Optical modulator

Abstract

To provide an optical modulator capable of reducing electrical loss while suppressing an increase in size.SOLUTION: The optical modulation device (100) includes optical waveguides (1), first electrodes (2R, 2L), second electrodes (3), and first wiring electrodes (4OR, 4OL). The first electrodes (2R, 2L) are arranged on one side in a height direction (HD) with respect to the optical waveguides (1) and extend along a part of the optical waveguides (1). The second electrode (3) is disposed on the other side in the height direction of the optical modulator (100) with respect to the optical waveguide (1). The first wiring electrodes (40 R, 40 L) are disposed on the side opposite to the optical waveguide (1) with respect to the first electrodes (2R, 2L) in the height direction (HD) of the optical modulator (100) and are electrically connected to the first electrodes (2R, 2L). The first line electrodes (4OR, 4OL) include line portions disposed so as to be drawn out from end portions in the extending direction of the first electrodes (2R, 2L) when viewed along the height direction (HD).SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] The present disclosure relates to optical modulators. [Background technology]

[0002] Optical communications require optical transceivers that convert optical signals to electrical signals and vice versa. An optical transceiver has an optical modulator as its main component, which converts electrical signals into optical signals.

[0003] For example, FIG. 1 of Patent Document 1 illustrates an example of a conventional optical modulator having a coplanar electrode arrangement. In this optical modulator, an optical control substrate having an optical waveguide and a control electrode and a circuit board having a wiring electrode are stacked. The control electrode is formed on the surface of the optical control substrate facing the circuit board to apply an electric field to the optical waveguide in the optical control substrate. The wiring electrode is formed on the surface of the circuit board facing the optical control substrate to supply or extract a modulation signal to the control electrode. The control electrode includes a signal electrode and a ground electrode. The wiring electrode is provided corresponding to the signal electrode and the ground electrode and is connected to each end of the signal electrode and the ground electrode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-068071 Summary of the Invention [Problem to be solved by the invention]

[0005] In the optical modulator of Patent Document 1, a wiring electrode connected to a signal electrode and a wiring electrode connected to a ground electrode are arranged in parallel on a circuit board. These wiring electrodes are not electrodes intended to apply an electric field to the optical waveguide, so it is preferable to arrange them as far apart as possible. If the distance between the wiring electrodes is short, the electric field formed by the wiring electrodes may be applied to areas other than the optical modulation section of the optical waveguide, which may result in increased electrical loss. However, in order to ensure the distance between the wiring electrodes in the optical modulator of Patent Document 1, it is necessary to separate the wiring electrodes in the in-plane direction of the circuit board, which poses a problem of increasing the size of the optical modulator, particularly in the width direction.

[0006] An object of the present disclosure is to provide an optical modulator that can reduce electrical loss while suppressing an increase in size. [Means for solving the problem]

[0007] The optical modulator according to the present disclosure includes an optical waveguide, a first electrode, a second electrode, and a first wiring electrode. The optical waveguide has an electro-optic effect. The first electrode is disposed on one side of the optical waveguide in the height direction of the optical modulator and extends along a portion of the optical waveguide. The second electrode is disposed on the other side of the optical waveguide in the height direction of the optical modulator and generates a potential difference between itself and the first electrode to apply an electric field to the optical waveguide together with the first electrode. The first wiring electrode is disposed on the opposite side of the first electrode from the optical waveguide in the height direction of the optical modulator and is electrically connected to the first electrode. The first wiring electrode includes a wiring portion disposed so as to be drawn out from an end of the first electrode in the extension direction when viewed along the height direction of the optical modulator. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to reduce electrical loss while suppressing an increase in the size of an optical modulator. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a plan view of the optical modulator according to the first embodiment. [Figure 2A]FIG. 2A is a schematic diagram showing the configuration of the optical modulator according to the first embodiment. [Figure 2B] FIG. 2B is a schematic diagram showing the configuration of the optical modulator according to the first embodiment. [Figure 2C] FIG. 2C is a schematic diagram showing the configuration of the optical modulator according to the first embodiment. [Figure 2D] FIG. 2D is a schematic diagram showing the configuration of the optical modulator according to the first embodiment. [Figure 2E] FIG. 2E is a schematic diagram showing the configuration of the optical modulator according to the first embodiment. [Figure 2F] FIG. 2F is a schematic diagram showing the configuration of the optical modulator according to the first embodiment. [Figure 3A] FIG. 3A is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 3B] FIG. 3B is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 3C] FIG. 3C is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 3D] FIG. 3D is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 3E] FIG. 3E is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 4A] FIG. 4A is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 4B] FIG. 4B is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 4C] FIG. 4C is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 4D] FIG. 4D is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 4E] FIG. 4E is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 4F] FIG. 4F is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 4G] FIG. 4G is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 5A] FIG. 5A is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 5B] FIG. 5B is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 5C] FIG. 5C is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 5D] FIG. 5D is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 5E] FIG. 5E is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 5F] FIG. 5F is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 6A] FIG. 6A is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 6B] FIG. 6B is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 6C] FIG. 6C is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 6D] FIG. 6D is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 6E] FIG. 6E is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 6F] FIG. 6F is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 6G] FIG. 6G is a schematic view showing an example of a method for manufacturing the optical modulator according to the first embodiment. [Figure 7] FIG. 7 is a schematic diagram showing the configuration of an optical modulator according to the second embodiment. [Figure 8] FIG. 8 is a schematic diagram showing the configuration of an optical modulator according to the third embodiment. [Figure 9] FIG. 9 is a schematic diagram showing the configuration of an optical modulator according to the third embodiment. [Figure 10] FIG. 10 is a plan view of the optical modulator according to the fourth embodiment. [Figure 11] FIG. 11 is a schematic diagram showing the configuration of an optical modulator according to the fourth embodiment. [Figure 12] FIG. 12 is a schematic diagram showing the configuration of an optical modulator according to the fifth embodiment. [Figure 13] FIG. 13 is a plan view of the optical modulator according to the sixth embodiment. [Figure 14] FIG. 14 is a schematic diagram showing the configuration of an optical modulator according to the sixth embodiment. [Figure 15] FIG. 15 is a schematic diagram showing the configuration of an optical modulator according to the seventh embodiment. [Figure 16] FIG. 16 is a schematic diagram showing the configuration of an optical modulator according to the eighth embodiment. [Figure 17] FIG. 17 is a schematic diagram showing the configuration of an optical modulator according to the ninth embodiment. [Figure 18] FIG. 18 is a schematic diagram showing a modified example of the optical modulator according to the ninth embodiment. [Figure 19] FIG. 19 is a schematic diagram showing a modified example of the optical modulator according to the ninth embodiment. [Figure 20] FIG. 20 is a schematic diagram showing the configuration of an optical modulator according to the tenth embodiment. [Figure 21] FIG. 21 is a schematic diagram showing the configuration of an optical modulator according to the eleventh embodiment. [Figure 22] FIG. 22 is a schematic diagram showing a modified example of the optical modulator according to the eleventh embodiment. [Figure 23A] FIG. 23A is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 23B] FIG. 23B is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 23C] FIG. 23C is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 23D]FIG. 23D is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 23E] FIG. 23E is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 23F] FIG. 23F is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 24A] FIG. 24A is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 24B] FIG. 24B is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 24C] FIG. 24C is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 24D] FIG. 24D is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 24E] FIG. 24E is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 24F] FIG. 24F is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 25A] FIG. 25A is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 25B] FIG. 25B is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 25C] FIG. 25C is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 25D] FIG. 25D is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 25E] FIG. 25E is a schematic view showing an example of a method for manufacturing the optical modulator according to the eleventh embodiment. [Figure 26] FIG. 26 is a schematic diagram showing the configuration of an optical modulator according to the twelfth embodiment. [Figure 27] FIG. 27 is a schematic diagram showing the configuration of an optical modulator according to the thirteenth embodiment. [Figure 28] FIG. 28 is a schematic diagram showing the configuration of an optical modulator according to the fourteenth embodiment. [Figure 29] FIG. 29 is a schematic diagram showing the configuration of an optical modulator according to the fifteenth embodiment. [Figure 30] FIG. 30 is a schematic diagram showing the configuration of an optical modulator according to the fifteenth embodiment. [Figure 31] FIG. 31 is a schematic diagram showing the configuration of an optical modulator according to the fifteenth embodiment. [Figure 32] FIG. 32 is a schematic diagram showing the configuration of an optical modulator according to the fifteenth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described. Note that in the following description, examples of embodiments of the present disclosure will be described, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and specific materials may be exemplified, but the present disclosure is not limited to these examples.

[0011] An optical modulator according to an embodiment of the present disclosure includes an optical waveguide, a first electrode, a second electrode, and a first wiring electrode. The optical waveguide has an electro-optic effect. The first electrode is disposed on one side of the optical waveguide in the height direction of the optical modulator and extends along a portion of the optical waveguide. The second electrode is disposed on the other side of the optical waveguide in the height direction of the optical modulator and generates a potential difference between itself and the first electrode to apply an electric field to the optical waveguide together with the first electrode. The first wiring electrode is disposed on the opposite side of the first electrode from the optical waveguide in the height direction of the optical modulator and is electrically connected to the first electrode. The first wiring electrode includes a wiring portion disposed so as to be drawn out from an end of the first electrode in the extension direction when viewed along the height direction of the optical modulator (first configuration).

[0012] In the first configuration, a first electrode is disposed on one side of the optical waveguide in the height direction of the optical modulator. The first wiring electrode, electrically connected to the first electrode and supplying or retrieving an electrical signal from the first electrode, includes a wiring portion extending from an end of the first electrode as viewed along the height direction of the optical modulator. The first wiring electrode is disposed on the opposite side of the optical waveguide from the first electrode in the height direction of the optical modulator. Meanwhile, a second electrode, which applies an electric field to the optical waveguide together with the first electrode, is disposed on the opposite side of the optical modulator from the first electrode and the first wiring electrode in the height direction of the optical modulator. Therefore, the wiring electrode for supplying or retrieving an electric signal from the second electrode is naturally spaced apart from the wiring portion of the first wiring electrode in the height direction of the optical modulator. This makes it difficult for an electric field to be generated between the wiring electrodes, thereby preventing an excessive electric field from being applied to portions of the optical waveguide other than the optical modulation portion. Therefore, the first configuration reduces electrical loss while suppressing an increase in the size of the optical modulator, particularly in the width direction.

[0013] In the optical modulator of the first configuration, for example, the first electrode is disposed in a cavity provided in the optical modulator (second configuration). In this case, the first electrode can be disposed relatively freely by utilizing the cavity.

[0014] In the optical modulator of the second configuration, the first wiring electrode is preferably disposed within the cavity and supported by the sidewall that defines the cavity (third configuration).

[0015] In the third configuration, the first wiring electrode is supported by the sidewall that defines the cavity, which makes it possible to suppress buckling of the first wiring electrode. For example, even if the first wiring electrode is formed with internal stress and is no longer able to withstand the internal stress during use of the optical modulator, buckling of the first wiring electrode is unlikely to occur. Therefore, deformation of the optical modulator can be suppressed.

[0016] In the optical modulator of any one of the first to third configurations, the first wiring electrode may include a main body portion disposed at a distance from the first electrode in the height direction and a portion of which constitutes the wiring portion, and a connecting portion connecting the main body portion and the first electrode. The connecting portion may be inclined with respect to the height direction when viewed in a cross section perpendicular to the extension direction of the first electrode (fourth configuration).

[0017] For example, when viewed in a cross section perpendicular to the extension direction of the first electrode, if the connecting portion connecting the first electrode and the main body of the first wiring electrode is arranged parallel to the height direction of the optical modulator, a right-angled corner is formed at the junction between the first electrode and the first wiring electrode, causing high-frequency signal loss at this corner. However, in the fourth configuration, when viewed in a cross section perpendicular to the extension direction of the first electrode, the connecting portion of the first wiring electrode is inclined with respect to the height direction of the optical modulator. Therefore, the first wiring electrode can be joined to the first electrode at a gentle angle. This reduces high-frequency signal loss at the junction between the first electrode and the first wiring electrode, enabling wideband modulation.

