Optical device, optical modulator and optical communication device

Abstract

To provide an optical device and the like that improve modulation efficiency while reducing power consumption.SOLUTION: An optical device includes: a slot waveguide; and a coplanar-structured electrode including a signal electrode and a ground electrode running in parallel with the slot waveguide. The optical device further includes: a plurality of electro-optic polymers that are inserted into slots in the slot waveguide in a divided state; and a bridge that is disposed at a boundary portion between the divided electro-optic polymers and electrically connects the ground electrode and another ground electrode.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] FIG. 19 is a plan view schematic diagram showing an example of a conventional optical modulator 100. The optical modulator 100 shown in FIG. 19 has an optical waveguide 101 and an electrode 102 of a coplanar structure (CPW: Coplanar Waveguide) including a signal electrode and a ground electrode. The optical waveguide 101 is a PN junction optical waveguide composed of N-doped silicon (hereinafter simply referred to as doped Si) 105A and P-doped Si 105B. The optical waveguide 101 has an input section 101A, a branching section 101B, two waveguides 101C, a multiplexing section 101D, and an output section 101E. The input section 101A is an input section of the optical modulator that inputs light to the optical modulator 100. The branching section 101B optically branches the light from the input section 101A and outputs the branched light to two waveguides 101C. The two waveguides 101C are arms of the optical modulator that guide the light from the branching section 101B and act on the guided light in response to the electric field between the electrodes 102. The multiplexing section 101D multiplexes the light from the two waveguides 101C and outputs the multiplexed light. The output section 101E is an output section of the optical modulator 100 that outputs the light from the multiplexing section 101D.

[0003] The electrode 102 has a coplanar structure and includes a first ground electrode 102A1, a first signal electrode 102B1, a second ground electrode 102A2, a second signal electrode 102B2, and a third ground electrode 102A3.

[0004] The first signal electrode 102B1 is disposed between the first ground electrode 102A1 and the second ground electrode 102A2 in a state of running in parallel, and the second signal electrode 102B2 is disposed between the second ground electrode 102A2 and the third ground electrode 102A3 in a state of running in parallel.

[0005] Of the two waveguides 101C, the first waveguide 101C1 is an optical waveguide located below the portion between the first ground electrode 102A1 and the first signal electrode 102B1. Of the two waveguides 101C, the second waveguide 101C2 is an optical waveguide located below the portion between the second signal electrode 102B2 and the third ground electrode 102A3.

[0006] When the optical modulator 100 performs high-speed modulation, a high-frequency driving voltage having a band of, for example, several tens of GHz is input to the signal electrodes 102B1 and 102B2 arranged along the waveguide 101C.

[0007] Fig. 20 is a schematic cross-sectional view of the MM line shown in Fig. 19. The schematic cross-sectional portion of the MM line shown in Fig. 20 includes a silicon substrate 131, an intermediate layer 132 made of SiO2 stacked on the silicon substrate 131, and an optical waveguide 101 formed on the intermediate layer 132. The schematic cross-sectional portion further includes a buffer layer 133 made of SiO2 stacked on the intermediate layer 132 including the optical waveguide 101, and an electrode 102. The electrode 102 includes a first ground electrode 102A1, a first signal electrode 102B1, and a second ground electrode 102A2.

[0008] The buffer layer 133 has a via 106 formed between the first ground electrode 102A1 and the N-doped Si 105A in the first waveguide 101C1, and has a portion that joins the first ground electrode 102A1 and the N-doped Si 105A of the first waveguide 101C1 through the via 106. The buffer layer 133 has a via 106 formed between the first signal electrode 102B1 and the P-doped Si 105B of the first waveguide 101C1, and has a portion that joins the first signal electrode 102B1 and the P-doped Si 105B of the first waveguide 101C1 through the via 106.

[0009] Although not shown, the buffer layer 133 also has a via 106 formed between the third ground electrode 102A3 and the N-doped Si 105A of the second waveguide 101C2. The via 106 is a portion that joins the third ground electrode 102A3 and the N-doped Si 105A of the second waveguide 101C2. The buffer layer 133 also has a via 106 formed between the second signal electrode 102B2 and the P-doped Si 105B of the second waveguide 101C2. The via 106 is a portion that joins the second signal electrode 102B2 and the P-doped Si 105B of the second waveguide 101C2.

[0010] In the optical modulator 100, when a high-frequency driving voltage is applied to the first signal electrode 102B1, the carrier density of the PN junction of the first waveguide 101C1 between the first signal electrode 102B1 and the first ground electrode 102A1 changes. In the optical modulator 100, the refractive index of the first waveguide 101C1 changes in response to the change in carrier density, thereby changing the phase of light guided through the first waveguide 101C. Similarly, in the optical modulator 100, when a high-frequency driving voltage is applied to the second signal electrode 102B2, the carrier density of the PN junction of the second waveguide 101C2 between the second signal electrode 102B2 and the third ground electrode 102A3 changes. In the optical modulator 100, the refractive index of the second waveguide 101C2 changes in response to the change in carrier density, thereby changing the phase of light guided through the second waveguide 101C2. As a result, the optical modulator 100 can convert the phase-modulated light from the first waveguide 101C1 and the phase-modulated light from the second waveguide 101C2 into a multi-level light intensity change according to the phase difference of the light by combining them in the combining section 101D. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] US Patent Application Publication No. 2014 / 0086523 [Patent Document 2] Patent Publication No. 2021-43263 [Patent Document 3] U.S. Patent No. 10,962,811 Summary of the Invention [Problem to be solved by the invention]

[0012] However, since the optical waveguide 101 of the conventional optical modulator 100 is constructed of a silicon PN junction, the change in the refractive index of light is small, and the driving voltage applied to the first signal electrode 102B1 and the second signal electrode 102B2 is large, resulting in increased power consumption.

[0013] 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 while suppressing power consumption. [Means for solving the problem]

[0014] In one aspect, the optical device disclosed herein includes a slot waveguide and a coplanar electrode structure including a signal electrode and a ground electrode running parallel to the slot waveguide. The optical device also includes a plurality of electro-optic polymers inserted into slots in the slot waveguide in a divided state, and bridges disposed at boundaries between the divided electro-optic polymers to electrically connect the ground electrode to another ground electrode. [Effects of the Invention]

[0015] According to one aspect of the optical device etc. disclosed in the present application, modulation efficiency is improved while power consumption is suppressed. [Brief explanation of the drawings]

