Optical modulators, phase shifters, and optical communication devices

Abstract

To provide an optical modulator and the like that can achieve fine adjustment of output light, while ensuring the amount of phase shift.SOLUTION: An optical modulator has a first phase shifter and a second phase shifter. The first phase shifter has a first optical waveguide through which first signal light passes, and a first DC electrode that applies electric power according to driving voltage to the first optical waveguide. The first phase shifter shifts the phase of the first signal light passing through the first optical waveguide according to the driving voltage to the first DC electrode. The second phase shifter has a second optical waveguide through which second signal light passes, and a second DC electrode that applies electric power according to the driving voltage to the second optical waveguide. The second phase shifter shifts the phase of the second signal light passing through the second optical waveguide according to the driving voltage to the second DC electrode. The second phase shifter has a small amount of phase shift according to a predetermined amount of driving voltage compared with the first phase shifter.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an optical modulator, a phase shifter, and an optical communication device.

Background Art

[0002] The optical modulator integrates four-channel Mach-Zehnder modulators. Each Mach-Zehnder interferometer (MZI) has a radio frequency phase shifter (RFPS) and a direct current phase shifter (DCPS). The RFPS is, for example, an MZI that inputs a high-speed signal having a bandwidth of several tens of GHz and performs high-speed modulation. The DCPS is, for example, composed of a heater electrode, and is an MZI that changes the refractive index of an optical waveguide by flowing a current through the heater electrode to heat the optical waveguide and adjusts the phase of light. The optical modulator adjusts the current flowing through the heater electrode of the DCPS so that the ON / OFF of the electrical signal input to the RFPS corresponds to the ON / OFF of the optical signal.

[0003] The optical modulator has a DC-side MZM that adjusts the phase of the signal light. FIG. 12 is a schematic plan view showing an example of the configuration of the DC-side MZM 200. The DC-side MZM 200 shown in FIG. 12 includes a DCPS 210, a multiplexing section 220, and a cladding layer 230. The DCPS 210 includes a first DCPS 210A that shifts the phase of the first signal light and a second DCPS 210B that shifts the phase of the second signal light. The first signal light and the second signal light are, for example, signal lights obtained by branching input light.

[0004] The first DCPS210A has a first optical waveguide 211A through which the first signal light passes, provided on a Si substrate, and a first DC electrode 212A that runs parallel to the first optical waveguide 211A and heats the first optical waveguide 211A with power corresponding to the drive voltage. The first DC electrode 212A is a heater electrode made of a resistive metallic material such as Ti. The first DCPS210A heats the first optical waveguide 211A with power corresponding to the drive voltage and changes the optical refractive index of the first optical waveguide 211A due to the thermo-optic effect of Si. By changing the optical refractive index of the first optical waveguide 211A, the first DCPS210A shifts the phase of the first signal light passing through the first optical waveguide 211A and outputs the phase-shifted first signal light to the multiplexer 220.

[0005] The second DCPS210B has a second optical waveguide 211B through which the second signal light passes, provided on a Si substrate, and a second DC electrode 212B that runs parallel to the second optical waveguide 211B and heats the second optical waveguide 211B with power corresponding to the drive voltage. The second DC electrode 212B is a heater electrode made of a resistive metallic material such as Ti. The second DCPS210B heats the second optical waveguide 211B with power corresponding to the drive voltage and changes the optical refractive index of the second optical waveguide 211B due to the thermo-optic effect of Si. By changing the optical refractive index of the second optical waveguide 211B, the second DCPS210B shifts the phase of the second signal light passing through the second optical waveguide 211B and outputs the phase-shifted second signal light to the multiplexer 220.

[0006] The wave-combining unit 220 combines the first signal light after phase shift and the second signal light after phase shift. The cladding layer 230 is a layer of, for example, SiO2 that covers the first DCPS210A, the second DCPS210B, and the wave-combining unit 220. In other words, the DC-side MZM200 combines the first signal light after phase shift in the first DCPS210A and the second signal light after phase shift in the second DCPS210B to output a phase-adjusted signal light. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2016-133664 [Patent Document 2] U.S. Patent Application Publication No. 2017 / 0099529 Specification [Patent Document 3] Japanese Patent Publication No. 2019-191252 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, the maximum drive voltage applied to the DCPS is limited by the power supply, and it is necessary to compensate for the phase instability caused by component variations in RFPS and other components below that maximum voltage over the long term.

[0009] Figure 13A is an explanatory diagram showing an example of the relationship between the drive voltage and output light in the DCPS210 within the conventional DC-side MZM200. When the maximum voltage applied to the DCPS210 is 5V and the phase shift amount required to compensate for phase instability is 4π, the relationship between the drive voltage applied to the heater electrode and the output light (transmittance) is as shown in Figure 13A.

[0010] Figure 13B is an explanatory diagram showing an example of the gradient (amount of change) with respect to the drive voltage in the DCPS210 within the conventional DC-side MZM200. As shown in Figure 13B, the relationship between the drive voltage applied to the heater electrode and the amount of change in output light is such that the gradient (amount of change) of the output light with respect to the drive voltage becomes large. In particular, when trying to reduce the output light, the gradient (amount of change) of the output light with respect to the drive voltage becomes large. For example, when trying to adjust the output light to -15dB, the gradient (amount of change) at that time becomes large at 55dB / V. Therefore, it is necessary to control the drive voltage with high precision, but high-precision drive control is difficult. As a result, it is difficult to fine-tune the output light while ensuring the amount of phase shift in the DCPS.

[0011] The disclosed technology was developed in view of these points, and aims to provide an optical modulator, etc., that can achieve fine adjustment of the output light while ensuring a certain amount of phase shift. [Means for solving the problem]

[0012] In one embodiment, the optical modulator disclosed herein includes a first phase shifter and a second phase shifter. The first phase shifter includes a first optical waveguide through which a first signal light passes, and a first DC electrode running parallel to the first optical waveguide and applying power to the first optical waveguide in accordance with a drive voltage. The first phase shifter shifts the phase of the first signal light passing through the first optical waveguide in accordance with the drive voltage to the first DC electrode. The second phase shifter includes a second optical waveguide through which a second signal light passes, and a second DC electrode running parallel to the second optical waveguide and applying power to the second optical waveguide in accordance with a drive voltage. The second phase shifter shifts the phase of the second signal light passing through the second optical waveguide in accordance with the drive voltage to the second DC electrode. The second phase shifter is configured to produce a smaller phase shift amount in response to a predetermined drive voltage compared to the first phase shifter. [Effects of the Invention]

[0013] According to one embodiment of the optical modulator, etc. disclosed in this application, it is possible to fine-tune the output light while ensuring a phase shift amount. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a block diagram showing an example of the configuration of an optical communication device in this embodiment. [Figure 2] Figure 2 is a schematic plan view showing an example of the configuration of an optical modulator. [Figure 3] Figure 3 is a schematic plan view showing an example of the configuration of the DC side MZM of Example 1. [Figure 4A] Figure 4A is an explanatory diagram illustrating an example of the relationship between the drive voltage and output light in the first DCPS and the second DCPS within the DC side MZM. [Figure 4B]FIG. 4B is an explanatory diagram showing an example of the relationship between the gradients (change amounts) with respect to the driving voltages in the first DCPS and the second DCPS in the DC-side sub-MZM. [Figure 5] FIG. 5 is a schematic plan view showing an example of the configuration of the DC-side sub-MZM of Example 2. [Figure 6] FIG. 6 is a schematic plan view showing an example of the configuration of the DC-side sub-MZM of Example 3. [Figure 7] FIG. 7 is a schematic plan view showing an example of the configuration of the DC-side sub-MZM of Example 4. [Figure 8] FIG. 8 is a schematic plan view showing an example of the configuration of the DC-side sub-MZM of Example 5. [Figure 9] FIG. 9 is a schematic plan view showing an example of the configuration of the DC-side sub-MZM of Example 6. [Figure 10] FIG. 10 is a schematic plan view showing an example of the configuration of the DC-side sub-MZM of Example 7. [Figure 11] FIG. 11 is a schematic plan view showing an example of the configuration of the DC-side sub-MZM of Example 8. [Figure 12] FIG. 12 is a schematic plan view showing an example of the configuration of the conventional DC-side MZM. [Figure 13A] FIG. 13A is an explanatory diagram showing an example of the relationship between the driving voltage and the output light in the DCPS in the conventional DC-side MZM. [Figure 13B] FIG. 13B is an explanatory diagram showing an example of the gradient (change amount) with respect to the driving voltage in the DCPS in the conventional DC-side MZM.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of an optical communication device and the like disclosed in the present application will be described in detail with reference to the drawings. Note that the present invention is not limited by this embodiment.

