Optical device, optical transmitter, and optical transceiver

Abstract

To provide a compact optical device or the like.SOLUTION: The optical device includes a first MZI including a first waveguide having an electro-optic effect and a first electrode, and a second MZI including a second waveguide having an electro-optic effect and a second electrode. The first waveguide has a first input side arm waveguide, a first output side arm waveguide, and a first folded waveguide, and the second waveguide has a second input side arm waveguide, a second output side arm waveguide, and a second folded waveguide. The first and second waveguides are arranged such that the first input arm waveguide and the second input arm waveguide are adjacent to each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical device, an optical transmitter, and an optical transceiver. [Background technology]

[0002] An example of an optical device is an optical modulator chip with an optical waveguide formed on its surface. A signal electrode is disposed on the optical waveguide of the optical modulator chip, and when a voltage is applied to the signal electrode, an electric field is generated in the optical waveguide in a direction perpendicular to the surface of the optical modulator chip. This electric field changes the refractive index of the optical waveguide, thereby changing the phase of the light propagating through the optical waveguide and enabling light modulation. That is, the optical waveguide of the optical modulator chip constitutes, for example, a Mach-Zehnder interferometer (MZI), and can output, for example, an XY polarization multiplexed IQ signal due to the phase difference of light between multiple optical waveguides arranged in parallel.

[0003] Fig. 6 is an explanatory diagram showing an example of a conventional DP-IQ modulator 100. The DP-IQ modulator 100 shown in Fig. 6 is a modulator in which a thin-film LN chip 102 having a modulator body 151 of an X-polarized IQ modulator 100B and a modulator body 151 of a Y-polarized IQ modulator 100A is mounted on a SiPh (silicon photonics) chip 101. The DP-IQ modulator 100 has an input waveguide 111, a branching section 112, the Y-polarized IQ modulator 100A, the X-polarized IQ modulator 100B, a PR (Polarization Rotator) 117, and a PBC (Polarization Beam Combiner) 118. The DP-IQ modulator 100 includes an output waveguide 119 , an RF (Radio Frequency) electrode 160 , a first DC (Direct Current) electrode 171 , and a second DC electrode 172 .

[0004] Input waveguide 111 is, for example, a Si waveguide that receives input light from optical fiber F1 connected to a light source. Branching unit 112 is, for example, an XY-branching MMI (Multi-Mode Interferometer) that branches the input light from input waveguide 111 into input light of an X-polarized component and input light of a Y-polarized component.

[0005] The Y-polarized IQ modulator 100A modulates the Y-polarized IQ component input light and outputs the modulated Y-polarized IQ component signal light to the PR 117. The X-polarized IQ modulator 100B modulates the X-polarized IQ component input light and outputs the modulated X-polarized IQ component signal light to the PBC 118. The PR 117 rotates the polarization of the Y-polarized IQ component signal light and outputs the Y-polarized IQ component signal light after the polarization rotation to the PBC 118. The PBC 118 multiplexes the X-polarized IQ component signal light and the Y-polarized IQ component signal light after the polarization rotation, and outputs the multiplexed signal light to the output waveguide 119.

[0006] The Y-polarized IQ modulator 100A has a first branching section 113, a first adjusting section 114, a first MZI 150A (150), a second MZI 150B (150), and a first multiplexing section 116. The first MZI 150A is an optical modulator for the I component of the Y-polarized wave. The second MZI 150B is an optical modulator for the Q component of the Y-polarized wave.

[0007] The first branching unit 113 branches and outputs the Y-polarized input light from the branching unit 112 to two first adjusting units 114. The first adjusting unit 114 is configured, for example, with an optical waveguide and a heater or the like arranged below the optical waveguide, and shifts the phase of the input light guided through the optical waveguide by heating the optical waveguide with heating of the heater in response to an electrical signal from the first DC electrode 171. Furthermore, the first adjusting unit 114 outputs the phase-shifted input light to the MZI 150.

[0008] The first MZI 150A modulates the phase-shifted Y-polarized I-component input light, and outputs the modulated Y-polarized I-component signal light to the first multiplexing unit 116. Similarly, the first MZI 150A modulates the phase-shifted Y-polarized Q-component input light, and outputs the modulated Y-polarized Q-component signal light to the first multiplexing unit 116. The first multiplexing unit 116 multiplexes the modulated Y-polarized I-component signal light and the modulated Y-polarized Q-component signal light, and outputs the combined Y-polarized IQ-component signal light to the PR 117.

[0009] The X-polarized IQ modulator 100B has a first branching section 113, a first adjusting section 114, a third MZI 150C (150), a fourth MZI 150D (150), and a first multiplexing section 116. The third MZI 150C is an optical modulator for the I component of the X-polarized wave. The fourth MZI 150D is an optical modulator for the Q component of the X-polarized wave.

[0010] The first branching unit 113 branches and outputs the X-polarized input light from the second branching unit 121 to two first adjusting units 114. The first adjusting unit 114 is configured, for example, with an optical waveguide and a heater or the like arranged below the optical waveguide, and shifts the phase of the input light guided through the optical waveguide by heating the optical waveguide with the heater in response to an electrical signal from the first DC electrode 171. Furthermore, the first adjusting unit 114 outputs the phase-shifted input light to the MZI 150. The third MZI 150C modulates the phase-shifted X-polarized I-component input light and outputs the modulated X-polarized I-component signal light to the first multiplexing unit 116. Similarly, the fourth MZI 150D modulates the phase-shifted X-polarized Q-component input light and outputs the modulated X-polarized Q-component signal light to the first multiplexing unit 116. The first multiplexing section 116 multiplexes the modulated X-polarized I-component signal light with the modulated X-polarized Q-component signal light, and outputs the multiplexed X-polarized IQ-component signal light to the PBC 118.

[0011] Each MZI 150 includes a second branching unit 121, a first waveguide 130, a second waveguide 140, a second adjusting unit 122, a modulator body 151, and a second multiplexing unit 123. The second branching unit 121 branches and outputs branched input light from the first branching unit 113 to the first waveguide 130 and the second waveguide 140. The second adjusting unit 122 is configured, for example, with a first input waveguide 133 and a heater or the like arranged below a portion of the first input waveguide 133, and heats the portion of the first input waveguide 133 by heating the heater in response to an electrical signal from a second DC electrode 172. As a result, the second adjusting unit 122 shifts the phase of the input light guided through the first input waveguide 133.

[0012] The first waveguide 130 has a first input waveguide 133, a first folded waveguide 132, and a first arm waveguide 131. The first input waveguide 133 is, for example, a Si waveguide that connects between the second branching portion 121 and the first folded waveguide 132. The first folded waveguide 132 is, for example, a Si waveguide with a folded structure that connects between the first input waveguide 133 and the first arm waveguide 131.

[0013] The first arm waveguide 131 constitutes a part of the modulator body 151 and is, for example, an arm waveguide made of thin-film LN, which modulates input light guided in response to a high-frequency signal from a signal electrode 161 to a ground electrode 162 of an RF electrode 160 arranged on the side of the first arm waveguide 131 at high speed.

[0014] The second waveguide 140 has a second input waveguide 143, a second folded waveguide 142, and a second arm waveguide 141. The second input waveguide 143 is, for example, a Si waveguide that connects between the second branching portion 121 and the second folded waveguide 142. The second folded waveguide 142 is, for example, a Si waveguide with a folded structure that connects between the second input waveguide 143 and the second arm waveguide 141.

[0015] The second arm waveguide 141 constitutes a part of the modulator body 151 and is, for example, an arm waveguide made of thin-film LN, which modulates at high speed the input light guided in response to a high-frequency signal from a signal electrode 161 to a ground electrode 162 of an RF electrode 160 arranged on the side of the second arm waveguide 141.

[0016] The second multiplexing section 123 multiplexes the signal light from the first arm waveguide 131 and the signal light from the second arm waveguide 141, and outputs the signal light after high-speed modulation according to the phase difference between the signal light from the first arm waveguide 131 and the signal light from the second arm waveguide 141.

[0017] The RF electrode 160 has a signal electrode 161 arranged for each MZI 150, a ground electrode 162 arranged for each MZI 150, and an RF termination 164. The signal electrodes 161 are arranged in parallel to the side surfaces of the first arm waveguide 131 and the second arm waveguide 141 in the MZI 150. The signal electrodes 161 near the inputs of the first arm waveguide 131 and the second arm waveguide 141 are electrically connected to an electrode wire 181 arranged on a PCB between the RF driver 180 and the RF driver 180. The RF driver 180 outputs a high-frequency signal to the signal electrode 161 of the RF electrode 160 through the electrode wire 181.

[0018] The ground electrode 162 is arranged in parallel to the side surfaces of the first arm waveguide 131 and the second arm waveguide 141 in the MZI 150. The ground electrodes 162 near the inputs of the first arm waveguide 131 and the second arm waveguide 141 are electrically connected to a ground electrode line 182 arranged on a PCB between the RF driver 180 and the ground electrode 162.

[0019] The RF terminal 164 is disposed near the outputs of the first arm waveguide 131 and the second arm waveguide 141, and is connected to the signal electrode 161 and the ground electrode 162 to terminate the high frequency signal.

