JP5898125B2 - Optical receiver for coherent communication - Google Patents

Optical receiver for coherent communication Download PDF

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JP5898125B2
JP5898125B2 JP2013114432A JP2013114432A JP5898125B2 JP 5898125 B2 JP5898125 B2 JP 5898125B2 JP 2013114432 A JP2013114432 A JP 2013114432A JP 2013114432 A JP2013114432 A JP 2013114432A JP 5898125 B2 JP5898125 B2 JP 5898125B2
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JP2014236230A (en
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敏洋 伊藤
敏洋 伊藤
秀之 野坂
秀之 野坂
村田 浩一
浩一 村田
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日本電信電話株式会社
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Description

  The present invention relates to an optical communication technique, and more particularly to an optical receiver for coherent communication used for large-capacity optical communication.

In recent years, with the spread of smartphones and cloud computing, the demand for increasing the bandwidth of communication lines has been increasing year by year, and communication companies are increasing the transmission capacity of networks every year.
Against this background, research and development of technology for increasing transmission capacity in optical fibers has been actively conducted, and at present, digital coherent communication technology capable of performing transmission at 100 Gb / s at one wavelength has begun to spread. . In this 100 Gb / s digital coherent communication, transmission exceeding 1000 km is possible, and widespread use is promising in the backbone optical network.

The 100 Gb / s digital coherent optical receiver (optical receiver module), which is currently popularized, has been standardized by a standardization organization OIF (Optical Internet Forum) (see, for example, Non-Patent Document 1).
FIG. 5 is a block diagram showing a conventional optical receiver for coherent communication. FIG. 6 is an explanatory view showing the standardized module size of the optical receiver. The size on the plane is 27 mm wide and 40 mm long.

  In such a conventional technology, the optical receiver for coherent communication is a planar lightwave circuit PLC comprising a polarization beam splitter PBS (Polarization Beam Splitter), a beam splitter BS (Beam Splitter), and a 90-degree optical hybrid OH (Optical Hybrid). (Planar Lightwave Circuit), a photodiode array PDA (Photo-Diode Array) having eight photodiodes PD (Photo-Diode), two for each of the four channels, and a total of four channels A transimpedance amplifier IC (TIA-IC) having a differential transimpedance amplifier TIA and a DC block DCB for removing a DC output component.

The cathode (cathode) terminal of each PD is connected to an independent power supply terminal PS, and an external power supply VPD is supplied through the power supply terminal PS. The reason why the power supply terminal PS is independent for each PD is to measure the photocurrent flowing through each PD and confirm the variation in these photocurrents.
At this time, in a normal use state, a positive operating power supply such as +3.3 V is supplied to the cathode terminal of each PD. Although the bias voltage value of the TIA signal input terminal depends on the IC, for example, when it is designed to be about +1 V, the PD requires a reverse bias potential of +2.3 V (in contrast to the anode, which is necessary for optical reception). A positive voltage) is applied to the cathode.

"Implementation Agreement for Integrated Dual Polarization Intradyne Coherent Receivers", Optical Internet Forum, IA # OIF-DPC-RX-01.1, Septermber 20, 2011, OIF-2010.442.02 Yves Painchaud, Michel Poulin, Michel Morin, and Michel Tetu, "Performance of balanced detection in a coherent receiver", OPTICS EXPRESS, Vol. 17, Issue 5, pp. 3659-3672 (2009)

In such coherent communication, in recent years, further increase in capacity has been demanded, and it is required to mount more communication devices and communication modules in the same mounting space. For this purpose, it is necessary to greatly reduce the size of each module including the optical receiver.
FIG. 7 is a diagram showing an ultra-compact optical receiver according to a future generation. In this generation of optical receiver, it is required that the module be of this size (width 12 mm, length 20 mm). However, when trying to secure the same number of 40 DC pins as in the conventional package with such a package, the DC terminal width and the DC terminal interval are very narrow widths and intervals of less than 0.5 mm. Since optical receivers contain optical components that cannot withstand high temperatures such as fibers, reflow mounting cannot be performed, and manual mounting is required. There has been a problem that it tends to cause a decrease and a yield decrease, resulting in an increase in cost.

