Optical waveguide element, optical modulator, and optical transmission device

Abstract

The purpose of the present invention is to provide an optical waveguide element which suppresses the absorption of light waves propagating through an optical waveguide by an electrode, suppresses the peeling of the electrode, and prevents a decrease in the efficiency of an electric field applied to the optical waveguide by the electrode. This optical waveguide element is provided with an optical waveguide substrate (1) on which an optical waveguide (10) is formed, a support substrate (3) for supporting the optical waveguide substrate (1), and an electrode (2) for applying an electric field to the optical waveguide (10), the electrode (2) being provided with an upper electrode (M) and a base layer (m) for joining the upper electrode (M), the optical waveguide element being characterized in that the base layer (m) is formed at least directly on the support substrate (3).

Description

Technical Field

[0001] The present invention relates to an optical waveguide element, an optical modulator using the optical waveguide element, and an optical transmission device, and more particularly to an optical waveguide element, an optical modulator using the optical waveguide element, and an optical transmission device, wherein the optical waveguide element includes an optical waveguide substrate on which an optical waveguide is formed, a support substrate for supporting the optical waveguide substrate, and an electrode for applying an electric field to the optical waveguide, and the electrode includes an upper electrode and a base layer for bonding the upper electrode. Background Art

[0002] In the fields of optical measurement technology and optical communication technology, optical waveguide elements using substrates on which optical waveguides are formed, such as optical modulators, are frequently used. In a general optical waveguide element, an optical waveguide is formed on a substrate having an electro-optic effect, such as lithium niobate (LN), and an electrode for applying an electric field to the optical waveguide is formed on the substrate.

[0003] In recent years, high-bandwidth coherent driver modulators (HB-CDM: High Bandwidth-Coherent Driver Modulator) have attracted attention, and it is expected to develop optical waveguide elements corresponding to high speed and miniaturization. Therefore, the width of the optical waveguide has also been miniaturized to less than 1 μm, and the electrode also needs to be arranged closer to the optical waveguide.

[0004] Generally, when a metal such as Au is arranged as an electrode on an LN substrate, the adhesion between the LN substrate and Au is low. Therefore, as a base layer of the electrode, metals such as Ti and Nb are formed together with Au, and an Au electrode layer is formed thereon.

[0005] The metal of the base layer has a higher light absorption rate than the Au electrode layer. When the base layer is arranged near the optical waveguide, the light wave propagating in the optical waveguide is absorbed by the base layer, resulting in a problem of increased light loss. In particular, with the miniaturization of the optical modulator, the electrode is closer to the optical waveguide, so the influence of light absorption of the base layer of the electrode becomes more significant than before.

[0006] In Patent Document 1, as Figure 1 shown, an electrode is composed of a base layer m and an upper electrode (electrode layer) M. The base layer m is formed on the optical waveguide substrate 1, and the upper electrode M extends from the base layer m toward the optical waveguide 10 side, and the upper electrode is in direct contact with the optical waveguide substrate.

[0007] In Figure 1 's structure, since the base layer m is separated from the optical waveguide 10, it is expected to reduce the light absorption loss caused by the base layer m. However, since the base layer m is arranged on the optical waveguide substrate, the base layer may absorb the light in the slab waveguide portion (the thin portion extending left and right of the optical waveguide 10 toward Figure 1 the optical waveguide 10) of the optical waveguide substrate 1.

[0008] In addition, in Patent Document 2, as Figure 2 shown, in order to provide an optical waveguide device with low scattering loss and high electric field efficiency, an electrode EL is disclosed to be disposed at a position lower than the surface of the buffer layer BF. In Figure 2 , an LN substrate (LN) is disposed on a substrate SUB with an intermediate layer IL therebetween, and a buffer layer BF is provided thereon. However, there is no mention of the material of the intermediate layer or the base layer of the electrode EL. Therefore, there is a problem with the adhesion of the electrode EL, and the electrode may also peel off.

