JP2021184110A - 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, specifically, 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 the communication capacity per channel has been developed and is being introduced into commercial use. In digital coherent communication, a polarization multiplexing method is generally applied in which different signals are given to two orthogonally polarized lights (polarized light) to double the transmission amount.

There are various signal formats for applying signals to each polarization, but the system that is currently being most actively introduced for commercial use is QPSK (Quadrature Phase), which has a communication capacity of 100 gigabits / second per channel. Most of them use Shift Keying).

(Conventional optical transmission circuit)
FIG. 1A shows the functional configuration of a digital coherent polarization multiplex QPSK optical transmission circuit as an optical circuit used in a polarization multiplex optical transmission system according to the prior art. FIG. 1 (a) shows a light source (9100) that generates continuous light, a polarization multiplex QPSK optical modulator (9101), a variable optical attenuator (VOA) (9102), and an optical branch circuit (9103). , PhotoDetector (PD) (9104) is shown.

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

In the polarization multiplex optical transmission circuit, further miniaturization of the circuit is required in the future. For this purpose, research and development are underway to integrate a plurality of elemental optical circuits on the same chip by using an InP (indium phosphide) optical waveguide or a silicon optical waveguide (PIC: Photonic Integrated Circuit).

Specifically, in addition to the optical modulator (9101), the VOA (9102), optical branch circuit (9103), and PD (9104) can all be integrated on one chip, and the light source (9100) can also be integrated. It is being considered. On the other hand, in general, the characteristics of an optical circuit using an InP optical waveguide or a silicon optical waveguide have a strong polarization dependence. For this reason, the polarization multiplexing optical transmission circuit or optical reception circuit usually has a polarization diversity configuration having a circuit system corresponding to each of the two polarizations.

FIG. 1 (b) shows in detail the configuration of the optical transmission circuit (9116) having a polarization diversity configuration, which realizes the optical transmission circuit of FIG. 1 (a) as an optical integrated circuit. Here, it is assumed that the light source (9100) is not integrated.

In FIG. 1 (b), as the main signal path, an optical power splitter (9105) that branches continuous light from a light source (not shown) and the branched continuous light are modulated by modulated electrical signals corresponding to two polarizations, respectively. The Y-polarized light modulation circuit (9106) and the X-polarized light modulation circuit (9107), the polarization-rotating rotor (9108) that rotates the modulated light from the Y-polarized light modulation circuit (9106), and the different polarizations 2 A polarization beam combiner (9109), which is a circuit that converges two modulated lights by polarization, is shown.

Further, FIG. 1 (b) shows a VOA (variable optical attenuator) (9110) (9111), an optical branch circuit (9112) (9113), and a PD (photodetector) (photodetector) (VOA (variable optical attenuator) (9110) (9111), as optical signal intensity monitoring and adjustment functions. 9114) (9115) is shown. In FIG. 1 (b), the element circuits of the optical transmission circuit (9116) surrounded by the alternate long and short dash line 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, and is split into two by an optical power splitter (9105). It 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), along with the modulated TE polarization output from the X polarization light modulation circuit (9107). It is synthesized into a polarization multiplex signal by a polarization beam combiner (9109) and output to the transmission path.

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

In addition, VOA (9110) (9111), optical branch circuit (9112) (9113), PD (9114) (9115) are located after the Y polarization optical modulation circuit (9106) and X polarization optical modulation circuit (9107). Each is installed and has a function to monitor and adjust the optical signal intensity for each polarization component. Each VOA (9110) (9111), optical branch circuit (9112) (9113), PD (9114) (9115) has the same design, and is designed to operate for TE polarized light.

Originally, as shown in FIG. 1 (a), the functions of the optical monitor and the VOA are sufficient if they operate collectively for the polarized wave-multiplexed signal before transmission. However, since the integrated optical circuit has a strong polarization dependence, it is difficult to realize a VOA or an optical branching circuit that operates in the same manner regardless of the polarization of light. Therefore, as a realistic configuration, the polarization diversity configuration is also used for the VOA and the optical monitor, and the optical signal intensity is monitored and adjusted for each polarization component.

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

FIG. 2A shows an optical input path (9201) from a station emission source (not shown), an input path (9202) for signal light received from a transmission path, an optical reception circuit (9203), an optical branch circuit (9204), and the like. A PD (photodetector) (9205) and a VOA (variable light attenuator) (9206) that adjusts the optical power in response to a detected monitor signal (not shown) are shown.

The optical receiving circuit (9203) has a function of inputting continuous light and signal light from a station light emitting source, demodulating the signal light, and converting the signal light into an electric signal. At this time, a part of the optical power is branched as the monitor light from the signal light on the main signal path by the optical branch circuit (9204), the optical signal intensity received and input by the PD (9205) is monitored, and the VOA (VOA) ( In general, it further has an optical monitor function for adjusting the optical signal intensity according to 9206). It is also a generally required function to be able to detect a state in which an optical signal is not input (signal interruption) due to some abnormality by monitoring the optical signal intensity.

FIG. 2B shows in detail the configuration of the optical receiving circuit (9220) having a polarization diversity configuration, which realizes the optical receiving circuit of FIG. 2A as an optical integrated circuit.

FIG. 2B shows a polarization beam splitter (9207) and a polarization rotator (9208), which are polarization separation circuits that separate polarization multiplex signal light received from the path (9202) as the main signal path. ), Optical power splitter (9209), Optical coherent mixer for Y polarization (9210), Optical coherent mixer for X polarization (9211), PD (9212) (9213) that converts the demodulated optical signal into an electrical signal. ) Is shown. Further, optical branch circuits (9214) (9215), PD (9216) (9217), and VOA (9218) (9219) are shown as related to the optical monitor and the accommodation function.

In FIG. 2B, the element circuits of the optical receiving circuit (9220) surrounded by the frame of the alternate long and short dash line are integrated on the same chip by, for example, a silicon optical waveguide.

From the right side of FIG. 2 (b), continuous light of TE polarized light is input to the path (9201) from the light source of the station emission for demodulation (not shown) to the chip of the optical receiving circuit (9220), and the optical power splitter (9209) is used. It is branched into two and input to the optical coherent mixer (9210) (9211) respectively. At the same time, the polarization-multiplexed optical signal received from the transmission path and input to the path (9202) is separated into TE-polarized light and TM-polarized light by the polarization beam splitter (9207), which is a polarization separation circuit, and TM-polarized light is further separated. It is converted to TE polarized light by the polarization rotator (9208) and input to the optical coherent mixer (9210) (9211), respectively. In each optical coherent mixer (9210) (9211), the signal is demodulated by the interference between the signal light and the station emission, and further converted into an electric signal by 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 respect to TE polarization. Further, in front of the optical coherent mixer (9210) for Y polarization and the optical coherent mixer (9211) for X polarization, optical branch circuits (9214) (9215), PD (9216) (9217), VOA ( 9218) (9219) are installed respectively, and have the function of monitoring and adjusting the optical signal intensity for each polarization component. Each optical branch circuit (9214) (9215), PD (9216) (9217), VOA (9218) (9219) has the same design and is designed to operate for TE polarized light.

Even in the optical receiving circuit, the purpose of the optical monitor and the VOA is sufficient if they operate collectively for the polarized wave-multiplexed signal immediately after the input, as shown in FIG. 2 (a). However, since the integrated optical circuit has a strong polarization dependence, it is difficult to realize a VOA or an optical branching circuit that operates in the same manner regardless of the polarization of light. Therefore, as a realistic configuration, the polarization diversity configuration is also used for the VOA and the optical monitor, and the optical signal intensity is monitored and adjusted for each polarization component.

