Optical device, optical transmitter, optical receiver, and optical communication device

Abstract

To provide an optical device and the like that can evaluate a semiconductor optical amplifier (SOA).SOLUTION: An optical device has an optical coupler for inputting an optical signal from a light source, a semiconductor optical amplifier for amplifying the optical signal from the optical coupler, and a light receiving element for receiving spontaneous emission light from the semiconductor optical amplifier. The optical coupler has a first input port for inputting the optical signal from the light source, a second input port which is connected to an input stage of the light receiving element, and which is different from the first input port, and an output port connected to an input stage of the semiconductor optical amplifier and outputting the optical signal from the first input port to the semiconductor optical amplifier. The light receiving element receives the spontaneous emission light from the semiconductor optical amplifier via the output port and the second input port.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] In the field of optical communications, digital coherent communication technologies using modulation methods such as DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying) and multilevel QAM (Quadrature Amplitude Modulation) are known as means for transmitting large amounts of information over long distances.

[0003] An optical communication device for digital coherent optical communication includes, for example, a tunable light source that emits high-power, narrow-linewidth laser light and an optical modulator that modulates the laser light into a DP-QPSK signal or a multilevel QAM signal using an electrical signal. Furthermore, the optical communication device also includes, for example, an optical receiver that demodulates the DP-QPSK signal or the multilevel QAM signal to obtain an electrical signal. To miniaturize these elements, the optical modulator and the optical receiver can be integrated onto a single chip as an optical integrated circuit using silicon photonics technology.

[0004] However, in order to transmit information at speeds of, for example, 400 to 800 Gbps (Giga bit per second) over long distances, it is necessary to achieve high-power optical signals and high-sensitivity reception. Therefore, to achieve this, it is necessary to incorporate an optical amplification function into an optical integrated circuit. Therefore, by arranging a semiconductor optical amplifier (SOA) between a light source and an optical modulator, the SOA optically amplifies the laser light from the light source and outputs the amplified laser light to the optical modulator. As a result, the optical modulator can achieve high-power optical signals. Furthermore, by arranging an SOA between a light source and an optical receiver, the SOA optically amplifies the local light from the light source and outputs the amplified local light to the optical receiver. As a result, the optical receiver can achieve high-sensitivity reception.

[0005] However, while optical integrated circuits such as optical modulators and optical couplers can be fabricated using silicon, elements such as SOAs cannot be realized using indirect transition silicon. Therefore, SOAs are generally formed using direct transition compound semiconductors, which are different from optical integrated circuits, and are hybrid-integrated with optical integrated circuits. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-57412 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-29069 [Patent Document 3] U.S. Patent No. 10,754,091 Summary of the Invention [Problem to be solved by the invention]

[0007] Because SOAs are hybrid-integrated with optical integrated circuits, initial defects in the SOA must be removed before hybrid integration. Therefore, in the burn-in process for evaluating the SOA, a current is passed through the SOA in a high-temperature atmosphere, the optical output from the SOA is detected, and SOAs with optical output fluctuations below a reference value are selected. The selected SOAs are then hybrid-integrated with optical integrated circuits. Furthermore, SOAs with optical output below the reference value are replaced.

[0008] However, when evaluating an SOA after hybrid integration into an optical integrated circuit, it becomes difficult to detect amplified spontaneous emission (ASE) from all input / output ports due to losses in the optical modulator connected to the SOA in the downstream stage. Therefore, to detect the optical intensity of the optical signal from the SOA incorporated in an optical integrated circuit element, an optical branching section is provided downstream of the SOA in the optical integrated circuit, a photodetector is integrated at the branching point, and the SOA is evaluated based on the optical intensity of the optical signal detected by the photodetector. However, the optical branching section placed downstream of the SOA is unnecessary and not used during normal communication (operation), so branching the light to this photodetector adds unnecessary optical loss.

[0009] The disclosed technology has been made in view of the above points, and aims to provide an optical device or the like that can evaluate a semiconductor optical amplifier (SOA). [Means for solving the problem]

[0010] In one embodiment, the optical device disclosed herein includes an optical coupler that inputs an optical signal from a light source, a semiconductor optical amplifier that amplifies the optical signal from the optical coupler, and a photodetector that receives spontaneous emission from the semiconductor optical amplifier. The optical coupler has a first input port that inputs the optical signal from the light source, a second input port different from the first input port and connected to an input stage of the photodetector, and an output port that connects to the input stage of the semiconductor optical amplifier and outputs the optical signal from the first input port to the semiconductor optical amplifier. The photodetector receives the spontaneous emission from the semiconductor optical amplifier via the output port and the second input port. [Effects of the Invention]

[0011] According to one aspect of the optical device etc. disclosed in the present application, a semiconductor optical amplifier (SOA) can be evaluated using spontaneous emission light from the SOA. [Brief explanation of the drawings]

[0012] [Figure 1]FIG. 1 is an explanatory diagram illustrating an example of the configuration of an optical communication device according to a first embodiment. [Figure 2] FIG. 2 is a schematic plan view showing an example of the configuration of the optical modulator according to the first embodiment. [Figure 3] FIG. 3 is an explanatory diagram illustrating an example of the first MPD and the optical coupler in the optical modulator shown in FIG. [Figure 4] FIG. 4 is an explanatory diagram showing an example of the SOA evaluation criteria. [Figure 5] FIG. 5 is a flowchart showing an example of the processing operation of the DSP involved in the first evaluation processing. [Figure 6] FIG. 6 is an explanatory diagram illustrating an example of the configuration of an optical communication device according to the second embodiment. [Figure 7] FIG. 7 is a schematic plan view illustrating an example of the configuration of an optical modulator and an optical receiver according to the second embodiment. [Figure 8] FIG. 8 is an explanatory diagram illustrating an example of the first MPD and optical coupler in the optical modulator and optical receiver illustrated in FIG. [Figure 9] FIG. 9 is a flowchart showing an example of the processing operation of the DSP involved in the second evaluation processing. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the optical device and the like disclosed in the present application will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments. [Example]

