optical modulator

Abstract

This invention discloses an optical modulator. The optical modulator (100) includes a substrate (1), an optical waveguide (2) formed on the substrate, signal electrodes (7a, 7b) formed on the optical waveguide via a first buffer layer (41A) and applying a modulation signal to the optical waveguide, and bias electrodes (9a, 9b) formed on the optical waveguide via a second buffer layer (42A) and applying a DC bias voltage to the optical waveguide. The first buffer layer and the second buffer layer are formed such that, at the boundary between the first buffer layer and the second buffer layer, the end face of either the first buffer layer or the second buffer layer covers the end face of the other buffer layer. According to this invention, a highly reliable optical modulator can be provided.

Description

Technical Field

[0001] This invention relates to an optical modulator used in the fields of optical communication and optical measurement. Background Technology

[0002] With the widespread adoption of the internet and the dramatic increase in communication volume, fiber optic communication has become extremely important. Fiber optic communication is a technology that converts electrical signals into optical signals and transmits them through optical fibers, featuring wide bandwidth, low loss, and noise immunity.

[0003] As methods for converting electrical signals into optical signals, direct modulation using semiconductor lasers and external modulation using optical modulators are known. Direct modulation does not require an optical modulator and is low in cost, but it has limitations for high-speed modulation. In high-speed and long-distance applications, external modulation is used.

[0004] As an optical modulator, lithium niobate (LiN) was used. b Optical modulators formed by optical waveguides (hereinafter referred to as "LN") have advantages such as high speed, low loss, and less distortion of the controlled optical waveform. However, compared with semiconductor optical devices, they have disadvantages such as large driving voltage and large size.

[0005] To overcome the above-mentioned drawbacks, there are known optical waveguides that utilize LN films formed by applying thin film technology on sapphire substrates, thereby enabling significant miniaturization and lower driving voltage compared to existing optical devices (see Patent Documents 1 and 2).

[0006] In such optical devices, the voltage applied to the optical waveguide changes immediately after a voltage is applied to the electrodes and after a sufficiently long period of time, resulting in a change in the emitted light from the optical modulator. This change in the voltage applied to the optical waveguide is called DC drift, and it is desirable to suppress DC drift as much as possible in optical modulators. Patent Document 3 proposes an optical modulator with a device structure that can reduce DC drift and provide stable control over a long period.

[0007] However, the aforementioned optical devices utilizing thin-film technology suffer from drawbacks such as long manufacturing processes, temperature variations due to heat treatment, and exposure to water for monolithic fabrication. Consequently, such optical devices exhibit low reliability. For example, the general structure of a conventional optical modulator is shown below. Figure 1As shown, in the structure formed by stacking substrate 1, waveguide layer 2 and buffer layer 4, buffer layer 4 includes a first buffer layer 41 and a second buffer layer 42 made of different materials. The first buffer layer 41 and the second buffer layer 42 are arranged in a direction parallel to the main surface of substrate 1 with the end faces of the first buffer layer 41 and the second buffer layer 42 in contact with each other. Therefore, there is a problem that the boundary between the first buffer layer 41 and the second buffer layer 42 is prone to peeling or cracking due to stress, etc.

[0008] Therefore, especially in the aforementioned optical devices utilizing thin-film technology, there is a demand for highly reliable optical devices that can withstand such process stresses.

[0009] Prior art literature

[0010] Patent documents

[0011] Patent Document 1: JP 2006-195383A

[0012] Patent Document 2: JP 2014-6348A

[0013] Patent Document 3: WO2019 / 069815A Summary of the Invention

[0014] The present invention is the result of careful research in view of the above-mentioned problems, and its purpose is to provide a highly reliable optical modulator.