[0020] In the conventional DP-IQ modulator 100, a signal electrode 161 is arranged between the first arm waveguide 131 and the second arm waveguide 141 for each MZI 150. The RF driver 180 connects the signal electrodes 161 for each MZI 150 with electrode wires 181, and outputs a high-frequency signal from the RF driver 180 to the signal electrodes 161 of each MZI 150 via the electrode wires 181. [Prior art documents] [Patent documents]

[0021] [Patent Document 1] Patent Publication No. 2021-162641 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-102686 [Patent Document 3] U.S. Patent No. 05930412 Summary of the Invention [Problem to be solved by the invention]

[0022] However, in the conventional DP-IQ modulator 100, the electrode length of the signal electrode 161 running parallel to the first arm waveguide 131 and the second arm waveguide 141 of each MZI 150 is increased in order to reduce the drive voltage of the signal electrode 161. As a result, when the electrode length of the signal electrode 161 in the longitudinal direction is increased, the longitudinal size of each MZI is increased, and the chip size of the entire DP-IQ modulator 100 becomes larger. Therefore, there is a demand for miniaturization of the chip size of optical modulators.

[0023] In one aspect, an object is to provide an optical device or the like that allows for a reduction in chip size. [Means for solving the problem]

[0024] In one embodiment, the optical device disclosed herein includes a first waveguide having an electro-optic effect and a first Mach-Zehnder interferometer disposed near the first waveguide and having a first electrode for applying an electric signal to the first waveguide. The optical device also includes a second waveguide having the electro-optic effect and a second Mach-Zehnder interferometer disposed near the second waveguide and having a second electrode for applying an electric signal to the second waveguide. The first waveguide includes a first input arm waveguide, a first output arm waveguide, and a first folded waveguide connecting the first input arm waveguide and the first output arm waveguide. The second waveguide includes a second input arm waveguide, a second output arm waveguide, and a second folded waveguide connecting the second input arm waveguide and the second output arm waveguide. The first waveguide and the second waveguide are arranged so that the first input arm waveguide and the second input arm waveguide are adjacent to each other. [Effects of the Invention]

[0025] According to one aspect, an optical device that allows for a reduction in chip size can be provided. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is an explanatory diagram illustrating an example of a DP-IQ modulator according to a first embodiment. [Figure 2] FIG. 2 is an explanatory diagram in which the signal electrode portions of the first folded arm waveguide and the second folded arm waveguide are omitted. [Figure 3] FIG. 3 is an explanatory diagram illustrating an example of a DP-IQ modulator according to a second embodiment. [Figure 4] FIG. 4 is an explanatory diagram illustrating an example of an optical transceiver according to this embodiment. [Figure 5] FIG. 5 is an explanatory diagram showing an example of a DP-IQ modulator of a comparative example. [Figure 6] FIG. 6 is an explanatory diagram showing an example of a conventional DP-IQ modulator. DETAILED DESCRIPTION OF THE INVENTION

[0027] Therefore, in order to reduce the chip size of the optical modulator, the applicant has proposed a comparative example of a DP-IQ modulator in which the first arm waveguide, the second arm waveguide, and the signal electrode in the MZI have a folded structure.

[0028] <Comparative Example> Fig. 5 is an explanatory diagram showing an example of a DP-IQ modulator 200 of a comparative example. The DP-IQ modulator 200 shown in Fig. 5 is a modulator in which a thin-film LN chip 203 having a modulator body 251 of an X-polarized IQ modulator 200B and a modulator body 251 of a Y-polarized IQ modulator 200A is mounted on a SiPh chip 202. The DP-IQ modulator 200 has an input waveguide 211, a branching section 212, the Y-polarized IQ modulator 200A, the X-polarized IQ modulator 200B, a PR 217, a PBC 218, and an output waveguide 219. The DP-IQ modulator 200 has an RF electrode 260, a first DC electrode 271, and a second DC electrode 272.

[0029] Input waveguide 211 is, for example, a Si waveguide that receives input light from optical fiber F1 connected to a light source. Branching unit 212 is, for example, an XY branching MMI that branches the input light from input waveguide 211 into input light of an X polarization component and input light of a Y polarization component.

[0030] The Y-polarized IQ modulator 200A modulates the Y-polarized IQ component input light and outputs the modulated Y-polarized IQ component signal light to the PR 217. The X-polarized IQ modulator 200B modulates the X-polarized IQ component input light and outputs the modulated X-polarized IQ component signal light to the PBC 218. The PR 217 performs polarization rotation on the Y-polarized IQ component signal light and outputs the Y-polarized IQ component signal light after the polarization rotation to the PBC 218. The PBC 218 multiplexes the X-polarized IQ component signal light and the Y-polarized IQ component signal light after the polarization rotation, and outputs the multiplexed signal light to the output waveguide 219.

[0031] The Y-polarized IQ modulator 200A has a first branching section 213, a first adjusting section 214, a first MZI 250A (250), a second MZI 250B (250), and a first multiplexing section 216. The first MZI 250A is an optical modulator for the I component of the Y-polarized wave. The second MZI 250B is an optical modulator for the Q component of the Y-polarized wave.

[0032] The first branching unit 213 branches and outputs the Y-polarized input light from the branching unit 212 to two first adjustment units 214. The first adjustment unit 214 is configured, for example, with an optical waveguide and a heater or the like arranged below the optical waveguide, and shifts the phase of the input light guided through the optical waveguide by heating the optical waveguide with heating of the heater in response to an electrical signal from the first DC electrode 271. The first adjustment unit 214 outputs the phase-shifted input light to the MZI 250.

[0033] The first MZI 250A modulates the phase-shifted Y-polarized I-component input light and outputs the modulated Y-polarized I-component signal light to the first multiplexing unit 216. Similarly, the first MZI 250A modulates the phase-shifted Y-polarized Q-component input light and outputs the modulated Y-polarized Q-component signal light to the first multiplexing unit 216. The first multiplexing unit 216 multiplexes the modulated Y-polarized I-component signal light and the modulated Y-polarized Q-component signal light, and outputs the combined Y-polarized IQ-component signal light to the PR 217.

[0034] The X-polarized IQ modulator 200B has a first branching unit 213, a first adjusting unit 214, a third MZI 250C and a fourth MZI 250D, and a first multiplexing unit 216. The third MZI 250C is an optical modulator for the I component of the X-polarized wave. The fourth MZI 250D is an optical modulator for the Q component of the X-polarized wave.

[0035] The first branching unit 213 branches and outputs the X-polarized input light from the branching unit 212 to two first adjustment units 214. The first adjustment unit 214 is configured, for example, with an optical waveguide and a heater or the like arranged below the optical waveguide, and shifts the phase of the input light guided through the optical waveguide by heating the optical waveguide with heating of the heater in response to an electrical signal from the first DC electrode 271. The first adjustment unit 214 outputs the phase-shifted input light to the MZI 250.

[0036] The third MZI 250C modulates the phase-shifted X-polarized I-component input light and outputs the modulated X-polarized I-component signal light to the first multiplexing unit 216. Similarly, the fourth MZI 250D modulates the phase-shifted X-polarized Q-component input light and outputs the modulated X-polarized Q-component signal light to the first multiplexing unit 216. The first multiplexing unit 216 multiplexes the modulated X-polarized I-component signal light and the modulated X-polarized Q-component signal light, and outputs the combined X-polarized IQ-component signal light to the PBC 218.

[0037] Each MZI 250 includes a second branching unit 221, a first waveguide 230, a second waveguide 240, a second adjusting unit 222, a modulator body 251, and a second multiplexing unit 223. The second branching unit 221 branches and outputs branched input light from the first branching unit 213 to the first waveguide 230 and the second waveguide 240. The second adjusting unit 222 is configured, for example, with a first input waveguide 235 and a heater or the like arranged below a portion of the first input waveguide 235, and heats a portion of the first input waveguide 235 by heating the heater in response to an electrical signal from a second DC electrode 272. As a result, the second adjusting unit 222 shifts the phase of the input light guided through the first input waveguide 235.

[0038] The first waveguide 230 has a first input waveguide 235, a first folded waveguide 234, and a first arm waveguide 231. The first input waveguide 235 is, for example, a Si waveguide, and connects between the second branching portion 221 and the first folded waveguide 234. The first folded waveguide 234 is, for example, a Si waveguide with a folded structure, and connects between the first input waveguide 235 and the first arm waveguide 231.

[0039] The first arm waveguide 231 constitutes a part of the modulator body 251, and is, for example, a thin-film LN arm waveguide that modulates input light at high speed in response to a radio frequency signal from a signal electrode 261A of an RF electrode 260 arranged on a side surface of the first arm waveguide 231 to a ground electrode 262. The radio frequency signal is, for example, a high-speed radio frequency signal including a band of several tens of GHz or more.

[0040] The second waveguide 240 has a second input waveguide 245, a second folded waveguide 244, and a second arm waveguide 241. The second input waveguide 245 is, for example, a Si waveguide, and connects between the second branching portion 221 and the second folded waveguide 244. The second folded waveguide 244 is, for example, a Si waveguide with a folded structure, and connects between the second input waveguide 245 and the second arm waveguide 241.

[0041] The second arm waveguide 241 constitutes a part of the modulator body 251 and is, for example, a thin-film LN arm waveguide that modulates input light at high speed in response to a high-frequency signal from the signal electrode 261B of the RF electrode 260 arranged on the side of the second arm waveguide 241 to the ground electrode 262.