[0014] FIG. 1 is an explanatory diagram illustrating an example of the configuration of an optical communication device 1 according to a first embodiment. The optical communication device 1 illustrated in FIG. 1 is connected to an optical fiber 2A(2) on the output side and an optical fiber 2B(2) on the input side. The optical communication device 1 is a digital coherent transceiver having a DSP (Digital Signal Processor) 3, a light source 4, an optical modulator 5, and an optical receiver 6. The DSP 3 is an electrical component that performs digital signal processing. For example, the DSP 3 performs processing such as encoding of transmission data, generates an electrical signal including the transmission data, and outputs the generated electrical signal to the optical modulator 5. The DSP 3 also obtains an electrical signal including reception data from the optical receiver 6 and performs processing such as decoding of the obtained electrical signal to obtain reception data.

[0015] The light source 4 includes, for example, a laser diode, and generates CW (Continuous Wave) light of a predetermined wavelength and supplies it to the optical modulator 5 and the optical receiver 6. The optical modulator 5 is an optical device that modulates the laser light supplied from the light source 4 using an electrical signal output from the DSP 3 and outputs the resulting optical transmission signal to the optical fiber 2A. The optical modulator 5 is, for example, an optical device such as an optical modulator including a silicon optical waveguide and a modulation unit. The silicon waveguide is formed on, for example, an SOI (Silicon On Insulator) substrate. The optical modulator 5 generates an optical transmission signal by modulating the laser light supplied from the light source 4 using an electrical signal input to the modulation unit as the laser light propagates through the silicon waveguide.

[0016] The optical receiver 6 receives received light, which is an optical signal, from the optical fiber 2B, and demodulates the received light using local light, which is laser light supplied from the light source 4. Then, the optical receiver 6 converts the demodulated received light into an electrical signal and outputs the converted electrical signal to the DSP 3.

[0017] FIG. 2 is a schematic plan view illustrating an example of the configuration of an optical modulator 5 according to a first embodiment. The optical modulator 5 illustrated in FIG. 2 is, for example, a DP-IQ (Dual Polarization-Inphase and Quadrature) optical modulator. The optical modulator 5 includes an input unit 11, an optical coupler 12, a first SOA (Semiconductor Optical Amplifier) ​​13A, a second SOA 13B, a first IQ optical modulator 14A for the X-polarized component, and a second IQ optical modulator 14B for the Y-polarized component. The optical modulator 5 further includes a third SOA 15A and a fourth SOA 15B. The optical modulator 5 includes a first VOA (Variable Optical Attenuator) 16A, a second VOA 16B, a PR (Polarization Rotator) 17, a PBC (Polarization Beam Combiner) 18, and an output unit 19. Furthermore, the optical modulator 5 has a first MPD (Monitor Photo Diode) 21, a second MPD 22A, and a third MPD 22B, which are light receiving elements.

[0018] The input unit 11 is a portion where laser light from the light source 4 is input via a connection fiber 4A. The optical coupler 12 is, for example, an optical coupler with two input ports and two output ports. The optical coupler 12 optically branches the laser light from the input unit 11 and outputs the branched laser light to the first SOA 13A and the second SOA 13B. The optical coupler 12 has a first input port 12A, a second input port 12B, a first output port 12C, and a second output port 12D. The first input port 12A is connected to the input unit 11 and is a port through which the laser light from the input unit 11 is input. The second input port 12B is connected to the first MPD 21 and is a port through which ASE from the first SOA 13A and the second SOA 13B is monitored. The first output port 12C is connected to the first SOA 13A and is a port through which the laser light is output to the first SOA 13A. The second output port 12D is connected to the second SOA 13B and outputs the laser light to the second SOA 13B.

[0019] The first SOA 13A is a first modulator semiconductor optical amplifier that optically amplifies the laser light from the first output port 12C in the optical coupler 12 and outputs the optically amplified laser light to the first IQ optical modulator 14A. The second SOA 13B is a second modulator semiconductor optical amplifier that optically amplifies the laser light from the second output port 12D in the optical coupler 12 and outputs the optically amplified laser light to the second IQ optical modulator 14B.

[0020] The first IQ optical modulator 14A is a first optical modulator that modulates the optically amplified laser light from the first SOA 13A and outputs the modulated X-polarized IQ component signal light to the third SOA 15A. The second IQ optical modulator 14B is a second optical modulator that modulates the optically amplified laser light from the second SOA 13B and outputs the modulated Y-polarized IQ component signal light to the fourth SOA 15B.

[0021] The third SOA 15A optically amplifies the X-polarized IQ component signal light from the first IQ optical modulator 14A and outputs the optically amplified X-polarized IQ component signal light to the first VOA 16A. The fourth SOA 15B optically amplifies the Y-polarized IQ component signal light from the second IQ optical modulator 14B and outputs the optically amplified Y-polarized IQ component signal light to the second VOA 16B.