[0016] [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 taken along line AA shown in FIG. [Figure 4] FIG. 4 is a schematic cross-sectional view taken along line BB shown in FIG. [Figure 5]FIG. 5 is a schematic plan view showing an example of the configuration of the optical modulator according to the second embodiment. [Figure 6] FIG. 6 is a schematic cross-sectional view taken along line CC shown in FIG. [Figure 7] FIG. 7 is a schematic cross-sectional view taken along line DD shown in FIG. [Figure 8] FIG. 8 is a schematic plan view showing an example of the configuration of the optical modulator according to the third embodiment. [Figure 9] FIG. 9 is a schematic cross-sectional view taken along line EE shown in FIG. [Figure 10] FIG. 10 is a schematic cross-sectional view taken along the line FF shown in FIG. [Figure 11] FIG. 11 is a schematic plan view showing an example of the configuration of the optical modulator according to the fourth embodiment. [Figure 12] FIG. 12 is a schematic cross-sectional view taken along line GG shown in FIG. [Figure 13] FIG. 13 is a schematic cross-sectional view taken along line HH shown in FIG. [Figure 14] FIG. 14 is a schematic plan view showing an example of the configuration of the optical modulator according to the fifth embodiment. [Figure 15] FIG. 15 is a schematic cross-sectional view taken along line JJ shown in FIG. [Figure 16] FIG. 16 is a schematic cross-sectional view taken along line KK shown in FIG. [Figure 17] FIG. 17 is a schematic plan view showing an example of the configuration of an optical modulator of a comparative example. [Figure 18] FIG. 18 is a schematic cross-sectional view taken along line LL shown in FIG. [Figure 19] FIG. 19 is a schematic plan view showing an example of the configuration of a conventional optical modulator. [Figure 20] FIG. 20 is a schematic cross-sectional view taken along line MM shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0017] [Comparative Example] In the optical modulator, in order to suppress the drive voltage applied to the first signal electrode and the second signal electrode, it is possible to use an optical waveguide including an EO polymer instead of a silicon PN junction optical waveguide. Fig. 17 is a plan view schematic diagram showing an example of the configuration of an optical modulator 50 of the comparative example.

[0018] The optical modulator 50 of the comparative example shown in FIG. 17 includes an optical waveguide 51 and a coplanar electrode 52 including a signal electrode and a ground electrode. The optical waveguide 51 is a slot waveguide formed of two N-doped Si electrodes 55A. The optical waveguide 51 includes an input section 51A, a branching section 51B, two waveguides 51C, a multiplexing section 51D, and an output section 51E. The input section 51A is an input section of the optical modulator 50 that inputs light to the optical modulator 50. The branching section 51B branches the light from the input section 51A and outputs the branched light to two waveguides 51C. The two waveguides 51C are arms of the optical modulator 50 that guide the light from the branching section 51B and act on the guided light in response to the electric field between the electrodes 52. The multiplexing section 51D multiplexes the light from the two branched waveguides 51C and outputs the multiplexed light. The output section 51E is an output section of the optical modulator 50 that outputs the light from the multiplexing section 51D.

[0019] The electrode 52 has a coplanar structure and includes a first ground electrode 52A1, a first signal electrode 52B1, a second ground electrode 52A2, a second signal electrode 52B2, and a third ground electrode 52A3. The first signal electrode 52B1 is disposed in parallel between the first ground electrode 52A1 and the second ground electrode 52A2. The second signal electrode 52B2 is disposed in parallel between the second ground electrode 52A2 and the third ground electrode 52A3.

[0020] Of the two waveguides 51C, the first waveguide 51C1 is an optical waveguide located below the portion between the first ground electrode 52A1 and the first signal electrode 52B1. The first waveguide 51C1 is a slot waveguide having a slot 55B formed of two N-doped Si electrodes 55A.

[0021] Of the two waveguides 51C, the second waveguide 51C2 is an optical waveguide located below the portion between the second signal electrode 52B2 and the third ground electrode 52A3. The second waveguide 51C2 is a slot waveguide having slots 55B each formed of two N-doped Si electrodes 55A.

[0022] Figure 18 is a schematic cross-sectional view taken along line LL in Figure 17. The schematic cross-sectional portion taken along line LL in Figure 18 includes a silicon substrate 31, an intermediate layer 32 made of SiO2 laminated on the silicon substrate 31, an optical waveguide 51 formed on the intermediate layer 32, a buffer layer 33 made of SiO2 laminated on the intermediate layer 32 including the optical waveguide 51, and an electrode 52. The electrode 52 includes a first ground electrode 52A1, a first signal electrode 52B1, and a second ground electrode 52A2.

[0023] The buffer layer 33 has a via 56 formed between the first ground electrode 52A1 and the N-doped Si 55A of the first waveguide 51C1. The via 56 connects the first ground electrode 52A1 and the N-doped Si 55A of the first waveguide 51C1. The buffer layer 33 has a via 56 formed between the first signal electrode 52B1 and the N-doped Si 55A of the first waveguide 51C1. The via 56 connects the first signal electrode 52B1 and the N-doped Si 55A of the first waveguide 51C1. Furthermore, the buffer layer 33 has an opening 33A formed between the first ground electrode 52A1 and the first signal electrode 52B1. An electro-optic (EO) polymer 53 is disposed on the N-doped Si 55A in the first waveguide 51C1 so that a portion of the EO polymer 53 disposed in the opening 33A fills the slot 55B between the N-doped Si 55A in the first waveguide 51C1.

[0024] The buffer layer 33 has a via 56 formed between the third ground electrode 52A3 and the N-doped Si 55A of the second waveguide 51C2. The via 56 connects the third ground electrode 52A3 and the N-doped Si 55A of the second waveguide 51C2. The buffer layer 33 has a via 56 formed between the second signal electrode 52B2 and the N-doped Si 55A of the second waveguide 51C2. The via 56 connects the second signal electrode 52B2 and the N-doped Si 55A of the second waveguide 51C2. Furthermore, the buffer layer 33 has an opening 33A formed between the third ground electrode 52A3 and the second signal electrode 52B2. The EO polymer 53 is disposed on the N-doped Si 55A in the second waveguide 51C2 so that the slot 55B between the N-doped Si 55A in the second waveguide 51C2 is filled with a portion of the EO polymer 53 disposed in the opening 33A.

[0025] The optical modulator 50 uses an EO polymer 53 in the slot 55B in the optical waveguide 51, which increases the change in the refractive index of light guided through the optical waveguide 51. When a high-frequency drive voltage is applied to the first signal electrode 52B1 of the optical modulator 50, the refractive index of the first waveguide 51C1 between the first signal electrode 52B1 and the first ground electrode 52A1 changes, thereby changing the phase of the light guided through the first waveguide 51C1. Similarly, when a high-frequency drive voltage is applied to the second signal electrode 52B2 of the optical modulator 50, the refractive index of the second waveguide 51C2 between the second signal electrode 52B2 and the third ground electrode 52A3 changes, thereby changing the phase of the light guided through the second waveguide 51C2. As a result, the optical modulator 50 can convert the phase-modulated light from the first waveguide 51C1 and the phase-modulated light from the second waveguide 51C2 into a multi-level light intensity change according to the phase difference of the light by combining them in the combining section 51D.

[0026] In the optical modulator 50 of the comparative example, an EO polymer 53 is used in the slot 55B in the optical waveguide 51, which increases the change in the refractive index of light guided through the optical waveguide 51. As a result, the drive voltage applied to the first signal electrode 52B1 and the second signal electrode 52B2 can be reduced, thereby suppressing power consumption.

