Optical devices and optical communication devices

Abstract

To provide an optical device and the like capable of improving modulation efficiency and coupling efficiency while suppressing crosstalk.SOLUTION: The optical device includes: an electro-optical crystal layer; a first optical waveguide formed on the electro-optical crystal layer; and an electrode for applying electrical signals to the first optical waveguide. The optical device also has a second optical waveguide in an amorphous state that is formed on the electro-optical crystal layer and is connected to the first optical waveguide.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an optical device and an optical communication apparatus. [Background technology]

[0002] For example, an optical device such as an optical modulator has a signal electrode arranged on a surface optical waveguide. When a voltage is applied to the signal electrode, an electric field perpendicular to the surface of the optical modulator is generated in the optical waveguide. This electric field changes the refractive index of the optical waveguide, changing the phase of the light propagating through the optical waveguide and enabling light modulation. That is, the optical waveguide of the optical modulator constitutes, for example, a Mach-Zehnder interferometer, and the phase difference of the light between multiple parallel optical waveguides can output, for example, an XY polarization multiplexed IQ signal.

[0003] Fig. 7 is a schematic plan view showing an example of the configuration of optical modulator 100, and Fig. 8 is a schematic cross-sectional view showing an example of the cross-sectional portion taken along the line E-E shown in Fig. 7. Optical modulator 100 shown in Fig. 7 has an input section 101, a branching section 102, two optical waveguides 103, an electrode section 104, a multiplexing section 105, and an output section 106. The length direction of optical modulator 100 is defined as the Y direction, the width direction as the Z direction, and the thickness direction as the X direction.

[0004] The input unit 101 inputs light from an optical fiber. The branching unit 102 branches the light from the input unit 101. The two optical waveguides 103 are arranged in parallel and modulate each of the lights branched by the branching unit 102. The electrode unit 104 is an electrode that applies an electric signal to the two optical waveguides 103. The electrode unit 104 has a pair of ground electrodes 104B and a signal electrode 104A that is arranged so as to be sandwiched between the pair of ground electrodes 104B. The signal electrode 104A is an electrode that applies an electric signal to the optical waveguide 103. The ground electrode 104B is an electrode that grounds the electric signal applied to the optical waveguide 103. Each optical waveguide 103 is a Mach-Zehnder (MZ) interaction unit that modulates light by changing the optical refractive index in response to the electric signal from the signal electrode 104A, thereby changing the phase of the light. Then, each optical waveguide 103 outputs the modulated light to the multiplexing section 105. The multiplexing section 105 multiplexes the modulated light from each optical waveguide 103. The output section 106 outputs the modulated light from the multiplexing section 105 to an optical fiber.

[0005] 8 includes a substrate 111, an intermediate layer 112 stacked on the substrate 111, and a thin-film LN layer 113 made of an LN (LiNbO3) material stacked on the intermediate layer 112. The optical modulator 100 further includes two optical waveguides 103 formed of the thin-film LN layer 113, a buffer layer 114 formed on the thin-film LN layer 113, and an electrode portion 104 formed on the buffer layer 114.

[0006] The substrate 111 is made of a material such as Si or LN. The intermediate layer 112 is made of a material with a lower optical refractive index than LN, such as a layer of SiO. The thin-film LN layer 113 is a thin-film substrate that has strong optical confinement and is advantageous for miniaturization. The crystal axis of the thin-film LN layer 113 is in the Z direction.

[0007] The optical waveguide 103 is formed of a thin-film LN layer 113, and is therefore excellent in terms of, for example, insertion loss and transmission characteristics. Because the thin-film LN layer 113 is an X-cut substrate, its structural symmetry enables chirp-free operation and makes it suitable for long-distance transmission. Each optical waveguide 103 is disposed between a ground electrode 104B and a signal electrode 104A. The signal electrode 104A is an electrode made of a metal material such as gold or copper. The ground electrode 104B is an electrode made of a metal material such as gold or copper. The buffer layer 114 is, for example, a layer of SiO2, and is provided to prevent light propagating through the optical waveguide 103 from being absorbed by the electrode portion 104.

[0008] The crystal direction in which the electro-optic effect of the thin film LN layer 113 is most pronounced is the width direction (Z direction) perpendicular to the signal propagation direction (Y direction). The optical refractive index of each optical waveguide 103 changes depending on the electric field in the electric field direction from the signal electrode 104A to the ground electrode 104B.

[0009] Fig. 9 is an explanatory diagram showing an example of the TE mode and the TM mode. In the optical waveguide 103, two modes exist depending on the direction of the main component of the electric field of the optical field. As shown in Fig. 9, there is the TE mode, in which the main component of the electric field is in the planar direction, and the TM mode, in which the main component of the electric field is in the vertical direction. Note that the arrows in Fig. 9 indicate the direction of the main component of the electric field, and the range enclosed by the dotted lines in Fig. 9 is the light distribution range.

[0010] 9A, in the optical modulator 100 with the X-cut thin film LN layer 113, the Z direction is positioned in the planar direction of the optical waveguide 103, so the signal light modulated by the electric field applied from the electrode part 104 is in the TE mode, the main component of which is the electric field in the planar direction. Therefore, it can be said that the TM mode, in which the main component of the electric field is in the vertical direction, is a mode unnecessary for the operation of the optical modulator 100.

[0011] Furthermore, the modulation efficiency of the optical modulator 100 is greatly affected by the length of the interaction section of each optical waveguide 103 to which the electric field is applied, i.e., the optical length, and therefore, in order to achieve miniaturization while maintaining modulation efficiency, a structure in which the interaction section is lengthened and folded back is required.

[0012] Fig. 10 is a schematic plan view showing an example of the configuration of an optical modulator 100A with a folded structure, and Fig. 11 is a schematic cross-sectional view showing an example of the cross-sectional portion taken along line FF and line GG shown in Fig. 10. Note that the same components as those of the optical modulator 100 shown in Figs. 7 and 8 are denoted by the same reference numerals, and redundant descriptions of the configuration and operation will be omitted. The optical waveguide of the optical modulator 100A shown in Fig. 10 has an outgoing optical waveguide 103A (103), a folded optical waveguide 108, and a returning optical waveguide 103B (103).

[0013] The outgoing optical waveguide 103A and the returning optical waveguide 103B are optical waveguides formed in the thin film LN layer 113 along the Y direction, in which the propagation direction (propagation angle) is 0 degrees. The FF line cross section shown in FIG. 11A corresponds to the outgoing optical waveguide 103A. The outgoing optical waveguide 103A and the returning optical waveguide 103B have the same core thickness. The cores of the outgoing optical waveguide 103A and the returning optical waveguide 103B have refractive indices of 2.21 in the X and Y directions and 2.14 in the Z direction, for example.

[0014] The folded optical waveguide 108 is an optical waveguide formed in the thin-film LN layer 113 along the Z direction, whose propagation direction (propagation angle) is other than 0 degrees, for example, 90 degrees. The cross section taken along line GG shown in FIG. 11B corresponds to the folded optical waveguide 108. The core thickness of the folded optical waveguide 108 is the same as the core thicknesses of the outgoing optical waveguide 103A and the returning optical waveguide 103B. The core of the folded optical waveguide 108 has, for example, a refractive index of 2.21 in the X and Y directions and a refractive index of 2.14 in the Z direction. In other words, the refractive indexes of the cores of the folded optical waveguide 108, the outgoing optical waveguide 103A, and the returning optical waveguide 103B are the same for each orientation.

