Optical devices and optical communication equipment

Abstract

The present application relates to an optical device and an optical communication device. An optical device includes an X-cut substrate and a first optical waveguide and a second optical waveguide each formed on the substrate and having a folded structure. The optical device includes a first signal electrode that generates a first electric field and a second signal electrode that generates a second electric field that is opposite in phase to the first electric field. The first optical waveguide includes a first optical waveguide on the outer side to which a first electric field is applied from the first signal electrode; and a first optical waveguide on the return side to which a second electric field is applied from the second signal electrode. The second optical waveguide includes a second optical waveguide on the outer side to which a first electric field is applied from the first signal electrode; and a second optical waveguide on the return side to which a second electric field is applied from the second signal electrode.

Description

Technical Field

[0001] The embodiments discussed herein relate to optical devices and optical communication equipment. Background Art

[0002] For example, an optical device such as an optical modulator is constructed so that a signal electrode is arranged on an optical waveguide on its surface, and if a voltage is applied to the signal electrode, an electric field whose direction is perpendicular to the surface of the optical modulator is generated inside the optical waveguide. The refractive index of the optical waveguide changes due to the electric field, and the phase of the light propagating through the optical waveguide is changed, so that the light can be modulated. In other words, the optical waveguide of the optical modulator constitutes, for example, a Mach-Zehnder interferometer, and is capable of outputting, for example, an IQ signal that is x-polarized and y-polarized due to the phase difference of light between a plurality of optical waveguides arranged in parallel.

[0003] Fig.10 is a schematic plan view illustrating a configuration example of the optical modulator 100, and Fig.11 is along Fig.10 A schematic cross-sectional view of a portion taken along line CC of FIG. Fig.10 and Fig.11 The optical modulator 100 shown includes a substrate 101, an intermediate layer 102 stacked on the substrate 101, and a thin film LN substrate 103 stacked on the intermediate layer 102 and made of a LN (LiNbO3) material. In addition, the optical modulator 100 includes two optical waveguides, that is, an eleventh optical waveguide 104A and a twelfth optical waveguide 104B formed by the thin film LN substrate 103, and includes an eleventh ground electrode 105A and a twelfth ground electrode 105B formed as a pair on the thin film LN substrate 103. In addition, the optical modulator 100 includes an eleventh signal electrode 106 arranged to be sandwiched between the pair of the eleventh ground electrode 105A and the twelfth ground electrode 105B on the thin film LN substrate 103.

[0004] The substrate 101 is, for example, a substrate made of a specific material such as Si or LN. The intermediate layer 102 is, for example, a layer made of SiO2 having a lower refractive index than LN. The thin film LN substrate 103 is a thin film substrate capable of confining high-intensity light and is advantageous in reducing the size of the device.

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

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

[0007] The crystal direction of the thin film LN substrate 103 is the width direction (Z direction) perpendicular to the traveling direction (Y direction). The optical refractive index of the eleventh optical waveguide 104A changes according to the electric field in the electric field direction a101 from the eleventh ground electrode 105A to the eleventh signal electrode 106. In addition, the optical refractive index of the twelfth optical waveguide 104B changes according to the electric field in the electric field direction b101 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 portion such as the eleventh optical waveguide 104A and the twelfth optical waveguide 104B to which the electric field is applied, and a structure is required in which the interaction portion is folded to reduce the device size while maintaining the modulation efficiency.

[0009] Fig.12 is a schematic plan view illustrating an example of the configuration of an optical modulator 100A having a folded structure, and Fig.13 is along Fig.12 An exemplary schematic cross-sectional view of a portion taken along line DD in FIG. Fig.10 and Fig.11 The same components of the optical modulator 100 shown in FIG. 1 are denoted by the same reference numerals, and description of the same configuration and operation will be omitted. Fig.12 The optical modulator 100A shown has a folded structure in which the eleventh optical waveguide 104A, the twelfth optical waveguide 104B, the eleventh ground electrode 105A, the twelfth ground electrode 105B, and the eleventh signal electrode 106 are folded. The optical modulator 100A includes an interaction portion 110A on the outward side and an interaction portion 110B on the return side.

[0010] The eleventh optical waveguide 104A includes an eleventh optical waveguide 104A1 on the outer side and an eleventh optical waveguide 104A2 on the return side. The twelfth optical waveguide 104B includes a twelfth optical waveguide 104B1 on the outer side and a twelfth optical waveguide 104B2 on the return side. The eleventh ground electrode 105A includes an eleventh ground electrode 105A1 on the outer side and an eleventh ground electrode 105A2 on the return side. The twelfth ground electrode 105B includes a twelfth ground electrode 105B1 on the outer side and a twelfth ground electrode 105B2 on the return side. The eleventh signal electrode includes an eleventh signal electrode 106A1 on the outer side and an eleventh signal electrode 106A2 on the return side.

[0011] The interaction portion 110A on the outer side includes an eleventh ground electrode 105A1 on the outer side, an eleventh signal electrode 106A1 on the outer side, an eleventh optical waveguide 104A1 on the outer side, a twelfth optical waveguide 104B1 on the outer side, and a twelfth ground electrode 105B1 on the outer side. The eleventh optical waveguide 104A1 on the outer side is arranged between the eleventh ground electrode 105A1 on the outer side and the eleventh signal electrode 106A1 on the outer side. The twelfth optical waveguide 104B1 on the outer side is arranged between the twelfth ground electrode 105B1 on the outer side and the eleventh signal electrode 106A1 on the outer side.

[0012] The crystal direction of the thin film LN substrate 103 is the width direction (Z direction) perpendicular to the traveling direction (Y direction). The light refractive index of the eleventh optical waveguide 104A1 on the outer side changes according to the electric field in the electric field direction a101 from the eleventh ground electrode 105A1 on the outer side to the eleventh signal electrode 106A1 on the outer side. In addition, the light refractive index of the twelfth optical waveguide 104B1 on the outer side changes according to the electric field in the electric field direction b101 from the twelfth ground electrode 105B1 on the outer side to the eleventh signal electrode 106A1 on the outer side.

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

[0014] The light refractive index of the eleventh optical waveguide 104A2 on the return side changes according to the electric field in the electric field direction a102 from the eleventh ground electrode 105A2 on the return side to the eleventh signal electrode 106A2 on the return side. In addition, the light refractive index of the twelfth optical waveguide 104B2 on the return side changes according to the electric field in the electric field direction b102 from the twelfth ground electrode 105B2 on the return side to the eleventh signal electrode 106A2 on the return side.