[0018] In the optical modulator of any one of the first to fourth configurations, the first wiring electrode may include a main body portion disposed apart from the first electrode in the height direction and partly constituting the wiring portion, and a connecting portion connecting the main body portion and the first electrode. The connecting portion includes a surface continuous with an end portion of the first electrode in the extension direction, and the surface may be inclined with respect to the height direction so that the main body portion side is separated from the first electrode side in the extension direction when viewed along the width direction of the optical modulator (fifth configuration).

[0019] For example, when viewed along the width direction of the optical modulator, if the surface of a connecting portion connecting the first electrode and the main portion of the first wiring electrode, which is continuous with the end of the first electrode in the extension direction, is arranged parallel to the height direction of the optical modulator, this surface forms a right-angle corner with the end of the first electrode, causing high-frequency signal loss at this corner. However, in the fifth configuration, when viewed along the width direction of the optical modulator, the surface of the connecting portion of the first wiring electrode is inclined with respect to the height direction of the optical modulator so that the main portion side is away from the first electrode in the extension direction. Therefore, the surface of the connecting portion of the first wiring electrode can be made continuous with the first electrode at a gentle angle. This reduces high-frequency signal loss at the boundary between the surface of the connecting portion and the first electrode, enabling wideband modulation.

[0020] In the optical modulator of the second configuration, at least a part of the first wiring electrode may be disposed freestanding in the cavity (sixth configuration).

[0021] For example, in an optical modulator, if a first wiring electrode is provided on a surface that has been roughened by processing, the first wiring electrode is likely to peel off, and the surface roughness may cause loss of electrical signals. In contrast, in the sixth configuration, at least a portion of the first wiring electrode is free-standing within the cavity. In this case, peeling of the first wiring electrode does not occur, and loss of electrical signals caused by surface roughness can be prevented.

[0022] The optical modulator of any one of the first to sixth configurations may further include a through electrode connected to the wiring portion of the first wiring electrode and extending from the first electrode side to the second electrode side (seventh configuration).

[0023] In the seventh configuration, a through electrode is provided extending from the first electrode side to the second electrode side. The through electrode is connected to the wiring portion of the first wiring electrode. In this case, an electrical signal from the first electrode is extracted to the second electrode side via the wiring portion of the first wiring electrode and the through electrode. Therefore, the electrode pad for the first electrode and the electrode pad for the second electrode can be arranged on the same plane, simplifying the electrical wiring. Furthermore, since the electrical wiring for the first electrode and the second electrode can be arranged close to each other, loss of electrical signals can be reduced.

[0024] In the optical modulator of the seventh configuration, it is preferable that the through electrode is inclined with respect to the height direction of the optical modulator (eighth configuration).

[0025] For example, if the through electrodes are arranged parallel to the height direction of the optical modulator, a right-angle corner is formed at the junction between the through electrodes and the first wiring electrode, causing loss of high-frequency signals at this corner. However, in the eighth configuration, the through electrodes are inclined relative to the height direction of the optical modulator. This allows for a gentle junction between the through electrodes and the first wiring electrode. This reduces loss of high-frequency signals at the junction between the through electrodes and the first wiring electrode, enabling modulation over a wide bandwidth.

[0026] In the optical modulator of any one of the first to eighth configurations, it is preferable that the thickness of the first electrode is greater than the thickness of the first wiring electrode (ninth configuration).

[0027] The first electrode is an electrode that applies an electric field to the optical waveguide together with the second electrode to modulate the optical signal. In the ninth configuration, the thickness of this first electrode is made larger than the thickness of the first wiring electrode. This reduces the resistance of the first electrode in the portion of the optical modulator that performs optical modulation, thereby reducing the loss of the electrical signal.

[0028] In the optical modulator of any one of the first to ninth configurations, the first electrode and the first wiring electrode may be joined, and a gap may exist at the interface between the first electrode and the first wiring electrode (tenth configuration).

[0029] In the tenth configuration, a gap exists at the interface between the first electrode and the first wiring electrode. This gap can add capacitance and adjust the characteristic impedance. Furthermore, the gap has a lower dielectric constant than the electro-optic material. This reduces the effective refractive index of the electrical signal, thereby minimizing electrical signal loss in the first electrode and the first wiring electrode.

[0030] In the optical modulator of any one of the first to ninth configurations, the first electrode and the first wiring electrode may be joined, and oxygen may be present at the interface between the first electrode and the first wiring electrode (eleventh configuration).

[0031] In the eleventh configuration, oxygen is present at the interface between the first electrode and the first wiring electrode. This oxygen can add capacitance and adjust the characteristic impedance. Furthermore, when oxygen is bonded to a metal, its dielectric constant becomes lower than that of the electro-optic material. This reduces the effective refractive index of the electrical signal, thereby reducing the loss of the electrical signal in the first electrode and the first wiring electrode.

[0032] In the optical modulator of any one of the first to ninth configurations, the first electrode and the first wiring electrode may be joined, and a eutectic may exist between the first electrode and the first wiring electrode (twelfth configuration).

[0033] In the twelfth configuration, since a eutectic is formed between the first electrode and the first wiring electrode, it is possible to increase the bonding strength between the first electrode and the first wiring electrode and to reduce loss of electrical connection between the first electrode and the first wiring electrode.

[0034] In the optical modulator of any one of the first to ninth configurations, the first electrode and the first wiring electrode may be bonded, and a resin may be present at the interface between the first electrode and the first wiring electrode (thirteenth configuration).

[0035] In the thirteenth configuration, the resin is present at the interface between the first electrode and the first wiring electrode, which allows for adding capacitance and adjusting the characteristic impedance. Furthermore, the resin has a lower dielectric constant than the electro-optic material. This reduces the effective refractive index of the electrical signal, thereby minimizing electrical signal loss in the first electrode and the first wiring electrode.

[0036] In the optical modulator of any one of the first to thirteenth configurations, the length of the first electrode in the width direction of the optical modulator is preferably greater than the length of the optical waveguide (fourteenth configuration).

[0037] In the fourteenth configuration, the width of the first electrode (the length in the width direction of the optical modulator) is larger than the width of the optical waveguide (the length in the width direction of the optical modulator), so that a uniform electric field can be applied from the first electrode to the optical waveguide, thereby improving the quality of the optical signal generated by the optical modulator.

[0038] It is preferable that the optical modulator of any one of the first to fourteenth configurations further comprises a low dielectric layer provided at least either between the optical waveguide and the first electrode or between the optical waveguide and the second electrode, the low dielectric layer having a refractive index smaller than that of the optical waveguide (fifteenth configuration).

[0039] In the fifteenth configuration, a low-dielectric layer is provided between the optical waveguide and the first electrode and / or the second electrode. This reduces the absorption of light from the optical waveguide into the first electrode and / or the second electrode, thereby reducing optical loss. Furthermore, the provision of the low-dielectric layer allows the effective refractive index of the high-frequency signal to be adjusted to match the effective refractive index of the light wave, enabling optical modulation up to higher frequencies. Furthermore, the provision of the low-dielectric layer reduces the effective dielectric constant for the electrical signal, thereby reducing high-frequency signal loss and enabling optical modulation up to higher frequencies.

[0040] In the optical modulator of the 15th configuration, when the low dielectric layer is provided in the height direction from the optical waveguide to the first electrode and from the optical waveguide to the first wiring electrode, it is preferable that the length in the height direction of the low dielectric layer from the optical waveguide to the first wiring electrode is greater than the length in the height direction of the low dielectric layer from the optical waveguide to the first electrode (16th configuration).

[0041] It is preferable that the optical modulator of any one of the first to sixteenth configurations further includes a support substrate that is arranged on the opposite side of the first electrode from the optical waveguide and is formed of a low-dielectric-constant material having a refractive index smaller than that of the optical waveguide (seventeenth configuration).

[0042] In the seventeenth configuration, a support substrate made of a low-dielectric-constant material is provided on the opposite side of the first electrode from the optical waveguide. This allows the effective refractive index of the high-frequency signal to be adjusted to match the effective refractive index of the light wave, enabling optical modulation over a wider bandwidth. Furthermore, providing a support substrate made of a low-dielectric-constant material reduces the effective dielectric constant for the electrical signal, thereby suppressing high-frequency signal loss and enabling optical modulation up to higher frequencies.

[0043] Any one of the optical modulators of the first to seventeenth configurations may further include a second wiring electrode that is arranged on the opposite side of the optical waveguide from the second electrode in the height direction of the optical modulator and is electrically connected to the second electrode (18th configuration).

[0044] The optical modulator of the eighteenth configuration may further include a through electrode connected to the second wiring electrode and extending from the second electrode side to the first electrode side (nineteenth configuration).

[0045] In the optical modulator of the eighteenth or nineteenth configuration, it is preferable that the thickness of the second electrode is greater than the thickness of the second wiring electrode (twentieth configuration).

[0046] The optical modulator of any one of the eighteenth to twentieth configurations may further include a first low-dielectric layer provided in the height direction from the optical waveguide to the first electrode and from the optical waveguide to the first wiring electrode, the first low-dielectric layer having a refractive index smaller than that of the optical waveguide, and a second low-dielectric layer provided in the height direction from the optical waveguide to the second electrode and from the optical waveguide to the second wiring electrode, the second low-dielectric layer having a refractive index smaller than that of the optical waveguide. In this case, it is preferable that the length in the height direction of the first low-dielectric layer from the optical waveguide to the first wiring electrode is greater than the length in the height direction of the first low-dielectric layer from the optical waveguide to the first electrode, and the length in the height direction of the second low-dielectric layer from the optical waveguide to the second wiring electrode is greater than the length in the height direction of the second low-dielectric layer from the optical waveguide to the second electrode (twenty-first configuration).

[0047] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or equivalent components are designated by the same reference numerals, and redundant description will not be repeated.

[0048] First Embodiment [Configuration of optical modulator] FIG. 1 is a plan view of an optical modulator 100 according to a first embodiment. Referring to FIG. 1, in this embodiment, the optical modulator 100 is a so-called Mach-Zehnder optical modulator. The optical modulator 100 includes an optical waveguide 1, first electrodes 2R and 2L, a second electrode 3, and first wiring electrodes 4IR, 4IL, 4OR, and 4OL. FIG. 1 illustrates the optical waveguide 1, the first electrodes 2R and 2L, the second electrode 3, and the first wiring electrodes 4IR, 4IL, 4OR, and 4OL when projected onto a plane perpendicular to a height direction HD of the optical modulator 100. In FIG. 1, the second electrode 3 is indicated by a dashed-dotted line, and the first wiring electrodes 4IR, 4IL, 4OR, and 4OL are indicated by dashed lines. In this specification, the height direction HD refers to the stacking direction of the elements of the optical modulator 100, which has a stacked structure. The direction in which the optical waveguide 1 substantially extends and which is perpendicular to the height direction HD is defined as the longitudinal direction LD of the optical modulator 100. The direction perpendicular to the height direction HD and the longitudinal direction LD is the width direction WD of the optical modulator 100.

[0049] The optical waveguide 1 functions as an optical transmission path. The optical waveguide 1 includes an input optical waveguide 11, which is the input side of light, two branch optical waveguides 12R and 12L branching from the input optical waveguide 11, and an output optical waveguide 13, which is the output side of light formed by combining the two branch optical waveguides 12R and 12L. The input optical waveguide 11 and the output optical waveguide 13 extend linearly, for example, along the longitudinal direction LD. The branch optical waveguides 12R and 12L include input relay sections 121R and 121L, straight sections 122R and 122L, and output relay sections 123R and 123L. The straight sections 122R and 122L are arranged side by side in the width direction WD. The straight sections 122R and 122L are connected to the input optical waveguide 11 by the input relay sections 121R and 121L. The straight portions 122R and 122L are connected to the output optical waveguide 13 by output relay portions 123R and 123L.

