtain a substrate S8 having the structure shown in Figure 32(c).

[0157] In the manufacturing method of the optical modulator 1B of this embodiment, the support substrate 10 prepared in the first step is a wafer (for example, a silicon wafer), and the substrates S1 to S5, S46, and S8 are wafers having different structures from each other. In the manufacturing method of the optical modulator 1B of this embodiment, by performing each of the steps from the first to the seventh step, a wafer containing multiple optical modulators 1B can be obtained as the substrate S8. In the manufacturing method of the optical modulator 1B of this embodiment, after the seventh step, multiple optical modulators 1B can be obtained by cutting the substrate S8 with, for example, a dicing saw or a laser dicing device.

[0158] The manufacturing method for the optical modulator 1B according to Embodiment 9 comprises an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the side of the second main surface 202 of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator 1B according to Embodiment 9 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate 100 is formed which includes a second cladding layer 7 having a planar main surface 701 and a support substrate 10 and has a planar main surface 111. In the joining process, a second substrate 200 is prepared having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate 100 and the second substrate 200 are joined together. According to the manufacturing method of the optical modulator 1B of Embodiment 9, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed. Furthermore, since the optical modulator 1B of Embodiment 9 can employ the above-described manufacturing method of the optical modulator 1B, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0159] Furthermore, in the manufacturing method of the optical modulator 1B according to Embodiment 9, the first substrate 100 further includes a first cladding layer 6, and the first cladding layer 6 is supported by a support substrate 10. The main surface 111 of the first substrate 100 includes the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer 7. The second substrate 200 has an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a third cladding layer 3, and a second support substrate 230 which is different from the first support substrate 10, which is the support substrate 10. The optical waveguide material layer 20 includes an optical waveguide 2. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2, and a voltage is applied between it and the first electrode 4. The third cladding layer 3 is in contact with the optical waveguide 2 and has a refractive index smaller than that of the optical waveguide 2. The second support substrate 230 overlaps the third cladding layer 3. After the bonding process, the second support substrate 230 is removed. According to this manufacturing method, the optical waveguide 2 can be formed before the bonding process.

[0160] (Embodiment 10) The optical modulator 1C according to Embodiment 10 will be described with reference to Figure 33. With respect to the optical modulator 1C according to Embodiment 10, components that are the same as those in the optical modulator 1B according to Embodiment 7 (see Figure 21) are denoted by the same reference numerals and their description is omitted. Note that in Figure 33, the illustration of one of the two optical waveguides 2 described in Embodiment 4 is omitted, and the illustration of one of the two first electrodes 4 is omitted.

[0161] (1) Optical modulator configuration The optical modulator 1C according to embodiment 10 differs from the optical modulator 1B according to embodiment 7 in that the inner surface of the recess 92 of the low dielectric constant layer 9 is tapered, and the inner surface of the slit 72 formed in the second cladding layer 7 is tapered. Furthermore, the optical modulator 1C according to embodiment 10 differs from the optical modulator 1B according to embodiment 7 in that the width of the first cladding layer 6 in the width direction (X-axis direction) of the optical waveguide 2 becomes smaller as it moves away from the optical waveguide material layer 20 in the thickness direction of the optical waveguide material layer 20.

[0162] In this embodiment, the reference thickness of the first cladding layer 6 is the maximum value of the difference tb between the length ta from the bottom surface of the second cladding layer 7 to the top surface of the first cladding layer 6 and the length tc from the bottom surface of the second cladding layer 7 to the bottom surface of the first cladding layer 6 in the thickness direction of the optical waveguide material layer 20, in the region where the second cladding layer 7 overlaps the first cladding layer 6 between the first electrode 4 and the second electrode 5 in a plan view from the Z-axis direction. The lengths ta, tc, and difference tb described above are values ​​measured from the cross-sectional SEM image obtained by cutting the optical modulator 1C with a plane perpendicular to the optical propagation direction of the optical waveguide 2 and observing the cross-section with an SEM (Scanning Electron Microscope).

[0163] (2) Method for Manufacturing an Optical Modulator The method for manufacturing the optical modulator 1C according to Embodiment 10 is the same as the method for manufacturing the optical modulator 1B according to Embodiment 7, except that the process conditions in the second step of forming the recess 92 in the low dielectric constant layer 9 are different. In the second step of this embodiment, for example, the etching conditions of the low dielectric constant layer 9 are changed, but it is also possible to form a resist layer using photolithography technology with a grayscale mask without changing the etching conditions, and then perform dry etching.

[0164] (3) The method for manufacturing the optical modulator 1C according to Embodiment 10 has the same effects as the method for manufacturing the optical modulator 1B according to Embodiment 7.

[0165] (4) Modified Example The optical modulator 1C according to a modified example of Embodiment 10 will be described with reference to Figure 34. With respect to the optical modulator 1C according to a modified example of Embodiment 10, components that are the same as those in the optical modulator 1C according to Embodiment 10 (see Figure 33) are denoted by the same reference numerals and their description is omitted. Note that in Figure 34, the illustration of one of the two optical waveguides 2 described in Embodiment 4 is omitted, and the illustration of one of the two first electrodes 4 is omitted.

[0166] The optical modulator 1C according to a modified example of Embodiment 10 differs from the optical modulator 1C according to Embodiment 10 in that the first cladding layer 6 has a multilayer structure and the second cladding layer 7 has a multilayer structure. In this modified example, the first cladding layer 6 has a stacked first low dielectric constant material layer 6a and a second low dielectric constant material layer 6b. In this modified example, the second cladding layer 7 has a stacked first high dielectric constant material layer 7a and a second high dielectric constant material layer 7b.

[0167] In the modified first cladding layer 6, the first low dielectric constant material layer 6a is in contact with the second cladding layer 7, while the second low dielectric constant material layer 6b is not in contact with the second cladding layer 7 and is in contact with the second main surface 202 of the optical waveguide material layer 20.

[0168] In this modified example, the material of the second low dielectric constant material layer 6b is the same as the material of the first cladding layer 6 in Embodiment 10. The material of the first low dielectric constant material layer 6a is different from, but may be the same as, the material of the second low dielectric constant material layer 6b. The dielectric constant of the first low dielectric constant material layer 6a and the second low dielectric constant material layer 6b is smaller than the dielectric constant of the first high dielectric constant material layer 7a and the second high dielectric constant material layer 7b. The refractive index of the first low dielectric constant material layer 6a and the second low dielectric constant material layer 6b is smaller than the refractive index of the two optical waveguides 2. The refractive index of the first low dielectric constant material layer 6a and the second low dielectric constant material layer 6b is smaller than the refractive index of the optical waveguide material layer 20.

[0169] The materials of the first low dielectric constant material layer 6a and the second low dielectric constant material layer 6b are, for example, SiO ２ Al ２ O ３ , LaAlO ３ LaYO ３ ZnO, HfO ２ , MgO, Y ２ O ３ The material is selected from the group of oxides such as BCB (benzocyclobutene) and polymers such as PI (polyimide).

[0170] In the second cladding layer 7 of this modified example, the first high dielectric constant material layer 7a is in contact with the low dielectric constant layer 9, and the second high dielectric constant material layer 7b is in contact with the second main surface 202 of the optical waveguide material layer 20.

[0171] In this modified example, the material of the second high dielectric constant material layer 7b is the same as that of the second cladding layer 7 in Embodiment 10. The material of the first high dielectric constant material layer 7a may be different from that of the second high dielectric constant material layer 7b, or may be the same. The dielectric constant of each of the first high dielectric constant material layer 7a and the second high dielectric constant material layer 7b is greater than that of the optical waveguide 2. Also, the refractive index of each of the first high dielectric constant material layer 7a and the second high dielectric constant material layer 7b is smaller than that of the optical waveguide 2. The material of each of the first high dielectric constant material layer 7a and the second high dielectric constant material layer 7b is, for example, SrTiO ３ (strontium titanate), BaTiO ３ (barium titanate), PbLaTiO ３ (lead lanthanum titanate), PZT (lead zirconate titanate), PLZT (lead lanthanum zirconate titanate), LiNbO ３ (lithium niobate), LiTaO ３ (lithium tantalate), KNbO ３ (potassium niobate), PbTiO ３ (lead titanate), PKNO (lead potassium niobate), PMN (lead magnesium niobate), Bi ４ Ti ３ O １２ (bismuth titanate), BST (barium strontium titanate), KLN (potassium lanthanum niobate), Al ２ O ３ 、LaAlO ３ 、LaYO ３ 、ZnO、HfO ２ 、MgO、Y ２ O ３ 、TiO ２ 、Ta ２ O ５ 、SiN, ALN, and is a material selected from the group consisting of.

[0172] The manufacturing method of the optical modulator 1C according to the modified example of Embodiment 10 is the same as that of the optical modulator 1C according to Embodiment 10, and thus the description thereof is omitted.

[0173] The manufacturing method of the optical modulator 1C according to the modified example of Embodiment 10 has the same effect as that of the manufacturing method of the optical modulator 1B according to Embodiment 7.

[0174] (Embodiment 11) The optical modulator 1D according to Embodiment 11 will be described with reference to Figure 35. With respect to the optical modulator 1D according to Embodiment 11, components that are the same as those in the optical modulator 1B according to Embodiment 7 (see Figure 21) are denoted by the same reference numerals and their description is omitted.

[0175] (1) Optical modulator configuration The optical modulator 1D according to embodiment 11 differs from the optical modulator 1B according to embodiment 7 in that two second electrodes 5 are arranged between two optical waveguides 2 in a plan view from the Z-axis direction, and two third electrodes 8 are further arranged on the opposite side of each of the two first electrodes 4 from the optical waveguide 2 side in a plan view from the Z-axis direction.

[0176] The two first electrodes 4, the two second electrodes 5, and the two third electrodes 8 are arranged on the first main surface 201 of the optical waveguide material layer 20. The two first electrodes 4, the two second electrodes 5, and the two third electrodes 8 are in contact with the first main surface 201 of the optical waveguide material layer 20.