[0015] 12A is an explanatory diagram showing an example of the dependence of the effective refractive index on the propagation angle when the core thickness of the optical waveguide 103 is 1 μm. When the core thickness of the optical waveguide 103 is 1 μm, in the X-cut thin-film LN layer 113, the refractive index in the planar direction changes depending on the propagation direction of the optical waveguide 103, so the effective refractive index of the TE mode also changes. In addition, the refractive index in the vertical direction is constant regardless of the propagation direction of the optical waveguide 103, so the effective refractive index of the TM mode hardly changes even when the propagation direction of the optical waveguide 103 changes. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] U.S. Patent No. 07970241 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-156454 Summary of the Invention [Problem to be solved by the invention]

[0017] In the optical modulator 100A, when the propagation angle of the optical waveguide 103 is 0 degrees in the Y direction and 90 degrees in the Z direction, as shown in Fig. 12A, the effective refractive index of the TE mode increases as the propagation angle of the optical waveguide 103 approaches 90 degrees. Therefore, in the optical modulator 100A, when the core of the optical waveguide 103 is thickened, a propagation angle occurs at which the effective refractive index of the TE mode and the effective refractive index of the TM mode match. As a result, the TE mode of the signal light is converted into the TM mode of unwanted light, and the unwanted TM mode causes crosstalk with respect to the TE mode.

[0018] Therefore, if the core thickness of the optical waveguide 103 is reduced, crosstalk to the TM mode can be suppressed. Fig. 12B is an explanatory diagram showing an example of the dependence of the propagation angle on the effective refractive index when the core thickness of the optical waveguide 103 is set to 0.4 µm. When the core thickness of the optical waveguide 103 is set to, for example, 0.4 µm, no propagation angle occurs at which the effective refractive index of the TE mode and the effective refractive index of the TM mode match, so crosstalk to the TE mode can be suppressed.

[0019] However, in the optical modulator 100A, if the core thickness of the optical waveguide 103 is reduced to suppress crosstalk, the confinement of light in the thin-film LN layer 113 is weakened. FIG. 13 is an explanatory diagram showing an example of how the modulation efficiency changes depending on the core thickness of the optical waveguide 103. In the optical modulator 100A, if the core thickness of the optical waveguide 103 is reduced, the confinement of light in the thin-film LN layer 113 is weakened, resulting in a deterioration in modulation efficiency. FIG. 14 is an explanatory diagram showing an example of how the coupling efficiency changes depending on the core thickness of the optical waveguide 103. In the optical modulator 100A, if the core thickness of the optical waveguide 103 is reduced, the confinement of light in the thin-film LN layer 113 is weakened, resulting in a reduction in the optical mode field due to the reduced core thickness, resulting in a deterioration in the coupling efficiency with the optical fiber. Therefore, in the optical modulator 100A, there is a trade-off between suppressing crosstalk for the TE mode and improving modulation efficiency and coupling efficiency.

[0020] The disclosed technology has been made in view of the above points, and aims to provide an optical device or the like that improves modulation efficiency and coupling efficiency while suppressing crosstalk. [Means for solving the problem]

[0021] In one embodiment, the optical device disclosed herein comprises an electro-optic crystal layer, a first optical waveguide formed in the electro-optic crystal layer, and an electrode for applying an electric signal to the first optical waveguide. The optical device further comprises a second optical waveguide in an amorphous state formed in the electro-optic crystal layer and connected to the first optical waveguide. [Effects of the Invention]

[0022] According to one aspect of the optical device etc. disclosed in the present application, crosstalk is suppressed while modulation efficiency and coupling efficiency are improved. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a block diagram illustrating an example of the configuration of an optical communication device according to a first embodiment. [Figure 2] FIG. 2 is a schematic plan view showing an example of the configuration of the optical modulator according to the first embodiment. [Figure 3] FIG. 3 is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line AA and line BB shown in FIG. [Figure 4] FIG. 4 is a schematic plan view showing an example of the configuration of the optical modulator according to the second embodiment. [Figure 5] FIG. 5 is a schematic plan view showing an example of the configuration of the optical modulator according to the third embodiment. [Figure 6] FIG. 6 is a schematic plan view showing an example of the configuration of an optical modulator according to a fourth embodiment. [Figure 7] FIG. 7 is a schematic plan view showing an example of the configuration of an optical modulator. [Figure 8] FIG. 8 is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line EE shown in FIG. [Figure 9] FIG. 9 is an explanatory diagram showing an example of the TE mode and the TM mode. [Figure 10] FIG. 10 is a schematic plan view showing an example of the configuration of an optical modulator with a folded structure. [Figure 11] FIG. 11 is a schematic cross-sectional view showing an example of the cross-sectional portion taken along line FF and line GG shown in FIG. [Figure 12A] FIG. 12A is an explanatory diagram showing an example of the dependence of the effective refractive index on the propagation angle when the core thickness of the optical waveguide is 1 μm. [Figure 12B] FIG. 12B is an explanatory diagram showing an example of the dependence of the effective refractive index on the propagation angle when the core thickness of the optical waveguide is set to 0.4 μm. [Figure 13] FIG. 13 is an explanatory diagram showing an example of the change in modulation efficiency depending on the thickness of the core of the optical waveguide. [Figure 14] FIG. 14 is an explanatory diagram showing an example of the change in coupling efficiency depending on the thickness of the core of the optical waveguide. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the optical device and the like disclosed in the present application will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments. [Example]

[0025] FIG. 1 is a block diagram showing an example of the configuration of an optical communication device 1 according to a first embodiment. The optical communication device 1 shown in FIG. 1 is connected to an optical fiber 2A(2) on the output side and an optical fiber 2B(2) on the input side. The optical communication device 1 includes a DSP (Digital Signal Processor) 3, a light source 4, an optical modulator 5, and an optical receiver 6. The DSP 3 is an electrical component that performs digital signal processing. For example, the DSP 3 performs processing such as encoding of transmission data, generates an electrical signal including the transmission data, and outputs the generated electrical signal to the optical modulator 5. The DSP 3 also obtains an electrical signal including reception data from the optical receiver 6 and performs processing such as decoding of the obtained electrical signal to obtain the reception data.

[0026] The light source 4 is, for example, a laser diode or the like, which generates light of a predetermined wavelength and supplies it to the optical modulator 5 and the optical receiver 6 through the optical fiber 4A. The optical modulator 5 is an optical device that modulates the light supplied from the light source 4 with an electrical signal output from the DSP 3 and outputs the obtained optical transmission signal to the optical fiber 2A. The optical modulator 5 is, for example, an optical device such as an LN (Lithium Niobate) optical modulator that includes an LN optical waveguide and a signal electrode with a coplanar waveguide (CPW) structure.

[0027] The optical receiver 6 receives an optical signal from the optical fiber 2B and demodulates the received optical signal using light supplied from the light source 4. The optical receiver 6 then converts the demodulated received optical signal into an electrical signal and outputs the converted electrical signal to the DSP 3.

[0028] Fig. 2 is a schematic plan view showing an example of the configuration of the optical modulator 5 of Example 1. The optical modulator 5 shown in Fig. 2 has an input section 11, a branching section 12, two first optical waveguides 13A (13) on the outgoing path side, an electrode section 14, a multiplexing section 15, a second optical waveguide 16, a first optical waveguide 13B (13) on the returning path side, and an output section 17. The length direction (propagation direction) of the optical modulator 5 is defined as the Y direction, the width direction (planar direction) as the Z direction, and the thickness direction as the X direction.