[0050] The first electrodes 2R, 2L extend along a portion of the optical waveguide 1. More specifically, the first electrodes 2R, 2L extend along the straight portions 122R, 122L of the branch optical waveguides 12R, 12L, respectively. The first electrodes 2R, 2L are arranged so as to overlap the straight portions 122R, 122L of the branch optical waveguides 12R, 12L, respectively, when viewed, for example, along the height direction HD.

[0051] The second electrode 3 is disposed so that at least a portion thereof overlaps with the optical waveguide 1 and the first electrodes 2R, 2L when viewed along the height direction HD. For example, the second electrode 3 overlaps with the straight line portions 122R, 122L of the branch optical waveguides 12R, 12L when viewed along the height direction HD.

[0052] The second electrode 3 forms a potential difference between itself and each of the first electrodes 2R and 2L, and applies an electric field to the optical waveguide 1 together with the first electrodes 2R and 2L. The first electrodes 2R and 2L and the second electrode 3 function, for example, as control electrodes for controlling light passing through the optical waveguide 1. The first electrode 2R and the second electrode 3 are arranged so as to apply an electric field to the branch optical waveguide 12R. The first electrode 2L and the second electrode 3 are arranged so as to apply an electric field to the branch optical waveguide 12L. The straight portions 122R and 122L are essentially optical modulation portions of the optical waveguide 1. For example, the first electrodes 2R and 2L can be used as signal electrodes, and the second electrode 3 can be used as a ground electrode. Alternatively, the first electrodes 2R and 2L can be used as ground electrodes, and the second electrode 3 can be used as a signal electrode.

[0053] The first wiring electrodes 4IR, 4IL, 4OR, and 4OL are arranged in the optical modulator 100 to supply electrical signals to the first electrodes 2R and 2L or to extract electrical signals from the first electrodes 2R and 2L. The first wiring electrodes 4IR and 4OR are electrically connected to the first electrode 2R. The first wiring electrodes 4IL and 4OL are electrically connected to the first electrode 2L. The first wiring electrodes 4IR and 4IL are arranged on the input sides of the first electrodes 2R and 2L, and the first wiring electrodes 4OR and 4OL are arranged on the output sides of the first electrodes 2R and 2L. In this embodiment, the first wiring electrodes 4IL and 4OL protrude from one of the first electrodes 2L in the width direction WD when viewed along the height direction HD. Specifically, the first wiring electrode 4IL includes a wiring portion 4aIL. This wiring portion 4aIL is arranged to be drawn from one end 2aL of the first electrode 2L in the extension direction when viewed along the height direction HD. The first wiring electrode 4OL includes a wiring portion 4aOL. This wiring portion 4aOL is arranged so as to be drawn out from the other end 2bL of the first electrode 2L in the extension direction, as viewed along the height direction HD. The first wiring electrodes 4IR, 4OR also protrude in the width direction WD from the other first electrode 2R, as viewed along the height direction HD. Specifically, the first wiring electrode 4IR includes a wiring portion 4aIR. This wiring portion 4aIR is arranged so as to be drawn out from one end 2aR of the first electrode 2R in the extension direction, as viewed along the height direction HD. The first wiring electrode 4OR includes a wiring portion 4aOR. This wiring portion 4aOR is arranged so as to be drawn out from the other end 2bR of the first electrode 2R in the extension direction, as viewed along the height direction HD.

[0054] Next, a more specific configuration of the optical modulator 100 shown in Fig. 1 will be described with reference to Fig. 2A to Fig. 2F. Fig. 2A is a cross-sectional view taken along line IIA-IIA in Fig. 1. In other words, Fig. 2A is a cross-sectional view (transverse cross-sectional view) of the optical modulator 100 cut along a plane perpendicular to the longitudinal direction LD at the positions of the straight portions 122R, 122L of the branch optical waveguides 12R, 12L (the optical modulation portions of the optical waveguide 1).

[0055] Referring to FIG. 2A, the optical waveguide 1 has an electro-optic effect. In this embodiment, the optical waveguide 1 is formed in a base layer 15. In this embodiment, the optical waveguide 1 protrudes from the surface of the base layer 15. That is, the optical waveguide 1 is a ridge-type optical waveguide. However, the optical waveguide 1 does not necessarily have to be a ridge-type optical waveguide. The optical waveguide 1 may have a substantially trapezoidal cross section as shown in FIG. 2A, but may also have a cross section of another shape, such as a rectangular shape.

[0056] The optical waveguide 1 is made of an electro-optical material. Examples of the electro-optical material include LiNbO3 (lithium niobate), LiTaO3 (lithium tantalate), PLZT (lead lanthanum zirconate titanate), KTN (potassium tantalate niobate), and BaTiO3 (barium titanate). An electro-optical polymer (EO polymer) may also be used. The base layer 15 may be made of the same electro-optical material as the optical waveguide 1. However, the base layer 15 may be omitted from the optical modulator 100.

[0057] The first electrodes 2R, 2L are arranged on one side of the optical waveguide 1 in the height direction HD of the optical modulator 100. That is, the centers C2 of the first electrodes 2R, 2L in the height direction HD are located on one side of the center C1 of the optical waveguide 1 (branch optical waveguides 12R, 12L) in the height direction HD of the optical modulator 100. In this embodiment, the entire first electrodes 2R, 2L are arranged on one side of the optical waveguide 1 in the height direction HD. The first electrode 2R is stacked on one side of the branch optical waveguide 12R in the height direction HD. The first electrode 2L is stacked on one side of the branch optical waveguide 12L in the height direction HD. In this embodiment, the first electrodes 2R, 2L have a substantially rectangular cross section. However, the cross-sectional shape of the first electrodes 2R, 2L is not limited to this.

[0058] The width w2 of the first electrodes 2R, 2L is preferably larger than the width w1 of the optical waveguide 1. However, the width w2 of the first electrodes 2R, 2L may be equal to or smaller than the width w1 of the optical waveguide 1. The width w2 of the first electrodes 2R, 2L is the maximum length of the first electrodes 2R, 2L in the width direction WD. The width w1 of the optical waveguide 1 is the maximum length in the width direction WD of the portions of the optical waveguide 1 corresponding to the first electrodes 2R, 2L. In this embodiment, the width w1 is the maximum length in the width direction WD of each of the branch optical waveguides 12R, 12L.

[0059] The first wiring electrodes 4OR, 4OL are arranged on the opposite side of the optical waveguide 1 with respect to the first electrodes 2R, 2L in the height direction HD. The first wiring electrode 4OR includes a main body portion 41R and a connecting portion 42R. The first wiring electrode 4OL includes a main body portion 41L and a connecting portion 42L.

[0060] The main body 41R is disposed at a distance from the first electrode 2R in the height direction HD. The main body 41L is disposed at a distance from the first electrode 2L in the height direction HD. The main bodies 41R and 41L are disposed, for example, directly below the first electrodes 2R and 2L in a cross-sectional view of the optical modulator 100. The main bodies 41R and 41L face the first electrodes 2R and 2L, respectively, with a gap in the height direction HD. The connecting portion 42R connects the main body 41R to the first electrode 2R. The connecting portion 42L connects the main body 41L to the first electrode 2L. The connecting portion 42R may, for example, connect outer ends of the main body 41R and the first electrode 2R to each other in the width direction WD. Similarly, the connecting portion 42L may connect outer ends of the main body 41L and the first electrode 2L to each other in the width direction WD. The connecting portions 42R and 42L extend from the main body portions 41R and 41L toward the first electrodes 2R and 2L in a cross-sectional view of the optical modulator 100.

[0061] In this embodiment, the main body portions 41R, 41L and the connecting portions 42R, 42L have a substantially rectangular cross section, although the cross-sectional shape of the first electrodes 2R, 2L is not limited to this.

[0062] The optical modulator 100 may further include a support substrate 6. The support substrate 6 supports the optical waveguide 1, the first electrodes 2R and 2L, the second electrode 3, and the first wiring electrodes 4OR and 4OL. A semiconductor material may be used for the support substrate 6. Examples of the semiconductor material include single-element semiconductors such as silicon (Si) or germanium (Ge), or compound semiconductors such as gallium arsenide (GaAs). The support substrate 6 may also be made of oxides such as SiO2, Al2O3, LaAlO3, LaYO3, ZnO, HfO2, MgO, or YO3. Alternatively, the support substrate 6 may be made of an electro-optical material, specifically, LiNbO3, LiTaO3, PLZT, KTN, or BaTiO3.

[0063] In this embodiment, a cavity C is provided in the optical modulator 100. The cavity C is formed between the support substrate 6 and the optical waveguide 1. In this embodiment, the cavity C is a closed space when viewed in cross section of the optical modulator 100. The cavity C can be formed, for example, by a recess 61 provided in the support substrate 6 and a base layer 15. Specifically, the cavity C is defined by side walls 61a, 61a and a bottom wall 61b of the recess 61, and the base layer 15. The first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL are disposed in this cavity C. The first wiring electrodes 4OR, 4OL are supported by the side walls 61a, 61a. More specifically, the connecting portion 42R of the first wiring electrode 4OR is provided along one side wall 61a, and the connecting portion 42L of the first wiring electrode 4OL is provided along the other side wall 61a. Furthermore, the main bodies 41R and 41L of the first wiring electrodes 4OR and 4OL are provided along the bottom wall 61b.

[0064] The second electrode 3 is disposed on the other side of the optical waveguide 1 in the height direction HD of the optical modulator 100 (opposite the first electrodes 2R and 2L). That is, the center C3 of the second electrode 3 in the height direction HD of the optical modulator 100 is located on the other side of the center C1 of the optical waveguide 1 in the height direction HD. In this embodiment, the second electrode 3 is stacked on the optical waveguide 1 on the opposite side of the first electrodes 2R and 2L in the height direction HD. More specifically, the second electrode 3 is stacked on the branch optical waveguides 12R and 12L on the opposite side of the first electrodes 2R and 2L, respectively. The second electrode 3 is disposed on the opposite side of the first electrodes 2R and 2L with respect to the branch optical waveguides 12R and 12L so that the branch optical waveguides 12R and 12L are positioned between the second electrode 3 and the first electrodes 2R and 2L.

[0065] In this embodiment, the second electrode 3 is provided in common to the two branch optical waveguides 12R and 12L. However, the second electrode 3 may be provided for each of the branch optical waveguides 12R and 12L.

[0066] 2B and 2C are cross-sectional views taken along lines IIB-IIB and IIC-IIC in FIG. 1, respectively. FIG. 2B is a cross-sectional view of the optical modulator 100 taken along a plane perpendicular to the longitudinal direction LD at the positions of the output relay sections 123R and 123L of the branched optical waveguides 12R and 12L. FIG. 2C is a cross-sectional view of the optical modulator 100 taken along a plane perpendicular to the longitudinal direction LD at a position of the output relay sections 123R and 123L of the branched optical waveguides 12R and 12L closer to the output optical waveguide 13 than the cross section shown in FIG. 2B.

[0067] Referring to FIG. 2B, the second electrode 3 is not present at a position closer to the output side of the optical waveguide 1 than the optical modulation section. Referring to FIG. 2C, at a position closer to the output side, not only the second electrode 3 but also the connecting portions 42R, 42L of the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL are absent. Therefore, the electric field from the first electrodes 2R, 2L and the second electrode 3 is not substantially applied to the portion of the optical waveguide 1 other than the optical modulation section. Furthermore, because the main portions 41R, 41L of the first wiring electrodes 4OR, 4OL are spaced apart from the optical waveguide 1 in the height direction HD, the electric field from the first wiring electrodes 4OR, 4OL is not substantially affected by the portion of the optical waveguide 1 other than the optical modulation section. At this position, the main portions 41R, 41L of the first wiring electrodes 4OR, 4OL are arranged to be drawn out from the first electrodes 2R, 2L when viewed along the height direction HD, and form the wiring portion 4aOL.

[0068] Fig. 2D is a cross-sectional view taken along line IID-IID in Fig. 1. In other words, Fig. 2D is a cross-sectional view of the first wiring electrodes 4OR, 4OL, which are drawn out from the first electrodes 2R, 2L in the width direction WD, cut along a plane perpendicular to the width direction WD.