[0177] In the following explanation, to distinguish between the two optical waveguides 2, the first optical waveguide 2 may be referred to as the first optical waveguide 2A, and the second optical waveguide 2 may be referred to as the second optical waveguide 2B. Also, in the following explanation, to distinguish between the two first electrodes 4, one of the two first electrodes 4 may be referred to as the first electrode 4A, and the other as the first electrode 4B. Also, in the following explanation, to distinguish between the two second electrodes 5, one of the two second electrodes 5 may be referred to as the second electrode 5A, and the other as the second electrode 5B. Also, in the following explanation, to distinguish between the two third electrodes 8, one of the two third electrodes 8 may be referred to as the third electrode 8A, and the other third electrode 8 may be referred to as the third electrode 8B.

[0178] In this embodiment, in the direction along the width direction of the optical waveguide 2 (parallel to the X-axis), the third electrode 8A, first electrode 4A, first optical waveguide 2A, second electrode 5A, second electrode 5B, second optical waveguide 2B, first electrode 4B, and third electrode 8B are arranged in the order of third electrode 8A, first electrode 4A, first optical waveguide 2A, second electrode 5A, second electrode 5B, second optical waveguide 2B, first electrode 4B, and third electrode 8B. In the optical modulator 1D of this embodiment, each of the first electrode 4A, second electrode 5A, first electrode 4B, and second electrode 5B is a signal electrode, and each of the third electrode 8A and third electrode 8B is a ground electrode. In the optical modulator 1D of this embodiment, a first differential signal voltage is applied between the first electrode 4A and the second electrode 5A, and a differential signal voltage is applied between the first electrode 4B and the second electrode 5B.

[0179] The materials of the two first electrodes 4, the two second electrodes 5, and the two third electrodes 8 are, for example, the same as the materials of the first electrodes 4 and the second electrodes 5 of the optical modulator 1 according to Embodiment 1.

[0180] The third cladding layer 3 covers the third electrode 8A, the first electrode 4A, the first optical waveguide 2A, the second electrode 5A, the second electrode 5B, the second optical waveguide 2B, the first electrode 4B, and the third electrode 8B, as well as the first main surface 201 of the optical waveguide material layer 20.

[0181] The second cladding layer 7, like the second cladding layer 7 of the optical modulator 1B according to Embodiment 7 (see Figure 21), has a portion 73 that overlaps with the first optical waveguide 2A in the thickness direction of the optical waveguide material layer 20, and, like the optical modulator 1 according to Embodiment 1 (see Figures 1 to 4), a slit 72 penetrating the second cladding layer 7 is formed in the region that overlaps with the second optical waveguide 2B in the thickness direction of the optical waveguide material layer 20.

[0182] (2) Method for manufacturing an optical modulator The method for manufacturing the optical modulator 1D according to Embodiment 11 is substantially the same as the method for manufacturing the optical modulator 1B according to Embodiment 7. After obtaining a substrate S53 (see Figure 22(c)) by performing the first to third steps, a slit 72 is formed in the second cladding layer 7 using photolithography and etching techniques. Then, the fourth to eighth steps of the method for manufacturing the optical modulator 1B according to Embodiment 7 are performed, followed by a dicing step.

[0183] (3) The method for manufacturing the optical modulator 1D according to Embodiment 11 has the same effects as the method for manufacturing the optical modulator 1B according to Embodiment 7.

[0184] (Embodiment 12) The optical modulator 1E according to Embodiment 12 will be described with reference to Figure 36. With respect to the optical modulator 1E according to Embodiment 12, components that are the same as those in the optical modulator 1A according to Embodiment 4 (see Figures 14 and 15) are denoted by the same reference numerals and their description is omitted. Note that in Figure 36, the illustration of one of the two optical waveguides 2 described in Embodiment 4 is omitted, and the illustration of one of the two first electrodes 4 is omitted.

[0185] (1) Optical modulator configuration The optical modulator 1E according to embodiment 12 differs from the optical modulator 1A according to embodiment 4 in that the first electrode 4 and the second electrode 5 are in contact with the main surface 701 of the second cladding layer 7. The first electrode 4 is positioned away from the side surface 204 of the optical waveguide material layer 20. The second electrode 5 is positioned away from the side surface 205 of the optical waveguide material layer 20.

[0186] In this embodiment, the third cladding layer 3 covers the optical waveguide material layer 20, the first electrode 4, the second electrode 5, and a portion of the main surface 701 of the second cladding layer 7.

[0187] (2) Method for Manufacturing an Optical Modulator The method for manufacturing the optical modulator 1E according to Embodiment 12 is substantially the same as the method for manufacturing the optical modulator 1A according to Embodiment 4. After obtaining a substrate S7 (see Figure 17(c)) by performing steps 1 through 7, in step 8, an optical waveguide material layer 20 is formed, a first electrode 4 and a second electrode 5 are formed, and a third cladding layer 3 is formed. In the method for manufacturing the optical modulator 1E according to Embodiment 12, a dicing step is performed after step 8.

[0188] (3) The method for manufacturing the optical modulator 1E according to Embodiment 12 has the same effects as the method for manufacturing the optical modulator 1A according to Embodiment 4.

[0189] (Embodiment 13) The optical modulator 1F according to Embodiment 13 will be described with reference to Figure 37. With respect to the optical modulator 1F according to Embodiment 13, components that are the same as those in the optical modulator 1C according to Embodiment 10 (see Figure 33) are denoted by the same reference numerals and their description is omitted. Note that in Figure 37, the illustration of one of the two optical waveguides 2 described in Embodiment 2 is omitted, and the illustration of one of the two first electrodes 4 is omitted.

[0190] (1) Configuration of the optical modulator The optical modulator 1F according to Embodiment 13 differs from the optical modulator 1C according to Embodiment 10 in that the optical waveguide material layer 20, the first electrode 4 and the second electrode 5 are in contact with the main surface 701 of the second cladding layer 7. In this embodiment, the second cladding layer 7 is arranged inside a recess 92 formed in the main surface 91 of the low dielectric constant layer 9, and a part of the first electrode 4, the second electrode 5 and the third cladding layer 3 are in contact with a part of the main surface 91 of the low dielectric constant layer 9. In this embodiment, the first electrode 4 is in contact with the side surface 204 of the optical waveguide material layer 20. In addition, the second electrode 5 is in contact with the side surface 205 of the optical waveguide material layer 20.

[0191] In this embodiment, the third cladding layer 3 covers the optical waveguide material layer 20, the first electrode 4, the second electrode 5, and a portion of the main surface 91 of the low dielectric constant layer 9.

[0192] (2) Method for manufacturing an optical modulator The method for manufacturing the optical modulator 1F according to Embodiment 13 is substantially the same as the method for manufacturing the optical modulator 1B according to Embodiment 7 (see Figures 21 to 23). After performing steps 1 through 7, in step 8, an optical waveguide material layer 20 is formed, the first electrode 4 and the second electrode 5 are formed, and the third cladding layer 3 is formed. In the method for manufacturing the optical modulator 1F according to Embodiment 13, a dicing step is performed after step 8.

[0193] (3) Effects The method for manufacturing the optical modulator 1F according to Embodiment 13 has the same effects as the method for manufacturing the optical modulator 1B according to Embodiment 7.

[0194] (Embodiment 14) The optical modulator 1G according to Embodiment 14 will be described with reference to Figure 38, and then the manufacturing method of the optical modulator 1G will be described with reference to Figures 39 to 41. With respect to the optical modulator 1G according to Embodiment 14, components that are the same as those in the optical modulator 1A according to Embodiment 4 (see Figures 14 and 15) are denoted by the same reference numerals and their description is omitted. Note that in Figure 38, the illustration of one of the two optical waveguides 2 described in Embodiment 4 is omitted, and the illustration of one of the two first electrodes 4 is omitted.

[0195] (1) Optical modulator configuration The optical modulator 1G according to embodiment 14 differs from the optical modulator 1A according to embodiment 4 in that the first electrode 4 and the second electrode 5 are arranged across the first main surface 201 and the second main surface 202 of the optical waveguide material layer 20.

[0196] In this embodiment, the first electrode 4 and the second electrode 5 are U-shaped in a cross-sectional view perpendicular to the optical propagation direction of the optical waveguide 2, and are in contact with both the first main surface 201 and the second main surface 202 of the optical waveguide material layer 20. The first electrode 4 is in contact with the side surface 204 of the optical waveguide material layer 20, and the second electrode 5 is in contact with the side surface 205 of the optical waveguide material layer 20.

[0197] The first electrode 4 includes an electrode layer 4a in contact with the second main surface 202 of the optical waveguide material layer 20, and an electrode layer 4b in contact with the first main surface 201 and the side surface 204 of the optical waveguide material layer 20. The electrode layer 4a is located inside the first recess 77 of the second cladding layer 7.

[0198] The second electrode 5 includes an electrode layer 5a in contact with the second main surface 202 of the optical waveguide material layer 20, and an electrode layer 5b in contact with the first main surface 201 and the side surface 205 of the optical waveguide material layer 20. The electrode layer 5a is located inside the second recess 78 of the second cladding layer 7.

[0199] In the first electrode 4, the electrode layer 4b is covered by the third cladding layer 3. In the second electrode 5, the electrode layer 5b is covered by the third cladding layer 3.

[0200] (2) Method for manufacturing an optical modulator The method for manufacturing the optical modulator 1G according to Embodiment 14 will be described below with reference to Figures 39 to 41.

[0201] In the manufacturing method of the optical modulator 1G according to Embodiment 14, for example, steps 1 to 9 are performed sequentially. Regarding the manufacturing method of the optical modulator 1G according to Embodiment 14, steps similar to those in the manufacturing method of the optical modulator 1A according to Embodiment 4 will be omitted from explanation as appropriate.

[0202] In the first step, a support substrate 10 is prepared, and a low dielectric constant layer 9 is formed on the main surface 101 of the support substrate 10 to obtain a substrate S81 with the structure shown in Figure 39(a).