Examples

[0016] Figure 1 is a block diagram showing an example of the configuration of an optical communication device in this embodiment. The optical communication device 1 shown in Figure 1 is, for example, an optical coherent transceiver connected to the output optical fiber 2A(2) and the input optical fiber 2B(2). 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. The DSP 3 performs processing such as encoding of transmission data and outputs a data signal corresponding to the transmission data after processing to the optical modulator 5. The DSP 3 also performs processing such as decoding on the received data corresponding to the data signal obtained from the optical receiver 6.

[0017] The light source 4 is, for example, an ITLA (Integrated Tunable Laser Assembly) equipped with a tunable laser diode or the like, which generates light of a predetermined wavelength and supplies it to the optical modulator 5 and the optical receiver 6.

[0018] Figure 2 is a schematic plan view showing an example of the configuration of an optical modulator 5. The optical modulator 5 shown in Figure 2 includes an optical waveguide 11, an optical input section 12, a first branching section 13, an X-polarized MZM14A(14), and a Y-polarized MZM14B(14). The optical modulator 5 also includes a polarization rotator (PR) 15, a polarization beam combiner (PBC) 16, and an optical output section 17.

[0019] Optical waveguide 11 is a Si waveguide having optical waveguide 11A, optical waveguide 11B, and optical waveguide 11C. Optical waveguide 11A is an optical waveguide connecting the optical input section 12 and the first branching section 13. Optical waveguide 11B is an optical waveguide connecting the second multiplexing section 27A(27) in the X-polarized MZM14A and the optical output section 17, and the second multiplexing section 27B(27) in the Y-polarized MZM14B and the optical output section 17. Optical waveguide 11C is an optical waveguide connecting the first branching section 13 and the second multiplexing section 27.

[0020] The optical input unit 12 receives laser light from the light source 4. The first branching unit 13 optically branches the laser light from the optical input unit 12 and outputs the resulting laser light to the X-polarized MZM14A and the Y-polarized MZM14B.

[0021] The X-polarized MZM14A quadrature-phase modulates the laser beam after branching at the first branching section 13 with an X-polarized data signal, and outputs the X-polarized IQ component signal light to the PBC16. The Y-polarized MZM14B quadrature-phase modulates the laser beam after branching at the first branching section 13 with a Y-polarized data signal, and outputs the Y-polarized IQ component signal light to the PR15. The PR15 polarizes the Y-polarized IQ component signal light from the Y-polarized MZM14B to convert it into an X-polarized IQ component signal light, and outputs the converted X-polarized IQ component signal light to the PBC16. Furthermore, the PBC16 combines the X-polarized IQ component signal light from the X-polarized MZM14A and the converted X-polarized IQ component signal light from the PR15 to output a polarization-multiplexed signal light to the optical output section 17.

[0022] The X-polarized MZM14A has a second branching section 21A (21), two third branching sections 22 (22A), two RF-side MZM23 (23A, 23B), two DC-side sub-MZM24 (24A, 24B), and two first multiplexing sections 26 (26A, 26B). Furthermore, the X-polarized MZM14A has a DC-side parent MZM25 (25A) and a second multiplexing section 27 (27A).

[0023] The third branching section 22A branches the laser light from the second branching section 21A to each RFPS41 in the RF-side MZM23A. The RF-side MZM23A has two RF electrodes 28 and two RFPS41. Each RFPS41 in the RF-side MZM23A modulates the laser light at high speed in response to the high-speed signal from the RF electrode 28, and outputs the high-speed modulated laser light to each child DCPS42 in the DC-side child MZM24A.

[0024] The DC side unit MZM24A has two DC electrodes 30A and 30B (30) and two child DCPS42. The DC electrodes 30 are DC heater electrodes made of a resistive metallic material such as Ti. Each child DCPS42 in the DC side unit MZM24A phase modulates the laser light after high-speed modulation according to the data signal from the DC electrodes 30 and outputs the phase-modulated I component signal light to the first multiplexer 26A. The first multiplexer 26A combines the I component signal light from each child DCPS42 and outputs the combined I component signal light to one of the parent DCPS43 in the DC side parent unit MZM25A.

[0025] The DC side unit MZM24B has two DC electrodes 30A and 30B (30) and two child DCPS42. Each child DCPS42 in the DC side unit MZM24B phase modulates the laser light after high-speed modulation according to the data signal from the DC electrode 30 and outputs the phase-modulated Q component signal light to the first multiplexer 26B. The first multiplexer 26B combines the Q component signal light from each child DCPS42 and outputs the combined Q component signal light to the other parent DCPS43 in the DC side parent unit MZM25A.

[0026] The DC-side parent MZM25A has two DC electrodes 30C(30) and two parent DCPS43. One parent DCPS43 in the DC-side parent MZM25A orthogonally modulates the phase-modulated I component signal light in response to the drive voltage signal from the DC electrode 30C, and outputs the orthogonally modulated X-polarized I component signal light to the second multiplexer 27A. The other parent DCPS43 in the DC-side parent MZM25A orthogonally modulates the phase-modulated Q component signal light in response to the drive voltage signal from the DC electrode 30C, and outputs the orthogonally modulated X-polarized Q component signal light to the second multiplexer 27A.

[0027] The second combiner 27A combines the X-polarized I component signal light from one parent DCPS43 in the DC-side parent MZM25A with the X-polarized Q component signal light from the other parent DCPS43 in the DC-side parent MZM25A. The second combiner 27A then outputs the combined X-polarized IQ component signal light to the PBC16.

[0028] The Y-polarized MZM14B has a second branching section 21B (21), two third branching sections 22B (22), two RF-side MZM23 (23C, 23D), and two DC-side sub-MZM24 (24C, 24D). Furthermore, the Y-polarized MZM14B has two first multiplexing sections 26 (26C, 26D), a DC-side parent MZM25 (25B), a second multiplexing section 27 (27B), and an adjustment section 32.

[0029] The third branching section 22B branches the laser beam from the second branching section 21B to each RFPS41 in the RF-side MZM23C. The RF-side MZM23C has two RF electrodes 28 and two RFPS41. Each RFPS41 in the RF-side MZM23C modulates the laser beam at high speed in response to the high-speed signal from the RF electrode 28, and outputs the high-speed modulated laser beam to each child DCPS42 in the DC-side child MZM24C.

[0030] The DC side unit MZM24C has two DC electrodes 30A and 30B (30) and two child DCPS42. Each child DCPS42 in the DC side unit MZM24C phase modulates the laser light after high-speed modulation according to the data signal from the DC electrode 30 and outputs the phase-modulated I component signal light to the first multiplexer 26C. The first multiplexer 26C combines the I component signal light from each child DCPS42 and outputs the combined I component signal light to one of the parent DCPS43 in the DC side parent unit MZM25B.

[0031] The DC side unit MZM24D has two DC electrodes 30A and 30B (30) and two child DCPS42. Each child DCPS42 in the DC side unit MZM24D phase modulates the laser light after high-speed modulation according to the data signal from the DC electrode 30 and outputs the phase-modulated Q component signal light to the first multiplexer 26D. The first multiplexer 26D combines the Q component signal light from each child DCPS42 and outputs the combined Q component signal light to the other parent DCPS43 in the DC side parent unit MZM25B.