[0015] To achieve the above objectives, one aspect of the present invention relates to an optical modulator comprising a substrate, an optical waveguide formed on the substrate, a signal electrode formed on the optical waveguide via a first buffer layer and applying a modulation signal to the optical waveguide, and a bias electrode formed on the optical waveguide via a second buffer layer and applying a DC bias voltage to the optical waveguide. The first buffer layer and the second buffer layer are formed such that, at the boundary between the first buffer layer and the second buffer layer, the end face of either the first buffer layer or the second buffer layer covers the end face of the other buffer layer. Thus, by forming the first buffer layer and the second buffer layer such that, at their boundary, either the first buffer layer or the second buffer layer covers the end face of the other buffer layer, a highly reliable structure free from peeling and cracking occurs, and the product yield is improved.

[0016] Furthermore, in the optical modulator according to one aspect of the present invention described above, it is preferable that the first buffer layer and the second buffer layer are formed in a manner that overlaps when viewed from the thickness direction of the substrate at the boundary portion.

[0017] Furthermore, in the optical modulator according to one aspect of the present invention described above, it is preferable that the end face of the buffer layer of the other party is formed at an angle relative to the substrate.

[0018] Furthermore, in the optical modulator according to one aspect of the present invention described above, it is preferable that the end face of the buffer layer of the other party is formed as a curved surface.

[0019] Furthermore, in the optical modulator according to one aspect of the present invention described above, it is preferable that the first buffer layer is formed on the second buffer layer, or the second buffer layer is formed on the first buffer layer, at the boundary portion.

[0020] Furthermore, in the optical modulator according to one aspect of the present invention described above, it is preferable that the length of the end face of the buffer layer of the other party projected onto the substrate along the thickness direction of the substrate is 2 to 100 times the thickness of the buffer layer of the other party.

[0021] Furthermore, in the optical modulator according to one aspect of the present invention described above, it is preferable that the first buffer layer and the second buffer layer are formed of different compositions.

[0022] Furthermore, in the optical modulator according to one aspect of the present invention described above, it is preferable that the first buffer layer is an M-Si-O compound, wherein M is selected from at least one of Al, Zr, Hf, La, Ba, Bi, Ti, Ca, Mo, and In.

[0023] Furthermore, in the optical modulator according to one aspect of the present invention described above, it is preferable that the elements constituting the second buffer layer include at least one or more of the elements constituting the first buffer layer.

[0024] According to one aspect of the present invention, a highly reliable optical modulator is provided. Attached Figure Description

[0025] Figure 1 This is a cross-sectional view of an existing optical modulator.

[0026] Figure 2 This is a top view of the optical modulator 100 according to the first embodiment of the present invention.

[0027] Figure 3 This is a top view of the optical modulator 100 including the traveling wave electrodes.

[0028] Figure 4 It is along Figure 2 A cross-sectional view of the optical modulator along line A-A' in the diagram.

[0029] Figure 5 It is along Figure 2A cross-sectional view of the optical modulator along the B-B' line.

[0030] Figure 6 It is along Figure 2 A cross-sectional view of the optical modulator along the C-C' line.

[0031] Figure 7 This is a cross-sectional view of an optical modulator according to a variation of the first embodiment of the present invention.

[0032] Figure 8 This is a cross-sectional view of an optical modulator according to another variation of the first embodiment of the present invention.

[0033] Figure 9 This is a top view of the optical modulator 200 according to the second embodiment of the present invention.

[0034] Figure 10 This is a cross-sectional view of the optical modulator according to the third embodiment of the present invention. Detailed Implementation

[0035] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are marked with the same symbols, and repeated descriptions are omitted.

[0036] (First Implementation)

[0037] Figure 2 This is a top view of the optical modulator 100 according to the first embodiment of the present invention. Figure 3 This is a top view of the optical modulator 100 including the traveling wave electrodes. Figure 4 It is along Figure 2 A cross-sectional view of the optical modulator along line A-A' in the diagram. Figure 5 It is along Figure 2 A cross-sectional view of the optical modulator along the B-B' line. Figure 6 It is along Figure 2 A cross-sectional view of the optical modulator along the C-C' line.