[0069] 2D, in a cross section of a portion of the first wiring electrodes 4OR, 4OL drawn out from the first electrodes 2R, 2L in the width direction WD, the first electrodes 2R, 2L, the second electrode 3, and the connecting portions 42R, 42L of the first wiring electrodes 4OR, 4OL are absent, but the main portions 41R, 41L of the first wiring electrodes 4OR, 4OL are present. The main portions 41R, 41L of the first wiring electrodes 4OR, 4OL at this position are portions arranged to be drawn out from the first electrodes 2R, 2L when viewed along the height direction HD, and form a wiring portion 4aOL.

[0070] Fig. 2E is a cross-sectional view taken along line IIE-IIE in Fig. 1. In other words, Fig. 2E is a cross-sectional view of the optical modulator 100 taken along a plane perpendicular to the width direction WD, and is a view of the first electrode 2R and the first wiring electrode 4OR viewed along the width direction WD. Fig. 2E also shows line IIA-IIA, line IIB-IIB, and line IIC-IIC in Fig. 1.

[0071] 2E, the connecting portion 42R of the first wiring electrode 4OR includes a surface 42a that is continuous with an end portion of the first electrode 2R in the extension direction (longitudinal direction LD). When viewed along the width direction WD, the surface 42a is inclined with respect to the height direction HD so that the main body portion 41R side of the first wiring electrode 4OR is spaced apart from the first electrode 2R in the extension direction relative to the first electrode 2R. When viewed along the width direction WD, the surface 42a of the connecting portion 42R may be linear or curved.

[0072] Although not shown in the figures, the connecting portion 42L of the first wiring electrode 4OL can also have a configuration similar to that of the connecting portion 42R of the first wiring electrode 4OR. That is, of the connecting portion 42L, the surface continuing to the end portion in the extension direction of the first electrode 2L may be inclined with respect to the height direction HD so that the main body portion 41L side of the first wiring electrode 4OL is away from the first electrode 2L in the extension direction with respect to the first electrode 2L side.

[0073] FIG. 2F is a cross-sectional view showing an enlarged portion of the first electrode 2L and the first wiring electrode 4OL. Referring to FIG. 2F, the first electrode 2L is bonded to the first wiring electrode 4OL. More specifically, the first electrode 2L is bonded to the connecting portion 42L of the first wiring electrode 4OL. When the first electrode 2L and the first wiring electrode 4OL are bonded, minute gaps V may exist at the interface between the first electrode 2L and the first wiring electrode 4OL. Furthermore, oxygen may exist at the interface between the first electrode 2L and the first wiring electrode 4OL. This oxygen may be, for example, the oxygen content of an oxide. In this case, the oxygen content at the interface between the first electrode 2L and the first wiring electrode 4OL is, for example, 1% by mass or more higher than the oxygen content inside the first electrode 2L and the first wiring electrode 4OL. Furthermore, a eutectic may exist between the first electrode 2L and the first wiring electrode 4OL. This eutectic is formed when the first electrode 2L and the first wiring electrode 4OL are bonded using a eutectic reaction of metals. Furthermore, a resin may be present at the interface between the first electrode 2L and the first wiring electrode 4OL. This resin is, for example, a conductive resin. When any of voids, oxygen, eutectic, and resin exists between the first electrode 2L and the connecting portion 42L, the electrical connection between the first electrode 2L and the connecting portion 42L is ensured.

[0074] Although not shown, voids, oxygen, or resin may also exist at the interface between the first electrode 2R and the first wiring electrode 4OR. Alternatively, a eutectic may exist between the first electrode 2R and the first wiring electrode 4OR.

[0075] 2A to 2F mainly show the configuration of the output side of the optical modulator 100. The input side of the optical modulator 100 can have the same configuration as the output side. Therefore, a detailed description of the input side configuration will be omitted.

[0076] [Method for manufacturing the optical modulator 100] The following describes an example of a method for manufacturing the optical modulator 100. Figures 3A to 3E are schematic views for explaining an example of a method for manufacturing the optical modulator 100. As shown in Figure 3A, a support substrate 6 and an electro-optic material substrate 16 are prepared.

[0077] 3B, a recess 61 is formed in the support substrate 6 by dry etching, wet etching, dicing, or the like. This recess 61 becomes the cavity C. Meanwhile, the electro-optic material substrate 16 is patterned by lithography or the like, and then a base layer 15 having an optical waveguide 1 is formed by dry etching, wet etching, dicing, or the like.

[0078] 3C, electrodes are formed on the support substrate 6 having the recesses 61, and then patterning is performed using lithography or the like to form first wiring electrodes 4OR, 4OL in the recesses 61. Meanwhile, electrodes are formed on the base layer 15 having the optical waveguide 1, and then patterning is performed using lithography or the like to form first electrodes 2R, 2L on the surface of the base layer 15.

[0079] 3D, the first electrodes 2R, 2L of the base layer 15 are bonded to the first wiring electrodes 4OR, 4OL of the support substrate 6. The bonding is performed by bonding using a metal, bonding using a conductive resin, or the like.

[0080] 3E, the second electrode 3 is formed on the base layer 15 having the optical waveguide 1 by sputtering, vapor deposition, epitaxial film formation, or the like. By such a method, the optical modulator 100 having the cavity C can be manufactured.

[0081] 4A to 4G are schematic diagrams illustrating another example of a method for manufacturing the optical modulator 100. As shown in Fig. 4A, recesses 61 are formed in a prepared support substrate 6 by the same method as shown in Figs. 3B and 3C above, and first wiring electrodes 4OR, 4OL are formed in the recesses 61.

[0082] 4B, the recesses 61 in which the first wiring electrodes 4OR, 4OL have been formed are filled with a sacrificial layer 70. The sacrificial layer 70 can be filled by CVD, vapor deposition, sputtering, spin coating, or the like.

[0083] Next, as shown in FIG. 4C, the first electrodes 2R and 2L are formed on the support substrate 6 filled with the sacrificial layer 70 by sputtering, vapor deposition, epitaxial film formation, or the like.

[0084] Next, as shown in Fig. 4D, the electro-optic material substrate 16 is bonded to the support substrate 6 on which the first electrodes 2R, 2L are formed. The bonding can be performed by bonding using a metal or a conductive resin. Instead of bonding the electro-optic material substrate 16, a film of an electro-optic material may be formed on the support substrate 6 on which the first electrodes 2R, 2L are formed by epitaxial film formation, spin coating, or the like.

[0085] Next, as shown in FIG. 4E, the electro-optical material substrate 16 is patterned by lithography or the like, and then the base layer 15 having the optical waveguide 1 is formed by dry etching, wet etching, dicing or the like.

[0086] Next, as shown in FIG. 4F, the second electrode 3 is formed on the base layer 15 having the optical waveguide 1 by sputtering, vapor deposition, epitaxial film formation, or the like.

[0087] 4G, the sacrificial layer 70 is removed from the base layer 15 on which the second electrode 3 is formed by dry etching, wet etching, or the like. By this method, the optical modulator 100 having the cavity C can be manufactured.

[0088] 5A to 5F are schematic diagrams illustrating another example of a method for manufacturing the optical modulator 100. As shown in FIG. 5A, a C-SOI (Cavity Silicon On Insulator) 10 having a cavity C is prepared. Furthermore, a base layer 15 having an optical waveguide 1 is prepared. First electrodes 2R and 2L are formed on the surface of the base layer 15 by a method similar to the method shown in FIG. 3C above.

[0089] Next, as shown in Fig. 5B, a base layer 15 is bonded to the C-SOI 10. The bonding can be performed by bonding using a metal or a conductive resin. However, instead of bonding the base layer 15, the first electrodes 2R, 2L may be formed directly on the C-SOI 10, and an electro-optical material may be formed on the surface by epitaxial deposition, spin coating, or the like.

[0090] 5C, dry etching and wet etching are performed on the rear surface of the C-SOI 10, thereby opening a cavity C. The first wiring electrodes 4OR, 4OL are formed in the opened cavity C by sputtering, vapor deposition, epitaxial film formation, or the like.

[0091] 5D, the cavities C in which the first wiring electrodes 4OR, 4OL have been formed are filled with a sacrificial layer 70. The sacrificial layer 70 can be filled by CVD, vapor deposition, sputtering, spin coating, or the like.

[0092] 5E, a sealing film 71 is formed on the surface of the sacrificial layer 70. This film 71 can be formed by sputtering, CVD, vapor deposition, or the like.

[0093] Next, as shown in FIG. 5F, the sacrificial layer 70 is removed. The sacrificial layer 70 can be removed by dry etching, wet etching, or the like. Then, the second electrode 3 is formed on the base layer 15 having the optical waveguide 1 by the same method as that shown in FIG. 3E above. By this method, the optical modulator 100 having the cavity C can be manufactured.

[0094] 6A to 6G are schematic views illustrating another example of a method for manufacturing the optical modulator 100. As shown in Fig. 6A, a support substrate 6 is prepared on which a second electrode 3, a base layer 15 having an optical waveguide 1, and first electrodes 2R and 2L are laminated in this order.

[0095] 6B, a sacrificial layer 70 is deposited on the first electrodes 2R and 2L. The sacrificial layer 70 can be deposited by CVD, vapor deposition, sputtering, spin coating, or the like.

[0096] 6C, through holes 72, 72 reaching the first electrodes 2R, 2L are formed in the sacrificial layer 70. The through holes 72, 72 can be formed by patterning using lithography or the like, followed by dry etching, wet etching, dicing, or the like.

[0097] Next, as shown in FIGS. 6D and 6E, the first wiring electrodes 4OR and 4OL are formed in the through holes 72 and 72 by sputtering, vapor deposition, epitaxial film formation, or the like.

[0098] Next, as shown in Fig. 6F, a sealing film is formed on the first wiring electrodes 4OR, 4OL. This film can be formed by sputtering, CVD, vapor deposition, or the like.

[0099] 6G, the sacrificial layer 70 located inside the first wiring electrodes 4OR, 4OL is removed. The above-described method can be used to remove the sacrificial layer 70. By using this method, the optical modulator 100 having the cavity C can be manufactured.

[0100] [effect] In the optical modulator 100 according to this embodiment, the first electrodes 2R and 2L are disposed on one side of the optical waveguide 1 in the height direction HD of the optical modulator 100. First wiring electrodes 4IR, 4IL, 4OR, and 4OL, which supply electric signals to the first electrodes 2R and 2L or extract electric signals from the first electrodes 2R and 2L, include wiring portions 4aIR, 4aIL, 4aOR, and 4aOL that are disposed so as to be drawn from ends 2aR, 2aL, 2bR, and 2bL of the first electrodes 2R and 2L as viewed along the height direction HD, and are disposed on the opposite side of the first electrodes 2R and 2L from the optical waveguide 1 in the height direction HD. On the other hand, the second electrode 3, which applies an electric field to the optical waveguide 1 together with the first electrodes 2R and 2L, is disposed on the opposite side of the first electrodes 2R and 2L and the first wiring electrodes 4IR, 4IL, 4OR, and 4OL in the height direction HD of the optical modulator 100. Therefore, the wiring electrodes for supplying or extracting an electrical signal to or from the second electrode 3 are naturally spaced apart in the height direction HD of the optical modulator 100 from the wiring portions 4aIR, 4aIL, 4aOR, and 4aOL of the first wiring electrodes 4IR, 4IL, 4OR, and 4OL. This makes it difficult for an electric field to be formed between the wiring electrodes, and it is possible to prevent an extra electric field from being generated in portions other than the optical modulation portion of the optical waveguide 1. Therefore, it is possible to reduce electrical loss while preventing the optical modulator 100 from becoming larger, particularly in the width direction.

[0101] In the optical modulator 100 according to this embodiment, the first electrodes 2R, 2L are provided in a cavity C. The cavity C is disposed on the first electrode 2R, 2L side of the optical waveguide 1 in the height direction HD of the optical modulator 100, and accommodates the first electrodes 2R, 2L. In this case, the cavity C can be used to arrange the first wiring electrodes 4IR, 4IL, 4OR, 4OL relatively freely.