[0032] The DC-side parent MZM25B has two DC electrodes 30C(30) and two parent DCPS43. One parent DCPS43 in the DC-side parent MZM25B orthogonally modulates the phase-modulated I component signal light in response to the drive voltage signal from the DC electrode 30C, and outputs the orthogonally modulated Y-polarized I component signal light to the second multiplexer 27B. The other parent DCPS43 in the DC-side parent MZM25B orthogonally modulates the phase-modulated Q component signal light in response to the drive voltage signal from the DC electrode 30C, and outputs the orthogonally modulated Y-polarized Q component signal light to the second multiplexer 27B.

[0033] The second multiplexer 27B combines the Y-polarized I component signal light from one parent DCPS43 in the DC-side parent MZM25B with the Y-polarized Q component signal light from the other parent DCPS43 in the DC-side parent MZM25B. The second multiplexer 27B then outputs the combined Y-polarized IQ component signal light to PR15. PR15 polarizes the Y-polarized IQ component signal light from the second multiplexer 27B and outputs the X-polarized IQ component signal light after polarization rotation to PBC16. PBC16 polarization multiplexes the X-polarized IQ component signal light from the second multiplexer 27A with the X-polarized IQ component signal light from PR15 and outputs the polarization multiplexed signal from the optical output unit 17.

[0034] Figure 3 is a schematic plan view showing an example of the configuration of the DC side MZM24A of Embodiment 1. For the sake of explanation, the DC side MZM24A will be described, but since the DC side MZM24B, 24C, and 24D have the same configuration as the DC side MZM24A, they are given the same reference numerals, and the explanation of their overlapping configurations and operations will be omitted. The DC side MZM24A shown in Figure 3 has a first DCPS42A which is a sub-DCPS42 that shifts the phase of the first signal light, a second DCPS42B which is a sub-DCPS42 that shifts the phase of the second signal light, a first multiplexer 26A, and a cladding layer 51.

[0035] The first DCPS42A has a first optical waveguide 11C1 through which the first signal light passes, and a first DC electrode 30A that runs parallel to the first optical waveguide 11C1 and heats the first optical waveguide 11C1 with power corresponding to the drive voltage. The first DCPS42A heats the first optical waveguide 11C1 with power corresponding to the drive voltage and changes the optical refractive index of the first optical waveguide 11C1 due to the thermo-optic effect of Si. By changing the optical refractive index of the first optical waveguide 11C1, the first DCPS42A shifts the phase of the first signal light passing through the first optical waveguide 11C1 and outputs the phase-shifted first signal light to the first multiplexer 26A.

[0036] The second DCPS42B has a second optical waveguide 11C2 through which the second signal light passes, and a second DC electrode 30B that runs parallel to the second optical waveguide 11C2 and heats the second optical waveguide 11C2 with power corresponding to the drive voltage. The second DCPS42B heats the second optical waveguide 11C2 with power corresponding to the drive voltage and changes the optical refractive index of the second optical waveguide 11C2 due to the thermo-optic effect of Si. By changing the optical refractive index of the second optical waveguide 11C2, the second DCPS42B shifts the phase of the second signal light passing through the second optical waveguide 11C2 and outputs the phase-shifted second signal light to the first multiplexer 26A.

[0037] The first multiplexer 26A combines the phase-shifted first signal light and the phase-shifted second signal light. The cladding layer 51 is a layer of, for example, SiO2 that covers the first DCPS42A, the second DCPS42B, and the first multiplexer 26A.

[0038] The electrode width W2 of the second DC electrode 30B in the second DCPS42B is narrower than the electrode width W1 of the first DC electrode 30A in the first DCPS42A. As a result, the electrical resistance of the second DC electrode 30B is higher than that of the first DC electrode 30A.

[0039] The electrode width W1 of the first DC electrode 30A is wider than the electrode width W2 of the second DC electrode 30B. As a result, the current flowing through the first DC electrode 30A is larger than that of the second DC electrode 30B, and the first optical waveguide 11C1 is heated, resulting in a larger phase shift of the first DCPS42A. In contrast, the current flowing through the second DC electrode 30B is smaller than that of the first DC electrode 30A, and the second optical waveguide 11C2 is not heated, resulting in a smaller phase shift of the second DCPS42B.

[0040] Figure 4A is an explanatory diagram illustrating an example of the relationship between the drive voltage and output light in the first DCPS42A and second DCPS42B within the DC side unit MZM24A. Assume that the electrode width W2 of the second DC electrode 30B is 1 / 4 of the electrode width W1 of the first DC electrode 30A. When a drive voltage of 5V is applied to the second DC electrode 30B, the phase shift amount of the second DCPS42B is 1 / 4 of the phase shift amount of the first DCPS42A. The relationship between the drive voltage of the first DCPS42A and the second DCPS42B and the output light is as shown in Figure 4A.

[0041] Figure 4B is an explanatory diagram showing an example of the gradient (amount of change) with respect to the drive voltage in the first DCPS42 and the second DCPS42 within the DC side unit MZM24A. As shown in Figure 4B, the gradient (amount of change) of the output light with respect to the drive voltage is smaller for the second DCPS42B compared to the first DCPS42A. As a result, fine adjustment of the output light can be achieved with the second DCPS42B while ensuring a phase shift amount of 4π with the first DCPS42A.

[0042] In other words, with the DC side unit MZM24A, the phase shift amount of 4π is controlled by the first DCPS42A, and then the output light is finely adjusted by the second DCPS42B. Therefore, it is possible to easily control the phase while compensating for long-term phase instability.

[0043] In the DC side MZM24A of Example 1, the second DCPS42B is configured to have a smaller phase shift amount corresponding to a predetermined drive voltage compared to the first DCPS42A. Specifically, the first DC electrode 30A and the second DC electrode 30B are configured such that the electrode width W2 of the second DC electrode 30B in the second DCPS42B is narrower than the electrode width W1 of the first DC electrode 30A in the first DCPS42A. As a result, it is possible to fine-tune the output light with the second DCPS42B while ensuring a phase shift amount of 4π with the first DCPS42A.

[0044] For the sake of explanation, I have described the DC side child MZM24A, but the DC side parent MZM25 has the same configuration as the DC side child MZM24A, so the same effect can be said.

[0045] The DC side MZM24A of Example 1 exemplifies a structure in which the electrode width W2 of the second DC electrode 30B is narrower than the electrode width W1 of the first DC electrode 30A. However, the electrode widths of the first DC electrode 30A and the second DC electrode 30B may be made the same, and the number of folds of the first optical waveguide 11C1 and the second optical waveguide 11C2 acting on the DC electrode 30 may be changed. This embodiment will be described below as Example 2. Note that components identical to those of the optical modulator 5 in Example 1 are denoted by the same reference numerals, and the description of their overlapping components and operations will be omitted. [Examples]

[0046] Figure 5 is a schematic plan view showing an example of the configuration of the DC side MZM24A1 of Embodiment 2. The DC side MZM24A1 shown in Figure 5 has a first DCPS42A1 which is a sub-DCPS42 that shifts the phase of the first signal light, a second DCPS42B1 which is a sub-DCPS42 that shifts the phase of the second signal light, a first multiplexer 26A, and a cladding layer 51.

[0047] The first DCPS42A1 has a first optical waveguide 11C11 through which the first signal light passes, and a first DC electrode 30A1 that runs parallel to the first optical waveguide 11C11 and heats the first optical waveguide 11C11 with power corresponding to the drive voltage. The first DCPS42A1 heats the first optical waveguide 11C11 with power corresponding to the drive voltage and changes the optical refractive index of the first optical waveguide 11C11 due to the thermo-optic effect of Si caused by the heating of the first optical waveguide 11C11. By changing the optical refractive index of the first optical waveguide 11C11, the first DCPS42A1 shifts the phase of the first signal light passing through the first optical waveguide 11C11 and outputs the phase-shifted first signal light to the first multiplexer 26A.

