Optical devices and optical communication devices

Abstract

To provide an optical device and the like that improve modulation efficiency.SOLUTION: An optical device comprises: a X cut substrate; and a first optical waveguide and a second optical waveguide that have two lines of folding structures formed on the substrate. Further, the optical device comprises: a first signal electrode that is arranged on the substrate and generates a first electrical field; and a second signal electrode that is arranged on the substrate and generates a second electrical field having an opposite phase of the first electrical field. The first optical waveguide comprises: an outward-path-side first optical waveguide applied with the first electrical field from the first signal electrode; and a homeward-path-side first optical waveguide applied with the second electrical field from the second signal electrode. The second optical waveguide comprises: an outward-path-side second optical waveguide applied with the first electrical field from the first signal electrode; and a homeward-path-side second optical waveguide applied with the second electrical field from the second signal electrode.SELECTED DRAWING: Figure 3

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. 10 is a schematic plan view showing an example of the configuration of an optical modulator 100, and FIG. 11 is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line CC shown in FIG. 10. The optical modulator 100 shown in FIGS. 10 and 11 includes a substrate 101, an intermediate layer 102 stacked on the substrate 101, and a thin-film LN substrate 103 made of LN (LiNbO) material stacked on the intermediate layer 102. The optical modulator 100 further includes two optical waveguides (104A and 104B) formed in the thin-film LN substrate 103, and a pair of ground electrodes (105A and 105B) formed on the thin-film LN substrate 103. The optical modulator 100 further includes an eleventh signal electrode 106 formed on the thin-film LN substrate 103 and sandwiched between the pair of ground electrodes (105A and 105B).

[0004] The substrate 101 is made of a material such as Si or LN. The intermediate layer 102 is made of a material with a lower optical refractive index than LN, such as a SiO2 layer. The thin-film LN substrate 103 is a thin-film substrate that has strong optical confinement and is advantageous for miniaturization.

[0005] The eleventh optical waveguide 104A and the twelfth optical waveguide 104B are formed of the thin-film LN substrate 103, and therefore are excellent in terms of, for example, insertion loss and transmission characteristics. The thin-film LN substrate 103 is an X-cut substrate, and therefore, due to its structural symmetry, chirp-free operation is possible, making it suitable for long-distance transmission.

[0006] The eleventh optical waveguide 104A is disposed between the eleventh ground electrode 105A and the eleventh signal electrode 106. Furthermore, the twelfth optical waveguide 104B is disposed between the twelfth ground electrode 105B and the eleventh signal electrode 106.

[0007] The crystal orientation of the thin-film LN substrate 103 is the width direction (Z direction) perpendicular to the propagation direction (Y direction). The optical refractive index of the eleventh optical waveguide 104A changes in response to the electric field in the electric field direction a11 from the eleventh ground electrode 105A to the eleventh signal electrode 106. Furthermore, the optical refractive index of the twelfth optical waveguide 104B changes in response to the electric field in the electric field direction b11 from the twelfth ground electrode 105B to the eleventh signal electrode 106.

[0008] The modulation efficiency of the optical modulator 100 is greatly affected by the length of the interaction section, such as the eleventh optical waveguide 104A and the twelfth optical waveguide 104B to which the electric field is applied, and a structure in which the interaction section is folded back is required to achieve miniaturization while maintaining the modulation efficiency.

[0009] FIG. 12 is a schematic plan view showing an example of the configuration of an optical modulator 100A with a folded structure, and FIG. 13 is a schematic cross-sectional view showing an example of the cross-sectional portion taken along line DD shown in FIG. 12. Note that the same components as those of the optical modulator 100 shown in FIGS. 10 and 11 are designated by the same reference numerals, and redundant descriptions of the configuration and operation will be omitted. The optical modulator 100A shown in FIG. 12 has a folded structure in which an eleventh optical waveguide 104A, a twelfth optical waveguide 104B, an eleventh ground electrode 105A, a twelfth ground electrode 105B, and an eleventh signal electrode 106 are folded back. The optical modulator 100A has an interaction section 110A on the outgoing path and an interaction section 110B on the returning path.

[0010] The eleventh optical waveguide 104A has an outgoing optical waveguide 104A1 and a homeward optical waveguide 104A2. The twelfth optical waveguide 104B has an outgoing optical waveguide 104B1 and a homeward optical waveguide 104B2. The eleventh ground electrode 105A has an outgoing ground electrode 105A1 and a homeward ground electrode 105A2. The twelfth ground electrode 105B has an outgoing ground electrode 105B1 and a homeward ground electrode 105B2.

[0011] The outgoing path interaction section 110A includes an outgoing path-side eleventh ground electrode 105A1, an outgoing path-side eleventh signal electrode 106A1, an outgoing path-side eleventh optical waveguide 104A1, an outgoing path-side twelfth optical waveguide 104B1, and an outgoing path-side twelfth ground electrode 105B1. The outgoing path-side eleventh optical waveguide 104A1 is disposed between the outgoing path-side eleventh ground electrode 105A1 and the outgoing path-side eleventh signal electrode 106A1. The outgoing path-side twelfth optical waveguide 104B1 is disposed between the outgoing path-side twelfth ground electrode 105B1 and the outgoing path-side eleventh signal electrode 106A1.

[0012] The crystal orientation of the thin-film LN substrate 103 is the width direction (Z direction) perpendicular to the propagation direction (Y direction). The optical refractive index of the outgoing eleventh optical waveguide 104A1 changes in response to the electric field in the electric field direction a101 from the outgoing eleventh ground electrode 105A1 to the outgoing eleventh signal electrode 106A1. Furthermore, the optical refractive index of the outgoing twelfth optical waveguide 104B1 changes in response to the electric field in the electric field direction b101 from the outgoing twelfth ground electrode 105B1 to the outgoing eleventh signal electrode 106A1.

[0013] The interaction section 110B on the return path includes an eleventh ground electrode 105A2 on the return path, an eleventh signal electrode 106A2 on the return path, a twelfth ground electrode 105B2 on the return path, an eleventh optical waveguide 104A2 on the return path, and a twelfth optical waveguide 104B2 on the return path. The eleventh optical waveguide 104A2 on the return path is disposed between the eleventh ground electrode 105A2 on the return path and the eleventh signal electrode 106A2 on the return path. The twelfth optical waveguide 104B2 on the return path is disposed between the twelfth ground electrode 105B2 on the return path and the eleventh signal electrode 106A2 on the return path.