[0009] [Prior Art Documents]

[0010] [Patent Documents]

[0011] Patent Document 1: PCT / JP2022 / 37614 (filing date: October 7, 2022)

[0012] Patent Document 2: Japanese Patent Application Laid-Open No. 2021-173791 (JP2021-173791A) Summary of the Invention

[0013] [Problems to be Solved by the Invention]

[0014] The problem to be solved by the present invention is to solve the above problems and provide an optical waveguide element that suppresses the absorption of light waves propagating in the optical waveguide by the electrode, suppresses the peeling of the electrode, and prevents a decrease in the efficiency of the electric field applied by the electrode to the optical waveguide. Further, an optical modulator and an optical transmission device using the optical waveguide element are provided.

[0015] [Means for Solving the Problems]

[0016] To solve the above problems, the optical waveguide element, the optical modulator, and the optical transmission device using the optical waveguide element of the present invention have the following technical features.

[0017] (1) An optical waveguide element including an optical waveguide substrate on which an optical waveguide is formed, a support substrate that supports the optical waveguide substrate, and an electrode that applies an electric field to the optical waveguide, the electrode including an upper electrode and a base layer for bonding the upper electrode, characterized in that the base layer is formed directly on at least the support substrate.

[0018] (2) The optical waveguide element according to (1) above, characterized in that the upper electrode is disposed to extend on a part of the upper surface of the optical waveguide substrate other than the optical waveguide.

[0019] (3) The optical waveguide element according to (2) above, characterized in that the contact range of the upper electrode with the upper surface of the optical waveguide substrate extends 0.05 μm or more from the end face of the optical waveguide substrate toward the optical waveguide.

[0020] (4) In the optical waveguide element described in (2) above, it is characterized in that, with respect to the end portion of the optical waveguide substrate, the thickness tapers in a wedge shape, and the angle of the front end is 50 degrees or less.

[0021] (5) In the optical waveguide element described in (2) above, it is characterized in that a base layer is disposed below the upper electrode extending on the upper surface of the optical waveguide substrate.

[0022] (6) In the optical waveguide element described in (1) above, it is characterized in that the upper electrode is disposed to extend on a part of the lower surface of the optical waveguide substrate other than the optical waveguide.

[0023] (7) In the optical waveguide element described in (6) above, it is characterized in that the contact range of the upper electrode with the lower surface of the optical waveguide substrate extends 0.05 μm or more from the end surface of the optical waveguide substrate toward the optical waveguide.

[0024] (8) In the optical waveguide element described in (6) above, it is characterized in that the upper electrode is further disposed to extend on a part of the optical waveguide substrate other than the optical waveguide.

[0025] (9) In the optical waveguide element described in (1) above, it is characterized in that an air layer is formed in the gap between the optical waveguide substrate and the support substrate and at a position closer to the optical waveguide side than the position where the base layer is formed.

[0026] (10) An optical modulator, characterized by comprising: the optical waveguide element according to any one of (1) to (9) above; a housing for accommodating the optical waveguide element; and an optical fiber for inputting or outputting light waves to or from the optical waveguide.

[0027] (11) In the optical modulator described in (10) above, it is characterized in that the electrode is a modulation electrode for modulating the light wave propagating in the optical waveguide, and an electronic circuit for amplifying the modulation signal input to the modulation electrode is provided inside the housing.

[0028] (12) An optical transmission device, characterized by comprising: the optical modulator described in (10) above; a light source for inputting light waves to the optical modulator; and an electronic circuit for outputting a modulation signal to the optical modulator.

[0029] [Advantages of the Invention]

[0030] The optical waveguide element of the present invention includes an optical waveguide substrate on which an optical waveguide is formed, a support substrate that supports the optical waveguide substrate, and an electrode that applies an electric field to the optical waveguide. The electrode includes an upper electrode and a base layer for bonding the upper electrode. The base layer is formed at least directly on the support substrate, so that absorption of light waves propagating in the optical waveguide by the electrode can be suppressed.

[0031] Moreover, the upper electrode is disposed to extend on a part of the upper surface or the lower surface of the optical waveguide substrate other than the optical waveguide, so that peeling of the electrode can be suppressed and a reduction in the efficiency of the electric field applied by the electrode to the optical waveguide can be prevented.