In order to reduce the number of terminals, it is beneficial not only to digitize the control terminals but also to share eight PD power supplies. Also, reducing the number of terminals here also leads to a reduction in the internal wiring, control circuit, and number of terminals of the transceiver module including the optical receiver, leading to miniaturization and cost reduction of the transceiver module.
When the PD power supply is shared in the optical receiver in this way, the eight power supply terminals are not brought out independently as in Non-Patent Document 1 described above.
Moreover, in addition to the problem of the number of terminals, another problem of an increase in crosstalk (interference) between channels arises with such miniaturization. In particular, in a TIA in which 2 or 4 channels are integrated for miniaturization, crosstalk between channels increases, and a signal of a certain channel deteriorates transmission characteristics of adjacent channels as noise.

Therefore, in order to reduce the size of the optical receiver under such circumstances, it is necessary to first quantify the crosstalk between the channels, and further, if possible, to remove this. At this time, in order to accurately measure the crosstalk between channels, it is necessary to disable the specific PD by controlling the PD of any channel on / off.
However, in the configuration in which the operation power supply is shared as described above, the PDs of all channels are always operated. That is, a specific PD cannot be invalidated by changing the operating power supply.

  In such a case, a method of shutting down (stopping output) the TIA instead of the PD at the time of crosstalk evaluation can be considered. However, according to this method, the output of each channel of the TIA is stopped at the output stage of the TIA of the channel for measuring the leaked output from the other channel. For this reason, the component leaking into the output measurement channel inside the TIA, that is, the crosstalk from the input stage to the output stage cannot be evaluated, and in a multi-channel TIA-IC chip equipped with a plurality of differential TIA circuits. There was a problem that inter-channel crosstalk could not be accurately measured.

  An object of the present invention is to solve such problems, and an object of the present invention is to provide an optical receiver for coherent communication that can accurately measure crosstalk between channels.

In order to achieve such an object, an optical receiver for coherent communication according to the present invention includes a DP-QPSK (Dual Polarization Quadrature Phase Shift Keying) method, a DP-QAM ( Dual Polarization Quadrature Amplitude Modulation (Coherent communication optical receiver used in coherent communication), a polarization beam splitter (PBS) that splits input signal light by polarization A beam splitter (BS) for branching the local light, and two 90-degree optical hybrid circuits that demodulate QPSK or QAM signals from these branched lights and output signals as two channels per one A planar lightwave circuit and two photodiodes provided for each channel, and an optical signal separated by the planar lightwave circuit; A photodiode array that converts the signal into an input photocurrent signal and outputs the received voltage signal by differentially amplifying the two input photocurrent signals output from the photodiode corresponding to the channel for each channel. A transimpedance amplifier IC for outputting, and the transimpedance amplifier IC individually controls the supply of operation power to each photodiode according to a control signal input from the outside. A control unit, and the power supply control unit is provided for each photodiode, and switches either the operating power source or the invalid power source that disables the photodiode to the cathode terminal of the photodiode. A switch to be supplied and a switch designated by the control signal among the switches By switching control, it is intended to include a supply control circuit for controlling the switching supply of the operating power supply or said disable power to the photodiode.

Other optical receivers for coherent communication according to the present invention include DP-QPSK (Dual Polarization Quadrature Phase Shift Keying) method and DP-QAM (Dual Polarization Quadrature Amplitude Modulation): Optical receiver for coherent communication used in dual-polarization quadrature amplitude modulation (coherent communication) system, polarization beam splitter (PBS) that splits input signal light by polarization, branching local light A beam splitter (BS), and a planar lightwave circuit composed of two 90-degree optical hybrid circuits that demodulate a QPSK or QAM signal from these branched lights and output signals as two channels per one; Two photodiodes are provided for each channel, and an optical signal separated by the planar lightwave circuit is used as an input photocurrent signal. A photodiode array that outputs the converted signal, and a transimpedance amplifier IC that differentially amplifies two input photocurrent signals output from the photodiode corresponding to the channel and outputs a received voltage signal for each channel. The transimpedance amplifier IC includes a power supply control unit that individually controls the supply of operation power to the photodiodes in accordance with a control signal input from the outside; The supply control unit is provided for each of the photodiodes, one end of which is commonly connected to the operation power supply, and the other end of which is connected to the cathode terminal of the photodiode, and among the variable resistance elements, The photodiode is controlled by controlling the resistance value of the variable resistance element specified by the control signal. And a supply control circuit for controlling a resistance value at the time of supplying the operation power.