[0048] The second DCPS42B1 has a second optical waveguide 11C21 through which the second signal light passes, and a second DC electrode 30B1 that runs parallel to the second optical waveguide 11C21 and heats the second optical waveguide 11C21 with power corresponding to the drive voltage. The second DCPS42B1 heats the second optical waveguide 11C21 with power corresponding to the drive voltage, and changes the optical refractive index of the second optical waveguide 11C21 due to the thermo-optic effect of Si caused by the heating of the second optical waveguide 11C21. By changing the optical refractive index of the second optical waveguide 11C21, the second DCPS42B1 shifts the phase of the second signal light passing through the second optical waveguide 11C21 and outputs the phase-shifted second signal light to the first multiplexer 26A.

[0049] The first multiplexer 26A combines the phase-shifted first signal light and the phase-shifted second signal light. The cladding layer 51 is a layer of, for example, SiO2 that covers the first DCPS42A1, the second DCPS42B1, and the first multiplexer 26A.

[0050] The second optical waveguide 11C21, on which the power of the second DC electrode 30B1 in the second DCPS42B1 acts, is a straight waveguide. In contrast, the first optical waveguide 11C11, on which the power of the first DC electrode 30A1 in the first DCPS42A1 acts, is a folded waveguide that folds twice. The second optical waveguide 11C21 has one circuit on which the power of the second DC electrode 30B1 acts, while the first optical waveguide 11C11 has three circuits on which the power of the first DC electrode 30A1 acts. The phase shift amount of the second DCPS42B1 with respect to the drive voltage is 1 / 3 of the phase shift amount of the first DCPS42A1 with respect to the same drive voltage. As a result, it is possible to achieve fine adjustment of the output light in the second DCPS42B1 while securing a phase shift amount of 4π in the first DCPS42A1.

[0051] In Example 2, the DC side MZM24A1 is configured such that the waveguide length of the second optical waveguide 11C21 in the second DCPS42B1 is shorter than the waveguide length of the first optical waveguide 11C11 in the first DCPS42A1. As a result, it is possible to fine-tune the output light in the second DCPS42B1 while ensuring a phase shift amount of 4π in the first DCPS42A1.

[0052] Furthermore, the number of folds in the first optical waveguide 11C11 within the first DCPS42A1 and the second optical waveguide 11C21 within the second DCPS42B1 are different. In addition, the first optical waveguide 11C11 and the second optical waveguide 11C21 are configured such that the waveguide length of the first optical waveguide 11C11 is longer than the waveguide length of the second optical waveguide 11C21. As a result, it is possible to achieve fine adjustment of the output light in the second DCPS42B1 while securing a phase shift amount of 4π in the first DCPS42A1.

[0053] However, in Example 2, the optical losses differ because the waveguide lengths of the first optical waveguide 11C11 in the first DCPS42A1 and the second optical waveguide 11C21 in the second DCPS42B1 are different. Consequently, an imbalance occurs between the first DCPS42A1 and the second DCPS42B1. Therefore, an embodiment of the optical modulator 5 that addresses this situation will be described below as Example 3. Note that components identical to those of the optical modulator 5 in Example 1 are denoted by the same reference numerals, and the explanation of their overlapping components and operations will be omitted. [Examples]

[0054] Figure 6 is a schematic plan view showing an example of the configuration of the DC side MZM24A2 of Example 3. The DC side MZM24A2 shown in Figure 6 has a first DCPS42A2 which is a sub-DCPS42 that shifts the phase of the first signal light, a second DCPS42B2 which is a sub-DCPS42 that shifts the phase of the second signal light, a first multiplexer 26A, and a cladding layer 51.

[0055] The first DCPS42A2 has a first optical waveguide 11C12 through which the first signal light passes, and a first DC electrode 30A2 that runs parallel to the first optical waveguide 11C12 and heats the first optical waveguide 11C12 with power corresponding to the drive voltage. The first DCPS42A2 heats the first optical waveguide 11C12 with power corresponding to the drive voltage and changes the optical refractive index of the first optical waveguide 11C12 due to the thermo-optic effect of Si caused by the heating of the first optical waveguide 11C12. By changing the optical refractive index of the first optical waveguide 11C12, the first DCPS42A2 shifts the phase of the first signal light passing through the first optical waveguide 11C12 and outputs the phase-shifted first signal light to the first multiplexer 26A.

[0056] The second DCPS42B2 has a second optical waveguide 11C22 through which the second signal light passes, and a second DC electrode 30B2 that runs parallel to the second optical waveguide 11C22 and heats the second optical waveguide 11C22 with power corresponding to the drive voltage. The second DCPS42B2 heats the second optical waveguide 11C22 with power corresponding to the drive voltage, and changes the optical refractive index of the second optical waveguide 11C22 due to the thermo-optic effect of Si caused by the heating of the second optical waveguide 11C22. By changing the optical refractive index of the second optical waveguide 11C22, the second DCPS42B2 shifts the phase of the second signal light passing through the second optical waveguide 11C22 and outputs the phase-shifted second signal light to the first multiplexer 26A.

[0057] The first combined wave section 26A combines the phase-shifted first signal light and the phase-shifted second signal light. The cladding layer 51 is a layer of, for example, SiO2 that covers the first DCPS42A2, the second DCPS42B2, and the first combined wave section 26A.

[0058] The first optical waveguide 11C12, on which the power of the first DC electrode 30A2 in the first DCPS42A2 acts, is a folded waveguide that folds twice. The second optical waveguide 11C22, on which the power of the second DC electrode 30B2 in the second DCPS42B2 acts, is also a folded waveguide that folds twice. The waveguide lengths of the first optical waveguide 11C12 and the second optical waveguide 11C22 are the same. In other words, because the waveguide lengths of the first optical waveguide 11C12 and the second optical waveguide 11C22 are the same, the light loss is approximately equal, and since the number of folds is also the same, the radiation loss of light at the folded portion is also approximately equal. As a result, the extinction ratio when the light is turned off can be improved while ensuring a balance between the optical waveguides 11C.

[0059] In the first DCPS42A2, the first optical waveguide 11C12 is acted upon by three circuits of the first DC electrode 30A2. In contrast, in the second DCPS42B2, the second optical waveguide 11C22 is acted upon by one circuit of the second DC electrode 30B2. The phase shift amount of the second DCPS42B2 with respect to the drive voltage is 1 / 3 of the phase shift amount of the first DCPS42A2 with respect to the same drive voltage. As a result, a phase shift amount of 4π can be secured in the first DCPS42A2 while fine adjustment of the output light can be achieved in the second DCPS42B2.

[0060] In the DC side MZM24A2 of Example 3, the waveguide length of the first optical waveguide 11C12 in the first DCPS42A2 and the waveguide length of the second optical waveguide 11C22 in the second DCPS42B2 are made the same. Furthermore, the effective length over which the power of the second DC electrode 30B2 of the second optical waveguide 11C22 in the second DCPS42B2 acts is made shorter than the effective length over which the power of the first DC electrode 30A2 of the first optical waveguide 11C12 in the first DCPS42A2 acts. As a result, it is possible to achieve fine adjustment of the output light in the second DCPS42B2 while securing a phase shift amount of 4π in the first DCPS42A2. Furthermore, the extinction ratio can also be improved.

[0061] Even if the waveguide lengths of the first optical waveguide 11C1 in the first DCPS42A and the second optical waveguide 11C2 in the second DCPS42B are the same in Example 1, the effective length over which the power of the first DC electrode 30A acts and the effective length over which the power of the second DC electrode 30B acts may be different. This embodiment will be described below as Example 4. Note that components identical to those in the optical modulator 5 of Example 1 are denoted by the same reference numerals, and the description of their overlapping components and operations will be omitted. [Examples]

[0062] Figure 7 is a schematic plan view showing an example of the configuration of the DC side MZM24A3 of Embodiment 4. The DC side MZM24A3 shown in Figure 7 has a first DCPS42A3 which is a sub-DCPS42 that shifts the phase of the first signal light, a second DCPS42B3 which is a sub-DCPS42 that shifts the phase of the second signal light, a first multiplexer 26A, and a cladding layer 51.