[0102] In this embodiment, the first wiring electrodes 4IR, 4IL, 4OR, and 4OL are arranged on the opposite side of the first electrodes 2R and 2L from the optical waveguide 1 in the height direction HD of the optical modulator 100. Therefore, even if the wiring portions 4aIR, 4aIL, 4aOR, and 4aOL of the first wiring electrodes 4IR, 4IL, 4OR, and 4OL cross the optical waveguide 1 when viewed along the height direction HD of the optical modulator 100, the wiring portions 4aIR, 4aIL, 4aOR, and 4aOL can be arranged at positions away from the optical waveguide 1 in the height direction HD of the optical modulator 100. In this case, no unnecessary electric field is applied to the optical waveguide 1 from the wiring portions 4aIR, 4aIL, 4aOR, and 4aOL of the first wiring electrodes 4IR, 4IL, 4OR, and 4OL, and noise in the generated signal can be reduced. Furthermore, since it is possible to reduce the absorption of light from the optical waveguide 1 to the wiring portions 4aIR, 4aIL, 4aOR, and 4aOL, it is possible to reduce the loss of light passing through the optical waveguide 1 and suppress the output of the laser that supplies the light wave to the optical waveguide 1. As a result, it is possible to reduce the amount of power consumption.

[0103] In this embodiment, the wiring portions 4aIR, 4aIL, 4aOR, and 4aOL of the first wiring electrodes 4IR, 4IL, 4OR, and 4OL are drawn out from the first electrodes 2R and 2L to one side in the width direction WD and arranged in parallel in a plan view of the optical modulator 100. In this case, it is not necessary to route the first wiring electrodes 4IR, 4IL, 4OR, and 4OL widely. This reduces electrical signal loss and saves footprint. Furthermore, by arranging the wiring portions 4aIR, 4aIL, 4aOR, and 4aOL of the first wiring electrodes 4IR, 4IL, 4OR, and 4OL in parallel, it is possible to simplify the electrical connection between the wiring portions 4aIR, 4aIL, 4aOR, and 4aOL and a digital signal processor, a driver, and the like.

[0104] In this embodiment, the first wiring electrodes 4IR, 4IL, 4OR, and 4OL, which are not intended to apply an electric field to the optical waveguide 1, are spaced apart from the optical waveguide 1 in the height direction HD. Therefore, the first wiring electrodes 4IR, 4IL, 4OR, and 4OL have substantially no effect on the optical waveguide 1, and an electric field can be applied uniformly to the branch optical waveguides 12L and 12R by the first electrodes 2L and 2R and the second electrode 3. This reduces the amount of light leaking from the optical waveguide 1 when the voltage is turned on and off, and improves the extinction ratio of the optical modulator 100.

[0105] For example, in the optical modulator 100, the first wiring electrodes 4IR, 4IL, 4OR, and 4OL are formed with internal stress due to film formation, bonding, and the like. If the first wiring electrodes 4IR, 4IL, 4OR, and 4OL cannot withstand the internal stress during use of the optical modulator 100, buckling of the first wiring electrodes 4IR, 4IL, 4OR, and 4OL may occur. If buckling of the first wiring electrodes 4IR, 4IL, 4OR, and 4OL occurs, the first electrodes 2R and 2L buckle along with the first wiring electrodes 4IR, 4IL, 4OR, and 4OL, resulting in deformation of the entire optical modulator 100. In this embodiment, the first wiring electrodes 4IR, 4IL, 4OR, and 4OL are supported by the side walls 61a, 61a, thereby suppressing buckling of the first wiring electrodes 4IR, 4IL, 4OR, and 4OL. As a result, deformation of the optical modulator 100 can be suppressed.

[0106] For example, when viewed along the width direction WD of the optical modulator 100, of the coupling portions 42R, 42L that couple the first electrodes 2R, 2L to the main bodies 41R, 41L of the first wiring electrodes 4IR, 4IL, 4OR, 4OL, if the surfaces 42a continuous with the ends of the first electrodes 2R, 2L in the extension direction are arranged parallel to the height direction HD of the optical modulator 100, this surface 42a forms a right-angled corner with the end of the first electrode 2R, and high-frequency signal loss occurs at this corner. However, in this embodiment, when viewed along the width direction WD of the optical modulator 100, the surface 42a of the coupling portion 42R of the first wiring electrode 4OR is inclined with respect to the height direction HD so that the main bodies 41R, 41L side is away from the first electrodes 2R, 2L in the extension direction relative to the first electrodes 2R, 2L side. Therefore, the surfaces 42a of the connecting portions 42R, 42L of the first wiring electrodes 4OR, 4OL can be made continuous with the first electrodes 2R, 2L at a gentle angle. This reduces the loss of high-frequency signals at the boundaries between the surfaces 42a of the connecting portions 42R, 42L and the first electrodes 2R, 2L. As a result, modulation over a wide band can be achieved.

[0107] In the optical modulator 100 according to this embodiment, when the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL are joined, minute gaps V may exist at the interfaces between the first electrodes 2R, 2L and the connecting portions 42R, 42L. In this case, the gaps V can add capacitance, thereby adjusting the characteristic impedance. Furthermore, because the gaps V have a lower dielectric constant than the electro-optic material, they can reduce the effective refractive index of the electrical signal, thereby reducing electrical signal loss in the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL.

[0108] When the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL are joined, oxygen may be present at the interface between the first electrodes 2R, 2L and the connecting portions 42R, 42L. In this case, oxygen can add capacitance, thereby adjusting the characteristic impedance. Furthermore, when oxygen is bonded to a metal and exists as an oxide, its dielectric constant is lower than that of an electro-optic material. This reduces the effective refractive index of the electrical signal, thereby reducing electrical signal loss in the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL.

[0109] When the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL are bonded together, a eutectic may exist between the first electrodes 2R, 2L and the connecting portions 42R, 42L. In this case, the bonding strength between the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL can be increased. Furthermore, loss of electrical connection between the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL can be reduced.

[0110] When the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL are joined, resin may be present at the interface between the first electrodes 2R, 2L and the connecting portions 42R, 42L. In this case, the resin can add capacitance, thereby adjusting the characteristic impedance. Furthermore, resin has a lower dielectric constant than electro-optical materials. This can reduce the effective refractive index of the electrical signal, thereby reducing electrical signal loss in the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL.

[0111] In this embodiment, the width w2 of the first electrodes 2R, 2L is preferably larger than the width w1 of the optical waveguide 1. In this case, a uniform electric field can be applied to the optical waveguide 1. Therefore, the quality of the generated optical signal is improved.

[0112] The optical modulator 100 according to this embodiment may include a support substrate 6. The support substrate 6 is disposed on the opposite side of the first electrodes 2R and 2L from the optical waveguide 1. The support substrate 6 is preferably formed of a low-dielectric-constant material having a refractive index smaller than that of the optical waveguide 1. This allows the effective refractive index of the high-frequency signal to be adjusted to match the effective refractive index of the light wave. This enables optical modulation over a wider bandwidth. Furthermore, since the effective dielectric constant for the electrical signal can be reduced, loss of the high-frequency signal can be suppressed, enabling optical modulation up to higher frequencies.

[0113] Second Embodiment The configuration of an optical modulator 100A according to the second embodiment will be described with reference to Fig. 7. Fig. 7 is a schematic diagram showing the configuration of the optical modulator 100A according to the second embodiment, and is a cross-sectional view corresponding to Fig. 2A. In other words, Fig. 7 is a cross-sectional view of the optical modulator 100A cut along a plane perpendicular to the longitudinal direction LD at the positions of the straight portions 122R, 122L of the branch optical waveguides 12R, 12L. The optical modulator 100A differs from the optical modulator 100 according to the first embodiment in the configuration of the coupling portions 42R, 42L of the first wiring electrodes 4OR, 4OL.

[0114] 7, in a cross section perpendicular to the extension direction (longitudinal direction LD) of the first electrodes 2R, 2L, the connecting portions 42R, 42L of the first wiring electrodes 4OR, 4OL are inclined with respect to the height direction HD of the optical modulator 100A. The connecting portions 42R, 42L are inclined with respect to the height direction HD so as to move inward in the width direction WD as they approach the main bodies 41R, 41L. The connecting portions 42R, 42L are provided along the side walls 61a, 61a that define the cavity C. The surfaces of the side walls 61a, 61a are also inclined like the connecting portions 42R, 42L.

[0115] In the optical modulator 100A according to this embodiment, the connecting portions 42R, 42L are inclined with respect to the height direction HD when viewed in a cross section perpendicular to the longitudinal direction LD. This allows the first wiring electrodes 4OR, 4OL to be joined to the first electrodes 2R, 2L at a gentle angle θ. This reduces high-frequency signal loss at the joints between the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL, and enables modulation over a wide band.

[0116] Third Embodiment The configuration of an optical modulator 100B according to the third embodiment will be described with reference to FIGS. 8 and 9. FIG. 8 is a cross-sectional view corresponding to FIG. 2A. In other words, FIG. 8 is a cross-sectional view of the optical modulator 100B cut along a plane perpendicular to the longitudinal direction LD at the position of the straight portions 122R, 122L of the branch optical waveguides 12R, 12L (the optical modulation portion of the optical waveguide 1). FIG. 9 is a cross-sectional view corresponding to FIG. 2E. In other words, FIG. 9 is a cross-sectional view of the optical modulator 100B cut along a plane perpendicular to the width direction WD, showing the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL as viewed along the width direction WD. The optical modulator 100B differs from the optical modulator 100 according to the first embodiment in the configuration of the first wiring electrodes 4OR, 4OL.

[0117] As shown in FIGS. 8 and 9, the first wiring electrodes 4OR, 4OL are not present in the cross section of the optical waveguide 1 at the position of the optical modulation section. The first wiring electrodes 4OR, 4OL are connected only to the ends of the first electrodes 2R, 2L in the extension direction. As in the first embodiment, the connecting portion 42R of the first wiring electrode 4OR includes a surface 42a that is continuous with the end of the first electrode 2R in the extension direction (longitudinal direction LD). In addition, in this embodiment, when viewed along the width direction WD, the surface of the connecting portion 42R of the first wiring electrode 4OR opposite to the surface 42a is also inclined with respect to the height direction HD, similar to the surface 42a. Therefore, as in the third embodiment, high-frequency signal loss at the boundary between the surfaces 42a of the connecting portions 42R, 42L and the first electrodes 2R, 2L can be reduced.

[0118] <Fourth embodiment> The configuration of an optical modulator 100C according to the fourth embodiment will be described with reference to Fig. 10 and Fig. 11. Fig. 10 is a plan view of the optical modulator 100C according to the fourth embodiment. Fig. 11 is a cross-sectional view showing the configuration of the optical modulator 100C according to the fourth embodiment. The optical modulator 100C differs from the optical modulator 100 according to the first embodiment in the configuration of the first wiring electrodes 4OR, 4OL.

[0119] As shown in FIGS. 10 and 11, the first electrodes 2R, 2L are provided in the regions of the straight portions 122R, 122L of the branched optical waveguides 12R, 12L. The first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL are disposed within the cavity C. At least a portion of the first wiring electrodes 4OR, 4OL is free-standing within the cavity C. More specifically, the connecting portions 42R, 42L of the first wiring electrodes 4OR, 4OL are free-standing within the cavity C. Specifically, the connecting portions 42R, 42L are disposed at positions away from the sidewalls 61a, 61a that define the cavity C and are not in contact with the sidewalls 61a, 61a. On the other hand, the main portions 41R, 41L of the first wiring electrodes 4OR, 4OL are provided along the bottom wall 61b that defines the cavity C.

[0120] In the optical modulator 100C according to this embodiment, the connecting portions 42R, 42L of the first wiring electrodes 4OR, 4OL are arranged independently within the cavity C. The connecting portions 42R, 42L are not in contact with the side walls 61a, 61a of the cavity C. Therefore, even if the surfaces of the side walls 61a, 61a are roughened by processing, for example, this does not affect the first wiring electrodes 4OR, 4OL. In other words, the first wiring electrodes 4OR, 4OL will not peel off from the side walls 61a, 61a, and no loss of electrical signals will occur due to surface roughness.