According to the present invention, at the time of crosstalk evaluation, the PD corresponding to the channel other than the evaluation target is set in an invalid state, so that the crosstalk is evaluated while all the portions after the TIA located after the PD are normally operated. can do.
This makes it possible to evaluate the crosstalk within the TIA, that is, from the input stage to the output stage, as compared with the case where the TIA is shut down and the TIA output of the channel other than the evaluation target is stopped at the time of crosstalk evaluation. . Therefore, it is possible to accurately measure the crosstalk between channels in the IC when the multi-channel TIA is used.
Further, according to the present embodiment, in the case of crosstalk evaluation, a transmission signal can be input as a signal, and crosstalk can be evaluated with output amplitude. However, CW (Continuous Wave) light is incident as a signal. The frequency dependence of crosstalk can also be measured by making a beat signal having a frequency difference from the local light incident on the optical receiver.

Furthermore, by inputting the intensity-modulated light into the signal input fiber, enabling only one PD, and measuring the intensity and phase of the output intensity-modulated signal, only the inter-channel crosstalk of the optical receiver. Instead, the frequency characteristics of the size and phase of the transfer in the channel can be measured.
Alternatively, the frequency dependence of the magnitude and phase of crosstalk and transfer can also be obtained by branching one intensity-modulated light and making it incident as local light and signal light and observing the amplitude and phase of the output signal. (For example, refer nonpatent literature 2 etc.).
Furthermore, using the obtained crosstalk frequency characteristic, it is possible to improve the transmission characteristic by compensating the crosstalk characteristic in a DSP (Digital Signal Processor) connected to the subsequent stage of the optical receiver.

It is a block diagram which shows the structure of the optical receiver for coherent communication concerning 1st Embodiment. It is a block diagram which shows the structure of the power supply control part concerning 1st Embodiment. It is a block diagram which shows the structure of the power supply control part concerning 2nd Embodiment. It is a block diagram which shows the structure of the power supply control part concerning 3rd Embodiment. It is a block diagram which shows the conventional optical receiver for coherent communication. It is explanatory drawing which shows the size of the standardized optical receiving package. It is explanatory drawing of the micro optical receiver concerning a future generation.

Next, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
First, an optical receiver 10 for coherent communication according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of an optical receiver for coherent communication according to the first embodiment.

  As shown in FIG. 1, the coherent communication optical receiver 10 includes, as main functional units, a planar lightwave circuit PLC (Planar Lightwave Circuit), a photodiode array PDA (Photo-Diode Array), a transimpedance amplifier IC ( TIA-IC) and DC block DCB.

  The PLC includes a polarization beam splitter PBS (Polarization Beam Splitter), a beam splitter BS (Beam Splitter), and a 90-degree optical hybrid OH (Optical Hybrid), and performs coherent detection that interferes with local light and received signal light. Thus, each of the four channels CH1 to CH4 has a function of outputting two optical signals indicating normal phase / reverse phase.

  The PDA has a total of eight photodiodes PD1p, PD1n, PD2p, PD2n, PD3p, PD3n, PD4p, and PD4n provided for each optical signal obtained by the PLC, and is obtained by photoelectrically converting these optical signals. Each of the input photocurrent signals is output.