[0042] The second multiplexing section 223 multiplexes the signal light from the first arm waveguide 231 and the signal light from the second arm waveguide 241, and outputs modulated signal light according to the phase difference between the signal light from the first arm waveguide 231 and the signal light from the second arm waveguide 241.

[0043] The RF electrode 260 has a signal electrode 261 arranged for each MZI 250, a ground electrode 262 arranged for each MZI 250, and an RF termination 264. The signal electrodes 261 are arranged in parallel to the side surfaces of the first arm waveguide 231 and the second arm waveguide 241 in the MZI 250. The signal electrodes 261 near the inputs of the first arm waveguide 231 and the second arm waveguide 241 are electrically connected to an electrode wire 281 arranged on a PCB between the RF driver 280 and the signal electrode 261. The RF driver 280 outputs a high-frequency signal to the signal electrode 261 through the electrode wire 281. The signal electrodes 261 are signal electrodes 261A, 261B, 261C, and 261D.

[0044] The ground electrode 262 is arranged in parallel to the side surfaces of the first arm waveguide 231 and the second arm waveguide 241 in the MZI 250. The ground electrodes 262 near the inputs of the first arm waveguide 231 and the second arm waveguide 241 are electrically connected to a ground electrode line 282 arranged on a PCB between the RF driver 280 and the ground electrode 262.

[0045] The RF terminal 264 is disposed near the outputs of the first arm waveguide 231 and the second arm waveguide 241, and is connected to the signal electrode 261 and the ground electrode 262 to terminate the high frequency signal.

[0046] The first arm waveguide 231 of the first MZI 250A has a folded structure. The first input arm waveguide 231A has a first input arm waveguide 231A, a first output arm waveguide 232A, and a first folded arm waveguide 233A. The first input arm waveguide 231A is a linear arm waveguide made of, for example, thin-film LN, that connects between the first folded arm waveguide 234 and the first folded arm waveguide 233A. The first output arm waveguide 232A is a linear arm waveguide made of, for example, thin-film LN, that connects between the first folded arm waveguide 233A and the second multiplexing section 223. The first folded arm waveguide 233A is, for example, an S-shaped folded waveguide made of thin-film LN, which connects the first input arm waveguide 231A and the first output arm waveguide 232A. The first folded arm waveguide 233A has a bent waveguide connecting the input end of the first folded arm waveguide 233A and the first input arm waveguide 231A. Furthermore, the first folded arm waveguide 233A has a bent waveguide connecting the output end of the first folded arm waveguide 233A and the first output arm waveguide 232A, and a straight arm waveguide connecting these bent waveguides together.

[0047] The second arm waveguide 241 of the first MZI 250A has a folded structure. The second arm waveguide 241 has a second input arm waveguide 241A, a second output arm waveguide 242A, and a second folded arm waveguide 243A. The second input arm waveguide 241A is a linear arm waveguide made of, for example, thin-film LN, that connects between the second folded arm waveguide 244 and the second folded arm waveguide 243A. The second output arm waveguide 242A is a linear arm waveguide made of, for example, thin-film LN, that connects between the second folded arm waveguide 243A and the second multiplexing section 223. The second folded arm waveguide 243A is, for example, an S-shaped folded waveguide made of thin-film LN, which connects the second input arm waveguide 241A and the second output arm waveguide 242A. The second folded arm waveguide 243A has a bent waveguide connecting the input end of the second folded arm waveguide 243A and the second input arm waveguide 241A. The second folded arm waveguide 243A has a bent waveguide connecting the output end of the second folded arm waveguide 243A and the second output arm waveguide 242A, and a straight arm waveguide connecting these bent waveguides together.

[0048] The bent waveguide in the first folded arm waveguide 233A of the first MZI 250A and the bent waveguide in the second folded arm waveguide 243A form an intersecting waveguide.

[0049] The RF electrode 260 of the first MZI 250A has a signal electrode 261A including a signal electrode with a folded structure arranged in parallel between the first arm waveguide 231 and the second arm waveguide 241. The signal electrode 261A near the input of the first input side arm waveguide 231A in the first arm waveguide 231 and the second input side arm waveguide 241A of the second arm waveguide 241 is electrically connected to a first electrode wire 281A arranged on a PCB between the RF driver 280 and the RF driver 280. The RF driver 280 outputs a high frequency signal to the signal electrode 261A through the first electrode wire 281A.

[0050] The first arm waveguide 231 of the second MZI 250B has a folded structure. The first arm waveguide 231 has a first input arm waveguide 231B, a first output arm waveguide 232B, and a first folded arm waveguide 233B. The first input arm waveguide 231B is a linear arm waveguide made of, for example, thin-film LN, that connects between the first folded arm waveguide 234 and the first folded arm waveguide 233B. The first output arm waveguide 232B is a linear arm waveguide made of, for example, thin-film LN, that connects between the first folded arm waveguide 233B and the second multiplexing section 223. The first folded arm waveguide 233B is, for example, an S-shaped folded waveguide made of thin-film LN that connects the first input arm waveguide 231B and the first output arm waveguide 232B. The first folded arm waveguide 233B has a bent waveguide that connects the input end of the first folded arm waveguide 233B and the first input arm waveguide 231B. The first folded arm waveguide 233B has a bent waveguide that connects the output end of the first folded arm waveguide 233B and the first output arm waveguide 232B, and a straight arm waveguide that connects these bent waveguides together.

[0051] The second arm waveguide 241 of the second MZI 250B has a folded structure. The second arm waveguide 241 has a second input arm waveguide 241B, a second output arm waveguide 242B, and a second folded arm waveguide 243B. The second input arm waveguide 241B is a linear arm waveguide made of, for example, thin-film LN, that connects the second folded arm waveguide 244 and the second folded arm waveguide 243B. The second output arm waveguide 242B is a linear arm waveguide made of, for example, thin-film LN, that connects the second folded arm waveguide 243B and the second multiplexing section 223. The second folded arm waveguide 243B is, for example, an S-shaped folded waveguide made of thin-film LN that connects the second input arm waveguide 241B and the second output arm waveguide 242B. The second folded arm waveguide 243B has a bent waveguide that connects the input end of the second folded arm waveguide 243B and the second input arm waveguide 241B. The second folded arm waveguide 243B has a bent waveguide that connects the output end of the second folded arm waveguide 243B and the second output arm waveguide 242B, and a straight arm waveguide that connects these bent waveguides together.

[0052] The bent waveguide in the first folded arm waveguide 233B of the second MZI 250B and the bent waveguide in the second folded arm waveguide 243B form an intersecting waveguide.

[0053] The RF electrode 260 of the second MZI 250B has a signal electrode 261B including a signal electrode with a folded structure arranged in parallel between the first arm waveguide 231 and the second arm waveguide 241. The signal electrode 261B near the input of the first input side arm waveguide 231B in the first arm waveguide 231 and the second input side arm waveguide 241B of the second arm waveguide 241 is electrically connected to a second electrode wire 281B arranged on a PCB between the RF driver 280 and the RF driver 280. The RF driver 280 outputs a high frequency signal to the signal electrode 261B of the RF electrode 260 through the second electrode wire 281B.

[0054] The first arm waveguide 231 of the third MZI 250C has a folded structure. The first arm waveguide 231 has a first input arm waveguide 231C, a first output arm waveguide 232C, and a first folded arm waveguide 233C. The first input arm waveguide 231C is a linear arm waveguide made of, for example, thin-film LN, that connects between the first folded arm waveguide 234 and the first folded arm waveguide 233C. The first output arm waveguide 232C is a linear arm waveguide made of, for example, thin-film LN, that connects between the first folded arm waveguide 233C and the second multiplexing section 223. The first folded arm waveguide 233C is, for example, an S-shaped folded waveguide made of thin-film LN that connects the first input arm waveguide 231C and the first output arm waveguide 232C. The first folded arm waveguide 233C has a bent waveguide that connects the input end of the first folded arm waveguide 233C and the first input arm waveguide 231C. The first folded arm waveguide 233C has a bent waveguide that connects the output end of the first folded arm waveguide 233C and the first output arm waveguide 232C, and a straight arm waveguide that connects these bent waveguides together.

[0055] The second arm waveguide 241 of the third MZI 250C has a folded structure. The second arm waveguide 241 includes a second input arm waveguide 241C, a second output arm waveguide 242C, and a second folded arm waveguide 243C. The second input arm waveguide 241C is a linear arm waveguide made of, for example, thin-film LN, that connects the second folded arm waveguide 244 and the second folded arm waveguide 243C. The second output arm waveguide 242C is a linear arm waveguide made of, for example, thin-film LN, that connects the second folded arm waveguide 243C and the second multiplexing section 223. The second folded arm waveguide 243C is, for example, an S-shaped folded waveguide made of thin-film LN that connects the second input arm waveguide 241C and the second output arm waveguide 242C. The second folded arm waveguide 243C has a bent waveguide that connects the input end of the second folded arm waveguide 243C and the second input arm waveguide 241C. The second folded arm waveguide 243C has a bent waveguide that connects the output end of the second folded arm waveguide 243C and the second output arm waveguide 242C, and a straight arm waveguide that connects these bent waveguides together.

[0056] The bent waveguide in the first folded arm waveguide 233C of the third MZI 250C and the bent waveguide in the second folded arm waveguide 243C form an intersecting waveguide.

