JP2019078908A - Light monitor circuit - Google Patents

Abstract

To provide a light monitor circuit capable of controlling by monitoring the power of polarization multiplexed signal light using a single PD with a simple control circuit at low cost.SOLUTION: The light monitor circuit has a polarization diversity configuration including a polarization splitting and merging circuit and a polarization rotation circuit. The light monitor circuit comprises: an optical branch circuit for TE polarization component on a route on which a signal of TE polarization component passes; an optical branch circuit for TM polarization component on a route on which a signal of TM polarization component passes; and a single photodetector with two light inputs, which is connected to two waveguides for guiding monitor light which is branched by the optical branch circuit for the TE polarization component and monitor light which is branched by the optical branch circuit for the TM polarization component.SELECTED DRAWING: Figure 9

Description

  The present invention relates to an optical monitor circuit of an optical circuit, and more particularly to an optical monitor circuit in an optical circuit having a polarization diversity configuration.

  In recent years, especially in long-distance optical communication, a digital coherent optical transmission system capable of dramatically increasing communication capacity per channel has been developed, and commercial introduction is also in progress. In digital coherent communication, a polarization multiplexing method is generally applied, in which light (polarization) of two orthogonal polarizations is provided with another signal to double the transmission amount.

  There are various signal formats for applying signals to each polarization, but the systems that are currently most actively introduced for commercial use have QPSK (Quadrature Phase) having a communication capacity of 100 gigabits per second per channel. Most use Shift Keying).

(Conventional optical transmitter circuit)
FIG. 1A shows a functional configuration of a digital coherent polarization multiplexing QPSK optical transmission circuit as an optical circuit used in a polarization multiplexing optical transmission system according to the prior art. In FIG. 1 (a), a light source (9100) for generating continuous light, a polarization multiplexing QPSK optical modulator (9101), a variable optical attenuator (VOA: Variable Optical Attenuator) (9102), an optical branching circuit (9103) , Photodetector (PD: Photo Detector) (9104) is shown.

  The light modulator (9101) has a function of receiving continuous light from the light source (9100) and a transmission electric signal (not shown), modulating the continuous light with the electric signal, and transmitting the light as a light signal to the transmission path. At this time, a part of optical power is branched as monitor light from the signal light on the main signal path by the optical branching circuit (9103), and the optical signal intensity (optical power) received by PD (9104) and sent out is monitored It is common to provide an optical monitor circuit to The VOA (Variable Optical Attenuator) (9102) can be driven according to the monitoring result to adjust the light signal intensity.

  In the polarization multiplexing optical transmission circuit, further miniaturization of the circuit is required in the future. For this purpose, research and development has been advanced in which a plurality of element optical circuits are integrated on the same chip by an optical integrated circuit (PIC: Photonic Integrated Circuit) using an InP (indium phosphorus) optical waveguide or a silicon optical waveguide.

  Specifically, in addition to the light modulator (9101), the VOA (9102), the light branching circuit (9103), and the PD (9104) may all be integrated on one chip, and further the light source (9100) may be integrated. It is being considered. On the other hand, generally, the characteristics of an optical circuit composed of an InP optical waveguide or a silicon optical waveguide have strong polarization dependency. Therefore, a polarization multiplexing optical transmission circuit or an optical reception circuit usually has a polarization diversity configuration having circuit systems respectively corresponding to two polarizations.

  FIG. 1B shows in detail the configuration of the optical transmission circuit (9116) of the polarization diversity configuration in which the optical transmission circuit of FIG. 1A is realized as an integrated optical circuit. Here, the light source (9100) was not integrated.

  In FIG. 1B, as a main signal path, an optical power splitter (9105) that splits continuous light from a light source (not shown) and modulates the split continuous light with modulated electrical signals corresponding to two polarizations, respectively. A Y-polarization light modulation circuit (9106) and an X-polarization light modulation circuit (9107), a polarization rotator (9108) that polarization-rotates modulated light from the Y-polarization light modulation circuit (9106); A polarization beam combiner (9109) is shown, which is a circuit for polarization combining of two modulated lights.

  Further, in FIG. 1B, VOA (variable light attenuator) (9110) (9111), light branching circuit (9112) (9113), PD (light detector) (monitoring of light signal intensity, adjustment function) 9114) (9115) are shown. In FIG. 1 (b), the above-mentioned respective component circuits of the light transmission circuit (9116) surrounded by a dashed-dotted frame are integrated on the same chip by, for example, a silicon optical waveguide.

  Continuous light of TE polarized light is input to the chip of the optical transmission circuit (9116) from a light source (not shown) on the left side of the figure, branched into two by the optical power splitter (9105), and modulation circuits (9106) and (9107) Each is modulated by. The modulated TE polarization output from the Y polarization light modulation circuit (9106) is converted to TM polarization by the polarization rotator (9108) and, together with the modulated TE polarization output from the X polarization light modulation circuit (9107), The polarization beam combiner (9109) combines it into a polarization multiplexed signal and outputs it to the transmission line.

  The Y polarization light modulation circuit (9106) and the X polarization light modulation circuit (9107) have the same design, and are designed to operate with TE polarization.

  In addition, VOA (9110) (9111), light branching circuit (9112) (9113), PD (9114) (9115) are provided at the subsequent stages of the Y polarization light modulation circuit (9106) and the X polarization light modulation circuit (9107). Each has a function of monitoring and adjusting the optical signal strength for each polarization component. The VOAs 9110 and 9111, the optical branching circuits 9112 and 9113, and the PDs 9114 and 9115 have the same design, and are designed to operate with TE polarization.

  Essentially, as shown in FIG. 1A, the functions of the optical monitor and the VOA can be achieved by collectively operating on polarization multiplexed signals before transmission. However, since the integrated optical circuit has strong polarization dependency, it is difficult to realize a VOA or an optical branching circuit which performs the same operation regardless of the polarization of light. Therefore, as a practical configuration, the polarization diversity configuration is used also for the VOA and the optical monitor, and the optical signal strength is monitored and adjusted for each polarization component.

(Conventional optical receiver circuit)
FIG. 2A shows a functional configuration of a digital coherent optical receiver as an optical circuit according to the prior art.

  In FIG. 2A, an optical input path (9201) from a local light source (not shown), an input path (9202) of signal light received from a transmission path, an optical receiving circuit (9203), an optical branching circuit (9204), A PD (light detector) (9205) and a VOA (variable light attenuator) (9206) for adjusting the optical power upon receiving a detected monitor signal (not shown) are shown.

  The light receiving circuit (9203) has a function of receiving continuous light and signal light from the local light source and demodulating the signal light to convert it into an electric signal. At this time, a part of optical power from the signal light on the main signal path is branched as monitor light by the optical branching circuit (9204), and the light received by the PD (9205) is monitored to monitor the intensity of the inputted optical signal. It is common to further have a light monitoring function to adjust the light signal strength according to 9206). In addition, it is a generally required function to be able to detect a state (signal disconnection) in which an optical signal is not input due to some abnormality by monitoring the optical signal intensity.

  FIG. 2B shows in detail the configuration of an optical reception circuit (9220) of a polarization diversity configuration in which the optical reception circuit of FIG. 2A is realized as an optical integrated circuit.

  In FIG. 2B, as a main signal path, a polarization beam splitter (9207), which is a polarization separation circuit for polarization-demultiplexing polarization multiplexed signal light received from the path (9202), a polarization rotator (9208) ), An optical power splitter (9209), an optical coherent mixer for Y polarization (9210), an optical coherent mixer for X polarization (9211), and a PD (9212) (9213) for converting a demodulated optical signal into an electric signal. Is shown. Also, light branching circuits (9214) (9215), PD (9216) (9217), VOAs (9218) (9219) are shown as related to the light monitoring and adjusting function.

  In FIG. 2B, the component circuits of the light receiving circuit (9220) surrounded by a dashed-dotted frame are integrated on the same chip by, for example, a silicon optical waveguide.

  In the chip of the light receiving circuit (9220), continuous light of TE polarized light is inputted from the right side of FIG. 2 (b) from the light source for station light for demodulation to the path (9201) and the light power splitter (9209) The light is branched into two and input to the optical coherent mixers (9210) and (9211), respectively. At the same time, the polarization multiplexed optical signal received from the transmission path and input to the path (9202) is split into TE polarization and TM polarization by the polarization beam splitter (9207) which is a polarization separation circuit, and TM polarization is further added. The light is converted to TE polarization by the polarization rotator (9208) and input to the optical coherent mixers (9210) and (9211), respectively. In each of the optical coherent mixers (9210) and (9211), the signal is demodulated by interference between the signal light and the local light, and further converted to an electrical signal by the PD (9212) (9213) and output.

  The optical coherent mixer (9210) for Y polarization and the optical coherent mixer (9211) for X polarization have the same design, and are designed to operate with TE polarization. In addition, optical branching circuits (9214) (9215), PD (9216) (9217), VOA (VOC) are provided at the front stage of the Y-polarization optical coherent mixer (9210) and the X-polarization optical coherent mixer (9211). 9218) and 9219) are provided, respectively, and have a function of monitoring and adjusting the optical signal strength for each polarization component. The respective optical branching circuits (9214) (9215), PD (9216) (9217), and VOA (9218) (9219) have the same design and are designed to operate with TE polarization.

  Also in the optical receiving circuit, originally, the functions of the optical monitor and the VOA are sufficient if they operate collectively on polarization multiplexed signals immediately after the input as shown in FIG. 2A. However, since the integrated optical circuit has strong polarization dependency, it is difficult to realize a VOA or an optical branching circuit which performs the same operation regardless of the polarization of light. Therefore, as a practical configuration, the polarization diversity configuration is used also for the VOA and the optical monitor, and the optical signal strength is monitored and adjusted for each polarization component.