  The TIA-IC includes an IC in which a differential transimpedance amplifier TIA (TransImpedance Amplifier) and a power supply control unit PCNT are integrated on the same chip for each of the channels CH1 to CH4, and includes photodiodes PD1p, PD1n, PD2p, and PD2n. , PD3p, PD3n, PD4p, PD4n, the function of differentially amplifying and outputting the input photocurrent signal for each of the channels CH1 to CH4, and the function of individually controlling the power supply to these photodiodes Have.

  The DCB has a function of removing a DC output component from the differential output signal of each TIA and outputting it from the signal output terminals Q1p, Q1n, Q2p, Q2n, Q3p, Q3n, Q4p, and Q4n to the outside of the module.

  As coherent communication to which the optical receiver 10 for coherent communication according to the present invention is applied, for example, DP-QPSK (Dual Polarization Quadrature Phase Shift Keying) method, DP-QAM (DP-QAM) Dual Polarization Quadrature Amplitude Modulation).

  This coherent communication optical receiver 10 has a local light source that outputs local light having substantially the same wavelength as the signal light received inside, and converts this local light into an electric signal by interfering with the received signal light. So-called coherent detection is performed. At this time, since coherent detection has strong polarization dependence, a single optical receiver can receive only signal light having the same polarization state as that of local light. For this reason, a polarization beam splitter PBS is provided in the input stage to separate the received signal light into two orthogonal X and Y polarization components, and then a 90 degree optical hybrid provided for each of these X and Y polarizations. OH causes interference with local light.

  Thereby, from the 90-degree optical hybrid OH (X) of X polarization, two optical outputs (channel CH # 1, I component) of the normal phase / reverse phase in which both lights interfere with each other in the same phase and the opposite phase, A total of four output lights of two light outputs (channel CH # 2, Q component) of normal phase / reverse phase obtained by causing both lights to interfere with each other at orthogonal (90 degrees) and inverse orthogonal (-90 degrees) are obtained. Similarly, from the 90-degree optical hybrid OH (Y) of Y polarization, two optical outputs (channel CH # 3, I component) of normal phase / reverse phase in which both lights interfere with each other in the same phase and opposite phase, A total of four output lights of two optical outputs (channel CH # 4, Q component) of normal phase / reverse phase obtained by causing both lights to interfere at orthogonal (90 degrees) and inverse orthogonal (-90 degrees) are obtained.

  The four optical outputs of X polarization are received by PD1p, PD1n, PD2p, and PD2n individually provided for each of these optical outputs and converted into current signals of normal phase / reverse phase, respectively, and then channel CH # 1, Differential amplification is performed by TIA1 and TIA2 provided for each channel CH # 2. Accordingly, a reception signal (voltage signal) corresponding to the I component of X polarization is output from TIA1, and a reception signal (voltage signal) corresponding to the Q component of X polarization is output from TIA2.

  Similarly, the four optical outputs of Y-polarized light are received by PD3p, PD3n, PD4p, and PD4n individually provided for each of these optical outputs and converted into current signals of normal phase / reverse phase, and then channel CH # 3 and differentially amplified by TIA3 and TIA4 provided for each channel CH # 4. Thus, a reception signal (voltage signal) corresponding to the I component of Y polarization is output from TIA3, and a reception signal (voltage signal) corresponding to the Q component of Y polarization is output from TIA4.

In this embodiment, in the optical receiver 10 for coherent communication, the operation power supply VPD is supplied to each PD in the TIA-IC according to the control signal S input from the outside of the module to the control terminal ST. A power supply control unit PCNT that is individually controlled is provided.
That is, the cathode (cathode) terminal of each PD is connected to the power supply terminal PS corresponding to the PD in the power supply control unit PCNT, and the anode (anode) terminal of each PD is the TIA-IC. The PD is connected to a signal input terminal TIN corresponding to the PD.

  Accordingly, the supply of the operating power supply VPD to each PD is individually controlled by the power supply control unit PCNT according to the control signal S input from a host device such as a PC connected outside the module. Accordingly, any PD can be stopped by inputting the control signal S to the coherent communication optical receiver 10 at the time of crosstalk evaluation.