(Optical branch circuit)
FIG. 3 shows that the optical branch circuit (9112) (9113) of the monitor light of FIG. 1 (b) or the optical branch circuit (9214) (9215) of the monitor light of FIG. It shows a concrete configuration when it is realized as an integrated circuit. Such an optical branch circuit is realized by a directional coupler as shown in the figure.

FIG. 3 shows input / output optical waveguides (9301) (9302) (9303) (9304) and directional couplers (9305). As an example of the design, the width of the waveguide core made of silicon is 0.5 μm, the thickness is 0.22 μm, the overclad and underclad are quartz, and the gap between the waveguides of the directional coupler (9305) is 0.3. The length is μm and the length is 15 μm. This makes it possible to realize an optical branch circuit with a branching fraction of 7%, 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). can.

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

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

(Photo detector)
FIG. 5 shows PD (9114) (9115) of FIG. 1 (b) or PD (9216) (9217) of FIG. 2 (b), which is a light receiving element of monitor light in the prior art, as a silicon optical integrated circuit. As a realized example, the structure of a general germanium photodetector is shown. Here, FIG. 5 (a) is a plan view seen from above, and FIG. 5 (b) is a diagram showing a cross-sectional configuration of A-A'in FIG. 5 (a).

In FIG. 5, the silicon waveguide (521) to which the monitor light is input, the p-implant region (522) to the silicon waveguide, the p ++ implant region (523) to the silicon waveguide, and the Ge crystal grown on the silicon waveguide are shown. (524), n-implant region into Ge crystal (525), electrode (526), upper clad made of quartz (527), lower clad also made of quartz (528), silicon substrate (529). Is done.

As an example of the design of a germanium photodetector with a general structure, the thickness of the lower clad 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, and the optical The length of the Ge crystal (524) in the traveling direction is 50 μm, and the width is 10 μm.

(Polarization separation and merging circuit)
FIG. 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. A concrete configuration when (9207) is realized as a silicon optical integrated circuit is shown. The polarization separation merging circuit that performs such polarization merging or separation can be realized by the directional coupler as shown in FIG. 6 due to the bidirectionality of the optical signal.

The same applies hereinafter, but in an optical circuit having a polarization diversity configuration, a polarization separation circuit (polarization) of an optical reception circuit that separates received polarized multiple signal light into signals of TE polarization component and TM polarization component. The beam splitter) and the polarization merging circuit (polarization beam combiner) of the optical transmission circuit that merges the signals of the TE polarization component and TM polarization component to be transmitted into the polarization multiplex signal light are combined to separate and merge the polarization. It can be called a circuit.

FIG. 6A is an example of configuring a polarization separation merging circuit with a single directional coupler. FIG. 6A shows an input / output optical waveguide (9601) (9602) (9603) (9604) and a directional coupler (9605). As an example of the design, the width of the waveguide core made of silicon is 0.5 μm, the thickness is 0.22 μm, the overclad and underclad are quartz, and the gap between the waveguides of the directional coupler (9305) is 0.4. It is said to be μm.

FIG. 7 is a diagram showing changes in the coupling ratios of TE polarized waves and TM polarized waves (depending on the circuit length of the coupling characteristics) with respect to the length of the directional coupler. Since TM polarization has stronger coupling than TE polarization, assuming that the length of the directional coupler is 15 μm in Fig. 7, TM polarization (solid line) has almost 100% optical power coupled. On the other hand, the coupling rate of TE polarized waves (dotted lines) is only a few percent. Therefore, in FIG. 6A, the TE / TM polarization multiplex light input from the upper right optical waveguide (9603) is output from the lower left optical waveguide (9602), and the TE polarization is almost the same. It functions as a polarization separation circuit output from the optical waveguide (9601) on the upper left. Further, as shown by the bidirectional arrows in FIG. 6, it functions as a polarization merging circuit from left to right in the opposite direction. 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 having a larger polarization extinction ratio is required, it is realized by forming the directional coupler in a plurality of stages as shown in FIG. 6 (b). In FIG. 6 (b), there are two input / output optical waveguides (9611) (9612) (9613) (9614) and two directional couplers (9605) in FIG. 6 (a) having the same design in between. Directional couplers (9615) (9616) are shown. As a result, the TM polarized light input from the optical waveguide (9611) is separated and output to the optical waveguide (9614), and 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 input / output optical waveguides (9802) (9809) are shown on the left and right, and the rib portion (9803) of the rib waveguide, the slab portion (9804) of the rib waveguide, the branch circuit (9805), and the delay are shown from the right. Waveguides (9806) (9807) and merging circuits (9808) are shown. This polarization rotation circuit (9801) can operate in both directions. For example, TM polarized light input from the right optical waveguide (9802) is converted to TE polarized light and output from the left optical waveguide (9809). On the contrary, 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).

The realization of polarization rotation is performed by a combination of polarization conversion that converts the basic mode light of TM polarization into the primary mode of TE polarization and mode conversion that converts the primary mode of TE polarization into the basic mode of TE polarization. .. Here, the rib waveguide (9803) (9804) has the function of polarization conversion, and the interference circuit composed of the branch circuit (9805), the delayed waveguide (9806) (9807), and the merging circuit (9808) is It has a mode conversion function.

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

In the monitoring of the transmitted / received optical power in the optical transmission circuit and optical receiving circuit having a polarization diversity configuration in the digital coherent polarization multiplexing method, each polarization is performed upstream of polarization rotation / merging or polarization separation / rotation downstream. The monitor light is branched from the signal light on the main signal path of the above, and the light is received by the monitor PD and monitored.

However, the optical power that should actually be monitored is the total power of the polarized multiple signal light, and in the conventional configuration, the monitor signal that is received in each polarization path and converted to the current level is sent 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, which makes the control circuit of the optical transmitter / receiver complicated and costly. (2) There are many wirings to take out the monitor signal from the silicon optical integrated circuit to the outside, and the package. The design and implementation are complicated. (3) There is a problem that the monitoring accuracy of the optical power deteriorates due to the individual difference in the light receiving sensitivity of the PD that receives the optical power of each polarization path.

(Conventional solutions and their problems)
In response to the above problem, light is branched from each polarization path, and the branched light is combined by a directional coupler or a multimode interferometer (MMI), and a single photodiode (PD) is used. 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, on the other hand, in the above method of combining light by MMI in the waveguide in front of a single PD and introducing the combined light into the PD, there is a problem that the combined optical circuit itself is lost and different biases occur. Since it is necessary to design a circuit that combines waves, the problem of low wave combining efficiency, and when MMI is used, an additional 3 dB loss occurs due to the principle loss (principle loss) of MMI. There was a new challenge, such as doing so.

The present invention has been made in view of the above problems, and an object thereof is to monitor a transmission / reception optical power in an optical transmission circuit and an optical reception circuit having a polarization diversity configuration on a path through which a signal of a TE polarization component passes. A first monitor optical branch circuit is provided in the light, and a second monitor optical branch circuit is provided on the path through which the signal of the TM polarization component passes, and the power of the polarization multiplex signal light is provided by a single PD of two optical inputs. By making it possible to monitor the light, it is possible to control with a simple and low-cost control circuit, the number of required wirings can be suppressed to a small number, and a monitor with excellent transmission / reception optical power can be provided. ..

Here, the path through which the signal of the TE polarization component passes and the path through which the signal of the TM polarization component passes are not necessarily the path through which only the optical signal of TE polarization or only the optical signal of TM polarization passes. 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, for example, an optical signal with polarization multiplexing may be used. Further, the monitor optical branch circuit does not have to be a dedicated circuit for branching the monitor light.