(Optical branch circuit)
FIG. 3 shows silicon light of the optical branch circuit (9112) (9113) of monitor light of FIG. 1 (b) or the optical branch circuit (9214) (9215) of monitor light of FIG. 2 (b) in the prior art. It shows a specific configuration when realized as an integrated circuit. Such an optical branching circuit is realized by a directional coupler as shown.

  FIG. 3 shows input / output optical waveguides (9301) (9302) (9303) (9304) and directional couplers (9305). As an example of the design, assuming that the waveguide core made of silicon has a width of 0.5 μm, a thickness of 0.22 μm, and the overcladding and undercladding of quartz, the gap between waveguides of the directional coupler (9305) is 0.3 The μm and the length are 15 μm. As a result, an optical branching circuit with a branching ratio of 7% is realized, which outputs 93% of the optical power input from the optical waveguide (9301) to the optical waveguide (9303) and outputs 7% to the optical waveguide (9304). it can.

  Similarly, FIG. 4 shows another configuration in the case where the monitor light optical branch circuit (9112) (9113) or the optical branch circuit (9214) (9215) in the prior art is realized as a silicon optical integrated circuit. It is. The configuration is referred to as WINC (Wavelength Independent Coupler), and it is possible to suppress the wavelength dependency of the branching ratio as compared to the case where the optical branching circuit is configured by a simple directional coupler.

  FIG. 4 shows input / output optical waveguides (9501) (9502) (9503) (9504), directional couplers (9505) (9506), and delay waveguides (9507) (9508). As an example of the design, the waveguide core made of silicon has a width of 0.5 μm, a thickness of 0.22 μm, the overcladding and the undercladding are quartz, and the gap between waveguides of the directional coupler (9505) (9506) Is 0.3 μm, the length is 67 μm, and the delay amount of the delay waveguides (9507) (9508) is 0.25 μm. As a result, it is possible to realize a 7% optical branching circuit that outputs 93% of the optical power input from the optical waveguide (9501) to the optical waveguide (9503) and outputs 7% to the optical waveguide (9504).

(Photo detector)
FIG. 5 shows PD (9114) (9115) of FIG. 1 (b) or PD (9216) (9217) of FIG. As a realized example, the structure of a general germanium photodetector is shown. Here, FIG. 5 (a) is a plan view seen from the top, and FIG. 5 (b) is a view showing a cross-sectional structure taken along line AA 'in FIG. 5 (a).

  In FIG. 5, a silicon waveguide (521) to which monitor light is input, a p implant region (522) to the silicon waveguide, ap ++ implant region (523) to the silicon waveguide, Ge crystal grown on the silicon waveguide (524), n implant area to Ge crystal (525), electrode (526), upper cladding (527) formed of quartz, lower cladding (528) also formed of quartz, silicon substrate (529) Be

  As an example of a common design germanium photodetector design, the thickness of the lower cladding is 2 μm, the core thickness of the silicon waveguide (521) is 0.22 μm, the thickness of the Ge crystal (524) is 0.4 μm, The Ge crystal (524) has a length of 50 μm and a width of 10 μm in the traveling direction.

(Polarization splitting and merging circuit)
6 shows the polarization beam combiner (polarization merging circuit) (9109) of FIG. 1 (b) or the polarization beam splitter (polarization separation circuit) of FIG. 2 (b) on the main signal path in the prior art. The specific configuration in the case where (9207) is realized as a silicon optical integrated circuit is shown. The polarization separation junction circuit that performs such polarization junction or separation can be realized by a directional coupler as shown in FIG. 6 due to the bidirectionality of the optical signal.

  The same applies to the following, but in an optical circuit of a polarization diversity configuration, a polarization separation circuit (polarization (polarization) of an optical reception circuit that separates received polarization multiplexed signal light into signals of TE polarization component and TM polarization component Beam splitter) and polarization combining circuit (polarization beam combiner) of an optical transmission circuit that combines signals of TE polarization component and TM polarization component to be transmitted with polarization multiplexed signal light It can be called a circuit.

  FIG. 6A shows an example in which a polarization separation and merging circuit is configured by a single directional coupler. In FIG. 6A, input / output optical waveguides (9601) (9602) (9603) (9604) and directional couplers (9605) are shown. As an example of the design, assuming that the waveguide core made of silicon has a width of 0.5 μm, a thickness of 0.22 μm, and the overcladding and undercladding of quartz, the gap between waveguides of the directional coupler (9305) is 0.4 It is assumed to be μm.

  FIG. 7 is a diagram showing the change in the coupling ratio of TE polarization and TM polarization (the circuit length dependency of the coupling characteristic) with respect to the length of the above-mentioned directional coupler. Since the TM polarization is strongly coupled compared to the TE polarization, assuming that the length of the directional coupler is 15 μm in FIG. 7, the TM polarization (solid line) combines approximately 100% of the optical power. In contrast, the coupling rate of TE polarization (dotted line) is only a few percent. Therefore, in FIG. 6A, the polarization multiplexed light of TE / TM input from the upper right optical waveguide (9603) is output from the lower left optical waveguide (9602) and the TM polarization is almost It functions as a polarization separation circuit output from the upper left optical waveguide (9601). Also, as shown by the two-way arrows in FIG. 6, from left to right in the reverse direction, it functions as a polarization merging circuit. Here, the polarization extinction ratio that can be realized by a single directional coupler as a polarization separation circuit is about 15 dB.

  When a polarization separation circuit with a larger polarization extinction ratio is required, it can be realized by configuring the directional couplers in a plurality of stages as shown in FIG. 6 (b). In FIG. 6 (b), there are two optical waveguides (9611) (9612) (9613) (9614) of the input / output, and two directional couplers (9605) in FIG. Directional couplers (9615) (9616) are shown. As a result, although TM polarized light input from the optical waveguide (9611) is separated and output to the optical waveguide (9614), the polarization extinction ratio at that time is improved to about 30 dB through the two-stage polarization separation.

(Polarization rotation circuit)
FIG. 8 is a plan view showing the configuration of the polarization rotation circuit (9801) on the main signal path in the prior art. In FIG. 8, the left and right optical waveguides (9802) (9809), the rib part (9803) of the rib waveguide from the right between them, the slab part of the rib waveguide (9804), the branch circuit (9805), the delay Waveguides (9806) (9807) and merging circuits (9808) are shown. Although this polarization rotation circuit (9801) can operate bi-directionally, for example, it converts TM polarization input from the right optical waveguide (9802) into TE polarization and outputs it from the left optical waveguide (9809), Conversely, it has a function of converting TE polarized light input from the left optical waveguide (9809) into TM polarized light and outputting it from the right optical waveguide (9802).

  Realization of polarization rotation is achieved by a combination of polarization conversion to convert fundamental mode light of TM polarization to 1st mode of TE polarization and mode conversion to convert 1st mode of TE polarization to fundamental mode of TE polarization. . Here, an interference circuit including rib waveguides (9803) and (9804) having a polarization conversion function and configured by a branch circuit (9805), delay waveguides (9806) and (9807), and a merging circuit (9808) is It has the function of mode conversion.

H Fukuda et al, Silicon photonic circuit with polarization diversity, Optics Express vol. 16 p4872-p4880 (2008)

  In monitoring of transmission / reception light power in the polarization diversity configuration optical transmission circuit and optical reception circuit in the digital coherent polarization multiplexing system, each polarization in the polarization rotating / merging upstream or polarization separating / rotating downstream The monitor light is branched from the signal light on the main signal path of (1), and received by the monitor PD for monitoring.

  However, the optical power to be actually monitored is the total power of polarization multiplexed signal light, and in the conventional configuration, the monitor signal received in each polarization path and converted to the current level is outside the optical circuit. It was necessary to add and take the sum.

In this regard,
(1) It is necessary to add an electric circuit to perform addition, and the control circuit of the optical transceiver becomes complicated and expensive (2) There are many wires for taking monitor signals from the silicon optical integrated circuit to the outside, The design and mounting become complicated (3) There is a problem that the monitoring accuracy of the light power is deteriorated due to the individual difference of the light receiving sensitivity of the PD which receives the light power of the path of each polarization.

(Conventional solutions and their problems)
In order to solve the above problems, light is branched from the path of each polarization, and the branched light is multiplexed by a directional coupler or a multimode interference circuit (MMI), etc., and is single photodiode (PD). The method of receiving light has been previously filed by the inventors of the present application (Japanese Patent Application No. 2016-174932).

  This method can solve all the problems (1) to (3) described above. However, in the above-mentioned method of combining light by MMI in a waveguide in front of a single PD and introducing the combined light into PD, there is a problem of loss of the optical circuit itself to be combined or different polarization Since it is necessary to design a circuit that combines waves, the problem of low multiplexing efficiency, and additionally the principle loss (principle loss) of MMI when using MMI causes an additional 3 dB loss New challenges have arisen.

  The present invention has been made in view of such problems, and an object thereof is a path through which a signal of a TE polarization component passes in monitoring of transmission / reception light power in an optical transmission circuit and an optical reception circuit in a polarization diversity configuration. The first monitor light branch circuit is provided in the second monitor light branch circuit on the path through which the signal of TM polarization component passes, and the power of the polarization multiplexed signal light by a single PD of two light inputs To enable control with simple and low-cost control circuits, reduce the number of required wires, and provide a monitor of transmit / receive optical power with excellent monitor accuracy. .

  Here, the path through which the TE polarization component signal passes, and the path through which the TM polarization component signal passes are paths through which only the TE polarization optical signal or only the TM polarization optical signal passes. There is no need. That is, as long as it is a path through which an optical signal of TE polarization to be detected or an optical signal corresponding to an optical signal of TM polarization passes, it may be, for example, a polarization multiplexed optical signal. Also, the monitor light branch circuit does not have to be a dedicated circuit for branch of monitor light.

  The present invention is characterized by having the following configuration in order to achieve such an object.