FIG. 2 is a block diagram illustrating a configuration of the power supply control unit according to the first embodiment.
The power supply control unit PCNT according to the present embodiment includes a power supply changeover switch PSW, a supply control circuit CNT, and a PD protection circuit PV as main circuit units.

The power supply changeover switch PSW includes a plurality of switches provided for each PD, and has a function of individually controlling the supply of the operation power supply VPD to the PD in accordance with an instruction from the supply control circuit CNT.
In this embodiment, since eight PDs are provided, the PSW is also provided with eight switches corresponding to these PDs. One end of these switches is commonly connected to a power input terminal PIN to which the operation power supply VPD is input, and the other end of these switches is connected to the power supply terminal PS corresponding to the PD via the PD protection circuit PV. It is connected.

  The supply control circuit CNT includes a general logic circuit such as a decoder or a latch. According to a digital / serial control signal S input to the control terminal ST from the outside of the module, the power supply changeover switch PSW includes: The switch corresponding to the PD designated by the control signal S has a function of ON / OFF control with a digital signal.

The PD protection circuit PV includes an overcurrent protection circuit provided for each PD, and has a function of suppressing overcurrent with respect to a current supplied from the VPD to the PD.
Each overcurrent protection circuit has one end connected to the other end of the switch corresponding to the PD of the PSW, the other end connected to the PS corresponding to the PD, and one end connected to the other end of the R. The capacitor C is connected to the other end and connected to the ground potential. The overcurrent protection circuit is not limited to these, and other circuit configurations may be used.

[Operation of First Embodiment]
Next, the operation of the coherent communication optical receiver 10 according to the present embodiment will be described with reference to FIGS.

  First, during a normal optical reception operation, each switch provided in the power supply switching switch PSW of the power supply control unit PCNT is held in a closed on state. Therefore, the operation power VPD input to the power input terminal PIN is supplied to the PD protection circuit PV through these switches, and after stabilization, is supplied from the power supply terminal PS to the cathode terminal of each PD. .

At this time, when a positive power supply of + 3.3V, for example, is used as the VPD, the bias potential of the signal input terminal TIN of the TIA is normally designed to be about + 1V. A reverse bias of 3 V (positive voltage on the cathode) is applied.
As a result, the optical signal output from the 90-degree optical hybrid OH of the planar lightwave circuit PLC is received by the PD, converted into a current signal, input to the signal input terminal TIN of the corresponding TIA, and differentially converted into a voltage signal. After the amplification, the DC bias is removed by the DC block DCB and the received signal is output from the output terminal Q to the outside of the module.

On the other hand, at the time of crosstalk evaluation, the coherent communication optical receiver 10 is instructed from the outside of the module to supply power only to the PD corresponding to the input channel for evaluating crosstalk to the control terminal ST, and to other channels. A control signal S instructing to stop power supply is input to the corresponding PD.
In response to this control signal S, the supply control circuit CNT of the power supply control unit PCNT closes the switch corresponding to the PD instructed to supply power among the power supply changeover switches PSW and turns it on, An instruction to open the switch corresponding to the PD to turn it off is output. In response to this instruction, the PSW switches each switch to control the supply of the operation power VPD to each PD.

  As a result, the VPD is supplied only to the PD corresponding to the crosstalk measurement target channel, and a high-frequency optical modulation signal can be received. Also, the supply of VPD to the PD corresponding to the other channel is stopped, the cathode terminal of the PD is released, and a response to a high-frequency optical modulation signal is caused due to an increase in electric capacity between the terminals of the PD. And the function is substantially disabled.

  For example, when evaluating crosstalk from channel CH # 1 to channel CH # 2, power is supplied only to PD1p and PD1n corresponding to channel CH # 1, and other channels CH # 2 and channel CH # 3 are supplied. The control signal S for stopping the power supply to the PD2p, PD2n, PD3p, PD3n, PD4p, and PD4n of the channel CH # 4 is input. Thereby, only the PD1p and PD1n of the channel CH # 1 operate to convert the input optical signal into a current signal and output it to the TIA1.