[0203] In the second step, a substrate S82 having the structure shown in Figure 39(b) is obtained by forming a second cladding material layer 70 on the low dielectric constant layer 9. The second cladding material layer 70 is the base layer for the second cladding layer 7.

[0204] In the third step, the second cladding material layer 70 is patterned to form the second cladding layer 7, thereby obtaining a substrate S83 with the structure shown in Figure 39(c). In the third step, the second cladding layer 7 is formed by using, for example, photolithography and etching techniques to create slits 72 that do not penetrate the second cladding material layer 70, a first recess 77, and a second recess 78 in the second cladding material layer 70. As the etching technique, for example, dry etching or wet etching techniques can be employed.

[0205] In the fourth step, a first electrode material layer 40, which will become the electrode layer 4a, and a second electrode material layer 50, which will become the electrode layer 5a, are formed. Then, a first cladding material layer 60 is formed to cover the first electrode material layer 40, the second electrode material layer 50, and the second cladding layer 7, thereby obtaining a substrate S84 with the structure shown in Figure 40(a). In the fourth step, a part of the first electrode material layer 40 is formed inside the first recess 77, and a part of the second electrode material layer 50 is formed inside the second recess 78. The thickness of the first electrode material layer 40 is greater than the depth of the first recess 77. The thickness of the second electrode material layer 50 is greater than the depth of the second recess 78. The first cladding material layer 60 is the layer that will become the first cladding layer 6. The main surface 600 of the first cladding material layer 60 formed in the fourth step has an uneven shape due to the shape of the substrate of the first cladding material layer 60.

[0206] In the fifth step, the outermost surface of the substrate S84 is flattened from the main surface 600 side of the first cladding material layer 60 to form the first cladding layer 6, electrode layer 4a and electrode layer 5a, and expose the second cladding layer 7, thereby obtaining a substrate S85 with the structure shown in Figure 40(b). The first cladding layer 6 is a part of the first cladding material layer 60. In the substrate S85, the outermost surface, which includes the main surface 601 of the first cladding layer 6, the main surface 701 of the second cladding layer 7, the main surface 401 of the electrode layer 4a and the main surface 501 of the electrode layer 5a, is planar. The substrate S85 includes a first cladding layer 6, a second cladding layer 7 having a greater dielectric constant than the first cladding layer 6, and a support substrate 10 supporting the first cladding layer 6 and the second cladding layer 7, and its outermost surface, including the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer, is planarized. In this embodiment, the substrate S85 constitutes the first substrate 100. The first substrate 100 has a planar main surface 111 that includes the main surface 601 of the first cladding layer 6 and the main surface 701 of the second cladding layer. In this embodiment, the main surface 111 of the first substrate 100 includes the main surface 601 of the first cladding layer 6, the main surface 701 of the second cladding layer 7, the main surface 401 of the electrode layer 4a, and the main surface 501 of the electrode layer 5a.

[0207] In the sixth step, a second substrate 200 is prepared, and the first substrate 100 and the second substrate 200 are joined to obtain a substrate S86 having the structure shown in Figure 40(c). The second substrate 200 has a first main surface 211 and a second main surface 212. The optical waveguide material is exposed on the second main surface 212 of the second substrate 200. In the sixth step, the main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are faced towards each other, and then the first substrate 100 and the second substrate 200 are joined. In this embodiment, the sixth step constitutes the joining process. In this embodiment, the second substrate 200 is an optical waveguide material substrate formed from an optical waveguide material.

[0208] In the seventh step, the second substrate 200 is thinned by grinding or the like, and the thinned second substrate 200 is processed to form an optical waveguide material layer 20 containing two optical waveguides 2, thereby obtaining a substrate S87 with the structure shown in Figure 41(a).

[0209] In the eighth step, a substrate S88 having the structure shown in Figure 41(b) is obtained by forming the electrode layer 4b of the first electrode 4 and the electrode layer 5b of the second electrode 5. The substrate S88 includes the first electrode 4 having an electrode layer 4a and an electrode layer 4b. The substrate S88 also includes the second electrode 5 having an electrode layer 5a and an electrode layer 5b.

[0210] In the ninth step, a third cladding layer 3 is formed to obtain a substrate S89 with the structure shown in Figure 40(c).

[0211] In the manufacturing method of the optical modulator 1G of this embodiment, the support substrate 10 prepared in the first step is a wafer (for example, a silicon wafer), and the substrates S81 to S89 are wafers having different structures from each other. In the manufacturing method of the optical modulator 1G of this embodiment, by performing each of the steps from the first to the ninth step, a wafer containing multiple optical modulators 1G can be obtained as the substrate S89. In the manufacturing method of the optical modulator 1G of this embodiment, after the ninth step, multiple optical modulators 1G can be obtained by cutting the substrate S89 with, for example, a dicing saw or a laser dicing device.

[0212] (3) The method for manufacturing the optical modulator 1G according to Embodiment 14 has the same effects as the method for manufacturing the optical modulator 1A according to Embodiment 2.

[0213] (Embodiment 15) The optical modulator 1H according to Embodiment 15 will be described with reference to Figure 42. With respect to the optical modulator 1H according to Embodiment 15, components that are the same as those in the optical modulator 1G according to Embodiment 14 (see Figure 38) are denoted by the same reference numerals and their description is omitted. Note that in Figure 42, the illustration of one of the two optical waveguides 2 described in Embodiment 4 is omitted, and the illustration of one of the two first electrodes 4 is omitted.

[0214] (1) Configuration of the optical modulator In this embodiment, the first electrode 4 is in contact only with the second main surface 202 of the optical waveguide material layer 20, out of the first main surface 201 and the second main surface 202. The first electrode 4 is located inside the first recess 77 of the second cladding layer 7. In this embodiment, the thickness of the first electrode 4 is the same as the depth of the first recess 77.

[0215] In this embodiment, the second electrode 5 is in contact only with the second main surface 202 of the optical waveguide material layer 20, out of the first main surface 201 and the second main surface 202. The second electrode 5 is located inside the second recess 78 of the second cladding layer 7. In this embodiment, the thickness of the second electrode 5 is the same as the depth of the second recess 78.

[0216] In this embodiment, the main surface 401 of the first electrode 4 that is in contact with the second main surface 202 of the optical waveguide material layer 20, the main surface 501 of the second electrode 5 that is in contact with the second main surface 202 of the optical waveguide material layer 20, the main surface 601 of the first cladding layer 6, and the main surface 701 of the second cladding layer 7 are all flush.

[0217] In this embodiment, the third cladding layer 3 is in contact with the first main surface 201 of the optical waveguide material layer 20 and the optical waveguide 2.

[0218] (2) Method for manufacturing an optical modulator The method for manufacturing the optical modulator 1H according to Embodiment 15 is substantially the same as the method for manufacturing the optical modulator 1G according to Embodiment 14 (see Figures 39 to 41), except that in the fifth step, the first electrode 4 and the second electrode 5 are formed instead of the electrode layer 4a and electrode layer 5a (see Figure 40(b)), and the third cladding layer 3 is formed after the seventh step.

[0219] (3) The method for manufacturing the optical modulator 1H according to Embodiment 15 has the same effects as the method for manufacturing the optical modulator 1G according to Embodiment 14.

[0220] (Embodiment 16) (1) Method for manufacturing an optical modulator Hereinafter, the method for manufacturing an optical modulator according to Embodiment 16 will be described with reference to Figures 43 and 44.

[0221] In the manufacturing method of the optical modulator according to Embodiment 16, for example, steps 1 to 8 are performed sequentially. Regarding the manufacturing method of the optical modulator according to Embodiment 16, steps similar to those used in the manufacturing method of the optical modulator 1B according to Embodiment 7 (see Figure 21) will be omitted from explanation as appropriate.

[0222] In the first step, a support substrate 10 is prepared, and a low dielectric constant layer 9 is formed on the main surface 101 of the support substrate 10 to obtain a substrate S101 with the structure shown in Figure 43(a). As a method for forming the low dielectric constant layer 9, for example, the CVD method can be used. Note that the support substrate 10 is a silicon substrate and the material of the low dielectric constant layer 9 is SiO ２ In this case, for example, a CVD method or a thermal oxidation method can be used as a method for forming the low dielectric constant layer 9.

[0223] In the second step, a substrate S102 having the structure shown in Figure 43(b) is obtained by forming recesses 92 on the main surface 91 of the low dielectric constant layer 9. In the second step, for example, photolithography and etching techniques are used to form the recesses 92 in the low dielectric constant layer 9. As the etching technique, for example, dry etching or wet etching techniques can be employed.

[0224] In the third step, a substrate S103 having the structure shown in Figure 43(c) is obtained by forming a second cladding layer 7 on the low dielectric constant layer 9. For example, sputtering, vapor deposition, or CVD can be used as the method for forming the second cladding layer 7. The second cladding layer 7 formed in the third step has an uneven shape due to the shape of the low dielectric constant layer 9 which is the base of the second cladding layer 7, but it also has a planar main surface 701.

[0225] In the fourth step, a metal material layer 800, which will become the bonding metal layer 80 (see Figure 44(a)), is formed by covering the planar main surface 701 of the second cladding layer 7, thereby obtaining a substrate S104 with the structure shown in Figure 43(d). The metal material layer 800 is formed, for example, by depositing a film using the sputtering method or the CVD method and then removing unnecessary parts by dry etching or wet etching, but it may also be formed using the lift-off method.