(Structure 1 of the Invention)
An optical circuit of a polarization diversity configuration having a polarization separation / merging circuit and a polarization rotation circuit that performs polarization rotation between TM polarization and TE polarization, and branches part of the optical power from the main signal path; An optical monitor circuit that monitors the power of the signal light;
The optical monitor circuit
A first monitor light branch circuit on a path through which a signal of TE polarization component passes;
A second monitor light branch circuit is provided on a path through which the signal of the TM polarization component passes,
Two light inputs connected to a waveguide for guiding monitor light branched by the first monitor light branch circuit and a waveguide for guiding monitor light branched by the second monitor light branch circuit An optical monitor circuit characterized by having a single photodetector.

(Structure 2 of the Invention)
The polarization separation junction circuit is a polarization junction circuit, and
The polarization rotation circuit is on a path through which the signal of the TM polarization component in the front stage of the polarization merging circuit passes;
The first monitor light branch circuit is on a path through which the signal of the TE polarization component in the previous stage of the polarization merging circuit passes,
The second monitor light branch circuit may be on the path of the rear stage of the polarization merging circuit, or on the path from the rear stage of the polarization rotation circuit to the polarization merging circuit, or in the front stage of the polarization rotation circuit. Characterized in that the polarization merging circuit also has the function of an optical branching circuit for the TM polarization component, with an output port on the path or not contributing to the polarization merging function of the polarization merging circuit being a branching port. An optical monitor circuit according to configuration 1 of the invention.

(Composition 3 of the Invention)
The polarization separation junction circuit is a polarization separation circuit, and
The polarization rotation circuit is on a path through which the signal of the TM polarization component in the subsequent stage of the polarization separation circuit passes;
The first monitor light branch circuit is on a path through which a signal of a TE polarization component in a subsequent stage of the polarization separation circuit passes;
The second monitor light branch circuit may be on the path of the front stage of the polarization separation circuit, or on the path from the rear stage of the polarization separation circuit to the polarization rotation circuit, or in the rear stage of the polarization rotation circuit. Characterized in that the polarization separation circuit also has the function of an optical branching circuit for the TM polarization component, with an output port on the path or not contributing to the polarization separation function of the polarization separation circuit as a branching port. An optical monitor circuit according to configuration 1 of the invention.

(Structure 4 of the Invention)
The light monitoring circuit is formed of a silicon based waveguide,
The optical monitor circuit according to the configuration 1 of the invention, wherein the polarization separation junction circuit is formed of a directional coupler or a WINC comprising a directional coupler and a delay circuit.

(Structure 5 of the Invention)
The optical monitor circuit according to the configuration 1 of the invention, wherein the two input waveguides of the single photodetector of the two optical inputs are arranged to face each other so as to shift the optical axis.

(Structure 6 of the Invention)
The optical monitor circuit according to any one of the constitutions 1 to 5, wherein the monitor optical branching circuit is formed of a directional coupler or a WINC comprising a directional coupler and a delay circuit.

(Structure 7 of the Invention)
The optical circuit of the polarization diversity configuration is
An optical power splitter,
Optical modulation circuits for TE polarization component and TM polarization component connected to the optical power splitter;
The polarization rotation circuit further connected to the light modulation circuit for the TM polarization component;
The optical monitor according to the configuration 2 of the invention, characterized in that it is an optical transmission circuit comprising the optical modulation circuit for the TE polarization component and the polarization combining circuit further connected to the polarization rotation circuit circuit.

(Structure 8 of the Invention)
The optical circuit of the polarization diversity configuration is
The polarization separation circuit connected to the input port;
The polarization rotation circuit connected to the polarization separation circuit;
And an optical power splitter connected to another input port,
An optical coherent mixer for TE polarization components connected to one output of the polarization separation circuit and one output of the optical power splitter;
The polarization rotation circuit, and an optical coherent mixer for TM polarization component connected to the other output of the optical power splitter;
An optical monitor circuit according to a third aspect of the invention, which is an optical receiving circuit comprising a photodetector connected to each of the optical coherent mixers for the TE polarization component and the TM polarization component.

  As described above, according to the present invention, it is possible to monitor the power of polarization multiplexed signal light with a single PD in the optical transmission circuit of the polarization diversity configuration and the monitoring of transmission / reception optical power in the optical reception circuit. It is possible to provide a monitor of transmitted / received optical power which enables control with a simple and low-cost control circuit, reduces the number of required wires, and has excellent monitor accuracy.

It is a figure which shows the implementation | achievement structure of the optical power monitor in the conventional optical transmission circuit (optical modulation circuit). It is a figure which shows the implementation | achievement structure of the optical power monitor in the conventional optical receiving circuit. It is an implementation example of the optical branching circuit in the conventional optical transmitter circuit or optical receiver circuit. It is another implementation example (WINC) of the optical branching circuit in the conventional optical transmitter circuit or optical receiver circuit. It is a figure which shows the structure of a common germanium photodetector. It is a figure which shows the example of implementation of the polarization joint / isolation | separation circuit in the conventional polarized light transmission circuit or light receiving circuit. It is a figure which shows the circuit length dependence of the coupling characteristic of TE / TM light in the directional coupler of FIG. It is a figure which shows the example of implementation of the polarization rotation circuit in the conventional light transmission circuit or light receiving circuit. It is a figure which shows the implementation | achievement structure of the optical power monitor in the optical transmission circuit (polarization multiplexing light modulation circuit) of Example 1 of this invention. It is a figure which shows the structure of the germanium photodetector of 2 light input used for the optical power monitor of this invention. It is a figure which shows the implementation | achievement structure of the optical power monitor in the light receiving circuit of Example 1 of this invention. It is a figure which shows the implementation example of the optical branch circuit for TM polarization | polarized-light in the optical transmission circuit of Example 1 of this invention, or an optical receiving circuit. It is a figure which shows the circuit length and wavelength dependence of the coupling characteristic of TE / TM light in the directional coupler of FIG. It is another implementation of the optical branch circuit for TM polarization | polarized-light in the optical transmission circuit of Example 1 of this invention, or an optical receiving circuit. It is a figure which shows the wavelength dependency of the branch characteristic of TE / TM light in the optical branch circuit of FIG. It is a figure which shows the implementation | achievement structure of the optical power monitor in the optical transmission circuit (polarization multiplexing light modulation circuit) of Example 2 of this invention. It is a figure which shows the implementation | achievement structure of the optical power monitor in the optical receiving circuit of Example 2 of this invention. It is a figure which shows the implementation | achievement structure of the optical power monitor in the optical transmission circuit (polarization multiplexing light modulation circuit) of Example 3 of this invention. It is a figure which shows the implementation | achievement structure of the optical power monitor in the optical receiving circuit of Example 3 of this invention. It is a figure which shows the structural example 1 of the polarization | polarized-light beam combiner of the optical transmission circuit of Example 3 of this invention. It is a figure which shows the structural example 2 of the polarization | polarized-light beam combiner of the optical transmission circuit of Example 3 of this invention. It is a figure which shows the structural example 3 of the polarization | polarized-light beam combiner of the optical transmission circuit of Example 3 of this invention. It is a figure which shows the structural example 4 of the polarization | polarized-light beam combiner of the optical transmission circuit of Example 3 of this invention. It is a figure which shows the structural example 1 of the polarization | polarized-light beam splitter of the light receiving circuit of Example 3 of this invention. It is a figure which shows the structural example 2 of the polarization | polarized-light beam splitter of the light receiving circuit of Example 3 of this invention. (A) shows the circuit length dependence of the coupling characteristics of TE / TM polarized light in the directional couplers 2109, 2512 and 2712 in FIG. 20, FIG. 22 and FIG. 24, (b) shows the TM polarized light at a circuit length of 11 .mu.m. It is a figure which shows a branching rate. (A) shows the circuit length dependency of the branching characteristic of TM polarization in WINC 2109, 2612, 2812 in FIG. 21, FIG. 23, FIG. 25, (b) shows WINC 2109, 2612, 2812 in FIG. It is a figure which shows the circuit length dependence of the branch characteristic of TM and TE polarization | polarized-light in. It is a figure which shows the implementation | achievement structure of the optical power monitor in the optical transmission circuit (polarization multiplexing light modulation circuit) of Example 4 of this invention. It is a figure which shows the implementation | achievement structure of the optical power monitor in the light receiving circuit of Example 4 of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First Embodiment
An optical monitor circuit according to a first embodiment of the present invention will be described.

(Optical transmission circuit of the first embodiment)
FIG. 9 is a plan view showing the configuration of the optical transmission circuit (polarization multiplexed light modulation circuit) (116) of the polarization diversity configuration including the optical monitor circuit in the first embodiment.

  In FIG. 9, an optical power splitter (105) that splits TE-polarized continuous light from a light source (not shown) from the left as a main signal path, Y-polarized light that modulates the split continuous light with two modulation signals (not shown) A modulation circuit (106) and an X polarization light modulation circuit (107), a polarization rotator (108) for converting modulated light of TE polarization modulated from the Y polarization light modulation circuit (106) into TM polarization, TE polarization A polarization beam combiner (109) is shown that combines the modulated light of TM polarization, merges polarization, and outputs as polarization multiplexed light.

  Further, in FIG. 9, in relation to the optical monitor and adjustment function, two optical branch circuits (112) (113) for branching monitor light on the main signal path, and two optical waveguides for respectively guiding the two branched monitor lights. Also shown are a single PD (115) with two light inputs connected to the optical waveguide and two VOAs (110) (111) that receive the detected monitor signal (not shown) and adjust the optical power.

  The feature of the optical transmission circuit (116) of the first embodiment of FIG. 9 is that one optical branching circuit (113) is disposed on the main signal path before polarization merging by the polarization beam combiner (109). However, the other optical branch circuit (112) is installed on the main signal path after polarization merging. In addition, the optical waveguides through which the two monitor lights branched by the optical branching circuits (112) and (113) are connected to a single PD (115).