[0029] The input unit 11 inputs light from an optical fiber 4A. The light from the optical fiber 4A is light from the light source 4. The branching unit 12 branches the light from the input unit 11. The two first optical waveguides 13A on the outgoing path side are arranged in parallel and are optical waveguides of a Mach-Zehnder (MZ) interaction part that modulate each light branched by the branching unit 12. The two first optical waveguides 13A on the outgoing path side are, for example, ridge-type waveguides having a core and slabs on both sides of the core that are thinner than the core. The two first optical waveguides 13A on the outgoing path side are optical waveguides formed in the thin-film LN layer 33 along a direction substantially perpendicular to the Z direction of the crystal axis of the thin-film LN layer 33 described later, for example, along the Y direction.

[0030] The electrode unit 14 is an electrode that applies an electric signal to the two first optical waveguides 13A on the outgoing path. The two first optical waveguides 13A on the outgoing path change their optical refractive index in response to the electric signal from the electrode unit 14 to modulate light, and output each modulated light to the multiplexing unit 15. The electrode unit 14 has a signal electrode 14A and a pair of ground electrodes 14B. The signal electrode 14A is an electrode that applies an electric signal to the first optical waveguide 13A on the outgoing path. The ground electrode 14B is an electrode that grounds the electric signal applied to the first optical waveguide 13A on the outgoing path. The two first optical waveguides 13A on the outgoing path change their optical refractive index in response to the electric signal from the signal electrode 14A to change the phase of the light, modulating the light, and outputting the modulated light to the multiplexing unit 15. The multiplexing unit 15 multiplexes each modulated light modulated by the two first optical waveguides 13A on the outgoing path. The optical modulator 5 has a modulation section 20 formed by the two first optical waveguides 13A on the outgoing path side and the electrode section 14.

[0031] The second optical waveguide 16 is a folded optical waveguide that passes the modulated light from the multiplexing section 15. The second optical waveguide 16 is an optical waveguide that includes at least one of a straight waveguide formed in the thin-film LN layer 33 along a direction other than the Y direction that is substantially perpendicular to the Z direction, and a curved waveguide in which the propagation direction changes smoothly.

[0032] The first optical waveguide 13B on the return path is an optical waveguide that passes the modulated light from the second optical waveguide 16. The first optical waveguide 13B on the return path is an optical waveguide formed in the thin-film LN layer 33 along the Y direction that is approximately perpendicular to the Z direction of the crystal axis of the thin-film LN layer 33. The output unit 17 is connected to the optical fiber 2A, and outputs the modulated light from the first optical waveguide 13B on the return path to the optical fiber 2A.

[0033] Fig. 3 is a schematic cross-sectional view showing an example of the cross-sectional portions taken along line AA and line BB shown in Fig. 2. The portion of the first optical waveguide 13 shown in Fig. 3(A) has a substrate 31, an intermediate layer 32 laminated on the substrate 31, a thin-film LN layer 33 laminated on the intermediate layer 32, two first optical waveguides 13 formed with the thin-film LN layer 33, and a buffer layer 34 on the thin-film LN layer 33. Furthermore, the portion of the second optical waveguide 16 shown in Fig. 3(B) has the substrate 31, the intermediate layer 32 laminated on the substrate 31, the thin-film LN layer 33 laminated on the intermediate layer 32, the second optical waveguide 16 formed with the thin-film LN layer 33, and a buffer layer 34 on the thin-film LN layer 33.

[0034] The substrate 31 is made of a material such as SiO2 (silicon dioxide), TiO2 (titanium dioxide), Si, or LN. The intermediate layer 32 is made of a material with a lower optical refractive index than LN, such as SiO2 or TiO2. The intermediate layer 32 has a certain thickness to ensure a sufficient optical distance between the thin-film LN layer 33 and the substrate 31 so that optical signals propagating through the first optical waveguide 13 and the second optical waveguide 16 formed in the thin-film LN layer 33 are not radiated toward the substrate 31. The thickness of the intermediate layer 32 is, for example, approximately 2 μm to 6 μm. The thin-film LN layer 33 is a substrate using a thin film of LN crystal, which is an electro-optic crystal, and has the first optical waveguide 13 formed thereon with a convex shape that protrudes upward at a predetermined location. The LN material provides strong light confinement, which is advantageous for miniaturization. Furthermore, the LN material is an anisotropic material whose refractive index changes when an electric field is applied, for example, with a Pockels coefficient of approximately 30 pm / V.

[0035] The thin-film LN layer 33 is an X-cut substrate. The thin-film LN layer 33 is a substrate made of electro-optic crystal, for example, LN (LiNbO3) material. The two first optical waveguides 13A on the outgoing path side are formed of the thin-film LN layer 33, and since the material is LN, it is excellent in terms of, for example, insertion loss and transmission characteristics. The optical modulator 5 is capable of chirp-free operation due to its structural symmetry, and is suitable for long-distance transmission.

[0036] The buffer layer 34 is, for example, a layer of SiO2, and is provided to prevent light propagating through the first optical waveguide 13 from being absorbed by the electrode portion 14. A thin-film LN layer 33 having a thickness of 0.5 to 3 μm is sandwiched between the intermediate layer 32 and the buffer layer 34. The width of the convex protrusions formed on the thin-film LN layer 33 to become the first optical waveguide 13 is, for example, about 1 to 8 μm. The thin-film LN layer 33 and the first optical waveguide 13 are covered with the buffer layer 34.

[0037] The signal electrode 14A is made of a metal material such as gold or copper and has a width of 2 to 10 μm and a thickness of 1 to 20 μm. The ground electrode 14B is made of a metal material such as gold or copper and has a thickness of 1 μm or more. When a drive voltage corresponding to an electrical signal output from the DSP 3 is transmitted by the signal electrode 14A, an electric field is generated in a direction from the signal electrode 14A to the ground electrode 14B, and this electric field is applied to the first optical waveguide 13. As a result, the refractive index of the first optical waveguide 13 changes in response to the application of the electric field to the first optical waveguide 13, making it possible to modulate the light propagating through the first optical waveguide 13.

[0038] The two first optical waveguides 13A on the outgoing path are linear optical waveguides formed in the chip of the optical modulator 5 along the Y direction at approximately 0 degrees, assuming that the Z direction of the crystal axis of the thin-film LN layer 33 is 90 degrees and the Y direction is 0 degrees. Note that "approximately 0 degrees" includes not only 0 degrees but also a range of manufacturing error of the first optical waveguide 13 when manufacturing an optical waveguide aiming for 0 degrees, for example, within ±20 degrees. The cores of the two first optical waveguides 13A on the outgoing path are formed in the thin-film LN layer 33 along the Y direction, which is approximately perpendicular to the Z direction of the crystal axis of the thin-film LN layer 33, and are therefore non-amorphous. The cores of the first optical waveguide 13B on the return path, the input section 11, and the output section 17 are also non-amorphous, similar to the cores of the two first optical waveguides 13A on the outgoing path. The cores of the outgoing first optical waveguide 13A and the returning first optical waveguide 13B are in a non-amorphous state, and therefore, for example, the refractive index in the X and Y directions is approximately 2.21, and the refractive index in the Z direction is approximately 2.14.