[0027] In the optical modulator 50 of the comparative example, in order to fill the slots 55B between the N-doped Si 55A in the optical waveguide 51 with the EO polymer 53, it is necessary to etch an opening 33A in the buffer layer 33 and inject the EO polymer 53 into the opening 33A. In the optical modulator 50 of the comparative example, in order to provide the opening 33A in the buffer layer 33 between the first ground electrode 52A1 and the first signal electrode 52B1, it is necessary to ensure a gap between the first ground electrode 52A1 and the first signal electrode 52B1.

[0028] However, in the optical modulator 50 of the comparative example, when the spacing between the first ground electrode 52A1 and the first signal electrode 52B1 is increased, the distance between the first ground electrode 52A1 and the first signal electrode 52B1 increases. Therefore, the potentials of the first ground electrode 52A1 and the second ground electrode 52A2 on both sides of the first signal electrode 52B1 become unstable at high frequencies. Similarly, in the optical modulator 50 of the comparative example, when the spacing between the third ground electrode 52A3 and the second signal electrode 52B2 is increased, the distance between the third ground electrode 52A3 and the second signal electrode 52B2 increases. Therefore, the potentials of the second ground electrode 52A2 and the third ground electrode 52A3 on both sides of the second signal electrode 52B2 become unstable at high frequencies. In other words, in the optical modulator 50 of the comparative example, when the spacing between the ground electrode and the signal electrode is increased, the potentials between the ground electrodes on both sides of the signal electrode become unstable at high frequencies, resulting in degradation of high-frequency band characteristics.

[0029] For example, when a high-frequency drive voltage of several tens of GHz is applied to the signal electrode, the potential applied at the input stage of the waveguide 51C fluctuates, causing a phase change. The degree of this change increases with the propagation distance of the electrical signal (electric field). Even if the potential between the ground electrodes on both sides of the input stage of the waveguide 11C is the same, the potential differs depending on the propagation distance of the electrical signal (electric field). As a result, if the distance between the signal electrode and the ground electrode increases, the potential between the ground electrodes on both sides of the signal electrode becomes unstable at high frequencies. If the potential between the ground electrodes on both sides becomes unstable at high frequencies, the voltage between the signal electrode and the ground electrode decreases, causing a decrease in the voltage applied to the waveguide 11C. As a result, the modulation efficiency at high frequencies decreases, degrading the characteristics in the high-frequency band.

[0030] Therefore, even when an EO polymer is used, an embodiment of an optical modulator that stabilizes the potential between the ground electrodes on both sides of the signal electrode, prevents a decrease in high frequency modulation efficiency, and suppresses deterioration of characteristics in the high frequency band will be described below as Example 1. Note that the present invention is not limited to this embodiment. [Example]

[0031] 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.

[0032] The light source 4 includes, for example, a laser diode, and 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 resulting optical transmission signal to the optical fiber 2A. The optical modulator 5 is, for example, an optical device such as a Si optical modulator that includes an optical waveguide 11 and an electrode 12 with a coplanar (CPW) structure. The optical waveguide 11 is formed from a Si crystal substrate. When the light supplied from the light source 4 propagates through the optical waveguide 11, the optical modulator 5 modulates the light with an electrical signal input to a signal electrode in the electrode 12, thereby generating an optical transmission signal.

[0033] 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.

[0034] Fig. 2 is a schematic plan view showing an example of the configuration of the optical modulator 5 of Example 1. The optical modulator 5 shown in Fig. 2 includes an optical waveguide 11, a coplanar electrode 12 including a signal electrode and a ground electrode running parallel to the optical waveguide 11, and a plurality of EO polymers 13 that are separated and inserted into slots 15B in the optical waveguide 11. The optical modulator 5 further includes bridges 14 that are disposed at boundary regions 21A between the separated EO polymers and electrically connect the ground electrodes to other ground electrodes.

[0035] The optical waveguide 11 is a slot waveguide composed of two N-doped Si 15A. The optical waveguide 11 has an input section 11A, a branching section 11B, two waveguides 11C, a combining section 11D, and an output section 11E. The input section 11A is an input section of the optical modulator 5 that receives light from the light source 4. The branching section 11B branches the light from the input section 11A and outputs the branched light to the two waveguides 11C. The two waveguides 11C are arms of the optical modulator 5 that guide the light from the branching section 11B and act on the guided light in response to the electric field between the electrodes 12. The combining section 11D combines the light from the two branched waveguides 11C and outputs the combined light. The output section 11E is an output section of the optical modulator 5 that outputs the light from the combining section 11D.

[0036] The electrode 12 is made of a material such as aluminum, gold, silver, or copper. The electrode 12 has a coplanar structure and includes a first ground electrode 12A1, a first signal electrode 12B1, a second ground electrode 12A2, a second signal electrode 12B2, and a third ground electrode 12A3. The first signal electrode 12B1 is disposed between the first ground electrode 12A1 and the second ground electrode 12A2 in a parallel arrangement. The second signal electrode 12B2 is disposed between the second ground electrode 12A2 and the third ground electrode 12A3 in a parallel arrangement.

[0037] Of the two waveguides 11C, the first waveguide 11C1 is an optical waveguide located below the portion between the first ground electrode 12A1 and the first signal electrode 12B1. The first waveguide 11C1 is a slot waveguide having slots 15B each made of two N-doped Si electrodes 15A.

[0038] Of the two waveguides 11C, the second waveguide 11C2 is an optical waveguide located below the portion between the second signal electrode 12B2 and the third ground electrode 12A3. The second waveguide 11C2 is a slot waveguide having slots 15B each made of two N-doped Si electrodes 15A.

[0039] The optical modulator 5 has a first portion 20A located in the light propagation direction of the optical waveguide 11, a second portion 20B located in the light propagation direction of the optical waveguide 11, and a third portion 20C located in the light propagation direction of the optical waveguide 11. The optical modulator 5 has a first boundary portion 21A located between the first portion 20A and the second portion 20B, and a second boundary portion 21B located between the second portion 20B and the third portion 20C.

[0040] In the optical modulator 5, depending on the direction of travel of the light in the optical waveguide 11, the light is guided through the waveguide 11C in the order of the first portion 20A, the first boundary portion 21A, the second portion 20B, the second boundary portion 21B, and the third portion 20C.

[0041] Fig. 3 is a schematic cross-sectional view taken along line AA in Fig. 2. The schematic cross-sectional view taken along line AA in Fig. 3 is, for example, the first portion 20A on the first waveguide 11C1 side. The first portion 20A includes a silicon substrate 31, an intermediate layer 32 made of SiO2 laminated on the silicon substrate 31, an optical waveguide 11 formed on the intermediate layer 32, a buffer layer 33 made of SiO2 laminated on the intermediate layer 32 including the optical waveguide 11, and an electrode 12. The electrode 12 includes a first ground electrode 12A1, a first signal electrode 12B1, and a second ground electrode 12A2.

[0042] The electrode 12 has a first layer M1 and a second layer M2 disposed below the first layer M1. The first ground electrode 12A1 has a portion 12A11 on the first layer M1 and a portion 12A12 on the second layer M2. The second ground electrode 12A2 has a portion 12A21 on the first layer M1 and a portion 12A22 on the second layer M2. The first signal electrode 12B1 has a portion 12B11 on the first layer M1 and a portion 12B12 on the second layer M2.