[0022] The first VOA 16A adjusts the output of the X-polarized IQ component signal light and outputs the adjusted X-polarized IQ component signal light to the PBC 18. The second VOA 16B adjusts the output of the Y-polarized IQ component signal light and outputs the adjusted Y-polarized IQ component signal light to the PR 17. 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 XY-polarized signal light to the output unit 19. The output unit 19 outputs the multiplexed XY-polarized signal light to the optical fiber 2A.

[0023] The first IQ optical modulator 14A has a first branching unit 31A, a first I component modulator 32A, a first Q component modulator 33A, and a first multiplexing unit 34A. The first branching unit 31A optically branches the optically amplified laser light from the first SOA 13A, and outputs the branched laser light to the first I component modulator 32A and the first Q component modulator 33A.

[0024] The first I-component modulator 32A optically modulates the laser light from the first branching unit 31A into an X-polarized I-component signal light and outputs the X-polarized I-component signal light to the first multiplexing unit 34A. The first Q-component modulator 33A optically modulates the laser light from the first branching unit 31A into an X-polarized Q-component signal light and outputs the X-polarized Q-component signal light to the first multiplexing unit 34A. The first multiplexing unit 34A multiplexes the X-polarized I-component signal light from the first I-component modulator 32A and the X-polarized Q-component signal light from the first Q-component modulator 33A, and outputs the X-polarized I-Q-component signal light to the third SOA 15A.

[0025] The first I-component modulator 32A includes a third branching unit 41, two RFPSs (Radio Frequency Phase Shifters) 42, two daughter-side DCPSs (Direct Current Phase Shifters) 43, a third multiplexing unit 44, and a parent-side DCPS 45. The third branching unit 41 optically branches the laser light from the first branching unit 31 and outputs the branched laser light to each RFPS 42. The RFPS 42 is, for example, an MZI (Mach-Zehnder Interferometer) that receives a high-speed signal having a bandwidth of several tens of GHz and performs high-speed modulation. The RFPS 42 high-speed-modulates the laser light in response to the high-speed signal from the RF electrode and outputs the high-speed-modulated laser light to the daughter-side DCPS 43.

[0026] The daughter DCPS 43 is, for example, an MZI that is configured with a heater electrode and that adjusts the phase of the signal light by changing the refractive index of the optical waveguide by passing a current through the heater electrode to heat the optical waveguide. The daughter DCPS 43 phase-modulates the high-speed modulated laser light in response to an electrical signal from the DC electrode and outputs the phase-modulated I-component signal light to the third multiplexer 44. The third multiplexer 44 multiplexes the I-component signal lights from each daughter DCPS 43 and outputs the multiplexed I-component signal light to the parent DCPS 45. The parent DCPS 45 quadrature-modulates the phase-modulated I-component signal light in response to a drive voltage signal from the DC electrode and outputs the quadrature-modulated X-polarized I-component signal light to the first multiplexer 34A.

[0027] The first Q-component modulator 33A includes a third branching unit 41, two RFPSs 42, two daughter DCPSs 43, a third multiplexing unit 44, and a parent DCPS 45. The third branching unit 41 branches the laser light from the first branching unit 31 and outputs the branched laser light to each RFPS 42. The RFPS 42 high-speed-modulates the laser light in response to a high-speed signal from the RF electrode and outputs the high-speed-modulated laser light to the daughter DCPS 43. The daughter DCPS 43 phase-modulates the high-speed-modulated laser light in response to a data signal from the DC electrode and outputs the phase-modulated Q-component signal light to the third multiplexing unit 44. The third multiplexing unit 44 multiplexes the Q-component signal light from each daughter DCPS 43 and outputs the multiplexed Q-component signal light to the parent DCPS 45. The parent DCPS 45 quadrature-modulates the phase-modulated Q-component signal light in response to the drive voltage signal from the DC electrode, and outputs the quadrature-modulated X-polarized Q-component signal light to the first multiplexer 34 A. The first multiplexer 34 A multiplexes the X-polarized I-component signal light from the parent DCPS 45 and the X-polarized Q-component signal light from the parent DCPS 45, and outputs the multiplexed X-polarized IQ-component signal light to the third SOA 15 A.

[0028] The second IQ optical modulator 14B includes a second branching unit 31B, a second I-component modulator 32B, a second Q-component modulator 33B, and a second multiplexing unit 34B. The second branching unit 31B optically branches the optically amplified signal light from the second SOA 13B and outputs the branched signal light to the second I-component modulator 32B and the second Q-component modulator 33B. The second I-component modulator 32B optically modulates the signal light from the second branching unit 31B into a Y-polarized I-component signal light and outputs the Y-polarized I-component signal light to the second multiplexing unit 34B. The second Q-component modulator 33B optically modulates the signal light from the second branching unit 31B into a Y-polarized Q-component signal light and outputs the Y-polarized Q-component signal light to the second multiplexing unit 34B. The second multiplexing section 34B multiplexes the Y-polarized I-component signal light from the second I-component modulator 32B and the Y-polarized Q-component signal light from the second Q-component modulator 33B, and outputs the Y-polarized IQ-component signal light to the second multiplexing section 34B.