[0039] The core of the second optical waveguide 16 is an optical waveguide formed in the thin-film LN layer 33 in a direction not orthogonal to the Z direction, i.e., a direction other than the Y direction at approximately 0 degrees, and is an amorphous core. The direction not orthogonal to the Z direction refers, for example, to a direction greater than the actual angle from the Y direction and less than 90 degrees from the Z direction. Because the cores of the second optical waveguide 16, the branching section 12, and the multiplexing section 15 are amorphous, the refractive indices in the X, Y, and Z directions are, for example, approximately 2.175. Because the core of the second optical waveguide 16 is amorphous, there is no propagation angle at which the effective refractive index of the TE mode intersects with the effective refractive index of the TM mode. As a result, unwanted crosstalk of the TM mode with respect to the TE mode can be suppressed. The cores of the branching section 12 and the multiplexing section 15 are also amorphous, like the core of the second optical waveguide 16. The second optical waveguide 16, the branching section 12, and the multiplexing section 15 are a second optical waveguide that is routed and connected to the first optical waveguide 13.

[0040] The cores of the outgoing first optical waveguide 13A, the returning first optical waveguide 13B, the input section 11, and the output section 17 are in a non-amorphous state, and therefore, for example, the refractive index in the X and Y directions is about 2.21, and the refractive index in the Z direction is about 2.14. In contrast, the cores of the second optical waveguide 16, the branching section 12, and the multiplexing section 15 are in an amorphous state, and therefore, for example, the refractive index in the X, Y, and Z directions is about 2.175.

[0041] In the process of forming the amorphous state and the non-amorphous state, for example, the core to be made non-amorphous is masked and argon (Ar + ) ions are implanted. + By implanting ions, the LN crystal orientation of the core of the thin-film LN layer 33 is disrupted, creating an amorphous state that eliminates the anisotropy of the optical refractive index. The masked core remains in a non-amorphous state. As a result, by creating an amorphous state, the angle at which the effective refractive index of the TE mode of the signal light and the effective refractive index of the TM mode of the unwanted light match disappears, thereby suppressing crosstalk.

[0042] In the optical modulator 5 of the first embodiment, the cores of the first optical waveguide 13A on the outgoing path, the first optical waveguide 13B on the incoming path, the input section 11, and the output section 17 are in a non-amorphous state, and the cores of the second optical waveguide 16, the branching section 12, and the multiplexing section 15 are in an amorphous state. In an amorphous core, there is no propagation angle at which the effective refractive index of the TE mode intersects with the effective refractive index of the TM mode. As a result, unwanted crosstalk of the TM mode relative to the TE mode can be suppressed. Moreover, even if the core thickness is increased, unwanted crosstalk of the TM mode relative to the TE mode can be suppressed, thereby improving modulation efficiency and coupling efficiency. In other words, modulation efficiency and coupling efficiency can be improved while suppressing crosstalk.

[0043] The second optical waveguide 16 is a straight or curved waveguide formed in the thin-film LN layer 33 along a direction other than the direction in which light propagates, that is, the Y-axis direction of the crystal axis of the X-cut thin-film LN layer 33. As a result, the core of the second optical waveguide 16 is in an amorphous state, which can suppress unnecessary crosstalk of the TM mode with respect to the TE mode.

[0044] For ease of explanation, an X-cut thin-film LN layer 33 is illustrated, but the optical modulator 5 may also use a Y-cut thin-film LN layer. The optical modulator 5 includes a Y-cut thin-film LN layer 33, a first optical waveguide 13 formed in the thin-film LN layer 33 along a direction substantially perpendicular to the Z direction of the crystal axis of the thin-film LN layer, and a second optical waveguide 16 routed to connect to the first optical waveguide 13. The second optical waveguide 16 is a straight or curved waveguide formed in the thin-film LN layer 33 along a direction other than the direction in which light propagates, i.e., the X-axis direction of the crystal axis of the thin-film LN layer 33. The cores of the outgoing first optical waveguide 13A, the incoming first optical waveguide 13B, the input section 11, and the output section 17 are in a non-amorphous state, and the cores of the second optical waveguide 16, the branching section 12, and the multiplexing section 15 are in an amorphous state. In an amorphous core, there is no propagation angle at which the effective refractive index of the TE mode intersects with the effective refractive index of the TM mode. As a result, unwanted crosstalk of the TM mode to the TE mode can be suppressed. Moreover, even if the core thickness is increased, unwanted crosstalk of the TM mode to the TE mode can be suppressed, thereby improving modulation efficiency and coupling efficiency.

[0045] Although the thin film LN layer 33 is exemplified, the material of the electro-optic crystal is not limited to LN and may be any anisotropic electro-optic crystal. For example, perovskite oxides such as PZT (lead zirconate titanate), PLZT (lanthanum-doped lead zirconate titanate), and BaTiO3 (barium titanate) may also be used, and the material can be changed as appropriate. Note that the Pockels coefficient of PZT is approximately 110 pm / V, the Pockels coefficient of PLZT is approximately 700 pm / V, and the Pockels coefficient of BaTiO3 is approximately 1850 pm / V. Therefore, the Pockels coefficient of the electro-optic crystal used in the present invention is within the range of 10 to 2000 pm / V.

[0046] Furthermore, the first optical waveguide 13 and the second optical waveguide 16 are exemplified as ridge-type waveguides, but are not limited to ridge-type waveguides and may also be, for example, channel-type waveguides.

[0047] Although the second optical waveguide 16, the branching unit 12, and the multiplexing unit 15 have been exemplified as optical waveguides for routing connected to the first optical waveguide 13, the present invention is not limited to these and can be modified as appropriate. Also, the cores of the second optical waveguide 16 other than the first optical waveguide 13 to which the electrical signal from the electrode unit 14 is applied are exemplified as being in an amorphous state. However, for example, among the cores of the second optical waveguide 16, the core whose light propagation direction is parallel to the first optical waveguide 13 may be in a non-amorphous state, and this can be modified as appropriate.

[0048] The optical modulator 5 in Example 1 has been exemplified as applying an electrical signal from the electrode portion 14 to the two first optical waveguides 13A on the outgoing path side. However, in addition to the two first optical waveguides 13A on the outgoing path side, an interaction portion may also be disposed in the two first optical waveguides 13C on the return path side, and this embodiment will be described below as Example 2. [Example]

[0049] FIG. 4 is a schematic plan view showing an example of the configuration of an optical modulator 5A according to a second embodiment. The same components as those in the optical modulator 5A according to the second embodiment are denoted by the same reference numerals, and redundant descriptions of the configuration and operation will be omitted. The optical modulator 5A shown in FIG. 4 includes an input section 11, a branching section 12, two first optical waveguides 13A on the outgoing path, and two second optical waveguides 16B on the return path. Furthermore, the optical modulator 5A includes two first optical waveguides 13C on the return path, a first electrode section 141 (14), a second electrode section 142 (14), a multiplexing section 15A, and an output section 17.

[0050] The input unit 11 inputs light from the optical fiber 4A. The branching unit 12 branches the light from the input unit 11. The two first optical waveguides 13A on the outgoing path are arranged in parallel and are optical waveguides in the interaction part of the MZ that modulate each light branched by the branching unit 12. The two second optical waveguides 16B are folded optical waveguides that connect to the two first optical waveguides 13A on the outgoing path. The two first optical waveguides 13C on the return path are arranged in parallel and are optical waveguides in the interaction part of the MZ that connect to the two second optical waveguides 16B.