  The element circuits of the light transmission circuit (116) surrounded by a dashed-dotted frame are integrated on the same chip by, for example, a silicon optical waveguide.

In FIG. 9, the optical branch circuit (113) for monitor light is an optical branch circuit operating for TE polarization, and the directional coupler and WINC described in FIGS. 3 and 4 of the conventional example can be applied as they are.
On the other hand, since the optical branch circuit (112) for monitor light branches only TM polarization from polarization multiplexed light, it operates with respect to TM polarization, and an optical branch circuit where light substantially does not branch for TE polarization is required. Be A method of realizing such an optical branching circuit will be described later.

  Accordingly, in FIG. 9, the light branched by the light branch circuit (113) of the monitor light is TE polarized light, and the light branched by the light branch circuit (112) is TM polarized light. The PD (115) is required to detect as a single electrical signal obtained by adding the intensities of TE polarization and TM polarization.

  With the above configuration, monitor light branched from the signal (optical signal power transmitted as TE polarization) modulated by the X polarization light modulation circuit is input to the two light input PD (115) which is a light receiving element for monitor light. The monitor light branched from the signal (optical signal power transmitted as TM polarization) modulated by the Y polarization optical modulation circuit with TE polarization is input with TM polarization.

  FIG. 10 shows the structure of this two-light input PD (115) used in the present invention. A difference from the conventional PD of FIG. 5 is that two silicon waveguides (521) and (521 ') are arranged as two light inputs. In FIG. 10 (a), two silicon waveguides (521) and (521 ') are disposed to face each other in plane symmetry on the left and right with respect to the central AA' plane, and in FIG. 10 (b) Two silicon waveguides (521) and (521 ') are disposed adjacent to the right side of the' plane. The cross-sectional structure in the A-A ′ plane is the same as that in FIG.

  For example, the waveguide (521) of FIG. 10 (a) is connected to the waveguide from the light branching circuit (112) of FIG. 9, and the waveguide (521 ') of FIG. 10 (a) is the light branching circuit of FIG. Connected with the waveguide from 113). The light entering the PD (115) from the light branching circuit (112) (113) is converted into semiconductor carriers without interference by the Ge crystal 524 in the PD (115), and merged to form a single electrical signal. Is output as

  When Ge crystal (524) absorbs light, if it has sufficient length, thickness, and width in the light traveling direction (for example, for 1550 nm, it is 20 μm long, 10 μm wide and 1 μm thick at a temperature of 27 degrees) The light input intensity (about 0 dBm) and the light input from the silicon waveguide (521) are absorbed by the Ge crystal (524) and exhausted. For this reason, the light input from the silicon waveguide (521) does not combine or interfere as light with the light input from the silicon waveguide (521 '), and this is not transmitted from the waveguide (521'). The same is true for the input light.

  Therefore, in this two-light input PD (115), the light coming from the light branching circuit (112) (113) is absorbed as a semiconductor carrier by the PD without being multiplexed as light and is merged as an electric signal. Interference can not occur. In this PD (115), it becomes possible to add and observe the intensities of both optical inputs as an electrical carrier. There is no need for merging means like MMI, and there is no principle loss due to MMI. For this reason, it is a structure which solves a subject (1)-(3), solving the problem which the conventional invention has.

  The 2-light input PD (115) may input light from the end face on the same side as shown in FIG. 10 (b). However, in this case, the light input from the waveguides (521) and (521 ') may interfere while propagating in the PD, so the waveguides are arranged sufficiently apart from each other so as not to cause interference. It is necessary to have some design ideas such as

Alternatively, although not shown, even if the two silicon waveguides 521 and 521 'are arranged as shown in FIG. 10A, the optical axes of the two opposing input waveguides may be offset. It is possible to reduce the length of the PD device while reducing the light interference.
Germanium photodetectors (GePD, Germanium PD) as illustrated in FIGS. 10 (a), (b) are typically used for TE polarization input but also have sensitivity to TM polarization input. The present invention can be applied to the two light input PD (115) of the present invention.

(Optical Reception Circuit of Example 1)
FIG. 11 is a plan view showing the configuration of the light receiving circuit (220) of the polarization diversity configuration including the light monitoring circuit in the first embodiment.

  11, an input path (201) of local light from a local light source (not shown) from the right, an input path (202) of polarization multiplexed signal light received from a transmission path as a main signal path, polarization multiplexed signal light A polarization beam splitter (207) for polarization separation and a polarization rotator (208) for polarization-rotating TM polarization from polarization beam splitter (207) to TE polarization are shown.

  Further, in FIG. 11, an optical power splitter (209) for branching local light, an optical coherent mixer (210) for Y polarization, an optical coherent mixer (211) for X polarization, and an electric signal for the demodulated optical signal The PD (212) (213) is shown to convert to.

  Furthermore, in FIG. 11, two optical branch circuits (214) and (215) for branching monitor light on the main signal path and two for respectively guiding the two branched monitor lights are provided in relation to the optical monitor and adjustment function. A single PD (217) of two light inputs connected to one waveguide and two VOAs (218) (219) are shown that adjust the optical power in response to the detected monitor signal (not shown).

  The feature of the optical receiver circuit of the first embodiment in FIG. 11 is that one optical branch circuit (215) is installed on the main signal path after polarization splitting by the polarization beam splitter (207), The optical branch circuit (214) is placed on the main signal path before polarization separation. Also, the two monitor lights branched by the optical branch circuits (214) (215) are connected to a single 2-light input PD (217).

  The element circuits of the light receiving circuit (220) surrounded by a dashed-dotted frame are integrated on the same chip by, for example, a silicon optical waveguide.

  The optical branching circuit (215) that branches monitor light from the signal light after polarization separation shown in FIG. 11 is an optical branching circuit that operates on TE polarization, and the directions described in FIGS. 3 and 4 of the conventional example. Sexual coupling and WINC can be applied as they are. On the other hand, the optical branching circuit (214) that branches the monitor light from the signal light before polarization separation operates on the TM polarization in order to branch only the TM polarization from the polarization multiplexed light, and There is a need for an optical branch circuit that substantially does not branch light. A method of realizing such an optical branching circuit will be described later.

Therefore, the light branched by the optical branching circuit (215) is TE polarized light, and the light branched by the optical branching circuit (214) is TM polarized light, so the PD (217) of the two optical inputs receives the received signal The light branched from the TE polarized light component is TE polarized light, and the light branched from the TM polarized light component of the received signal is input as TM polarized light. Germanium photodetectors as illustrated in FIGS. 10 (a) and 10 (b) are typically used for TE polarization input, but also have sensitivity to TM polarization input, so the PD of the present invention (217 It is applicable to).

(Optical branching circuit for TM polarization in Example 1)
FIG. 12 is an optical branch circuit (112) of monitor light for TM polarization in the optical transmission circuit (116) of the first embodiment of FIG. 9 or TM in the optical reception circuit (220) of the first embodiment of FIG. It shows a specific configuration of an optical branch circuit (214) of monitor light for polarization.

  In FIG. 12, the light branching circuit (112) or (214) is required to have a characteristic that a part of TM polarized light is branched and substantially no branch is made for TE polarized light. In order to realize such characteristics, the optical branching circuit (112) or (214) adopts the configuration of a directional coupler.

  FIG. 12 shows input / output waveguides (401) (402) (403) (404) of the directional coupler. The waveguide core of the directional coupler made of silicon has a width of 0.5 μm and a thickness of 0.22 μm, the overcladding and the undercladding are quartz, and the gap between the waveguides is 0.4 μm. The core width and thickness of the input and output waveguides are also the same as the waveguides of the directional coupler.

(Coupling ratio for length and wavelength of directional coupler)
FIG. 13A shows the coupling of TE polarization and TM polarization to the length (circuit length) of the directional coupler with respect to the directional coupler forming the light branching circuit of the monitor light for TM polarization in FIG. It shows the change of the rate. For TE polarization, the confinement of TM polarization in the waveguide is weak, resulting in a difference in coupling factor. In this example, the length of the directional coupler is set to 3 μm. At this time, the coupling ratio of TE polarized light is only 0.1%, and it can be said that almost no branching occurs.

  FIG. 13B shows the wavelength dependency of the TM polarization coupling ratio, that is, the branching ratio, of the optical branching circuit (112) or (214) according to the directional coupler whose length is set to 3 μm. In the general C-band operating range (wavelengths 1525 to 1565 nm), the branching ratio of TM polarization is 8% at the short wavelength end and 12% at the long wavelength end.

  The characteristics of the optical monitor circuit are required to be able to monitor optical power in a specific range as an electric signal, and the design of the branching ratio of the optical branch circuit is determined according to the range. In particular, it is important to be able to monitor light of weak power, and in the optical branching circuit, it is important to design the minimum branching ratio in the operating wavelength range.

  The optical branching circuit (112) or (214) for TM polarization of the first embodiment shown in FIG. 12 is designed to satisfy the required specifications based on the branching ratio at the short wavelength end. As shown in FIG. 13B, the branching ratio of TM polarization at the short wavelength end is 8% in the first embodiment. At this time, as a matter of course, the power of the signal light transmitted without branching decreases in accordance with the branching ratio.

  In the optical transmitter circuit and the optical receiver circuit, it is desirable to avoid the decrease in the power of signal light as much as possible, so it is desirable to minimize the fluctuation of the branching ratio due to the wavelength of the optical branching circuit. In this respect, the optical branching circuit of the first embodiment has a branching ratio of 12%, which is larger than the branching ratio originally required, in the region of the long wavelength end in FIG. An inefficient situation has arisen in which the

(Another Example of the Optical Branching Circuit for TM Polarization in Example 1)
FIG. 14 shows another example of the light branching circuit for TM polarization which can further improve the above point. By adopting the WINC configuration, it is possible to suppress the wavelength dependency of the branching ratio as compared to the configuration with a mere directional coupler as shown in FIG.