[0043] A via 16 connects a portion 12A11 of the first layer M1 in the first ground electrode 12A1 to a portion 12A12 of the second layer M2 in the first ground electrode 12A1, and a via 16 connects the portion 12A12 of the second layer M2 in the first ground electrode 12A1 to the N-doped Si 15A. A via 16 connects a portion 12B11 of the first layer M1 in the first signal electrode 12B1 to a portion 12B12 of the second layer M2 in the first signal electrode 12B1, and a via 16 connects the portion 12B12 of the second layer M2 in the first signal electrode 12B1 to the N-doped Si 15A. A via 16 connects a portion 12A21 of the first layer M1 in the second ground electrode 12A2 and a portion 12A22 of the second layer M2 in the second ground electrode 12A2.

[0044] The first portion 20A on the first waveguide 11C1 side has an opening 33A1 formed in the buffer layer 33 between the first ground electrode 12A1 and the first signal electrode 12B1, and a first EO polymer 13A inserted into the opening 33A1. The first waveguide 11C1 is in a state where a portion of the first EO polymer 13A is inserted into the slot 15B. The EO polymer is inserted into the opening 33A1 using, for example, a dispenser.

[0045] The first portion 20A on the second waveguide 11C2 side has a second ground electrode 12A2, a second signal electrode 12B2, and a third ground electrode 12A3. The first portion 20A on the second waveguide 11C2 side has an opening 33A1 formed in the buffer layer 33 between the third ground electrode 12A3 and the second signal electrode 12B2, and a first EO polymer 13A inserted into the opening 33A1. The second waveguide 11C2 is in a state where a portion of the first EO polymer 13A is inserted into the slot 15B.

[0046] The second portion 20B on the first waveguide 11C1 side has a first ground electrode 12A1, a first signal electrode 12B1, and a second ground electrode 12A2. The second portion 20B on the first waveguide 11C1 side has an opening 33A1 formed in the buffer layer 33 between the first ground electrode 12A1 and the first signal electrode 12B1, and a second EO polymer 13B inserted into the opening 33A1. The first waveguide 11C1 is in a state where a portion of the second EO polymer 13B is inserted into the slot 15B.

[0047] The second portion 20B on the second waveguide 11C2 side has a second ground electrode 12A2, a second signal electrode 12B2, and a third ground electrode 12A3. The second portion 20B on the second waveguide 11C2 side has an opening 33A1 formed in the buffer layer 33 between the third ground electrode 12A3 and the second signal electrode 12B2, and a second EO polymer 13B inserted into the opening 33A1. The second waveguide 11C2 is in a state where a portion of the second EO polymer 13B is inserted into the slot 15B.

[0048] The third portion 20C on the first waveguide 11C1 side has a first ground electrode 12A1, a first signal electrode 12B1, and a second ground electrode 12A2. The third portion 20C on the first waveguide 11C1 side has an opening 33A1 formed in the buffer layer 33 between the first ground electrode 12A1 and the first signal electrode 12B1, and a third EO polymer 13C inserted in the opening 33A1. The first waveguide 11C1 is in a state where a portion of the third EO polymer 13C is inserted into the slot 15B.

[0049] The third portion 20C on the second waveguide 11C2 side has a second ground electrode 12A2, a second signal electrode 12B2, and a third ground electrode 12A3. The third portion 20C on the second waveguide 11C2 side has an opening 33A1 formed in the buffer layer 33 between the third ground electrode 12A3 and the second signal electrode 12B2, and a third EO polymer 13C inserted into the opening 33A1. The second waveguide 11C2 is in a state where a portion of the third EO polymer 13C is inserted into the slot 15B.

[0050] 4 is a schematic cross-sectional view of line BB shown in FIG. 4. The schematic cross-sectional portion of line BB shown in FIG. 4 is, for example, first boundary portion 21A on the first waveguide 11C1 side. First boundary portion 21A corresponds to the boundary portion between first portion 20A and second portion 20B, i.e., the portion separating first EO polymer 13A and second EO polymer 13B. First boundary portion 21A has first waveguide 11C1 that joins first waveguide 11C1 of first portion 20A and first waveguide 11C1 of second portion 20B.

[0051] The first boundary region 21A on the first waveguide 11C1 side has a first ground electrode 12A1, a first signal electrode 12B1, and a second ground electrode 12A2. The first boundary region 21A on the first waveguide 11C1 side has a first bridge 14A (14) that electrically connects the first ground electrode 12A1 and the second ground electrode 12A2. The first waveguide 11C1 in the first boundary region 21A on the first waveguide 11C1 side is composed of two N-doped Si electrodes 15A, but there is no EO polymer in the slots 15B. The first bridge 14A in the first boundary region 21A on the first waveguide 11C1 side electrically connects the portion 12A11 of the first layer M1 in the first ground electrode 12A1 to the portion 12A21 of the first layer M1 in the second ground electrode 12A2. The first signal electrode 12B1 in the first boundary region 21A on the first waveguide 11C1 side has only the portion 12B12 of the second layer M2, and does not have the portion of the first signal electrode 12B1 on the first layer M1.

[0052] The first boundary region 21A on the second waveguide 11C2 side has a second ground electrode 12A2, a second signal electrode 12B2, and a third ground electrode 12A3. The first boundary region 21A on the second waveguide 11C2 side has a first bridge 14A (14) that electrically connects the second ground electrode 12A2 and the third ground electrode 12A3. The second waveguide 11C2 in the first boundary region 21A on the second waveguide 11C2 side is composed of two N-doped Si electrodes 15A, but has no EO polymer in the slots 15B. The first bridge 14A in the first boundary region 21A on the second waveguide 11C2 side electrically connects the portion 12A21 of the first layer M1 in the second ground electrode 12A2 to the portion 12A31 of the first layer M1 in the third ground electrode 12A3. The second signal electrode 12B2 in the first boundary region 21A on the second waveguide 11C2 side has only the portion 12B22 of the second layer M2, and does not have the portion of the first layer M1 of the second signal electrode 12B2.

[0053] The second boundary region 21B corresponds to the boundary region between the second region 20B and the third region 20C, i.e., the region separating the second EO polymer 13B and the third EO polymer 13C. The second boundary region 21B has a first waveguide 11C1 that joins the first waveguide 11C1 in the second region 20B and the first waveguide 11C1 in the third region 20C. Furthermore, the second boundary region 21B has a second waveguide 11C2 that joins the second waveguide 11C2 in the second region 20B and the second waveguide 11C2 in the third region 20C.