[0051] The first optical waveguide 13A on one outgoing path side is connected to the second optical waveguide 16B on one side, and the second optical waveguide 16B is connected to the first optical waveguide 13C on one returning path side. The first optical waveguide 13A on the other outgoing path side is connected to the second optical waveguide 16B on the other side, and the second optical waveguide 16B on the other returning path side is connected to the first optical waveguide 13C on the other returning path side.

[0052] The first electrode unit 141 has a first electrode 141A arranged between the two first optical waveguides 13A on the outward path side, and a second electrode 141B and a third electrode 141C arranged outside the two first optical waveguides 13C on the return path side. The second electrode unit 142 has a fourth electrode 142A arranged between the two first optical waveguides 13C on the return path side, and a fifth electrode 142B and a sixth electrode 142C arranged outside the two first optical waveguides 13A on the outward path side. The second electrode unit 142 has a higher potential than the first electrode unit 141.

[0053] The first optical waveguide 13A on one outgoing path applies an electric field in the -Z direction from the sixth electrode 142C of the second electrode portion 142 to the first electrode 141A of the first electrode portion 141. The first optical waveguide 14C on one returning path applies an electric field in the -Z direction from the fourth electrode 142A of the second electrode portion 142 to the third electrode 141C of the first electrode portion 141. As a result, since the direction of the electric field applied to the first optical waveguide 13A on one outgoing path and the first optical waveguide 13C on one returning path is the same as the -Z direction, a phase change occurs in the same direction, and modulation efficiency is improved.

[0054] The first optical waveguide 13A on the other outgoing path applies an electric field in the +Z direction from the fifth electrode 142B of the second electrode portion 142 to the first electrode 141A of the first electrode portion 141. The first optical waveguide 13C on the other returning path applies an electric field in the +Z direction from the fourth electrode 142A of the second electrode portion 142 to the second electrode 141B of the first electrode portion 141. As a result, since the direction of the electric field applied to the first optical waveguide 13A on the other outgoing path and the first optical waveguide 13C on the other returning path is the same as the +Z direction, a phase change occurs in the same direction, and modulation efficiency is improved.

[0055] The multiplexing section 15A multiplexes the modulated light passing through the two first optical waveguides 13C on the return path side. The output section 17 outputs the modulated light multiplexed by the multiplexing section 15A to the optical fiber 4A.

[0056] The cores of the two first optical waveguides 13A on the outgoing path, the two first optical waveguides 13C on the return path, the input section 11, and the output section 17 are made non-amorphous. Because the cores of the first optical waveguide 13A on the outgoing path, the first optical waveguide 13C on the return path, the input section 11, and the output section 17 are made non-amorphous, the refractive indexes in the X and Y directions are, for example, approximately 2.21, and the refractive index in the Z direction is, for example, approximately 2.14. The cores of the second optical waveguide 16B, the branching section 12, and the multiplexing section 15A are made amorphous. Because the cores of the second optical waveguide 16, the branching section 12, and the multiplexing section 15A are made amorphous, the refractive indexes in the X, Y, and Z directions are, for example, approximately 2.175.

[0057] In the process of forming the amorphous state and the non-amorphous state, for example, the core to be made non-amorphous is masked and Ar is introduced from the surface of the thin film LN layer 33. + Ion implantation: Ar + By implanting ions, the LN crystal orientation of the core of the thin-film LN layer 33 is disrupted, creating an amorphous state that eliminates the anisotropy of the optical refractive index. The masked core remains in a non-amorphous state. As a result, by creating an amorphous state, the angle at which the effective refractive index of the TE mode of the signal light and the effective refractive index of the TM mode of the unwanted light match disappears, thereby suppressing crosstalk.

[0058] In the optical modulator 5A of the second embodiment, the cores of the two first optical waveguides 13A on the outgoing path, the two first optical waveguides 13C on the return path, the input section 11, and the output section 17 are in a non-amorphous state, and the cores of the second optical waveguide 16B, the branching section 12, and the multiplexing section 15A are in an amorphous state. In an amorphous core, there is no propagation angle at which the effective refractive index of the TE mode intersects with the effective refractive index of the TM mode. As a result, unwanted crosstalk of the TM mode with respect to the TE mode can be suppressed. Moreover, even if the core thickness is increased, unwanted crosstalk of the TM mode with respect to the TE mode can be suppressed, thereby improving modulation efficiency and coupling efficiency.

[0059] In the optical modulator 5A, an electric field is applied to the two first optical waveguides 13A on the outgoing path before and after the return and the two first optical waveguides 13C on the returning path, thereby improving modulation efficiency and achieving miniaturization.

[0060] In the optical modulator 5 of Example 1, an electrode portion 14 is disposed in the first optical waveguide 13A on the outgoing path side to serve as an interaction portion. However, in addition to the first optical waveguide 13A on the outgoing path side, another electrode portion 14 may be disposed in the first optical waveguide 13C on the return path side to provide another interaction portion, and such an embodiment will be described below as Example 3. [Example]

[0061] 5 is a plan view schematic diagram showing an example of the configuration of an optical modulator 5B of Example 3. Note that the same components as those of the optical modulator 5 of Example 1 are denoted by the same reference numerals, and redundant descriptions of the configuration and operation will be omitted. The optical modulator 5B shown in FIG. 5 has an input section 11, a branching section 12, two first optical waveguides 13A on the outgoing path side, a third electrode section 143, a second optical waveguide 16B, two first optical waveguides 13C on the incoming path side, a fourth electrode section 144, a multiplexing section 15A, and an output section 17.

[0062] The input unit 11 inputs light from the optical fiber 4A. The branching unit 12 branches the light from the input unit 11. The two first optical waveguides 13A on the outgoing path side are arranged in parallel and are first optical waveguides 13 of the MZ interaction unit that modulate each light branched by the branching unit 12. The third electrode unit 143 has a signal electrode 143A that applies a first electrical signal to the two first optical waveguides 13A on the outgoing path side, and a ground electrode 143B that grounds the first electrical signal from the two first optical waveguides 13A on the outgoing path side. The two first optical waveguides 13A on the outgoing path side and the third electrode unit 143 constitute a first modulation unit 20A (20). The first modulation section 20A is, for example, a DC (Direct Current) modulation section that applies a bias voltage as a first electrical signal from the third electrode section 143 to the two first optical waveguides 13A on the outgoing path side.

[0063] The second optical waveguide 16B is arranged in parallel, connected to the two first optical waveguides 13A on the outgoing path, and is a folded optical waveguide through which light modulated by the two first optical waveguides 13A on the outgoing path passes.

[0064] The two first optical waveguides 13C on the return path side are arranged in parallel and are first optical waveguides 13 connected to the two second optical waveguides 16B. The fourth electrode unit 144 has a signal electrode 144A that applies a second electrical signal to the two first optical waveguides 13C on the return path side and a ground electrode 114B that grounds the second electrical signal from the two first optical waveguides 13C on the return path side. The two first optical waveguides 13C on the return path side and the fourth electrode unit 144 constitute a second modulation unit 20B (20). The second modulation unit 20B is, for example, an RF (Radio Frequency) modulation unit in which the fourth electrode unit 144 applies a high-frequency signal as the second electrical signal to the two first optical waveguides 13C on the return path side.