[0038] like Figure 2 and Figure 3As shown, the optical modulator 100 includes: a Mach-Zehnder optical waveguide 10 formed on a substrate 1, having first and second optical waveguides 10a and 10b arranged parallel to each other; a first signal electrode 7a, which overlaps with the first optical waveguide 10a; a second signal electrode 7b, which overlaps with the second optical waveguide 10b; first and second ground electrodes 8a and 8b, which are arranged to sandwich the first and second signal electrodes 7a and 7b; a first bias electrode 9a, which overlaps with the first optical waveguide 10a; a second bias electrode 9b, which overlaps with the second optical waveguide 10b; a third bias electrode 9c, which is adjacent to the first bias electrode 9a; and a fourth bias electrode 9d, which is adjacent to the second bias electrode 9b.

[0039] The Mach-Zehnder waveguide 10 is an optical waveguide constructed with a Mach-Zehnder interferometer. The Mach-Zehnder waveguide 10 has first and second optical waveguides 10a and 10b branched from an input optical waveguide 10i by a wave-splitting section 10c. The first and second optical waveguides 10a and 10b are converged into an output optical waveguide 10o via a combining section 10d. The input light Si is split at the wave-splitting section 10c. After traveling through the first and second optical waveguides 10a and 10b, the split light is combined at the combining section 10d. The combined light is output as modulated light So from the output optical waveguide 10o.

[0040] The first and second signal electrodes 7a and 7b are located between the first and second ground electrodes 8a and 8b when viewed from above. One end 7a1 and 7b1 of the first and second signal electrodes 7a and 7b are signal input terminals, and the other ends 7a2 and 7b2 of the first and second signal electrodes 7a and 7b are connected to each other via terminating resistor 12. Alternatively, the other end 7a2 of the first signal electrode 7a can be connected to the first ground electrode 8a via the first terminating resistor, and the other end 7b2 of the second signal electrode 7b can be connected to the second ground electrode 8b via the second terminating resistor. Thus, the first and second signal electrodes 7a and 7b together with the first and second ground electrodes 8a and 8b function as differential coplanar traveling wave electrodes.

[0041] The first and second bias electrodes 9a and 9b are independently disposed from the first and second signal electrodes 7a and 7b to apply a DC bias voltage to the first and second optical waveguides 10a and 10b. One end 9a1 and 9b1 of the first and second bias electrodes 9a and 9b are the input terminals of the DC bias voltage. In this embodiment, the formation regions of the first and second bias electrodes 9a and 9b are disposed closer to the output terminal side of the Mach-Zehnder optical waveguide 10 than the formation regions of the first and second signal electrodes 7a and 7b, but they can also be disposed closer to the input terminal side. Alternatively, the first and second bias electrodes 9a and 9b can be omitted, and a modulation signal pre-overlapping with a DC bias voltage can be input to the first and second signal electrodes 7a and 7b.

[0042] An AC (alternating current) signal (modulation signal) is input at one end 7a1 of the first signal electrode 7a and one end 7b1 of the second signal electrode 7b. Since the first and second optical waveguides 10a and 10b are made of materials with electro-optic effects, such as lithium niobate, their refractive indices change according to the electric field applied to them, such as +Δn and -Δn respectively, thus changing the phase difference between the pair of waveguides. The signal light modulated by this phase difference is output from the output optical waveguide 10o.

[0043] like Figures 4-6 As shown, the optical modulator 100 according to this embodiment has a multilayer structure in which a substrate 1, a waveguide layer 2, a protective layer 3, a buffer layer 4A, and an electrode layer 5 are stacked sequentially. The substrate 1 is, for example, a sapphire substrate, and a waveguide layer 2 made of an electro-optic material, such as lithium niobate, is formed on the surface of the substrate 1. The waveguide layer 2 has first and second optical waveguides 10a and 10b formed by ridges 2r.