[0121] Fifth Embodiment The configuration of an optical modulator 100D according to the fifth embodiment will be described with reference to Fig. 12. Fig. 12 is a cross-sectional view showing the configuration of the optical modulator 100D according to the fifth embodiment. The optical modulator 100D differs from the optical modulator 100C according to the fourth embodiment in the configuration of the first wiring electrodes 4OR, 4OL.

[0122] 12, the main bodies 41R, 41L of the first wiring electrodes 4OR, 4OL are disposed outside the cavity C. The connecting portions 42R, 42L of the first wiring electrodes 4OR, 4OL penetrate the bottom wall 61b that defines the cavity C and are connected to the main bodies 41R, 41L. Portions of the connecting portions 42R, 42L are freestanding within the cavity C. Therefore, the optical modulator 100D according to the fifth embodiment has the same effects as the optical modulator 100C according to the fourth embodiment.

[0123] Sixth Embodiment The configuration of an optical modulator 100E according to the sixth embodiment will be described with reference to FIGS. 13 and 14. FIG. 13 is a plan view of the optical modulator 100E according to the sixth embodiment. FIG. 14 is a cross-sectional view taken along line XIV-XIV in FIG. 13. In other words, FIG. 14 shows a cross section of a first wiring electrode 4OL extending from a first electrode 2L in the width direction WD, cut along a plane perpendicular to the longitudinal direction LD, and a cross section of the optical modulator 100E cut along a plane perpendicular to the longitudinal direction LD at the positions of the straight portions 122R and 122L of the branched optical waveguides 12R and 12L. The optical modulator 100E differs from the optical modulator 100 according to the first embodiment in that it includes through-electrodes 8IR, 8IL, 8OR, and 8OL.

[0124] As shown in FIGS. 13 and 14, the optical modulator 100E includes through electrodes 8IR, 8IL, 8OR, and 8OL. The through electrodes 8IR, 8IL, 8OR, and 8OL are connected to the ends of the wiring portions 4aIR, 4aIL, 4aOR, and 4aOL of the first wiring electrodes 4IR, 4IL, 4OR, and 4OL. More specifically, the through electrodes 8IR, 8IL, 8OR, and 8OL are connected to the ends of the wiring portions 4aIR, 4aIL, 4aOR, and 4aOL formed by the main portions 41R and 41L of the first wiring electrodes 4OR and 4OL. That is, the through electrodes 8IR, 8IL, 8OR, and 8OL are electrically connected to the first electrodes 2R and 2L via the first wiring electrodes 4OR and 4OL. The through electrodes 8IR, 8IL, 8OR, and 8OL extend from the first electrodes 2R and 2L to the second electrode 3. In this embodiment, the through electrodes 8IR, 8IL, 8OR, and 8OL extend along the height direction HD. In this case, electrical signals from the first electrodes 2R and 2L are extracted to the second electrode 3 side via the through electrodes 8IR, 8IL, 8OR, and 8OL, or electrical signals are supplied to the first electrodes 2R and 2L via the through electrodes 8IR, 8IL, 8OR, and 8OL. In this embodiment, the through electrodes 8IR, 8IL, 8OR, and 8OL penetrate the base layer 15 in which the optical waveguide 1 is formed.

[0125] According to the optical modulator 100E of this embodiment, the electrode pads for the first electrodes 2R, 2L and the electrode pad for the second electrode 3 can be arranged on the same plane, simplifying the electrical wiring. Furthermore, since the electrical wiring for the first electrodes 2R, 2L and the second electrode 3 can be arranged close to each other, loss of electrical signals can be reduced.

[0126] Seventh Embodiment The configuration of an optical modulator 100F according to the seventh embodiment will be described with reference to Fig. 15. Fig. 15 is a cross-sectional view showing the configuration of the optical modulator 100F according to the seventh embodiment, and is a cross-sectional view corresponding to Fig. 14. The optical modulator 100F differs from the optical modulator 100E according to the sixth embodiment in the configuration of the through electrodes 8IR, 8IL, 8OR, and 8OL.

[0127] 15, the through electrodes 8OR, 8OL are provided along the side walls 61a that define the cavity C. The through electrodes 8OR, 8OL are inclined with respect to the height direction HD of the optical modulator 100F. More specifically, surfaces 811 of the through electrodes 8OR, 8OL that contact the side walls 61a are inclined with respect to the height direction HD so as to move inward in the width direction WD as they approach the bottom wall 61b. The surfaces of the side walls 61a are also inclined in the same manner as the through electrodes 8OR, 8OL.

[0128] In the optical modulator 100F according to this embodiment, the through electrodes 8IR, 8IL, 8OR, and 8OL are inclined with respect to the height direction HD. This allows the surfaces 811 of the through electrodes 8IR, 8IL, 8OR, and 8OL to be gently joined to the first electrodes 2R and 2L. This reduces the loss of high-frequency signals at the joints between the through electrodes 8IR, 8IL, 8OR, and 8OL and the first wiring electrodes 4IR, 4IL, 4OR, and 4OL, and enables modulation over a wide band.

[0129] Eighth Embodiment The configuration of an optical modulator 100G according to the eighth embodiment will be described with reference to Fig. 16. Fig. 16 is a cross-sectional view showing the configuration of the optical modulator 100G according to the eighth embodiment. The optical modulator 100G differs from the optical modulator 100 according to the first embodiment in the configurations of the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL.

[0130] As shown in FIG. 16, the thickness t2 of the first electrodes 2R, 2L is greater than the thickness t4 of the first wiring electrodes 4OR, 4OL. The thickness t2 of the first electrodes 2R, 2L is the maximum length of the first electrodes 2R, 2L in the height direction HD. The thickness t4 of the first wiring electrodes 4OR, 4OL is the maximum thickness among the thickness t41 of the main bodies 41R, 41L and the thickness t42 of the connecting portions 42R, 42L. The thickness t41 of the main bodies 41R, 41L is based on the surface of the bottom wall 61b of the recess 61 in which the main bodies 41R, 41L are provided, and is the maximum dimension from this surface in a direction perpendicular to this surface. The thickness t42 of the connecting portions 42R, 42L is based on the surfaces of the side walls 61a, 61a of the recess 61 in which the connecting portions 42R, 42L are provided, and is the maximum dimension from this surface in a direction perpendicular to this surface.

[0131] In the optical modulator 100G according to this embodiment, the thickness t2 of the first electrodes 2R, 2L is made larger than the thickness t4 of the first wiring electrodes 4IR, 4IL, 4OR, 4OL, which reduces the electrical resistance of the first electrodes 2R, 2L in the portions (straight portions 122R, 122L) where optical modulation is performed in the optical modulator 100G, thereby reducing the loss of electrical signals.

[0132] Ninth Embodiment The configuration of an optical modulator 100H according to the ninth embodiment will be described with reference to Fig. 17. Fig. 17 is a cross-sectional view showing the configuration of the optical modulator 100H according to the ninth embodiment. The optical modulator 100H differs from the optical modulator 100 according to the first embodiment in that it includes a low dielectric constant layer 9.

[0133] 17, the optical modulator 100H includes a low-dielectric layer 9 between the optical waveguide 1 and the second electrode 3. The low-dielectric layer 9 has a refractive index smaller than that of the optical waveguide 1. In this embodiment, the low-dielectric layer 9 is provided so as to cover the optical waveguide 1 and the base layer 15.

[0134] In the optical modulator 100H according to this embodiment, a low-dielectric layer 9 is provided between the optical waveguide 1 and the second electrode 3. This makes it difficult for light passing through the optical waveguide 1 to be absorbed by the second electrode 3, thereby suppressing optical loss. Furthermore, by providing the low-dielectric layer 9, the effective refractive index of the high-frequency signal can be adjusted to match the effective refractive index of the light wave. This allows optical modulation up to higher frequencies. Furthermore, by providing the low-dielectric layer 9, the effective dielectric constant for the electrical signal can be lowered. This allows suppressing high-frequency signal loss, allowing optical modulation up to higher frequencies.

[0135] 18 and 19 show modified examples of an optical modulator 100H according to the ninth embodiment. The optical modulator 100H shown in FIG. 18 includes a low-dielectric layer 9A between the optical waveguide 1 and the first electrodes 2R and 2L. The optical modulator 100H shown in FIG. 19 includes a low-dielectric layer 9 between the optical waveguide 1 and the second electrode 3, and further includes a low-dielectric layer 9A between the optical waveguide 1 and the first electrodes 2R and 2L. In this embodiment, the low-dielectric layer 9A is provided between the base layer 15 and the first electrodes 2R and 2L. The low-dielectric layer 9A reduces the absorption of light passing through the optical waveguide 1 by the first electrodes 2R and 2L. Similar to the low-dielectric layer 9, the effective refractive index of high-frequency signals can be adjusted, thereby reducing the effective dielectric constant for electrical signals.

[0136] Tenth Embodiment The configuration of an optical modulator 100I according to the tenth embodiment will be described with reference to Fig. 20. Fig. 20 is a cross-sectional view showing the configuration of the optical modulator 100I according to the tenth embodiment. The optical modulator 100I differs from the optical modulator 100H according to the ninth embodiment in the arrangement of the cavity C relative to the optical waveguide 1.

[0137] As shown in FIG. 20 , the optical waveguide 1, the first electrodes 2R and 2L, and the second electrode 3 are disposed on a support substrate 6. Specifically, the second electrode 3 is provided on the support substrate 6 side with respect to the optical waveguide 1, with a low-dielectric layer 9 interposed therebetween. A cavity C is defined by a low-dielectric layer 9A disposed on the opposite side of the support substrate 6 with respect to the optical waveguide 1. The first electrodes 2R and 2L and the first wiring electrodes 4IR, 4IL, 4OR, and 4OL are disposed within this cavity C. In this case, the cavity C can be disposed on the upper side with respect to the support substrate 6. If the cavity C is disposed on the upper side, the cavity C can be formed using a cap that is placed on the optical modulator 100I.

[0138] Eleventh Embodiment The configuration of an optical modulator 100J according to the eleventh embodiment will be described with reference to Fig. 21. Fig. 21 is a schematic diagram showing the configuration of the optical modulator 100J according to the eleventh embodiment, and is a cross-sectional view corresponding to Fig. 2A. In other words, Fig. 21 is a cross-sectional view of the optical modulator 100J cut along a plane perpendicular to the longitudinal direction LD at the positions of the straight portions 122R, 122L of the branch optical waveguides 12R, 12L. The optical modulator 100J differs from the optical modulator 100 according to the first embodiment in the arrangement of the first electrodes 2R, 2L and the second electrode 3 relative to the optical waveguide 1.

[0139] As shown in FIG. 21 , the first electrodes 2R and 2L are arranged on one side of the optical waveguide 1 in the height direction HD. The first electrodes 2R and 2L are arranged, for example, directly above the branch optical waveguides 12R and 12L, respectively. On the other hand, the second electrode 3 is arranged on the other side of the optical waveguide 1 in the height direction HD. The second electrode 3 is arranged, for example, on one of both surfaces of the base layer 15, opposite the ridge-type optical waveguide 1. In addition, the second electrode 3 is arranged on a support substrate 6.

[0140] Similar to the first embodiment, the first wiring electrodes 4OR, 4OL are electrically connected to the first electrodes 2R, 2L. The first wiring electrodes 4OR, 4OL are disposed on the opposite side of the optical waveguide 1 from the first electrodes 2R, 2L in the height direction HD. More specifically, the main bodies 41R, 41L of the first wiring electrodes 4OR, 4OL are disposed spaced apart from the first electrodes 2R, 2L in the height direction HD. The main bodies 41R, 41L are disposed offset outward from the first electrodes 2R, 2L in the width direction WD. The connecting portions 42R, 42L of the first wiring electrodes 4OR, 4OL connect the main bodies 41R, 41L to the first electrodes 2R, 2L. The connecting portions 42R, 42L connect, for example, outer ends of the first electrodes 2R, 2L in the width direction WD to inner ends of the main bodies 41R, 41L in the width direction WD.