[0029] The second I-component modulator 32B includes a third branching unit 41, two RFPSs 42, two daughter DCPSs 43, a third multiplexing unit 44, and a parent DCPS 45. The third branching unit 41 optically branches the signal light from the second branching unit 31B and outputs the branched signal light to each RFPS 42. The RFPS 42 high-speed-modulates laser light in response to a high-speed signal from the RF electrode and outputs the high-speed-modulated laser light to the daughter DCPS 43. The daughter DCPS 43 phase-modulates the high-speed-modulated laser light in response to an electrical signal from the DC electrode and outputs the phase-modulated I-component signal light to the third multiplexing unit 44. The third multiplexing unit 44 multiplexes the I-component signal light from each daughter DCPS 43 and outputs the multiplexed I-component signal light to the parent DCPS 45. The parent DCPS 45 quadrature-modulates the phase-modulated I-component signal light in response to the drive voltage signal from the DC electrode, and outputs the quadrature-modulated Y-polarized I-component signal light to the second multiplexer 34B.

[0030] The second Q-component modulator 33B includes a third branching unit 41, two RFPSs 42, two daughter DCPSs 43, a third multiplexing unit 44, and a parent DCPS 45. The third branching unit 41 optically branches the signal light from the second branching unit 31B and outputs the branched signal light to each RFPS 42. The RFPS 42 high-speed-modulates laser light in response to a high-speed signal from the RF electrode and outputs the high-speed-modulated laser light to the daughter DCPS 43. The daughter DCPS 43 phase-modulates the high-speed-modulated laser light in response to an electrical signal from the DC electrode and outputs the phase-modulated Q-component signal light to the third multiplexing unit 44. The third multiplexing unit 44 multiplexes the Q-component signal light from each daughter DCPS 43 and outputs the multiplexed Q-component signal light to the parent DCPS 45. The parent DCPS 45 quadrature-modulates the phase-modulated Q-component signal light in response to the drive voltage signal from the DC electrode, and outputs the quadrature-modulated Y-polarized Q-component signal light to the second multiplexer 34 B. The second multiplexer 34 B multiplexes the Y-polarized I-component signal light from the parent DCPS 45 and the Y-polarized Q-component signal light from the parent DCPS 45, and outputs the combined Y-polarized IQ-component signal light to the fourth SOA 15 B.

[0031] The second MPD 22A monitors a part of the IQ component signal light of the X polarization after the output adjustment by the first VOA 16A, and adjusts the attenuation amount of the first VOA 16A based on the monitoring result. Also, the third MPD 22B monitors a part of the IQ component signal light of the Y polarization after the output adjustment by the second VOA 16B, and adjusts the attenuation amount of the second VOA 16B based on the monitoring result.

[0032] FIG. 3 is an explanatory diagram showing an example of the first MPD 21 and optical coupler 12 in the optical modulator 5 shown in FIG. 2. The first MPD 21 detects ASE from the first SOA 13A via the first output port 12C and the second input port 12B in the optical coupler 12 in response to the energization of the first SOA 13A. The SOA is an element that amplifies and outputs input light by injecting current. The driving principle is the same as that of an LED, in that the SOA itself generates ASE from the input and output sides of the light when current is injected. In other words, when the first SOA 13A optically amplifies laser light in response to energization, ASE is emitted in all directions of the first SOA 13A, for example, from the input and output ports of the first SOA 13A. The first MPD 21 electrically converts the optical intensity of the detected ASE into an MPD current. Furthermore, in response to the energization of the second SOA 13B, the first MPD 21 detects the ASE from the second SOA 13B via the second output port 12D and the second input port 12B in the optical coupler 12. Note that when the second SOA 13B optically amplifies the laser light in response to the energization, the ASE is emitted in all directions of the second SOA 13B, for example, from the input port and output port of the second SOA 13B. The first MPD 21 electrically converts the optical intensity of the detected ASE into an MPD current.

[0033] Next, a method for evaluating the first SOA 13A and the second SOA 13B of the optical modulator 5 of the first embodiment will be described. FIG. 4 is an explanatory diagram showing an example of SOA evaluation criteria. The SOA is evaluated by passing electricity through the SOA in a high-temperature atmosphere under certain evaluation conditions and determining whether the MPD current of the first MPD 21 after a burn-in period is equal to or less than a reference value. The certain evaluation conditions include, for example, an ambient temperature of 80°C to 120°C, a current value of 300mA to 500mA passed through the SOA, an evaluation time of 6 hours to 24 hours, and a reference value of ASE light intensity fluctuations of 5% to 10% from the initial value. The evaluation conditions can be changed as appropriate depending on the SOA element structure and mounting conditions. The DSP 3 executes a first evaluation process before operation begins, for example, before shipping from the factory. If the MPD current corresponding to the ASE light intensity of the SOA is less than the reference value, the DSP 3 evaluates the SOA as abnormal. If the MPD current corresponding to the ASE light intensity of the SOA is equal to or greater than the reference value, the DSP 3 evaluates the SOA as normal. The term "operation" refers to a communication state in which the optical communication device 1 is used to communicate signal light.

[0034] FIG. 5 is a flow chart showing an example of the processing operation of the DSP3 related to the first evaluation process. The first evaluation process is a process for evaluating the first SOA 13A and the second SOA 13B in the optical modulator 5 under certain evaluation conditions before shipping from the factory. In FIG. 5, the DSP3 energizes the first SOA 13A and the second SOA 13B in a high-temperature atmosphere (step S11). The DSP3 measures the MPD current relative to the optical intensity of the ASE from the first SOA 13A and the second SOA 13B through the first MPD 21 (step S12). The first MPD 21 detects the optical intensity of the ASE from the first SOA 13A and the second SOA 13B via the first output port 12C and the second output port 12D in the optical coupler 12 and from the second input port 12B. The first MPD 21 electrically converts the optical intensity of the ASE into an MPD current and outputs the electrically converted MPD current to the DSP3.