[0044] The buffer layer 4A is formed on the upper surface of the ridge 2r of the waveguide layer 2 to prevent light propagating in the first and second optical waveguides 10a and 10b from being absorbed by the first and second signal electrodes 7a and 7b. The buffer layer 4A is preferably made of a material with a lower refractive index and higher transparency than the waveguide layer 2, and its thickness can be approximately 0.2 to 1.2 μm. In this embodiment, the buffer layer 4A covers not only the upper surfaces of the first and second optical waveguides 10a and 10b, but also the entire surface of the substrate including the upper surface of the protective layer 3. However, it can also be a layer patterned selectively covering only the area near the upper surfaces of the first and second optical waveguides 10a and 10b. Alternatively, the protective layer 3 can be omitted, and the buffer layer 4A can be formed directly on the upper surface of the waveguide layer 2.

[0045] To reduce light absorption by the electrodes, a thicker buffer layer 4A is preferable, while a thinner buffer layer 4A is preferable to apply a high electric field to the optical waveguides 10a and 10b. Since the light absorption of the electrodes is a trade-off with the applied voltage, it is necessary to set an appropriate film thickness according to the objective. A higher dielectric constant of the buffer layer 4A results in a smaller VπL (an indicator of electric field efficiency), which is preferable. Conversely, a lower refractive index of the buffer layer 4A allows for a thinner buffer layer, which is also preferable. Generally, since materials with high dielectric constants also have high refractive indices, it is important to select a material with a high dielectric constant and a relatively low refractive index, considering the balance between the two. For example, Al₂O₃, with a relative dielectric constant of approximately 9 and a refractive index of approximately 1.6, is a preferred material. LaAlO₃, with a relative dielectric constant of approximately 13 and a refractive index of approximately 1.7, and LaYO₃, with a relative dielectric constant of approximately 17 and a refractive index of approximately 1.7, are particularly preferred materials.

[0046] The buffer layer 4A includes a first buffer layer 41A located on the protective layer 3 and the waveguide layer 2 (specifically, the ridge 2r of the waveguide layer 2) and a second buffer layer 42A located on the protective layer 3 and the waveguide layer 2 (specifically, the ridge 2r of the waveguide layer 2). The first buffer layer 41A and the second buffer layer 42A are formed such that the first buffer layer 41A directly covers the end face 42AS of the second buffer layer 42A at the boundary D between the first buffer layer 41A and the second buffer layer 42A. In this way, by forming the first buffer layer and the second buffer layer in such a way that the first buffer layer directly covers the end face of the second buffer layer at the boundary between the first buffer layer and the second buffer layer, a highly reliable structure without peeling and cracking occurs is achieved, and the product yield is improved.

[0047] Furthermore, in this embodiment, the first buffer layer 41A covers not only the end face 42AS of the second buffer layer 42A, but also the entire upper surface of the second buffer layer 42A. However, it is not limited to this; the first buffer layer 41A may also cover only a portion of the upper surface of the second buffer layer 42A.

[0048] Specifically, in this embodiment, the first buffer layer 41A and the second buffer layer 42A are formed in a manner that overlaps when viewed from the thickness direction Z of the substrate 1 on the boundary portion D. That is, the first buffer layer 41A is formed on the second buffer layer 42A on the boundary portion D.

[0049] However, it is not limited to this; it can also be like... Figure 7 The buffer layer 4B shown includes a first buffer layer 41B and a second buffer layer 42B, which are formed in a manner that do not overlap when viewed from the thickness direction Z of the substrate 1 on the boundary portion D1.

[0050] In the case where the first buffer layer 41A and the second buffer layer 42A are formed in an overlapping manner when viewed from the thickness direction Z of the substrate 1 at the boundary portion D, as a specific example, for instance... Figure 6 As shown, the end face 42AS of the second buffer layer 42A is formed at an angle relative to the substrate 1. However, it is not limited to this, and can also be formed as follows: Figure 8 The buffer layer 4C shown includes a first buffer layer 41C and a second buffer layer 42C, and the end face 42CS of the second buffer layer 42C is formed into a curved surface.

[0051] Furthermore, the length L of the end face 42AS of the second buffer layer 42A projected onto the substrate 1 along the thickness direction Z of the substrate 1 is preferably 2 to 100 times the thickness of the second buffer layer 42A.