[0057] The RF electrode 260 of the third MZI 250C has a signal electrode 261C including a signal electrode with a folded structure arranged in parallel between the first arm waveguide 231 and the second arm waveguide 241. The signal electrode 261C near the input of the first input side arm waveguide 231C of the first arm waveguide 231 and the second input side arm waveguide 241C in the second arm waveguide 241 is electrically connected to a third electrode wire 281C arranged on a PCB between the RF driver 280 and the RF driver 280. The RF driver 280 outputs a high frequency signal to the signal electrode 261C of the RF electrode 260 through the third electrode wire 281C.

[0058] The first arm waveguide 231 of the fourth MZI 250D has a folded structure. The first arm waveguide 231 includes a first input arm waveguide 231D, a first output arm waveguide 232D, and a first folded arm waveguide 233D. The first input arm waveguide 231D is a linear arm waveguide made of, for example, thin-film LN, that connects between the first folded arm waveguide 234 and the first folded arm waveguide 233D. The first output arm waveguide 232D is a linear arm waveguide made of, for example, thin-film LN, that connects between the first folded arm waveguide 233D and the second multiplexing section 223. The first folded arm waveguide 233D is, for example, an S-shaped folded waveguide made of thin-film LN, which connects between the first input arm waveguide 231D and the first output arm waveguide 232D. The first folded arm waveguide 233D has a bent waveguide connecting between the input end of the first folded arm waveguide 233D and the first input arm waveguide 231D. The first folded arm waveguide 233D has a bent waveguide connecting between the output end of the first folded arm waveguide 233D and the first output arm waveguide 232D, and a straight arm waveguide connecting these bent waveguides together.

[0059] The second arm waveguide 241 of the fourth MZI 250D has a folded structure. The second arm waveguide 241 includes a second input arm waveguide 241D, a second output arm waveguide 242D, and a second folded arm waveguide 243D. The second input arm waveguide 241D is a linear arm waveguide made of, for example, thin-film LN, that connects the second folded arm waveguide 244 and the second folded arm waveguide 243D. The second output arm waveguide 242D is a linear arm waveguide made of, for example, thin-film LN, that connects the second folded arm waveguide 243D and the second multiplexing section 223. The second folded arm waveguide 243D is, for example, an S-shaped folded waveguide made of thin-film LN, which connects the second input arm waveguide 241D and the second output arm waveguide 242D. The second folded arm waveguide 243D has a bent waveguide connecting the input end of the second folded arm waveguide 243D and the second input arm waveguide 241D. The second folded arm waveguide 243D has a bent waveguide connecting the output end of the second folded arm waveguide 243D and the second output arm waveguide 242D, and a straight arm waveguide connecting these bent waveguides together.

[0060] The bent waveguide in the first folded arm waveguide 233D of the fourth MZI 250D and the bent waveguide in the second folded arm waveguide 243D form an intersecting waveguide.

[0061] The RF electrode 260 of the fourth MZI 250D has a signal electrode 261D including a signal electrode with a folded structure arranged in parallel between the first arm waveguide 231 and the second arm waveguide 241. The signal electrode 261D near the input of the first input side arm waveguide 231D of the first arm waveguide 231 and the second input side arm waveguide 241D in the second arm waveguide 241 is electrically connected to a fourth electrode wire 281D arranged on a PCB between the RF driver 280 and the RF driver 280. The RF driver 280 outputs a high-frequency signal to the signal electrode 261D of the RF electrode 260 through the fourth electrode wire 281D.

[0062] In the DP-IQ modulator 200 of the comparative example, the first arm waveguide 231 and second arm waveguide 241 of the modulator body 251 and the signal electrode 261 have a folded structure, so that the chip size in the longitudinal direction can be reduced.

[0063] However, in the DP-IQ modulator 200 of the comparative example, the first arm waveguide 231 and the second arm waveguide 241 of the modulator body 251 and the signal electrode 261 are configured to be folded back, so the short-side direction of the modulator body 251 for each MZI 250 is long. Also, the distance L100 between the input of the signal electrode 261A of the first MZI 250A and the input of the signal electrode 261B of the second MZI 250B used in the Y-polarized IQ modulator 200A is large. As a result, the electrode lengths of the first electrode wire 281A and the second electrode wire 281B from the RF driver 280 are long.

[0064] Furthermore, a distance L100 is provided between the input of the signal electrode 261C of the third MZI 250C and the input of the signal electrode 261D of the fourth MZI 250D used in the X-polarized IQ modulator 200B. As a result, the electrode lengths of the third electrode wire 281C and the fourth electrode wire 281D from the RF driver 280 become longer.

[0065] That is, the electrode lengths of the first electrode wire 281A and the second electrode wire 281B used in the Y-polarized IQ modulator 200A and the electrode lengths of the third electrode wire 281C and the fourth electrode wire 281D used in the X-polarized IQ modulator 200B are longer. As a result, the electrode lengths of the first electrode wire 281A, the second electrode wire 281B, the third electrode wire 281C, and the fourth electrode wire 281D are longer, which causes a loss of high-frequency signals, which are electrical signals, and deteriorates the modulation band.

[0066] Therefore, in this embodiment, the inputs of the signal electrodes of each adjacent MZI of each IQ modulator are brought closer to each other, and the electrode length of the electrode wire connecting the RF driver and the signal electrode is shortened.Then, an embodiment that can suppress the loss of the high frequency signal and suppress the deterioration of the modulation band will be described below. [Example]

[0067] FIG. 1 is an explanatory diagram illustrating an example of a DP-IQ modulator 1 according to a first embodiment. The DP-IQ modulator 1 shown in FIG. 1 is a modulator in which a thin-film LN chip 3 having a modulator body 51 for an X-polarized IQ modulator 1B and a modulator body 51 for a Y-polarized IQ modulator 1A is mounted on a SiPh (silicon photonics) chip 2. The DP-IQ modulator 1 includes an input waveguide 11, a branching section 12, the Y-polarized IQ modulator 1A, the X-polarized IQ modulator 1B, a PR (polarization rotator) 17, and a PBC (polarization beam combiner) 18. The DP-IQ modulator 1 also includes an output waveguide 19, an RF (radio frequency) electrode 60, a first DC (direct current) electrode 71, and a second DC electrode 72.

[0068] Input waveguide 11 is, for example, a Si waveguide, which receives input light from optical fiber F1 connected to a light source. Branching unit 12 is, for example, an XY-branching MMI (Multi-Mode Interferometer), which branches the input light from input waveguide 11 into input light of an X-polarized component and input light of a Y-polarized component.

[0069] The Y-polarized IQ modulator 1A modulates the Y-polarized IQ component input light and outputs the modulated Y-polarized IQ component signal light to the PR 17. The X-polarized IQ modulator 1B modulates the X-polarized IQ component input light and outputs the modulated X-polarized IQ component signal light to the PBC 18. The PR 17 rotates the polarization of the Y-polarized IQ component signal light and outputs the Y-polarized IQ component signal light after the polarization rotation to the PBC 18. The PBC 18 multiplexes the X-polarized IQ component signal light and the Y-polarized IQ component signal light after the polarization rotation and outputs the multiplexed signal light to the output waveguide 19.

[0070] The Y-polarized IQ modulator 1A has a first branching unit 13, a first adjusting unit 14, a first MZI 25A (25), a second MZI 25B (25), and a first multiplexing unit 16. The first MZI 25A is an optical modulator for the I component of the Y-polarized wave. The second MZI 25B is an optical modulator for the Q component of the Y-polarized wave.

[0071] The first branching unit 13 branches and outputs the Y-polarized input light from the branching unit 12 to two first adjustment units 14. The first adjustment unit 14 is configured, for example, with a Si waveguide and a heater or the like arranged below the Si waveguide, and heats the Si waveguide by heating the heater in response to an electrical signal from the first DC electrode 71. Note that the electrical signal from the first DC electrode 71 is, for example, an ON / OFF bias voltage. The first adjustment unit 14 shifts the phase of the input light that is guided through the Si waveguide. The first adjustment unit 14 outputs the phase-shifted input light to the MZI 25.

[0072] The first MZI 25A modulates the phase-shifted Y-polarized I-component input light and outputs the modulated Y-polarized I-component signal light to the first multiplexing unit 16. Similarly, the first MZI 25A modulates the phase-shifted Y-polarized Q-component input light and outputs the modulated Y-polarized Q-component signal light to the first multiplexing unit 16. The first multiplexing unit 16 multiplexes the modulated Y-polarized I-component signal light and the modulated Y-polarized Q-component signal light, and outputs the combined Y-polarized IQ-component signal light to the PR 17.

[0073] The X-polarized IQ modulator 1B has a first branching unit 13, a first adjusting unit 14, a third MZI 25C (25), a fourth MZI 25D (25), and a first multiplexing unit 16. The third MZI 25C is an optical modulator for the I component of the X-polarized wave. The fourth MZI 25D is an optical modulator for the Q component of the X-polarized wave.