  FIG. 14 shows input / output optical waveguides (601) (602) (603) (604), directional couplers (605) (606), and delay waveguides (607) (608). As an example of the design, the waveguide core made of silicon has a width of 0.5 μm, a thickness of 0.22 μm, and the overcladding and undercladding is quartz, and the waveguides of the directional coupler (605) (606) are separated. The gap is 0.3 μm, the length is 7 μm, and the delay amount of the delay waveguides 607 and 608 is 0.34 μm.

(Wavelength dependence of branching characteristics in the optical branching circuit of FIG. 14)
FIG. 15 shows the light power output to the optical waveguide (604) of the optical power input from the optical waveguide (601) in the TM-polarization optical branching circuit of FIG. 14, that is, the branching ratio of the TM polarization of the optical branching circuit. Shows the wavelength dependency of (in solid line in FIG. 15). The branching ratio is 8% at the short wavelength end and is equivalent to the optical branching circuit of FIG. 12, but the branching ratio is 11% at the long wavelength end, and the wavelength dependence of the branching ratio is greater than the optical branching circuit of FIG. It is suppressed.
Similarly, FIG. 15 also shows the branching ratio for TE polarization (dotted line in FIG. 15). The branching ratio of TE polarization is only 0.1% in the illustrated wavelength range, and it can be said that almost no branching occurs.

  As described above, the light transmitting circuit (116) (FIG. 9) or the light receiving circuit (220) (FIG. 11) of the first embodiment can monitor the power of polarization multiplexed signal light with a single PD. Therefore, according to the first embodiment, in the optical transmission or reception circuit, control with a simple and low-cost control circuit is possible, the number of required wires is reduced, and the transmission or reception optical power is excellent in monitor accuracy. A monitor can be provided.

Second Embodiment
An optical monitor circuit according to a second embodiment of the present invention will be described.

(Optical Transmission Circuit of Example 2)
FIG. 16 is a plan view showing the configuration of an optical transmission circuit (polarization multiplexed light modulation circuit) (1116) of a polarization diversity configuration including an optical monitor circuit in the second embodiment.

  In FIG. 16, an optical power splitter (1105), a Y polarization light modulation circuit (1106), an X polarization light modulation circuit (1107), a polarization rotator (1108), a polarization beam combiner (1109), and a VOA (1110) (1111), a light branch circuit (1112) (1113) of monitor light, a single PD (1115) of two light inputs are shown.

  The optical transmission circuit (1116) of the second embodiment is characterized in that the optical branch circuit (1113) of one monitor light is installed before the polarization merging, and the optical branch circuit (1112) of the other monitor light is also polarized. It is to be installed before wave merging and in the middle of polarization rotation and polarization merging. Further, the waveguide branched by the light branching circuit (1112) (1113) of the monitor light is connected to a single PD (1115) of two light inputs.

  The element circuits of the light transmission circuit (1116) surrounded by a dashed-dotted frame are integrated on the same chip by, for example, a silicon optical waveguide.

  In FIG. 16, the optical branch circuit (1113) for monitor light is an optical branch circuit operating on TE polarization, and the directional coupler and WINC described in FIGS. 3 and 4 of the conventional example can be applied as they are. On the other hand, although it is required that the optical branching circuit (1112) of the monitor light of the second embodiment operates on TM polarization, since the optical branching circuit (1112) of the second embodiment is placed before polarization merging unlike the first embodiment, The light to be is only TM polarization, and the characteristics for TE polarization are arbitrary. This is realized by optimizing the directional coupler or WINC to TM polarization, as in the first embodiment.

  For example, in the case of applying a directional coupler, in Example 1, the splitting ratio of TE polarization needs to be substantially zero, and it was not possible to set the splitting ratio for TM polarization too large. This is because if the branch ratio of TM polarization is to be set to 20% or more, the branch ratio of TE polarization increases to an unignorable extent although it is almost out of the range in FIG. 13A.

  On the other hand, in the second embodiment, since it is not necessary to consider the branching ratio for TE polarization, the degree of freedom in setting the branching ratio is expanded. Therefore, it can be said that this embodiment is more advantageous than the first embodiment when, for example, it is desired to relatively increase the branching ratio in order to monitor smaller optical power.

  Therefore, in FIG. 16, the light branched by the light branch circuit (1113) of monitor light is TE polarized light, and the light branched by the light branch circuit (1112) of monitor light is TM polarized light. As a result, in the 2-light input PD (1115), which is a light receiving element for monitor light, light branched from the signal modulated by the X polarization light modulation circuit (light signal power transmitted as TE polarization) is TE polarization The light branched from the signal (light signal power transmitted as TM polarization) modulated by the Y polarization light modulation circuit is input as TM polarization.

  Germanium photodetectors as described in the prior art, as illustrated in FIGS. 10 (a) and 10 (b), are typically used for TE polarization input, but also have sensitivity to TM polarization input, so PD (1115, It is applicable to).

(Optical Reception Circuit of Example 2)
FIG. 17 is a plan view showing the configuration of an optical receiving circuit (1220) of a polarization diversity configuration including an optical monitor circuit in the second embodiment.

  In FIG. 17, an optical input path (1201) for local light, an input path (1202) for signal light, a polarization beam splitter (1207), a polarization rotator (1208), an optical power splitter (1209), Y polarization Optical coherent mixer (1210) includes an optical coherent mixer (1211) for X polarization, a PD (1212) (1213) for converting a demodulated optical signal into an electric signal, and an optical branching circuit (1214) for monitor light (1215) A two-light input single PD (1217) for detecting monitor light and two VOAs (1218) and (1219) for adjusting the optical power upon receiving the detected monitor signal (not shown) are shown. .

  The feature of the optical receiver circuit (1220) of the second embodiment is that the optical branch circuit (1215) of one monitor light is installed after polarization separation, and the optical branch circuit (1214) of the other monitor light is also polarized. It is to be installed after wave separation and in the middle of polarization separation and polarization rotation. The waveguides branched by the optical branching circuits (1214) and (1215) are connected to a single PD (1217) of two light inputs. The element circuits of the light receiving circuit (1220) surrounded by a dashed-dotted frame are integrated on the same chip by, for example, a silicon optical waveguide.

  In FIG. 17, the optical branching circuit (1215) for monitor light is an optical branching circuit operating on TE polarization, and the directional coupler and WINC described in FIGS. 3 and 4 of the conventional example can be applied as they are. On the other hand, the optical branching circuit (1214) is required to operate with respect to TM polarization, but unlike the first embodiment, since the light branching circuit is installed after polarization separation in the second embodiment, Only the TM polarization is used, and the characteristics of the TE polarization are irrelevant. As described in the example of the optical transmitter (1116), it can be said that this embodiment is more advantageous than the first embodiment when the degree of freedom in setting the branching ratio is expanded and the branching ratio is desired to be relatively increased.

  Therefore, the monitor light branched by the light branching circuit (1215) is TE polarized light, and the monitor light branched by the light branching circuit (1214) is TM polarized light. As a result, the monitor light branched from the TE polarization component of the reception signal is input as TE polarization to the 2-light input PD (1217) which is a light receiving element of monitor light, and is branched from the TM polarization component of the reception signal The monitor light is input with TM polarization.

  Germanium photodetectors as illustrated in Figures 10 (a), (b) are typically used for TE polarization input but are also sensitive to TM polarization input, so they apply to PD (1217) Is possible.

  As described above, the optical transmission circuit (1116) or the optical reception circuit (1220) of the second embodiment can monitor the power of polarization multiplexed signal light with a single PD. Therefore, according to the second embodiment, in the optical transmission or reception circuit, control with a simple and low-cost control circuit is possible, the number of required wires is reduced, and the transmission or reception optical power is excellent in monitoring accuracy. A monitor can be provided.

Third Embodiment
An optical monitor circuit according to a third embodiment of the present invention will be described.

(Optical Transmission Circuit of Example 3)
FIG. 18 is a plan view showing the configuration of an optical transmission circuit (polarization multiplexed light modulation circuit) (2116) of a polarization diversity configuration including an optical monitor circuit according to the third embodiment.

  In FIG. 18, an optical power splitter (2105), a Y polarization light modulation circuit (2106), an X polarization light modulation circuit (2107), a polarization rotator (2108), and a polarization beam combiner (monitoring light branching function) 2109), VOA (2110) (2111), optical branch circuit for monitor light (2113), single PD (2115) are shown.

  The feature of the optical transmission circuit (2116) of the third embodiment is that although the optical branch circuit (2113) of one monitor light is installed before the polarization merging, the optical branch function of the other monitor light is a polarization It is to be incorporated in a polarization beam combiner (2109) which is a merging circuit. The waveguide of monitor light branched by the polarization beam combiner (2109) and the optical branching circuit (2113) is connected to a single PD (2115) of two light inputs. The element circuits of the light transmission circuit (2116) surrounded by a dashed-dotted frame are integrated on the same chip by, for example, a silicon optical waveguide.

  In FIG. 18, the optical branching circuit (2113) for monitor light is an optical branching circuit operating for TE polarization, and the directional coupler and WINC described in FIGS. 3 and 4 of the conventional example can be applied as they are.

  On the other hand, the branch function of monitor light incorporated in the polarization beam combiner (2109) in the third embodiment is required to operate with respect to TM polarization. The polarization beam combiner (2109) having such a configuration will be described later.

  Therefore, in FIG. 18, the light branched by the light branching circuit (2113) of the monitor light is TE polarized light, and the light branched by the polarized beam combiner (2109) is TM polarized light. As a result, in the 2-light input PD (2115) which is a light receiving element for monitor light, the signal (light signal power transmitted as TE polarization) modulated by the X polarization light modulation circuit (2107) is divided into The monitor light branched in 2113) is input as TE polarization, and is branched by the polarization beam combiner (2109) from the signal (optical signal power transmitted as TM polarization) modulated by the Y polarization light modulation circuit (2106) Monitor light is input as TM polarized light.