[0052] In this embodiment, the first buffer layer 41A and the second buffer layer 42A can be formed with different compositions or with the same composition. For example, the first buffer layer 41A is an M-Si-O compound, wherein M is selected from at least one of Al, Zr, Hf, La, Ba, Bi, Ti, Ca, Mo, and In. Furthermore, the elements constituting the second buffer layer 42A may also include at least one of the elements constituting the first buffer layer 41A.

[0053] A first signal electrode 7a, a second signal electrode 7b, a first ground electrode 8a, and a second ground electrode 8b are provided in electrode layer 5. The first signal electrode 7a is disposed overlapping the ridge 2r corresponding to the first optical waveguide 10a for modulating light traveling within the first optical waveguide 10a, and is opposite to the first optical waveguide 10a via a first buffer layer 41A. The second signal electrode 7b is disposed overlapping the ridge 2r corresponding to the second optical waveguide 10b for modulating light traveling within the second optical waveguide 10b, and is opposite to the second optical waveguide 10b via a first buffer layer 41A. When viewed from the first signal electrode 7a, the first ground electrode 8a is disposed on the opposite side from the second signal electrode 7b, and when viewed from the second signal electrode 7b, the second ground electrode 8b is disposed on the opposite side from the first signal electrode 7a.

[0054] Additionally, a first bias electrode 9a, a second bias electrode 9b, a third bias electrode 9c, and a fourth bias electrode 9d are provided in electrode layer 5. The first bias electrode 9a is disposed overlapping the ridge 2r corresponding to the first optical waveguide 10a to apply a DC bias voltage to the first optical waveguide 10a, and is opposite to the first optical waveguide 10a via the second buffer layer 42A. The second bias electrode 9b is disposed overlapping the ridge 2r corresponding to the second optical waveguide 10b to apply a DC bias voltage to the second optical waveguide 10b, and is opposite to the second optical waveguide 10b via the second buffer layer 42A.

[0055] The waveguide layer 2 is not particularly limited to any electro-optic material, but it is preferably composed of lithium niobate (LiNbO3). This is because lithium niobate has a large electro-optic constant, making it suitable as a constituent material for optical devices such as optical modulators. The structure of this embodiment, in which the waveguide layer 2 is a lithium niobate film, will be described in detail below.

[0056] As for substrate 1, there are no particular limitations as long as it is a substrate with a refractive index lower than that of the lithium niobate film, but it is preferable to be a substrate that can be formed as an epitaxial film using the lithium niobate film, preferably a sapphire single crystal substrate or a silicon single crystal substrate. The crystal orientation of the single crystal substrate is not particularly limited. Compared with single crystal substrates with various crystal orientations, the lithium niobate film has the property of being easily formed as an epitaxial film with c-axis orientation. Since the c-axis oriented lithium niobate film has triple symmetry, it is preferable that the single crystal substrate of the substrate also has the same symmetry. In the case of a sapphire single crystal substrate, the c-plane is preferred, and in the case of a silicon single crystal substrate, the (111) plane is preferred.

[0057] Here, an epitaxial film refers to a film in which the crystal orientation of the substrate or substrate film is consistent with that of the substrate. When the in-plane of the film is defined as the XY plane and the film thickness direction (i.e., the thickness direction of substrate 1) is defined as the Z axis, the crystal is consistently oriented along the X-axis, Y-axis and Z-axis directions.

[0058] The lithium niobate film is composed of Li x NbA y O z A represents an element other than Li, Nb, and O. x is 0.5–1.2, preferably 0.9–1.05. y is 0–0.5. z is 1.5–4, preferably 2.5–3.5. Elements that can be A include K, Na, Rb, Cs, Be, Mg, Ca, Sr, Ba, Ti, Zr, Hf, V, Cr, Mo, W, Fe, Co, Ni, Zn, Sc, Ce, etc., or combinations of two or more.