[0065] The multiplexing unit 15A is connected to the two first optical waveguides 13C on the return path side, and multiplexes the modulated light passing through the two first optical waveguides 13C on the return path side. The output unit 17 outputs the modulated light multiplexed by the multiplexing unit 15A to the optical fiber 2A.

[0066] The cores of the two first optical waveguides 13A on the outgoing path, the two first optical waveguides 13C on the return path, the input section 11, and the output section 17 are made non-amorphous. Because the cores of the first optical waveguide 13A on the outgoing path, the first optical waveguide 13C on the return path, the input section 11, and the output section 17 are made non-amorphous, the refractive indexes in the X and Y directions are, for example, approximately 2.21, and the refractive index in the Z direction is, for example, approximately 2.14. The cores of the second optical waveguide 16B, the branching section 12, and the multiplexing section 15A are made amorphous. Because the cores of the second optical waveguide 16, the branching section 12, and the multiplexing section 15A are made amorphous, the refractive indexes in the X, Y, and Z directions are, for example, approximately 2.175.

[0067] In the process of forming the amorphous state and the non-amorphous state, for example, the core to be made non-amorphous is masked and Ar is introduced from the surface of the thin film LN layer 33. + Ion implantation: Ar + By implanting ions, the LN crystal orientation of the core of the thin-film LN layer 33 is disrupted, creating an amorphous state that eliminates the anisotropy of the optical refractive index. The masked core remains in a non-amorphous state. As a result, by creating an amorphous state, the angle at which the effective refractive index of the TE mode of the signal light and the effective refractive index of the TM mode of the unwanted light match disappears, thereby suppressing crosstalk.

[0068] In the optical modulator 5B of the third embodiment, the cores of the two first optical waveguides 13A on the outgoing path, the two first optical waveguides 13C on the return path, the input section 11, and the output section 17 are non-amorphous, while the cores of the second optical waveguide 16B, the branching section 12, and the multiplexing section 15A are amorphous. Because the core of the second optical waveguide 16 is amorphous, there is no propagation angle at which the effective refractive index of the TE mode intersects with the effective refractive index of the TM mode. As a result, even when the first modulation section 20A is located before the return and the second modulation section 20B is located after the return, unwanted crosstalk of the TM mode relative to the TE mode can be suppressed. Furthermore, even when the core thickness is increased, unwanted crosstalk of the TM mode relative to the TE mode can be suppressed, resulting in improved modulation efficiency and coupling efficiency.

[0069] For ease of explanation, the first modulation unit 20A is a DC modulation unit and the second modulation unit 20B is an RF modulation unit, but this is not limited to this. For example, the second modulation unit 20B may be a DC modulation unit, and changes can be made as appropriate. [Example]

[0070] FIG. 6 is a plan view schematic diagram showing an example of the configuration of an optical modulator 5C according to a fourth embodiment. The optical modulator 5C shown in FIG. 6 is an IQ modulator. The optical modulator 5C includes an input section 11, a first branching section 12A, a pair of second branching sections 12B, two first optical waveguides 13A1 and 13A2 on the forward path side of the previous stage, a fifth electrode section 145, and second optical waveguides 16A1 and 16A2 on the backward path side of the previous stage. The optical modulator 5C also includes two first optical waveguides 13C1 and 13C2 on the backward path side of the previous stage, a sixth electrode section 146, a pair of first multiplexing sections 15B, and two second optical waveguides 16B1 on the middle path side. Furthermore, the optical modulator 5C has two first optical waveguides 13D on the outward side of the subsequent stage, a seventh electrode portion 147, a second optical waveguide 16C on the subsequent stage, an optical waveguide 13E on the return side of the subsequent stage, and an output portion 17.

[0071] The input unit 11 receives light from the optical fiber 4A. The first branching unit 12A branches the light from the input unit 11. Each second branching unit 12B outputs the light branched by the first branching unit 12A to two first optical waveguides 13A1 and 13A2 on the outgoing path, which modulate the light.

[0072] The two first optical waveguides 13A1 and 13A2 on the forward path side of each front stage are arranged in parallel and are optical waveguides in the interaction section of the MZ that modulate each light branched at the second branch section 12B. The fifth electrode section 145 has a first signal electrode 145A1 and a second signal electrode 145A2, and a first ground electrode 145C1, a second ground electrode 145C2, and a third ground electrode 145C3. The first signal electrode 145A1 applies a first electrical signal to the two first optical waveguides 13A1 on the forward path side of one front stage. The first ground electrode 145B1 grounds the first electrical signal from one of the two first optical waveguides 13A1 on the forward path side. The second ground electrode 145B2 grounds the first electrical signal from the other of the two first optical waveguides 13A1 on the forward path side of the preceding stage. The first optical waveguide 13A1 on the forward path side of the preceding stage and the fifth electrode unit 145 form the first RF modulation unit 20A1.

[0073] The second signal electrode 145A2 applies a second electrical signal to the two first optical waveguides 13A2 on the forward path side of the other preceding stage. The third ground electrode 145B3 grounds the second electrical signal from the first optical waveguide 13A2 on the forward path side of the other preceding stage, among the two first optical waveguides 13A2 on the forward path side of the other preceding stage. The second ground electrode 145B2 grounds the second electrical signal from one of the two first optical waveguides 13A2 on the forward path side of the other preceding stage, among the two first optical waveguides 13A2 on the forward path side of the other preceding stage. The first optical waveguide 13A2 on the forward path side of the other preceding stage and the fifth electrode unit 145 form a second RF modulation unit 20A2.

[0074] The second optical waveguides 16A in the front stage are arranged in parallel and include two second optical waveguides 16A1 in one front stage and two second optical waveguides 16A2 in the other front stage. The two second optical waveguides 16A1 in one front stage are connected to the two first optical waveguides 13A1 on the outward path side of one of the front stages and are folded optical waveguides through which light modulated by the two first optical waveguides 13A1 on the outward path side of one of the front stages passes. The two second optical waveguides 16A2 in the other front stage are connected to the two first optical waveguides 13A2 on the outward path side of the other front stage and are folded optical waveguides through which light modulated by the two first optical waveguides 13A2 on the outward path side of the other front stage passes.

[0075] The two first optical waveguides 13C1 on the return path side of one of the preceding stages are arranged in parallel and are first optical waveguides that connect to the two second optical waveguides 16A1 on one of the preceding stages. The two first optical waveguides 13C2 on the return path side of the other preceding stage are arranged in parallel and are first optical waveguides that connect to the two second optical waveguides 16A2 on the other preceding stage.

[0076] The sixth electrode unit 146 has a first signal electrode 146A1 and a second signal electrode 146A2, and a first ground electrode 146B1, a second ground electrode 146B2, and a third ground electrode 146B3. The first signal electrode 146A1 of the sixth electrode unit 146 applies a third electrical signal to two first optical waveguides 13C1 on the return path side of one of the preceding stages. The first ground electrode 146B1 of the sixth electrode unit 146 grounds the third electrical signal from one of the two first optical waveguides 13C1 on the return path side of one of the preceding stages. The second ground electrode 146B2 of the sixth electrode unit 146 grounds the third electrical signal from the first optical waveguide 13C1 on the return path side of the other of the two first optical waveguides 13C1 on the return path side of the one preceding stage. The first optical waveguide 13C1 on the return path side of the one preceding stage and the sixth electrode unit 146 form a first DC modulation unit 20B1(20).