[0014] The optical refractive index of the eleventh optical waveguide 104A2 on the homeward side changes in response to the electric field in the electric field direction a102 from the eleventh ground electrode 105A2 on the homeward side to the eleventh signal electrode 106A2 on the homeward side. Furthermore, the optical refractive index of the twelfth optical waveguide 104B2 on the homeward side changes in response to the electric field in the electric field direction b102 from the twelfth ground electrode 105B2 on the homeward side to the eleventh signal electrode 106A2 on the homeward side. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] International Publication No. 2007 / 058366 [Patent Document 2] U.S. Patent No. 7,212,326 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-221874 Summary of the Invention [Problem to be solved by the invention]

[0016] However, in the optical modulator 100A with a folded structure, the electric field direction a102 of the eleventh optical waveguide 104A2 on the return path is the same as the crystal direction (Z direction) of the LN crystal, while the electric field direction a101 of the eleventh optical waveguide 104A1 on the outgoing path is different from the crystal direction (Z direction) of the LN crystal. The electric field direction a101 of the eleventh optical waveguide 104A1 on the outgoing path is opposite to the electric field direction a102 of the eleventh optical waveguide 104A2 on the return path. Therefore, the electric field of the electric field direction a101 of the eleventh optical waveguide 104A1 on the outgoing path is canceled out by the electric field of the electric field direction a102 of the eleventh optical waveguide 104A2 on the return path, resulting in a decrease in modulation efficiency.

[0017] Similarly, the electric field direction b101 of the twelfth optical waveguide 104B1 on the outgoing path is the same as the crystal direction (Z direction) of the LN crystal, while the electric field direction b102 of the twelfth optical waveguide 104B2 on the homeward path is different from the crystal direction (Z direction) of the LN crystal. Furthermore, the electric field direction b101 of the twelfth optical waveguide 104B1 on the outgoing path is opposite to the electric field direction b102 of the twelfth optical waveguide 104B2 on the homeward path. Therefore, the electric field in the electric field direction b101 of the twelfth optical waveguide 104B1 on the outgoing path is canceled out by the electric field in the electric field direction b102 of the twelfth optical waveguide 104B2 on the homeward path, resulting in a decrease in modulation efficiency.

[0018] In the optical modulator 100A, which is an X-cut LN modulator with a single signal electrode and single-ended drive, the crystal axis is reversed with respect to the propagation direction (Y direction) between the outgoing path and the returning path. As a result, a phase change occurs in the opposite direction, and the phase change in the outgoing path is canceled out by the phase change in the returning path, resulting in a decrease in modulation efficiency.

[0019] Another possible method is to switch the left and right positions of the optical waveguides relative to the direction of travel between the outbound and return paths, but a crossing waveguide or a reflective structure using an external mirror to switch the optical waveguides would cause reflection and attenuation of the optical signal.

[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. [Means for solving the problem]

[0021] In one embodiment, the optical device disclosed herein includes an X-cut substrate and two folded first and second optical waveguides formed on the substrate. The optical device further includes a first signal electrode disposed on the substrate and generating a first electric field, and a second signal electrode disposed on the substrate and generating a second electric field opposite in phase to the first electric field. The first optical waveguide includes a first optical waveguide on the outgoing path to which the first electric field from the first signal electrode is applied, and a first optical waveguide on the return path to which the second electric field from the second signal electrode is applied. The second optical waveguide includes a second optical waveguide on the outgoing path to which the first electric field from the first signal electrode is applied, and a second optical waveguide on the return path to which the second electric field from the second signal electrode is applied. [Effects of the Invention]

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

[0023] [Figure 1] FIG. 1 is a block diagram showing an example of the configuration of an optical communication device according to this 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 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 cross-sectional view showing an example of a cross-sectional portion taken along line BB shown in FIG. [Figure 6] FIG. 6 is a schematic plan view showing an example of the configuration of the optical modulator according to the third embodiment. [Figure 7] FIG. 7 is a schematic plan view showing an example of the configuration of an optical modulator according to the fourth embodiment. [Figure 8] FIG. 8 is a schematic plan view showing an example of the configuration of the optical modulator according to the fifth embodiment. [Figure 9] FIG. 9 is a schematic plan view showing an example of the configuration of the optical modulator according to the sixth embodiment. [Figure 10] FIG. 10 is a schematic plan view showing an example of the configuration of an optical modulator. [Figure 11] FIG. 11 is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line CC shown in FIG. [Figure 12] FIG. 12 is a schematic plan view showing an example of the configuration of an optical modulator with a folded structure. [Figure 13] FIG. 13 is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line DD shown in FIG. 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 this 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 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. 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 an optical modulator 5 according to a first embodiment, and FIG. 3 is a schematic cross-sectional view showing an example of a cross-sectional portion taken along line AA in FIG. 2. The optical modulator 5 shown in FIGS. 2 and 3 includes a substrate 11, an intermediate layer 12 stacked on the substrate 11, and a thin-film LN substrate 13 made of LN (LiNbO) material stacked on the intermediate layer 12. The optical modulator 5 further includes a first optical waveguide 14A and a second optical waveguide 14B having two folded structures formed on the thin-film LN substrate 13, and a first ground electrode 15A, a second ground electrode 15B, and a third ground electrode 15C formed on the thin-film LN substrate 13. The optical modulator 5 further includes a first signal electrode 16A and a second signal electrode 16B formed on the thin-film LN substrate 13.

[0029] The substrate 11 is made of a material such as SiO2 (silicon dioxide), TiO2 (titanium dioxide), Si, or LN. The intermediate layer 12 is a layer of, for example, SiO2 or TiO2, which has a lower optical refractive index than LN. The thin-film LN substrate 13 is a substrate using a thin film of LN crystal, and is formed with a first optical waveguide 14A and a second optical waveguide 14B that are convex and protrude upward at predetermined locations. The use of an LN material provides strong optical confinement, which is advantageous for miniaturization. The thin-film LN substrate 13 is an X-cut substrate.

[0030] The first optical waveguide 14A and the second optical waveguide 14B are formed on a thin-film LN substrate 13, and because the material is LN, they are 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, making it suitable for long-distance transmission. The first signal electrode 16A and the second signal electrode 16B are electrodes made of a metal material such as gold or copper. The first ground electrode 15A, the second ground electrode 15B, and the third ground electrode 15C are electrodes made of a metal material such as aluminum.

[0031] The first signal electrode 16A is disposed on the thin-film LN substrate 13 and generates a first electric field to be applied to the first optical waveguide 14A or the second optical waveguide 14B. The second signal electrode 16B is disposed on the thin-film LN substrate 13 and generates a second electric field to be applied to the first optical waveguide 14A or the second optical waveguide 14B. The second electric field has an electric field direction that is opposite in phase to the electric field direction of the first electric field.