[0054] The second boundary region 21B on the first waveguide 11C1 side has a first ground electrode 12A1, a first signal electrode 12B1, and a second ground electrode 12A2. The second boundary region 21B on the first waveguide 11C1 side has a first bridge 14A (14) that electrically connects the first ground electrode 12A1 and the second ground electrode 12A2. The first waveguide 11C1 in the second boundary region 21B on the first waveguide 11C1 side is composed of two N-doped Si electrodes 15A, but there is no EO polymer in the slots 15B. The first bridge 14A in the second boundary region 21B on the first waveguide 11C1 side electrically connects the portion 12A11 of the first layer M1 in the first ground electrode 12A1 to the portion 12A21 of the first layer M1 in the second ground electrode 12A2. The first signal electrode 12B1 in the second boundary region 21B on the first waveguide 11C1 side only has the portion 12B12 of the second layer M2. The portion 12B12 is connected to the N-doped Si 15A of the first waveguide 11C1 by a via 16. The first signal electrode 12B1 in the second boundary region 21B on the first waveguide 11C1 side only has the portion 12B12 of the second layer M2, and the portion of the first signal electrode 12B1 on the first layer M1 is absent.

[0055] The second boundary region 21B on the second waveguide 11C2 side has a second ground electrode 12A2, a second signal electrode 12B2, and a third ground electrode 12A3. The second boundary region 21B on the second waveguide 11C2 side has a first bridge 14A (14) that electrically connects the second ground electrode 12A2 and the third ground electrode 12A3. The second waveguide 11C2 in the second boundary region 21B on the second waveguide 11C2 side is composed of two N-doped Si electrodes 15A, but has no EO polymer in the slots 15B. The first bridge 14A in the second boundary region 21B on the second waveguide 11C2 side electrically connects the portion 12A21 of the first layer M1 in the second ground electrode 12A2 to the portion 12A31 of the first layer M1 in the third ground electrode 12A3. The second signal electrode 12B2 in the second boundary region 21B on the second waveguide 11C2 side only has the portion 12B22 of the second layer M2. The portion 12B22 is connected to the N-doped Si 15A of the second waveguide 11C2 by a via 16. The second signal electrode 12B2 in the second boundary region 21B on the second waveguide 11C2 side only has the portion 12B22 of the second layer M2, and the portion of the second signal electrode 12B2 on the first layer M1 is absent.

[0056] The first waveguide 11C1 in the optical modulator 5 changes the phase of the guided light by changing the refractive index in response to the drive voltage of the high-frequency signal applied to the first signal electrode 12B1 in the first portion 20A, the second portion 20B, and the third portion 20C. Furthermore, the first waveguide 11C1 electrically connects the first ground electrode 12A1 and the second ground electrode 12A2 in the first boundary portion 21A and the second boundary portion 21B via a first bridge 14A. A current flows between the first ground electrode 12A1 and the second ground electrode 12A2, equalizing their potentials and stabilizing the potential between the first ground electrode 12A1 and the second ground electrode 12A2. As a result, the potential between the first ground electrode 12A1 and the second ground electrode 12A2 is stabilized, thereby suppressing a decrease in the high-frequency drive voltage between the first signal electrode 12B1 and the first ground electrode 12A1. As a result, the high frequency band can be widened without reducing the modulation efficiency at high frequencies.

[0057] The second waveguide 11C2 in the optical modulator 5 changes the phase of the guided light by changing the refractive index in response to the drive voltage of the high-frequency signal applied to the second signal electrode 12B2 in the first region 20A, the second region 20B, and the third region 20C. Furthermore, the second waveguide 11C2 electrically connects the third ground electrode 12A3 and the second ground electrode 12A2 in the first boundary region 21A and the second boundary region 21B via a first bridge 14A. A current flows between the second ground electrode 12A2 and the third ground electrode 12A3, equalizing the potential and stabilizing the potential between the second ground electrode 12A2 and the third ground electrode 12A3. As a result, the potential between the third ground electrode 12A3 and the second ground electrode 12A2 is stabilized, thereby suppressing a decrease in the high-frequency drive voltage between the second signal electrode 12B2 and the third ground electrode 12A3. As a result, the high frequency band can be widened without reducing the modulation efficiency at high frequencies.

[0058] In the optical modulator 5 of the first embodiment, it is effective to electrically connect the ground electrodes on both sides with the first bridge 14A at a distance between the signal electrode and the ground electrode, for example, a distance of several hundred micrometers to several millimeters. That is, when the electrical signal has propagated a certain distance, the ground electrodes on both sides are electrically connected with the first bridge 14A, and a current flows between the ground electrodes, thereby returning the potentials to the same. When the potential between the ground electrodes on both sides of the signal electrode is stabilized, the voltage between the signal electrode and the ground electrode is prevented from decreasing at high frequencies. As a result, the high-frequency band can be widened without reducing the modulation efficiency at high frequencies.

[0059] In the optical modulator 5 of Example 1, the EO polymer 13 is disposed by inserting the EO polymer into each opening 33A1 in the first region 20A, the second region 20B, and the third region 20C using a dispenser. However, the process of inserting the EO polymer into each divided opening 33A1 using a dispenser is complicated. Therefore, if the EO polymer is inserted into the first region 20A, the first boundary region 21A, the second region 20B, the second boundary region 21B, and the third region 20C using a dispenser, the process becomes easier even when the opening 33A1 is divided. Therefore, an embodiment of the optical modulator 5 manufactured by this manufacturing method will be described below as Example 2. [Example]

[0060] FIG. 5 is a schematic plan view showing an example of the configuration of an optical modulator 5A according to a second embodiment. The same components as those in the optical modulator 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 5A shown in FIG. 5 differs from the optical modulator 5 shown in FIG. 2 in that an EO polymer 13E is disposed on the surface of the buffer layer 33 within the first boundary region 21A and the second boundary region 21B. The optical modulator 5A shown in FIG. 5 also differs from the optical modulator 5 shown in FIG. 2 in that the bridges 14 within the first boundary region 21A and the second boundary region 21B are formed on the second layer M2, not the first layer M1.

[0061] Fig. 6 is a schematic cross-sectional view taken along line CC in Fig. 5, and Fig. 7 is a schematic cross-sectional view taken along line DD in Fig. 5. In this structure, the EO polymer 13D on the surface of the buffer layer 33 in the first region 20A shown in Fig. 6 is flush with the EO polymer 13E on the surface of the buffer layer 33 in the first boundary region 21A shown in Fig. 7. The second region 20B and the third region 20C have the same configuration as the first region 20A, and the second boundary region 21B has the same configuration as the first boundary region 21A.

[0062] In other words, the EO polymer 13D on the surface of the buffer layer 33 in the first region 20A, the second region 20B, and the third region 20C is flush with the EO polymer 13E on the surface of the buffer layer 33 in the first boundary region 21A and the second boundary region 21B.

[0063] 7 has a second bridge 14B that electrically connects a portion 12A12 of the second layer M2 in the first ground electrode 12A1 and a portion 12A22 of the second layer M2 in the second ground electrode 12A2. The first signal electrode 12B1 in the first boundary portion 21A on the first waveguide 11C1 side has only a portion 12B11 of the first layer M1, and does not have a portion of the second layer M2 of the first signal electrode 12B1.

[0064] The first boundary region 21A on the second waveguide 11C2 side has a second bridge 14B that electrically connects a portion 12A32 of the second layer M2 in the third ground electrode 12A3 and a portion 12A22 of the second layer M2 in the second ground electrode 12A2. The second signal electrode 12B2 in the first boundary region 21A on the second waveguide 11C2 side has only a portion 12B21 of the first layer M1, and does not have a portion of the second signal electrode 12B2 on the second layer M2.