[0015] Patent Document 1: International Publication No. WO2007 / 058366

[0016] Patent Document 2: Specification of U.S. Patent No. 7,212,326

[0017] Patent Document 3: Japanese Unexamined Patent Publication No. 2005-221874

[0018] However, in the optical modulator 100A having a folded structure, the electric field direction a102 of the eleventh optical waveguide 104A2 on the return side is the same as the crystal direction (Z direction) of the LN crystal, but the electric field direction a101 of the eleventh optical waveguide 104A1 on the outside is different from the crystal direction (Z direction) of the LN crystal. In addition, the electric field direction a101 of the eleventh optical waveguide 104A1 on the outside is opposite to the electric field direction a102 of the eleventh optical waveguide 104A2 on the return side. Therefore, the electric field in the electric field direction a101 of the eleventh optical waveguide 104A1 on the outside is offset by the electric field in the electric field direction a102 of the eleventh optical waveguide 104A2 on the return side, so that the modulation efficiency is reduced.

[0019] Similarly, the electric field direction b101 of the twelfth optical waveguide 104B1 on the outside is the same as the crystal direction (Z direction) of the LN crystal, but the electric field direction b102 of the twelfth optical waveguide 104B2 on the return side is different from the crystal direction (Z direction) of the LN crystal. In addition, the electric field direction b101 of the twelfth optical waveguide 104B1 on the outside is opposite to the electric field direction b102 of the twelfth optical waveguide 104B2 on the return side. Therefore, the electric field in the electric field direction b101 of the twelfth optical waveguide 104B1 on the outside is offset by the electric field in the electric field direction b102 of the twelfth optical waveguide 104B2 on the return side, so that the modulation efficiency is reduced.

[0020] In the optical modulator 100A which is a single-end driven X-cut LN modulator using a single signal electrode, the crystal axis is reversed between the outward path and the return path with respect to the propagation direction (Y direction). As a result, phase changes in opposite directions occur, so that the phase change on the outward side is offset by the phase change on the return side, so that the modulation efficiency is reduced.

[0021] In addition, a method of changing the horizontal position relationship between the outward path and the return path of the optical waveguide in the traveling direction may be adopted, but the cross waveguide used to switch between the optical waveguides and the reflective structure using an external reflector cause reflection, attenuation, etc. of the optical signal.

[0022] Therefore, an object of one aspect of an embodiment of the present invention is to provide an optical device or the like that improves modulation efficiency. Summary of the invention

[0023] According to one aspect of the embodiment, an optical device includes: an X-cut substrate, a first optical waveguide, a second optical waveguide, a first signal electrode, and a second signal electrode. The first optical waveguide and the second optical waveguide are formed on the substrate and have a folded structure. The first signal electrode is arranged on the substrate and generates a first electric field. The second signal electrode is arranged on the substrate and generates a second electric field with a phase opposite to that of the first electric field. The first optical waveguide includes a first optical waveguide on the outer side to which a first electric field is applied from the first signal electrode; and a first optical waveguide on the return side to which a second electric field is applied from the second signal electrode. The second optical waveguide includes a second optical waveguide on the outer side to which a first electric field is applied from the first signal electrode; and a second optical waveguide on the return side to which a second electric field is applied from the second signal electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a block diagram illustrating a configuration example of an optical communication device according to an embodiment;

[0025] Figure 2 is a schematic plan view illustrating a configuration example of an optical modulator according to a first embodiment;

[0026] Figure 3 is along Figure 2 An exemplary schematic cross-sectional view of a portion taken along line AA in FIG.

[0027] Figure 4 is a schematic plan view illustrating a configuration example of an optical modulator according to a second embodiment;

[0028] Figure 5 is along Figure 4 An exemplary schematic cross-sectional view of a portion taken along line BB in FIG.

[0029] Figure 6 is a schematic plan view illustrating a configuration example of an optical modulator according to a third embodiment;

[0030] Figure 7 is a schematic plan view illustrating a configuration example of an optical modulator according to a fourth embodiment;

[0031] Figure 8 is a schematic plan view illustrating a configuration example of an optical modulator according to a fifth embodiment;

[0032] Fig. 9 is a schematic plan view illustrating a configuration example of an optical modulator according to a sixth embodiment;

[0033] Fig.10 is a schematic plan view illustrating a configuration example of a light modulator;

[0034] Fig.11 is along Fig.10 An exemplary schematic cross-sectional view of a portion taken along line CC in FIG.

[0035] Fig.12 is a schematic plan view illustrating a configuration example of an optical modulator having a folded structure; and

[0036] Fig.13 is along Fig.12 An exemplary schematic cross-sectional view of a portion taken along line DD in FIG. DETAILED DESCRIPTION

[0037] Preferred embodiments of the present invention will be described with reference to the accompanying drawings. The present invention is not limited to the following embodiments.

[0038] [a] First Embodiment

[0039] Figure 1 is a block diagram illustrating a configuration example of an optical communication device 1 according to one embodiment. Figure 1 The optical communication device 1 shown 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 digital signal processor (DSP) 3, a light source 4, an optical modulator 5, and an optical receiver 6. The DSP 3 is an electronic component that performs digital signal processing. For example, the DSP 3 performs processing such as encoding on transmission data, generates an electrical signal including the transmission data, and outputs the generated electrical signal to the optical modulator 5. In addition, the DSP 3 acquires an electrical signal including reception data from the optical receiver 6, performs processing such as decoding on the acquired electrical signal, and obtains reception data.

[0040] The light source 4 is, for example, a laser diode, etc., generates light of a predetermined wavelength, and supplies the light 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 using the electrical signal output from the DSP 3 and outputs an optical transmission signal obtained to the optical fiber 2A. For example, the optical modulator 5 is an optical device such as a lithium niobate (LN) optical modulator including an optical waveguide made of LN and a signal electrode having a coplanar waveguide (CPW) structure.

[0041] The optical receiver 6 receives the optical signal from the optical fiber 2B, and demodulates the received optical signal using the light supplied from the light source 4. Furthermore, the optical receiver 6 converts the demodulated received optical signal into an electrical signal, and outputs the converted electrical signal to the DSP 3.