  At this time, since PD2p, PD2n, PD3p, PD3n, PD4p, and PD4n of other channels are in an invalid state, no current signal is output from these PDs. For this reason, even if TIA2, TIA3, and TIA4 are operated, they are not affected by the current signals from PD2p, PD2n, PD3p, PD3n, PD4p, and PD4n. Therefore, it is possible to evaluate crosstalk from channel CH # 1 to channel CH # 2 including crosstalk in circuits after TIA2, TIA3, and TIA4.

[Effect of the first embodiment]
As described above, the present embodiment is provided with the power supply control unit PCNT that individually controls the supply of the operation power supply VPD to each PD in accordance with the control signal S input to the control terminal ST from the outside of the module. is there.
Therefore, at the time of crosstalk evaluation, by disabling the PD corresponding to the channel other than the evaluation target, it is possible to evaluate the crosstalk while all the portions after the TIA located after the PD are normally operated. .

  This makes it possible to evaluate the crosstalk within the TIA, that is, from the input stage to the output stage, as compared with the case where the TIA is shut down and the TIA output of the channel other than the evaluation target is stopped at the time of crosstalk evaluation. . Therefore, it is possible to accurately measure the crosstalk between channels in the IC when the multi-channel TIA is used.

  Further, according to the present embodiment, in the case of crosstalk evaluation, a transmission signal can be input as a signal, and crosstalk can be evaluated with output amplitude. However, CW (Continuous Wave) light is incident as a signal. The frequency dependence of crosstalk can also be measured by making a beat signal having a frequency difference from the local light incident on the optical receiver.

  Further, the intensity-modulated light is input to the signal input fiber, and seven of the eight PDs are invalidated, thereby enabling only one PD, and the intensity and phase of the output intensity-modulated signal. By measuring the above, it is possible to measure not only the crosstalk between channels of the optical receiver but also the frequency characteristics of the magnitude and phase of the transfer in the channel.

Alternatively, the frequency dependence of the magnitude and phase of crosstalk and transfer can also be obtained by branching one intensity-modulated light and making it incident as local light and signal light and observing the amplitude and phase of the output signal. (For example, refer nonpatent literature 2 etc.).
Furthermore, using the obtained crosstalk frequency characteristic, it is possible to improve the transmission characteristic by compensating the crosstalk characteristic in a DSP (Digital Signal Processor) connected to the subsequent stage of the optical receiver.

  In the present embodiment, since the power supply control unit PCNT is mounted in the multi-channel TIA-IC chip on which a plurality of differential amplifiers are mounted, a circuit unit separate from the multi-channel TIA-IC chip. Thus, the coherent communication optical receiver 10 can be downsized as compared with the case where the power supply control unit PCNT is configured.

  In the present embodiment, since the power supply control unit PCNT includes the PD protection circuit PV and is mounted on the multi-channel TIA-IC chip, the circuit unit is separate from the multi-channel TIA-IC chip. Compared with the case where the protection circuit PV is configured, the coherent communication optical receiver 10 can be downsized.

  In the present embodiment, each switch in the power supply changeover switch PSW may be digitally controlled or analog controlled. Further, the operation power supply VPD supplied during normal operation may be a power supply common to the TIA.

  In FIG. 2, the case where the power supply control unit PCNT collectively controls the operation power supply control for the photodiodes PD of all the channels has been described as an example. However, the present invention is not limited to this. For example, the PCNT may be configured by a channel-specific power supply control unit provided for each channel, and the channel-specific power supply control unit may individually control the operation power supply to the PD regarding the corresponding channel. Thereby, the operation power supply control for the PD can be optimized for each channel. This configuration can also be applied to FIGS. 3 and 4 to be described later.

As a specific configuration example of the power supply control unit for each channel, in FIG. 2, among the power supply changeover switches PSW, two switches related to the channel and these switches are turned on / off according to the control signal S. The channel-specific supply control circuit and the PD protection circuit PV include two sets of resistance elements R and capacitance elements C related to the channel. In this case, S is commonly input to each channel supply control circuit.
Note that the channel-specific power supply control unit is not limited to this configuration example. For example, the channel-specific power supply control circuit may be common to all channels as in FIG. Similarly, it may be common to all channels.