[0032] Moreover, by using the optical waveguide element having such excellent characteristics, an optical modulator and an optical transmission device that achieve the same effects can also be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a cross-sectional view showing an example of a conventional optical waveguide element.

[0034] Figure 2 It is a cross-sectional view showing another example of a conventional optical waveguide element.

[0035] Figure 3 It is a cross-sectional view showing a first embodiment of the optical waveguide element of the present invention.

[0036] Figure 4 It is a cross-sectional view showing a second embodiment of the optical waveguide element of the present invention.

[0037] Figure 5 It is a cross-sectional view showing a third embodiment of the optical waveguide element of the present invention.

[0038] Figure 6 It is a cross-sectional view showing a fourth embodiment of the optical waveguide element of the present invention.

[0039] Figure 7 It is a cross-sectional view showing a fifth embodiment of the optical waveguide element of the present invention.

[0040] Figure 8 It is a cross-sectional view showing a sixth embodiment of the optical waveguide element of the present invention.

[0041] Figure 9 It is a cross-sectional view showing a seventh embodiment of the optical waveguide element of the present invention.

[0042] Figure 10 It is a cross-sectional view showing an eighth embodiment of the optical waveguide element of the present invention.

[0043] Figure 11 It is a diagram for explaining a simulation model of the optical waveguide element of the present invention.

[0044] Figure 12 is a diagram showing an existing structure used for standardization of simulation.

[0045] Figure 13 is a graph showing simulation results represented by the model of Figure 11 .

[0046] Figure 14 is a diagram (part 1) illustrating the manufacturing process of the optical waveguide element of the present invention.

[0047] Figure 15 is a diagram (part 2) illustrating the manufacturing process of the optical waveguide element of the present invention.

[0048] Figure 16 is a diagram (part 3) illustrating the manufacturing process of the optical waveguide element of the present invention.

[0049] Figure 17 is a cross-sectional view showing a ninth embodiment of the optical waveguide element of the present invention.

[0050] Figure 18 is a diagram for explaining the electric field efficiency in the optical waveguide element of the present invention.

[0051] Figure 19 is a cross-sectional view showing a tenth embodiment of the optical waveguide element of the present invention.

[0052] Figure 20 is a diagram showing an example of the optical transmission device of the present invention. Detailed Description of the Invention

[0053] Hereinafter, preferred examples will be used to describe in detail the optical waveguide element, the optical modulator, and the optical transmission device using the optical waveguide element of the present invention.

[0054] A cross-sectional view showing an example of the optical waveguide element of the present invention is shown in Figures 3 to 10 , Figure 17 and Figure 19 .

[0055] The optical waveguide element of the present invention includes: an optical waveguide substrate 1 on which an optical waveguide 10 is formed; a support substrate 3 that supports the optical waveguide substrate 1; and an electrode 2 that applies an electric field to the optical waveguide 10. The electrode 2 includes an upper electrode M and a base layer m for bonding the upper electrode M, and is characterized in that the base layer m is formed directly on at least the support substrate 3.

[0056] As the substrate (optical waveguide substrate) 1 used in the optical waveguide element of the present invention, a substrate having an electro-optic effect can be used. Specifically, substrates such as lithium niobate (LN), lithium tantalate (LT), PLZT (lanthanum lead zirconate titanate), and substrates doped with MgO or the like in these substrate materials can be used. In addition, film formation can be performed on these materials by a vapor growth method such as a sputtering method, an evaporation method, or a CVD method. In addition, a substrate obtained by thin-film processing of an electro-optic substrate after bonding a substrate having an electro-optic effect to another substrate can also be used. Furthermore, a semiconductor substrate, a substrate of an organic material such as an EO polymer, or the like can be used.