[0032] The optical modulator 5 has a folded structure in which the first optical waveguide 14A, the second optical waveguide 14B, the first ground electrode 15A, the second ground electrode 15B, the first signal electrode 16A, and the second signal electrode 16B are folded back in an outward path and a return path. The optical modulator 5 has a first interaction section 20A in the outward path, a second interaction section 20B in the return path, and an intermediate section 20C connecting the first interaction section 20A in the outward path and the second interaction section 20B in the return path.

[0033] The first optical waveguide 14A having a folded structure includes a first optical waveguide 14A1 on the outgoing path, a first optical waveguide 14A2 on the returning path, and a first intermediate optical waveguide 14A3 connecting the first optical waveguide 14A1 on the outgoing path and the first optical waveguide 14A2 on the returning path. The second optical waveguide 14B having a folded structure includes a second optical waveguide 14B1 on the outgoing path, a second optical waveguide 14B2 on the returning path, and a second intermediate optical waveguide 14B3 connecting the second optical waveguide 14B1 on the outgoing path and the second optical waveguide 14B2 on the returning path.

[0034] The first ground electrode 15A of the folded structure has a first ground electrode 15A1 on the outward path, a first ground electrode 15A2 on the return path, and a first intermediate ground electrode 15A3 connecting the first ground electrode 15A1 on the outward path and the first ground electrode 15A2 on the return path. The second ground electrode 15B of the folded structure has a second ground electrode 15B1 on the outward path, a second ground electrode 15B2 on the return path, and a second intermediate ground electrode 15B3 connecting the second ground electrode 15B1 on the outward path and the second ground electrode 15B2 on the return path.

[0035] The first signal electrode 16A having a folded structure has a first signal electrode 16A1 on the outgoing path, a first signal electrode 16A2 on the returning path, and a first signal electrode 16A3 on the intermediate side connecting the first signal electrode 16A1 on the outgoing path and the first signal electrode 16A2 on the returning path. The second signal electrode 16B having a folded structure has a second signal electrode 16B1 on the outgoing path, a second signal electrode 16B2 on the returning path, and a second signal electrode 16B3 on the intermediate side connecting the second signal electrode 16B1 on the outgoing path and the second signal electrode 16B2 on the returning path.

[0036] The first interaction section 20A of the outgoing path includes an outgoing path first ground electrode 15A1, an outgoing path first optical waveguide 14A1, an outgoing path first signal electrode 16A1, an outgoing path second ground electrode 15B1, an outgoing path second optical waveguide 14B1, and a third ground electrode 15C. The outgoing path first optical waveguide 14A1 is disposed between the outgoing path second ground electrode 15B1 and the outgoing path second signal electrode 16B1. The outgoing path second optical waveguide 14B1 is disposed between the third ground electrode 15C and the outgoing path second signal electrode 16B1.

[0037] The crystal orientation of the thin-film LN substrate 13 is the width direction (Z direction) perpendicular to the propagation direction (Y direction). The optical refractive index of the outgoing first optical waveguide 14A1 changes in response to the electric field in the electric field direction a11 from the outgoing second signal electrode 16B1 to the outgoing second ground electrode 15B1. Furthermore, the optical refractive index of the outgoing second optical waveguide 14B1 changes in response to the electric field in the electric field direction b11 from the outgoing second signal electrode 16B1 to the third ground electrode 15C.

[0038] The intermediate portion 20C includes a first intermediate ground electrode 15A3, a first intermediate signal electrode 16A3, a second intermediate ground electrode 15B3, a first intermediate optical waveguide 14A3, a second intermediate optical waveguide 14B3, a second intermediate signal electrode 16B3, and a third ground electrode 15C.

[0039] The second interaction section 20B on the return path includes a first ground electrode 15A2 on the return path, a first optical waveguide 14A2 on the return path, a first signal electrode 16A2 on the return path, a second optical waveguide 14B2 on the return path, and a second ground electrode 15B2 on the return path. The second interaction section 20B on the return path also includes a second signal electrode 16B2 on the return path and a third ground electrode 15C. The first optical waveguide 14A2 on the return path is disposed between the first ground electrode 15A2 on the return path and the first signal electrode 16A2 on the return path. The second optical waveguide 14B2 on the return path is disposed between the second ground electrode 15B2 on the return path and the first signal electrode 16A2 on the return path.

[0040] The optical refractive index of the first optical waveguide 14A2 on the homeward path changes in response to the electric field in the electric field direction a12 applied from the first ground electrode 15A2 on the homeward path to the first signal electrode 16A2 on the homeward path. Furthermore, the optical refractive index of the second optical waveguide 14B2 on the homeward path changes in response to the electric field in the electric field direction b12 applied from the second ground electrode 15B2 on the homeward path to the first signal electrode 16A2 on the homeward path.

[0041] That is, in the first optical waveguide 14A, the electric field direction a11 of the electric field applied to the outgoing first optical waveguide 14A1 and the electric field direction a12 of the electric field applied to the returning first optical waveguide 14A2 are the same as the crystal direction of the thin-film LN substrate 13. In addition, in the second optical waveguide 14B, the electric field direction b11 of the electric field applied to the outgoing second optical waveguide 14B1 and the electric field direction b12 of the electric field applied to the returning second optical waveguide 14B2 are the same as the crystal direction of the thin-film LN substrate 13.

[0042] In the optical modulator 5 of the first embodiment, a first optical waveguide 14A1 on the outgoing path is disposed between a second ground electrode 15B1 on the outgoing path and a second signal electrode 16B1 on the outgoing path, and a second optical waveguide 14B1 on the outgoing path is disposed between the second signal electrode 16B1 on the outgoing path and a third ground electrode 15C. In the optical modulator 5, a first optical waveguide 14A2 on the homeward path is disposed between a first ground electrode 15A2 on the homeward path and a first signal electrode 16A2 on the homeward path, and a second optical waveguide 14B2 on the homeward path is disposed between the first signal electrode 16A2 on the homeward path and a second ground electrode 15B2 on the homeward path. As a result, the electric field direction a11 of the electric field applied to the first optical waveguide 14A1 on the outward path is the same as the electric field direction a12 of the electric field applied to the first optical waveguide 14A2 on the return path, and therefore modulation efficiency is high. Similarly, the electric field direction b11 of the electric field applied to the second optical waveguide 14B1 on the outward path is the same as the electric field direction b12 of the electric field applied to the second optical waveguide 14B2 on the return path, and therefore modulation efficiency is high.

[0043] Furthermore, the crystal orientation of the X-cut substrate is the same as the direction a11 of the first electric field applied to the first optical waveguide 14A1 on the outgoing path and the direction a12 of the second electric field applied to the first optical waveguide 14A2 on the returning path. As a result, the direction of the electric field applied from the signal electrode to each optical waveguide is the same for the outgoing and returning paths relative to the Z axis of the LN crystal. This allows the device to be made more compact by shortening the length of the interaction section while maintaining modulation efficiency. Moreover, there is no need for an optical waveguide intersection or a reflective structure using an external mirror, and reflection and attenuation of the optical signal at the returning section can be suppressed.