[0059] The thickness of the lithium niobate film is preferably 2 μm or less. This is because if the film thickness is greater than 2 μm, it is difficult to form a high-quality film. On the other hand, if the lithium niobate film is too thin, the light confinement within the lithium niobate film weakens, and light leaks to the substrate 1 and / or the buffer layer 4A. Even when an electric field is applied to the lithium niobate film, there is concern that the effective refractive index change of the optical waveguides 10a and 10b will be reduced. Therefore, the lithium niobate film is preferably at least 1 / 10 of the wavelength of the light used.

[0060] As a method for forming a lithium niobate film, sputtering, CVD, or sol-gel methods are preferred. The c-axis of the lithium niobate is oriented perpendicular to the main surface of the substrate 1, and an electric field is applied parallel to the c-axis, causing the optical refractive index to change proportionally to the electric field. When using sapphire as a single-crystal substrate, the lithium niobate film can be directly epitaxially grown on the sapphire single-crystal substrate. When using silicon as a single-crystal substrate, the lithium niobate film is formed by epitaxial growth via a cladding layer (not shown in the figure). As the cladding layer (not shown in the figure), a material with a lower refractive index than the lithium niobate film and suitable for epitaxial growth is used. For example, when Y₂O₃ is used as the cladding layer (not shown in the figure), a high-quality lithium niobate film can be formed.

[0061] Furthermore, as a method for forming lithium niobate films, methods for thinly polishing or slicing lithium niobate single-crystal substrates are also known. These methods have advantages such as being able to obtain properties similar to those of single crystals, and are applicable to the present invention.

[0062] (Second Implementation)

[0063] Figure 9 This is a top view of the optical modulator 200 according to the second embodiment of the present invention. Figure 9 As shown, the optical modulator 200 of this embodiment differs from the optical modulator 100 of the first embodiment in that the Mach-Zehnder waveguide 10 is composed of a combination of straight and curved portions. The other structures of the optical modulator 200 of this embodiment are the same as those of the optical modulator 100 of the first embodiment, therefore detailed descriptions are omitted.

[0064] Specifically, the Mach-Zehnder waveguide 10 includes first to third straight sections 10e1, 10e2, and 10e3 arranged in parallel with each other, a first curved section 10f1 connecting the first straight section 10e1 and the second straight section 10e2, and a second curved section 10f1 connecting the second straight section 10e2 and the third straight section 10e3.

[0065] Therefore, in this embodiment, the input light Si is input to one end of the first straight section 10e1, travels from one end of the first straight section 10e1 to the other end, turns back at the first curved section 10f1, and travels from one end of the second straight section 10e2 to the other end in the opposite direction to the first straight section 10e1. It further turns back at the second curved section 10f2 and travels from one end of the third straight section 10e3 to the other end in the same direction as the first straight section 10e1.

[0066] In optical modulators, long component length is a significant practical technical problem. However, as shown in the figure, by constructing the optical waveguide in reverse, the component length can be significantly shortened, resulting in remarkable improvements. In particular, the optical waveguide formed from a lithium niobate film exhibits low loss even when the radius of curvature is reduced to, for example, around 50 μm, making it suitable for this embodiment.

[0067] (Third embodiment)

[0068] Figure 10 This is a cross-sectional view of an optical modulator according to a third embodiment of the present invention. The optical modulator according to this embodiment differs from the optical modulator 100 according to the first embodiment in that the buffer layer 4D includes a first buffer layer 41D and a second buffer layer 42D.

[0069] The first buffer layer 41D and the second buffer layer 42D are formed such that the second buffer layer 42D directly covers the end face 41DS of the first buffer layer 41D at the boundary portion D2 of the first buffer layer 41D and the second buffer layer 42D. The other structures of the optical modulator according to this embodiment are the same as those of the optical modulator 100 according to the first embodiment, so detailed descriptions are omitted.

[0070] Furthermore, in this embodiment, the second buffer layer 42D covers not only the end face 41DS of the first buffer layer 41D, but also a portion of the upper surface of the first buffer layer 41D. However, it is not limited to this; the second buffer layer 42D may also cover the entire upper surface of the first buffer layer 41D.