[0057] As the optical waveguide 10, an optical waveguide formed by thermally diffusing a high refractive index material such as Ti on a substrate (optical waveguide substrate) 1, an optical waveguide formed by a proton exchange method, and etching of a substrate 1 other than the optical waveguide or forming grooves on both sides of the optical waveguide can be used. As shown in Figure 3 FIG., a rib-type optical waveguide 10 obtained by forming a portion corresponding to the optical waveguide on the substrate in a convex shape can be used. Furthermore, by diffusing Ti or the like on the substrate surface in cooperation with the rib-type optical waveguide using a thermal diffusion method, a proton exchange method, or the like, the refractive index can be further increased. As the size of the rib-type optical waveguide, in order to improve the confinement of light, it is an optical waveguide having a fine structure with a width and height of about 1 μm.

[0058] In order to achieve the speed matching between the microwave and the light wave of the modulation signal, the thickness (maximum thickness) of the optical waveguide substrate (thin plate) 1 on which the optical waveguide 10 is formed is set to 10 μm or less, more preferably set to 5 μm or less, and further preferably set to 1 μm or less. In addition, the height of the rib-type optical waveguide 10 (the height of the portion protruding from the planar waveguide) is set to 80% or less of the maximum thickness of the optical waveguide substrate, specifically, set to 4 μm or less, more preferably 3 μm or less, and further preferably 0.8 μm or less, 0.4 μm or less.

[0059] Forming an optical waveguide substrate with an optical waveguide 1. To improve the mechanical strength, a support substrate 3 is bonded to the lower side of the optical waveguide substrate 1. The optical waveguide substrate 1 and the support substrate 3 are directly bonded or bonded and fixed via an adhesive layer such as resin. As the directly bonded support substrate, it is preferably a substrate with a refractive index lower than that of the optical waveguide and the substrate on which the optical waveguide is formed, but it is not limited thereto. In addition, in the case of direct bonding, an intermediate layer such as a metal oxide or metal may be included in the bonding portion. Further, the support substrate 3 is preferably made of a material with a thermal expansion coefficient close to that of the optical waveguide substrate 1, such as a substrate including an oxide layer such as quartz or glass. Furthermore, a composite substrate in which a silicon oxide layer is formed on a silicon substrate, abbreviated as SOI or LNOI, or a composite substrate in which a silicon oxide layer is formed on an LN substrate, which is the same as the optical waveguide substrate 1, may also be used. When the refractive index of the support substrate 3 is higher than that of the optical waveguide substrate 1, a layer with a refractive index lower than that of the optical waveguide substrate 1 is provided between the optical waveguide substrate 1 and the support substrate 3.

[0060] In addition, as described later, the support substrate of the present invention is not limited to being formed of a single substrate, and also includes a substrate obtained by overlapping and integrating a plurality of substrates.

[0061] The electrode 2 for applying an electric field to the optical waveguide 10 is composed of an upper electrode M and a base layer m. The upper electrode M is made of a metal such as Au or Cu. The base layer m is used to improve the adhesion between the support substrate 3 and the electrode 2 (electrode layer M1). The upper electrode M is formed in a manner covering the base layer by using an electroplating method using the base layer, an electroless plating method using a resist pattern, a vapor phase method such as evaporation or sputtering, or a combination thereof.

[0062] Since the base layer m is at least directly formed on the support substrate 3, the adhesion is good and electrode peeling does not occur.

[0063] As the material of the base layer m, it is necessary that the binding energy of oxygen to the metal such as Ti, Nb, Ni, Cr, or Al is greater than that of the material used for the upper electrode M. Especially in the case of metals above 300 kj·(mol-O) -1 or more, since they firmly bind to oxygen in the LN substrate, they are preferred. The film forming method can use a sputtering method, an evaporation method, etc.

[0064] The optical waveguide element of the present invention is characterized in that, as Figure 3 shown, the base layer m is directly formed on the support substrate 3. In this case, for example, the support substrate 3 uses a low dielectric constant material such as SiO2 with a dielectric constant lower than that of the optical waveguide substrate 1. The optical waveguide substrate is LN, the base layer uses Ti or Nb, and the upper electrode uses Au.