[0042] Figure 2 is a schematic plan view illustrating a configuration example of the optical modulator 5 according to the first embodiment, and Figure 3 is along Figure 2 An exemplary schematic cross-sectional view of a portion taken along line AA in FIG. Figure 2 and Figure 3 The optical modulator 5 shown includes a substrate 11, an intermediate layer 12 stacked on the substrate 11, and a thin film LN substrate 13 stacked on the intermediate layer 12 and made of a LN (LiNbO3) material. In addition, the optical modulator 5 includes a first optical waveguide 14A and a second optical waveguide 14B each formed by the thin film LN substrate 13 and each having a folded structure folded in two, and includes a first ground electrode 15A, a second ground electrode 15B, and a third ground electrode 15C formed on the thin film LN substrate 13. In addition, the optical modulator 5 includes a first signal electrode 16A and a second signal electrode 16B formed on the thin film LN substrate 13.

[0043] The substrate 11 is a substrate made of a specific material such as silicon dioxide (SiO2), titanium dioxide (TiO2), Si or LN. The intermediate layer 12 is a layer made of SiO2 or TiO2 having a low light refractive index compared to LN. The thin film LN substrate 13 is a substrate using a thin film of LN crystal, and includes a predetermined portion formed with a first optical waveguide 14A and a second optical waveguide 14B having a protruding shape protruding upward. By using the LN material, high-intensity light can be confined, and there is an advantage in reducing the size of the device. The thin film LN substrate 13 is an X-cut substrate.

[0044] For example, the first optical waveguide 14A and the second optical waveguide 14B are formed of the thin film LN substrate 13 and are made of LN material, and therefore have excellent characteristics in terms of insertion loss and transmission characteristics. The optical modulator 5 can perform chirp-free operation due to the symmetry of the structure and is suitable for long-distance transmission. For example, the first signal electrode 16A and the second signal electrode 16B are electrodes made of a metal material such as gold or copper. For example, 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.

[0045] The first signal electrode 16A is arranged 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 arranged 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 is an electric field in an electric field direction of an opposite phase to the electric field direction of the first electric field.

[0046] The optical modulator 5 has a folded structure in which each of 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 is folded into an outward path and a return path. The optical modulator 5 includes a first interaction portion 20A on the outward side, a second interaction portion 20B on the return side, and an intermediate portion 20C connecting the first interaction portion 20A on the outward side and the second interaction portion 20B on the return side.

[0047] The first optical waveguide 14A having a folded structure includes a first optical waveguide 14A1 on the outer side, a first optical waveguide 14A2 on the return side, and a first optical waveguide 14A3 located on the middle side and connecting the first optical waveguide 14A1 on the outer side and the first optical waveguide 14A2 on the return side. The second optical waveguide 14B having a folded structure includes a second optical waveguide 14B1 on the outer side, a second optical waveguide 14B2 on the return side, and a second optical waveguide 14B3 located on the middle side and connecting the second optical waveguide 14B1 on the outer side and the second optical waveguide 14B2 on the return side.

[0048] The first ground electrode 15A having a folded structure includes a first ground electrode 15A1 on the outer side, a first ground electrode 15A2 on the return side, and a first ground electrode 15A3 located on the middle side and connected to the first ground electrode 15A1 on the outer side and the first ground electrode 15A2 on the return side. The second ground electrode 15B having a folded structure includes a second ground electrode 15B1 on the outer side, a second ground electrode 15B2 on the return side, and a second ground electrode 15B3 located on the middle side and connected to the second ground electrode 15B1 on the outer side and the second ground electrode 15B2 on the return side.

[0049] First signal electrode 16A having a folded structure includes first signal electrode 16A1 on the outer side, first signal electrode 16A2 on the return side, and first signal electrode 16A3 located on the middle side and connected to first signal electrode 16A1 on the outer side and first signal electrode 16A2 on the return side. Second signal electrode 16B having a folded structure includes second signal electrode 16B1 on the outer side, second signal electrode 16B2 on the return side, and second signal electrode 16B3 located on the middle side and connected to second signal electrode 16B1 on the outer side and second signal electrode 16B2 on the return side.

[0050] The first interaction portion 20A on the outer side includes a first ground electrode 15A1 on the outer side, a first optical waveguide 14A1 on the outer side, a first signal electrode 16A1 on the outer side, a second ground electrode 15B1 on the outer side, a second optical waveguide 14B1 on the outer side, and a third ground electrode 15C. The first optical waveguide 14A1 on the outer side is arranged between the second ground electrode 15B1 on the outer side and the second signal electrode 16B1 on the outer side. The second optical waveguide 14B1 on the outer side is arranged between the third ground electrode 15C and the second signal electrode 16B1 on the outer side.

[0051] The crystal direction of the thin film LN substrate 13 is the width direction (Z direction) perpendicular to the traveling direction (Y direction). The light refractive index of the first optical waveguide 14A1 on the outer side changes according to the electric field in the electric field direction a11 from the second signal electrode 16B1 on the outer side to the second ground electrode 15B1 on the outer side. In addition, the light refractive index of the second optical waveguide 14B1 on the outer side changes according to the electric field in the electric field direction b11 from the second signal electrode 16B1 on the outer side to the third ground electrode 15C.

[0052] The middle portion 20C includes a first ground electrode 15A3 on the middle side, a first signal electrode 16A3 on the middle side, a second ground electrode 15B3 on the middle side, a first optical waveguide 14A3 on the middle side, and a second optical waveguide 14B3 on the middle side. In addition, the middle portion 20C includes a second signal electrode 16B3 and a third ground electrode 15C on the middle side.

[0053] The second interaction part 20B on the return side includes a first ground electrode 15A2 on the return side, a first optical waveguide 14A2 on the return side, a first signal electrode 16A2 on the return side, a second optical waveguide 14B2 on the return side, and a second ground electrode 15B2 on the return side. In addition, the second interaction part 20B on the return side includes a second signal electrode 16B2 on the return side and a third ground electrode 15C. The first optical waveguide 14A2 on the return side is arranged between the first ground electrode 15A2 on the return side and the first signal electrode 16A2 on the return side. The second optical waveguide 14B2 on the return side is arranged between the second ground electrode 15B2 on the return side and the first signal electrode 16A2 on the return side.