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

One embodiment is polarization that separates the polarized light from the TE polarized component and the signal of the TM polarized component, or joins the signal of the TE polarized component and the TM polarized component into the polarized multiple signal light. In an optical circuit having a polarization diversity configuration, which includes a separation / merging circuit and a polarization rotation circuit that is further connected to the TM polarization path to convert TM polarization and TE polarization.
It is an optical monitor circuit that monitors the power of signal light by branching and receiving a part of the optical power as monitor light from the signal light on the main signal path.
The optical monitor circuit is
In the optical circuit having the polarization diversity configuration, a first monitor optical branch circuit for the TE polarization component is provided on the path through which the signal of the TE polarization component passes.
It has a second monitor optical branch circuit for the TM polarization component on the path through which the signal of the TM polarization component passes.
Further, it has an optical merging means for merging the monitor light branched by the optical branch circuit for the TE polarization component and the monitor light branched by the optical branch circuit for the TM polarization component.
A waveguide further connected to the output of the optical merging means and guided by the monitor light branched by the first monitor optical branch circuit and the monitor light branched by the second monitor optical branch circuit are guided. Consists of a single photodetector with two optical inputs connected to the waveguide
In the second monitor optical branching circuit for the TM polarization component, the optical waveguide for output that does not contribute to the polarization separation / merging function of the polarization separation / merging circuit is used as the branching optical waveguide, and the polarization separation is performed. It is an optical monitor circuit characterized in that the merging circuit also has the function of an optical branching circuit for the TM polarization component.
(Structure 1 of the invention)
In an optical circuit having a polarization diversity configuration having a polarization separation merging circuit and a polarization rotation circuit that rotates polarization between TM polarization and TE polarization, a part of the optical power is branched from the main signal path to receive light. An optical monitor circuit that monitors the power of signal light.
The optical monitor circuit is
It has a first monitor optical branch circuit on the path through which the signal of the TE polarization component passes.
It has a second monitor optical branch circuit on the path through which the signal of the TM polarization component passes.
Two optical inputs connected to a waveguide that guides the monitor light branched by the first monitor optical branch circuit and a waveguide that guides the monitor light branched by the second monitor optical branch circuit. An optical monitor circuit, characterized by having a single photodetector.

(Structure 2 of the invention)
The polarization separation merging circuit is a polarization merging circuit,
The polarization rotation circuit is on a path through which the signal of the TM polarization component in the previous stage of the polarization merging circuit passes.
The first monitor optical 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 optical branch circuit is on the path after the polarization merging circuit, or on the path between the back of the polarization merging circuit and the polarization merging circuit, or in the front of the polarization merging circuit. The feature is that the polarization merging circuit also has the function of an optical branching circuit for the TM polarization component, with the output port on the path or not contributing to the polarization merging function of the polarization merging circuit as a branch port. The optical monitor circuit according to the configuration 1 of the present invention.

(Structure 3 of the invention)
The polarization separation merging circuit is a polarization separation circuit,
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 optical branch circuit is on the path through which the signal of the TE polarization component in the subsequent stage of the polarization separation circuit passes.
The second monitor optical branch circuit is on the path before the polarization separation circuit, or on the path between the latter stage of the polarization separation circuit and the polarization rotation circuit, or after the polarization rotation circuit. The feature is that the polarization separation circuit also has the function of an optical branch circuit for the TM polarization component, with the output port on the path or not contributing to the polarization separation function of the polarization separation circuit as a branch port. The optical monitor circuit according to the configuration 1 of the present invention.

(Structure 4 of the invention)
The optical monitor circuit is formed of a silicon-based waveguide.
The optical monitor circuit according to the first aspect of the present invention, wherein the polarization separation merging circuit is composed of a directional coupler or a WINC including a directional coupler and a delay circuit.

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

(Structure 6 of the invention)
The optical monitor circuit according to any one of configurations 1 to 5 of the present invention, wherein the monitor optical branch circuit is composed of a directional coupler or a WINC including a directional coupler and a delay circuit.

(Structure 7 of the invention)
The optical circuit having the polarization diversity configuration is
With an optical power splitter,
An optical modulation circuit for TE polarization component and TM polarization component connected to the optical power splitter,
The polarization rotation circuit further connected to the optical modulation circuit for the TM polarization component,
The optical monitor according to the second aspect of the invention, which is an optical transmission circuit including the optical modulation circuit for the TE polarization component and the polarization merging circuit further connected to the polarization rotation circuit. circuit.

(Structure 8 of the invention)
The optical circuit having the polarization diversity configuration is
The polarization separation circuit connected to the input port and
Having the polarization rotation circuit connected to the polarization separation circuit,
It has an optical power splitter that connects to yet another input port,
One output of the polarization separation circuit and an optical coherent mixer for the TE polarization component connected to one output of the optical power splitter.
The polarization rotation circuit and the optical coherent mixer for the TM polarization component connected to the other output of the optical power splitter.
The optical monitor circuit according to the third aspect of the invention, which is an optical receiving circuit composed of 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, in the monitoring of the transmission / reception optical power in the optical transmission circuit and the optical reception circuit having the polarization diversity configuration, the power of the polarization multiplex signal light can be monitored by a single PD. It is possible to control with a simple and low-cost control circuit, reduce the number of required wirings, and provide a monitor with excellent transmission / reception optical power.

It is a figure which shows the realization configuration of the optical power monitor in the conventional optical transmission circuit (optical modulation circuit). It is a figure which shows the realization configuration of the optical power monitor in the conventional optical receiving circuit. This is an example of realizing an optical branch circuit in a conventional optical transmission circuit or optical reception circuit. It is another implementation example (WINC) of the optical branch circuit in the conventional optical transmission circuit or optical reception circuit. It is a figure which shows the structure of a general germanium photodetector. It is a figure which shows the realization example of the polarization merging / separation circuit in a conventional polarization transmission circuit or an optical reception 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 realization example of the polarization rotation circuit in the conventional optical transmission circuit or the optical reception circuit. It is a figure which shows the realization structure of the optical power monitor in the optical transmission circuit (polarization multiplex optical modulation circuit) of Example 1 of this invention. It is a figure which shows the structure of the germanium photodetector of 2 light inputs used in the optical power monitor of this invention. It is a figure which shows the realization structure of the optical power monitor in the optical receiving circuit of Example 1 of this invention. It is a figure which shows the realization example of the optical branch circuit for TM polarization in the optical transmission circuit or the optical reception circuit of Example 1 of this invention. 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 realization example of the optical branch circuit for TM polarization in the optical transmission circuit or the optical reception circuit of the first embodiment of the present invention. It is a figure which shows the wavelength dependence of the branch characteristic of TE / TM light in the optical branch circuit of FIG. It is a figure which shows the realization structure of the optical power monitor in the optical transmission circuit (polarization multiplex optical modulation circuit) of Example 2 of this invention. It is a figure which shows the realization structure of the optical power monitor in the optical receiving circuit of Example 2 of this invention. It is a figure which shows the realization structure of the optical power monitor in the optical transmission circuit (polarization multiplex optical modulation circuit) of Example 3 of this invention. It is a figure which shows the realization 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 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 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 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 beam combiner of the optical transmission circuit of Example 3 of this invention. It is a figure which shows the configuration example 1 of the polarization beam splitter of the light receiving circuit of Example 3 of this invention. It is a figure which shows the configuration example 2 of the polarization beam splitter of the light receiving circuit of Example 3 of this invention. (A) is the circuit length dependence of the coupling characteristics of TE / TM polarized light in the directional couplers 2109, 2512, 2712 of FIGS. 20, 22, and 24, and (b) is the circuit length dependence of the TM polarized light when the circuit length is 11 μm. It is a figure which shows the branching fraction. (A) is the circuit length dependence of the branch characteristic of TM polarized light in WINC 2109, 2612, 2812 of FIGS. 21, 23, 25, and (b) is the circuit length dependence of WINC 2109, 2612, 2812 of FIGS. 21, 23, 25. It is a figure which shows the circuit length dependence of the branch characteristic of TM and TE polarization in. It is a figure which shows the realization structure of the optical power monitor in the optical transmission circuit (polarization multiplex optical modulation circuit) of Example 4 of this invention. It is a figure which shows the realization structure of the optical power monitor in the optical 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]
The optical monitor circuit according to the first embodiment of the present invention will be described.