[0044] In the outbound path, the first optical waveguide 14A is on the +Z side and the second optical waveguide 14B is on the -Z side with respect to the Z-axis direction of the LN crystal, and in the return path, the first optical waveguide 14A is on the -Z side and the second optical waveguide 14B is on the +Z side. Therefore, the direction of the electric field applied in the Z-axis direction of the LN crystal and from the single signal electrode toward the ground electrode is interchanged between the outbound path and the return path. As a result, the direction of the electric field applied from the signal electrode to each optical waveguide is the same with respect to the Z-axis of the LN crystal on the outbound path and the return path, allowing the length of the interaction section to be shortened while maintaining modulation efficiency. [Example]

[0045] Fig. 4 is a schematic plan view showing an example of the configuration of an optical modulator 5A of Example 2, and Fig. 5 is a schematic cross-sectional view showing an example of the cross-sectional portion taken along line BB shown in Fig. 4. Note that the same components as those of the optical modulator 5 of Example 1 are given the same reference numerals, and redundant explanations of the configurations and operations will be omitted.

[0046] 4 and 5 includes a substrate 11, an intermediate layer 12, a thin-film LN substrate 13, and two optical waveguides, a first optical waveguide 14A and a second optical waveguide 14B. The optical modulator 5A further includes a first ground electrode 15A and a third ground electrode 15C formed on the thin-film LN substrate 13, and a first signal electrode 16A and a second signal electrode 16B formed on the thin-film LN substrate 103. The optical modulator 5A of the first embodiment differs from the optical modulator 5A of the second embodiment in that the second ground electrode 15B is not provided between the first signal electrode 16A and the second signal electrode 16B.

[0047] The optical modulator 5A includes a first interaction section 20A1 on the outgoing path, a second interaction section 20B1 on the return path, and an intermediate section 20C1 connecting the first interaction section 20A1 on the outgoing path and the second interaction section 20B1 on the return path. The first interaction section 20A1 on the outgoing path includes a first ground electrode 15A1 on the outgoing path, a first signal electrode 16A1 on the outgoing path, a first optical waveguide 14A1 on the outgoing path, a second signal electrode 16B1 on the outgoing path, a second optical waveguide 14B1 on the outgoing path, and a third ground electrode 15C. The first optical waveguide 14A1 on the outgoing path is disposed between the first signal electrode 16A1 on the outgoing path and the second signal electrode 16B1 on the outgoing path. The second optical waveguide 14B1 on the outgoing path is disposed between the third ground electrode 15C and the second signal electrode 16B1 on the outgoing path.

[0048] The crystal orientation of the thin-film LN substrate 13 is the width direction (Z direction) perpendicular to the propagation direction (Y direction). The optical refractive index of the outgoing first optical waveguide 14A1 changes in response to the electric field in the electric field direction a21 from the outgoing second signal electrode 16B1 to the outgoing first signal electrode 16A1. Furthermore, the optical refractive index of the outgoing second optical waveguide 14B1 changes in response to the electric field in the electric field direction b21 from the outgoing second signal electrode 16B1 to the third ground electrode 15C.

[0049] The intermediate portion 20C1 has a first ground electrode 15A3 on the intermediate side, a first signal electrode 16A3 on the intermediate side, a first optical waveguide 14A3 on the intermediate side, a second optical waveguide 14B3 on the intermediate side, a second signal electrode 16B3 on the intermediate side, and a third ground electrode 15C.

[0050] The second interaction section 20B1 of the return path includes a first ground electrode 15A2 on the return path, a first optical waveguide 14A2 on the return path, a first signal electrode 16A2 on the return path, a second optical waveguide 14B2 on the return path, a second signal electrode 16B2 on the return path, and a third ground electrode 15C. The first optical waveguide 14A2 on the return path is disposed between the first ground electrode 15A2 on the return path and the first signal electrode 16A2 on the return path. The second optical waveguide 14B2 on the return path is disposed between the second signal electrode 16B2 on the return path and the first signal electrode 16A2 on the return path.

[0051] The first optical waveguide 14A2 on the return path side is Ground electrode 15A2 From the first one on the return side Signal electrode 16A2 The optical refractive index of the second optical waveguide 14B2 on the return path changes in response to the electric field in the electric field direction a22 directed from the second signal electrode 16B2 on the return path to the first signal electrode 16A2 on the return path.

[0052] That is, in the first optical waveguide 14A, the electric field direction a21 of the electric field applied to the outgoing first optical waveguide 14A1 and the electric field direction a22 of the electric field applied to the returning first optical waveguide 14A2 are the same as the crystal direction of the thin-film LN substrate 13. In addition, in the second optical waveguide 14B, the electric field direction b21 of the electric field applied to the outgoing second optical waveguide 14B1 and the electric field direction b22 of the electric field applied to the returning second optical waveguide 14B2 are the same as the crystal direction of the thin-film LN substrate 13.

[0053] In the optical modulator 5A of the second embodiment, a first outgoing path optical waveguide 14A1 is disposed between a first outgoing path signal electrode 16A1 and a second outgoing path signal electrode 16B1, and a second outgoing path optical waveguide 14B1 is disposed between the second outgoing path signal electrode 16B1 and a third ground electrode 15C. In the optical modulator 5A, a first homeward path optical waveguide 14A2 is disposed between a first homeward path ground electrode 15A2 and a first homeward path signal electrode 16A2, and a second homeward path optical waveguide 14B2 is disposed between the first homeward path signal electrode 16A2 and a second homeward path signal electrode 16B2. As a result, the electric field direction a21 of the electric field applied to the first optical waveguide 14A1 on the outward path and the electric field direction a22 of the electric field applied to the first optical waveguide 14A2 on the return path are the same in the first optical waveguide 14A, resulting in high modulation efficiency. Similarly, the electric field direction b21 of the electric field applied to the second optical waveguide 14B1 on the outward path and the electric field direction b22 of the electric field applied to the second optical waveguide 14B2 on the return path are the same in the second optical waveguide 14B, resulting in high modulation efficiency. Furthermore, because the second ground electrode 15B is not disposed between the first optical waveguide 14A and the second optical waveguide 14B, the width in the Z-axis direction can be reduced, thereby achieving miniaturization. [Example]

[0054] FIG. 6 is a schematic plan view showing an example of the configuration of an optical modulator 5B according to a third embodiment. The same components as those of the optical modulator 5 according to the first embodiment are designated by the same reference numerals, and redundant descriptions of the configuration and operation will be omitted. The optical modulator 5B shown in FIG. 6 has a first interaction section 20A on the outgoing path, a second interaction section 20B on the returning path, and an intermediate section 20C connecting the first interaction section 20A on the outgoing path and the second interaction section 20B on the returning path. The intermediate section 20C is defined as the section from the O-Zin plane to the O-Zout plane shown in FIG. 6.