  Germanium photodetectors as described in Figure 10 (a), (b) are typically used for TE polarization input, but are also sensitive to TM polarization input, so they apply to PD (2115) It is possible.

(Optical Reception Circuit of Example 3)
FIG. 19 is a plan view showing the configuration of an optical receiving circuit (2220) of a polarization diversity configuration including an optical monitor circuit in the third embodiment.

  In FIG. 19, an optical input path (2201) from a local light source, an input path (2202) for signal light, a polarization beam splitter (2207) having a monitor light splitting function, a polarization rotator (2208), and light Power splitter (2209), optical coherent mixer for Y polarization (2210), optical coherent mixer for X polarization (2211), PD (2212) (2213) for converting a demodulated optical signal into an electric signal, monitor A light branching circuit (2215), a single PD (2217) of two light inputs to which two branched monitor lights are input, and a monitor signal (not shown) detected to adjust the light power 2 One VOA 2218 (2219) is shown.

  The feature of the light receiving circuit (2220) of the third embodiment is that although the light branching circuit (2215) of one monitor light is installed after polarization separation, the light branching function of the other monitor light is a polarization beam It is that the splitter (2207) incorporates the function. The waveguides of monitor light branched by the polarization beam splitter (2207) and the optical branching circuit (2215) are connected to a single PD (2217) of two light inputs. The light receiving circuit (2220) component circuits surrounded by a dashed-dotted line are integrated on the same chip by, for example, a silicon optical waveguide.

  In FIG. 19, the optical branch circuit (2215) for monitor light is an optical branch circuit operating on TE polarization, and the directional coupler and WINC described in FIGS. 3 and 4 of the conventional example can be applied as they are. On the other hand, the optical branching circuit incorporated in the polarization beam splitter (2207) is required to operate on TM polarization. The configuration of such a polarization beam splitter will be described later.

  Therefore, the monitor light branched by the optical branching circuit (2215) is TE polarization, and the monitor light branched by the polarization beam splitter (2207) is TM polarization. The light branched from the TE polarization component of the reception signal is TE polarization, and the light branched from the TM polarization component of the reception signal is input as TM polarization. Germanium photodetectors as illustrated in Figures 10 (a), (b) are typically used for TE polarized input but are also sensitive to TM polarized input, so they apply to PD (2217) Is possible.

  In the following, in Example 3, a polarization beam combiner (2109) incorporating the optical branching function of monitor light on the optical transmission circuit side, and a polarization beam incorporating the optical branching function of monitor light on the optical reception circuit side A specific configuration example of the splitter (2207) will be described. A combination of polarization beam combiner (polarization merging circuit) and an optical polarization beam splitter (polarization splitting circuit) can be referred to as a polarization splitting and merging circuit.

(Configuration Example 1 of Polarization Beam Combiner of Optical Transmission Circuit of Embodiment 3)
FIG. 20 is a diagram showing a configuration example 1 of a polarization beam combiner (2109) which is a polarization merging circuit in which a monitor light branching function of TM polarization is incorporated in the optical transmission circuit of the third embodiment. Similar to FIG. 6 (a) of the prior art, the input / output optical waveguides (2301) (2302) (2303) (2304) are shown, and the polarization beam combiner (2109) is a directional coupler.

  In FIG. 20, in order to incorporate the light branching function with respect to TM polarization, the design is different from that of the conventional example shown in FIG. Here, assuming that the waveguide core made of silicon has a width of 0.5 μm and a thickness of 0.22 μm, and the overcladding and undercladding is quartz, the gap between waveguides of the directional coupler (2109) is 0.4 μm. .

  FIG. 26 (a) is a diagram showing coupling rates of TE polarized light (dotted line) and TM polarized light (practice) at a wavelength of 1545 nm with respect to the length of the directional coupler at this time. Here, in the third embodiment, the length of the directional coupler is 11 μm. In this design, 80% or more of the power of TM polarization input from the optical waveguide (2302) of FIG. 20 is output to the optical waveguide (2303), and the power of the remaining TM polarization is output to the optical waveguide (2304) as monitor light It is output.

  FIG. 26 (b) shows a change with respect to wavelength of the ratio of the TM polarized light output to the optical waveguide (2304) when the length of the directional coupler is 11 μm. From this, the optical power of TM polarization of 7% or more in the C band wavelength region is output to the optical waveguide (2304). The polarization extinction ratio that can be realized by a single directional coupler as shown in FIG. 20 is about 15 dB.

  On the other hand, since the TE polarization is weakly coupled to the TM polarization, as shown in FIG. 26A, the TE polarization coupling ratio is only a few% when the length of the directional coupler is 11 μm. Therefore, almost 100% power of TE polarized light input from the optical waveguide (2301) of FIG. 20 is output from the optical waveguide (2303), and most power of TM polarized light input from the optical waveguide (2302) A part of the TM polarization input from the optical waveguide (2302) is branched and output as monitor light from the optical waveguide (2304), that is, a polarization beam combiner incorporating an optical branching function for the TM polarization is realized can do.

(Configuration Example 2 of Polarization Beam Combiner of Optical Transmission Circuit of Embodiment 3)
FIG. 21 is a diagram showing a configuration example 2 of a polarization beam combiner (2109) which is a polarization merging circuit in which a monitor light branching function of TM polarization is incorporated in the optical transmission circuit of the third embodiment. This example achieves the reduction of the wavelength dependence of the splitting ratio for TM polarization by the so-called WINC, which consists of two directional couplers and a delay waveguide.

  FIG. 21 shows input / output optical waveguides (2401) (2402) (2403) (2404), directional couplers (2411) (2412), and delay waveguides (2413) (2414). Assuming that the waveguide core made of silicon has a width of 0.5 μm, a thickness of 0.22 μm, and the overcladding and undercladding of quartz, the gap between waveguides of the directional couplers (2411) and (2412) is 0.4 μm and long The length is 7 μm, and the delay amount of the delay waveguides 2413 and 2414 is 0.065 μm.

  Here, with regard to TE polarization input from the optical waveguide (2401), almost 100% of the power is output to the optical waveguide (2403) because the coupling ratio is almost 0% in the directional couplers (2411) and (2412). Ru. Here, the coupling ratio of the directional couplers 2411 and 2412 to TE polarized light can be confirmed by referring to the value (dotted line) at 7 μm in length of the directional coupler in FIG.

  FIG. 27A is a diagram showing the wavelength dependency of the power ratio of the TM polarized light input from the optical waveguide (2402) of FIG. 21 at this time to the optical waveguide (2304). While the branching ratio in FIG. 26B fluctuates in the range of about 7 to 22% in the C band wavelength region, it can be confirmed that the branching ratio in FIG. 27A can be suppressed to about 10 to 17%.

  FIG. 27B is a diagram showing the wavelength dependency of the power ratio of TM polarized light and TE polarized light input from the optical waveguide (2402) to the optical waveguide (2403). From this, an optical power of 83% or more of TM polarization in the C band wavelength region is output to the optical waveguide (2403). The polarization extinction ratio that can be realized by the WINC configuration as shown in FIG. 21 is about 15 dB.

  On the other hand, since TE polarization has weak coupling in the directional couplers 2411 and 2412, there is almost no power to be output to the optical waveguide 2404. Therefore, almost 100% of the TE polarized light input from the optical waveguide (2401) is output from the optical waveguide (2403).

  As a result, it is possible to realize a polarization beam combiner incorporating an optical branching function for TM polarization, in which the wavelength dependence of the branching ratio at which TM polarization is output to the optical waveguide (2404) is smaller.

(Configuration Example 3 of Optical Transmission Circuit Polarization Beam Combiner of Embodiment 3)
FIG. 22 is a diagram showing a configuration example 3 of a polarization beam combiner (2109) which is a polarization merging circuit in which a monitor light branching function of TM polarization is incorporated in the optical transmission circuit of the third embodiment. Similar to FIG. 6 (b) of the prior art, the directional couplers are connected in two stages, and FIG. 22 shows input / output optical waveguides (2501) (2502) (2503) (2505), directional couplers. (2511) (2512), an optical waveguide (2504) connecting two directional couplers is shown.

  Here, the directional coupler (2512) is designed differently from the conventional example shown in FIG. 6 (b) in order to incorporate the light branching function for TM polarization. Here, assuming that the waveguide core made of silicon has a width of 0.5 μm and a thickness of 0.22 μm, and the overcladding and undercladding is quartz, the gap between waveguides of the directional couplers 2511 and 2512 is 0.4 It is assumed to be μm.

  Referring again to FIG. 26A, the coupling ratio of TE polarization and TM polarization at a wavelength of 1545 nm to the length of the directional coupler at this time is shown. Here, in the present embodiment, the length of the directional coupler (2512) is 11 μm, and the length of the directional coupler (2511) is 15 μm as in the prior art. In this design, 80% or more of the power of the TM polarization input from the optical waveguide (2501) is output to the optical waveguide (2504) by the directional coupler (2512), and the power of the remaining TM polarization is the optical waveguide (2503) Output to).

  Referring again to FIG. 26 (b), this shows the ratio of the TM polarized light output to the optical waveguide (2503) in the 11 μm-long directional coupler (2512). From this, the optical power of TM polarization of 7% or more in the C band wavelength region is output to the optical waveguide (2503). As for the TM polarized light input to the directional coupler (2511) through the optical waveguide (2504), almost all the power is output to the optical waveguide (2505) as in the conventional example. At this time, the TE polarized light that is input from the optical waveguide (2501) and output to the optical waveguide (2505) is suppressed in two steps in the directional couplers (2512) and 2511), so the polarization that can be realized in this example The wave extinction ratio is about 30 dB.