[0065] Since the base layer m is not disposed on the optical waveguide substrate 1, an increase in propagation loss such as absorption of light waves propagating in the slab waveguide of the optical waveguide substrate 1 can be suppressed.

[0066] The base layer m can not only be formed on the support substrate 3 adjacent to the optical waveguide substrate 1 as Figure 3 described, but also be disposed separately from the optical waveguide substrate 1 as Figure 4 described. Thus, absorption loss of the electrode can be further suppressed.

[0067] In addition, as Figure 5 shown, by disposing a part of the base layer m on the lower side of the upper electrode M and disposing the base layer m separately from the optical waveguide substrate 1, not only can absorption loss of the electrode be suppressed, but also the upper electrode M is close to the optical waveguide 10, so the electric field efficiency is improved, and low drive voltage can also be achieved in optical waveguide elements such as optical modulators.

[0068] Figures 6 to 10 is characterized in that the upper electrode M extends and is disposed on at least one of a part of the upper surface or a part of the lower surface of the optical waveguide substrate 1 other than the optical waveguide 10.

[0069] In Figure 6 , the upper electrode M is disposed so as to cover a part of the upper surface of the optical waveguide substrate 1. With this structure, since the upper electrode M is, for example, Au, it is difficult to absorb light waves propagating in the planar waveguide, so electrode absorption loss can be suppressed. Moreover, since the upper electrode is disposed close to the optical waveguide 10, low drive voltage can also be achieved.

[0070] In Figure 7 , a part of the support substrate 3 is removed by wet etching to form a recess 30. Specifically, the support substrate 3 is wet-etched to form a stepped structure (trapezoidal part), and over-etching is performed on the bottom part of the stepped structure to make the depth of the recess 30 deeper. Since a gap is formed between a part of the lower surface of the optical waveguide substrate 1 and the support substrate 3, a part of the upper electrode M is disposed to wrap around to the lower surface of the optical waveguide substrate. In addition, the upper electrode M can be not only disposed on the lower surface of the optical waveguide substrate 1, but also disposed on the upper surface of the optical waveguide substrate 1 Figure 6 similarly.

[0071] In Figure 7 , the upper electrode M does not enter a part of the recess 30, and an air layer (void) G is formed. Since the refractive index of such an air layer G is lower than the refractive index of the support substrate (low dielectric constant substrate) 3, due to the presence of the air layer G, the confinement intensity of light becomes locally high. As a result, it can exert an effect of suppressing the expansion of the optical mode field diameter that expands from the optical waveguide 10 toward the surrounding planar waveguide, and has an effect of suppressing the expansion of light waves to reach the base layer.

[0072] That is, preferably, the air layer G is formed in the gap between the optical waveguide substrate 1 and the support substrate 3 and at a position closer to the optical waveguide (10) side than the position where the base layer m is formed.

[0073] Figure 8 This is the case where the support substrate 3 is etched into a stepped structure (trapezoidal portion), and the upper electrode M is arranged to dive into the lower surface side of the optical waveguide substrate 1. Figure 8 The case of Figure 7 is also provided with the air layer G in the same manner.

[0074] Figure 9 Unlike Figure 8 , the upper electrode M completely fills the gap between the optical waveguide substrate 1 and the support substrate 3, and no air layer is formed. If the contact area between the upper electrode M and the optical waveguide substrate 1 increases, low driving voltage can be achieved. In addition, as the contact area between the upper electrode M and the low dielectric constant substrate as the support substrate 3 increases, it contributes to low driving voltage.

[0075] As Figures 7 to 9 shown, in the case where the support substrate 3 has a stepped structure, as the interval between the lower layer sides of the steps of the optical waveguide substrate 1 and the support substrate 3 becomes larger, it is difficult to arrange the upper electrode M on the upper surface of the optical waveguide substrate 1. Therefore, as Figure 10 shown, at the end of the optical waveguide substrate 1, it is formed in a wedge shape with a thinner thickness, and the front angle θ2 is set to 50 degrees or less. Preferably, it is 35 degrees or less, and more preferably 20 degrees or less. By forming it in a wedge shape, it is not affected by the thickness of the optical waveguide substrate 1 (the thickness of the slab waveguide portion) and the thickness of the electrode 2, and the upper electrode can be easily extended on the optical waveguide substrate 1.