[0055] The optical waveguide lengths of the first optical waveguide 14A3 on the intermediate side and the second optical waveguide 14B3 on the intermediate side are adjusted to make the optical waveguide lengths of the first optical waveguide 14A and the second optical waveguide 14B the same. For ease of explanation, as shown in FIG. 6, the first optical waveguide 14A3 on the intermediate side and the second optical waveguide 14B3 on the intermediate side are depicted as being located on the first signal electrode 16A, the second signal electrode 16B, the first ground electrode 15A, and the second ground electrode 15B so that their optical waveguide lengths can be understood. The first signal electrode 16A3 on the intermediate side has a length Lr(S2) from the O-Zin plane to the O-Zout plane. The waveguide length of the first optical waveguide 14A3 on the intermediate side is a length Lr(W1) from the O-Zin plane to the O-Zout plane. The waveguide length of the intermediate-side second optical waveguide 14B3 is the length Lr(W2) from the O-Zin plane to the O-Zout plane. By satisfying Lr(S2) = Lr(W2) = Lr(W1), the optical waveguide lengths of the first optical waveguide 14A, the second optical waveguide 14B, and the electrode length of the first signal electrode 16A are made the same. The shapes of the intermediate-side first optical waveguide 14A3 and the intermediate-side second optical waveguide 14B3 can be modified as needed. As a result, the phases of the forward and backward paths can be aligned to achieve broadband operation. Furthermore, by making the waveguide lengths of the first optical waveguide 14A and the second optical waveguide 14B equal, the difference in propagation loss between the first optical waveguide 14A and the second optical waveguide 14B is suppressed, improving the extinction ratio and wavelength dependency of the optical modulator 5B.

[0056] In the optical modulator 5B of the third embodiment, the optical waveguide length of the first optical waveguide 14A3 on the intermediate side and the optical waveguide length of the second optical waveguide 14B3 on the intermediate side are adjusted to make the optical waveguide length of the first optical waveguide 14A the same as the optical waveguide length of the second optical waveguide 14B. As a result, the optical waveguide lengths of the first optical waveguide 14A and the second optical waveguide 14B are made the same, thereby suppressing the difference in propagation loss between the optical waveguides and improving the extinction ratio and wavelength dependency of the optical modulator 5B. [Example]

[0057] FIG. 7 is a schematic plan view showing an example of the configuration of an optical modulator 5C according to a fourth embodiment. The same components as those of the optical modulator 5 according to the first embodiment are designated by the same reference numerals, and redundant descriptions of the configuration and operation will be omitted. The optical modulator 5C shown in FIG. 7 includes a substrate 11, an intermediate layer 12, a thin-film LN substrate 13, a first optical waveguide 14A, a second optical waveguide 14B, a first signal electrode 16A, and a second signal electrode 16B. Furthermore, the optical modulator 5C includes a fourth ground electrode 15D and a fifth ground electrode 15E having a folded structure, instead of the first ground electrode 15A, the second ground electrode 15B, and the third ground electrode 15C.

[0058] The first optical waveguide 14A having a two-fold structure includes a first outgoing first optical waveguide 14A1, a homeward first optical waveguide 14A2, and a second outgoing first optical waveguide 14A4. The first optical waveguide 14A further includes a first intermediate first optical waveguide 14A5 connecting the first outgoing first optical waveguide 14A1 and the homeward first optical waveguide 14A2. The first optical waveguide 14A further includes a second intermediate first optical waveguide 14A6 connecting the homeward first optical waveguide 14A2 and the second outgoing first optical waveguide 14A4.

[0059] The second optical waveguide 14B having a two-fold structure includes a first outward second optical waveguide 14B1, a return second optical waveguide 14B2, and a second outward second optical waveguide 14B4. The second optical waveguide 14B further includes a first intermediate second optical waveguide 14B5 connecting the first outward second optical waveguide 14B1 and the return second optical waveguide 14B2. The second optical waveguide 14B further includes a second intermediate second optical waveguide 14B6 connecting the return second optical waveguide 14B2 and the second outward second optical waveguide 14B4.

[0060] The first signal electrode 16A having a two-fold structure includes a first outward-side first signal electrode 16A1, a return-side first signal electrode 16A2, and a second outward-side first signal electrode 16A4. The first signal electrode 16A also includes a first intermediate-side first signal electrode 16A5 that connects the first outward-side first signal electrode 16A1 and the return-side first signal electrode 16A2. The first signal electrode 16A also includes a second intermediate-side first signal electrode 16A6 that connects the return-side first signal electrode 16A2 and the second outward-side first signal electrode 16A4.

[0061] The second signal electrode 16B having a two-fold structure includes a first outward-side second signal electrode 16B1, a return-side second signal electrode 16B2, and a second outward-side second signal electrode 16B4. The second signal electrode 16B also includes a first intermediate-side second signal electrode 16B5 connecting the first outward-side second signal electrode 16B1 and the return-side second signal electrode 16B2. The second signal electrode 16B also includes a second intermediate-side second signal electrode 16B6 connecting the return-side second signal electrode 16B2 and the second outward-side second signal electrode 16B4.

[0062] The fourth ground electrode 15D includes a fourth ground electrode 15D1 on the outward path, a fourth ground electrode 15D2 on the return path, and an intermediate fourth ground electrode 15D3 connecting the fourth ground electrode 15D1 on the outward path and the fourth ground electrode 15D2 on the return path. The fifth ground electrode 15E includes a fifth ground electrode 15E1 on the outward path, a fifth ground electrode 15E2 on the return path, and an intermediate fifth ground electrode 15E3 connecting the fifth ground electrode 15E1 on the outward path and the fifth ground electrode 15E2 on the return path.

[0063] The optical modulator 5C includes a first interaction section 20A3, a second interaction section 20B3, a third interaction section 20D3, and a second intermediate section 20E3 connecting the first interaction section 20A3 and the second interaction section 20B3. The optical modulator 5C further includes a second intermediate section 20F3 connecting the second interaction section 20B3 and the third interaction section 20D3.