[0035] The DSP 3 determines whether the MPD current measured by the first MPD 21 is equal to or greater than a reference value (step S13). If the MPD current is equal to or greater than the reference value (step S13: Yes), the DSP 3 evaluates that the first SOA 13A and the second SOA 13B are normal (step S14), outputs the evaluation result (step S15), and ends the processing operation shown in FIG.

[0036] If the MPD current is not equal to or greater than the reference value (step S13: No), the DSP3 selects the first SOA 13A (step S16) and applies current only to the first SOA 13A in a high-temperature atmosphere (step S17). The DSP3 measures the MPD current relative to the ASE optical intensity from the first SOA 13A through the first MPD 21 (step S18). The first MPD 21 detects the ASE optical intensity from the first SOA 13A via the first output port 12C in the optical coupler 12 and the second input port 12B. The first MPD 21 electrically converts the ASE optical intensity into an MPD current and outputs the electrically converted MPD current to the DSP3.

[0037] The DSP3 determines whether the MPD current measured by the first MPD 21 is equal to or greater than a reference value (step S19). If the MPD current is equal to or greater than the reference value (step S19: Yes), the DSP3 evaluates the first SOA 13A as normal (step S20). If the MPD current is not equal to or greater than the reference value (step S19: No), the DSP3 evaluates the first SOA 13A as abnormal (step S21). In other words, the first MPD 21 evaluates the first SOA 13A individually.

[0038] Furthermore, after the DSP3 evaluates the first SOA 13A as normal in step S20 or the second SOA 13B as abnormal in step S21, the DSP3 designates the second SOA 13B (step S22). Then, the DSP3 energizes only the second SOA 13B in a high-temperature atmosphere (step S23). The DSP3 measures the MPD current relative to the optical intensity of the ASE from the second SOA 13B through the first MPD 21 (step S24). The first MPD 21 detects the optical intensity of the ASE from the second SOA 13B via the second input port 12B via the second output port 12D in the optical coupler 12. The first MPD 21 electrically converts the optical intensity of the ASE into an MPD current and outputs the electrically converted MPD current to the DSP3.

[0039] The DSP3 determines whether the MPD current measured by the first MPD 21 is equal to or greater than the reference value (step S25). If the MPD current is equal to or greater than the reference value (step S25: Yes), the DSP3 evaluates that the second SOA 13B is normal (step S26) and proceeds to step S15 to output the evaluation result.

[0040] If the MPD current is not equal to or greater than the reference value (step S25: No), the DSP 3 evaluates that the second SOA 13B is abnormal (step S27) and proceeds to step S15 to output the evaluation result. That is, the first MPD 21 individually evaluates the second SOA 13B.

[0041] The optical coupler 12 of the first embodiment has a first input port 12A that receives laser light from the light source 4 and a second input port 12B that connects to the input stage of the first MPD 21. The optical coupler 12 also has a first output port 12C that connects to the input stage of the first SOA 13A and outputs the laser light from the first input port 12A to the first SOA 13A. The optical coupler 12 also has a second output port 12D that connects to the input stage of the second SOA 13B and outputs the laser light from the first input port 12A to the second SOA 13B. The first MPD 21 receives the ASE from the first SOA 13A via the first output port 12C and the second input port 12B, and also receives the ASE from the second SOA 13B via the second output port 12D and the second input port 12B. As a result, the DSP 3 can evaluate the first SOA 13A and the second SOA 13B using the MPD current corresponding to the optical intensity of the ASE before shipping from the factory. Moreover, because the first MPD 21 is connected to the second input port 12B of the optical coupler 12, it does not become a factor of signal loss during operation, and the SOA can be evaluated.

[0042] The first SOA 13A and the second SOA 13B are formed of a direct transition compound semiconductor different from that of the optical integrated circuit, so that the DSP 3 can evaluate the first SOA 13A and the second SOA 13B using the MPD current corresponding to the ASE optical intensity, even if the first SOA 13A and the second SOA 13B are hybrid-integrated on the optical integrated circuit.

[0043] The optical modulator 5 includes a first SOA 13A connected between the first IQ optical modulator 14A and the first output port 12C to amplify the laser light from the first output port 12C. The optical modulator 5 further includes a second SOA 13B connected between the second IQ optical modulator 14B and the second output port 12D to amplify the laser light from the second output port 12D. The first MPD 21 receives the ASE from the first SOA 13A via the first output port 12C and the second input port 12B, and also receives the ASE from the second SOA 13B via the second output port 12D and the second input port 12B. As a result, the DSP 3 can evaluate the first SOA 13A and the second SOA 13B in the optical modulator 5 using an MPD current corresponding to the ASE optical intensity. Moreover, since the first MPD 21 is connected to the second input port 12B of the optical coupler 12, it does not become a factor of signal loss during operation, and the SOA can be evaluated.

[0044] In addition, although an example has been given in which DSP3 executes the first evaluation process before shipping from the factory, an evaluation device (not shown) may be connected instead of DSP3, and the evaluation device may execute the first evaluation process before shipping from the factory, and modifications can be made as appropriate.