  On the other hand, TE polarized light is input from the optical waveguide (2502), but in the directional coupler (2511) having the same design as that of the conventional example, almost 100% of the power is output from the optical waveguide (2505).

  As a result, it is possible to realize a polarization beam combiner incorporating an optical branching function for TM polarization, which is superior to the polarization extinction ratio performance.

(Configuration Example 4 of Polarization Beam Combiner of Optical Transmission Circuit of Embodiment 3)
FIG. 23 is a diagram showing a configuration example 4 of a polarization beam combiner (2109) which is a polarization merging circuit in which a monitor light branching function of TM polarization is incorporated in the optical transmission circuit of the third embodiment. Here, the WINC (2612) has the same configuration as that of the WINC shown in FIG. 21, and a directional coupler (2611) is further connected to the subsequent stage thereof. 23, input / output optical waveguides (2601) (2602) (2605) (2605), directional couplers (2611) (2621) (2622), delay waveguides (2623) (2624), WINC (2612). ) And an optical waveguide (2604) connecting the directional coupler (2611).

  Here, assuming that the waveguide core made of silicon has a width of 0.5 μm, a thickness of 0.22 μm, and the overcladding and undercladding is quartz, the waveguides of the directional couplers (2611) (2621) (2622) The gap is 0.4 μm. The length of the directional coupler (2611) is 15 μm, the length of the directional couplers (2621) (2622) is 7 μm, and the delay amount of the delay waveguides (2623) (2624) is 0.065 μm, as in the conventional example. I assume.

  Here, since WINC (2612) has the same configuration as that of FIG. 21, the power of 83% or more of the TM polarization input from the optical waveguide (2601) is output to the optical waveguide (2604), and 10 to 17% of the optical It is branched into a waveguide (2603). The wavelength dependency of this branching rate is suppressed more than that of a single directional coupler.

  As for the TM polarized light input to the directional coupler (2611) through the optical waveguide (2604), almost all the power is output to the optical waveguide (2605) as in the conventional example. At this time, the TE polarized light that is input from the optical waveguide (2601) and output to the optical waveguide (2605) is suppressed in two steps in the WINC (2612) and the directional coupler (2611), so this example realizes The polarization extinction ratio that can be achieved is about 30 dB.

  On the other hand, TE polarized light is input from the optical waveguide (2602), but in the directional coupler (2611) having the same design as that of the conventional example, almost 100% of the power is output from the optical waveguide (2605).

  The polarization shown in FIGS. 20-23 in the optical transmission circuit according to the third embodiment is superior in polarization extinction ratio performance, and wavelength dependency of the branching ratio is further suppressed. A beam combiner can be realized.

  As described above, the monitor optical branching circuit of the optical transmission circuit uses the polarization merging circuit by using the output port that does not contribute to the polarization merging function of the polarization merging circuit (polarization beam combiner) as a branching port. It can be realized as having a function of a monitor light branch circuit for TM polarization component.

(Configuration Example 1 of Polarization Beam Splitter of Optical Reception Circuit of Embodiment 3)
FIG. 24 is a diagram showing a configuration example 1 of a polarization beam splitter (2207) which is a polarization separation circuit incorporating a monitor light branching function of TM polarization in the light receiving circuit of the third embodiment. Similar to the polarization beam splitter shown in FIG. 6 (b) of the conventional example, the configuration is such that directional couplers are connected in two stages, and in FIG. 24, input / output optical waveguides (2701) (2702) (2704) (2705), a directional coupler (2711) (2712), an optical waveguide (2703) connecting two directional couplers is shown.

  Here, the directional coupler (2712) has a design different from that of the conventional example shown in FIG. Here, assuming that the waveguide core made of silicon has a width of 0.5 μm and a thickness of 0.22 μm and the overcladding and undercladding is quartz, the gap between waveguides of the directional couplers 2711 and 2712 is 0.4. It is assumed to be μm.

  Referring to FIG. 26A, the coupling ratio of TE polarization and TM polarization at a wavelength of 1545 nm with respect to the length of the directional coupler at this time is shown. Here, in the present embodiment, the length of the directional coupler (2712) is 11 μm, and the length of the directional coupler (2711) is 15 μm as in the prior art. In this design, almost all power is output to the optical waveguide (2703) by the directional coupler (2511), as in the prior art, as TM polarized light input from the optical waveguide (2701).

  Also, referring to FIG. 26 (b), this is the power of the TM polarized light input from the optical waveguide (2703) and output to the optical waveguide (2705) in the directional coupler (2712) having a length of 11 μm. It shows the ratio. The power of 80% or more is output to the optical waveguide (2704), and the remaining power is output as the monitor light to the optical waveguide (2705) through the optical waveguide (2703) and the directional coupler (2712). Be done. At this time, the TE polarized light that is input from the optical waveguide (2701) and output to the optical waveguide (2705) is suppressed in two steps in the directional couplers (2711) and (2712), so the polarization that can be realized in this example The wave extinction ratio is about 30 dB.

  On the other hand, TE polarized light is input from the optical waveguide (2701), but in the directional coupler (2711) having the same design as that of the conventional example, almost 100% of the power is output from the optical waveguide (2702).

  Thereby, it is possible to realize a polarization beam splitter incorporating an optical branching function for TM polarization.

(Configuration Example 2 of Polarization Beam Splitter of Optical Reception Circuit of Embodiment 3)
FIG. 25 is a diagram showing a configuration example 2 of a polarization beam splitter (2207) which is a polarization separation circuit incorporating a monitor light branching function of TM polarization in the light receiving circuit of the third embodiment. Here, the WINC (2812) has the same configuration as that of the WINC shown in FIG. 21, and further connects the WINC (2812) to the subsequent stage of the directional coupler (2811). 25, input / output optical waveguides (2801) (2802) (2804) (2805), directional couplers (2811) (2821) (2822), delay waveguides (2823) (2824), and WINC An optical waveguide (2803) connecting the directional coupler (2811) with the 2812) is shown.

  Here, assuming that the waveguide core made of silicon has a width of 0.5 μm, a thickness of 0.22 μm, and the overcladding and undercladding is quartz, the waveguides of the directional couplers (2811) (2821) (2822) The gap is 0.4 μm. The directional coupler (2811) has a length of 15 μm as in the prior art, the directional coupler (2821) (2822) has a length of 7 μm, and the delay waveguide (2823) (2824) has a delay of 0.065 μm. I assume.

  Here, as for the TM polarized light input from the optical waveguide (2801) to the directional coupler (2811), almost all the power is output to the optical waveguide (2803) as in the conventional example. Furthermore, since the WINC (2812) has the same configuration as that of FIG. 21, again referring to FIGS. 27 (a) and 27 (b), the TM polarization input to the WINC (2812) via the optical waveguide (2803) A power of 83% or more is output to the optical waveguide (2804), and 10 to 17% is branched to the optical waveguide (2805) as monitor light. It can be seen that the wavelength dependency of this branching ratio is suppressed as compared with the configuration of a mere directional coupler as in the example of FIG.

  At this time, the TE polarized light that is input from the optical waveguide (2801) and output to the optical waveguide (2804) is suppressed in two steps by the directional coupler (2811) and the WINC (2812), so in this example The polarization extinction ratio that can be realized is about 30 dB.

  On the other hand, TE polarized light is input from the optical waveguide (2801), but in the directional coupler (2811) having the same design as that of the conventional example, almost 100% of the power is output from (2802).

  With the configuration shown in FIGS. 24 and 25 in the optical receiving circuit of the third embodiment, it is possible to realize a polarization beam splitter incorporating an optical branching function for TM polarization in which the wavelength dependency of the branching ratio is further suppressed. .

  As described above, the monitor light branching circuit of the light receiving circuit uses the polarization separation circuit by using the output port that does not contribute to the polarization separation function of the polarization separation circuit (polarization beam splitter) as the branch port. It can be realized as having a function of a monitor light branch circuit for TM polarization component.

  From the above, the optical transmitting circuit (2116) (FIG. 18) or the optical receiving circuit (2220) (FIG. 19) of the third embodiment monitors the power of polarization multiplexed signal light with a single PD of two optical inputs. be able to. Therefore, according to the third embodiment, in the optical transmission or reception circuit, control with a simple and low-cost control circuit is possible, the number of required wires is reduced, and the transmission or reception optical power is excellent in monitoring accuracy. A monitor can be provided.

Fourth Embodiment
An optical monitor circuit according to a fourth embodiment of the present invention will be described.

(Optical Transmission Circuit of Example 4)
FIG. 28 is a plan view showing the configuration of an optical transmission circuit (4116) of a polarization diversity configuration including an optical monitor circuit in the fourth embodiment.

  FIG. 28 shows the detected optical power splitter (4105), Y polarization light modulation circuit (4106), X polarization light modulation circuit (4107), polarization rotator (4108), polarization beam combiner (4109), Two VOAs (4110) and (4111) for adjusting optical power upon receiving a monitor signal (not shown), optical branch circuits for monitor light (4112) and (4113), and PD (4115) of two optical inputs are shown.

  The feature of the optical transmission circuit of the fourth embodiment is that the optical branch circuits (4112) and (4113) of monitor light are installed before the polarization rotation merging, that is, both the optical branch circuits (4112) and (4113) are TE. It is designed to operate with polarization, and the branched monitor light is connected to a single PD (4115) of two light inputs. The element circuits of the light transmission circuit (4116) surrounded by a dashed-dotted frame are integrated on the same chip by, for example, a silicon optical waveguide.