[0226] In the fifth step, a bonding metal layer 80 is formed by planarizing the outermost surface of the substrate S104 from the main surface 801 side of the metal material layer 800 using CMP or the like, thereby obtaining a substrate S105 with the structure shown in Figure 44(a). The bonding metal layer 80 is a part of the metal material layer 800. In the substrate S105, the main surface 81 of the bonding metal layer 80 is planar. In this embodiment, the substrate S105 constitutes the first substrate 100. The first substrate 100 has a planar main surface 111 that includes the main surface 81 of the bonding metal layer 80. The bonding metal layer 80 is very thin, and the entire bonding metal layer 80 becomes passivated and loses its metallic properties, so it does not contribute to increased losses such as light absorption. However, as the thickness of the bonding metal layer 80 increases, the areas in the bonding metal layer 80 that do not become passivated and maintain metallic properties also increase, which leads to increased losses such as light absorption. Therefore, the thickness of the bonding metal layer 80 is preferably very thin, and preferably 10 nm or less. In this embodiment, the first substrate formation step for forming the first substrate 100 includes the first to fifth steps.

[0227] In the sixth step, a second substrate 200 is prepared, and the first substrate 100 and the second substrate 200 are joined to obtain a substrate S106 with the structure shown in Figure 44(b). The second substrate 200 has a first main surface 211 and a second main surface 212. The optical waveguide material is exposed on the second main surface 212 of the second substrate 200. In the sixth step, the main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are faced towards each other, and then the first substrate 100 and the second substrate 200 are joined. In this embodiment, the sixth step constitutes the joining process. In this embodiment, the second substrate 200 is an optical waveguide material substrate formed from an optical waveguide material. In this embodiment, the first cladding layer 6 interposed between the portion 73 located inside the recess 92 in the second cladding layer 7 and the second main surface 212 of the second substrate 200 is an air cladding layer.

[0228] In the seventh step, the second substrate 200 is thinned by grinding or the like.

[0229] In the eighth step, the thinned second substrate 200 is processed to form an optical waveguide material layer 20 containing two optical waveguides 2, then the first electrode 4 and the second electrode 5 are formed, and then the third cladding layer 3 is formed.

[0230] In the optical modulator manufacturing method of this embodiment, the support substrate 10 prepared in the first step is a wafer (for example, a silicon wafer), and after the eighth step, a dicing step is performed using, for example, a dicing saw or a laser dicing apparatus, to obtain multiple optical modulators.

[0231] (2) The method for manufacturing an optical modulator according to the effect embodiment 16 comprises an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 side of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator according to Embodiment 16 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate 100 is formed which includes a second cladding layer 7 having a planar main surface 701 and a support substrate 10 and has a planar main surface 111. In the bonding process, a second substrate 200 is prepared, having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate 100 and the second substrate 200 are bonded together.

[0232] According to the optical modulator manufacturing method of Embodiment 16, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0233] In the method for manufacturing an optical modulator according to Embodiment 16, the first substrate 100 further includes a bonding metal layer 80 that covers the main surface of the second cladding layer 7. The main surface 111 of the first substrate 100 includes the main surface 81 of the bonding metal layer 80.

[0234] According to the above manufacturing method, it is possible to manufacture an optical modulator in which the second cladding layer 7 and the optical waveguide material layer 20 are joined via a bonding metal layer 80.

[0235] Furthermore, in the first substrate formation step of the optical modulator manufacturing method according to Embodiment 16, after forming the second cladding layer 7, a bonding metal layer 80 is formed on the main surface 701 of the second cladding layer 7. In the bonding step, the bonding metal layer 80 and the first cladding layer 6 of the first substrate 100 are placed facing the second main surface 202 of the second substrate 200, and then the first substrate 100 and the second substrate 200 are bonded together.

[0236] According to the above manufacturing method, it is possible to manufacture an optical modulator in which the second cladding layer 7 and the optical waveguide material layer 20 are joined via a bonding metal layer 80.

[0237] In the method for manufacturing an optical modulator according to Embodiment 16, the first cladding layer 6 is an air layer, but is not limited to an air layer. For example, after forming the bonding metal layer 80, a low dielectric constant material layer is formed, and by performing CMP or the like until the bonding metal layer 80 is exposed, the first cladding layer 6 can be composed of a part of the low dielectric constant material layer.

[0238] (Embodiment 17) (1) Method for manufacturing an optical modulator Hereinafter, the method for manufacturing an optical modulator according to Embodiment 17 will be described with reference to Figures 45 and 46.

[0239] In the manufacturing method of the optical modulator according to Embodiment 17, for example, steps 1 to 7 are performed sequentially. Regarding the manufacturing method of the optical modulator according to Embodiment 17, steps similar to those used in the manufacturing method of the optical modulator 1B according to Embodiment 7 (see Figure 21) will be omitted from explanation as appropriate.

[0240] In the first step, a support substrate 10 is prepared, and a low dielectric constant layer 9 is formed on the main surface 101 of the support substrate 10 to obtain a substrate S111 with the structure shown in Figure 45(a). As a method for forming the low dielectric constant layer 9, for example, the CVD method can be used. Note that the support substrate 10 is a silicon substrate and the material of the low dielectric constant layer 9 is SiO ２ In this case, for example, a CVD method or a thermal oxidation method can be used as a method for forming the low dielectric constant layer 9.

[0241] In the second step, a substrate S112 having the structure shown in Figure 45(b) is obtained by forming recesses 92 on the main surface 91 of the low dielectric constant layer 9. In the second step, for example, photolithography and etching techniques are used to form the recesses 92 in the low dielectric constant layer 9. As the etching technique, for example, dry etching or wet etching techniques can be employed.

[0242] In the third step, a substrate S113 having the structure shown in Figure 45(c) is obtained by forming a second cladding layer 7 on the low dielectric constant layer 9. For example, sputtering, vapor deposition, or CVD can be used as the method for forming the second cladding layer 7. The second cladding layer 7 formed in the third step has an uneven shape due to the shape of the low dielectric constant layer 9 which is the base of the second cladding layer 7, but it also has a planar main surface 701.

[0243] In the fourth step, a substrate S114 with the structure shown in Figure 45(d) is obtained by covering the planar main surface 701 of the second cladding layer 7 and forming a first cladding material layer 60 that will become the basis of the first cladding layer 6 (see Figure 46(a)). As a method for forming the first cladding material layer 60, for example, the CVD method can be used. The material of the first cladding material layer 60 is, for example, SiO ２ The material of the first cladding layer 60 is SiO ２ It may be a different material, and it may also be a different material from the material of the low dielectric constant layer 9.

[0244] In the fifth step, the first cladding layer 6 is formed by planarizing the outermost surface of the substrate S114 from the main surface 600 side of the first cladding material layer 60 using CMP or the like, thereby obtaining a substrate S115 with the structure shown in Figure 46(a). In this embodiment, the first cladding layer 6 covers the second cladding layer 7. The main surface 601 of the first cladding layer 6 is planar. In this embodiment, the first cladding layer 6 covers the portion 73 located within the recess 92 of the low dielectric constant layer 9 in the second cladding layer 7. Furthermore, in this embodiment, the first cladding layer 6 further includes a portion 61 that covers the planar main surface 701 of the second cladding layer 7. In this embodiment, the substrate S115 constitutes the first substrate 100. The first substrate 100 has a planar main surface 111 that includes the main surface 601 of the first cladding layer 6. In this embodiment, the first substrate formation step for forming the first substrate 100 includes steps 1 to 5.

[0245] In the sixth step, a second substrate 200 is prepared, and the first substrate 100 and the second substrate 200 are joined to obtain a substrate S116 with the structure shown in Figure 46(b). The second substrate 200 has a first main surface 211 and a second main surface 212. The optical waveguide material is exposed on the second main surface 212 of the second substrate 200. In the sixth step, the main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are faced towards each other, and then the first substrate 100 and the second substrate 200 are joined. In this embodiment, the sixth step constitutes the joining process. In this embodiment, the second substrate 200 is an optical waveguide material substrate formed from an optical waveguide material.

[0246] In the seventh step, the second substrate 200 is thinned by grinding or the like, and the thinned second substrate 200 is processed to form an optical waveguide material layer 20 containing two optical waveguides 2. Then, the first electrode 4 and the second electrode 5 are formed to obtain a substrate S117 with the structure shown in Figure 46(c).

[0247] In the manufacturing method of the optical modulator of this embodiment, the support substrate 10 prepared in the first step is a wafer (for example, a silicon wafer), and after the seventh step, a dicing step is performed using, for example, a dicing saw or a laser dicing apparatus, to obtain multiple optical modulators.

[0248] (2) The method for manufacturing an optical modulator according to the effect embodiment 17 comprises an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the side of the second main surface 202 of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator according to Embodiment 17 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate 100 is formed which includes a second cladding layer 7 having a planar main surface 701 and a support substrate 10 and has a planar main surface 111. In the bonding process, a second substrate 200 is prepared, having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate 100 and the second substrate 200 are bonded together.

[0249] According to the optical modulator manufacturing method of Embodiment 17, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0250] Furthermore, in the optical modulator manufacturing method according to Embodiment 17, the first substrate 100 further includes a first cladding layer 6. In addition, in the first substrate formation step in the optical modulator manufacturing method according to Embodiment 17, after forming the second cladding layer 7, the first cladding layer 6 having a planar main surface 611 is formed to cover the second cladding layer 7. In the bonding step, the first cladding layer 6 of the first substrate 100 and the second main surface 212 of the second substrate 200 are brought facing each other, and then the first substrate 100 and the second substrate 200 are bonded together.

[0251] According to the above manufacturing method, it is possible to manufacture an optical modulator in which the first cladding layer 6 is interposed between the second cladding layer 7 and the optical waveguide material layer 20.

[0252] (Embodiment 18) (1) Method for manufacturing an optical modulator Hereinafter, the method for manufacturing an optical modulator according to Embodiment 18 will be described with reference to Figure 47. The optical modulator manufactured by the method for manufacturing an optical modulator according to Embodiment 18 is optical modulator 1B according to modified example 2 of Embodiment 7 (see Figure 27).

[0253] In the manufacturing method of the optical modulator according to Embodiment 18, for example, steps 1 to 9 are performed sequentially. Regarding the manufacturing method of the optical modulator according to Embodiment 18, explanations of steps similar to those for the manufacturing method of the optical modulator 1B according to Embodiment 7 (see Figure 21) will be omitted as appropriate.