[0045] An embodiment of an optical communication device that evaluates the first SOA 13A and second SOA 13B of the optical modulator 5 of Example 1 as well as the fifth SOA 65 of the optical receiver 6 will be described below as Example 2. The same components as those in the optical communication device 1 of Example 1 are denoted by the same reference numerals, and redundant descriptions of the components and operations will be omitted. [Example]

[0046] 6 is an explanatory diagram showing an example of the configuration of an optical communication device 1A according to a second embodiment. The optical communication device 1A shown in FIG. 6 includes an optical coupler 12 that connects a light source 4 and an optical modulator 5 and also connects the light source 4 and an optical receiver 6. Furthermore, the optical communication device 1A detects the optical intensities of the ASE from the first SOA 13A and the second SOA 13B on the optical modulator 5 side and the fifth SOA 65 on the optical receiver 6 side using a first MPD 21A connected to a second input port 12B of the optical coupler 12.

[0047] FIG. 7 is a plan view showing an example of the configuration of the optical modulator 5 and the optical receiver 6 of the second embodiment, and FIG. 8 is an explanatory diagram showing an example of the first MPD 21A and the optical coupler 12 in the optical modulator 5 and the optical receiver 6 shown in FIG. 7. The optical coupler 12 has a first input port 12A, a second input port 12B, a first output port 12C, and a second output port 12D. The first input port 12A is connected to the light source 4 and is a port through which laser light from the light source 4 is input. The second input port 12B is connected to the first MPD 21A and is a port through which ASE from the first SOA 13A, the second SOA 13B, and the fifth SOA 65 is monitored. Note that when the fifth SOA 65 optically amplifies the local light in response to power application, ASE is emitted in all directions of the fifth SOA 65, for example, from the input port and output port of the fifth SOA 65. The first output port 12C is connected to the optical branching unit 8, which is connected to the first SOA 13 and the second SOA 13B in the optical modulator 5, and is a port that outputs the laser light to the optical branching unit 8. The optical branching unit 8 branches and outputs the laser light from the first output port 12C to the first SOA 13A and the second SOA 13B. The second output port 12D is connected to the fifth SOA 65 on the optical receiver 6 side, and is a port that outputs the laser light to the fifth SOA 65.

[0048] The optical receiver 6 includes a receiving-side input unit 61, a third VOA 62, a PBS (Polarization Beam Splitter) 63, a PR 64, a fifth SOA 65, and a receiving-side branching unit 66. The optical receiver 6 includes a first optical hybrid circuit 67A, a second optical hybrid circuit 67B, four PDs 68A, four PDs 68B, a fourth MPD 69A, and a fifth MPD 69B.

[0049] The receiving side input unit 61 receives the received light from the optical fiber 2B. The third VOA 62 adjusts the output level of the received light from the receiving side input unit 61 and outputs the adjusted received light to the PBS 63. The PBS 63 demultiplexes the received light into X-polarized IQ component signal light and Y-polarized IQ component signal light, outputs the X-polarized IQ component signal light to the first optical hybrid circuit 67A, and outputs the Y-polarized IQ component signal light to the PR 64. The PR 64 rotates the Y-polarized IQ component signal light by 90 degrees and outputs the Y-polarized IQ component signal light after the polarization rotation to the second optical hybrid circuit 67B.

[0050] The optical coupler 12 outputs the laser light from the light source 4 to the optical branching unit 8 in the upstream stage of the optical modulator 5, and also outputs the laser light to the fifth SOA 65 of the optical receiver 6. The fifth SOA 65 optically amplifies the local light, which is the laser light from the second output port 12D in the optical coupler 12, and outputs the optically amplified local light to the receiving-side branching unit 66.

[0051] The receiving-side branching unit 66 outputs the optically amplified local light from the fifth SOA 65 to the first optical hybrid circuit 67A and the second optical hybrid circuit 67B.

[0052] The first optical hybrid circuit 67A causes the local light to interfere with the X polarization component of the received light to obtain I and Q component optical signals. The first optical hybrid circuit 67A outputs the I component optical signal of the X polarization component to the PD 68A. The first optical hybrid circuit 67A outputs the Q component optical signal of the X polarization component to the PD 68A.

[0053] The second optical hybrid circuit 67B causes the local light to interfere with the Y polarization component of the received light to obtain I-component and Q-component optical signals. The second optical hybrid circuit 67B outputs the I-component optical signal of the Y polarization component to the PD 68B. The second optical hybrid circuit 67B outputs the Q-component optical signal of the Y polarization component to the PD 68B.

[0054] The PD68A electrically converts the I-component optical signal of the X-polarized component from the first optical hybrid circuit 67A and outputs the I-component electrical signal after the electrical conversion. The PD68A also electrically converts the Q-component optical signal of the X-polarized component from the first optical hybrid circuit 67A and outputs the Q-component electrical signal after the electrical conversion. The PD68B electrically converts the I-component optical signal of the Y-polarized component from the second optical hybrid circuit 67B and outputs the I-component electrical signal after the electrical conversion. The PD68B also electrically converts the Q-component optical signal of the Y-polarized component from the second optical hybrid circuit 67B and outputs the Q-component electrical signal after the electrical conversion.