[0063] The first DCPS42A3 has a first optical waveguide 11C13 through which the first signal light passes, and a first DC electrode 30A3 that runs parallel to the first optical waveguide 11C13 and heats the first optical waveguide 11C13 with power corresponding to the drive voltage. The first DCPS42A3 heats the first optical waveguide 11C13 with power corresponding to the drive voltage and changes the optical refractive index of the first optical waveguide 11C13 due to the thermo-optic effect of Si caused by the heating of the first optical waveguide 11C13. By changing the optical refractive index of the first optical waveguide 11C13, the first DCPS42A3 shifts the phase of the first signal light passing through the first optical waveguide 11C13 and outputs the phase-shifted first signal light to the first multiplexer 26A.

[0064] The second DCPS42B3 has a second optical waveguide 11C23 through which the second signal light passes, and a second DC electrode 30B3 that runs parallel to the second optical waveguide 11C23 and heats the second optical waveguide 11C23 with power corresponding to the drive voltage. The second DCPS42B3 heats the second optical waveguide 11C23 with power corresponding to the drive voltage, and changes the optical refractive index of the second optical waveguide 11C23 due to the thermo-optic effect of Si caused by the heating of the second optical waveguide 11C23. By changing the optical refractive index of the second optical waveguide 11C23, the second DCPS42B3 shifts the phase of the second signal light passing through the second optical waveguide 11C23 and outputs the phase-shifted second signal light to the first multiplexer 26A.

[0065] The first multiplexer 26A combines the phase-shifted first signal light and the phase-shifted second signal light. The cladding layer 51 is a layer of, for example, SiO2 that covers the first DCPS42A3, the second DCPS42B3, and the first multiplexer 26A.

[0066] The first optical waveguide 11C13 in the first DCPS42A3 and the second optical waveguide 11C23 in the second DCPS42B3 have equal waveguide lengths.

[0067] The second DC electrode 30B3 is bent so that a portion of it is separated from the second optical waveguide 11C23. The effective length of the second optical waveguide 11C23, on which the power of the second DC electrode 30B3 in the second DCPS42B3 acts, is shorter than the effective length of the first optical waveguide 11C13, on which the power of the first DC electrode 30A3 in the first DCPS42A3 acts. The phase shift amount of the second DCPS42B3 with respect to the drive voltage is 1 / 3 of the phase shift amount of the first DCPS42A3 with respect to the same drive voltage. As a result, fine adjustment of the output light can be achieved with the second DCPS42B3 while ensuring a phase shift amount of 4π in the first DCPS42A3.

[0068] In the DC side MZM24A3 of Example 4, the waveguide length of the first optical waveguide 11C13 in the first DCPS42A3 and the waveguide length of the second optical waveguide 11C23 in the second DCPS42B3 are made the same. Furthermore, the effective length over which the power of the second DC electrode 30B3 of the second optical waveguide 11C23 in the second DCPS42B3 acts is made shorter than the effective length over which the power of the first DC electrode 30A3 of the first optical waveguide 11C13 in the first DCPS42A3 acts. As a result, it is possible to fine-tune the output light in the second DCPS42B2 while securing a phase shift amount of 4π in the first DCPS42A2. Furthermore, the extinction ratio can also be improved.

[0069] The configuration of the DC side MZM24A in Example 1 is not limited to this and can be modified as appropriate. An embodiment thereof will be described below as Example 7. Note that components identical to those in the optical modulator 5 of Example 1 are denoted by the same reference numerals, and the description of their redundant components and operations will be omitted. [Examples]

[0070] Figure 8 is a schematic plan view showing an example of the configuration of the DC side MZM24A4 of Embodiment 5. The DC side MZM24A4 shown in Figure 8 has a first DCPS42A4 which is a sub-DCPS42 that shifts the phase of the first signal light, a second DCPS42B4 which is a sub-DCPS42 that shifts the phase of the second signal light, a first multiplexer 26A, and a cladding layer 51.

[0071] The first DCPS42A4 has a first optical waveguide 11C14 through which the first signal light passes, and a first DC electrode 30A4 that runs parallel to the first optical waveguide 11C14 and heats the first optical waveguide 11C14 with power corresponding to the drive voltage. The first DCPS42A4 heats the first optical waveguide 11C14 with power corresponding to the drive voltage and changes the optical refractive index of the first optical waveguide 11C14 due to the thermo-optic effect of Si caused by the heating of the first optical waveguide 11C14. By changing the optical refractive index of the first optical waveguide 11C14, the first DCPS42A4 shifts the phase of the first signal light passing through the first optical waveguide 11C14 and outputs the phase-shifted first signal light to the first multiplexer 26A.

[0072] The second DCPS42B4 has a second optical waveguide 11C24 through which the second signal light passes, and a second DC electrode 30B4 that runs parallel to the second optical waveguide 11C24 and heats the second optical waveguide 11C24 with power corresponding to the drive voltage. The second DCPS42B4 heats the second optical waveguide 11C24 with power corresponding to the drive voltage, and the optical refractive index of the second optical waveguide 11C24 is changed by the thermo-optic effect of Si due to the heating of the second optical waveguide 11C24. By changing the optical refractive index of the second optical waveguide 11C24, the second DCPS42B4 shifts the phase of the second signal light passing through the second optical waveguide 11C24 and outputs the phase-shifted second signal light to the first multiplexer 26A.

[0073] The first multiplexer 26A combines the phase-shifted first signal light and the phase-shifted second signal light. The cladding layer 51 is a layer of, for example, SiO2 that covers the first DCPS42A4, the second DCPS42B4, and the first multiplexer 26A.

[0074] The first optical waveguide 11C14 in the first DCPS42A4 is a straight waveguide, while the second optical waveguide 11C24 in the second DCPS42B4 has both a straight waveguide and a curved waveguide. The second optical waveguide 11C24 is separated from the second DC electrode 30B4 by the curved waveguide. The waveguide length of the first optical waveguide 11C14 and the waveguide length of the second optical waveguide 11C24 are different.

[0075] The effective length of the second optical waveguide 11C24, through which the power of the second DC electrode 30B4 in the second DCPS42B4 acts, is shorter than the effective length of the first optical waveguide 11C14, through which the power of the first DC electrode 30A4 in the first DCPS42A4 acts. The phase shift amount of the second DCPS42B4 with respect to the drive voltage is 1 / 3 of the phase shift amount of the first DCPS42A4 with respect to the same drive voltage. As a result, fine adjustment of the output light can be achieved with the second DCPS42B4 while maintaining a phase shift amount of 4π in the first DCPS42A4.

[0076] In the DC side MZM24A4 of Example 5, the first optical waveguide 11C14 in the first DCPS42A4 is a straight waveguide, and the second optical waveguide 11C24 in the second DCPS42B4 is a curved waveguide. In the DC side MZM24A4, the curved waveguide of the second optical waveguide 11C24 is positioned such that the effective length over which the power of the second DC electrode 30B4 of the second optical waveguide 11C24 acts is shorter than the effective length over which the power of the first DC electrode 30A4 of the first optical waveguide 11C14 in the first DCPS42A4 acts. As a result, it is possible to achieve fine adjustment of the output light in the second DCPS42B4 while securing a phase shift amount of 4π in the first DCPS42A4.

[0077] In Example 1, the waveguide length of the first optical waveguide 11C1 in the first DCPS42A is the same as the waveguide length of the second optical waveguide 11C2 in the second DCPS42B, but the electrode length of the second DC electrode 30B is made longer than the electrode length of the first DC electrode 30A. This embodiment is described below as Example 6. Note that components identical to those in the optical modulator 5 of Example 1 are denoted by the same reference numerals, and the description of their overlapping components and operations is omitted. [Examples]

[0078] Figure 9 is a schematic plan view showing an example of the configuration of the DC side MZM24A5 of Embodiment 6. The DC side MZM24A5 shown in Figure 9 has a first DCPS42A5 which is a sub-DCPS42 that shifts the phase of the first signal light, a second DCPS42B5 which is a sub-DCPS42 that shifts the phase of the second signal light, a first multiplexer 26A, and a cladding layer 51.