[0254] In the first step, a support substrate 10 is prepared, and a low dielectric constant layer 9 is formed on the main surface 101 of the support substrate 10 to obtain a substrate S121 with the structure shown in Figure 47(a). For example, the CVD method can be used as the method for forming the low dielectric constant layer 9. Note that the support substrate 10 is a silicon substrate and the material of the low dielectric constant layer 9 is SiO ２ In this case, for example, a CVD method or a thermal oxidation method can be used as a method for forming the low dielectric constant layer 9.

[0255] In the second step, a substrate S122 having the structure shown in Figure 47(b) is obtained by forming recesses 92 (grooves) on the main surface 91 of the low dielectric constant layer 9. In the second step, for example, photolithography and etching techniques are used to form the recesses 92 in the low dielectric constant layer 9. For the etching technique, for example, dry etching or wet etching techniques can be used. In this embodiment, grooves (recesses 92) are formed in the low dielectric constant layer 9 in the second step.

[0256] In the third step, a substrate S123 with the structure shown in Figure 47(c) is obtained by forming a second cladding material layer 70, which will be the basis for the second cladding layer 7, on the low dielectric constant layer 9. For example, sputtering, vapor deposition, or CVD can be used as the method for forming the second cladding material layer 70. The second cladding layer 7 formed in the third step has an uneven shape due to the shape of the low dielectric constant layer 9 which is the base shape of the second cladding layer 7, but it also has a planar main surface 701.

[0257] In the fourth step, a thinned portion 7122 is formed by thinning a portion of the second cladding material layer 70 that is located inside the recesses 92 (grooves) of the low dielectric constant layer 9 (the portion corresponding to the second portion 712 of the second cladding layer 7), thereby obtaining a substrate S124 with the structure shown in Figure 47(d). In the fourth step, the second cladding layer 7 is formed by thinning a portion of the second cladding material layer 70 that is located inside the grooves (recesses 92) of the low dielectric constant layer 9 (the portion corresponding to the second portion 712 of the second cladding layer 7), for example, by using photolithography and etching techniques. In other words, in the fourth step, the portion of the second cladding material layer 70 that is located inside the grooves (recesses 92) of the low dielectric constant layer 9 is locally thinned. As a result, the second cladding layer 7 is formed in the fourth step.

[0258] In this embodiment, after the fourth step, the same steps as the fourth step (step of forming the first cladding material layer 60), the fifth step (step of forming the first cladding layer 6 and exposing the second cladding layer 7), the sixth step (bonding step), the seventh step, and the eighth step, respectively, in the manufacturing method of the optical modulator 1B according to Embodiment 7 (see Figures 22 and 23) are performed as the fifth, sixth, seventh, eighth, and ninth steps, and then dicing is performed. In this embodiment, the first substrate formation step for forming the first substrate includes the first to fifth steps.

[0259] (2) The method for manufacturing an optical modulator according to the effect embodiment 18 comprises an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 side of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator according to Embodiment 18 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate having a planar main surface is formed, including a second cladding layer 7 having a planar main surface 701 and a support substrate 10. In the bonding process, a second substrate 200 is prepared, having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface of the first substrate and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate and the second substrate 200 are bonded together.

[0260] According to the optical modulator manufacturing method of Embodiment 18, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 (see Figure 27) is more likely to be as designed.

[0261] (Embodiment 19) (1) Method for manufacturing an optical modulator Hereinafter, the method for manufacturing an optical modulator according to Embodiment 19 will be described with reference to Figure 48.

[0262] In the method for manufacturing the optical modulator according to Embodiment 19, for example, steps 1 to 8 are performed sequentially. Regarding the method for manufacturing the optical modulator according to Embodiment 19, steps similar to those for manufacturing the optical modulator 1B according to Embodiment 7 (see Figure 21) will be omitted from explanation as appropriate.

[0263] In the first step, a support substrate 10 is prepared, and a low dielectric constant layer 9 is formed on the main surface 101 of the support substrate 10 to obtain a substrate S131 with the structure shown in Figure 48(a). As a method for forming the low dielectric constant layer 9, for example, the CVD method can be used. Note that the support substrate 10 is a silicon substrate and the material of the low dielectric constant layer 9 is SiO ２ In this case, for example, a CVD method or a thermal oxidation method can be used as a method for forming the low dielectric constant layer 9.

[0264] In the second step, a substrate S132 having the structure shown in Figure 48(b) is obtained by forming recesses 92 on the main surface 91 of the low dielectric constant layer 9. In the second step, for example, photolithography and etching techniques are used to form the recesses 92 in the low dielectric constant layer 9. As the etching technique, for example, dry etching or wet etching techniques can be employed.

[0265] In the third step, a substrate S133 with the structure shown in Figure 48(c) is obtained by forming a second cladding layer 7 having slits 72 on the low dielectric constant layer 9. For example, the lift-off method can be used as the method for forming the second cladding layer 7 having slits 72. The second cladding layer 7 formed in the third step also has a planar main surface 701.

[0266] After the third step, the fourth, fifth, sixth, seventh, and eighth steps are performed in the same manner as the fourth step (step of forming the first cladding material layer 60), the fifth step (step of forming the first cladding layer 6 and exposing the second cladding layer 7), the sixth step (bonding step), the seventh, and eighth steps, respectively, in the manufacturing method of the optical modulator 1B according to Embodiment 7 (see Figures 22 and 23), and then dicing is performed. In this embodiment, the first substrate formation step for forming the first substrate includes the first to fifth steps.

[0267] (2) The method for manufacturing an optical modulator according to the effect embodiment 19 comprises an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 side of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator according to Embodiment 19 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate having a planar main surface is formed, including a second cladding layer 7 having a planar main surface 701 and a support substrate 10. In the bonding process, a second substrate 200 is prepared, having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface of the first substrate and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate and the second substrate 200 are bonded together.

[0268] According to the optical modulator manufacturing method of Embodiment 19, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 (see Figure 30) is more likely to be as designed.

[0269] Further, in the method for manufacturing an optical modulator according to Embodiment 19, in the first substrate forming step, a low dielectric constant layer 9 having a lower dielectric constant than that of the second cladding layer 7 is formed on the main surface 101 of the support substrate 10, and then a groove (recess 92) is formed in the low dielectric constant layer 9. Thereafter, the second cladding layer 7 having the slit 72 is formed inside the groove (recess 92) of the low dielectric constant layer 9 by a lift-off method.

[0270] According to the above manufacturing method, when forming the second cladding layer 7, it is possible to prevent the second cladding layer 7 from being formed at unnecessary locations on the low dielectric constant layer 9.

[0271] (Embodiment 20) (1) Method for manufacturing an optical modulator Hereinafter, the method for manufacturing an optical modulator according to Embodiment 20 will be described with reference to FIG. 49.

[0272] In the method for manufacturing an optical modulator according to Embodiment 20, for example, the first to eighth steps are sequentially performed. Regarding the method for manufacturing an optical modulator according to Embodiment 20, descriptions of steps similar to those in the method for manufacturing the optical modulator 1B (see FIG. 21) according to Embodiment 7 will be appropriately omitted.

[0273] In the first step, a support substrate 10 is prepared, and by forming a low dielectric constant layer 9 on the main surface 101 of the support substrate 10, a substrate S141 having the structure shown in FIG. 49(a) is obtained. As a method for forming the low dielectric constant layer 9, for example, a CVD method can be employed. When the support substrate 10 is a silicon substrate and the material of the low dielectric constant layer 9 is SiO ２ In this case, as a method for forming the low dielectric constant layer 9, for example, a CVD method or a thermal oxidation method can be employed.

[0274] In the second step, by forming a recess 92 on the main surface 91 of the low dielectric constant layer 9, a substrate S142 having the structure shown in FIG. 49(b) is obtained. In the second step, for example, photolithography technology and etching technology are used to form the recess 92 in the low dielectric constant layer 9. As the etching technology, for example, a dry etching technology or a wet etching technology can be employed.

[0275] In the third step, a substrate S144 having the structure shown in Figure 49(d) is obtained by forming a second cladding layer 7 on the low dielectric constant layer 9. The second cladding layer 7 formed in this embodiment includes a first high dielectric constant material layer 7a and a second high dielectric constant material layer 7b. In the third step, first, a substrate S143 having the structure shown in Figure 49(c) is obtained by forming the first high dielectric constant material layer 7a of the second cladding layer 7 on the low dielectric constant layer 9, and then a substrate S144 having the structure shown in Figure 49(d) is obtained by forming the second high dielectric constant material layer 7b. The first high dielectric constant material layer 7a is formed to cover the low dielectric constant layer 9. As a method for forming the first high dielectric constant material layer 7a, for example, sputtering, vapor deposition, or CVD can be used. The second high dielectric constant material layer 7b is formed to cover a part of the first high dielectric constant material layer 7a. As a method for forming the second high dielectric constant material layer 7b, for example, the lift-off method can be employed. The materials of the first high dielectric constant material layer 7a and the second high dielectric constant material layer 7b are the same as the materials of the first high dielectric constant material layer 7a and the second high dielectric constant material layer 7b in the optical modulator 1C (see Figure 34) according to a modified example of Embodiment 10, so their explanation is omitted.

[0276] In the fourth step, similar to the fourth step of Embodiment 18, a thinned portion is formed by thinning a part of the second portion 712 located inside the recess 92 of the low dielectric constant layer 9 within the second cladding layer 7. In the fourth step, instead of forming a thinned portion, a slit may be formed that penetrates the second portion 712.

[0277] In this embodiment, after the fourth step, the same steps as the fourth step (step of forming the first cladding material layer 60), the fifth step (step of forming the first cladding layer 6 and exposing the second cladding layer 7), the sixth step (bonding step), the seventh step, and the eighth step, respectively, in the manufacturing method of the optical modulator 1B according to Embodiment 7 (see Figures 22 and 23) are performed as the fifth, sixth, seventh, eighth, and ninth steps, and then dicing is performed. In this embodiment, the first substrate formation step for forming the first substrate includes the first to fifth steps.