(Optical transmission circuit of Example 1)
FIG. 9 is a plan view showing the configuration of an optical transmission circuit (polarization multiplex optical modulation circuit) (116) having a polarization diversity configuration including an optical monitor circuit in the first embodiment.

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

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

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

The element circuit of the optical transmission circuit (116) surrounded by the frame of the alternate long and short dash line is integrated on the same chip by, for example, a silicon optical wave guide.

In FIG. 9, the optical branch circuit (113) of the monitor light is an optical branch circuit that operates with respect to TE polarized light, 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) of the monitor light branches only TM polarized light from the polarized multiplex light, an optical branch circuit that operates for TM polarized light and hardly branches light for TE polarized light is required. Be done. A method for realizing such an optical branch circuit will be described later.

Therefore, in FIG. 9, the light branched by the optical branch circuit (113) of the monitor light is TE polarized light, and the light branched by the optical branch circuit (112) is TM polarized light. It is required that PD (115) detect it as a single electric signal obtained by adding the intensities of TE polarized light and TM polarized light.

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

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

For example, the waveguide (521) of FIG. 10 (a) is connected to the waveguide from the optical branch circuit (112) of FIG. 9, and the waveguide (521') of FIG. 10 (a) is the optical branch circuit (521') of FIG. It is connected to the waveguide from 113). The light that enters the PD (115) from the optical branch circuit (112) (113) is converted into semiconductor carriers without interfering with the Ge crystal 524 in the PD (115), merges, and becomes a single electric signal. Is output as.

When the Ge crystal (524) absorbs light, if it has sufficient length, thickness, and width in the direction of light travel (for example, at a temperature of 27 degrees for 1550 nm, at a temperature of 27 degrees, at a length of 20 um, a width of 10 um, and a thickness of 1 um). The light input intensity is about 0 dBm), and the light input from the silicon waveguide (521) is completely absorbed by the Ge crystal (524). Therefore, the light input from the silicon waveguide (521) does not combine or interfere with the light input from the silicon waveguide (521') as light, which is from the waveguide (521'). The same applies to the input light.

Therefore, in this two-optical input PD (115), the light coming from the optical branch circuit (112) (113) is absorbed by the PD as a semiconductor carrier without being combined as light and merges as an electric signal. Interference cannot occur. In this PD (115), it is possible to observe the combined intensities of both optical inputs as an electrical carrier. No merging means such as MMI is required, and there is no principle loss due to MMI. Therefore, it is configured to solve the problems (1) to (3) while solving the problems of the conventional invention.

The two optical input PD (115) may input light from the end faces 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 with each other while propagating in the PD, so the waveguides are separated and arranged at a distance where interference does not occur. It is necessary to devise a design such as

Alternatively, although not shown, even if the two silicon waveguides (521) (521') are opposed to each other as shown in FIG. 10A, the optical axes of the two facing input waveguides may be shifted. It is possible to reduce the length of the PD device while reducing the interference of light.
Germanium photodetectors (GePD, germanium PD) as described in FIGS. 10 (a) and 10 (b) are usually used for TE polarized light inputs, but are also sensitive to TM polarized light inputs. It can be applied to the two-optical input PD (115) of the present invention.

(Optical receiving circuit of Example 1)
FIG. 11 is a plan view showing the configuration of the optical receiving circuit (220) having the polarization diversity configuration including the optical monitor circuit in the first embodiment.

In FIG. 11, from the right, an input path (201) for station emission from a station emission source (not shown), an input path (202) for polarized multiple signal light received from a transmission path as a main signal path, and polarized multiple signal light are shown. A polarization beam splitter (207) that separates polarization and a polarization rotator (208) that rotates TM polarization from the polarization beam splitter (207) into TE polarization are shown.

Further, in FIG. 11, an optical power splitter (209) for branching local emission, an optical coherent mixer for Y polarization (210), an optical coherent mixer for X polarization (211), and a demodulated optical signal are shown as electrical signals. PD (212) (213) to be converted to is shown.

Further, in FIG. 11, as related to the optical monitor and the adjustment function, two optical branch circuits (214) (215) for branching the monitor light on the main signal path and two for waveguideing the branched monitor light are shown. A single PD (217) with two optical inputs connected to one waveguide and two VOAs (218) (219) that adjust the optical power in response to a detected unshown monitor signal are shown.

The feature of the optical receiving circuit of the first embodiment of FIG. 11 is that one optical branching circuit (215) is installed on the main signal path after the polarization separation by the polarization beam splitter (207), while the other. The optical branch circuit (214) is installed on the main signal path before the polarization separation. Further, the two monitor lights branched by the optical branch circuit (214) (215) are connected to the PD (217) having a single two-light input.

The element circuits of the optical receiving circuit (220) surrounded by the frame of the alternate long and short dash line are integrated on the same chip by, for example, a silicon optical wave guide.

The optical branch circuit (215) of FIG. 11 that branches the monitor light from the signal light after polarization separation is an optical branch circuit that operates with respect to TE polarized light, and is the direction described with reference to FIGS. 3 and 4 of the conventional example. The sex combiner and WINC can be applied as they are. On the other hand, the optical branch circuit (214) that branches the monitor light from the signal light before polarization separation operates only for TM polarization because it branches only TM polarization from the polarization multiplex light, and for TE polarization, An optical branching circuit in which light hardly branches is required. A method for realizing such an optical branch circuit will be described later.

Therefore, the light branched by the optical branch circuit (215) is TE polarized light, and the light branched by the optical branch circuit (214) is TM polarized light. Therefore, the PD (217) having two optical inputs has a received signal. The light branched from the TE polarized light component of the above is input with TE polarized light, and the light branched from the TM polarized light component of the received signal is input with TM polarized light. Germanium photodetectors as described in FIGS. 10 (a) and 10 (b) are usually used for TE polarized light inputs, but are also sensitive to TM polarized light inputs, and thus the PD (217) of the present invention. ) Can be applied.

(Optical branch circuit for TM polarization of Example 1)
FIG. 12 shows the TM in the optical branch circuit (112) of the monitor light for TM polarization in the optical transmission circuit (116) of the first embodiment of FIG. 9, or the optical reception circuit (220) of the first embodiment of FIG. The concrete configuration of the optical branch circuit (214) of the monitor light for polarization is shown.

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

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

(Cupling ratio to length and wavelength of directional coupler)
FIG. 13A shows a combination of TE polarized light and TM polarized light with respect to the length (circuit length) of the directional coupler with respect to the directional coupler constituting the optical branch circuit of the monitor light for TM polarization shown in FIG. It shows the change in the rate. Since the confinement of TM polarized light in the waveguide is weaker than that of TE polarized light, there is a difference in the coupling ratio. In this example, the length of the directional coupler is set to 3 μm. At this time, the coupling rate of TE polarized light is only 0.1%, and it can be said that almost no branching occurs.

FIG. 13B shows the wavelength dependence of the TM polarized light coupling ratio, that is, the branching ratio of the optical branching circuit (112) or (214) using the directional coupler with the length set to 3 μm. In the general operating range of the C band (wavelength 1525 to 1565 nm), the branch ratio of TM polarized light is 8% at the short wavelength end, and the branch ratio is 12% at the long wavelength end.