[0074] The first branching unit 13 branches and outputs the X-polarized input light from the branching unit 12 to two first adjustment units 14. The first adjustment unit 14 is configured, for example, with a Si waveguide and a heater disposed below the Si waveguide. The first adjustment unit 14 shifts the phase of the input light guided through the Si waveguide by heating the Si waveguide with the heater in response to an electrical signal from the first DC electrode 71. The first adjustment unit 14 outputs the phase-shifted input light to the MZI 25. The third MZI 25C modulates the phase-shifted X-polarized I-component input light and outputs the modulated X-polarized I-component signal light to the first multiplexing unit 16. Similarly, the fourth MZI 25D modulates the phase-shifted X-polarized Q-component input light and outputs the modulated X-polarized Q-component signal light to the first multiplexing unit 16. The first multiplexer 16 multiplexes the modulated X-polarized I-component signal light with the modulated X-polarized Q-component signal light, and outputs the multiplexed X-polarized IQ-component signal light to the PBC 18.

[0075] Each MZI 25 includes a second branching unit 21, a first waveguide 30, a second waveguide 40, a second adjusting unit 22, a modulator body 51, and a second combining unit 23. The second branching unit 21 branches and outputs the branched input light from the first branching unit 13 to the first waveguide 30 and the second waveguide 40. The second adjusting unit 22 includes, for example, a first input waveguide 35 and a heater or the like disposed below a portion of the first input waveguide 35, and heats the portion of the first input waveguide 35 by heating the heater in response to an electrical signal from a second DC electrode 72. The electrical signal from the second DC electrode 72 is, for example, an ON / OFF bias voltage. The second adjusting unit 22 shifts the phase of the input light guided through the first input waveguide 35.

[0076] The first waveguide 30 has a first input waveguide 35, a first folded waveguide 34, and a first arm waveguide 31. The first input waveguide 35 is, for example, a Si waveguide, and connects between the second branching section 21 and the first folded waveguide 34. The first folded waveguide 34 is, for example, a Si waveguide with a folded structure, and connects between the first input waveguide 35 and the first arm waveguide 31.

[0077] The first arm waveguide 31 constitutes a part of the modulator body 51 having an electro-optic effect, and is, for example, a thin-film LN arm waveguide that modulates at high speed the input light guided in response to an electric signal from a signal electrode 61 arranged on the side surface of the first arm waveguide 31 to a ground electrode 62. The electric signal from the RF electrode 60 is, for example, a high-speed radio-frequency signal having a band of several tens of GHz or more.

[0078] The second waveguide 40 has a second input waveguide 45, a second folded waveguide 44, and a second arm waveguide 41. The second input waveguide 45 is, for example, a Si waveguide, which connects between the second branching unit 21 and the second folded waveguide 44. The second folded waveguide 44 is, for example, a Si waveguide with a folded structure, which connects between the second input waveguide 45 and the second arm waveguide 41.

[0079] The second arm waveguide 41 constitutes a part of the modulator body 51 having an electro-optic effect, and is, for example, a thin-film LN arm waveguide that modulates input light guided in response to a high-frequency signal from a signal electrode 61 arranged on the side of the second arm waveguide 41 to a ground electrode 62 at high speed.

[0080] The second multiplexing section 23 multiplexes the signal light from the first arm waveguide 31 and the signal light from the second arm waveguide 41, and outputs the signal light after high-speed modulation according to the phase difference between the signal light from the first arm waveguide 31 and the signal light from the second arm waveguide 41.

[0081] The RF electrode 60 has a signal electrode 61 arranged for each MZI 25, a ground electrode 62 arranged for each MZI 25, and an RF termination 64. The signal electrodes 61 are arranged in parallel to the side surfaces of the first arm waveguide 31 and the second arm waveguide 41 in the MZI 25. The signal electrodes 61 arranged near the inputs of the first arm waveguide 31 and the second arm waveguide 41 are electrically connected to electrode wires 81 arranged on a PCB (Printed Circuit Board) between the RF driver 80 and the RF driver 80. The RF driver 80 outputs a high-frequency signal to the signal electrodes 61 of the RF electrode 60 through the electrode wires 81. The signal electrodes 61 are, for example, signal electrodes 61A, 61B, 61C, and 61D.

[0082] The ground electrode 62 is arranged in parallel to the side surfaces of the first arm waveguide 31 and the second arm waveguide 41 in the MZI 25. The ground electrodes 62 near the inputs of the first arm waveguide 31 and the second arm waveguide 41 are electrically connected to a ground electrode line 82 arranged on a PCB between the RF driver 80 and the ground electrode 62. The RF driver 80 and the SiPh chip 2 are mounted on a PCB (not shown).

[0083] The RF termination 64 is disposed near the outputs of the first arm waveguide 31 and the second arm waveguide 41, and is connected to the signal electrode 61 and the ground electrode 62 to terminate the high frequency signal.

[0084] The first arm waveguide 31 of the first MZI 25A has a folded structure. The first arm waveguide 31 includes a first input arm waveguide 31A, a first output arm waveguide 32A, and a first folded arm waveguide 33A. The first input arm waveguide 31A is a linear arm waveguide made of, for example, thin-film LN, connecting the first folded waveguide 34 and the first folded arm waveguide 33A. The first output arm waveguide 32A is a linear arm waveguide made of, for example, thin-film LN, connecting the first folded arm waveguide 33A and the second multiplexing section 23. The first folded arm waveguide 33A is a reverse-S-shaped folded waveguide made of, for example, thin-film LN, connecting the first input arm waveguide 31A and the first output arm waveguide 32A. The first folded arm waveguide 33A has a bent waveguide connecting the input end of the first folded arm waveguide 33A and the first input arm waveguide 31A. The first folded arm waveguide 33A has a bent waveguide connecting the output end of the first folded arm waveguide 33A and the first output arm waveguide 32A, and a linear arm waveguide connecting these bent waveguides together.

[0085] The second arm waveguide 41 of the first MZI 25A has a folded structure. The second arm waveguide 41 includes a second input arm waveguide 41A, a second output arm waveguide 42A, and a second folded arm waveguide 43A. The second input arm waveguide 41A is, for example, a linear arm waveguide made of thin-film LN, and connects the second folded waveguide 44 and the second folded arm waveguide 43A. The second output arm waveguide 42A is, for example, a linear arm waveguide made of thin-film LN, and connects the second folded arm waveguide 43A and the second multiplexing section 23. The second folded arm waveguide 43A is, for example, an inverted-S-shaped folded waveguide made of thin-film LN, and connects the second input arm waveguide 41A and the second output arm waveguide 42A. The second folded arm waveguide 43A has a bent waveguide connecting the input end of the second folded arm waveguide 43A and the second input arm waveguide 41 A. The second folded arm waveguide 43A has a bent waveguide connecting the output end of the second folded arm waveguide 43A and the second output arm waveguide 42A, and a straight arm waveguide connecting these bent waveguides together.

[0086] 2 is an explanatory diagram in which the signal electrodes 61A of the first folded arm waveguide 33A and the second folded arm waveguide 43A are omitted. The bent waveguide in the first folded arm waveguide 33A of the first MZI 25A and the bent waveguide in the second folded arm waveguide 43A are configured as an intersecting waveguide X. As a result, the first arm waveguide 31 can suppress cancellation of electric fields in the first input arm waveguide 31A, the straight arm waveguide of the first folded arm waveguide 33A, and the first output arm waveguide 32A. Similarly, the second arm waveguide 41 can suppress cancellation of electric fields in the second input arm waveguide 41A, the straight arm waveguide of the second folded arm waveguide 43A, and the second output arm waveguide 42A.

[0087] The RF electrode 60 of the first MZI 25A has a signal electrode 61A including a folded-back signal electrode arranged in parallel between the first arm waveguide 31 and the second arm waveguide 41. The signal electrode 61A near the input of the first input-side arm waveguide 31A in the first arm waveguide 31 and the second input-side arm waveguide 41A in the second arm waveguide 41 is electrically connected to a first electrode wire 81A arranged on a PCB between the RF driver 80 and the RF driver 80. The RF driver 80 outputs a high-frequency signal to the signal electrode 61A through the first electrode wire 81A.

[0088] The first arm waveguide 31 of the second MZI 25B has a folded structure. The first arm waveguide 31 includes a first input arm waveguide 31B, a first output arm waveguide 32B, and a first folded arm waveguide 33B. The first input arm waveguide 31B is a linear arm waveguide made of, for example, thin-film LN, connecting the first folded waveguide 34 and the first folded arm waveguide 33B. The first output arm waveguide 32B is a linear arm waveguide made of, for example, thin-film LN, connecting the first folded arm waveguide 33B and the second multiplexing section 23. The first folded arm waveguide 33B is an S-shaped folded waveguide made of, for example, thin-film LN, connecting the first input arm waveguide 31B and the first output arm waveguide 32B. The first folded arm waveguide 33B has a bent waveguide connecting the input end of the first folded arm waveguide 33B and the first input arm waveguide 31B. The first folded arm waveguide 33B has a bent waveguide connecting the output end of the first folded arm waveguide 33B and the first output arm waveguide 32B, and a linear arm waveguide connecting these bent waveguides together.