[0141] In this embodiment, a low-dielectric layer 9A is provided in the height direction HD from the optical waveguide 1 to the first electrodes 2R and 2L. The low-dielectric layer 9A is also provided in the height direction HD from the optical waveguide 1 to the first wiring electrodes 4OR and 4OL. A thickness t9A4 of the low-dielectric layer 9A at the position of the first wiring electrodes 4OR and 4OL is greater than a thickness t9A2 of the low-dielectric layer 9A at the position of the first electrodes 2R and 2L. The thickness t9A4 is the length in the height direction HD of the low-dielectric layer 9A from the optical waveguide 1 to the first wiring electrodes 4OR and 4OL, and is, for example, the shortest distance in the height direction HD from the optical waveguide 1 to the main bodies 41R and 41L of the first wiring electrodes 4OR and 4OL. The thickness t9A2 is the length in the height direction HD of the low-dielectric layer 9A from the optical waveguide 1 to the first electrodes 2R and 2L, and is, for example, the shortest distance in the height direction HD from the optical waveguide 1 to the first electrodes 2R and 2L. The thickness t9A4 of the low-dielectric layer 9A at the positions of the first wiring electrodes 4OR and 4OL is preferably at least twice the thickness t9A2 of the low-dielectric layer 9A at the positions of the first electrodes 2R and 2L.

[0142] Fig. 22 shows a modified example of the optical modulator 100J according to the eleventh embodiment. The optical modulator 100J shown in Fig. 22 includes a low-dielectric layer 9A between the optical waveguide 1 and the first electrodes 2R and 2L. The optical modulator 100J further includes a low-dielectric layer 9 between the optical waveguide 1 and the second electrode 3.

[0143] [Method for manufacturing the optical modulator 100J] An example of a method for manufacturing the optical modulator 100J will be described below. Figures 23A to 23F are schematic views illustrating an example of a method for manufacturing the optical modulator 100J. As shown in Figure 23A, a second electrode 3 is formed on the surface of a support substrate 6.

[0144] 23B, the electro-optic material substrate 16 is bonded to the support substrate 6 having the second electrode 3 formed on its surface. The bonding method described above can be used as the bonding method. However, instead of bonding the electro-optic material substrate 16, a film of the electro-optic material may be formed by epitaxial film formation, spin coating, or the like.

[0145] 23C, the electro-optic material substrate 16 is patterned by lithography or the like, and then subjected to dry etching, wet etching, dicing, etc. In this way, a base layer 15 having an optical waveguide 1 is formed.

[0146] 23D, a low dielectric constant layer 9A is laminated on the base layer 15 having the optical waveguide 1. The low dielectric constant layer 9A can be formed by sputtering, vapor deposition, epitaxial film formation, or the like.

[0147] Next, as shown in FIG. 23E, the low dielectric constant layer 9A is patterned by lithography or the like, and then recesses 73 are formed by dry etching, wet etching, dicing or the like.

[0148] 23F, the recess 73 is subjected to sputtering, vapor deposition, epitaxial film formation, etc., thereby forming the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL in the recess 73. By this method, the optical modulator 100J can be manufactured.

[0149] 24A to 24F are schematic views illustrating another example of a method for manufacturing an optical modulator 100J. As shown in Fig. 24A, a support substrate 6 having a second electrode 3 formed on its surface is prepared. In addition, a substrate 74 other than the support substrate 6 having the second electrode 3 formed on its surface is prepared.

[0150] Next, as shown in Fig. 24B, an electro-optic material substrate 16 is bonded to the support substrate 6 in the same manner as in Fig. 23B. Alternatively, instead of bonding the electro-optic material substrate 16, a film of an electro-optic material may be formed. Meanwhile, the substrate 74 is patterned by lithography or the like, and then dry etching, wet etching, dicing, or the like is performed. As a result, convex portions 75 are formed on the substrate 74.

[0151] Next, as shown in Fig. 24C, a base layer 15 having an optical waveguide 1 is formed in the same manner as in Fig. 23C. Meanwhile, the substrate 74 on which the convex portion 75 is formed is subjected to sputtering, vapor deposition, epitaxial film formation, etc., thereby forming the first electrodes 2R, 2L and the first wiring electrodes 4OR, 4OL around the convex portion 75.

[0152] 24D, low dielectric constant layer 9A is laminated on convex portion 75 of substrate 74. Low dielectric constant layer 9A can be formed by the methods described above.

[0153] 24E, the substrate 74 on which the low dielectric constant layer 9A is formed is bonded to the support substrate 6 on which the optical waveguide 1 is formed. As a bonding method, the above-mentioned bonding method can be used.

[0154] 24F, the substrate 74 is removed. The substrate 74 can be removed by dry etching, wet etching, etc. By this method, the optical modulator 100J can be manufactured.

[0155] 25A to 25E are schematic views illustrating another example of a method for manufacturing an optical modulator 100J. As shown in Fig. 25A, a C-SOI 10 having a cavity C is prepared.

[0156] 25B, the C-SOI 10 is then subjected to dry etching, wet etching, or the like to remove the active layer. A base layer 15 having an optical waveguide 1 is also prepared. A low-dielectric layer 9A is laminated on the surface of the base layer 15 facing the optical waveguide 1, and a second electrode 3 is formed on the surface opposite the low-dielectric layer 9A.

[0157] Next, as shown in FIG. 25C, a base layer 15 is bonded to the C-SOI 10.

[0158] Next, as shown in FIG. 25D, the rear surface of the C-SOI 10 is subjected to dry etching and wet etching to open a cavity C.

[0159] 25E, the first wiring electrodes 4OR, 4OL are formed in the opened cavity C by sputtering, vapor deposition, epitaxial film formation, etc. By this method, the optical modulator 100J can be manufactured.

[0160] <Twelfth embodiment> The configuration of an optical modulator 100K according to the twelfth embodiment will be described with reference to Fig. 26. Fig. 26 is a schematic diagram showing the configuration of the optical modulator 100K according to the twelfth embodiment, and is a cross-sectional view corresponding to Fig. 2A. In other words, Fig. 26 is a cross-sectional view of the optical modulator 100K cut along a plane perpendicular to the longitudinal direction LD at the positions of the straight portions 122R, 122L of the branch optical waveguides 12R, 12L. The optical modulator 100K differs from the optical modulator 100J according to the eleventh embodiment in that it includes second wiring electrodes 5I, 5O.

[0161] 26, the optical modulator 100K includes second wiring electrodes 5I and 5O. The second wiring electrodes 5I and 5O are electrically connected to the second electrode 3. The second wiring electrodes 5I and 5O are arranged on the opposite side of the second electrode 3 from the optical waveguide 1 in the height direction HD. The second wiring electrodes 5I and 5O include main body portions 51I and 51O and connecting portions 52I and 52O.

[0162] The main bodies 51I, 51O are disposed apart from the second electrode 3 in the height direction HD. The main bodies 51I, 51O are disposed offset outward from the second electrode 3 in the width direction WD. The connecting portions 52I, 52O connect the main bodies 51I, 51O to the second electrode 3. The connecting portions 52I, 52O connect, for example, the outer end of the second electrode 3 in the width direction WD to the inner end of the main bodies 51I, 51O in the width direction WD. The connecting portions 52I, 52O may be parallel to the height direction HD in a cross-sectional view of the optical modulator 100, or may be inclined with respect to the height direction HD.

[0163] The main body portions 51I, 51O and the connecting portions 52I, 52O may have, for example, a substantially rectangular cross section, although the cross-sectional shapes of the main body portions 51I, 51O and the connecting portions 52I, 52O are not limited to this.

[0164] In this embodiment, the low-dielectric layer 9 is provided in the height direction HD from the optical waveguide 1 to the second electrode 3. The low-dielectric layer 9 is also provided from the optical waveguide 1 to the second wiring electrodes 5I and 5O. In this case, the thickness t95 of the low-dielectric layer 9 at the position of the second wiring electrodes 5I and 5O is greater than the thickness t93 of the low-dielectric layer 9 at the position of the second electrode 3. The thickness t95 is the length in the height direction HD of the low-dielectric layer 9 from the optical waveguide 1 to the second wiring electrodes 5I and 5O, and is, for example, the shortest distance in the height direction HD from the base layer 15 to the main bodies 51I and 51O of the second wiring electrodes 5I and 5O. The thickness t93 is the length in the height direction HD of the low-dielectric layer 9A from the optical waveguide 1 to the second electrode 3, and is, for example, the shortest distance in the height direction HD from the base layer 15 to the second electrode 3. The thickness t95 of the low-dielectric layer 9 at the position of the second wiring electrodes 5I and 5O is preferably at least twice the thickness t93 of the low-dielectric layer 9 at the position of the second electrode 3.

[0165] In the optical modulator 100K according to this embodiment, the second wiring electrodes 5I and 5O are disposed on the opposite side of the second electrode 3 from the optical waveguide 1. This allows the second wiring electrodes 5I and 5O to be naturally spaced apart in the height direction HD from the optical waveguide 1 and the first wiring electrodes 4IR, 4IL, 4OR, and 4OL. This makes it difficult for an electric field to be formed between the first wiring electrodes 4IR, 4IL, 4OR, and 4OL and the second wiring electrodes 5I and 5O, which do not have the purpose of applying an electric field to the optical waveguide 1, and makes it possible to prevent the electric field due to the first wiring electrodes 4IR, 4IL, 4OR, and 4OL and the second wiring electrodes 5I and 5O from being applied to the optical waveguide 1. This further reduces electrical loss in the optical modulator 100K.

[0166] <Thirteenth embodiment> The configuration of an optical modulator 100L according to the thirteenth embodiment will be described with reference to Fig. 27. Fig. 27 is a cross-sectional view showing the configuration of the optical modulator 100L according to the thirteenth embodiment. The optical modulator 100L differs from the optical modulator 100K according to the twelfth embodiment in that it includes through electrodes 8AI and 8AO.

[0167] As shown in FIG. 27, the optical modulator 100L includes through electrodes 8AI and 8AO. The through electrodes 8AI and 8AO are connected to the ends of the second wiring electrodes 5I and 5O. More specifically, the through electrodes 8AI and 8AO are connected to the main bodies 51I and 51O of the second wiring electrodes 5I and 5O. That is, the through electrodes 8AI and 8AO are electrically connected to the second electrode 3 via the second wiring electrodes 5I and 5O. The through electrodes 8AI and 8AO extend from the second electrode 3 side to the first electrodes 2R and 2L side. In this embodiment, the through electrodes 8AI and 8AO extend along the height direction HD. In this case, an electrical signal from the second electrode 3 is extracted to the first electrodes 2R and 2L side via the through electrodes 8AI and 8AO, or an electrical signal is supplied to the second electrode 3 via the through electrodes 8AI and 8AO. In this embodiment, the through electrodes 8AI and 8AO penetrate the base layer 15 in which the optical waveguide 1 is formed, and the low dielectric layers 9 and 9A.

[0168] According to the optical modulator 100L of this embodiment, the electrode pads for the first electrodes 2R, 2L and the electrode pad for the second electrode 3 can be arranged on the same plane, simplifying the electrical wiring. Furthermore, since the electrical wiring for the first electrodes 2R, 2L and the second electrode 3 can be arranged close to each other, loss of electrical signals can be suppressed.

[0169] <Fourteenth embodiment> The configuration of an optical modulator 100M according to the fourteenth embodiment will be described with reference to Fig. 28. Fig. 28 is a cross-sectional view showing the configuration of the optical modulator 100M according to the fourteenth embodiment. The optical modulator 100M differs from the optical modulator 100L according to the thirteenth embodiment in the configuration of the through electrodes 8AI, 8AO.

[0170] 28, the through electrodes 8AI, 8AO are inclined with respect to the height direction HD of the optical modulator 100M. The through electrodes 8AI, 8AO are inclined with respect to the height direction HD so that the second wiring electrodes 5I, 5O are positioned further inward in the width direction WD. The through electrodes 8AI, 8AO penetrate the low dielectric layers 9, 9A.