[0071] Specifically, in this embodiment, the first buffer layer 41D and the second buffer layer 42D are formed in a manner that overlaps when viewed from the thickness direction Z of the substrate 1 on the boundary portion D2. That is, the second buffer layer 42D is formed on the first buffer layer 41D on the boundary portion D2.

[0072] The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Various modifications can be made without departing from the spirit of the present invention, and these modifications are also included within the scope of the present invention.

[0073] For example, in the above embodiment, an optical modulator having a pair of optical waveguides 10a and 10b formed by an epitaxially grown lithium niobate film on substrate 1 is described. However, the present invention is not limited to this structure, and an optical modulator with optical waveguides formed by electro-optic materials such as barium titanate or lead zirconate titanate can also be used. In addition, as the waveguide layer 2, semiconductor materials, polymer materials, etc., that have electro-optic effects can also be used.

[0074] Furthermore, this invention relates to the design of the relationship at the interface (the interface between the ends) of two buffer layers (i.e., the first buffer layer and the second buffer layer) existing in the same layer. Therefore, there is no particular limitation on the layers above and below the buffer layer of this invention; other layers may be included, or conversely, other layers may not be included.

[0075] Explanation of symbols

[0076] 1 substrate

[0077] 2 Waveguide layer

[0078] 3. Protective layer

[0079] 4A Buffer Layer

[0080] 4B Buffer Layer

[0081] 4C Buffer Layer

[0082] 4D Buffer Layer

[0083] 41A First Buffer Layer

[0084] 42A Second Buffer Layer

[0085] 41B First Buffer Layer

[0086] 42B Second Buffer Layer

[0087] 41C First Buffer Layer

[0088] 42C Second Buffer Layer

[0089] 41D First Buffer Layer

[0090] 42D Second Buffer Layer

[0091] 41DS end face

[0092] 42AS end face

[0093] 42CS end face

[0094] 5 Electrode layers

[0095] 7a First signal electrode

[0096] 7b Second signal electrode

[0097] 9a First bias electrode

[0098] 9b Second bias electrode

[0099] 10 Optical waveguide

[0100] 10a First Optical Waveguide

[0101] 10b Second Optical Waveguide

[0102] 100 optical modulator

[0103] 200 optical modulator

[0104] D Boundary section

[0105] D1 Boundary Section

[0106] D2 Boundary section.

Claims

1. An optical modulator, characterized in that, The device includes a substrate, an optical waveguide formed on the substrate, a signal electrode formed on the optical waveguide via a first buffer layer and applying a modulation signal to the optical waveguide, and a bias electrode formed on the optical waveguide via a second buffer layer and applying a DC bias voltage to the optical waveguide. The first buffer layer and the second buffer layer are formed such that, at the boundary between the first buffer layer and the second buffer layer, the end face of either the first buffer layer or the second buffer layer covers the end face of the other buffer layer. The first buffer layer and the second buffer layer are formed in an overlapping manner at the boundary portion when viewed from the thickness direction of the substrate. The length of the end face of the buffer layer of the other party projected onto the substrate along the thickness direction of the substrate is 2 to 100 times the thickness of the buffer layer of the other party.

2. The optical modulator as described in claim 1, characterized in that, The end face of the buffer layer of the other party is formed at an angle relative to the substrate.

3. The optical modulator as described in claim 1, characterized in that, The end face of the buffer layer on the other side is formed into a curved surface.

4. The optical modulator as described in any one of claims 1 to 3, characterized in that, On the boundary portion, the first buffer layer is formed on the second buffer layer, or the second buffer layer is formed on the first buffer layer.

5. The optical modulator as described in any one of claims 1 to 3, characterized in that, The first buffer layer and the second buffer layer are formed of different compositions.

6. The optical modulator as described in any one of claims 1 to 3, characterized in that, The first buffer layer is an M-Si-O compound. M is selected from at least one of Al, Zr, Hf, La, Ba, Bi, Ti, Ca, Mo, and In.

7. The optical modulator as described in any one of claims 1 to 3, characterized in that, The elements constituting the second buffer layer include at least one of the elements constituting the first buffer layer.

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