As a characteristic of the optical monitor circuit, it is required that the optical power in a specific range can be monitored as an electric signal, and the design of the branch ratio of the optical branch circuit is determined according to the range. In particular, it is often important how weak the power of light can be monitored, and in an optical branching circuit, it is important to design the minimum branching ratio in the operating wavelength range.

The optical branch circuit (112) or (214) for TM polarization according to the first embodiment of FIG. 12 is designed to meet the required specifications with reference to the branch ratio at the short wavelength end. As shown in FIG. 13 (b), the branch ratio of TM polarized light 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 according to the branching ratio.

In the optical transmission circuit and the optical reception circuit, it is desired to avoid a decrease in the power of the signal light as much as possible. Therefore, it is desirable to minimize the fluctuation of the branch ratio depending on the wavelength of the optical branch circuit. From this point of view, the optical branch circuit of the first embodiment has a branch ratio of 12% in the region at the long wavelength end of FIG. 13 (b), which is larger than the originally required branch ratio, and the optical signal power is larger than necessary. There is an inefficient situation in which is reduced.

(Another example of the optical branch circuit for TM polarization of Example 1)
FIG. 14 shows another example of an optical branching circuit for TM polarization that can further improve the above points. By adopting the WINC configuration, it is possible to suppress the wavelength dependence of the branch ratio as compared with the case where it is configured by a simple directional coupler as shown in FIG.

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

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

From the above, the optical transmission circuit (116) (FIG. 9) or the optical reception circuit (220) (FIG. 11) of the first embodiment can monitor the power of the polarized multiple signal light by a single PD. Therefore, according to the first embodiment, the optical transmission or reception circuit can be controlled by a simple and low-cost control circuit, the number of required wirings can be suppressed to a small number, and the transmission or reception optical power is excellent in monitor accuracy. A monitor can be provided.

[Second Embodiment]
The optical monitor circuit according to the 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 multiplex optical modulation circuit) (1116) having a polarization diversity configuration including an optical monitor circuit in the second embodiment.

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

The feature of the optical transmission circuit (1116) of the second embodiment is that one monitor light optical branch circuit (1113) is installed before the polarization confluence, and the other monitor light optical branch circuit (1112) is also biased. It is installed before the wave merging and between the polarization rotation and the polarization merging. Further, the waveguide branched by the optical branch circuit (1112) (1113) of the monitor light is connected to a single PD (1115) having two optical inputs.

The element circuit of the optical transmission circuit (1116) surrounded by the frame of the alternate long and short dash line is integrated on the same chip by, for example, a silicon optical wave guide.

In FIG. 16, the optical branch circuit (1113) of the monitor light is an optical branch circuit that operates with respect to TE polarized light, 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 (1112) of the monitor light of the second embodiment is required to operate with respect to TM polarized light, but unlike the first embodiment, it is installed before the polarization merging, so that the branching input is performed. The light that becomes is only TM polarized light, and the characteristics with respect to TE polarized light are irrelevant. This is achieved by optimizing the directional coupler and WINC for TM polarization, as in Example 1.

For example, when a directional coupler is applied, in Example 1, the branching ratio of TE polarized light needs to be almost zero, and the optical branching ratio to TM polarized light cannot be set so large. This is because when the branch ratio of TM polarized light is set to 20% or more, it is almost out of the range in FIG. 13 (a), but the branch ratio of TE polarized light increases to a non-negligible level.

On the other hand, in the second embodiment, since it is not necessary to worry about the branching ratio with respect to TE polarized light, the degree of freedom in setting the branching ratio is expanded. Therefore, it can be said that it is more advantageous than the first embodiment when it is desired to relatively increase the branch ratio in order to monitor to a smaller optical power.

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

Germanium photodetectors as described in FIGS. 10 (a) and 10 (b) of the conventional example are usually used for TE polarized light input, but are also sensitive to TM polarized light input, and therefore PD (1115). ) Can be applied.

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

FIG. 17 shows an optical input path (1201) for local emission, an input path for signal light (1202), a polarization beam splitter (1207), a polarization rotator (1208), an optical power splitter (1209), and Y polarization. Optical coherent mixers (1210) for X polarization are optical coherent mixers (1211), PDs (1212) (1213) that convert demodulated optical signals into electrical signals, and optical branch circuits for monitor light (1214). (1215), a single PD (1217) with two optical inputs to detect the monitor light and two VOAs (1218) (1219) to adjust the optical power in response to the detected unshown monitor signal are shown. ..

The feature of the optical reception circuit (1220) of the second embodiment is that one monitor light optical branch circuit (1215) is installed after polarization separation, and the other monitor light optical branch circuit (1214) is also biased. It is installed after wave separation and between polarization separation and polarization rotation. Further, the waveguide branched by the optical branch circuit (1214) (1215) is connected to a single PD (1217) having two optical inputs. The elemental circuits of the optical receiver circuit (1220) surrounded by the alternate long and short dash line frame are integrated on the same chip by, for example, a silicon optical waveguide.

In FIG. 17, the optical branch circuit (1215) of the monitor light is an optical branch circuit that operates with respect to TE polarized light, 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 branch circuit (1214) is required to operate with respect to TM polarization, but unlike the first embodiment, the optical branch circuit (1214) is installed after the polarization separation in the second embodiment, so that the light used as the branch input is Only TM polarized light is used, and the characteristics of TE polarized light are irrelevant. As described in the example of the optical transmitter (1116), it can be said that it is more advantageous than the first embodiment when the degree of freedom in setting the branch ratio is expanded and the branch ratio is relatively large.

Therefore, the monitor light branched by the optical branch circuit (1215) is TE polarized light, and the monitor light branched by the optical branch circuit (1214) is TM polarized light. As a result, the monitor light branched from the TE polarization component of the received signal was input by TE polarization to the dual light input PD (1217), which is the light receiving element of the monitor light, and branched from the TM polarization component of the received signal. The monitor light will be input with TM polarized light.

Germanium photodetectors as described in FIGS. 10 (a) and 10 (b) are usually used for TE polarized light inputs, but are also sensitive to TM polarized light inputs and are therefore applicable to PD (1217). Is possible.

From the above, the optical transmission circuit (1116) or the optical reception circuit (1220) of the second embodiment can monitor the power of the polarized multiple signal light by a single PD. Therefore, according to the second embodiment, the optical transmission or reception circuit can be controlled by a simple and low-cost control circuit, the number of required wirings can be suppressed to a small number, and the transmission or reception optical power is excellent in monitor accuracy. A monitor can be provided.

[Third Embodiment]
The optical monitor circuit according to the 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 multiplex optical modulation circuit) (2116) having a polarization diversity configuration including an optical monitor circuit in the third embodiment.

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

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

In FIG. 18, the optical branch circuit (2113) of the monitor light is an optical branch circuit that operates with respect to TE polarized light, 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 branching function of the 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 optical branch circuit (2113) of the monitor light is TE polarized light, and the light branched by the polarization beam combiner (2109) is TM polarized light. As a result, the two-light input PD (2115), which is the light receiving element of the monitor light, has an optical branch circuit (optical signal power transmitted as TE polarized light) modulated by the X-polarized light modulation circuit (2107). The monitor light branched in 2113) is input by TE polarization, and is branched by the polarization beam combiner (2109) from the signal modulated by the Y polarization light modulation circuit (2106) (optical signal power transmitted as TM polarization). The monitor light will be input with TM polarized light.

Germanium photodetectors as described in FIGS. 10 (a) and 10 (b) are usually used for TE polarized light inputs, but are also sensitive to TM polarized light inputs and are therefore applicable to PD (2115). It is possible to do.

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

FIG. 19 shows an optical input path (2201) from a local light source, a signal light input path (2202), a polarization beam splitter (2207) having a monitor optical branching 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) that converts the demodulated optical signal into an electrical signal, monitor The optical branch circuit (2215) of light, a single PD (2217) of two optical inputs to which two branched monitor lights are input, and the detected monitor signal (not shown) to adjust the optical power 2 Two VOAs (2218) (2219) are shown.