[0079] The first DCPS42A5 has a first optical waveguide 11C15 through which the first signal light passes, and a first DC electrode 30A5 that runs parallel to the first optical waveguide 11C15 and heats the first optical waveguide 11C15 with power corresponding to the drive voltage. The first DCPS42A5 heats the first optical waveguide 11C15 with power corresponding to the drive voltage and changes the optical refractive index of the first optical waveguide 11C15 due to the thermo-optic effect of Si caused by the heating of the first optical waveguide 11C15. By changing the optical refractive index of the first optical waveguide 11C15, the first DCPS42A5 shifts the phase of the first signal light passing through the first optical waveguide 11C15 and outputs the phase-shifted first signal light to the first multiplexer 26A.

[0080] The second DCPS42B5 has a second optical waveguide 11C25 through which the second signal light passes, and a second DC electrode 30B5 that runs parallel to the second optical waveguide 11C25 and heats the second optical waveguide 11C25 with power corresponding to the drive voltage. The second DCPS42B5 heats the second optical waveguide 11C25 with power corresponding to the drive voltage, and changes the optical refractive index of the second optical waveguide 11C25 due to the thermo-optic effect of Si caused by the heating of the second optical waveguide 11C25. By changing the optical refractive index of the second optical waveguide 11C25, the second DCPS42B5 shifts the phase of the second signal light passing through the second optical waveguide 11C25 and outputs the phase-shifted second signal light to the first multiplexer 26A.

[0081] The first multiplexer 26A combines the phase-shifted first signal light and the phase-shifted second signal light. The cladding layer 51 is a layer of, for example, SiO2 that covers the first DCPS42A5, the second DCPS42B5, and the first multiplexer 26A.

[0082] The first optical waveguide 11C15 in the first DCPS42A5 and the second optical waveguide 11C25 in the second DCPS42B5 are straight waveguides. The waveguide length of the first optical waveguide 11C15 is equal to the waveguide length of the second optical waveguide 11C25.

[0083] The electrode length of the second DC electrode 30B5 in the second DCPS42B5 is longer than the electrode length of the first DC electrode 30A5 in the first DCPS42A5. The phase shift amount of the second DCPS42B5 with respect to the drive voltage is 1 / 3 of the phase shift amount of the first DCPS42A5 with respect to the same drive voltage. As a result, while a phase shift amount of 4π can be secured in the first DCPS42A5, fine adjustment of the output light can be achieved with the second DCPS42B5.

[0084] In the DC side MZM24A5 of Example 6, the waveguide length of the first optical waveguide 11C15 in the first DCPS42A5 and the waveguide length of the second optical waveguide 11C25 in the second DCPS42B5 are made the same. Furthermore, in the DC side MZM24A5, the electrode length of the second DC electrode 30B5 in the second DCPS42B5 is made longer than the electrode length of the first DC electrode 30A5 in the first DCPS42A5. As a result, it is possible to fine-tune the output light in the second DCPS42B5 while securing a phase shift amount of 4π in the first DCPS42A5.

[0085] The configuration of the DC side MZM24 in Example 1 is not limited to this and can be modified as appropriate. An embodiment of this configuration will be described below as Example 7. In addition, components identical to those in the optical modulator 5 of Example 1 are denoted by the same reference numerals, and the description of their redundant components and operations will be omitted. [Examples]

[0086] Figure 10 is a schematic plan view showing an example of the configuration of the DC side MZM24A6 of Example 7. The DC side MZM24A6 shown in Figure 10 has a first DCPS42A6 which is a sub-DCPS42 that shifts the phase of the first signal light, a second DCPS42B6 which is a sub-DCPS42 that shifts the phase of the second signal light, a first multiplexer 26A, and a cladding layer 51.

[0087] The first DCPS42A6 has a first optical waveguide 11C16 through which the first signal light passes, a third DCPS42A61, and a fourth DCPS42A62. The third DCPS42A61 runs parallel to the first optical waveguide 11C16 and has a first DC electrode 30A61 that heats the first optical waveguide 11C16 with power corresponding to the drive voltage. The third DCPS42A61 heats the first optical waveguide 11C16 with power corresponding to the drive voltage and changes the optical refractive index of the first optical waveguide 11C16 due to the thermo-optic effect of Si caused by the heating of the first optical waveguide 11C16. The third DCPS42A61 changes the optical refractive index of the first optical waveguide 11C16, thereby shifting the phase of the first signal light passing through the first optical waveguide 11C16, and outputs the phase-shifted first signal light to the fourth DCPS42A62.

[0088] The fourth DCPS42A62 runs parallel to the first optical waveguide 11C16 and has a first DC electrode 30A62 that heats the first optical waveguide 11C16 with power corresponding to the drive voltage. The fourth DCPS42A62 heats the first optical waveguide 11C16 with power corresponding to the drive voltage and changes the optical refractive index of the first optical waveguide 11C16 due to the thermo-optic effect of Si caused by the heating of the first optical waveguide 11C16. By changing the optical refractive index of the first optical waveguide 11C16, the fourth DCPS42A62 shifts the phase of the first signal light passing through the first optical waveguide 11C16 and outputs the phase-shifted first signal light to the first multiplexer 26A.

[0089] The second DCPS42B6 has a second optical waveguide 11C26 through which the second signal light passes, a third DCPS42B61, and a fourth DCPS42B62. The third DCPS42B61 runs parallel to the second optical waveguide 11C26 and has a second DC electrode 30B61 that heats the second optical waveguide 11C26 with power corresponding to the drive voltage. The third DCPS42B61 heats the second optical waveguide 11C26 with power corresponding to the drive voltage, and the optical refractive index of the second optical waveguide 11C26 is changed by the thermo-optic effect of Si due to the heating of the second optical waveguide 11C26. The third DCPS42B61 changes the optical refractive index of the second optical waveguide 11C26, thereby shifting the phase of the second signal light passing through the second optical waveguide 11C26, and outputs the phase-shifted second signal light to the fourth DCPS42B62.

[0090] The fourth DCPS42B62 runs parallel to the second optical waveguide 11C26 and has a second DC electrode 30B62 that heats the second optical waveguide 11C26 with power corresponding to the drive voltage. The fourth DCPS42B62 heats the second optical waveguide 11C26 with power corresponding to the drive voltage and changes the optical refractive index of the second optical waveguide 11C26 due to the thermo-optic effect of Si caused by the heating of the second optical waveguide 11C26. By changing the optical refractive index of the second optical waveguide 11C26, the fourth DCPS42B62 shifts the phase of the second signal light passing through the second optical waveguide 11C26 and outputs the phase-shifted second signal light to the first multiplexer 26A.

[0091] The first multiplexer 26A combines the phase-shifted first signal light and the phase-shifted second signal light. The cladding layer 51 is a layer of, for example, SiO2 that covers the first DCPS42A6, the second DCPS42B6, and the first multiplexer 26A.

[0092] The first optical waveguide 11C16 in the first DCPS42A6 and the second optical waveguide 11C26 in the second DCPS42B6 are straight waveguides. The waveguide length of the first optical waveguide 11C16 is equal to the waveguide length of the second optical waveguide 11C26.

[0093] The electrode length of the first DC electrode 30A61 in the first DCPS42A6 is equal to the electrode length of the second DC electrode 30B61 in the second DCPS42B6. The electrode length of the first DC electrode 30A62 in the first DCPS42A6 is equal to the electrode length of the second DC electrode 30B62 in the second DCPS42B6. The electrode length of the first DC electrode 30A62 in the first DCPS42A6 is made shorter than the electrode length of the first DC electrode 30A61 in the first DCPS42A6. The electrode length of the second DC electrode 30B62 in the second DCPS42B6 is made shorter than the electrode length of the second DC electrode 30B61 in the second DCPS42B6.