[0278] (2) The method for manufacturing an optical modulator according to the 20th embodiment comprises an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 side of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The manufacturing method of the optical modulator according to Embodiment 20 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate having a planar main surface is formed, including a second cladding layer 7 having a planar main surface 701 and a support substrate 10. In the bonding process, a second substrate 200 is prepared, having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface of the first substrate and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate and the second substrate 200 are bonded together.

[0279] According to the manufacturing method of the optical modulator in embodiment 20, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0280] (Embodiment 21) (1) Method for manufacturing an optical modulator Hereinafter, the method for manufacturing an optical modulator according to Embodiment 21 will be described with reference to Figure 50.

[0281] In the manufacturing method of the optical modulator according to Embodiment 21, for example, steps 1 to 8 are performed sequentially. Regarding the manufacturing method of the optical modulator according to Embodiment 21, steps similar to those used in the manufacturing method of the optical modulator 1B according to Embodiment 7 (see Figure 21) will be omitted from explanation as appropriate.

[0282] In this embodiment, the first substrate 100 is formed by performing the first to fifth steps, which are the same as the manufacturing method for the optical modulator 1B according to Embodiment 7 (see Figure 21), and then the sixth step is performed. In the sixth step, a second substrate 200 having an optical waveguide 2 and a low dielectric constant cladding layer 610 is prepared, and the first substrate 100 and the second substrate 200 are joined together to obtain a substrate S151 with the structure shown in Figure 50(a). In this embodiment, the sixth step constitutes a joining step that joins the first substrate 100 and the second substrate 200. Furthermore, in the second substrate 200 of this embodiment, the optical waveguide 2 and the low dielectric constant cladding layer 610 are formed on the second main surface 212 side of the second substrate 200, and the planar second main surface 212 of the second substrate 200 includes the main surface of the optical waveguide 2 (the lower surface of the optical waveguide 2 in Figure 50(a)) and the main surface of the low dielectric constant cladding layer 610 (the lower surface of the low dielectric constant cladding layer 610 in Figure 50(a)). The dielectric constant of the low dielectric constant cladding layer 610 is smaller than the dielectric constant of the second cladding layer 7. The material of the low dielectric constant cladding layer 610 is the same as the material of the first cladding layer 6, but it may be different from the material of the first cladding layer 6.

[0283] In the seventh step of this embodiment, the second substrate 200 is thinned by grinding or the like to form an optical waveguide material layer 20, thereby obtaining a substrate S152 with the structure shown in Figure 50(b).

[0284] In the eighth step of this embodiment, two first electrodes 4 and a second electrode 5 are formed on the first main surface 201 of the optical waveguide material layer 20, and then a third cladding layer 3 is formed to obtain a substrate S153 with the structure shown in Figure 50(c).

[0285] (2) The method for manufacturing an optical modulator according to the effect embodiment 21 comprises an optical waveguide material layer 20, a first electrode 4, a second electrode 5, a first cladding layer 6, a second cladding layer 7, and a support substrate 10. The optical waveguide material layer 20 has a first main surface 201 and a second main surface 202. The optical waveguide material layer 20 includes an optical waveguide 2 formed on the first main surface 201 side. The first electrode 4 is spaced apart in the width direction of the optical waveguide 2 from the first end 21 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. The second electrode 5 is spaced apart in the width direction of the optical waveguide 2 from the second end 22 in the width direction of the optical waveguide 2 and is arranged along the optical propagation direction of the optical waveguide 2. A voltage is applied between the second electrode 5 and the first electrode 4. The first cladding layer 6 overlaps the optical waveguide 2 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the second main surface 202 of the optical waveguide material layer 20 between the first electrode 4 and the second electrode 5. The second cladding layer 7 overlaps at least the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 and is located on the side of the second main surface 202 of the optical waveguide material layer 20. The support substrate 10 supports the second cladding layer 7. The refractive index of the first cladding layer 6 is smaller than the refractive index of the optical waveguide 2. The dielectric constant of the second cladding layer 7 is larger than the dielectric constant of the first cladding layer 6. The method for manufacturing an optical modulator according to Embodiment 21 comprises a first substrate formation step and a bonding step. In the first substrate formation step, a first substrate 100 is formed which includes a second cladding layer 7 having a planar main surface 701 and a support substrate 10 and has a planar main surface 111. In the bonding process, a second substrate 200 is prepared, having a first main surface 211 and a planar second main surface 212, with the optical waveguide material that will become the optical waveguide material layer 20 containing the optical waveguide 2 exposed on the second main surface 212. The main surface 111 of the first substrate 100 and the second main surface 212 of the second substrate 200 are then placed facing each other, and the first substrate 100 and the second substrate 200 are bonded together.

[0286] According to the manufacturing method of the optical modulator in Embodiment 21, the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0287] (Embodiment 22) The optical modulator 1J according to Embodiment 22 will be described with reference to Figures 51 to 53. With respect to the optical modulator 1J according to Embodiment 22, components that are the same as those in the optical modulator 1A according to Embodiment 4 (see Figures 14 and 15) are denoted by the same reference numerals and their description is omitted. Note that in Figures 51 to 53, the illustration of one of the two optical waveguides 2 (see Figure 14) described in Embodiment 4 is omitted, and the illustration of one of the two first electrodes 4 (see Figure 14) is omitted. Also, in Figure 51, the illustration of the third cladding layer 3 (see Figures 52 and 53) is omitted.

[0288] (1) Optical modulator configuration The optical modulator 1J according to embodiment 22 differs from the optical modulator 1A according to embodiment 4 in that a part of the second cladding layer 7 is removed, as shown in Figures 51 and 52, in order to adjust the impedance or the effective refractive index for high-frequency signals. Therefore, in the optical modulator 1J of this embodiment, as shown in Figures 52 and 53, the cross-sectional shape perpendicular to the optical propagation direction (direction parallel to the Y axis) of the optical waveguide 2 is not constant. Furthermore, in an optical modulator in which the cross-sectional shape perpendicular to the optical propagation direction of the optical waveguide is constant and there is no second cladding layer, the impedance and the effective refractive index for high-frequency signals depend greatly on the distance between the first electrode and the second electrode, and therefore the adjustment range is limited. In contrast, the optical modulator 1J according to Embodiment 22 allows for adjustment of the impedance and the effective refractive index for high-frequency signals regardless of whether the dielectric constant of the second cladding layer 7, the shape of the second cladding layer 7, the shape of the slits 72 in the second cladding layer 7, or the arrangement range of the second cladding layer 7 is changed. Therefore, it offers a high degree of design freedom and a wide adjustment range for impedance and the effective refractive index for high-frequency signals.

[0289] (2) Method for manufacturing an optical modulator The method for manufacturing the optical modulator 1J according to Embodiment 22 is substantially the same as the method for manufacturing the optical modulator 1A according to Embodiment 4, except that in the third step of the first to eighth steps, a slit 72 is formed in the second cladding layer 7 and a part of the second cladding layer 7 is removed at a position different from the slit 72.

[0290] (3) Effect The optical modulator 1J according to Embodiment 22 is similar to the optical modulator 1A according to Embodiment 4 in that the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0291] Furthermore, the manufacturing method of the optical modulator 1J according to Embodiment 22 is similar to that of the optical modulator 1A according to Embodiment 4 in that the relationship between the second cladding layer 7 and the optical waveguide material layer 20 tends to be as designed.

[0292] (Embodiment 23) The optical modulator 1K according to Embodiment 23 will be described with reference to Figures 54 to 56. With respect to the optical modulator 1K according to Embodiment 23, components that are the same as those in the optical modulator 1J according to Embodiment 22 (see Figures 51 to 53) are denoted by the same reference numerals and their description is omitted. Note that in Figures 54 to 56, the illustration of one of the two optical waveguides 2 (see Figure 14) described in Embodiment 4 is omitted, and the illustration of one of the two first electrodes 4 (see Figure 14) is omitted. Also, in Figure 54, the illustration of the third cladding layer 3 (see Figures 55 and 56) is omitted.

[0293] (1) Configuration of the optical modulator In this embodiment, the optical modulator 1K differs from the optical modulator 1J according to embodiment 22 in that, as shown in Figures 54 and 56, a part of the second cladding layer 7 is removed along the entire length in the X-axis direction. In this embodiment, the optical modulator 1K, as shown in Figures 55 and 56, has a cross-sectional shape perpendicular to the optical propagation direction (direction parallel to the Y-axis) of the optical waveguide 2 that is not constant. The optical modulator 1K according to embodiment 23 has a high degree of design freedom and a wide adjustment range for impedance and effective refractive index for high-frequency signals because the impedance and effective refractive index for high-frequency signals can be adjusted regardless of whether the dielectric constant of the second cladding layer 7, the shape of the second cladding layer 7, the shape of the slit 72 in the second cladding layer 7, or the arrangement range of the second cladding layer 7 is changed.

[0294] (2) Method for manufacturing an optical modulator The method for manufacturing the optical modulator 1K according to Embodiment 23 is substantially the same as the method for manufacturing the optical modulator 1J according to Embodiment 22, and differs from the method for manufacturing the optical modulator 1A according to Embodiment 4 in that, among the first to eighth steps, the extent to which a part of the second cladding layer 7 is removed in the third step is different.

[0295] (3) Effect The optical modulator 1K according to Embodiment 23 is similar to the optical modulator 1J according to Embodiment 22 in that the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0296] Furthermore, the manufacturing method of the optical modulator 1K according to Embodiment 23, similar to the optical modulator 1J according to Embodiment 22, makes it easier for the relationship between the second cladding layer 7 and the optical waveguide material layer 20 to be as designed.