[0089] The second arm waveguide 41 of the second MZI 25B has a folded structure. The second arm waveguide 41 includes a second input arm waveguide 41B, a second output arm waveguide 42B, and a second folded arm waveguide 43B. The second input arm waveguide 41B is, for example, a linear arm waveguide made of thin-film LN, and connects the second folded waveguide 44 and the second folded arm waveguide 43B. The second output arm waveguide 42B is, for example, a linear arm waveguide made of thin-film LN, and connects the second folded arm waveguide 43B and the second multiplexing section 23. The second folded arm waveguide 43B is, for example, an S-shaped folded waveguide made of thin-film LN, and connects the second input arm waveguide 41B and the second output arm waveguide 42B. The second folded arm waveguide 43B has a bent waveguide connecting the input end of the second folded arm waveguide 43B and the second input arm waveguide 41B. The second folded arm waveguide 43B has a bent waveguide connecting the output end of the second folded arm waveguide 43B and the second output arm waveguide 42B, and a linear arm waveguide connecting these bent waveguides together.

[0090] The bent waveguide in the first folded arm waveguide 33B of the second MZI 25B and the bent waveguide in the second folded arm waveguide 43B are configured as an intersecting waveguide X. As a result, the first arm waveguide 31 can suppress cancellation of electric fields in the first input arm waveguide 31B, the straight arm waveguide of the first folded arm waveguide 33B, and the first output arm waveguide 32B. Similarly, the second arm waveguide 41 can suppress cancellation of electric fields in the second input arm waveguide 41B, the straight arm waveguide of the second folded arm waveguide 43B, and the second output arm waveguide 42B.

[0091] The RF electrode 60 of the second MZI 25B has a signal electrode 61B including a folded-back signal electrode arranged in parallel between the first arm waveguide 31 and the second arm waveguide 41. The signal electrode 61B near the input of the first input-side arm waveguide 31B in the first arm waveguide 31 and the second input-side arm waveguide 41B in the second arm waveguide 41 is electrically connected to a second electrode wire 81B arranged on a PCB between the RF driver 80 and the RF driver 80. The RF driver 80 outputs a high-frequency signal to the signal electrode 61B through the second electrode wire 81B.

[0092] In the Y-polarized IQ modulator 1A, the first input arm waveguide 31A and the second input arm waveguide 41A are arranged adjacent to the first input arm waveguide 31B and the second input arm waveguide 41B. The distance L1 between the input of the signal electrode 61A of the first MZI 25A and the input of the signal electrode 61B of the second MZI 25B is shorter than the distance L100 in the comparative example. As a result, the electrode lengths of the first electrode wire 81A and the second electrode wire 81B from the RF driver 80 are significantly shorter than the electrode lengths of the first electrode wire 281A and the second electrode wire 281B in the comparative example.

[0093] The first arm waveguide 31 of the third MZI 25C has a folded structure. The first arm waveguide 31 includes a first input arm waveguide 31C, a first output arm waveguide 32C, and a first folded arm waveguide 33C. The first input arm waveguide 31C is a linear arm waveguide made of, for example, thin-film LN, connecting the first folded waveguide 34 and the first folded arm waveguide 33C. The first output arm waveguide 32C is a linear arm waveguide made of, for example, thin-film LN, connecting the first folded arm waveguide 33C and the second multiplexing section 23. The first folded arm waveguide 33C is a reverse-S-shaped folded waveguide made of, for example, thin-film LN, connecting the first input arm waveguide 31C and the first output arm waveguide 32C. The first folded arm waveguide 33C has a bent waveguide connecting the input end of the first folded arm waveguide 33C and the first input arm waveguide 31C. The first folded arm waveguide 33C has a bent waveguide connecting the output end of the first folded arm waveguide 33C and the first output arm waveguide 32C, and a linear arm waveguide connecting these bent waveguides together.

[0094] The second arm waveguide 41 of the third MZI 25C has a folded structure. The second arm waveguide 41 includes a second input arm waveguide 41C, a second output arm waveguide 42C, and a second folded arm waveguide 43C. The second input arm waveguide 41C is a linear arm waveguide made of, for example, thin-film LN, connecting the second folded waveguide 44 and the second folded arm waveguide 43C. The second output arm waveguide 42C is a linear arm waveguide made of, for example, thin-film LN, connecting the second folded arm waveguide 43C and the second multiplexing section 23. The second folded arm waveguide 43C is a reverse-S-shaped folded waveguide made of, for example, thin-film LN, connecting the second input arm waveguide 41C and the second output arm waveguide 42C. The second folded arm waveguide 43C has a bent waveguide connecting the input end of the second folded arm waveguide 43C and the second input arm waveguide 41C. The second folded arm waveguide 43C has a bent waveguide connecting the output end of the second folded arm waveguide 43C and the second output arm waveguide 42C, and a linear arm waveguide connecting these bent waveguides together.

[0095] The bent waveguide in the first folded arm waveguide 33C of the third MZI 25C and the bent waveguide in the second folded arm waveguide 43C are configured as an intersecting waveguide X. As a result, the first arm waveguide 31 can suppress cancellation of electric fields in the first input arm waveguide 31C, the straight arm waveguide of the first folded arm waveguide 33C, and the first output arm waveguide 32C. Similarly, the second arm waveguide 41 can suppress cancellation of electric fields in the second input arm waveguide 41C, the straight arm waveguide of the second folded arm waveguide 43C, and the second output arm waveguide 42C.

[0096] The RF electrode 60 of the third MZI 25C has a signal electrode 61C including a folded-back signal electrode arranged in parallel between the first arm waveguide 31 and the second arm waveguide 41. The signal electrodes 61C near the inputs of the first input-side arm waveguide 31C in the first arm waveguide 31 and the second input-side arm waveguide 41C in the second arm waveguide 41 are electrically connected to a third electrode wire 81C arranged on a PCB between the RF driver 80 and the RF driver 80. The RF driver 80 outputs a high-frequency signal to the signal electrode 61C through the third electrode wire 81C.

[0097] The first arm waveguide 31 of the fourth MZI 25D has a folded structure. The first arm waveguide 31 includes a first input arm waveguide 31D, a first output arm waveguide 32D, and a first folded arm waveguide 33D. The first input arm waveguide 31D is a linear arm waveguide made of, for example, thin-film LN, connecting the first folded waveguide 34 and the first folded arm waveguide 33D. The first output arm waveguide 32D is a linear arm waveguide made of, for example, thin-film LN, connecting the first folded arm waveguide 33D and the second multiplexing section 23. The first folded arm waveguide 33D is an S-shaped folded waveguide made of, for example, thin-film LN, connecting the first input arm waveguide 31D and the first output arm waveguide 32D. The first folded arm waveguide 33D has a bent waveguide connecting the input end of the first folded arm waveguide 33D and the first input arm waveguide 31D. The first folded arm waveguide 33D has a bent waveguide connecting the output end of the first folded arm waveguide 33D and the first output arm waveguide 32D, and a linear arm waveguide connecting these bent waveguides together.

[0098] The second arm waveguide 41 of the fourth MZI 25D has a folded structure. The second arm waveguide 41 includes a second input arm waveguide 41D, a second output arm waveguide 42D, and a second folded arm waveguide 43D. The second input arm waveguide 41D is, for example, a linear arm waveguide made of thin-film LN, connecting the second folded waveguide 44 and the second folded arm waveguide 43D. The second output arm waveguide 42D is, for example, a linear arm waveguide made of thin-film LN, connecting the second folded arm waveguide 43D and the second multiplexing section 23. The second folded arm waveguide 43D is, for example, an S-shaped folded waveguide made of thin-film LN, connecting the second input arm waveguide 41D and the second output arm waveguide 42D. The second folded arm waveguide 43D has a bent waveguide connecting the input end of the second folded arm waveguide 43D and the second input arm waveguide 41D. The second folded arm waveguide 43D has a bent waveguide connecting the output end of the second folded arm waveguide 43D and the second output arm waveguide 42D, and a linear arm waveguide connecting these bent waveguides together.

[0099] The bent waveguide in the first folded arm waveguide 33D of the fourth MZI 25D and the bent waveguide in the second folded arm waveguide 43D are configured as an intersecting waveguide X. As a result, the first arm waveguide 31 can suppress cancellation of electric fields in the first input arm waveguide 31D, the straight arm waveguide of the first folded arm waveguide 33D, and the first output arm waveguide 32D. Similarly, the second arm waveguide 41 can suppress cancellation of electric fields in the second input arm waveguide 41D, the straight arm waveguide of the second folded arm waveguide 43D, and the second output arm waveguide 42D.

[0100] The RF electrode 60 of the fourth MZI 25D has a signal electrode 61D including a signal electrode with a folded structure arranged in parallel between the first arm waveguide 31 and the second arm waveguide 41. The signal electrode 61D near the input of the first input-side arm waveguide 31D in the first arm waveguide 31 and the second input-side arm waveguide 41D in the second arm waveguide 41 is electrically connected to a fourth electrode wire 81D arranged on a PCB between the RF driver 80 and the RF driver 80. The RF driver 80 outputs a high-frequency signal to the signal electrode 61D of the RF electrode 60 through the fourth electrode wire 81D.

[0101] In the X-polarized IQ modulator 1B, the first input arm waveguide 31C and the second input arm waveguide 41C are arranged adjacent to the first input arm waveguide 31D and the second input arm waveguide 41D. The distance L1 between the input of the signal electrode 61C of the third MZI 25C and the input of the signal electrode 61D of the fourth MZI 25D is shorter than the distance L100 in the comparative example. As a result, the electrode lengths of the third electrode wire 81C and the fourth electrode wire 81D from the RF driver 80 are significantly shorter than the electrode lengths of the third electrode wire 281C and the fourth electrode wire 281D in the comparative example.