[Second Embodiment]
Next, an optical receiver 10 for coherent communication according to the second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a block diagram illustrating a configuration of a power supply control unit according to the second embodiment.

  In the first embodiment, the case where the cathode terminal of the PD is set to the release state when any PD is set to the invalid state in the power supply control unit PCNT has been described as an example. In the present embodiment, when the power supply control unit PCNT disables an arbitrary PD, the disabling power supply VSUB for disabling the PD is used as the disabling power source VSUB for disabling the PD. The case where it applies to a cathode terminal is demonstrated. In the optical receiver 10 for coherent communication according to the present embodiment, the configuration other than the power supply control unit PCNT is the same as that of the first embodiment, and detailed description thereof is omitted here.

That is, in the present embodiment, the power supply control unit PCNT includes the invalidation power generation unit PSUB that generates the invalidation power VSUB for disabling the PD from the operation power supply VPD input from the power input terminal PIN. Is provided.
In the example of FIG. 3, the case where the invalidation power generation unit PSUB is composed of a potentiometer that generates VSUB by dividing VPD with a resistance element is shown, but the present invention is not limited to this. Other circuits such as an analog converter and an operational amplifier may be used.

In the present embodiment, the power supply changeover switch PSW is a switch provided for each PD, and switches either the operation power supply VPD or the invalidation power supply VSUB in accordance with an instruction from the supply control circuit CNT. A supply switch is provided.
In the example of FIG. 3, a case of 2 × 8 switches using two switches for each PD is shown. In accordance with an instruction from the supply control circuit CNT, the two switches are complementarily turned on / off. Controlled off. The PSW switch is not limited to this, and other circuits such as a 2-input / 1-output changeover switch may be used.

  As the invalidation power supply VSUB, for example, a potential at which forward bias (positive voltage at the anode [anode] with respect to the cathode [cathode]) is applied to both ends of the PD may be used. For example, when a voltage of +0.5 V with respect to the ground potential GND is applied as VSUB to the cathode terminal of the PD, the bias of the TIA signal input terminal TIN is normally designed to be about +1 V with respect to the GND. Is applied with a forward bias (positive bias to the anode with respect to the cathode) of 0.5V.

As a result, the PD can be invalidated in the same manner as in the first embodiment, and at the time of crosstalk evaluation, the PD corresponding to the channel other than the evaluation target is set in the invalid state, so that the PD is in a later stage. Crosstalk can be evaluated while all the portions after the TIA that are positioned are normally operated.
This makes it possible to evaluate the crosstalk within the TIA, that is, from the input stage to the output stage, as compared with the case where the TIA is shut down and the TIA output of the channel other than the evaluation target is stopped at the time of crosstalk evaluation. . Therefore, it is possible to accurately measure the crosstalk between channels in the IC when the multi-channel TIA is used.

In the present embodiment, each switch in the power supply changeover switch PSW may be digitally controlled or analog controlled. Further, instead of the 2 × 8 switch, an 8 × 8 switch may be provided to apply different voltages individually adjusted for each PD.
Further, the operation power supply VPD supplied during normal operation may be the same power supply as the TIA, and the invalidation power supply VSUB can be supplied from outside the module.

[Third Embodiment]
Next, a coherent communication optical receiver 10 according to a third exemplary embodiment of the present invention will be described with reference to FIG. FIG. 4 is a block diagram illustrating a configuration of a power supply control unit according to the third embodiment.

  In the first embodiment, the case where the switch for controlling the supply of VPD to the PD is used as the power supply changeover switch PSW of the power supply control unit PCNT has been described as an example. In this embodiment, a case where a variable resistance element is used instead of these switches will be described. In the optical receiver 10 for coherent communication according to the present embodiment, the configuration other than the power supply control unit PCNT is the same as that of the first embodiment, and detailed description thereof is omitted here.