[0077] The second signal electrode 146A2 of the sixth electrode unit 146 applies a fourth electrical signal to the two first optical waveguides 13C2 on the return path side of the other preceding stage. The third ground electrode 146B3 of the sixth electrode unit 146 grounds the fourth electrical signal from the first optical waveguide 13C2 on the return path side of the other preceding stage, among the two first optical waveguides 13C2 on the return path side of the other preceding stage. The second ground electrode 146B2 of the sixth electrode unit 146 grounds the fourth electrical signal from the first optical waveguide 13C2 on the return path side of one preceding stage, among the two first optical waveguides 13C2 on the return path side of the other preceding stage. The first optical waveguide 13C2 on the return path side of the other preceding stage and the sixth electrode unit 146 form a second DC modulation unit 20B2 (20).

[0078] One first multiplexing section 15B1 is connected to two first optical waveguides 13C1 on the return path side of one preceding stage and multiplexes modulated light passing through the two first optical waveguides 13C1 on the return path side of one preceding stage. The other first multiplexing section 15B2 is connected to two first optical waveguides 13C2 on the return path side of the other preceding stage and multiplexes modulated light passing through the two first optical waveguides 13C2 on the return path side of the other preceding stage.

[0079] The middle second optical waveguides 16B are arranged in parallel and include one middle second optical waveguide 16B1 and the other middle second optical waveguide 16B2. One middle second optical waveguide 16B1 is connected to one first multiplexing section 15B1 and is a folded optical waveguide through which light from one first multiplexing section 15B1 passes. The other middle second optical waveguide 16B2 is connected to the other first multiplexing section 15B2 and is a folded optical waveguide through which light from the other first multiplexing section 15B2 passes.

[0080] The two first optical waveguides 13D on the outward path side of the rear stage are first optical waveguides connected to the second optical waveguides 16B1 and 16B2 on the middle stage. The seventh electrode unit 147 has a signal electrode 147A that applies a fifth electrical signal to the two first optical waveguides 13D on the outward path side of the rear stage, and a pair of ground electrodes 147B that ground the fifth electrical signal from the two first optical waveguides 13D on the outward path side of the rear stage. The two first optical waveguides 13D on the outward path side of the rear stage and the seventh electrode unit 147 form a parent DC modulation unit 20C.

[0081] The second multiplexing section 15C is connected to the two first optical waveguides 13D on the outward path side of the subsequent stage and multiplexes the light modulated by the two first optical waveguides 13D on the outward path side of the subsequent stage. The second optical waveguide 16C on the subsequent stage is connected to the second multiplexing section 15C and is a return optical waveguide through which light from the second multiplexing section 15C passes. The single first optical waveguide 13E on the return path side of the subsequent stage is a first optical waveguide that connects to the second optical waveguide 16C on the subsequent stage. The output section 17 is connected to the first optical waveguide 13E on the return path side of the subsequent stage and outputs light from the first optical waveguide 13E on the return path side of the subsequent stage to the optical fiber 2A.

[0082] That is, the optical modulator 5C has a first RF modulation section 20A1 and a second RF modulation section 20A2 on the first optical waveguide 13A on the forward path side of the previous stage, and a first DC modulation section 20B1 and a second DC modulation section 20B2 on the first optical waveguide 13C on the backward path side of the previous stage. Furthermore, the optical modulator 5C has a parent DC modulation section 20C on the first optical waveguide 13D on the forward path side of the subsequent stage. As a result, the optical modulator 5C constitutes an IQ modulator.

[0083] The cores of the two first optical waveguides 13A1 and 13A2 on the forward path side of the front stage, the two first optical waveguides 13C1 and 13C2 on the return path side of the front stage, the two first optical waveguides 13D on the forward path side of the rear stage, the first optical waveguide 13E on the return path side of the rear stage, the input section 11, and the output section 17 are in a non-amorphous state. The cores of the two first optical waveguides 13A1 and 13A2 on the forward path side of the front stage, the two first optical waveguides 13C1 and 13C2 on the return path side of the front stage, the two first optical waveguides 13D on the forward path side of the rear stage, the first optical waveguide 13E on the return path side of the rear stage, the input section 11, and the output section 17 are in a non-amorphous state, and therefore the refractive indexes in the X and Y directions are set to about 2.21, and the refractive index in the Z direction is set to about 2.14, for example.

[0084] In contrast, the cores of the front-stage second optical waveguides 16A1 and 16A2, the middle-stage second optical waveguides 16B1 and 16B2, the rear-stage second optical waveguide 16C, the first branching portion 12A, the second branching portion 12B, the first multiplexing portion 15B, and the second multiplexing portion 15C are in an amorphous state. Because the cores of the front-stage second optical waveguides 16A1 and 16A2, the middle-stage second optical waveguides 16B1 and 16B2, the rear-stage second optical waveguide 16C, the first branching portion 12A, the second branching portion 12B, the first multiplexing portion 15B, and the second multiplexing portion 15C are in an amorphous state, the refractive indexes in the X, Y, and Z directions are set to, for example, approximately 2.175.

[0085] In the process of forming the amorphous state and the non-amorphous state, for example, the core to be made non-amorphous is masked and Ar is introduced from the surface of the thin film LN layer 33. + Ion implantation: Ar +By implanting ions, the LN crystal orientation of the core of the thin-film LN layer 33 is disrupted, creating an amorphous state that eliminates the anisotropy of the optical refractive index. The masked core remains in a non-amorphous state. As a result, by creating an amorphous state, the angle at which the effective refractive index of the TE mode of the signal light and the effective refractive index of the TM mode of the unwanted light match disappears, thereby suppressing crosstalk.

[0086] In the optical modulator 5C of the fourth embodiment, the cores of the two first optical waveguides 13A1 and 13A2 on the forward path of the front stage, the two first optical waveguides 13C1 and 13C2 on the backward path of the front stage, and the two first optical waveguides 13D on the forward path of the rear stage are made non-amorphous. Furthermore, the optical modulator 5C makes the cores of the first optical waveguide 13E on the backward path of the rear stage, the input section 11, and the output section 17 amorphous. In the amorphous core, there is no propagation angle at which the effective refractive index of the TE mode and the effective refractive index of the TM mode intersect. As a result, even when an IQ modulator is configured, it is possible to improve modulation efficiency and coupling efficiency while suppressing unnecessary crosstalk of the TM mode with respect to the TE mode. [Explanation of symbols]

[0087] 1 Optical communication equipment 3 DSP 4 light source 5, 5A, 5B, 5C Optical Modulator 11 Input section 12 Branch 13 First optical waveguide 13A: First optical waveguide on the outgoing path 13B First optical waveguide on the return path side 13C First optical waveguide on the return path side 14 Electrode part 15 Multiplexing section 16 Second optical waveguide 17 Output section 33 Thin film LN layer

Claims

1. an electro-optic crystal layer; a first optical waveguide formed in the electro-optic crystal layer; an electrode for applying an electric signal to the first optical waveguide; a second optical waveguide in an amorphous state formed in the electro-optic crystal layer and connected to the first optical waveguide; An optical device comprising:

2. The second optical waveguide is 2. The optical device according to claim 1, wherein when the electro-optic crystal layer is an X-cut thin film LN layer, the optical waveguide is other than an optical waveguide in which light propagates in the Y-axis direction of the crystal axis of the thin film LN layer.

3. The second optical waveguide is 2. The optical device according to claim 1, wherein when the electro-optic crystal layer is a Y-cut thin film LN layer, the optical waveguide is other than an optical waveguide in which light propagates in the X-axis direction of the crystal axis of the thin film LN layer.