[0076] In addition, the angle θ1 of the side surface of the optical waveguide 10 (trapezoidal portion) is set to 50 degrees or more and 80 degrees or less.

[0077] Next, using Figure 11 shown model, a simulation is performed to evaluate the influence of the extension amount UL of the upper electrode M to the upper surface of the optical waveguide substrate 1 and the extension amount DL to the lower surface. Figure 13 This is a coordinate diagram showing the results of this simulation.

[0078] In addition, as the boundary conditions of the simulation, the conditions are set as follows.

[0079] Under the conditions of each protrusion amount (UL, DL), the gap Gap between the upper electrodes is set to 4.0 to 4.8 μm, and through simulation, the relationship between the electrode absorption loss (y = Loss) and the driving voltage Vπ (x = VπL) (y = a × exp(b × x), where a and b are coefficients) is calculated (the coefficients a and b are obtained). According to the relationship, the electrode absorption loss (y) is compared when the driving voltage is the same value (x = 1.0). In addition, the comparison is made under the condition of the gap amount (Gap) of the upper electrode with VπL = 1.0.

[0080] Height of the optical waveguide 10: 0.1 to 1.0 μm

[0081] Thickness of the planar waveguide of the optical waveguide substrate 1: 0.1 to 1.0 μm

[0082] Material of the optical waveguide substrate 1: LN

[0083] Material of the support substrate 3: SiO2

[0084] Gap between the optical waveguide substrate 1 and the support substrate 3: 0.1 to 0.4 μm

[0085] The protrusion amount (upper Au amount) UL of the upper electrode M on the upper surface of the optical waveguide substrate 1 is changed at 0.05 μm intervals from 0 μm to 0.5 μm. Then, for each upper Au amount UL, the protrusion amount (lower Au amount) DL of the upper electrode M on the lower surface of the optical waveguide substrate 1 is changed at 0.05 μm intervals from 0 μm to 0.5 μm.

[0086] Perform simulation with Figure 12 the existing structure to calculate VπL and Loss, Figure 13 On the vertical axis of the coordinate graph of Figure 13 the calculated Loss (electrode absorption loss) is normalized to 1.0. Therefore,

[0087] Figures 14 to 16 is a diagram showing an example of the manufacturing process of the optical waveguide element of the present invention.

[0088] (a) Bond the support substrate 3 and the optical waveguide substrate 1.

[0089] (b) A photoresist PR1 is patterned on the upper surface of the optical waveguide substrate 1.

[0090] (c) The outer shape of the optical waveguide substrate (including the part of the planar waveguide) is formed by etching.

[0091] (d) A photoresist PR2 matching the optical waveguide is disposed. Regarding the photoresist PR2, a new resist film can be formed, or it can be formed by processing the photoresist PR1.

[0092] (e) After the optical waveguide 10 is formed, the side surface of the optical waveguide 10 is covered with the protective film 20, the photoresist PR2 is removed, and then the protective film 20 is also removed.

[0093] (f) It is the state where the photoresist PR2 and the like are removed.

[0094] (g) The base layer m and a part M1 of the upper electrode are formed by laminating over the entire surface.

[0095] (h) The part other than the part where the upper electrode M is formed is covered with the photoresist PR3.

[0096] (i) According to the pattern of the photoresist PR3, the upper electrode M is formed by plating. At this time, if necessary, the upper electrode M is grown in such a manner as to penetrate the lower surface of the optical waveguide substrate 1. By modulating the processing steps in this plating method, the growth of the electrode layer can be controlled. For example, the presence or absence of the formation of the air layer G and its size can be adjusted.

[0097] (j) The photoresist PR3 is removed.

[0098] (k) The thin upper electrode M1 disposed on the base layer m is removed.

[0099] (l) By removing the unnecessary base layer m, the optical waveguide element is completed.