[0054] The light refractive index of the first optical waveguide 14A2 on the return side changes according to the electric field in the electric field direction a12 from the first ground electrode 15A2 on the return side to the first signal electrode 16A2 on the return side. In addition, the light refractive index of the second optical waveguide 14B2 on the return side changes according to the electric field in the electric field direction b12 from the second ground electrode 15B2 on the return side to the first signal electrode 16A2 on the return side.

[0055] In other words, in the first optical waveguide 14A, the electric field direction a11 of the electric field applied to the first optical waveguide 14A1 on the outer side and the electric field direction a12 of the electric field applied to the first optical waveguide 14A2 on the return side are identical to 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 second optical waveguide 14B1 on the outer side and the electric field direction b12 of the electric field applied to the second optical waveguide 14B2 on the return side are identical to the crystal direction of the thin film LN substrate 13.

[0056] In the optical modulator 5 of the first embodiment, the first optical waveguide 14A1 on the outer side is arranged between the second ground electrode 15B1 on the outer side and the second signal electrode 16B1 on the outer side, and the second optical waveguide 14B1 on the outer side is arranged between the second signal electrode 16B1 on the outer side and the third ground electrode 15C. In addition, in the optical modulator 5, the first optical waveguide 14A2 on the return side is arranged between the first ground electrode 15A2 on the return side and the first signal electrode 16A2 on the return side, and the second optical waveguide 14B2 on the return side is arranged between the first signal electrode 16A2 on the return side and the second ground electrode 15B2 on the return side. As a result, in the first optical waveguide 14A, the electric field direction a11 of the electric field applied to the first optical waveguide 14A1 on the outer side and the electric field direction a12 of the electric field applied to the first optical waveguide 14A2 on the return side are the same, so that the modulation efficiency is improved. Similarly, in the second optical waveguide 14B, the electric field direction b11 of the electric field applied to the second optical waveguide 14B1 on the outer side and the electric field direction b12 of the electric field applied to the second optical waveguide 14B2 on the return side are the same, so that the modulation efficiency is improved.

[0057] In addition, with respect to the crystallographic direction of the X-cut substrate, the direction a11 of the first electric field applied to the first optical waveguide 14A1 on the outward side and the direction a12 of the second electric field applied to the first optical waveguide 14A2 on the return side are the same. As a result, the orientation of the electric field applied from the signal electrode to the corresponding optical waveguide is the same between the folded paths (i.e., between the outward path and the return path) with respect to the Z-axis of the LN crystal, making it possible to maintain the modulation efficiency and reduce the device size by reducing the length of the interaction portion. In addition, reflection, attenuation, etc. of the optical signal in the folded portion can be prevented without the intersection of the optical waveguides and the reflection structure using an external reflector.

[0058] On the outward path, the first optical waveguide 14A is located on the positive Z side, and the second optical waveguide 14B is located on the negative Z side, relative to the Z-axis direction of the LN crystal Z. On the return path, the first optical waveguide 14A is located on the negative Z side, and the second optical waveguide 14B is located on the positive Z side. Therefore, the Z-axis direction of the LN crystal and the orientation of the electric field applied in the direction from the single signal electrode to the ground electrode do not change between the outward path and the return path. As a result, the direction of the electric field applied from the signal electrode to the corresponding optical waveguide is the same direction between the outward path and the return path, relative to the Z-axis of the LN crystal, so that the length of the interaction portion can be reduced while maintaining the modulation efficiency.

[0059] [b] Second Embodiment

[0060] Figure 4 is a schematic plan view illustrating a configuration example of an optical modulator 5A according to the second embodiment, and Figure 5 is along Figure 4 2 is an exemplary schematic cross-sectional view of a portion taken along line BB in FIG. In addition, the same components as those of the optical modulator 5 of the first embodiment are denoted by the same reference numerals, and description of the same configuration and operation will be omitted.

[0061] Figure 4 and Figure 5 The optical modulator 5A illustrated in the second embodiment includes a substrate 11, an intermediate layer 12, a thin film LN substrate 13, and two optical waveguides, namely, a first optical waveguide 14A and a second optical waveguide 14B. In addition, the optical modulator 5A 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. In addition, the optical modulator 5A of the second embodiment is different from the optical modulator 5 of the first embodiment in that the second ground electrode 15B is not arranged between the first signal electrode 16A and the second signal electrode 16B.

[0062] The optical modulator 5A includes a first interaction portion 20A1 on the outer side, a second interaction portion 20B1 on the return side, and an intermediate portion 20C1 connecting the first interaction portion 20A1 on the outer side and the second interaction portion 20B1 on the return side. The first interaction portion 20A1 on the outer side includes a first ground electrode 15A1 on the outer side, a first signal electrode 16A1 on the outer side, a first optical waveguide 14A1 on the outer side, a second signal electrode 16B1 on the outer side, a second optical waveguide 14B1 on the outer side, and a third ground electrode 15C. The first optical waveguide 14A1 on the outer side is arranged between the first signal electrode 16A1 on the outer side and the second signal electrode 16B1 on the outer side. The second optical waveguide 14B1 on the outer side is arranged between the third ground electrode 15C and the second signal electrode 16B1 on the outer side.

[0063] The crystal direction of the thin film LN substrate 13 is the width direction (Z direction) perpendicular to the traveling direction (Y direction). The light refractive index of the first optical waveguide 14A1 on the outer side changes according to the electric field in the electric field direction a21 from the second signal electrode 16B1 on the outer side to the first signal electrode 16A1 on the outer side. In addition, the light refractive index of the second optical waveguide 14B1 on the outer side changes according to the electric field in the electric field direction b21 from the second signal electrode 16B1 on the outer side to the third ground electrode 15C.

[0064] The middle portion 20C1 includes a first ground electrode 15A3 on the middle side, a first signal electrode 16A3 on the middle side, a first optical waveguide 14A3 on the middle side, a second optical waveguide 14B3 on the middle side, a second signal electrode 16B3 on the middle side, and a third ground electrode 15C.

[0065] The second interaction part 20B1 on the return side includes a first ground electrode 15A2 on the return side, a first optical waveguide 14A2 on the return side, a first signal electrode 16A2 on the return side, a second optical waveguide 14B2 on the return side, a second signal electrode 16B2 on the return side, and a third ground electrode 15C. The first optical waveguide 14A2 on the return side is arranged between the first ground electrode 15A2 on the return side and the first signal electrode 16A2 on the return side. The second optical waveguide 14B2 on the return side is arranged between the second signal electrode 16B2 on the return side and the first signal electrode 16A2 on the return side.