[0171] In the optical modulator 100M according to this embodiment, the through electrodes 8AI, 8AO are inclined with respect to the height direction HD. This allows the through electrodes 8AI, 8AO to be gently joined to the second electrode 3. This reduces the loss of high-frequency signals at the joints between the through electrodes 8AI, 8AO and the second electrode 3, enabling modulation over a wide band.

[0172] <Fifteenth embodiment> The configuration of an optical modulator 100N according to the fifteenth embodiment will be described with reference to Figures 29 to 32. These figures are schematic diagrams showing the configuration of the optical modulator 100N according to the fifteenth embodiment, and are cross-sectional views corresponding to Figure 2A. In other words, these figures are cross-sectional views of the optical modulator 100N cut along a plane perpendicular to the longitudinal direction LD at the positions of the straight portions 122R, 122L of the branch optical waveguides 12R, 12L.

[0173] In each of the above embodiments, an example has been described in which the optical waveguide 1, the first electrodes 2R and 2L, and the second electrode 3 are arranged substantially along the height direction HD. In the optical modulator 100N according to this embodiment, the arrangement of the optical waveguide 1, the first electrodes 2R and 2L, and the second electrode 3 is different from that of the other embodiments.

[0174] In the optical modulator 100N shown in FIGS. 29 to 32, similarly to the other embodiments, the first electrodes 2R and 2L are arranged on one side of the optical waveguide 1 in the height direction HD, and the second electrode 3 is arranged on the other side of the optical waveguide 1 in the height direction HD. That is, in the height direction HD, the centers C2 of the first electrodes 2R and 2L are arranged on one side of the center C1 of the optical waveguide 1, and the center C3 of the second electrode 3 is arranged on the other side. In addition, the optical waveguide 1 is arranged between the first electrodes 2R and 2L and the second electrode 3 in the width direction WD. For example, the first electrodes 2R and 2L are arranged outside the optical waveguide 1 in the width direction WD, and the second electrode 3 is arranged inside the optical waveguide 1 in the width direction WD. Even in such a case, when the optical modulator 100N is divided into one side and the other side in the height direction HD from the underside of the optical modulator 100N, the first electrodes 2R, 2L are arranged on one side and the second electrode 3 is arranged on the other side, just like in other embodiments.

[0175] Although not shown, the optical modulator 100N shown in FIGS. 29 to 32 can have wiring electrodes configured in the same manner as any of the other embodiments.

[0176] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0177] The configuration of the optical modulator according to the present disclosure is summarized below.

[0178] <1> An optical modulator, an optical waveguide having an electro-optic effect; a first electrode disposed on one side of the optical waveguide in a height direction of the optical modulator and extending along a part of the optical waveguide; a second electrode that is disposed on the other side of the optical waveguide in the height direction, that forms a potential difference between itself and the first electrode, and that applies an electric field to the optical waveguide together with the first electrode; a first wiring electrode disposed on the opposite side of the optical waveguide with respect to the first electrode in the height direction and electrically connected to the first electrode; The optical modulator, wherein the first wiring electrode includes a wiring portion that is arranged so as to be drawn out from an end of the first electrode in an extending direction when viewed along the height direction.

[0179] <2> <1> The optical modulator according to claim 1, An optical modulator, wherein the first electrode is disposed within a cavity provided within the optical modulator.

[0180] <3> <2> The optical modulator according to claim 1, an optical modulator, wherein the first wiring electrode is disposed within the cavity and supported by a sidewall that defines the cavity;

[0181] <4> <1> ~ <3> 10. The optical modulator according to claim 9, the first wiring electrode includes a main body portion that is disposed apart from the first electrode in the height direction and a portion of which constitutes the wiring portion, and a connecting portion that connects the main body portion and the first electrode, The optical modulator, wherein the connecting portion is inclined with respect to the height direction when viewed in a cross section perpendicular to the extension direction of the first electrode.

[0182] <5> <1> ~ <4> 10. The optical modulator according to claim 9, the first wiring electrode includes a main body portion that is disposed apart from the first electrode in the height direction and a portion of which constitutes the wiring portion, and a connecting portion that connects the main body portion and the first electrode, the connecting portion includes a surface that is continuous with an end portion of the first electrode in an extension direction, An optical modulator, wherein the surface is inclined with respect to the height direction when viewed along the width direction of the optical modulator so that the main body side is spaced apart from the first electrode in the extension direction relative to the first electrode side.

[0183] <6> <2> The optical modulator according to claim 1, An optical modulator, wherein at least a portion of the first wiring electrode is disposed freestanding within the cavity.

[0184] <7> <1> ~ <6> The optical modulator according to any one of the above items, further comprising: an optical modulator comprising a through electrode connected to the wiring portion of the first wiring electrode and extending from the first electrode side to the second electrode side;

[0185] <8> <7> The optical modulator according to claim 1, The optical modulator, wherein the through electrode is inclined with respect to the height direction.

[0186] <9> <1> ~ <8> 10. The optical modulator according to claim 9, An optical modulator, wherein the thickness of the first electrode is greater than the thickness of the first wiring electrode.

[0187] <10> <1> ~ <9> 10. The optical modulator according to claim 9, an optical modulator in which the first electrode and the first wiring electrode are joined together, and a gap exists at the interface between the first electrode and the first wiring electrode;

[0188] <11> <1> ~ <9> 10. The optical modulator according to claim 9, an optical modulator in which the first electrode and the first wiring electrode are joined together, and oxygen exists at the interface between the first electrode and the first wiring electrode;

[0189] <12> <1> ~ <9> 10. The optical modulator according to claim 9, an optical modulator in which the first electrode and the first wiring electrode are joined together, and a eutectic exists between the first electrode and the first wiring electrode;

[0190] <13> <1> ~ <9> 10. The optical modulator according to claim 9, an optical modulator in which the first electrode and the first wiring electrode are bonded together, and a resin is present at the interface between the first electrode and the first wiring electrode;

[0191] <14> <1> ~ <13> 10. The optical modulator according to claim 9, An optical modulator, wherein the length of the first electrode in the width direction of the optical modulator is greater than the length of the optical waveguide.

[0192] <15> <1> ~ <14> The optical modulator according to any one of the above items, further comprising: an optical modulator comprising a low dielectric layer provided at least one between the optical waveguide and the first electrode and between the optical waveguide and the second electrode, the low dielectric layer having a refractive index smaller than that of the optical waveguide.

[0193] <16> <15> The optical modulator according to claim 1, the low dielectric layer is provided in the height direction from the optical waveguide to the first electrode and from the optical waveguide to the first wiring electrode, An optical modulator, wherein the length in the height direction of the low dielectric layer from the optical waveguide to the first wiring electrode is greater than the length in the height direction of the low dielectric layer from the optical waveguide to the first electrode.

[0194] <17> <1> ~ <16> The optical modulator according to any one of the above items, further comprising: An optical modulator comprising: a support substrate disposed on the opposite side of the first electrode from the optical waveguide, the support substrate being made of a low dielectric constant material having a refractive index smaller than that of the optical waveguide.

[0195] <18> <1> ~ <17> The optical modulator according to any one of the above items, further comprising: an optical modulator comprising a second wiring electrode disposed on the opposite side of the second electrode from the optical waveguide in the height direction, and electrically connected to the second electrode;

[0196] <19> <18> The optical modulator according to claim 1, further comprising: an optical modulator comprising a through electrode connected to the second wiring electrode and extending from the second electrode side to the first electrode side;

[0197] <20> <18> or <19> The optical modulator according to claim 1, An optical modulator, wherein the thickness of the second electrode is greater than the thickness of the second wiring electrode.

[0198] <21> <18> ~ <20> The optical modulator according to any one of the above items, further comprising: a first low dielectric layer provided in the height direction from the optical waveguide to the first electrode and from the optical waveguide to the first wiring electrode, the first low dielectric layer having a refractive index smaller than that of the optical waveguide; a second low dielectric constant layer provided in the height direction from the optical waveguide to the second electrode and from the optical waveguide to the second wiring electrode, the second low dielectric constant layer having a refractive index smaller than that of the optical waveguide; a length in the height direction of the first low dielectric layer from the optical waveguide to the first wiring electrode is greater than a length in the height direction of the first low dielectric layer from the optical waveguide to the first electrode, an optical modulator, wherein the length in the height direction of the second low dielectric layer from the optical waveguide to the second wiring electrode is greater than the length in the height direction of the second low dielectric layer from the optical waveguide to the second electrode. [Explanation of symbols]

[0199] 100, 100A, 100B, 100C, 100D, 100E, 100F, 100G, 100H, 100I, 100J, 100K, 100L, 100M, 100N: Optical modulator 1: Optical waveguide 11: Ingress optical waveguide path 12R, 12L: Branched optical waveguide path 13: Outgoing optical waveguide path 121R, 121L: the middle part of the entrance side 122R, 122L: Straight section 123R, 123L: middle part of the outlet side 15:ベースlayer 16: Electro-optical material substrate 2R,2L: First electrode 2aR,2bR,2aL,2bL: Endpieces 3: Second electrode 4IR, 4IL, 4OR, 4OL: First wiring electrode 4aIR, 4aIL, 4aOR, 4aOL: Wiring section 41R, 41L: Main body part 42R, 42L: Connecting parts 42a: Surface 5I,5O: Second wiring electrode 51I, 51O: Body section 52I, 52O: Connecting parts V: Gap C:キャビティ 6:Support substrate 61: concave part 61a: Sidewall 61b: Bottom wall 8IR, 8IL, 8OR, 8OL, 8AI, 8AO: Through-electrode 9,9A: Low induced conductivity layer HD: high direction WD: web direction LD: Long arm direction

Claims

1. An optical modulator, an optical waveguide having an electro-optic effect; a first electrode disposed on one side of the optical waveguide in a height direction of the optical modulator and extending along a part of the optical waveguide; a second electrode that is disposed on the other side of the optical waveguide in the height direction, that forms a potential difference between itself and the first electrode, and that applies an electric field to the optical waveguide together with the first electrode; a first wiring electrode disposed on the opposite side of the optical waveguide with respect to the first electrode in the height direction and electrically connected to the first electrode; the first wiring electrode includes a wiring portion arranged to be drawn out from an end of the first electrode in an extending direction when viewed along the height direction, and further includes a main body portion arranged apart from the first electrode in the height direction and a part of which constitutes the wiring portion, and a connecting portion connecting the main body portion and the first electrode, An optical modulator, wherein, when viewed in a cross section perpendicular to the extension direction of the first electrode, the width of the connecting portion is greater than the thickness of the first electrode, and both sides of the connecting portion are open.

2. 2. The optical modulator according to claim 1, further comprising: a through electrode connected to the wiring portion of the first wiring electrode and extending from the first electrode side to the second electrode side; An optical modulator, wherein one side of the wiring portion is open when viewed in a cross section perpendicular to the extending direction of the first electrode.

3. 3. The optical modulator according to claim 2, further comprising: a support substrate disposed on an opposite side of the first electrode from the optical waveguide, the support substrate having a sidewall defining a cavity; a portion of the through electrode inclined relative to the height direction and in contact with the side wall;

4. 2. The optical modulator according to claim 1, a low dielectric layer provided between the optical waveguide and the second electrode and having a refractive index smaller than that of the optical waveguide; an optical modulator, wherein both sides of the low dielectric layer are open when viewed in a cross section perpendicular to the extending direction of the first electrode;

5. 2. The optical modulator according to claim 1, further comprising: a low dielectric layer provided between the optical waveguide and the first electrode, the low dielectric layer having a refractive index smaller than that of the optical waveguide; an optical modulator, wherein both sides of the low dielectric layer are open when viewed in a cross section perpendicular to the extending direction of the first electrode;

6. 2. The optical modulator according to claim 1, low-dielectric-constant layers each having a refractive index smaller than that of the optical waveguide, the low-dielectric-constant layers being provided between the optical waveguide and the first electrode and between the optical waveguide and the second electrode, an optical modulator, wherein both sides of each of the low dielectric layers are open when viewed in a cross section perpendicular to the extending direction of the first electrode;

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