[0100] Multiple optical waveguide elements are formed on a single wafer substrate, and then they are cut into chips for each optical waveguide element and used. The description of the present invention is centered on the chip-sized optical waveguide element.

[0101] Next, in Figure 17 A base layer m1 is provided on a part of the optical waveguide substrate 1. Providing a base layer on the optical waveguide substrate 1 easily causes absorption of the light wave propagating in the planar waveguide, so it is not originally preferred. However, with the base layer m1, the adhesion of the upper electrode M can be improved. In addition, since there is also a base layer m on the support substrate 3 side, it is preferable to suppress the base layer m1 on the optical waveguide substrate to the minimum necessary.

[0102] Figure 18This represents a case where the electric field distribution changes depending on the configuration relationship between the optical waveguide substrate and the electrodes. In Figure 18 In (a), the optical waveguide substrate 1 and the electrodes (M, m) are arranged with a slight separation. Since the support substrate 3 is made of a low dielectric constant material, the electric field mainly concentrates on the optical waveguide substrate 1. However, at the part where the optical waveguide substrate and the electrodes are separated, the dielectric constant of the support substrate 3 is higher than that of air, so the electric field mainly passes through the support substrate 3.

[0103] In contrast, as Figure 18 shown in (b), when the electrode (upper electrode M) is in contact with the optical waveguide substrate 1, the electric field generated by the electrode directly enters the optical waveguide substrate 1, so the electric field efficiency is higher than that in Figure 18 (a). Moreover, by protruding the upper electrode M on the optical waveguide substrate 1, the interval between the electrodes sandwiching the optical waveguide 10 also becomes narrower, and the electric field efficiency can be further improved. Figure 18 The reference numeral L shown represents the cross-section of the light wave propagating in the optical waveguide 10.

[0104] Figure 19 An example of a case where a support substrate is formed by laminating multiple substrates is shown. The support substrate is composed of a low dielectric constant layer 30 such as SiO2 and a reinforcing substrate 31 for improving mechanical strength. The reinforcing substrate can be a Si substrate or the like.

[0105] In the present invention, the composite substrate (30, 31) shown as Figure 19 such can also be used as one of the "support substrates".

[0106] Next, an example of applying the optical waveguide element of the present invention to an optical modulator and an optical transmission device will be described. Hereinafter, an example of HB-CDM will be used for description, but the present invention is not limited thereto, and it can also be applied to an optical phase modulator, an optical modulator having a polarization synthesis function, an optical modulator integrating more or fewer Mach-Zehnder type optical waveguides, a bonding device with an optical waveguide substrate made of other materials such as silicon, a device for sensor applications, etc.

[0107] As Figure 20 shown, the optical waveguide element has an optical waveguide 10 formed on the optical waveguide substrate 1 and electrodes such as a modulation electrode (not shown) for modulating the light wave propagating in the optical waveguide 10, and the substrate 1 is housed in the housing CA. Moreover, by providing optical fibers (F) for inputting and outputting light waves in the optical waveguide, an optical modulator MD can be constituted. In Figure 20In this case, the optical fiber (F) is introduced into the housing through a through-hole penetrating the side wall of the housing CA, and the optical waveguide substrate 1 is directly joined to the optical fiber. Instead, it is also possible to optically couple the light wave L1 incident from the optical fiber F and the light wave L2 emitted from the optical fiber F to the optical waveguide 10 in the optical waveguide substrate 1 via an optical module having an optical lens, a lens barrel, a polarization multiplexing unit, etc. In addition, in order to stably join to the optical fiber and the optical module, the reinforcing member 4 may be overlapped and arranged along the end face of the substrate 1 on the optical waveguide substrate 1.