[0066] The light refractive index of the first optical waveguide 14A2 on the return side changes according to the electric field in the electric field direction a22 from the first signal electrode 16A2 on the return side to the first ground electrode 15A2 on the return side. In addition, the light refractive index of the second optical waveguide 14B2 on the return side changes according to the electric field in the electric field direction b22 from the second signal electrode 16B2 on the return side to the first signal electrode 16A2 on the return side.

[0067] In other words, in the first optical waveguide 14A, the electric field direction a21 of the electric field applied to the first optical waveguide 14A1 on the outer side and the electric field direction a22 of the electric field applied to the first optical waveguide 14A2 on the return side are identical to the crystal direction of the thin film LN substrate 13. Furthermore, in the second optical waveguide 14B, the electric field direction b21 of the electric field applied to the second optical waveguide 14B1 on the outer side and the electric field direction b22 of the electric field applied to the second optical waveguide 14B2 on the return side are identical to the crystal direction of the thin film LN substrate 13.

[0068] In the optical modulator 5A of the second embodiment, the first optical waveguide 14A1 on the outer side is arranged between the first signal electrode 16A1 on the outer side and the second signal electrode 16B1 on the outer side, and the second optical waveguide 14B1 on the outer side is arranged between the second signal electrode 16B1 on the outer side and the third ground electrode 15C. In addition, in the optical modulator 5A, the first optical waveguide 14A2 on the return side is arranged between the first ground electrode 15A2 on the return side and the first signal electrode 16A2 on the return side, and the second optical waveguide 14B2 on the return side is arranged between the first signal electrode 16A2 on the return side and the second signal electrode 16B2 on the return side. As a result, in the first optical waveguide 14A, the electric field direction a21 of the electric field applied to the first optical waveguide 14A1 on the outer side and the electric field direction a22 of the electric field applied to the first optical waveguide 14A2 on the return side are the same, so that the modulation efficiency is improved. Similarly, in the second optical waveguide 14B, the electric field direction b21 of the electric field applied to the second optical waveguide 14B1 on the outer side and the electric field direction b22 of the electric field applied to the second optical waveguide 14B2 on the return side are the same, so that the modulation efficiency is improved. In addition, since the second ground electrode 15B is not arranged between the first optical waveguide 14A and the second optical waveguide 14B, the width in the Z-axis direction can be reduced, and the device size can be reduced.

[0069] [c] Third Embodiment

[0070] Figure 6 3 is a schematic plan view illustrating a configuration example of the optical modulator 5B according to the third embodiment. In addition, the same components as those of the optical modulator 5 of the first embodiment are denoted by the same reference numerals, and description of the same configuration and operation will be omitted. Figure 6 The optical modulator 5B shown includes a first interaction portion 20A on the outer side, a second interaction portion 20B on the return side, and an intermediate portion 20C connecting the first interaction portion 20A on the outer side and the second interaction portion 20B on the return side. The intermediate portion 20C is Figure 6 The portion from the O-Zin surface to the O-Zout surface is shown.

[0071] The optical waveguide length of the first optical waveguide 14A3 on the middle side and the optical waveguide length of the second optical waveguide 14B3 on the middle side are adjusted so that the optical waveguide length of the first optical waveguide 14A and the optical waveguide length of the second optical waveguide 14B become the same. Figure 6As shown, the first optical waveguide 14A3 on the middle side and the second optical waveguide 14B3 on the middle side are illustrated 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 the optical waveguide length is clear. The length from the O-Zin plane to the O-Zout plane of the first signal electrode 16A3 on the middle side is Lr(S1). The waveguide length of the first optical waveguide 14A3 on the middle side is the length Lr(W1) from the O-Zin plane to the O-Zout plane. The waveguide length of the second optical waveguide 14B3 on the middle side is the length Lr(W2) from the O-Zin plane to the O-Zout plane. By setting the length so that Lr(S1)=Lr(W2)=Lr(W1), the optical waveguide length of the first optical waveguide 14A, the optical waveguide length of the second optical waveguide 14B, and the electrode length of the first signal electrode 16A are set to the same length. In addition, the shapes of the first optical waveguide 14A3 on the middle side and the second optical waveguide 14B3 on the middle side can be appropriately changed. As a result, the same phase can be set between the outward path and the return path and broadband operation can be achieved. In addition, because the waveguide length of the first optical waveguide 14A and the waveguide length of the second optical waveguide 14B are set to the same length, the propagation loss difference between the first optical waveguide 14A and the second optical waveguide 14B can be prevented, so that the extinction ratio and wavelength dependence of the optical modulator 5B can be improved.

[0072] In the optical modulator 5B of the third embodiment, the optical waveguide length of the first optical waveguide 14A3 on the middle side and the optical waveguide length of the second optical waveguide 14B3 on the middle side are adjusted so that the optical waveguide length of the first optical waveguide 14A and the optical waveguide length of the second optical waveguide 14B become the same. As a result, the optical waveguide length of the first optical waveguide 14A and the optical waveguide length of the second optical waveguide 14B are set to the same length, so that the difference in propagation loss between the optical waveguides can be prevented, and the extinction ratio and wavelength dependency of the optical modulator 5B can be improved.

[0073] [d] Fourth Embodiment

[0074] Figure 7 1 is a schematic plan view illustrating a configuration example of an optical modulator 5C according to the fourth embodiment. In addition, the same components as those of the optical modulator 5 of the first embodiment are denoted by the same reference numerals, and description of the same configuration and operation will be omitted. Figure 7 The optical modulator 5C shown 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. In addition, 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.

[0075] The first optical waveguide 14A having a folded structure folded at two portions includes a first optical waveguide 14A1 on a first outward side, a first optical waveguide 14A2 on a return side, and a first optical waveguide 14A4 on a second outward side. Furthermore, the first optical waveguide 14A includes a first optical waveguide 14A5 located on a first intermediate side and connected to the first optical waveguide 14A1 on the first outward side and the first optical waveguide 14A2 on the return side. Furthermore, the first optical waveguide 14A includes a first optical waveguide 14A6 located on a second intermediate side and connected to the first optical waveguide 14A2 on the return side and the first optical waveguide 14A4 on the second outward side.