[0065] The second boundary region 21B on the first waveguide 11C1 side has a second bridge 14B that electrically connects a portion 12A12 of the second layer M2 in the first ground electrode 12A1 and a portion 12A22 of the second layer M2 in the second ground electrode 12A2. The first signal electrode 12B1 in the second boundary region 21B on the first waveguide 11C1 side has only a portion 12B11 of the first layer M1, and does not have a portion of the second layer M2 of the first signal electrode 12B1.

[0066] The second boundary portion 21B on the second waveguide 11C2 side has a second bridge 14B that electrically connects a portion 12A32 of the second layer M2 in the third ground electrode 12A3 and a portion 12A22 of the second layer M2 in the second ground electrode 12A2. The second signal electrode 12B2 in the second boundary portion 21B on the second waveguide 11C2 side has only a portion 12B21 of the first layer M1, and does not have a portion of the second signal electrode 12B2 on the second layer M2.

[0067] In the optical modulator 5A of the second embodiment, the EO polymer 13 is inserted into each opening 33A1 in the first region 20A, the second region 20B, and the third region 20C while allowing the EO polymer to be applied to the surfaces of the first boundary region 21A and the second boundary region 21B. As a result, the work process related to the insertion of the EO polymer using a dispenser is simplified.

[0068] The first waveguide 11C1 electrically connects the second layer M2 between the first ground electrode 12A1 and the second ground electrode 12A2 in the first boundary region 21A and the second boundary region 21B via the second bridge 14B. As a result, the potential between the first ground electrode 12A1 and the second ground electrode 12A2 is stabilized, thereby stabilizing the high-frequency driving voltage between the first signal electrode 12B1 and the first ground electrode 12A1. Furthermore, since the second layer M2 is closer to the first waveguide 11C1 than the first layer M1, and the second bridge 14B passes current closer to the first waveguide 11C1, the efficiency of the electric field acting on the first waveguide 11C1 is increased.

[0069] The second waveguide 11C2 electrically connects the second layer M2 between the third ground electrode 12A3 and the second ground electrode 12A2 in the first boundary region 21A and the second boundary region 21B via the second bridge 14B. As a result, the potential between the third ground electrode 12A3 and the second ground electrode 12A2 is stabilized, thereby stabilizing the high-frequency driving voltage between the second signal electrode 12B2 and the third ground electrode 12A3. Furthermore, the second layer M2 is closer to the second waveguide 11C2 than the first layer M1, and the second bridge 14B allows current to flow closer to the second waveguide 11C2, thereby increasing the efficiency of the electric field acting on the second waveguide 11C2. [Example]

[0070] Fig. 8 is a schematic plan view showing an example of the configuration of an optical modulator 5B of Example 3, Fig. 9 is a schematic cross-sectional view taken along line EE shown in Fig. 8, and Fig. 10 is a schematic cross-sectional view taken along line FF shown in Fig. 8. Note that the same components as those of the optical modulator 5A of Example 2 are denoted by the same reference numerals, and redundant descriptions of the configurations and operations will be omitted.

[0071] The optical modulator 5B of the third embodiment differs from the optical modulator 5A of the second embodiment in that the waveguides 11C in the first boundary region 21A and the second boundary region 21B are made of undoped Si (Undoped-Si) 15A1.

[0072] The first boundary region 21A and the second boundary region 21B are free of EO polymer. The first waveguide 11C1 in the first boundary region 21A is a region that does not contribute to modulation even when an electric field is applied, so it is a waveguide with a slot 15B1 between two undoped Si 15A1. The second waveguide 11C2 in the first boundary region 21A is also a region that does not contribute to modulation even when an electric field is applied, so it is a waveguide with a slot 15B1 between two undoped Si 15A1.

[0073] The first waveguide 11C1 in the second boundary region 21B is also a location that does not contribute to modulation even when an electric field is applied, so it is a waveguide with a slot 15B1 between two undoped Si 15A1. The second waveguide 11C2 in the second boundary region 21B is also a location that does not contribute to modulation even when an electric field is applied, so it is a waveguide with a slot 15B1 between two undoped Si 15A1.

[0074] In the optical modulator 5B of the third embodiment, the first waveguide 11C1 and the second waveguide 11C2 in the first boundary region 21A and the second boundary region 21B are made of undoped Si, which reduces light absorption by the dopant in the first boundary region 21A and the second boundary region 21B, thereby reducing light loss. [Example]

[0075] Fig. 11 is a plan view showing an example of the configuration of an optical modulator 5C of Example 4, Fig. 12 is a schematic cross-sectional view taken along line GG shown in Fig. 11, and Fig. 13 is a schematic cross-sectional view taken along line HH shown in Fig. 11. Note that the same components as those of the optical modulator 5B of Example 3 are denoted by the same reference numerals, and redundant explanations of the configurations and operations will be omitted.

[0076] The optical modulator 5C of the fourth embodiment differs from the optical modulator 5B of the third embodiment in that the waveguides 11C in the first boundary region 21A and the second boundary region 21B are configured as rib waveguides 15D instead of slot waveguides.

[0077] The first waveguide 11C1 in the first boundary region 21A is an unslotted rib waveguide 15D made of undoped Si 15A1. The second waveguide 11C2 in the first boundary region 21A is an unslotted rib waveguide 15D made of undoped Si 15A1.

[0078] The first waveguide 11C1 in the second boundary region 21B is an unslotted rib waveguide 15D made of undoped Si 15A1. The second waveguide 11C2 in the second boundary region 21B is an unslotted rib waveguide 15D made of undoped Si 15A1.

[0079] In the optical modulator 5C of the fourth embodiment, the first waveguide 11C1 and the second waveguide 11C2 in the first boundary portion 21A and the second boundary portion 21B are configured as rib waveguides 15D made of undoped Si, thereby reducing the optical loss caused by the presence of a slot in the center of the optical waveguide.

[0080] In the optical modulator 5 of Examples 1 to 4, an optical modulator having a GSG structure including a first ground electrode 12A1, a first signal electrode 12B1, a second ground electrode 12A2, a second signal electrode 12B2, and a third ground electrode 12A3 has been exemplified. However, the present invention is not limited to this structure and can be modified as appropriate. Therefore, this embodiment will be described below as Example 5. Note that the same components as those of the optical modulator 5A of Example 2 are designated by the same reference numerals, and redundant descriptions of the components and operations will be omitted. [Example]

[0081] Fig. 14 is a plan view schematically illustrating an example of the configuration of an optical modulator 5D according to Example 5. The electrode 12 of the optical modulator 5D illustrated in Fig. 14 has a GSSG structure including a first ground electrode 12A1, a first signal electrode 12B1, a second signal electrode 12B2, and a second ground electrode 12A2.