[0108] By connecting an electronic circuit (digital signal processor, DSP) that outputs a modulation signal S0 for causing the optical modulator MD to perform a modulation operation to the optical modulator MD, an optical transmission device OTA can be configured. In order to obtain the modulation signal S applied to the optical waveguide element, it can operate even if the modulation signal S0 output from the digital signal processor DSP is amplified. Therefore, in Figure 20 a drive circuit DRV is used to amplify the modulation signal. The drive circuit DRV and the digital signal processor DSP can be arranged outside the housing CA, but can also be arranged inside the housing CA. In particular, by arranging the drive circuit DRV inside the housing, the propagation loss of the modulation signal from the drive circuit can be further reduced. If the degradation of the modulation signal is small, the DRV is not required, and the modulation operation of the optical modulator MD can also be directly performed by the DSP.

[0109] The input light L1 to the optical modulator MD can be supplied from the outside of the optical transmission device OTA, but a semiconductor laser (not shown) can also be integrally assembled in the optical transmission device OTA as a light source. The output light L2 modulated by the optical modulator MD is output to the outside through the optical fiber F.

[0110] [Industrial Applicability]

[0111] As described above, according to the present invention, an optical waveguide element can be provided that suppresses the absorption of the light wave propagating in the optical waveguide by the electrode pair, suppresses the peeling of the electrode, and prevents the reduction in the efficiency of the electric field applied to the optical waveguide by the electrode. Moreover, an optical modulator and an optical transmission device using the optical waveguide element can be provided.

[0112] [Description of Reference Numerals]

[0113] 1 Optical waveguide substrate (thin plate, film body)

[0114] 2 Electrode

[0115] 3 Support substrate

[0116] 4 Reinforcing member

[0117] 10 Optical waveguide

[0118] m, m1 base layer

[0119] M upper electrode

[0120] F optical fiber

[0121] CA housing

[0122] MD optical modulator

[0123] DRV drive circuit

[0124] DSP digital signal processor

[0125] OTA optical transmission device

Claims

1. An optical waveguide element includes an optical waveguide substrate on which an optical waveguide is formed, a support substrate that supports the optical waveguide substrate, and an electrode that applies an electric field to the optical waveguide. The electrode includes an upper electrode and a base layer for bonding the upper electrode, and is characterized in that, the base layer is formed directly on at least the support substrate.

2. The optical waveguide element according to claim 1, wherein, the upper electrode is disposed to extend on a part of the upper surface of the optical waveguide substrate.

3. The optical waveguide element according to claim 2, wherein, the contact range of the upper electrode with the upper surface of the optical waveguide substrate extends 0.05 μm or more from the end face of the optical waveguide substrate toward the optical waveguide.

4. The optical waveguide element according to claim 2, wherein, regarding the end of the optical waveguide substrate, the thickness tapers in a wedge shape, and the angle of the front end is 50 degrees or less.

5. The optical waveguide element according to claim 2, wherein, a base layer is disposed under the upper electrode extending on the upper surface of the optical waveguide substrate.

6. The optical waveguide element according to claim 1, wherein, the upper electrode is disposed to extend on a part of the lower surface of the optical waveguide substrate.

7. The optical waveguide element according to claim 6, wherein, the contact range of the upper electrode with the lower surface of the optical waveguide substrate extends 0.05 μm or more from the end face of the optical waveguide substrate toward the optical waveguide.

8. The optical waveguide element according to claim 6, wherein, the upper electrode also extends and is disposed on a part of the optical waveguide substrate other than the optical waveguide.

9. The optical waveguide element according to claim 1, wherein, an air layer is formed in a gap between the optical waveguide substrate and the support substrate and at a position closer to the optical waveguide side than the position where the base layer is formed.

10. An optical modulator, characterized in that, Comprising: the optical waveguide element according to any one of claims 1 to 9; a housing that houses the optical waveguide element; and an optical fiber that inputs or outputs light waves to or from the optical waveguide.

11. The optical modulator according to claim 10, wherein, the electrode is a modulation electrode for modulating light waves propagating in the optical waveguide, and an electronic circuit for amplifying a modulation signal input to the modulation electrode is provided inside the housing.

12. An optical transmission device, characterized in that, Having: the optical modulator according to claim 10; a light source that inputs light waves to the optical modulator; and an electronic circuit that outputs a modulation signal to the optical modulator.

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