4. 4. The optical device according to claim 1, wherein the Pockels coefficient of the electro-optic crystal layer is in the range of 10 to 2000 pm / V.

5. At least a portion of the core of the second optical waveguide is In addition to being in the amorphous state, The core of the first optical waveguide is It is in a non-amorphous state 5. The optical device according to claim 1, wherein the optical device is a semiconductor laser.

6. an input unit for inputting light; a branching unit that branches the light from the input unit; two first optical waveguides on the outgoing path side, which are the first optical waveguides branched at the branching portion; an electrode for applying an electric signal to the two first optical waveguides on the outgoing path side; a multiplexing unit connected to the two first optical waveguides on the outgoing path side and multiplexing light modulated by the two first optical waveguides on the outgoing path side in response to the electrical signal; the second optical waveguide connected to the multiplexing section and through which the modulated light multiplexed in the multiplexing section passes; a first optical waveguide on the return path side, which is the first optical waveguide and is connected to the second optical waveguide; an output section that outputs modulated light that passes through the first optical waveguide on the return path side, At least a portion of the core of the second optical waveguide is In addition to being in the amorphous state, The cores of the two first optical waveguides on the outgoing path side are It is in a non-amorphous state 5. The optical device according to claim 1, wherein the optical device is a semiconductor laser.

7. The cores of the second optical waveguide, the branching section, and the multiplexing section are In addition to being in the amorphous state, The two first optical waveguides on the outgoing path side, the first optical waveguide on the return path side, the cores of the input section and the output section are The non-amorphous state 7. The optical device according to claim 6.

8. an input unit for inputting light; a branching unit that branches the light from the input unit; two first optical waveguides on the outgoing path side, which are the first optical waveguides branched at the branching portion; the second optical waveguide connected to the two first optical waveguides on the outgoing path side; two first optical waveguides on the return path side, which are the first optical waveguides and are connected to the second optical waveguides; an electrode for applying voltage to the two first optical waveguides on the outgoing path side and the two first optical waveguides on the return path side; a multiplexing section that multiplexes modulated light passing through the two first optical waveguides on the return path side; an output unit that outputs modulated light multiplexed by the multiplexing unit, At least a portion of the core of the second optical waveguide is In addition to being in the amorphous state, The two first optical waveguides on the outgoing path side are It is in a non-amorphous state 5. The optical device according to claim 1, wherein the optical device is a semiconductor laser.

9. The cores of the second optical waveguide, the branching section, and the multiplexing section are In addition to being in the amorphous state, The two first optical waveguides on the outgoing path side, the two first optical waveguides on the return path side, and the cores of the input section and the output section are The non-amorphous state 9. The optical device according to claim 8.

10. an input unit for inputting light; a branching unit that branches the light from the input unit; two first optical waveguides on the outgoing path side, which are the first optical waveguides branched at the branching portion; a first electrode for applying a first electric signal to the two first optical waveguides on the outgoing path side; the second optical waveguide connected to the two first optical waveguides on the outgoing path side, through which light modulated by the two first optical waveguides on the outgoing path side in response to the first electrical signal passes; two first optical waveguides on the return path side, which are the first optical waveguides and are connected to the second optical waveguides; a second electrode for applying a second electric signal to the two first optical waveguides on the return path side; a multiplexing unit connected to the two first optical waveguides on the return path side and configured to multiplex modulated light passing through the two first optical waveguides on the return path side in response to the second electrical signal; an output unit that outputs modulated light multiplexed by the multiplexing unit, At least a portion of the core of the second optical waveguide is In addition to being in the amorphous state, The two first optical waveguides on the outgoing path side and the two first optical waveguides on the return path side are It is in a non-amorphous state 5. The optical device according to claim 1, wherein the optical device is a semiconductor laser.

11. The cores of the second optical waveguide, the branching section, and the multiplexing section are In addition to being in the amorphous state, The two first optical waveguides on the outgoing path side, the two first optical waveguides on the return path side, and the cores of the input section and the output section are The non-amorphous state 11. The optical device according to claim 10.

12. an input unit for inputting light; a first branching unit that branches the light from the input unit; a second branching unit that branches the light branched by the first branching unit; two first optical waveguides on the forward path side of the first stage, which are branched at the second branching portion; a first electrode for applying a first electric signal to the two first optical waveguides on the forward path side of the preceding stage; a first optical waveguide, which is the second optical waveguide, connected to the two first optical waveguides on the forward path side of the first stage and through which light modulated by the two first optical waveguides on the forward path side of the first stage in response to the first electrical signal passes; two first optical waveguides on the return path side of the preceding stage, which are the first optical waveguides and are connected to the second optical waveguides of the preceding stage; a second electrode for applying a second electric signal to the two first optical waveguides on the return path side of the preceding stage; a first multiplexing unit connected to the two first optical waveguides on the return path side of the preceding stage and configured to multiplex modulated light passing through the two first optical waveguides on the return path side of the preceding stage in response to the second electrical signal; a middle second optical waveguide, which is the second optical waveguide and is connected to the first multiplexing unit and through which light from the first multiplexing unit passes; two first optical waveguides on the outgoing path side of a rear stage, which are the first optical waveguides and are connected to the second optical waveguides in the middle stage; a third electrode for applying a third electric signal to the two first optical waveguides on the outgoing path side of the latter stage; a second multiplexing unit connected to the two first optical waveguides on the outgoing path side of the subsequent stage and configured to multiplex modulated light passing through the two first optical waveguides on the outgoing path side of the subsequent stage in response to the third electrical signal; a second optical waveguide at a subsequent stage, which is connected to the second multiplexing unit and through which light from the second multiplexing unit passes; a first optical waveguide on the return path side of the subsequent stage, which is the first optical waveguide and is connected to the second optical waveguide of the subsequent stage; an output section connected to the first optical waveguide on the return path side of the subsequent stage and outputting light from the first optical waveguide on the return path side of the subsequent stage, At least a portion of the cores of the front-stage second optical waveguide, the middle-stage second optical waveguide, and the rear-stage second optical waveguide are In addition to being in the amorphous state, The two first optical waveguides on the forward path side of the front stage, the two first optical waveguides on the backward path side of the front stage, and the two first optical waveguides on the forward path side of the rear stage are It is in a non-amorphous state 5. The optical device according to claim 1, wherein the optical device is a semiconductor laser.

13. The cores of the front-stage second optical waveguide, the middle-stage second optical waveguide, the rear-stage second optical waveguide, the first branching portion, the second branching portion, the first multiplexing portion, and the second multiplexing portion are: In addition to being in the amorphous state, The two first optical waveguides on the forward path side of the preceding stage, the two first optical waveguides on the return path side of the preceding stage, the two first optical waveguides on the forward path side of the subsequent stage, the first optical waveguide on the return path side of the subsequent stage, and cores of the input section and the output section are The non-amorphous state 13. The optical device according to claim 12.

14. a processor that performs signal processing on the electrical signal; A light source that generates light; an optical device that modulates light generated from the light source using the electrical signal output from the processor; The optical device is an electro-optic crystal layer; a first optical waveguide formed in the electro-optic crystal layer; an electrode for applying an electric signal to the first optical waveguide; a second optical waveguide in an amorphous state formed in the electro-optic crystal layer and connected to the first optical waveguide; An optical communication device comprising:

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