[0082] The electrode 12 has a coplanar structure and includes a first ground electrode 12A1, a first signal electrode 12B1, a second ground electrode 12A2, and a second signal electrode 12B2. The first signal electrode 12B1 is arranged parallel to the first ground electrode 12A1. The second signal electrode 12B2 is arranged parallel to the second ground electrode 12A2.

[0083] Of the two waveguides 11C, the first waveguide 11C1 is an optical waveguide located between the first ground electrode 12A1 and the first signal electrode 12B1. The first waveguide 11C1 is a slot waveguide having slots 15B each made of two N-doped Si electrodes 15A.

[0084] Of the two waveguides 11C, the second waveguide 11C2 is an optical waveguide located between the second signal electrode 12B2 and the second ground electrode 12A2. The second waveguide 11C2 is a slot waveguide having slots 15B each formed of two N-doped Si layers 15A.

[0085] The optical modulator 5D has a first portion 20A located in the light propagation direction of the optical waveguide 11, a second portion 20B located in the light propagation direction of the optical waveguide 11, and a third portion 20C located in the light propagation direction of the optical waveguide 11. The optical modulator 5D has a first boundary portion 21A between the first portion 20A and the second portion 20B, and a second boundary portion 21B between the second portion 20B and the third portion 20C.

[0086] In the optical modulator 5D, depending on the direction of travel of the light in the optical waveguide 11, the light is guided through the waveguide 11C in the order of the first portion 20A, the first boundary portion 21A, the second portion 20B, the second boundary portion 21B, and the third portion 20C.

[0087] Fig. 15 is a schematic cross-sectional view of the JJ line shown in Fig. 14. The schematic cross-sectional portion of the JJ line shown in Fig. 15 is, for example, a first portion 20A. The first portion 20A has a silicon substrate 31, an intermediate layer 32 made of SiO2 stacked on the silicon substrate 31, an optical waveguide 11 formed on the intermediate layer 32, a buffer layer 33 made of SiO2 stacked on the intermediate layer 32 including the optical waveguide 11, and an electrode 12. The electrode 12 has a first ground electrode 12A1, a first signal electrode 12B1, a second signal electrode 12B2, and a second ground electrode 12A2.

[0088] The first ground electrode 12A1 has a portion 12A11 on the first layer M1 and a portion 12A12 on the second layer M2. The first signal electrode 12B1 has a portion 12B11 on the first layer M1 and a portion 12B12 on the second layer M2.

[0089] A via 16 connects a portion 12A11 of the first layer M1 in the first ground electrode 12A1 to a portion 12A12 of the second layer M2 in the first ground electrode 12A1, and a via 16 connects the portion 12A12 of the second layer M2 in the first ground electrode 12A1 to the N-doped Si 15A. A via 16 connects a portion 12B11 of the first layer M1 in the first signal electrode 12B1 to a portion 12B12 of the second layer M2 in the first signal electrode 12B1, and a via 16 connects the portion 12B12 of the second layer M2 in the first signal electrode 12B1 to the N-doped Si 15A. A via 16 connects a portion 12A21 of the first layer M1 in the second ground electrode 12A2 and a portion 12A22 of the second layer M2 in the second ground electrode 12A2.

[0090] The first portion 20A has a first EO polymer 13A inserted into the opening 33A1 in the buffer layer 33, and a first waveguide 11C1 in which a portion of the first EO polymer 13A is inserted into the slot 15B.

[0091] The first portion 20A on the first waveguide 11C1 side has a first ground electrode 12A1 and a first signal electrode 12B1, and a first EO polymer 13A is disposed in an opening 33A1 formed in the buffer layer 33 between the first ground electrode 12A1 and the first signal electrode 12B1. A part of the first EO polymer 13A is inserted into a slot 15B in the first waveguide 11C1.

[0092] The first portion 20A on the second waveguide 11C2 side has a second signal electrode 12B2 and a second ground electrode 12A2, and the first EO polymer 13A is disposed in an opening 33A1 formed in the buffer layer 33 between the second ground electrode 12A2 and the second signal electrode 12B2. A portion of the first EO polymer 13A is inserted into a slot 15B in the second waveguide 11C2.

[0093] The second portion 20B and the third portion 20C have substantially the same configuration, and therefore the same reference numerals are used to denote the same components, and the overlapping description of the configuration and operation will be omitted. The second portion 20B has a second EO polymer 13B inserted into the opening 33A1 in the buffer layer 33, and a first waveguide 11C1 and a second waveguide 11C2, each of which has a portion of the second EO polymer 13B inserted into a slot 15B.

[0094] The third portion 20C also has a third EO polymer 13C inserted into an opening 33A1 in the buffer layer 33, and a first waveguide 11C1 and a second waveguide 11C2 with portions of the third EO polymer 13C inserted into slot 15B.

[0095] FIG. 16 is a schematic cross-sectional view of the KK line shown in FIG. 14. The schematic cross-sectional portion of the KK line shown in FIG. 16 is, for example, a first boundary portion 21A. The first boundary portion 21A corresponds to the boundary portion between the first portion 20A and the second portion 20B, i.e., the portion separating the first EO polymer 13A and the second EO polymer 13B. The first boundary portion 21A has a first waveguide 11C1 that joins the first waveguide 11C1 of the first portion 20A and the first waveguide 11C1 of the second portion 20B. The first boundary portion 21A has a third bridge 14C (14) that electrically connects the first ground electrode 12A1 and the second ground electrode 12A2.

[0096] The first boundary region 21A on the first waveguide 11C1 side has a first ground electrode 12A1 and a first signal electrode 12B1. The first waveguide 11C1 is composed of two non-N-doped Si 15A1 electrodes, and no EO polymer is present within the slot 15B1. The first boundary region 21A on the second waveguide 11C2 side has a second signal electrode 12B2 and a second ground electrode 12A2. The second waveguide 11C2 is also composed of two non-N-doped Si 15A1 electrodes, and no EO polymer is present within the slot 15B1.

[0097] The third bridge 14C electrically connects the portion 12A12 of the second layer M2 in the first ground electrode 12A1 and the portion 12A22 of the second layer M2 in the second ground electrode 12A2.

[0098] The configuration of the first boundary region 21A has been described above. The second boundary region 21B has a substantially identical configuration. Therefore, the same reference numerals are used, and a description of the overlapping configuration and operation will be omitted. The second boundary region 21B corresponds to the boundary region between the second region 20B and the third region 20C, i.e., the region separating the second EO polymer 13B from the third EO polymer 13C. The second boundary region 21B includes a first waveguide 11C1 that connects the first waveguide 11C1 in the second region 20B to the first waveguide 11C1 in the third region 20C. The second boundary region 21B includes a second waveguide 11C2 that connects the second waveguide 11C2 in the second region 20B to the second waveguide 11C2 in the third region 20C. The second boundary portion 21B has a third bridge 14C (14) that electrically connects the second layer M2 between the first ground electrode 12A1 and the second ground electrode 12A2. The third bridge 14C electrically connects a portion 12A12 of the second layer M2 in the first ground electrode 12A1 to a portion 12A22 of the second layer M2 in the second ground electrode 12A2.