[0064] The first interaction section 20A3 includes a fourth outward path ground electrode 15D1, a first outward path first signal electrode 16A1, a first outward path first optical waveguide 14A1, and a first outward path second signal electrode 16B1. The first interaction section 20A3 includes a first outward path second optical waveguide 14B1 and a fifth outward path ground electrode 15E1. The first outward path first optical waveguide 14A1 is disposed between the first outward path first signal electrode 16A1 and the first outward path second signal electrode 16B1. The first outward path second optical waveguide 14B1 is disposed between the first outward path second signal electrode 16B1 and the fifth outward path ground electrode 15E1.

[0065] The crystal orientation of the thin-film LN substrate 13 is the width direction (Z direction) perpendicular to the propagation direction (Y direction). The optical refractive index of the first optical waveguide 14A1 on the first outgoing path side of the first interaction section 20A3 changes in response to the electric field in the electric field direction a31 from the second signal electrode 16B1 on the first outgoing path side to the first signal electrode 16A1 on the first outgoing path side. Furthermore, the optical refractive index of the second optical waveguide 14B1 on the first outgoing path side changes in response to the electric field in the electric field direction b31 from the second signal electrode 16B1 on the first outgoing path side to the fifth ground electrode 15E1 on the outgoing path side.

[0066] The second intermediate portion 20E3 has a fourth ground electrode 15D3 on the intermediate side, a first signal electrode 16A5 on the first intermediate side, a first optical waveguide 14A5 on the first intermediate side, a second optical waveguide 14B5 on the first intermediate side, and a second signal electrode 16B5 on the first intermediate side.

[0067] The second interaction section 20B3 includes a fifth ground electrode 15E1 on the outgoing path, a second signal electrode 16B2 on the homeward path, a second optical waveguide 14B2 on the homeward path, a first signal electrode 16A2 on the homeward path, a first optical waveguide 14A2 on the homeward path, and a fourth ground electrode 15D2 on the homeward path. The first optical waveguide 14A2 on the homeward path is disposed between the fourth ground electrode 15D2 on the homeward path and the first signal electrode 16A2 on the homeward path. The second optical waveguide 14B2 on the homeward path is disposed between the first signal electrode 16A2 on the homeward path and the second signal electrode 16B2 on the homeward path.

[0068] The optical refractive index of the first optical waveguide 14A2 on the homeward path side of the second interaction portion 20B3 changes in response to the electric field in the electric field direction a32 from the fourth ground electrode 15D2 on the homeward path to the first signal electrode 16A2 on the homeward path. Furthermore, the optical refractive index of the second optical waveguide 14B2 on the homeward path changes in response to the electric field in the electric field direction b32 from the second signal electrode 16B2 on the homeward path to the first signal electrode 16A2 on the homeward path.

[0069] The second intermediate portion 20F3 has a fifth ground electrode 15E3 on the intermediate side, a first signal electrode 16A6 on the second intermediate side, a first optical waveguide 14A6 on the second intermediate side, a second optical waveguide 14B6 on the second intermediate side, and a second signal electrode 16B6 on the second intermediate side.

[0070] The third interaction section 20D3 includes a fourth ground electrode 15D2 on the return path side, a first signal electrode 16A4 on the second outward path side, a first optical waveguide 14A4 on the second outward path side, and a second signal electrode 16B4 on the second outward path side. The third interaction section 20D3 includes a second optical waveguide 14B4 on the second outward path side, and a fifth ground electrode 15E2 on the return path side. The first optical waveguide 14A4 on the second outward path side is disposed between the first signal electrode 16A4 on the second outward path side and the second signal electrode 16B4 on the second outward path side. The second optical waveguide 14B4 on the second outward path side is disposed between the second signal electrode 16B4 on the second outward path side and the fifth ground electrode 15E2 on the return path side.

[0071] The optical refractive index of the first optical waveguide 14A4 on the second outgoing path side of the third interaction section 20D2 changes in response to the electric field in the electric field direction a33 from the second signal electrode 16B4 on the second outgoing path side to the first signal electrode 16A4 on the second outgoing path side. Furthermore, the optical refractive index of the second optical waveguide 14B4 on the second outgoing path side changes in response to the electric field in the electric field direction b33 from the second signal electrode 16B4 on the second outgoing path side to the fifth ground electrode 15E2 on the return path side.

[0072] In the first optical waveguide 14A, the electric field direction a31 from the second signal electrode 16B1 on the first outbound path side to the first signal electrode 16A1 on the first outbound path side, the electric field direction a32 from the second signal electrode 16B1 on the first outbound path side to the first signal electrode 16A1 on the first outbound path side, and the electric field direction a32 from the fourth ground electrode 15D2 on the return path side to the first signal electrode 16A2 on the return path side are all in the same direction. In addition, in the second optical waveguide 14B, the electric field direction b31 from the second signal electrode 16B1 on the first outward path side to the fifth ground electrode 15E1 on the outward path side, the electric field direction b32 from the second signal electrode 16B2 on the return path side to the first signal electrode 16A2 on the return path side, and the electric field direction b33 from the second signal electrode 16B4 on the second outward path side to the fifth ground electrode 15E2 on the return path side are all in the same direction.

[0073] The optical waveguide length L2 of the first optical waveguide 14A2 on the return path side of the second interaction section 20B is made longer than the optical waveguide length L3 of the first optical waveguide 14A1 on the first outgoing path side of the first interaction section 20A or the optical waveguide length L3 of the first optical waveguide 14A4 on the second outgoing path side. The optical waveguide length L2 of the second optical waveguide 14B2 on the return path side of the second interaction section 20B is made longer than the optical waveguide length L1 of the second optical waveguide 14B1 on the first outgoing path side of the third interaction section 20D or the optical waveguide length L1 of the second optical waveguide 14B4 on the second outgoing path side.

[0074] In an optical modulator 5A having a single folded structure, if the electric field efficiency between the signal electrodes differs from the electric field efficiency between the signal electrode and the ground electrode, the electric signal attenuates as it propagates. Therefore, in the optical modulator 5A, the amount of phase change applied to the first optical waveguide 14A and the second optical waveguide 14B differs between the forward and backward paths, which can cause frequency-dependent chirp. Therefore, in the optical modulator 5C of the fifth embodiment, a two-fold structure is used, with three locations: a first interaction section 20A, a second interaction section 20B, and a third interaction section 20D. The optical waveguide length L2 of the second interaction section 20B is longer than the optical waveguide length L3 of the first interaction section 20A. The optical waveguide length L2 of the second interaction section 20B is longer than the optical waveguide length L1 of the third interaction section 20D. As a result, the phase change amounts of the first optical waveguide 14A and the second optical waveguide 14B can be made uniform, thereby reducing the dependence of the chirp on the wind wave number. [Example]

[0075] 8 is a schematic plan view showing an example of the configuration of an optical modulator 5D according to Example 5. Note that the same components as those of the optical modulator 5 according to Example 1 are denoted by the same reference numerals, and redundant descriptions of the configurations and operations will be omitted.