[0055] Next, the operation of the optical communication device 1A of the second embodiment will be described. FIG. 9 is a flowchart showing an example of the processing operation of the DSP3 related to the second evaluation process. The second evaluation process is a process for evaluating the first SOA 13A and the second SOA 13B in the optical modulator 5 and the fifth SOA 65 in the optical receiver 6 under certain evaluation conditions before shipping from the factory. In FIG. 9, the DSP3 energizes all SOAs in a high-temperature atmosphere (step S31). Note that all SOAs refer to, for example, the first SOA 13A and the second SOA 13B in the optical modulator 5 and the fifth SOA 65 in the optical receiver 6. The DSP3 measures the MPD current relative to the optical intensity of the ASE from all SOAs via the first MPD 21 (step S32). Note that the first MPD 21 detects the optical intensity of the ASE from the first SOA 13A and the second SOA 13B via the first output port 12C in the optical coupler 12 and the second input port 12B. The first MPD 21 electrically converts the optical intensity of the ASE into an MPD current and outputs the electrically converted MPD current to the DSP 3. Furthermore, the first MPD 21 detects the optical intensity of the ASE from the fifth SOA 65 via the second input port 12B via the second output port 12D in the optical coupler 12. The first MPD 21 electrically converts the optical intensity of the ASE into an MPD current and outputs the electrically converted MPD current to the DSP 3.

[0056] The DSP3 determines whether the MPD current measured by the first MPD 21 is equal to or greater than a reference value (step S33). If the MPD current is equal to or greater than the reference value (step S33: Yes), the DSP3 evaluates all SOAs as normal (step S34), outputs the evaluation result (step S35), and ends the processing operation shown in Fig. 9. Note that all SOAs include, for example, the first SOA 13A and the second SOA 13B in the optical modulator 5 and the fifth SOA 65 in the optical receiver 6.

[0057] If the MPD current is not equal to or greater than the reference value (step S33: No), the DSP3 designates an SOA (step S36). The DSP3 designates, for example, one SOA from the first SOA 13A, the second SOA 13B, and the fifth SOA 65. The DSP3 applies current only to the designated SOA in a high-temperature atmosphere (step S37). The DSP3 measures the MPD current relative to the ASE optical intensity from the designated SOA through the first MPD 21 (step S38). The first MPD 21 detects the ASE optical intensity from the designated SOA through the second input port 12B in the optical coupler 12. The first MPD 21 electrically converts the ASE optical intensity into an MPD current and outputs the electrically converted MPD current to the DSP3.

[0058] The DSP3 determines whether the MPD current measured by the first MPD 21 is equal to or greater than a reference value (step S39). If the MPD current is equal to or greater than the reference value (step S39: Yes), the DSP3 evaluates the designated SOA as normal (step S40) and determines whether there are any undesignated SOAs among all SOAs (step S42). In other words, the first MPD 21A evaluates the designated SOAs individually. Note that all SOAs include, for example, the first SOA 13A and the second SOA 13B in the optical modulator 5 and the fifth SOA 65 in the optical receiver 6.

[0059] If there is an unspecified SOA (step S42: Yes), the DSP3 proceeds to the process of step S36 to specify the unspecified SOA. If there is no unspecified SOA (step S42: No), the DSP3 proceeds to the process of step S35 to output the evaluation result.

[0060] If the MPD current is not equal to or greater than the reference value (step S39: No), the DSP 3 evaluates that the designated SOA is abnormal (step S41), and proceeds to the process of step S42 to determine whether or not there is an undesignated SOA.

[0061] The optical communication device 1A of the second embodiment includes a first SOA 13A and a second SOA 13B connected between an optical modulator 5 that modulates an optical signal using an electrical signal and a first output port 12C and amplifying laser light from the first output port 12C, and a fifth SOA 65 connected between an optical receiver 6 that obtains an electrical signal from received light using an optical signal and a second output port 12D and amplifying local light from the second output port 12D. The first MPD 21A detects ASE from the first SOA 13A and the second SOA 13B in the optical modulator 5 via the optical branching unit 8 and the first output port 12C, and also detects ASE from the fifth SOA 65 in the optical receiver 6 via the second output port 12D. As a result, the DSP 3 can evaluate the first SOA 13A and the second SOA 13B in the optical modulator 5 and the fifth SOA 65 in the optical receiver 6 using an MPD current corresponding to the ASE optical intensity before shipping from the factory. Moreover, since the first MPD 21A is connected to the second input port 12B of the optical coupler 12, it does not become a factor of signal loss during operation, and the SOA can be evaluated.

[0062] In addition, although an example has been given in which DSP3 performs the second evaluation process before shipping from the factory, an evaluation device (not shown) may be connected instead of DSP3, and the evaluation device may perform the second evaluation process before shipping from the factory, and modifications can be made as appropriate.

[0063] In the optical communication device 1A of the second embodiment, an optical modulator 5 and an optical receiver 6 are built in, an optical branching unit 8 is connected to a first output port 12C of an optical coupler 12, and a fifth SOA 65 on the optical receiver 6 side is connected to a second output port 12D in the optical coupler 12. However, the present invention can also be applied to an optical transmission device that only has an optical modulator 5 built in, and in this case, ASE from the first SOA 13A and second SOA 13B in the optical modulator 5 can be detected through the first MPD 21A.

[0064] The present invention is also applicable to an optical receiving device incorporating only the optical receiver 6, in which case the ASE from the fifth SOA 65 in the optical receiver 6 can be detected through the first MPD 21A.

[0065] Although the optical coupler 12 has been illustrated as having two input ports and two output ports, the number of input ports may be m and the number of output ports may be n, where m is 2 or more and n is 1 or more.