[0099] The first waveguide 11C1 in the optical modulator 5D changes the phase of the guided light by changing its refractive index in response to the driving voltage of a high-frequency signal applied to the first signal electrode 12B1 in the first portion 20A, the second portion 20B, and the third portion 20C. The second waveguide 11C2 in the optical modulator 5D changes the phase of the guided light by changing its refractive index in response to the driving voltage of a high-frequency signal applied to the second signal electrode 12B2 in the first portion 20A, the second portion 20B, and the third portion 20C. Furthermore, the first waveguide 11C1 and the second waveguide 11C2 electrically connect the first ground electrode 12A1 and the second ground electrode 12A2 in the first boundary portion 21A and the second boundary portion 21B by a third bridge 14C. As a result, even though the optical modulator 5D has a GSSG structure, the potential between the first ground electrode 12A1 and the second ground electrode 12A2 is stabilized, thereby stabilizing the high-frequency driving voltage between the first signal electrode 12B1 and the first ground electrode 12A1.

[0100] In addition, in the optical modulator 5 of Example 1 above, an example of a GSG structure having three ground electrodes and two signal electrodes is shown, but the number of ground electrodes and signal electrodes is not limited to this and can be changed as appropriate.

[0101] In the optical modulator 5, the first portion 20A, the first boundary portion 21A, the second portion 20B, the second boundary portion 21B, and the third portion 20C are sequentially arranged in the light propagation direction of the optical waveguide 11, and a case where two boundary portions 21B are arranged has been illustrated. However, the number of boundary portions is not limited to two, and may be one or more, and can be changed as appropriate.

[0102] Furthermore, the electrode 12 of the optical modulator 5 has been exemplified as having two layers, a first layer M1 and a second layer M2, but it may have three or more layers, and in the case of three or more layers, a bridge 14 may be provided to electrically connect the ground electrodes using at least one or more layers, and modifications can be made as appropriate. [Explanation of symbols]

[0103] 1 Optical communication equipment 3 DSP 4 light source 5 Optical Modulator 11 Optical waveguide 11C1 first waveguide 11C2 Second waveguide 12 electrodes 12A1 First ground electrode 12A2 Second ground electrode 12A3 Third ground electrode 12B1 First signal electrode 12B2 Second signal electrode 13 EO polymer 13A First EO polymer 13B Second EO polymer 14 Bridge 14A First Bridge 14B Second Bridge 14C Third Bridge 15A N-doped Si 15A1 N-doped Si 15B slot 20A First Section 20B Second part 21A First border area 33 Buffer layer 33A1 opening

Claims

1. a slot waveguide; a coplanar electrode including a signal electrode and a ground electrode running parallel to the slot waveguide; a plurality of electro-optic polymers inserted in a separated state into slots in the slot waveguide; a bridge disposed at a boundary between the divided electro-optic polymers, electrically connecting the ground electrode to another ground electrode; a first portion in a light propagation direction of the slot waveguide; a second portion in a light propagation direction of the slot waveguide; the boundary region between the first region and the second region, The boundary site is an optical device characterized in that the portion is a separation between a first electro-optic polymer disposed in an opening in the first portion and inserted into the slot in the slot waveguide, and a second electro-optic polymer disposed in an opening in the second portion and inserted into the slot in the slot waveguide.

2. 2. The optical device according to claim 1, wherein the driving voltage applied to the signal electrode is a high-frequency signal.

3. The electrode is a first layer; and a second layer disposed below the first layer; The bridge is 3. The optical device according to claim 2, wherein the first layer in the ground electrode and the first layer in the other ground electrode are electrically connected.

4. The electrode is a first layer; and a second layer disposed below the first layer; The bridge is 3. The optical device according to claim 2, wherein the second layer in the ground electrode and the second layer in the other ground electrode are electrically connected.

5. The electrode is a first layer; and a second layer disposed below the first layer, 2. The optical device of claim 1, wherein the electro-optic polymer is disposed on the surfaces of the first region, the second region, and the boundary region by inserting an electro-optic polymer into the opening in the buffer layer covering the first layer in the first region, the opening in the buffer layer covering the first layer in the second region, and the upper surface of the buffer layer covering the first layer in the boundary region.

6. The slot waveguide in the first section and the second section comprises: It is made of doped silicon, The slot waveguide in the boundary region is 6. The optical device of claim 5, wherein the optical device is made of undoped silicon.

7. The slot waveguide in the boundary region is 7. An optical device according to claim 6, wherein said slot waveguide is replaced by a rib waveguide.

8. The electrode is a first ground electrode; a first signal electrode arranged in parallel with the first ground electrode; a second ground electrode disposed in parallel with the first signal electrode; and The first portion and the second portion are The slot waveguide is disposed between the first ground electrode and the first signal electrode; The bridge within the boundary region is 2. The optical device according to claim 1, further comprising a bridge electrically connecting the first ground electrode and the second ground electrode.

9. The electrode is a first ground electrode; a first signal electrode arranged in parallel with the first ground electrode; a second signal electrode arranged in parallel with the first signal electrode; a second ground electrode arranged in parallel with the second signal electrode, The first portion and the second portion are The slot waveguide is disposed between the first ground electrode and the first signal electrode; The slot waveguide is disposed between the second signal electrode and the second ground electrode; The bridge within the boundary region is 2. The optical device according to claim 1, further comprising a bridge electrically connecting the first ground electrode and the second ground electrode.

10. a slot waveguide; an electrode having a coplanar structure including a signal electrode and a ground electrode running parallel to the slot waveguide, wherein the refractive index in the slot waveguide varies in response to a drive voltage applied to the signal electrode, a plurality of electro-optic polymers inserted in a separated state into slots in the slot waveguide; a bridge disposed at a boundary between the divided electro-optic polymers, electrically connecting the ground electrode to another ground electrode; a first portion in a light propagation direction of the slot waveguide; a second portion in a light propagation direction of the slot waveguide; the boundary region between the first region and the second region, The boundary site is an optical modulator characterized in that the first electro-optic polymer is disposed in an opening in the first region and is inserted into the slot in the slot waveguide, and the second electro-optic polymer is disposed in an opening in the second region and is inserted into the slot in the slot waveguide.

11. a processor that performs signal processing on the electrical signal; A light source that generates light; an optical modulator that modulates light generated from the light source using the electrical signal output from the processor; The optical modulator comprises: a slot waveguide; an electrode having a coplanar structure including a signal electrode and a ground electrode running parallel to the slot waveguide, wherein the refractive index in the slot waveguide varies in response to a drive voltage applied to the signal electrode, a plurality of electro-optic polymers inserted in a separated state into slots in the slot waveguide; a bridge disposed at a boundary between the divided electro-optic polymers, electrically connecting the ground electrode to another ground electrode; a first portion in a light propagation direction of the slot waveguide; a second portion in a light propagation direction of the slot waveguide; the boundary region between the first region and the second region, The boundary site is an optical communication device, characterized in that the portion is a portion that separates a first electro-optic polymer that is disposed in an opening in the first portion and inserted into the slot in the slot waveguide, and a second electro-optic polymer that is disposed in an opening in the second portion and inserted into the slot in the slot waveguide.

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