[0076] The optical modulator 5D shown in FIG. 8 has a configuration in which a driver 21 is electrically connected to the optical modulator 5 shown in FIG. 2. The driver 21 shown in FIG. 8 is connected to the first signal electrode 16A1 on the outgoing path and the second signal electrode 16B1 on the outgoing path in the optical modulator 5 shown in FIG. 2 by Au wires. Furthermore, the driver 21 is connected to the first ground electrode 15A1 on the outgoing path and the second ground electrode 15B1 and the third ground electrode 15C on the outgoing path by Au wires. The driver 21 amplifies the electrical signal and applies the amplified electrical signal to the first signal electrode 16A and the second signal electrode 16B. The driver 21 is electrically connected to a location near one side of the chip of the optical modulator 5D by an Au wire.

[0077] In the optical modulator 5D of the fifth embodiment, an Au wire is electrically connected to the vicinity of one side of the chip, so that efficient connection can be achieved over a short distance. [Example]

[0078] 9 is a schematic plan view showing an example of the configuration of an optical modulator 5E according to Example 6. Note that the same components as those of the optical modulator 5C according to Example 4 are denoted by the same reference numerals, and redundant descriptions of the configurations and operations will be omitted.

[0079] The optical modulator 5E shown in FIG. 9 has a configuration in which a driver 21 is electrically connected to the optical modulator 5C shown in FIG. 6. The driver 21 shown in FIG. 9 is connected to the first signal electrode 16A4 on the second outgoing path side and the second signal electrode 16B4 on the second outgoing path side in the optical modulator 5C shown in FIG. 7 by Au wires. The driver 21 is connected to the fourth ground electrode 15D2 on the return path side and the fifth ground electrode 15E2 on the return path side by Au wires. The driver 21 amplifies the electrical signal and applies the amplified electrical signal to the first signal electrode 16A and the second signal electrode 16B. The driver 21 is electrically connected to a location near one side of the chip of the optical modulator 5E by an Au wire.

[0080] The driver 21 electrically connects the first signal electrode 16A4 on the second outgoing path side, the second signal electrode 16B4 on the second outgoing path side, the fourth ground electrode 15D2 on the homeward path side, and the fifth ground electrode 15E2 on the homeward path side at an angle so that the first optical waveguide 14A and the second optical waveguide 14B are not parallel to each other. As a result, the oblique portions of the first signal electrode 16A4 on the second outgoing path side, the second signal electrode 16B4 on the second outgoing path side, the fourth ground electrode 15D2 on the homeward path side, and the fifth ground electrode 15E2 on the homeward path side do not function as an interaction portion.

[0081] In the optical modulator 5E of the sixth embodiment, an Au wire is used for electrical connection near one side of the chip, so that efficient connection can be achieved over a short distance. [Explanation of symbols]

[0082] 1 Optical communication equipment 3 DSP 4 light source 5, 5A, 5B, 5C Optical Modulator 13 Thin-film LN substrate 14A First Optical Waveguide 14A1 First optical waveguide on the outgoing path 14A2 First optical waveguide on the return path side 14B Second optical waveguide 14B1 Second optical waveguide on the outgoing path 14B2 Second optical waveguide on the return path side 15A First Ground Electrode 15A1 First ground electrode on the outgoing path 15A2 First earth electrode on the return path 15B Second ground electrode 15B1 Second ground electrode on the outgoing path 15B2 Second earth electrode on the return path 15C Third ground electrode 16A First signal electrode 16A1 First signal electrode on the outgoing path 16A2 First signal electrode on the return path 16B Second signal electrode 16B1 Second signal electrode on the outgoing path 16B2 Second signal electrode on the return path

Claims

1. X-cut board and a first optical waveguide and a second optical waveguide each having a folded structure formed on the substrate; a first signal electrode disposed on the substrate and generating a first electric field; a first ground electrode disposed on the substrate and arranged in parallel with the first signal electrode; a second ground electrode disposed on the substrate and arranged in parallel between the first signal electrode and the first optical waveguide; a second signal electrode disposed on the substrate and generating a second electric field in opposite phase to the first electric field; a third ground electrode disposed on the substrate and arranged in parallel with the second optical waveguide; and The first optical waveguide is a first optical waveguide on an outgoing path side to which the second electric field is applied from the second signal electrode to the second ground electrode; a first optical waveguide on a return path side to which the first electric field is applied from the first ground electrode to the first signal electrode, The second optical waveguide is a second optical waveguide on an outgoing path side to which the second electric field is applied from the second signal electrode to the third ground electrode; a second optical waveguide on the return path side to which the first electric field is applied from the second ground electrode to the first signal electrode.

2. a direction of the second electric field applied to the first optical waveguide on the outgoing path side is the same as a direction of the first electric field applied to the first optical waveguide on the return path side; 2. The optical device according to claim 1, wherein a direction of the second electric field applied to the second optical waveguide on the outgoing path side is the same as a direction of the first electric field applied to the second optical waveguide on the return path side.

3. 3. The optical device according to claim 1, wherein a crystal orientation of the substrate, a direction of the second electric field applied to the first optical waveguide on the outgoing path, and a direction of the first electric field applied to the first optical waveguide on the return path are the same.

4. the first ground electrode having a folded structure and including a first ground electrode on a forward path side and a first ground electrode on a return path side, the second ground electrode having a folded structure and including a second ground electrode on a forward path side and a second ground electrode on a return path side, and the third ground electrode are arranged in parallel on the substrate; the first signal electrode having a folded structure, which has a first signal electrode on a forward path side and a first signal electrode on a backward path side, and the second signal electrode having a folded structure, which has a second signal electrode on a forward path side and a second signal electrode on a backward path side, are arranged in parallel on the substrate; The first optical waveguide on the outgoing path side is disposed between the outgoing side second ground electrode and the outgoing side second signal electrode, The second optical waveguide on the outgoing path side is disposed between the second signal electrode on the outgoing path side and the third ground electrode, The first optical waveguide on the return path side is disposed between the first ground electrode on the return path side and the first signal electrode on the return path side; The second optical waveguide on the return path side is 4. The optical device according to claim 1, wherein the first signal electrode is disposed between the first signal electrode on the return path side and the second ground electrode on the return path side.