[0297] (Embodiment 24) The optical modulator 1L according to Embodiment 24 will be described with reference to Figures 57 to 60. With respect to the optical modulator 1L according to Embodiment 24, components that are the same as those in the optical modulator 1A according to Embodiment 4 (see Figures 14 and 15) are denoted by the same reference numerals and their description is omitted. Note that in Figures 57 to 60, the illustration of one of the two optical waveguides 2 (see Figure 14) described in Embodiment 4 is omitted, and the illustration of one of the two first electrodes 4 (see Figure 14) is omitted. Also, in Figure 57, the illustration of the third cladding layer 3 (see Figures 58 to 60) is omitted.

[0298] (1) Optical modulator configuration The optical modulator 1L according to embodiment 24 differs from the optical modulator 1A according to embodiment 4 in that a part of the second cladding layer 7 is removed, as shown in Figures 57, 59, and 60, in order to adjust the impedance or the effective refractive index for high-frequency signals. Therefore, in the optical modulator 1L of this embodiment, as shown in Figures 58 to 60, the cross-sectional shape perpendicular to the optical propagation direction (direction parallel to the Y axis) of the optical waveguide 2 is not constant. At the position of the cross section in Figure 58, the second cladding layer 7 is arranged along the entire length in the X-axis direction, at the position of the cross section in Figure 59, a part of the second cladding layer 7 is removed, and at the position of the cross section in Figure 60, the second cladding layer 7 is removed along the entire length in the X-axis direction. The optical modulator 1L according to Embodiment 24 allows for adjustment of impedance and effective refractive index for high-frequency signals regardless of whether the dielectric constant of the second cladding layer 7, the shape of the second cladding layer 7, the shape of the slits 72 in the second cladding layer 7, or the arrangement range of the second cladding layer 7 is changed. Therefore, it offers a high degree of design flexibility and a wide adjustment range for impedance and effective refractive index for high-frequency signals. The shape of the second cladding layer 7 in a plan view from the thickness direction of the optical waveguide material layer 20 is not limited to the example in Figure 57 and may be changed as appropriate.

[0299] (2) Method for manufacturing an optical modulator The method for manufacturing the optical modulator 1L according to Embodiment 24 is substantially the same as the method for manufacturing the optical modulator 1A according to Embodiment 4, except that in the third step of the first to eighth steps, a slit 72 is formed in the second cladding layer 7 and a part of the second cladding layer 7 is removed at a position different from the slit 72.

[0300] (3) Effect The optical modulator 1L according to Embodiment 24 is similar to the optical modulator 1A according to Embodiment 4 in that the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0301] Furthermore, the manufacturing method of the optical modulator 1L according to Embodiment 24 is similar to that of the optical modulator 1A according to Embodiment 4 in that the relationship between the second cladding layer 7 and the optical waveguide material layer 20 tends to be as designed.

[0302] (Embodiment 25) The optical modulator 1M according to Embodiment 25 will be described with reference to Figures 61 to 64. With respect to the optical modulator 1M according to Embodiment 25, components that are the same as those in the optical modulator 1A according to Embodiment 4 (see Figures 14 and 15) are denoted by the same reference numerals and their description is omitted. Note that in Figures 61 to 64, the illustration of one of the two optical waveguides 2 (see Figure 14) described in Embodiment 4 is omitted, and the illustration of one of the two first electrodes 4 (see Figure 14) is omitted. Also, in Figure 61, the illustration of the third cladding layer 3 (see Figures 62 to 64) is omitted.

[0303] (1) Optical modulator configuration The optical modulator 1M according to embodiment 25 differs from the optical modulator 1A according to embodiment 4 in that, as shown in Figures 61, 63, and 64, a portion of the second cladding layer 7 other than the slit 72 is removed in order to adjust the impedance or the effective refractive index for high-frequency signals. Therefore, in the optical modulator 1M of this embodiment, as shown in Figures 62 to 64, the shape of the second cladding layer 7 is not constant in the cross section perpendicular to the optical propagation direction (direction parallel to the Y axis) of the optical waveguide 2. At the position of the cross section in Figure 62, the second cladding layer 7 is arranged along the entire length in the X-axis direction, while at the position of the cross section in Figure 63, a portion of the second cladding layer 7 is removed, and at the position of the cross section in Figure 64, the second cladding layer 7 is removed along the entire length in the X-axis direction. The optical modulator 1M according to Embodiment 25 allows for adjustment of impedance and effective refractive index for high-frequency signals regardless of whether the dielectric constant of the second cladding layer 7, the shape of the second cladding layer 7, the shape of the slits 72 in the second cladding layer 7, or the arrangement range of the second cladding layer 7 is changed. Therefore, it offers a high degree of design freedom and a wide adjustment range for impedance and effective refractive index for high-frequency signals. The shape of the second cladding layer 7 in a plan view from the thickness direction of the optical waveguide material layer 20 is not limited to the example in Figure 61 and may be changed as appropriate.

[0304] Furthermore, the optical modulator 1M according to Embodiment 25 differs from the optical modulator 1A according to Embodiment 4 in that, as shown in Figures 61 to 64, the shapes of the first electrode 4 and the second electrode 5 are different from the shapes of the first electrode 4 and the second electrode 5 (elongated shape) in the optical modulator 1A according to Embodiment 4, in order to adjust the impedance or the effective refractive index for high-frequency signals. Alternatively, the optical modulator 1M according to Embodiment 25 differs from the optical modulator 1A according to Embodiment 4 in that a part of each of the first electrode 4 and the second electrode 5 is removed. In the optical modulator 1M of this embodiment, as shown in Figures 62 to 64, the shapes of the first electrode 4 and the second electrode 5 are not constant in the cross-section perpendicular to the optical propagation direction (direction parallel to the Y-axis) of the optical waveguide 2. In this embodiment, the shape of the first electrode 4 differs from that of the cross-section in Figure 62, Figure 63, and Figure 64. Furthermore, in this embodiment, the shape of the second electrode 5 differs from that of the cross-sectional positions in Figure 62, Figure 63, and Figure 64. In this embodiment, the distance between the first electrode 4 and the first end 21 of the optical waveguide 2 differs from that of the cross-sectional positions in Figure 62 and Figure 64. Furthermore, in this embodiment, the distance between the second electrode 5 and the second end 22 of the optical waveguide 2 differs from that of the cross-sectional positions in Figure 62 and Figure 64. Furthermore, in this embodiment, the distance between the first electrode 4 and the second electrode 5 differs from that of the cross-sectional positions in Figure 62 and Figure 64. The optical modulator 1M according to embodiment 25 has a high degree of design freedom and a wide adjustment range for impedance and effective refractive index for high-frequency signals, as it can adjust the impedance and effective refractive index for high-frequency signals even if the shapes of the two first electrodes 4 and second electrodes 5 are changed. The shapes of the first electrode 4 and the second electrode 5 in a plan view from the thickness direction of the optical waveguide material layer 20 are not limited to the example in Figure 61 and may be changed as appropriate.

[0305] (2) Method for Manufacturing an Optical Modulator The method for manufacturing the optical modulator 1M according to Embodiment 25 is substantially the same as the method for manufacturing the optical modulator 1A according to Embodiment 4, except that in the third step of the first to eighth steps, a slit 72 is formed in the second cladding layer 7 and a part of the second cladding layer 7 is removed at a position different from the slit 72. Furthermore, the method for manufacturing the optical modulator 1M according to Embodiment 25 differs from the method for manufacturing the optical modulator 1A according to Embodiment 4 in that the shapes of the two first electrodes 4 and second electrodes 5 formed in the eighth step are different.

[0306] (3) Effect The optical modulator 1M according to Embodiment 25 is similar to the optical modulator 1A according to Embodiment 4 in that the relationship between the second cladding layer 7 and the optical waveguide material layer 20 is more likely to be as designed.

[0307] Furthermore, the manufacturing method of the optical modulator 1M according to Embodiment 25 is similar to that of the optical modulator 1A according to Embodiment 4 in that the relationship between the second cladding layer 7 and the optical waveguide material layer 20 tends to be as designed.

[0308] (Other examples) Embodiments 1 to 25 described above are merely one of many embodiments of the present invention. Embodiments 1 to 25 described above can be modified in various ways depending on the design, etc., as long as the objective of the present invention is achieved, and may be combined as appropriate.

[0309] Optical modulators 1, 1A, 1E, 1G, 1H, 1J to 1M have two slits 72 in the second cladding layer 7 that overlap with two optical waveguides 2 (first optical waveguide 2, second optical waveguide 2), but it is sufficient that they have at least one slit 72 that overlaps with the first optical waveguide 2. Optical modulators 1, 1A, 1E, 1G, 1H, 1J to 1M have one slit 72 formed for each of the multiple optical waveguides 2 in the second cladding layer 7, but two or more slits 72 may be formed for each of the multiple optical waveguides 2 so as to be aligned in the direction of optical propagation of the optical waveguide 2.

[0310] Furthermore, the optical modulator 1A has a portion 712 in the second cladding layer 7 that overlaps with two optical waveguides 2 (first optical waveguide 2, second optical waveguide 2), but it is sufficient that it has at least a portion 712 that overlaps with the first optical waveguide 2. In the optical modulator 1A, one portion 712 is formed for each of the plurality of optical waveguides 2 in the second cladding layer 7, but two or more portions 712 may be formed for each of the plurality of optical waveguides 2 so as to be aligned in the direction of optical propagation of the optical waveguide 2.

[0311] In optical modulators 1, 1A to 1H, and 1J to 1M, the third cladding layer 3 may be air.

[0312] Optical modulators 1, 1A to 1H, and 1J to 1M may not have a low dielectric constant layer 9.

[0313] Optical modulators 1, 1A to 1H, and 1J to 1M may have a support substrate 10 that has a cavity overlapping the optical waveguide 2 in the thickness direction of the support substrate 10. In this case, optical modulators 1, 1A to 1H can improve their high-frequency characteristics. The cavity of the support substrate 10 may penetrate through the support substrate 10 in the thickness direction, or it may be formed from the main surface 101 of the support substrate 10 to a predetermined depth position.