The feature of the optical receiving circuit (2220) of the third embodiment is that the optical branching circuit (2215) of one monitor light is installed after the polarization separation, while the optical branching function of the other monitor light is the polarization beam. The function is built into the splitter (2207). Further, the waveguide of the monitor light branched by the polarization beam splitter (2207) and the optical branch circuit (2215) is connected to a single PD (2217) having two optical inputs. The optical receiving circuit (2220) element circuit surrounded by the frame of the alternate long and short dash line is integrated on the same chip by, for example, a silicon optical wave guide.

In FIG. 19, the optical branch circuit (2215) of the monitor light is an optical branch circuit that operates with respect to TE polarized light, 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 with respect to TM polarization. The configuration of such a polarization beam splitter will be described later.

Therefore, the monitor light branched by the optical branch circuit (2215) is TE polarized light, and the monitor light branched by the polarization beam splitter (2207) is TM polarized light. The light branched from the TE polarized light component of the received signal is input with TE polarized light, and the light branched from the TM polarized light component of the received signal is input with TM polarized light. Germanium photodetectors as described in FIGS. 10 (a) and 10 (b) are usually used for TE polarized light inputs, but are also sensitive to TM polarized light inputs and are therefore applicable to PD (2217). Is possible.

In the following, in the third embodiment, the polarization beam combiner (2109) incorporating the optical branching function of the monitor light on the optical transmission circuit side and the polarization beam incorporating the optical branching function of the monitor light on the optical receiving circuit side. A specific configuration example of the splitter (2207) will be described. These polarization beam combiners (polarization merging circuits) and optical polarization beam splitters (polarization separation circuits) can be combined to form a polarization separation merging circuit.

(Structure 1 of the polarization beam combiner of the optical transmission circuit of the third embodiment)
FIG. 20 is a diagram showing configuration example 1 of a polarization beam combiner (2109), which is a polarization merging circuit incorporating a monitor optical branching function for TM polarization in the optical transmission circuit of the third embodiment. Similar to FIG. 6 (a) of the conventional example, the input / output optical waveguides (2301) (2302) (2303) (2304) are shown, and the polarization beam combiner (2109) is a directional coupler.

In FIG. 20, since the optical branching function for TM polarized light is incorporated, the design is different from that of FIG. 6A of the conventional example. Here, the width of the waveguide core made of silicon is 0.5 μm, the thickness is 0.22 μm, the overclad and underclad are quartz, and the gap between the waveguides of the directional coupler (2109) is 0.4 μm. ..

FIG. 26A is a diagram showing the coupling ratio 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 set to 11 μm. In this design, more than 80% of the power of TM polarized light input from the optical waveguide (2302) in FIG. 20 is output to the optical waveguide (2303), and the remaining power of TM polarized light is used as monitor light to the optical waveguide (2304). It is output.

FIG. 26 (b) shows the change in the ratio of the power of the TM polarized light output to the optical waveguide (2304) with respect to the wavelength when the length of the directional coupler is 11 μm. From this, the optical power of TM polarized light 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 with a single directional coupler as shown in FIG. 20 is about 15 dB.

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

(Constituent Example 2 of the Polarized Beam Combiner of the Optical Transmission Circuit of Example 3)
FIG. 21 is a diagram showing configuration example 2 of a polarization beam combiner (2109), which is a polarization merging circuit incorporating a monitor optical branching function for TM polarization in the optical transmission circuit of the third embodiment. This example uses a so-called WINC, which consists of two directional couplers and a delayed waveguide, to reduce the wavelength dependence of the branch fraction on TM polarized light.

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

Regarding the TE polarized light input from the optical waveguide (2401), almost 100% of the power is output to the optical waveguide (2403) because the coupling ratio is close to 0% in the directional couplers (2411) (2412). NS. Here, the coupling ratio of the directional coupler (2411) (2412) to the TE polarized light can be confirmed by referring to the value (dotted line) at the length of 7 μm of the directional coupler in FIG. 26 (a).

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

Further, FIG. 27B is a diagram showing the wavelength dependence of the power ratio of the TM polarized light and the TE polarized light input from the optical waveguide (2402) to be output to the optical waveguide (2403). From this, the optical power of 83% or more of TM polarized light is output to the optical waveguide (2403) in the C band wavelength region. 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, TE polarized light has almost no power to be output to the optical waveguide (2404) because the coupling at the directional coupler (2411) (2412) is weak. Therefore, almost 100% of the power of the TE polarized light input from the optical waveguide (2401) is output from the optical waveguide (2403).

This makes it possible to realize a polarization beam combiner incorporating an optical branching function for TM polarized light, in which the wavelength dependence of the branching fraction of TM polarized light output to the optical waveguide (2404) is smaller.

(Structure Example 3 of Optical Transmission Circuit Polarized Beam Combiner of Example 3)
FIG. 22 is a diagram showing a configuration example 3 of a polarization beam combiner (2109), which is a polarization merging circuit incorporating a monitor optical branching function for TM polarization in the optical transmission circuit of the third embodiment. Similar to FIG. 6 (b) of the conventional example, the configuration is such that the directional couplers are connected in two stages. In FIG. 22, the input / output optical waveguides (2501) (2502) (2503) (2505) and the directional couplers are shown. (2511) (2512), an optical waveguide (2504) connecting two directional couplers is shown.

Here, in order to incorporate an optical branching function for TM polarized light, the directional coupler (2512) is designed differently from the conventional example FIG. 6 (b). Here, assuming that the width of the waveguide core made of silicon is 0.5 μm, the thickness is 0.22 μm, and the overclad and underclad are quartz, the gap between the waveguides of the directional couplers (2511) (2512) is 0.4. Let it be μm.

With reference to FIG. 26 (a) again, the coupling ratio of TE-polarized light and TM-polarized light at a wavelength of 1545 nm with respect to the length of the directional coupler at this time is shown. Here, in this 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 conventional example. In this design, more than 80% of the TM polarized light input from the optical waveguide (2501) is output to the optical waveguide (2504) by the directional coupler (2512), and the remaining TM polarized power is output to the optical waveguide (2503). ) Is output.

Referring again to FIG. 26 (b), this shows the ratio of the power of TM polarized light output to the optical waveguide (2503) in a directional coupler (2512) with a length of 11 μm. From this, the optical power of TM polarized light of 7% or more in the C band wavelength region is output to the optical waveguide (2503). Almost all the power of the TM polarized light input to the directional coupler (2511) via the optical waveguide (2504) is output to the optical waveguide (2505) as in the conventional example. At this time, the TE polarized light input from the optical waveguide (2501) and output to the optical waveguide (2505) is suppressed in two steps by the directional coupler (2512) (2511), so that the bias that can be realized in this example can be realized. The wave-guided 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 the conventional example, almost 100% of the power is output from the optical waveguide (2505).

This makes it possible to realize a polarization beam combiner incorporating an optical branching function for TM polarization, which is superior in polarization extinction ratio performance.

(Structure Example 4 of Polarized Beam Combiner of Optical Transmission Circuit of Example 3)
FIG. 23 is a diagram showing a configuration example 4 of a polarization beam combiner (2109), which is a polarization merging circuit incorporating a monitor optical branching function for TM polarization in the optical transmission circuit of the third embodiment. Here, the WINC (2612) has the same configuration as the WINC shown in FIG. 21, and a directional coupler (2611) is further connected to the subsequent stage. FIG. 23 shows input / output optical waveguides (2601) (2602) (2603) (2605), directional couplers (2611) (2621) (2622), delayed waveguides (2623) (2624), and WINC (2612). ) And the optical waveguide (2604) connecting the directional coupler (2611) are shown.