[0094] The electrode length of the first DC electrode 30A62 in the first DCPS42A6 is made shorter than the electrode length of the first DC electrode 30A61 in the first DCPS42A6. The phase shift amount of the fourth DCPS42A62 with respect to the driving voltage is 1 / 3 of the phase shift amount of the third DCPS42A61 with respect to the same driving voltage. The fourth DCPS42A62 fine-tunes the optical refractive index of the first optical waveguide 11C16 according to the power acting on the first DC electrode 30A62. Furthermore, the third DCPS42A61 adjusts the optical refractive index of the first optical waveguide 11C16 according to the power acting on the first DC electrode 30A61. As a result, fine-tuning of the output light can be achieved with the third DCPS42A61 while ensuring a phase shift amount of 4π with the fourth DCPS42A62.

[0095] The electrode length of the second DC electrode 30B62 in the second DCPS42B6 is made shorter than the electrode length of the second DC electrode 30B61 in the second DCPS42B6. The phase shift amount of the fourth DCPS42B62 with respect to the driving voltage is 1 / 3 of the phase shift amount of the third DCPS42B61 with respect to the same driving voltage. The fourth DCPS42B62 fine-tunes the optical refractive index of the second optical waveguide 11C26 according to the power acting on the second DC electrode 30B62. The third DCPS42B61 adjusts the optical refractive index of the second optical waveguide 11C26 according to the power acting on the second DC electrode 30B61. As a result, fine-tuning of the output light can be achieved with the third DCPS42B61 while ensuring a phase shift amount of 4π with the fourth DCPS42B62.

[0096] In the first DCPS42A6 of Example 7, a third DCPS42A61 having a first DC electrode 30A61 and a fourth DCPS42A62 having a first DC electrode 30A62 were arranged in series. The electrode length of the first DC electrode 30A62 was made shorter than that of the first DC electrode 30A61. As a result, the fourth DCPS42A62 was configured to have a smaller phase shift amount corresponding to a predetermined drive voltage compared to the third DCPS42A61. This allows for fine adjustment of the output light with the third DCPS42A61 while maintaining a phase shift amount of 4π with the fourth DCPS42A62. [Examples]

[0097] Figure 11 is a schematic plan view showing an example of the configuration of the DC side MZM24A7 of Embodiment 8. The DC side MZM24A7 shown in Figure 11 has a first DCPS42A7 which is a sub-DCPS42 that shifts the phase of the first signal light, a second DCPS42B7 which is a sub-DCPS42 that shifts the phase of the second signal light, a first multiplexer 26A, and a cladding layer 51.

[0098] The first DCPS42A7 has a first optical waveguide 11C17 through which the first signal light passes, a third DCPS42A71, and a fourth DCPS42A72. The third DCPS42A71 runs parallel to the first optical waveguide 11C17 and has a first DC electrode 30A71 that heats the first optical waveguide 11C17 with power corresponding to the drive voltage. The third DCPS42A71 heats the first optical waveguide 11C17 with power corresponding to the drive voltage, and changes the optical refractive index of the first optical waveguide 11C17 due to the thermo-optic effect of Si caused by the heating of the first optical waveguide 11C17. The third DCPS42A71 changes the optical refractive index of the first optical waveguide 11C17, thereby shifting the phase of the first signal light passing through the first optical waveguide 11C17, and outputs the phase-shifted first signal light to the fourth DCPS42A72.

[0099] The fourth DCPS42A72 runs parallel to the first optical waveguide 11C17 and has a first DC electrode 30A72 that heats the first optical waveguide 11C17 with power corresponding to the drive voltage. The fourth DCPS42A72 heats the first optical waveguide 11C17 with power corresponding to the drive voltage and changes the optical refractive index of the first optical waveguide 11C17 due to the thermo-optic effect of Si caused by the heating of the first optical waveguide 11C17. By changing the optical refractive index of the first optical waveguide 11C17, the fourth DCPS42A72 shifts the phase of the first signal light passing through the first optical waveguide 11C17 and outputs the phase-shifted first signal light to the first multiplexer 26A.

[0100] The second DCPS42B7 has a second optical waveguide 11C27 through which the second signal light passes, a third DCPS42B71, and a fourth DCPS42B72. The third DCPS42B71 runs parallel to the second optical waveguide 11C27 and has a second DC electrode 30B71 that heats the second optical waveguide 11C27 with power corresponding to the drive voltage. The third DCPS42B71 heats the second optical waveguide 11C27 with power corresponding to the drive voltage, and the optical refractive index of the second optical waveguide 11C27 is changed by the thermo-optic effect of Si due to the heating of the second optical waveguide 11C27. The third DCPS42B71 changes the optical refractive index of the second optical waveguide 11C27, thereby shifting the phase of the second signal light passing through the second optical waveguide 11C27, and outputs the phase-shifted second signal light to the fourth DCPS42B72.

[0101] The fourth DCPS42B72 runs parallel to the second optical waveguide 11C27 and has a second DC electrode 30B72 that heats the second optical waveguide 11C27 with power corresponding to the drive voltage. The fourth DCPS42B72 heats the second optical waveguide 11C27 with power corresponding to the drive voltage, and the thermo-optic effect of Si due to the heating of the second optical waveguide 11C27 changes the optical refractive index of the second optical waveguide 11C27. By changing the optical refractive index of the second optical waveguide 11C27, the fourth DCPS42B72 shifts the phase of the second signal light passing through the second optical waveguide 11C27 and outputs the phase-shifted second signal light to the first multiplexer 26A.

[0102] The first multiplexer 26A combines the phase-shifted first signal light and the phase-shifted second signal light. The cladding layer 51 is a layer of, for example, SiO2 that covers the first DCPS42A7, the second DCPS42B7, and the first multiplexer 26A.

[0103] The first optical waveguide 11C17 in the first DCPS42A7 and the second optical waveguide 11C27 in the second DCPS42B7 are straight waveguides. The waveguide length of the first optical waveguide 11C17 is equal to the waveguide length of the second optical waveguide 11C27.

[0104] The electrode length of the first DC electrode 30A71 in the first DCPS42A7 is equal to the electrode length of the second DC electrode 30B71 in the second DCPS42B7. The electrode length of the first DC electrode 30A72 in the first DCPS42A7 is equal to the electrode length of the second DC electrode 30B72 in the second DCPS42B7.

[0105] The electrode width W2 of the first DC electrode 30A72 in the first DCPS42A7 is made narrower than the electrode width W1 of the first DC electrode 30A71. The electrode width W2 of the second DC electrode 30B72 in the second DCPS42B7 is made narrower than the electrode width W1 of the second DC electrode 30B71.

[0106] The electrode width of the first DC electrode 30A72 in the fourth DCPS42A72 is made narrower than the electrode width of the first DC electrode 30A71 in the third DCPS42A71. The phase shift amount of the fourth DCPS42A72 with respect to the driving voltage is 1 / 3 of the phase shift amount of the third DCPS42A71 with respect to the same driving voltage. The third DCPS42A71 adjusts the optical refractive index of the first optical waveguide 11C17 according to the power acting on the first DC electrode 30A71. The fourth DCPS42A72 fine-tunes the optical refractive index of the first optical waveguide 11C17 according to the power acting on the first DC electrode 30A72. As a result, fine-tuning of the output light can be achieved in the fourth DCPS42A72 while ensuring a phase shift amount of 4π in the third DCPS42A71.

[0107] The electrode width of the second DC electrode 30B72 in the fourth DCPS42B72 is narrower than that of the second DC electrode 30B71 in the third DCPS42B71. The phase shift amount of the fourth DCPS42B72 with respect to the drive voltage is 1 / 3 of the phase shift amount of the third DCPS42B71 with respect to the same drive voltage. The third DCPS42B71 adjusts the optical refractive index of the second optical waveguide 11C27 according to the power acting on the second DC electrode 30B71. The fourth DCPS42B72 fine-tunes the optical refractive index of the second optical waveguide 11C27 according to the power acting on the second DC electrode 30B72. As a result, fine-tuning of the output light can be achieved in the fourth DCPS42B72 while ensuring a phase shift amount of 4π in the third DCPS42B71.