[0102] That is, the electrode lengths of the first electrode wire 81A and the second electrode wire 81B used in the Y-polarized IQ modulator 1A and the electrode lengths of the third electrode wire 81C and the fourth electrode wire 81D used in the X-polarized IQ modulator 1B are shorter than in the comparative example. As a result, by shortening the electrode lengths of the first electrode wire 81A, the second electrode wire 81B, the third electrode wire 81C, and the fourth electrode wire 81D, loss of high-frequency signals, which are electrical signals, is suppressed, thereby suppressing deterioration of the modulation band.

[0103] In the Y-polarized IQ modulator 1A of the first embodiment, the first input arm waveguide 31A and the second input arm waveguide 41A are arranged adjacent to each other. The Y-polarized IQ modulator 1A has a first electrode wire 81A connecting the signal electrode 61A and the RF driver 80 and a second electrode wire 81B connecting the signal electrode 61B and the RF driver 80. The electrode lengths of the first electrode wire 81A and the second electrode wire 81B used in the Y-polarized IQ modulator 1A are shorter than those of the comparative example. As a result, the shorter electrode lengths of the first electrode wire 81A and the second electrode wire 81B suppress loss of high-frequency signals, which are electrical signals, and thereby suppress deterioration of the modulation bandwidth.

[0104] In the X-polarized IQ modulator 1B, the first input arm waveguide 31C and the second input arm waveguide 41C are arranged adjacent to the first input arm waveguide 31D and the second input arm waveguide 41D. The X-polarized IQ modulator 1B has a third electrode wire 81C connecting the signal electrode 61C and the RF driver 80 and a fourth electrode wire 81D connecting the signal electrode 61D and the RF driver 80. The electrode lengths of the third electrode wire 81C and the fourth electrode wire 81D used in the X-polarized IQ modulator 1B are shorter than those of the comparative example. As a result, the shorter electrode lengths of the third electrode wire 81C and the fourth electrode wire 81D suppress loss of high-frequency signals, which are electrical signals, and thereby suppress deterioration of the modulation bandwidth.

[0105] The first arm waveguide 31 and the second arm waveguide 41 of the first MZI 25A have a folded structure at two locations, and the first arm waveguide 31 and the second arm waveguide 41 of the second MZI 25B also have a folded structure at two locations. The first arm waveguide 31 and the second arm waveguide 41 of the first MZI 25A are arranged axisymmetrically with the first arm waveguide 31 and the second arm waveguide 41 of the second MZI 25B. As a result, the first input arm waveguide 31A and the second input arm waveguide 41A of the first MZI 25A can be arranged adjacent to the first input arm waveguide 31A and the second input arm waveguide 41A of the second MZI 25B.

[0106] The first folded arm waveguide 33A and the second folded arm waveguide 43A of the first MZI 25A are inverted S-shaped. The first folded arm waveguide 33A and the second folded arm waveguide 43A of the second MZI 25B are S-shaped. The folding directions of the first MZI 25A and the second MZI 25B are reversed. That is, the folding directions of the signal electrode 61 are opposite between adjacent channels. As a result, the first input arm waveguide 31A and the second input arm waveguide 41A of the first MZI 25A and the first input arm waveguide 31A and the second input arm waveguide 41A of the second MZI 25B can be arranged adjacent to each other.

[0107] The DP-IQ modulator 1 incorporates a Y-polarized IQ modulator 1A and an X-polarized IQ modulator 1B. As a result, the electrode lengths of the Y-polarized IQ modulator 1A and the X-polarized IQ modulator 1B are shortened, and the DP-IQ modulator 1 can suppress the loss of high-frequency signals, which are electrical signals, thereby suppressing degradation of the modulation bandwidth.

[0108] In the DP-IQ modulator of Example 1, the waveguides constituting the first MZI 25A in the Y-polarized IQ modulator 1A and the waveguides constituting the second MZI 25B in the Y-polarized IQ modulator 1A have different waveguide lengths. As a result, a phase difference occurs between the waveguides constituting the first MZI 25A and the waveguides constituting the second MZI 25B in response to changes in the ambient temperature. A similar situation occurs between the waveguides of the third MZI 25C and the waveguides of the fourth MZI 25D in the X-polarized IQ modulator 1B. Therefore, an embodiment that addresses this situation will be described below as Example 2. [Example]

[0109] 3 is an explanatory diagram showing an example of a DP-IQ modulator 1X according to a second embodiment. The same components as those in the DP-IQ modulator 1 according to the first embodiment are denoted by the same reference numerals, and explanations of the overlapping components and operations will be omitted. The DP-IQ modulator 1X according to the second embodiment differs from the DP-IQ modulator 1 according to the first embodiment in that a delay waveguide 91A is disposed in the Si waveguide between the first branching unit 13 connected to the first MZI 25A in the Y-polarized IQ modulator 1A and the second branching unit 21.

[0110] The delay waveguide 91A is a waveguide that reduces, for example, zeros, the delay difference between the waveguide length between the second multiplexing section 23 and the first branching section 13 in the first MZI 25A in the Y-polarized IQ modulator 1A and the waveguide length between the second multiplexing section 23 and the first branching section 13 in the second MZI 25B in the Y-polarized IQ modulator 1A. As a result, the Y-polarized IQ modulator 1A can improve the phase difference caused by changes in environmental temperature between the waveguide that constitutes the first MZI 25A and the waveguide that constitutes the second MZI 25B.

[0111] Furthermore, a delay waveguide 91B was disposed in the Si waveguide between the first branching portion 13 connected to the third MZI 25C in the X-polarized IQ modulator 1B and the second branching portion 21.

[0112] Delay waveguide 91B is a waveguide that reduces, for example, zeros, the delay difference between the waveguide length between the second multiplexing section 23 and the first branching section 13 in the third MZI 25C in the X-polarized IQ modulator 1B and the waveguide length between the second multiplexing section 23 and the first branching section 13 in the fourth MZI 25D in the X-polarized IQ modulator 1B. As a result, the X-polarized IQ modulator 1B can improve the phase difference caused by changes in environmental temperature between the waveguide that constitutes the third MZI 25C and the waveguide that constitutes the fourth MZI 25D.

[0113] In the Y-polarized IQ modulator 1A of the second embodiment, a delay waveguide 91A is disposed in the Si waveguide between the first branching unit 13 connected to the first MZI 25A and the second branching unit 21. As a result, the Y-polarized IQ modulator 1A can improve the phase difference caused by changes in the environmental temperature between the waveguide constituting the first MZI 25A and the waveguide constituting the second MZI 25B. This also stabilizes the output of the Y-polarized IQ modulator 1A.

[0114] In the X-polarized IQ modulator 1B, a delay waveguide 91B is disposed in the Si waveguide between the first branch 13 connected to the third MZI 25C and the second branch 21. As a result, the X-polarized IQ modulator 1B can improve the phase difference caused by changes in environmental temperature between the waveguide constituting the third MZI 25C and the waveguide constituting the fourth MZI 25D. This also stabilizes the output of the X-polarized IQ modulator 1B.

[0115] The waveguide length of the delay waveguide 91A (91B) depends on the pitch of the coupling portion between the Si waveguide and the LN waveguide. Also, by making the bending direction different between adjacent MZIs, the pitch of the coupling portion between the Si waveguide and the LN waveguide becomes smaller. As a result, the waveguide length of the delay waveguide 91A (91B) can be shortened.

[0116] FIG. 4 is an explanatory diagram illustrating an example of an optical transceiver 90 according to this embodiment. The optical transceiver 90 shown in FIG. 4 is connected to an output optical fiber and an input optical fiber. The optical transceiver 90 includes a DSP (Digital Signal Processor) 91 and an optical transmitter / receiver 92. The optical transmitter / receiver 92 includes an optical transmitter 92A and an optical receiver 92B. The DSP 91 is an electrical component that performs digital signal processing. For example, the DSP 91 performs processing such as encoding transmission data, generates an electrical signal containing the transmission data, and outputs the generated electrical signal to the optical transmitter 92A. The DSP 91 also obtains an electrical signal containing reception data from the optical receiver 92B and performs processing such as decoding the obtained electrical signal to obtain the reception data.

[0117] The light source (not shown) includes, for example, a laser diode, and generates light of a predetermined wavelength and supplies it to the optical transmitter 92A and the optical receiver 92B. The optical transmitter 92A includes an optical modulator element 92A1 that modulates the light supplied from the light source (not shown) using an electrical signal output from the DSP 91 and outputs the modulated signal light to an optical fiber.

[0118] The optical modulator element 92A1 includes a first Mach-Zehnder interferometer and a second Mach-Zehnder interferometer. The first Mach-Zehnder interferometer includes a first waveguide having an electro-optic effect and a first electrode disposed near the first waveguide for applying an electric signal to the first waveguide. The second Mach-Zehnder interferometer includes a second waveguide having an electro-optic effect and a second electrode disposed near the second waveguide for applying an electric signal to the second waveguide. The first waveguide includes a first input arm waveguide, a first output arm waveguide, and a first folded waveguide connecting the first input arm waveguide and the first output arm waveguide. The second waveguide has a second input arm waveguide, a second output arm waveguide, and a second folded waveguide connecting the second input arm waveguide and the second output arm waveguide. The first waveguide and the second waveguide are arranged so that the first input arm waveguide and the second input arm waveguide are adjacent to each other. The optical device has a first electrode line connecting a first electrode arranged near the input of the first input arm waveguide and a driver that outputs an electrical signal to the first electrode. The optical device has a second electrode line connecting a second electrode arranged near the input of the second input arm waveguide and a driver that outputs an electrical signal to the second electrode, running parallel to the first electrode line.