Here, it is assumed that the width of the waveguide core made of silicon is 0.5 μm, the thickness is 0.22 μm, and the overclad and underclad are quartz, and between 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 as in the conventional example, the length of the directional coupler (2621) (2622) is 7 μm, and the delay amount of the delayed waveguide (2623) (2624) is 0.065 μm. And.

Here, since the WINC (2612) has the same configuration as that of FIG. 21, 83% or more of the power of the TM polarized light input from the optical waveguide (2601) is output to the optical waveguide (2604), and 10 to 17% is optical. Branched to the waveguide (2603). This wavelength dependence of branch fraction is less pronounced than with a single directional coupler.

Almost all the power of the TM polarized light input to the directional coupler (2611) via the optical waveguide (2604) is output to the optical waveguide (2605) as in the conventional example. At this time, the TE polarization 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 it is realized in this example. The possible polarization extinguishing ratio 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 the conventional example, almost 100% of the power is output from the optical waveguide (2605).

In the optical transmission circuit of the third embodiment, the polarization shown in FIGS. 20 to 23 is excellent in the polarization extinction ratio performance, and the wavelength dependence of the branch ratio is further suppressed. A beam combiner can be realized.

As described above, the monitor optical branch circuit of the optical transmission circuit uses the output port as a branch port, which does not contribute to the polarization confluence function of the polarization confluence circuit (polarization beam combiner), to form a polarization confluence circuit. It can also be realized as having the function of a monitor optical branch circuit for the TM polarization component.

(Configuration Example 1 of the Polarized Beam Splitter of the Optical Receiving Circuit of Example 3)
FIG. 24 is a diagram showing configuration example 1 of a polarization beam splitter (2207), which is a polarization splitting circuit incorporating a monitor optical branching function for TM polarization in the optical 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 the directional couplers are connected in two stages. In FIG. 24, the input / output optical waveguides (2701) (2702) (2704) are shown. ) (2705), directional couplers (2711) (2712), optical waveguides (2703) connecting the two directional couplers.

Here, in order to incorporate an optical branching function for TM polarized light, the directional coupler (2712) is designed differently from FIG. 6 (b) of the conventional example. Here, assuming that the width of the waveguide core made of silicon is 0.5 μm, the thickness is 0.22 μm, and the overclad and underclad are quartz, the gap between the waveguides of the directional couplers (2711) (2712) is 0.4. Let it be μm.

With reference to FIG. 26 (a), the coupling ratio of TE-polarized light and TM-polarized light at a wavelength of 1545 nm with respect to the length of the directional coupler at this time is shown. Here, in this 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 conventional example. In this design, the TM polarized light input from the optical waveguide (2701) is output to the optical waveguide (2703) by the directional coupler (2511) as in the conventional example.

Also, referring to FIG. 26 (b), this is the power of TM polarization input from the optical waveguide (2703) and output to the optical waveguide (2705) in a directional coupler (2712) with a length of 11 μm. It shows the ratio. For TM polarized light input to the directional coupler (2712) via the optical waveguide (2703), 80% or more of the power is output to the optical waveguide (2704), and the remaining power is output to the optical waveguide (2705) as monitor light. Will be done. At this time, the TE polarized light input from the optical waveguide (2701) and output to the optical waveguide (2705) is suppressed in two steps by the directional couplers (2711) and (2712), so that the bias that can be realized in this example can be realized. The wave-guided 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 the conventional example, almost 100% of the power is output from the optical waveguide (2702).

This makes it possible to realize a polarization beam splitter incorporating an optical branching function for TM polarization.

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

Here, it is assumed that the width of the waveguide core made of silicon is 0.5 μm, the thickness is 0.22 μm, and the overclad and underclad are quartz, and between the waveguides of the directional couplers (2811) (2821) (2822). The gap is 0.4 μm. The length of the directional coupler (2811) is 15 μm as in the conventional example, the length of the directional coupler (2821) (2822) is 7 μm, and the delay amount of the delayed waveguide (2823) (2824) is 0.065 μm. And.

Here, almost all the power of the TM polarized light input from the optical waveguide (2801) to the directional coupler (2811) is output to the optical waveguide (2803) as in the conventional example. Further, since the WINC (2812) has the same configuration as that of FIG. 21, referring to FIGS. 27 (a) and 27 (b) again, the TM polarized light input to the WINC (2812) via the optical waveguide (2803). More than 83% of the power 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 dependence of this branch fraction is suppressed as compared with the case of a simple directional coupler as in the example of FIG.

At this time, the TE polarized light input from the optical waveguide (2801) and output to the optical waveguide (2804) is suppressed in two steps by the directional coupler (2811) and WINC (2812). 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 (2801), but in the directional coupler (2811) having the same design as the conventional example, almost 100% of the power is output from (2802).

With the configurations 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 dependence of the branching ratio is further suppressed. ..

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

From the above, the optical transmission circuit (2116) (FIG. 18) or the optical reception circuit (2220) (FIG. 19) of the third embodiment monitors the power of the polarized multiple signal light by a single PD having two optical inputs. be able to. Therefore, according to the third embodiment, the optical transmission or reception circuit can be controlled by a simple and low-cost control circuit, the number of required wirings can be suppressed to a small number, and the transmission or reception optical power is excellent in monitor accuracy. A monitor can be provided.

[Fourth Embodiment]
The optical monitor circuit according to the 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) having a polarization diversity configuration including an optical monitor circuit in the fourth embodiment.

FIG. 28 shows an optical power splitter (4105), a Y-polarized light modulation circuit (4106), an X-polarized light modulation circuit (4107), a polarization rotator (4108), a polarization beam combiner (4109), and a detected diagram. Two VOAs (4110) (4111) that receive a monitor signal that cannot be shown and adjust the optical power, an optical branching circuit (4112) (4113) for the monitor light, and a PD (4115) for two optical inputs are shown.

The feature of the optical transmission circuit of the fourth embodiment is that the optical branch circuit (4112) (4113) of the monitor light is installed before the polarization rotation confluence, that is, both the optical branch circuits (4112) and (4113) are TE. Designed to operate against polarized light, the branched monitor light is connected to a single PD (4115) with two light inputs. The element circuit of the optical transmission circuit (4116) surrounded by the frame of the alternate long and short dash line is integrated on the same chip by, for example, a silicon optical wave guide.

The optical branch circuits (4112) and (4113) of the monitor light of FIG. 28 are both optical branch circuits that operate with respect to TE polarized light, and the directional coupler and WINC described in FIGS. 3 and 4 of the conventional example are used as they are. Applicable. Therefore, since the light branched by the optical branch circuit (4112) (4113) is both TE-polarized light, the PD (4115) has a signal modulated by the X-polarized light modulation circuit (optical signal power transmitted as TE-polarized light). ) And the light branched from the signal modulated by the Y-polarized light modulation circuit (optical signal power transmitted as TM polarized light) are both input with TE polarized light. As PD (4115), a germanium photodetector as described in FIGS. 10 (a) and 10 (b) can be applied. In this embodiment, unlike the other embodiments, TE light enters both of the two light inputs of the PD, so that the PD can absorb the light with a higher light coupling efficiency than in the other embodiments.

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

In FIG. 29, an optical input path (4201) from a local light source, a signal light input path (4202), a polarization beam splitter (4207), a polarization rotator (4208), an optical power splitter (4209), and Y. Optical coherent mixer for polarization (4210), Optical coherent mixer for X polarization (4211), PD (4212) (4213) that converts a demodulated optical signal into an electrical signal, Detected monitor signal (not shown) Two VOAs (4218) (4219) that receive and adjust the optical power, and a single PD (4217) with two optical inputs to detect the monitor light and an optical branch circuit (4214) (4215) of the monitor light are shown. Is done.