[0076] The second optical waveguide 14B having a folded structure folded at two portions includes a second optical waveguide 14B1 on a first outward side, a second optical waveguide 14B2 on a return side, and a second optical waveguide 14B4 on a second outward side. Furthermore, the second optical waveguide 14B includes a second optical waveguide 14B5 located on a first intermediate side and connected to the second optical waveguide 14B1 on the first outward side and the second optical waveguide 14B2 on the return side. Furthermore, the second optical waveguide 14B includes a second optical waveguide 14B6 located on a second intermediate side and connected to the second optical waveguide 14B2 on the return side and the second optical waveguide 14B4 on the second outward side.

[0077] First signal electrode 16A having a folded structure folded at two portions includes first signal electrode 16A1 on a first outward-facing side, first signal electrode 16A2 on a return side, and first signal electrode 16A4 on a second outward-facing side. Further, first signal electrode 16A includes first signal electrode 16A5 located on a first intermediate side and connected to first signal electrode 16A1 on the first outward-facing side and first signal electrode 16A2 on the return side. Further, first signal electrode 16A includes first signal electrode 16A6 located on a second intermediate side and connected to first signal electrode 16A2 on the return side and first signal electrode 16A4 on the second outward-facing side.

[0078] Second signal electrode 16B having a folded structure folded at two portions includes second signal electrode 16B1 on a first outward side, second signal electrode 16B2 on a return side, and second signal electrode 16B4 on a second outward side. Further, second signal electrode 16B includes second signal electrode 16B5 located on a first intermediate side and connected to second signal electrode 16B1 on the first outward side and second signal electrode 16B2 on the return side. Second signal electrode 16B includes second signal electrode 16B6 located on a second intermediate side and connected to second signal electrode 16B2 on the return side and second signal electrode 16B4 on the second outward side.

[0079] The fourth ground electrode 15D includes a fourth ground electrode 15D1 on the outer side, a fourth ground electrode 15D2 on the return side, and a fourth ground electrode 15D3 located between the fourth ground electrode 15D1 on the outer side and the fourth ground electrode 15D2 on the return side. The fifth ground electrode 15E includes a fifth ground electrode 15E1 on the outer side, a fifth ground electrode 15E2 on the return side, and a fifth ground electrode 15E3 between the fifth ground electrode 15E1 on the outer side and the fifth ground electrode 15E2 on the return side.

[0080] The optical modulator 5C includes a first interaction part 20A3, a second interaction part 20B3, a third interaction part 20D3 and a second intermediate part 20E3 connecting the first interaction part 20A3 and the second interaction part 20B3. In addition, the optical modulator 5C includes a second intermediate part 20F3 connecting the second interaction part 20B3 and the third interaction part 20D3.

[0081] The first interaction portion 20A3 includes a fourth ground electrode 15D1 on the outer side, a first signal electrode 16A1 on the first outer side, a first optical waveguide 14A1 on the first outer side, and a second signal electrode 16B1 on the first outer side. The first interaction portion 20A3 includes the second optical waveguide 14B1 on the first outer side and a fifth ground electrode 15E1 on the outer side. The first optical waveguide 14A1 on the first outer side is arranged between the first signal electrode 16A1 on the first outer side and the second signal electrode 16B1 on the first outer side. The second optical waveguide 14B1 on the first outer side is arranged between the second signal electrode 16B1 on the first outer side and the fifth ground electrode 15E1 on the outer side.

[0082] The crystal direction of the thin film LN substrate 13 is the width direction (Z direction) perpendicular to the traveling direction (Y direction). The light refractive index of the first optical waveguide 14A1 on the first outer side in the first interaction portion 20A3 changes according to the electric field in the electric field direction a31 from the second signal electrode 16B1 on the first outer side to the first signal electrode 16A1 on the first outer side. In addition, the light refractive index of the second optical waveguide 14B1 on the first outer side changes according to the electric field in the electric field direction b31 from the second signal electrode 16B1 on the first outer side to the fifth ground electrode 15E1 on the outer side.

[0083] The second intermediate portion 20E3 includes 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.

[0084] The second interaction part 20B3 includes a fifth ground electrode 15E1 on the outer side, a second signal electrode 16B2 on the return side, a second optical waveguide 14B2 on the return side, a first signal electrode 16A2 on the return side, a first optical waveguide 14A2 on the return side, and a fourth ground electrode 15D2 on the return side. The first optical waveguide 14A2 on the return side is arranged between the fourth ground electrode 15D2 on the return side and the first signal electrode 16A2 on the return side. The second optical waveguide 14B2 on the return side is arranged between the first signal electrode 16A2 on the return side and the second signal electrode 16B2 on the return side.

[0085] The optical refractive index of the first optical waveguide 14A2 on the return side in the second interaction portion 20B3 changes according to the electric field in the electric field direction a32 from the fourth ground electrode 15D2 on the return side to the first signal electrode 16A2 on the return side. In addition, the optical refractive index of the second optical waveguide 14B2 on the return side changes according to the electric field in the electric field direction b32 from the second signal electrode 16B2 on the return side to the first signal electrode 16A2 on the return side.

[0086] The second intermediate portion 20F3 includes 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.

[0087] The third interaction part 20D3 includes a fourth ground electrode 15D2 on the return side, a first signal electrode 16A4 on the second outer side, a first optical waveguide 14A4 on the second outer side, and a second signal electrode 16B4 on the second outer side. The third interaction part 20D3 includes a second optical waveguide 14B4 on the second outer side and a fifth ground electrode 15E2 on the return side. The first optical waveguide 14A4 on the second outer side is arranged between the first signal electrode 16A4 on the second outer side and the second signal electrode 16B4 on the second outer side. The second optical waveguide 14B4 on the second outer side is arranged between the second signal electrode 16B4 on the second outer side and the fifth ground electrode 15E2 on the return side.

[0088] The optical refractive index of the first optical waveguide 14A4 on the second outer side in the third interaction portion 20D3 changes according to the electric field in the electric field direction a33 from the second signal electrode 16B4 on the second outer side to the first signal electrode 16A4 on the second outer side. In addition, the optical refractive index of the second optical waveguide 14B4 on the second outer side changes according to the electric field in the electric field direction b33 from the second signal electrode 16B4 on the second outer side to the fifth ground electrode 15E2 on the return side.