[0119] The optical transmitter 92A generates signal light by modulating light supplied from a light source with an electrical signal as the light propagates through a waveguide. The optical receiver 92B has an optical receiver element 92B1 that receives incoming light from an optical fiber, converts the received light into an electrical signal using light supplied from the light source, and outputs the converted electrical signal to the DSP 91.

[0120] Although the optical transceiver 90 has been described as having an optical transmitter 92A and an optical receiver 92B built in, the present invention can also be applied to an optical transmitter that has only an optical transmitter 92A that has an optical device built in. Furthermore, the present invention is not limited to the optical transceiver 90, and the optical device can also be applied to the optical transmitter / receiver 92.

[0121] In this embodiment, a thin film LN chip is used as an example, but the present invention is not limited to this and may be, for example, TF-Barium Titanate, or may be changed as appropriate. The electro-optical effect material may be, for example, TF-BTO (BaTiO3), TF-PLZT (PbLaZrTiO3), or TF-PZT (PbZrTiO3), and may be changed as appropriate.

[0122] In this embodiment, the material of the electrode wire is not limited to Al, Au, Cu, etc., and can be changed as appropriate. [Explanation of symbols]

[0123] 1 DP-IQ Modulator 1A Y-polarized IQ modulator 1B X-polarized IQ modulator 25A First MZI 25B Second MZI 25C 3rd MZI 25D 4th MZI 30 First waveguide 31A First input arm waveguide 32A First output arm waveguide 33A First folded arm waveguide 40 Second waveguide 41A Second input arm waveguide 42A Second output arm waveguide 43A Second folded arm waveguide 61A signal electrode 61B Signal electrode 61C signal electrode 61D Signal electrode 80 RF Driver 81A First electrode wire 81B Second electrode wire 81C Third electrode wire 81D Fourth electrode wire

Claims

1. a first Mach-Zehnder interferometer having a first waveguide having an electro-optic effect and a first electrode disposed near the first waveguide and applying an electric signal to the first waveguide; an optical device comprising: a second waveguide having the electro-optic effect; and a second Mach-Zehnder interferometer disposed near the second waveguide and having a second electrode for applying an electric signal to the second waveguide, The first waveguide comprises: a first input arm waveguide, a first output arm waveguide, and a first folded waveguide connecting the first input arm waveguide and the first output arm waveguide; The second waveguide comprises: a second input arm waveguide, a second output arm waveguide, and a second folded waveguide connecting the second input arm waveguide and the second output arm waveguide; The first waveguide and the second waveguide are an optical device, wherein the first input arm waveguide and the second input arm waveguide are arranged adjacent to each other;

2. The first folded waveguide comprises: a waveguide having a folded structure at least at two locations between the first input arm waveguide and the first output arm waveguide; The second folded waveguide comprises: a waveguide having a folded structure at least at two locations between the second input arm waveguide and the second output arm waveguide; 2. The optical device according to claim 1, wherein the first waveguide and the second waveguide of the first Mach-Zehnder interferometer are arranged axisymmetrically with the first waveguide and the second waveguide of the second Mach-Zehnder interferometer.

3. 2. The optical device according to claim 1, wherein the first folded waveguide and the second folded waveguide are folded in opposite directions.

4. The first folded waveguide comprises: a first crossing waveguide that crosses and connects one of the two arms of the first input arm waveguide and the other of the two arms of the first output arm waveguide; The second folded waveguide comprises:

2. The optical device according to claim 1, wherein the second cross waveguide crosses and connects one of the two arms of the second input arm waveguide to the other of the two arms of the second output arm waveguide.

5. The first Mach-Zehnder interferometer comprises: a first modulation unit having the first waveguide and the first electrode, and modulating input light guided through the first waveguide in response to an electric signal from the first electrode; and a first adjustment unit having a third waveguide connected to the first waveguide in the first modulation unit, and adjusting a phase of the input light guided through the third waveguide, The second Mach-Zehnder interferometer comprises: a second modulation unit having the second waveguide and the second electrode, and modulating input light guided through the second waveguide in response to an electric signal from the second electrode; and a second adjustment unit having a fourth waveguide connected to the second waveguide in the second modulation unit, and adjusting a phase of the input light guided through the fourth waveguide, The third waveguide comprises:

2. The optical device according to claim 1, further comprising a delay waveguide such that a total length of the first waveguide and the third waveguide is equal to a total length of the second waveguide and the fourth waveguide.

6. a first Mach-Zehnder interferometer having a first waveguide having an electro-optic effect and a first electrode disposed near the first waveguide and applying an electric signal to the first waveguide; a first modulator including a second waveguide having the electro-optic effect and a second Mach-Zehnder interferometer disposed near the second waveguide and having a second electrode for applying an electric signal to the second waveguide; a third Mach-Zehnder interferometer having a third waveguide having the electro-optic effect and a third electrode disposed near the third waveguide and applying an electric signal to the third waveguide; a fourth Mach-Zehnder interferometer having a fourth waveguide having the electro-optic effect and a fourth electrode disposed near the fourth waveguide and applying an electric signal to the fourth waveguide, The first waveguide comprises: a first input arm waveguide, a first output arm waveguide, and a first folded waveguide connecting the first input arm waveguide and the first output arm waveguide; The second waveguide comprises: a second input arm waveguide, a second output arm waveguide, and a second folded waveguide connecting the second input arm waveguide and the second output arm waveguide; The third waveguide comprises: a third input waveguide, a third output waveguide, and a third folded waveguide connecting between the third input waveguide and the third output waveguide; The fourth waveguide comprises: a fourth input waveguide, a fourth output waveguide, and a fourth folded waveguide connecting between the fourth input waveguide and the fourth output waveguide; The first waveguide and the second waveguide are the first input arm waveguide and the second input arm waveguide are arranged adjacent to each other, The first modulator comprises: a first electrode line connecting the first electrode disposed near the input of the first input arm waveguide and a driver that outputs the electrical signal to the first electrode; a second electrode wire that connects the second electrode disposed near the input of the second input arm waveguide to the driver that outputs the electrical signal to the second electrode and runs parallel to the first electrode wire; The third waveguide and the fourth waveguide are the third input waveguide and the fourth input waveguide are arranged adjacent to each other, The second modulator comprises: a third electrode line connecting the third electrode disposed near the input of the third input waveguide and the driver that outputs the electrical signal to the third electrode; a fourth electrode wire that connects the fourth electrode disposed near the input of the fourth input waveguide to the driver that outputs the electrical signal to the fourth electrode and runs parallel to the third electrode wire; An optical device comprising:

7. a first Mach-Zehnder interferometer having a first waveguide having an electro-optic effect and a first electrode disposed near the first waveguide and applying an electric signal to the first waveguide; an optical transmitter including an optical modulator having the second waveguide having the electro-optic effect and a second Mach-Zehnder interferometer disposed near the second waveguide and having a second electrode for applying an electric signal to the second waveguide, The first waveguide comprises: a first input arm waveguide, a first output arm waveguide, and a first folded waveguide connecting the first input arm waveguide and the first output arm waveguide; The second waveguide comprises: a second input arm waveguide, a second output arm waveguide, and a second folded waveguide connecting the second input arm waveguide and the second output arm waveguide; The first waveguide and the second waveguide are the first input arm waveguide and the second input arm waveguide are arranged adjacent to each other, The optical modulator comprises: a first electrode line connecting the first electrode disposed near the input of the first input arm waveguide and a driver that outputs the electrical signal to the first electrode; a second electrode wire that connects the second electrode disposed near the input of the second input-side arm waveguide to the driver that outputs the electrical signal to the second electrode and runs parallel to the first electrode wire; An optical transmitter comprising:

8. An optical transceiver having an optical modulator element for transmitting signal light in response to an electrical signal, and an optical receiver element for receiving received light, The optical modulator element comprises: a first Mach-Zehnder interferometer having a first waveguide having an electro-optic effect and a first electrode disposed near the first waveguide and applying an electric signal to the first waveguide; a second Mach-Zehnder interferometer having a second waveguide having the electro-optic effect and a second electrode disposed near the second waveguide and applying an electric signal to the second waveguide; The first waveguide comprises: a first input arm waveguide, a first output arm waveguide, and a first folded waveguide connecting the first input arm waveguide and the first output arm waveguide; The second waveguide comprises: a second input arm waveguide, a second output arm waveguide, and a second folded waveguide connecting the second input arm waveguide and the second output arm waveguide; The first waveguide and the second waveguide are the first input arm waveguide and the second input arm waveguide are arranged adjacent to each other, The optical modulator element comprises: a first electrode line connecting the first electrode disposed near the input of the first input arm waveguide and a driver that outputs the electrical signal to the first electrode; an optical transceiver comprising: a second electrode wire that connects the second electrode disposed near an input of the second input-side arm waveguide to the driver that outputs the electrical signal to the second electrode, and that runs parallel to the first electrode wire.

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