The feature of the optical receiving circuit of the fourth embodiment is that the optical branching circuits (4214) (4215) of the monitor light are both installed after the polarization separation and the polarization rotation, that is, the optical branching circuits (4214) (4215) are both installed. Designed to operate against TE polarized light, the waveguide branched by the optical branch circuit (4214) (4215) of the monitor light is connected to a single PD (4217) with two optical inputs. be. The element circuit of the optical receiving circuit (4220) surrounded by the frame of the alternate long and short dash line is integrated on the same chip by, for example, a silicon optical wave guide.

The optical branching circuits (4214) and (4215) of the monitor light of FIG. 29 are both optical branching circuits that operate with respect to TE polarized light, and the directional coupler and WINC described in FIGS. 3 and 4 of the conventional example are used as they are. Applicable. Therefore, since the light branched by the optical branch circuit (4214) (4215) is both TE-polarized light, the two-light input PD (4217) contains the light branched from the TE-polarized light component of the received signal and the received signal. The light branched from the TM polarized light component is input with TE polarized light. A germanium photodetector as described in FIGS. 10 (a) and 10 (b) can be applied to the PD (4217).

Specific examples and configuration examples of the present invention have been described by the above four embodiments. In either embodiment, the transmitted or received polarized multiplex signal light is divided into two polarization components separately and then converted into an electric signal for monitoring, which is biased by a single PD with two optical inputs. It is possible to monitor the power of wave multiplex signal light, it is possible to control with a simple and low-cost control circuit, the number of required wirings is kept small, and the monitoring accuracy is excellent, and the transmission or reception light power is monitored. Can be provided.

As described above, according to the present invention, in an optical transmission or optical reception circuit having a polarization diversity configuration, it is possible to control with a simpler and lower cost control circuit as compared with the conventional case, and the number of required wirings is reduced. Therefore, it is possible to realize a monitor of transmission / reception optical power with excellent monitor accuracy.

9100 …… Light source
106, 107, 1106, 1107, 2106, 2107, 4106, 4107, 9101, 9106, 9107 …… Optical modulator
210, 211, 1210, 1211, 2210, 2211, 4210, 4211, 9210, 9211 …… Optical coherent mixer
110, 111, 218, 219, 1110, 1111, 1218, 1219, 2110, 2111, 2218, 2219, 4110, 4111, 4218, 4219, 9101, 9110, 9111, 9206, 9218, 9219 …… Variable optical attenuator ( 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 …… Polarized rotation circuit
109, 1109, 2109, 4109, 9109 …… Polarized beam combiner (polarized wave 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 …… (monitor) Optical branch circuit
115, 212, 213, 217, 1115, 1212, 1213, 1217, 2115, 2212, 2213, 2217, 4115, 4212, 4213, 4217, 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 with optical branching function (polarization separation circuit)
116, 1116, 2116, 4116, 9116 …… Optical transmission circuit
220, 1220, 2220, 4220, 9203, 9220 …… Optical receiving circuit
605, 606, 2411, 2412, 2511, 2512, 2611, 2621, 2622, 2711, 2712, 2811, 2821, 2822, 9305, 9505, 9506, 9605, 9515, 9516 …… Directional coupler
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, 2703, 2704, 2705, 2801, 2802, 2803, 2804, 2805, 4301, 4302, 9301, 9302, 9303, 9304, 9501, 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 part of rib waveguide
9804 …… Slavic part of rib waveguide
9805 …… Branch circuit
9808 …… Merge circuit
2612, 2812 …… WINC

Claims (8)

A polarization separation merging circuit that separates the polarization multiplex signal light into TE polarization component and TM polarization component signals, or merges the TE polarization component and TM polarization component signals into the polarization multiplex signal light, and its In an optical circuit having a polarization diversity configuration, which is further connected to a TM polarization path and includes a polarization rotation circuit that converts TM polarization and TE polarization.
It is an optical monitor circuit that monitors the power of signal light by branching and receiving a part of the optical power as monitor light from the signal light on the main signal path.
The optical monitor circuit is
In the optical circuit having the polarization diversity configuration, a first monitor optical branch circuit for the TE polarization component is provided on the path through which the signal of the TE polarization component passes.
It has a second monitor optical branch circuit for the TM polarization component on the path through which the signal of the TM polarization component passes.
Further, it has an optical merging means for merging the monitor light branched by the optical branch circuit for the TE polarization component and the monitor light branched by the optical branch circuit for the TM polarization component.
A waveguide further connected to the output of the optical merging means and guided by the monitor light branched by the first monitor optical branch circuit and the monitor light branched by the second monitor optical branch circuit are guided. Consists of a single photodetector with two optical inputs connected to the waveguide
In the second monitor optical branching circuit for the TM polarization component, the optical waveguide for output that does not contribute to the polarization separation / merging function of the polarization separation / merging circuit is used as the branching optical waveguide, and the polarization separation is performed. An optical monitor circuit, characterized in that the merging circuit also has the function of an optical branching circuit for the TM polarization component. The polarization separation merging circuit is a polarization merging circuit,
The polarization rotation circuit is on a path through which the signal of the TM polarization component in the previous stage of the polarization merging circuit passes.
The first monitor optical 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 optical branch circuit is on the path after the polarization merging circuit, or on the path between the back of the polarization merging circuit and the polarization merging circuit, or in the front of the polarization merging circuit. The feature is that the polarization merging circuit also has the function of an optical branching circuit for the TM polarization component, with the output port on the path or not contributing to the polarization merging function of the polarization merging circuit as a branch port. The optical monitor circuit according to claim 1. The polarization separation merging circuit is a polarization separation circuit,
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 optical branch circuit is on the path through which the signal of the TE polarization component in the subsequent stage of the polarization separation circuit passes.
The second monitor optical branch circuit is on the path before the polarization separation circuit, or on the path between the latter stage of the polarization separation circuit and the polarization rotation circuit, or after the polarization rotation circuit. The feature is that the polarization separation circuit also has the function of an optical branch circuit for the TM polarization component, with the output port on the path or not contributing to the polarization separation function of the polarization separation circuit as a branch port. The optical monitor circuit according to claim 1. The optical monitor circuit is formed of a silicon-based waveguide.
The optical monitor circuit according to claim 1, wherein the polarization separation merging circuit is composed of a directional coupler or a WINC including a directional coupler and a delay circuit. The optical monitor circuit according to claim 1, wherein the two input waveguides of the single photodetector having two optical inputs are arranged so as to face each other so as to shift the optical axes. The first monitor optical branch circuit and the second monitor optical branch circuit are characterized in that they are composed of a directional coupler or a WINC including a directional coupler and a delay circuit, according to claim 1. Item 5. The optical monitor circuit according to any one of Items 5. The optical circuit having the polarization diversity configuration is
With an optical power splitter,
An optical modulation circuit for TE polarization component and TM polarization component connected to the optical power splitter,
The polarization rotation circuit further connected to the optical modulation circuit for the TM polarization component,
The optical monitor circuit according to claim 2, further comprising the optical modulation circuit for the TE polarization component and the polarization merging circuit further connected to the polarization rotation circuit. .. The optical circuit having the polarization diversity configuration is
The polarization separation circuit connected to the input port and
Having the polarization rotation circuit connected to the polarization separation circuit,
It has an optical power splitter that connects to yet another input port,
One output of the polarization separation circuit and an optical coherent mixer for the TE polarization component connected to one output of the optical power splitter.
The polarization rotation circuit and the optical coherent mixer for the TM polarization component connected to the other output of the optical power splitter.
The optical monitor circuit according to claim 3, further comprising a photodetector connected to each of the optical coherent mixers for the TE polarization component and the TM polarization component.

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