[0108] In the first DCPS42A7 of Example 8, a third DCPS42A71 having a first DC electrode 30A71 and a fourth DCPS62A72 having a first DC electrode 30A72 are arranged in series. The electrode width of the first DC electrode 30A72 is made narrower compared to the electrode width of the first DC electrode 30A71. As a result, the fourth DCPS42A72 is configured to have a smaller phase shift amount corresponding to a predetermined drive voltage compared to the third DCPS42A71. While a phase shift amount of 4π can be secured in the fourth DCPS42A72, fine adjustment of the output light can be achieved with the third DCPS42A71.

[0109] For the sake of explanation, the DC side MZM24 is used as an example of the optical modulator in this embodiment, but it may also be applied to the DC side parent MZM25, and can be changed as appropriate.

[0110] In this embodiment, a polarization multiplexing method is illustrated in which an X-polarized signal light from an X-polarized MZM14A and a Y-polarized signal light from a Y-polarized MZM14B are polarization multiplexed. However, this method can also be applied to optical modulators that do not use polarization multiplexing. [Explanation of symbols]

[0111] 1. Optical communication device 3 DSP 4 light source 5. Optical modulator 11C optical waveguide 11C1, 11C11, 11C12, 11C13, 11C14 First optical waveguide path 11C2, 11C21, 11C22, 11C23, 11C24 Second optical waveguide path 24 DC side MZM 24A, 24A1, 24A2, 24A3, 24A4 DC side MZM 30 DC electrodes 30A, 30A1, 30A2, 30A3, 30A4 1st DC electrode 30B, 30B1, 30B2, 30B3, 30B4 - Second DC Electrode 42 DCPS 42A No. 1 DCPS 42B 2nd DCPS

Claims

1. The device includes a first optical waveguide through which a first signal light passes, a first DC electrode running parallel to the first optical waveguide and applying power to the first optical waveguide according to a driving voltage, and a first phase shifter that shifts the phase of the first signal light passing through the first optical waveguide according to the driving voltage applied to the first DC electrode, The device comprises a second optical waveguide through which a second signal light passes, a second DC electrode running parallel to the second optical waveguide and applying power to the second optical waveguide according to a driving voltage, and a second phase shifter that shifts the phase of the second signal light passing through the second optical waveguide according to the driving voltage applied to the second DC electrode. The second phase shifter is, Compared to the first phase shifter, the phase shift amount corresponding to a predetermined drive voltage is made smaller. An optical modulator characterized in that the first optical waveguide in the first phase shifter is a straight waveguide, the second optical waveguide in the second phase shifter is a curved waveguide, and the curved waveguide of the second optical waveguide is arranged such that the effective length over which the power of the second DC electrode in the second optical waveguide in the second phase shifter acts is shorter than the effective length over which the power of the first DC electrode in the first optical waveguide in the first phase shifter acts.

2. The device includes a first optical waveguide through which a first signal light passes, a first DC electrode running parallel to the first optical waveguide and applying power to the first optical waveguide according to a driving voltage, and a first phase shifter that shifts the phase of the first signal light passing through the first optical waveguide according to the driving voltage applied to the first DC electrode, The device comprises a second optical waveguide through which a second signal light passes, a second DC electrode running parallel to the second optical waveguide and applying power to the second optical waveguide according to a driving voltage, and a second phase shifter that shifts the phase of the second signal light passing through the second optical waveguide according to the driving voltage applied to the second DC electrode. The second phase shifter is, Compared to the first phase shifter, the phase shift amount corresponding to a predetermined drive voltage is made smaller. An optical modulator characterized in that the waveguide length of the first optical waveguide in the first phase shifter and the waveguide length of the second optical waveguide in the second phase shifter are the same, and the electrode length of the second DC electrode in the second phase shifter is longer than the electrode length of the first DC electrode in the first phase shifter, thereby configuring the first DC electrode and the second DC electrode.

3. The optical modulator according to claim 1 or 2, characterized in that the first DC electrode and the second DC electrode are configured such that the electrode width of the second DC electrode in the second phase shifter is narrower than the electrode width of the first DC electrode in the first phase shifter.

4. The optical modulator according to claim 1 or 2, characterized in that the first optical waveguide and the second optical waveguide are configured such that the waveguide length of the second optical waveguide in the second phase shifter is shorter than the waveguide length of the first optical waveguide in the first phase shifter.

5. The optical modulator according to claim 1 or 2, characterized in that the number of reversals of the first optical waveguide in the first phase shifter and the second optical waveguide in the second phase shifter are different, and the first optical waveguide and the second optical waveguide are configured such that the waveguide length of the first optical waveguide is longer than the waveguide length of the second optical waveguide.

6. The optical modulator according to claim 1 or 2, characterized in that the waveguide length of the first optical waveguide in the first phase shifter and the waveguide length of the second optical waveguide in the second phase shifter are the same, and the second DC electrode is arranged such that the working length over which the power of the second DC electrode in the second optical waveguide in the second phase shifter acts is shorter than the working length over which the power of the first DC electrode in the first optical waveguide in the first phase shifter acts.

7. A processor that performs signal processing on electrical signals, A light source that generates signal light, An optical communication device having an optical modulator that modulates signal light generated from a light source using an electrical signal output from the processor, The aforementioned optical modulator is The first optical waveguide through which the first signal light from the light source passes, and the first DC electrode running parallel to the first optical waveguide applies power to the first optical waveguide according to the driving voltage, and the first phase shifter shifts the phase of the first signal light passing through the first optical waveguide according to the driving voltage to the first DC electrode, The optical waveguide includes a second optical waveguide through which a second signal light from the light source passes, and a second DC electrode running parallel to the second optical waveguide and applying power to the second optical waveguide according to the driving voltage, and a second phase shifter that shifts the phase of the second signal light passing through the second optical waveguide according to the driving voltage to the second DC electrode, A combined wave unit that combines the first signal light after phase shifting by the first phase shifter and the second signal light after phase shifting by the second phase shifter to obtain a modulated signal light, It has, The second phase shifter is, Compared to the first phase shifter, the phase shift amount corresponding to a predetermined drive voltage is made smaller. An optical communication device characterized in that the first optical waveguide in the first phase shifter is a straight waveguide, the second optical waveguide in the second phase shifter is a curved waveguide, and the curved waveguide of the second optical waveguide is arranged such that the effective length over which the power of the second DC electrode in the second optical waveguide in the second phase shifter acts is shorter than the effective length over which the power of the first DC electrode in the first optical waveguide in the first phase shifter acts.

8. A processor that performs signal processing on electrical signals, A light source that generates signal light, An optical communication device having an optical modulator that modulates signal light generated from a light source using an electrical signal output from the processor, The aforementioned optical modulator is The first optical waveguide through which the first signal light from the light source passes, and the first DC electrode running parallel to the first optical waveguide applies power to the first optical waveguide according to the driving voltage, and the first phase shifter shifts the phase of the first signal light passing through the first optical waveguide according to the driving voltage to the first DC electrode, The optical waveguide includes a second optical waveguide through which a second signal light from the light source passes, and a second DC electrode running parallel to the second optical waveguide and applying power to the second optical waveguide according to the driving voltage, and a second phase shifter that shifts the phase of the second signal light passing through the second optical waveguide according to the driving voltage to the second DC electrode, A combined wave unit that combines the first signal light after phase shifting by the first phase shifter and the second signal light after phase shifting by the second phase shifter to obtain a modulated signal light, It has, The second phase shifter is, Compared to the first phase shifter, the phase shift amount corresponding to a predetermined drive voltage is made smaller. An optical communication device characterized in that the waveguide length of the first optical waveguide in the first phase shifter and the waveguide length of the second optical waveguide in the second phase shifter are the same, and the electrode length of the second DC electrode in the second phase shifter is longer than the electrode length of the first DC electrode in the first phase shifter, thereby configuring the first DC electrode and the second DC electrode.

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