[0314] If the material of the optical waveguide material layer 20 is lithium niobate, each of the two optical waveguides 2 may be a Ti-diffusing type optical waveguide.

[0315] 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1J, 1K, 1L, 1M Optical modulator 2 Optical waveguide 21 First end 22 Second end 20 Optical waveguide material layer 201 First main surface 202 Second main surface 3 Third cladding layer 4, 4B First electrode 5, 5B Second electrode 6 First cladding layer 7 Second cladding layer 72 Slit 701 Main surface 711 First part 712 Second part 9 Low dielectric constant layer 10 Support substrate (First support substrate) 80 Bonding metal layer 100 First substrate 111 Main surface 200 Second substrate 211 First main surface 212 Second main surface 230 Second support substrate t1 Thickness

Claims

1. A method for manufacturing an optical modulator, the optical modulator comprising: an optical waveguide material layer having a first main surface and a second main surface and including an optical waveguide; a first electrode spaced in the width direction from a first end in the width direction of the optical waveguide and arranged along the optical propagation direction of the optical waveguide; a second electrode spaced in the width direction from a second end in the width direction of the optical waveguide and arranged along the optical propagation direction of the optical waveguide, to which a voltage is applied between the first electrode and the second electrode; a first cladding layer overlapping the optical waveguide in a plan view from the thickness direction of the optical waveguide material layer and located on the second main surface of the optical waveguide material layer between the first electrode and the second electrode; a second cladding layer overlapping at least the first electrode and the second electrode in a plan view from the thickness direction of the optical waveguide material layer and located on the second main surface side of the optical waveguide material layer; and a support substrate supporting the second cladding layer. The refractive index of the first cladding layer is smaller than the refractive index of the optical waveguide, and the dielectric constant of the second cladding layer is larger than the dielectric constant of the first cladding layer. The method for manufacturing the optical modulator comprises: a first substrate forming step of forming a first substrate having a planar main surface, the second cladding layer having a planar main surface, and the support substrate; and a joining step of preparing a second substrate having a first main surface and a planar second main surface, the second main surface of which an optical waveguide material that will become the optical waveguide material layer containing the optical waveguide is exposed, the main surface of the first substrate and the second main surface of the second substrate are brought facing each other, and then the first substrate and the second substrate are joined.

2. The method for manufacturing an optical modulator according to claim 1, wherein the first substrate further comprises the first cladding layer, the first cladding layer is supported by the support substrate, and the main surface of the first substrate includes the main surface of the first cladding layer and the main surface of the second cladding layer.

3. The method for manufacturing an optical modulator according to claim 2, wherein in the first substrate formation step, a low dielectric constant layer having a lower dielectric constant than the second cladding layer is formed on the main surface of the support substrate, a second cladding material layer which will be the basis of the second cladding layer is formed on the low dielectric constant layer, a slit is formed in the second cladding material layer that penetrates the second cladding material layer, a first cladding material layer which will be the basis of the first cladding layer is formed by covering the second cladding material layer, and the first cladding layer and the first cladding layer located inside the slit in the second cladding layer are formed by planarizing the first cladding material layer.

4. The method for manufacturing an optical modulator according to claim 1, wherein the first substrate further includes a bonding metal layer covering the main surface of the second cladding layer, and the main surface of the first substrate includes the main surface of the bonding metal layer.

5. The method for manufacturing an optical modulator according to claim 4, wherein in the first substrate forming step, the bonding metal layer is formed on the main surface of the second cladding layer after the second cladding layer has been formed, and in the bonding step, the bonding metal layer of the first substrate and the first cladding layer are placed facing the second main surface of the second substrate, and then the first substrate and the second substrate are bonded together.

6. The method for manufacturing an optical modulator according to claim 1, wherein the first substrate further comprises the first cladding layer, the first cladding layer covers the main surface of the second cladding layer, and the main surface of the first substrate includes the main surface of the first cladding layer.

7. The method for manufacturing an optical modulator according to claim 6, wherein in the first substrate formation step, the second cladding layer is formed, and then the first cladding layer having a planar main surface is formed to cover the second cladding layer, and in the bonding step, the first cladding layer of the first substrate and the second main surface of the second substrate are faced towards each other before bonding the first substrate and the second substrate.

8. The method for manufacturing an optical modulator according to any one of claims 2, 4 to 7, wherein in the first substrate formation step, a low dielectric constant layer having a lower dielectric constant than the second cladding layer is formed on the main surface of the support substrate, a second cladding material layer which will be the basis of the second cladding layer is formed on the low dielectric constant layer, a slit is formed in the second cladding material layer, a first cladding material layer which will be the basis of the first cladding layer is formed by covering the second cladding material layer, and the first cladding layer and the first cladding layer located inside the slit in the second cladding layer are formed by planarizing the first cladding material layer.

9. The method for manufacturing an optical modulator according to any one of claims 2, 4 to 7, wherein in the first substrate formation step, a low dielectric constant layer having a dielectric constant lower than that of the second cladding layer is formed on the main surface of the support substrate, grooves are formed in the low dielectric constant layer, and then the second cladding layer having slits is formed inside the grooves of the low dielectric constant layer by a lift-off method.

10. The method for manufacturing an optical modulator according to any one of claims 2, 4 to 7, wherein in the first substrate formation step, a low dielectric constant layer having a lower dielectric constant than the second cladding layer is formed on the main surface of the support substrate, grooves are formed in the low dielectric constant layer, a second cladding material layer which will be the basis of the second cladding layer is formed by covering the low dielectric constant layer, and then the portion of the second cladding material layer located inside the grooves of the low dielectric constant layer is locally thinned.

11. The method for manufacturing an optical modulator according to any one of claims 2 to 10, wherein the second substrate is an optical waveguide material substrate formed of the optical waveguide material, and after the bonding step, the optical waveguide material layer including the optical waveguide is formed by processing the optical waveguide material substrate.

12. The method for manufacturing an optical modulator according to any one of claims 2 to 10, wherein the second substrate comprises a second support substrate different from the first support substrate which is the support substrate, and an optical waveguide material thin film laminated on the second support substrate which forms the basis of the optical waveguide material layer, and after the bonding step, the second support substrate is removed and the optical waveguide material thin film is processed to form the optical waveguide material layer including the optical waveguide.

13. The method for manufacturing an optical modulator according to any one of claims 2 to 10, wherein the second substrate comprises: an optical waveguide material layer including an optical waveguide; a first electrode spaced in the width direction from a first end in the width direction of the optical waveguide and arranged along the optical propagation direction of the optical waveguide; a second electrode spaced in the width direction from a second end in the width direction of the optical waveguide and arranged along the optical propagation direction of the optical waveguide, to which a voltage is applied between the second electrode and the first electrode; a third cladding layer in contact with the optical waveguide and having a refractive index smaller than that of the optical waveguide; and a second support substrate overlapping the third cladding layer and different from the first support substrate which is the support substrate, wherein the second support substrate is removed after the bonding step.

14. An optical modulator manufactured by the method for manufacturing an optical modulator described in any one of claims 1 to 13.

15. An optical waveguide material layer having a first main surface and a second main surface, including an optical waveguide formed on the first main surface side; a first electrode spaced in the width direction from a first end in the width direction of the optical waveguide and arranged along the optical propagation direction of the optical waveguide; a second electrode spaced in the width direction from a second end in the width direction of the optical waveguide and arranged along the optical propagation direction of the optical waveguide, to which a voltage is applied between the first electrode and the second electrode; a first cladding layer overlapping the optical waveguide in a plan view from the thickness direction of the optical waveguide material layer and located on the second main surface of the optical waveguide material layer between the first electrode and the second electrode; a second cladding layer overlapping at least the first electrode and the second electrode in a plan view from the thickness direction of the optical waveguide material layer, located on the second main surface side of the optical waveguide material layer, and having a planar main surface; and a support substrate supporting the first cladding layer and the second cladding layer. An optical modulator comprising: a third cladding layer in contact with the optical waveguide and having a refractive index smaller than that of the optical waveguide, wherein the second main surface of the optical waveguide material layer is planar, the refractive index of the first cladding layer is smaller than that of the optical waveguide, and the dielectric constant of the second cladding layer is greater than that of the first cladding layer and greater than that of the third cladding layer.

16. The optical modulator according to claim 15, wherein the main surface of the first cladding layer is planar, the main surface of the second cladding layer is planar, and the main surface of the first cladding layer and the main surface of the second cladding layer are in contact with the second main surface of the optical waveguide material layer.

17. The optical modulator according to claim 15, wherein the main surface of the second cladding layer is planar, and further comprises a bonding metal layer covering the main surface of the second cladding layer and having a planar main surface, wherein the main surface of the bonding metal layer is in contact with the second main surface of the optical waveguide material layer.

18. The optical modulator according to claim 15, wherein the main surface of the second cladding layer is planar, the first cladding layer covers the second cladding layer, the main surface of the first cladding layer is planar, and the main surface of the first cladding layer is in contact with the second main surface of the optical waveguide material layer.

19. The optical modulator according to claim 16, wherein the second cladding layer has a slit, the first cladding layer is located inside the slit of the second cladding layer, and when the thickness of the first portion of the second cladding layer that is in contact with the optical waveguide material layer is t1, and the thickness of the second portion of the optical waveguide material layer that overlaps with the optical waveguide in the thickness direction and is thinner than the first portion is t0, then t0 / t1 is 0 or more and 0.4 or less.

20. The optical modulator according to claim 19, wherein when W0 is the width of the second portion of the second cladding layer in the width direction of the optical waveguide, and W1 is the width of the slit in the width direction of the optical waveguide, W1 / W0 is 0.28 or more and 0.89 or less.

21. The optical modulator according to claim 19 or 20, wherein the relative permittivity of the material of the second cladding layer is greater than the relative permittivity of the material of the optical waveguide material layer.

22. The optical modulator according to any one of claims 15 to 21, wherein the third cladding layer is an air layer.

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