5. X-cut board and a first optical waveguide and a second optical waveguide each having a folded structure formed on the substrate; a first signal electrode disposed on the substrate and generating a first electric field; a first ground electrode disposed on the substrate and arranged in parallel with the first signal electrode; a second signal electrode disposed on the substrate and generating a second electric field in opposite phase to the first electric field; a third ground electrode disposed on the substrate and arranged in parallel with the second optical waveguide; and The first optical waveguide is a first optical waveguide on an outgoing path side to which the second electric field is applied from the second signal electrode to the first ground electrode; a first optical waveguide on a return path side to which the first electric field is applied from the first ground electrode to the first signal electrode, The second optical waveguide is a second optical waveguide on an outgoing path side to which the second electric field is applied from the second signal electrode to the third ground electrode; a second optical waveguide on a return path side to which the first electric field is applied from the third ground electrode to the first signal electrode, the first ground electrode having a folded structure, which has a first ground electrode on a forward path side and a first ground electrode on a return path side, and the third ground electrode are arranged in parallel on the substrate; the first signal electrode having a folded structure, which has a first signal electrode on a forward path side and a first signal electrode on a backward path side, and the second signal electrode having a folded structure, which has a second signal electrode on a forward path side and a second signal electrode on a backward path side, are arranged in parallel on the substrate; The first optical waveguide on the outgoing path side is disposed between the first signal electrode on the outgoing path side and the second signal electrode on the outgoing path side; The second optical waveguide on the outgoing path side is disposed between the second signal electrode on the outgoing path side and the third ground electrode, The first optical waveguide on the return path side is disposed between the first ground electrode on the return path side and the first signal electrode on the return path side; The second optical waveguide on the return path side is An optical device, characterized in that it is disposed between the first signal electrode on the return path side and the second signal electrode on the return path side.

6. The first optical waveguide is a first optical waveguide on the outgoing path side, a first optical waveguide on the returning path side, and an intermediate first optical waveguide connecting the first optical waveguide on the outgoing path side and the first optical waveguide on the returning path side; The second optical waveguide is a second optical waveguide on the outgoing path side, a second optical waveguide on the returning path side, and an intermediate second optical waveguide connecting the second optical waveguide on the outgoing path side and the second optical waveguide on the returning path side; 5. The optical device according to claim 1, wherein the optical waveguide length of the intermediate first optical waveguide and the optical waveguide length of the intermediate second optical waveguide are adjusted to make the optical waveguide length of the first optical waveguide and the optical waveguide length of the second optical waveguide the same.

7. X-cut board and a first optical waveguide and a second optical waveguide each having a folded structure formed on the substrate; a fourth ground electrode having a folded structure, the fourth ground electrode being disposed on the substrate and including a fourth ground electrode on a forward path side and a fourth ground electrode on a backward path side; a fifth ground electrode having a folded structure, the fifth ground electrode having a forward path side fifth ground electrode and a backward path side fifth ground electrode arranged on the substrate in parallel with the fourth ground electrode; a first signal electrode having a folded structure at two locations and disposed on the substrate, the first signal electrode generating a first electric field; a second signal electrode having a folded structure at two locations, the second signal electrode being arranged on the substrate in parallel with the first signal electrode and generating a second electric field having a phase opposite to that of the first electric field; and The first optical waveguide is a first outgoing path first optical waveguide, a second outgoing path first optical waveguide, and a return path first optical waveguide connecting the first outgoing path first optical waveguide and the second outgoing path first optical waveguide; The second optical waveguide is a first outgoing second optical waveguide, a second outgoing second optical waveguide, and a return second optical waveguide connecting the first outgoing second optical waveguide and the second outgoing second optical waveguide; The first signal electrode is a first outgoing path first signal electrode, a second outgoing path first signal electrode, and a return path first signal electrode connecting the first outgoing path first signal electrode and the second outgoing path first signal electrode; The second signal electrode is a first outgoing path second signal electrode, a second outgoing path second signal electrode, and a return path second signal electrode connecting the first outgoing path second signal electrode and the second outgoing path second signal electrode; The first outgoing path first optical waveguide includes: a fourth ground electrode disposed between the first signal electrode on the first outgoing path side and the second signal electrode on the first outgoing path side, and the two electric fields are applied from the second signal electrode on the first outgoing path side to the fourth ground electrode on the outgoing path side; The second optical waveguide on the first outgoing path side is a second signal electrode disposed between the first outgoing path side second signal electrode and the outgoing path side fifth ground electrode, and the second electric field is applied from the first outgoing path side second signal electrode to the outgoing path side fifth ground electrode; The first optical waveguide on the return path side is a fourth ground electrode on the return path side and a first signal electrode on the return path side, the first electric field being applied from the fourth ground electrode on the return path side to the first signal electrode on the return path side; The second optical waveguide on the return path side is a fifth ground electrode disposed between the first signal electrode on the return path side and the second signal electrode on the return path side, and the first electric field is applied from the fifth ground electrode on the forward path side to the first signal electrode on the return path side; The first optical waveguide on the second outgoing path side is a fourth ground electrode disposed between the first signal electrode on the second outgoing path side and the second signal electrode on the second outgoing path side, and the second electric field is applied from the second signal electrode on the second outgoing path side to the fourth ground electrode on the return path side; The second outgoing path second optical waveguide includes: a second signal electrode disposed between the second outgoing path side and the fifth ground electrode on the return path side, and the second electric field is applied from the second signal electrode on the second outgoing path side to the fifth ground electrode on the return path side; The optical waveguide length of the first optical waveguide on the return path side is The length of the first optical waveguide in the region where an electric field is applied is longer than the length of the first optical waveguide in the region where an electric field is applied in the first outgoing path side or the length of the first optical waveguide in the region where an electric field is applied in the second outgoing path side, The optical waveguide length of the second optical waveguide on the return path side is an optical waveguide length in a region where an electric field is applied in the second optical waveguide on the first outgoing path side, the optical waveguide length being longer than an optical waveguide length in a region where an electric field is applied in the second optical waveguide on the second outgoing path side.

8. 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 X-cut board and a first optical waveguide and a second optical waveguide each having a folded structure formed on the substrate; a first signal electrode disposed on the substrate and generating a first electric field; a first ground electrode disposed on the substrate and arranged in parallel with the first signal electrode; a second ground electrode disposed on the substrate and arranged in parallel between the first signal electrode and the first optical waveguide; a second signal electrode disposed on the substrate and generating a second electric field in opposite phase to the first electric field; a third ground electrode disposed on the substrate and arranged in parallel with the second optical waveguide; The first optical waveguide is a first optical waveguide on an outgoing path side to which the second electric field is applied from the second signal electrode to the second ground electrode; a first optical waveguide on a return path side to which the first electric field is applied from the first ground electrode to the first signal electrode, The second optical waveguide is a second optical waveguide on an outgoing path side to which the second electric field is applied from the second signal electrode to the third ground electrode; a second optical waveguide on the return path side to which the first electric field is applied from the second ground electrode to the first signal electrode.

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