[0089] In the first optical waveguide 14A, the electric field direction a31 from the second signal electrode 16B1 on the first outward side to the first signal electrode 16A1 on the first outward side, the electric field direction a32 from the second signal electrode 16B1 on the first outward side to the first signal electrode 16A1 on the first outward side, and the electric field direction a32 from the fourth ground electrode 15D2 on the return side to the first signal electrode 16A2 on the return side are 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 side to the fifth ground electrode 15E1 on the outward side, the electric field direction b32 from the second signal electrode 16B2 on the return side to the first signal electrode 16A2 on the return side, and the electric field direction b33 from the second signal electrode 16B4 on the second outward side to the fifth ground electrode 15E2 on the return side are the same direction.

[0090] The optical waveguide length L2 of the first optical waveguide 14A2 on the return side in the second interaction portion 20B is set longer than the optical waveguide length L3 of the first optical waveguide 14A1 on the first outer side in the first interaction portion 20A, or the optical waveguide length L3 of the first optical waveguide 14A4 on the second outer side in the first interaction portion 20A. The optical waveguide length L2 of the second optical waveguide 14B2 on the return side in the second interaction portion 20B is set longer than the optical waveguide length L1 of the second optical waveguide 14B1 on the first outer side in the third interaction portion 20D, or the optical waveguide length L1 of the second optical waveguide 14B4 on the second outer side in the third interaction portion 20D.

[0091] In the optical modulator 5A having a folded structure folded at a single portion, if the electric field efficiency between the signal electrodes and the electric field efficiency between the signal electrode and the ground electrode are different, the electric signal attenuates as it propagates. Therefore, in the optical modulator 5A, the phase change amount applied to the first optical waveguide 14A and the second optical waveguide 14B is different between the outward path and the return path, so that the frequency dependence of the chirp may occur in some cases. In response to this, in the optical modulator 5C of the fourth embodiment, the first interaction part 20A, the second interaction part 20B, and the third interaction part 20D are arranged at three positions in the two folded parts of the folded structure. The optical waveguide length L2 of the second interaction part 20B is set to be longer than the optical waveguide length L3 of the first interaction part 20A. The optical waveguide length L2 of the second interaction part 20B is set to be longer than the optical waveguide length L1 of the third interaction part 20D. As a result, the same phase change amount can be set between the first optical waveguide 14A and the second optical waveguide 14B, and the frequency dependence of the chirp is reduced.

[0092] [e] Fifth Embodiment

[0093] Figure 85 is a schematic plan view illustrating a configuration example of an optical modulator 5D according to the fifth embodiment. In addition, the same components as those of the optical modulator 5 of the first embodiment are denoted by the same reference numerals, and description of the same configuration and operation will be omitted.

[0094] Figure 8 The optical modulator 5D shown is constructed so that the driver 21 is electrically connected to Figure 2 The light modulator 5 is shown. Figure 8 The driver 21 shown is connected to the Figure 2 The first signal electrode 16A1 on the outer side and the second signal electrode 16B1 on the outer side in the optical modulator 5 shown. In addition, the driver 21 is connected to the first ground electrode 15A1 on the outer side, the second ground electrode 15B1 on the outer side, and the third ground electrode 15C through gold wiring. The driver 21 amplifies the electric signal and applies the amplified electric signal to the first signal electrode 16A and the second signal electrode 16B. The driver 21 is electrically connected to the vicinity of one side of the chip of the optical modulator 5D through gold wiring.

[0095] In the optical modulator 5D of the fifth embodiment, since the electrical connection is made to the vicinity of one side of the chip using the gold wiring, the connection can be achieved in a short distance and in an efficient manner.

[0096] [f] Sixth Embodiment

[0097] Fig. 9 5E according to the sixth embodiment. In addition, the same components as those of the light modulator 5C of the fourth embodiment are denoted by the same reference numerals, and description of the same configuration and operation will be omitted.

[0098] Fig. 9 The optical modulator 5E shown is constructed so that the driver 21 is electrically connected to Figure 6 The light modulator 5C is shown. Fig. 9 The driver 21 shown is connected to the Figure 7 The first signal electrode 16A4 on the second outer side and the second signal electrode 16B4 on the second outer side in the optical modulator 5C shown. The driver 21 is connected to the fourth ground electrode 15D2 on the return side and the fifth ground electrode 15E2 on the return side through gold wiring. The driver 21 amplifies the electric signal and applies the amplified electric signal to the first signal electrode 16A and the second signal electrode 16B. The driver 21 is electrically connected to the vicinity of one side of the chip of the optical modulator 5E through gold wiring.

[0099] Driver 21 is connected obliquely and electrically so that first signal electrode 16A4 on the second outward side, second signal electrode 16B4 on the second outward side, fourth ground electrode 15D2 on the return side, fifth ground electrode 15E2 on the return side, first optical waveguide 14A, and second optical waveguide 14B are arranged non-parallel to each other. As a result, oblique portions of first signal electrode 16A4 on the second outward side, second signal electrode 16B4 on the second outward side, fourth ground electrode 15D2 on the return side, and fifth ground electrode 15E2 on the return side are prevented from acting as an interaction portion.

[0100] In the optical modulator 5E of the sixth embodiment, since the electrical connection is made to the vicinity of one side of the chip using the gold wiring, the connection can be achieved in a short distance and in an efficient manner.

[0101] According to one embodiment of the optical device and the like disclosed in the present application, modulation efficiency can be improved.

Claims

1. An optical device, comprising: X-cut substrate; a first optical waveguide and a second optical waveguide, each of the first optical waveguide and the second optical waveguide being formed on the substrate and having a folded structure; a first signal electrode disposed on the substrate and generating a first electric field; as well as a second signal electrode disposed on the substrate and generating a second electric field having a phase opposite to that of the first electric field; The first optical waveguide comprises: In the first optical waveguide facing outward, applying the first electric field from the first signal electrode to the first optical waveguide facing outward; and the first optical waveguide on the return side, applying the second electric field from the second signal electrode to the first optical waveguide on the return side, and The second optical waveguide comprises: applying the first electric field from the first signal electrode to the second optical waveguide on the outer side; and In the second optical waveguide on the return side, the second electric field is applied from the second signal electrode to the second optical waveguide on the return side.