  The optical branch circuits (4112) and (4113) of monitor light shown in FIG. 28 are both optical branch circuits that operate on TE polarization, and the directional couplers and WINC described in FIGS. Applicable Therefore, since the light branched by the optical branching circuits (4112) and (4113) is both TE polarized light, the signal modulated by the X polarization light modulation circuit (the optical signal power transmitted as TE polarized light is transmitted to the PD (4115) ) And light branched from the signal modulated by the Y polarization light modulation circuit (optical signal power transmitted as TM polarization) are both input as TE polarization. As the PD (4115), application of a germanium photodetector as described in FIGS. 10 (a) and 10 (b) is possible. In this embodiment, unlike the other embodiments, TE light enters both of the two light inputs of PD, so that PD can absorb light with higher light coupling efficiency than the other embodiments.

(Optical Reception Circuit of Example 4)
FIG. 29 is a plan view showing the configuration of an optical receiving circuit (4220) of a polarization diversity configuration including an optical monitor circuit in the fourth embodiment.

  In FIG. 29, an optical input path (4201) from a local light source, an input path (4202) for signal light, a polarization beam splitter (4207), a polarization rotator (4208), an optical power splitter (4209), Y Optical coherent mixer (4210) for polarization, optical coherent mixer (4211) for X polarization, PD (4212) (4213) for converting a demodulated optical signal into an electric signal, detected monitor signal (not shown) The two VOAs (4218) (4219) that adjust the optical power upon receiving the signal, and the single PD (4217) with a two-light input that detects monitor light and the optical branch circuit (4214) (4215) for monitor light are also shown. Be

  The feature of the light receiving circuit of the fourth embodiment is that the optical branch circuits (4214) and (4215) of monitor light are both installed after polarization separation and polarization rotation, that is, the optical branch circuits (4214) and (4215) are both It is designed to operate with TE polarization, and the waveguide branched by the monitor light optical branch circuit (4214) (4215) is connected to a single PD (4217) of two optical inputs. is there. The element circuits of the light receiving circuit (4220) surrounded by a dashed-dotted frame are integrated on the same chip by, for example, a silicon optical waveguide.

  The monitor light optical branch circuits (2214) and (4215) in FIG. 29 are optical branch circuits that operate on TE polarization, and the directional couplers and WINC described in FIGS. Applicable Therefore, since the light branched by the optical branching circuits (2214) and (2215) is both TE polarized light, the PD (4217) with two light inputs receives the light branched from the TE polarized component of the received signal and the received signal. Both lights branched from the TM polarization component are input as TE polarization. As PD (4217), application of a germanium photodetector as described in FIGS. 10 (a) and 10 (b) is possible.

  The above four embodiments have described specific examples and configuration examples of the present invention. In any of the embodiments, polarization multiplexed signal light of transmission or reception is divided into two polarization components separately and then converted into electric signals for monitoring, and is polarized by a single PD of two optical inputs. A monitor of transmission or reception optical power which can monitor the power of wave multiplexed signal light, can be controlled by a simple and low-cost control circuit, can reduce the number of required wires, and has excellent monitor accuracy Can be provided.

  As described above, according to the present invention, in an optical transmission or an optical reception circuit of a polarization diversity configuration, control with a simpler and lower cost control circuit is possible compared to the prior art, and the required number of wirings is reduced. Thus, it is possible to realize a monitor of transmission and reception light power which is excellent in monitor accuracy.

9100 ...... Light source
106, 107, 1106, 1107, 2106, 2107, 4106, 4107, 9101, 9106, 9107 ...... Optical modulator
210, 211, 1210, 1211, 12210, 2211, 4210, 4211, 9210, 9211 ...... Optical coherent mixer
110, 111, 218, 219, 1110, 111, 11218, 1219, 2110, 2111, 2218, 2219, 4110, 4111, 4218, 4219, 9101, 9110, 9111, 9206, 9218, 9219 ..... VOA)
105, 209, 1105, 1209, 2105, 2209, 4105, 4209, 9105, 9209 ...... Optical power splitter
108, 208, 1108, 1208, 2108, 2208, 4108, 4208, 9108, 9208, 9801 ... polarization rotation circuit
109, 1109, 2109, 4109, 9109 ··· Polarization beam combiner (polarization merging circuit)
207, 1207, 2207, 4207, 9207 ・ ・ ・ Polarization beam splitter (polarization separation circuit)
112, 113, 214, 215, 1112, 1113, 1214, 1215, 2113, 2215, 4112, 4113, 4214, 4215, 9103, 9112, 9113, 9204, 9214, 9215 .....
115, 212, 213, 217, 1115, 1212, 1217, 2115, 2212, 2213, 2215, 4212, 4212, 4213, 4305, 9104, 9114, 9115, 9205, 9212, 9213, 9216, 9217 ... ... photodetector (PD)
521 ...... Silicon waveguide
522 ...... p implant area
523 ...... p ++ implant area
524 ...... Ge crystal
525 ...... n implant area
526 ...... Electrode
527 ...... Upper clad
528 ...... Lower clad
529 ...... Silicon substrate
2109 ...... Polarized beam combiner with optical branching function (polarization merging circuit)
2207 ... Polarization beam splitter (polarization split circuit) having an optical branching function
116, 1116, 2116, 4116, 9116 ..... Optical transmission circuit
220, 1220, 2220, 4220, 9203, 9220 ..... Light receiving circuit
605, 606, 2411, 2412, 2511, 2512, 2611, 2621, 2622, 2711, 2811, 2821, 2822, 9305, 9505, 9506, 9605, 9515, 9516 ... directional couplers
301, 302, 303, 304, 401, 402, 403, 404, 601, 602, 603, 604, 2301, 2302, 2303, 2304, 2401, 2402, 2403, 2404, 2501, 2502, 2503, 2504, 2505, 2601, 2602, 2603, 2604, 2605, 2701, 2702, 2704, 2705, 2801, 2802, 2803, 2804, 2805, 4301, 4302, 9301, 9302, 9303, 9501, 9502, 9503, 9504, 9503, 9504, 9502, 9503, 9504, 9601, 9602, 9603, 9604, 9611, 9612, 9613, 9614, 9802, 9809 ...... Optical waveguide
607, 608, 2413, 2414, 2623, 2624, 2823, 2824, 9507, 9508, 9806, 9807 ...... Optical delay circuit
9803 ...... Rib portion of rib waveguide
9804 ...... Slab part of rib waveguide
9805 ...... Branch circuit
9808 ...... Joining circuit
2612, 2812 ...... WINC

Claims (8)

An optical circuit of a polarization diversity configuration having a polarization separation / merging circuit and a polarization rotation circuit that performs polarization rotation between TM polarization and TE polarization, and branches part of the optical power from the main signal path; An optical monitor circuit that monitors the power of the signal light;
The optical monitor circuit
A first monitor light branch circuit on a path through which a signal of TE polarization component passes;
A second monitor light branch circuit is provided on a path through which the signal of the TM polarization component passes,
Two light inputs connected to a waveguide for guiding monitor light branched by the first monitor light branch circuit and a waveguide for guiding monitor light branched by the second monitor light branch circuit An optical monitor circuit characterized by having a single photodetector. The polarization separation junction circuit is a polarization junction circuit, and
The polarization rotation circuit is on a path through which the signal of the TM polarization component in the front stage of the polarization merging circuit passes;
The first monitor light branch circuit is on a path through which the signal of the TE polarization component in the previous stage of the polarization merging circuit passes,
The second monitor light branch circuit may be on the path of the rear stage of the polarization merging circuit, or on the path from the rear stage of the polarization rotation circuit to the polarization merging circuit, or in the front stage of the polarization rotation circuit. Characterized in that the polarization merging circuit also has the function of an optical branching circuit for the TM polarization component, with an output port on the path or not contributing to the polarization merging function of the polarization merging circuit being a branching port. The light monitoring circuit according to claim 1. The polarization separation junction circuit is a polarization separation circuit, and
The polarization rotation circuit is on a path through which the signal of the TM polarization component in the subsequent stage of the polarization separation circuit passes;
The first monitor light branch circuit is on a path through which a signal of a TE polarization component in a subsequent stage of the polarization separation circuit passes;
The second monitor light branch circuit may be on the path of the front stage of the polarization separation circuit, or on the path from the rear stage of the polarization separation circuit to the polarization rotation circuit, or in the rear stage of the polarization rotation circuit. Characterized in that the polarization separation circuit also has the function of an optical branching circuit for the TM polarization component, with an output port on the path or not contributing to the polarization separation function of the polarization separation circuit as a branching port. The light monitoring circuit according to claim 1. The light monitoring circuit is formed of a silicon based waveguide,
The optical monitor circuit according to claim 1, wherein said polarization separation junction circuit comprises a directional coupler or a WINC comprising a directional coupler and a delay circuit. The light monitoring circuit according to claim 1, wherein two input waveguides of the single light detector of the two light inputs are disposed to face each other so as to shift the optical axis. The optical monitor circuit according to any one of claims 1 to 5, wherein the monitor optical branching circuit is formed of a directional coupler or a WINC comprising a directional coupler and a delay circuit. The optical circuit of the polarization diversity configuration is
An optical power splitter,
Optical modulation circuits for TE polarization component and TM polarization component connected to the optical power splitter;
The polarization rotation circuit further connected to the light modulation circuit for the TM polarization component;
3. The optical monitor circuit according to claim 2, wherein the optical monitor circuit comprises an optical modulation circuit for the TE polarization component and the polarization combining circuit further connected to the polarization rotation circuit. . The optical circuit of the polarization diversity configuration is
The polarization separation circuit connected to the input port;
The polarization rotation circuit connected to the polarization separation circuit;
And an optical power splitter connected to another input port,
An optical coherent mixer for TE polarization components connected to one output of the polarization separation circuit and one output of the optical power splitter;
The polarization rotation circuit, and an optical coherent mixer for TM polarization component connected to the other output of the optical power splitter;
4. The light monitoring circuit according to claim 3, wherein the light monitoring circuit is a light receiving circuit including a photodetector connected to each of the light coherent mixers for the TE polarization component and the TM polarization component.

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