[0066] The optical communication device 1 can be applied to, for example, a communication device using DP-QPSK or QAM, and can be modified as appropriate. [Explanation of symbols]

[0067] 1, 1A Optical communication equipment 4 light source 5 Optical Modulator 6 Optical receiver 8 Optical branching section 12 Optical Coupler 12A First Input Port 12B Second input port 12C First output port 12D Second output port 13A First SOA 13B Second SOA 14A First IQ Optical Modulator 14B Second IQ Optical Modulator 21, 21A First MPD 65 The 5th SOA

Claims

1. an optical coupler that receives an optical signal from a light source, a semiconductor optical amplifier that amplifies the optical signal from the optical coupler, and a light-receiving element that receives spontaneous emission light from the semiconductor optical amplifier via the optical coupler; The optical coupler comprises: a first input port for receiving the optical signal from the light source; a second input port different from the first input port, the second input port being connected to an input stage of the light receiving element; an output port connected to an input stage of the semiconductor optical amplifier and outputting an optical signal from the first input port to the semiconductor optical amplifier; The light receiving element is an optical device for receiving the spontaneous emission light from the semiconductor optical amplifier via the output port and the second input port;

2. The semiconductor optical amplifier comprises:

2. The optical device according to claim 1, wherein the optical coupler is formed of a direct transition compound semiconductor different from that of the optical integrated circuit.

3. The output port is a first output port; and a second output port different from the first output port; The semiconductor optical amplifier comprises: a first semiconductor optical amplifier connected between the first optical modulator and the first output port, for amplifying the optical signal from the first output port; a second semiconductor optical amplifier connected between a second optical modulator different from the first optical modulator and the second output port, and amplifying the optical signal from the second output port; The light receiving element is 3. The optical device according to claim 1, wherein the spontaneous emission light from the first semiconductor optical amplifier and the second semiconductor optical amplifier is received via the output port and the second input port.

4. The output port is a first output port; and a second output port different from the first output port; The semiconductor optical amplifier comprises: a first semiconductor optical amplifier connected between an optical modulator that modulates the optical signal using an electrical signal and the first output port, and that amplifies the optical signal from the first output port; a second semiconductor optical amplifier connected between an optical receiver that obtains an electrical signal from received light using the optical signal and the second output port, and that amplifies the optical signal from the second output port; The light receiving element is 3. The optical device according to claim 1, wherein the spontaneous emission light from the first semiconductor optical amplifier and the second semiconductor optical amplifier is received via the output port and the second input port.

5. an optical branching unit connected between the first output port and the first semiconductor optical amplifier, which branches the optical signal from the first output port; The first semiconductor optical amplifier comprises: a first modulator semiconductor optical amplifier connected between the optical branching unit and a first optical modulator in the optical modulator, for amplifying the optical signal from the optical branching unit; a second modulator semiconductor optical amplifier connected between the optical branching unit and a second optical modulator in the optical modulator, for amplifying the optical signal from the optical branching unit; The light receiving element is 5. The optical device according to claim 4, wherein the spontaneous emission light from the first modulator semiconductor optical amplifier, the second modulator semiconductor optical amplifier, and the second modulator semiconductor optical amplifier is received via the output port and the second input port.

6. an optical coupler that receives an optical signal from a light source; a semiconductor optical amplifier that amplifies the optical signal from the optical coupler; an optical modulator that optically modulates the optical signal amplified by the semiconductor optical amplifier using an electric signal; and a light-receiving element that receives spontaneous emission light from the semiconductor optical amplifier via the optical coupler; The optical coupler comprises: a first input port for receiving the optical signal from the light source; a second input port different from the first input port, the second input port being connected to an input stage of the light receiving element; an output port connected to an input stage of the semiconductor optical amplifier and outputting an optical signal from the first input port to the semiconductor optical amplifier; The light receiving element is an optical transmitter receiving the spontaneous emission light from the semiconductor optical amplifier via the output port and the second input port;

7. an optical coupler that receives an optical signal from a light source; a semiconductor optical amplifier that amplifies the optical signal from the optical coupler; an optical receiver that obtains an electrical signal from received light by using the optical signal amplified by the semiconductor optical amplifier; and a light-receiving element that receives spontaneous emission light from the semiconductor optical amplifier via the optical coupler; The optical coupler comprises: a first input port for receiving the optical signal from the light source; a second input port different from the first input port, the second input port being connected to an input stage of the light receiving element; an output port connected to an input stage of the semiconductor optical amplifier and outputting an optical signal from the first input port to the semiconductor optical amplifier; The light receiving element is an optical receiving device for receiving the spontaneous emission light from the semiconductor optical amplifier via the output port and the second input port;

8. an optical coupler that receives an optical signal from a light source; a first semiconductor optical amplifier and a second semiconductor optical amplifier that amplify the optical signal from the optical coupler; an optical modulator that optically modulates the optical signal amplified by the first semiconductor optical amplifier using an electrical signal; an optical receiver that obtains an electrical signal from received light using the optical signal amplified by the second semiconductor optical amplifier; and a photodetector that receives spontaneous emission light from the first semiconductor optical amplifier and the second semiconductor optical amplifier via the optical coupler; The optical coupler comprises: a first input port for receiving the optical signal from the light source; a second input port different from the first input port, the second input port being connected to an input stage of the light receiving element; a first output port connected to an input stage of the first semiconductor optical amplifier and outputting an optical signal from the first input port to the first semiconductor optical amplifier; a second output port connected to an input stage of the second semiconductor optical amplifier and configured to output the optical signal from the first input port to the second semiconductor optical amplifier; and The light receiving element is an optical communication device receiving the spontaneously emitted light from the first semiconductor optical amplifier and the second semiconductor optical amplifier via the second input port;

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