2. The optical device according to claim 1, wherein: The direction of the first electric field applied to the first optical waveguide on the outward side is the same as the direction of the second electric field applied to the first optical waveguide on the return side, and The direction of the second electric field applied to the second optical waveguide on the outward side is the same as the direction of the first electric field applied to the second optical waveguide on the return side.

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

4. The optical device according to claim 1, wherein: A first ground electrode, a second ground electrode, and a third ground electrode are arranged on the substrate in parallel with each other, the first ground electrode having a folded structure and including a first ground electrode on the outer side and a first ground electrode on the return side, and the second ground electrode having a folded structure and including a second ground electrode on the outer side and a second ground electrode on the return side; A first signal electrode and a second signal electrode are arranged on the substrate in parallel with each other, the first signal electrode having a folded structure and including a first signal electrode on the outer side and a first signal electrode on the return side, the second signal electrode having a folded structure and including a second signal electrode on the outer side and a second signal electrode on the return side, The first optical waveguide on the outer side is arranged between the second ground electrode on the outer side and the second signal electrode on the outer side, The second optical waveguide on the outer side is arranged between the second signal electrode and the third ground electrode on the outer side, The first optical waveguide on the return side is arranged between the first ground electrode on the return side and the first signal electrode on the return side, and The second optical waveguide on the return side is arranged between the first signal electrode on the return side and the second ground electrode on the return side.

5. The optical device according to claim 1, wherein: A first ground electrode and a third ground electrode are arranged on the substrate in parallel with each other, the first ground electrode having a folded structure and including a first ground electrode on the outward side and a first ground electrode on the return side, A first signal electrode and a second signal electrode are arranged on the substrate in parallel with each other, the first signal electrode having a folded structure and including a first signal electrode on the outer side and a first signal electrode on the return side, the second signal electrode having a folded structure and including a second signal electrode on the outer side and a second signal electrode on the return side, The first optical waveguide on the outer side is arranged between the first signal electrode on the outer side and the second signal electrode on the outer side, The second optical waveguide on the outer side is arranged between the second signal electrode on the outer side and the third ground electrode, The first optical waveguide on the return side is arranged between the first ground electrode on the return side and the first signal electrode on the return side, and The second optical waveguide on the return side is arranged between the first signal electrode on the return side and the second signal electrode on the return side.

6. The optical device according to claim 1, wherein: The first optical waveguide includes a first optical waveguide on the outward side, a first optical waveguide on the return side, and a first intermediate optical waveguide connecting the first optical waveguide on the outward side and the first optical waveguide on the return side. The second optical waveguide includes a second optical waveguide on the outward side, a second optical waveguide on the return side, and a second intermediate optical waveguide connecting the second optical waveguide on the outward side and the second optical waveguide on the return side, and The optical waveguide length of the first intermediate optical waveguide and the optical waveguide length of the second intermediate optical waveguide are adjusted so that the optical waveguide length of the first optical waveguide and the optical waveguide length of the second optical waveguide become the same.

7. The optical device according to claim 1, wherein: a fourth ground electrode and a fifth ground electrode are arranged on the substrate, the fourth ground electrode having a folded structure and including a fourth ground electrode on the outward side and a fourth ground electrode on the return side, the fifth ground electrode having a folded structure and including a fifth ground electrode on the outward side and a fifth ground electrode on the return side, A first signal electrode and a second signal electrode are arranged on the substrate in parallel with each other, the first signal electrode has a folded structure, and the second signal electrode has a folded structure, The first optical waveguide includes a first optical waveguide on a first outer side, a first optical waveguide on a second outer side, and a first optical waveguide on the return side connecting the first optical waveguide on the first outer side and the first optical waveguide on the second outer side. The second optical waveguide includes a second optical waveguide on the first outer side, a second optical waveguide on the second outer side, and a second optical waveguide on the return side connecting the second optical waveguide on the first outer side and the second optical waveguide on the second outer side. The first signal electrode includes a first signal electrode on the first outward side, a first signal electrode on the second outward side, and a first signal electrode on the return side connecting the first signal electrode on the first outward side and the first signal electrode on the second outward side. The second signal electrode includes a second signal electrode on the first outward side, a second signal electrode on the second outward side, and a second signal electrode on the return side connecting the second signal electrode on the first outward side and the second signal electrode on the second outward side. The first optical waveguide on the first outward side is arranged between the first signal electrode on the first outward side and the second signal electrode on the first outward side, The second optical waveguide on the first outward side is arranged between the second signal electrode on the first outward side and the fifth ground electrode on the outward side, The first optical waveguide on the return side is arranged between the fourth ground electrode on the return side and the first signal electrode on the return side, The second optical waveguide on the return side is arranged between the first signal electrode on the return side and the second signal electrode on the return side, the first optical waveguide on the second outer side is arranged between the first signal electrode on the second outer side and the second signal electrode on the second outer side, The second optical waveguide on the second outer side is arranged between the second signal electrode on the second outer side and the fifth ground electrode on the return side, The optical waveguide length of the first optical waveguide on the return side is set to be longer than one of the optical waveguide length of the first optical waveguide on the first outward direction and the optical waveguide length of the first optical waveguide on the second outward direction; as well as The optical waveguide length of the second optical waveguide on the return side is set longer than one of the optical waveguide length of the second optical waveguide on the first outer side and the optical waveguide length of the second optical waveguide on the second outer side.

8. An optical communication device, comprising: a processor that performs signal processing on the electrical signal; a light source, the light source generating light; as well as an optical device that modulates light generated from the light source by using an electrical signal output by the processor, The optical device comprises: X-cut substrate; a first optical waveguide and a second optical waveguide, each of the first optical waveguide and the second optical waveguide being formed on the substrate and having a folded structure; 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 having a phase opposite to that of the first electric field; The first optical waveguide comprises: applying the first electric field from the first signal electrode to the first optical waveguide on the outer side; and the first optical waveguide on the return side, applying the second electric field from the second signal electrode to the first optical waveguide on the return side, and The second optical waveguide comprises: applying the first electric field from the first signal electrode to the second optical waveguide on the outer side; and In the second optical waveguide on the return side, the second electric field is applied from the second signal electrode to the second optical waveguide on the return side.

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