In other words, in the present embodiment, the power supply changeover switch PSW has a plurality of terminals, one end of which is commonly connected to the VPD and the other end is connected to the power supply terminal PS corresponding to the PD via the PD protection circuit PV. A variable resistance element (variable resistance array) is provided.
When invalidating each PD, each variable resistance element is adjusted to a resistance value at which the voltage drop due to the photocurrent flowing during use or inspection becomes approximately the same as the operating power supply voltage and the PD is invalidated.

  For example, when the operating power supply voltage is + 3.3V and the optical input is about −20 dBm, if the photosensitivity of a general optical receiver is 0.1 A / W, the photocurrent flows through about 10 uA in one PD. In this case, if the variable resistor is set to about 500 kΩ, for example, when a photocurrent flows, the voltage applied to the variable resistor exceeds the operating power supply voltage and the PD becomes forward biased, so this photocurrent actually flows. The PD is substantially invalidated.

  When the PD is operated normally without being invalidated, the resistance element R of the PD protection circuit PV can be used by setting the variable resistance to about 100Ω. In addition, by setting a variable resistance, the value of the protective resistance can be changed depending on the use, that is, the maximum normal light intensity assumed, and the optical receiver 10 for coherent communication having wide adaptability can be realized. It becomes possible.

[Extended embodiment]
The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. In addition, each embodiment can be implemented in any combination within a consistent range.

  DESCRIPTION OF SYMBOLS 10 ... Optical receiver for coherent communication, PLC ... Planar light wave circuit, PBS ... Polarization beam splitter, BS ... Beam splitter, OH ... 90 degree optical hybrid, PDA ... Photodiode array, PD1p, PD1n, PD2p, PD2n, PD3p, PD3n, PD4p, PD4n ... photodiode, TIA-IC ... transimpedance amplifier IC, TIA1, TIA2, TIA3, TIA4 ... transimpedance amplifier, TIN ... signal input terminal, PCNT ... power supply control unit, PS ... power supply terminal, PSW ... Power supply changeover switch, CNT ... Supply control circuit, PV ... PD protection circuit, PSUB ... Disabling power generation unit, VPD ... Operating power supply, VSUB ... Disabling power supply.

Claims (2)

  1. Used in DP-QPSK (Dual Polarization Quadrature Phase Shift Keying) and DP-QAM (Dual Polarization Quadrature Amplitude Modulation) coherent communications An optical receiver for coherent communication,
    A polarization beam splitter (PBS) for branching the input signal light by polarization, a beam splitter (BS) for branching local light, and a QPSK or QAM signal demodulated from these branched lights, 2 per signal A planar lightwave circuit composed of two 90-degree optical hybrid circuits that output as signals of two channels;
    A photodiode array that includes two photodiodes provided for each channel, converts the optical signal separated by the planar lightwave circuit into an input photocurrent signal, and outputs the input photocurrent signal;
    For each channel, a transimpedance amplifier IC that differentially amplifies two input photocurrent signals output from the photodiode corresponding to the channel and outputs a received voltage signal,
    The transimpedance amplifier IC includes a power supply control unit that individually controls the operation power supply to the photodiodes for each photodiode according to a control signal input from the outside .
    The power supply controller is
    A switch provided for each of the photodiodes, and a switch that supplies either one of the operating power source and the invalid power source that disables the photodiode to the cathode terminal of the photodiode;
    A coherent communication comprising: a supply control circuit that controls switching of the operating power supply or the reactive power supply to the photodiode by switching control of the switch designated by the control signal among the switches. Optical receiver.
  2. Used in DP-QPSK (Dual Polarization Quadrature Phase Shift Keying) and DP-QAM (Dual Polarization Quadrature Amplitude Modulation) coherent communications An optical receiver for coherent communication,
    A polarization beam splitter (PBS) for branching the input signal light by polarization, a beam splitter (BS) for branching local light, and a QPSK or QAM signal demodulated from these branched lights, 2 per signal A planar lightwave circuit composed of two 90-degree optical hybrid circuits that output as signals of two channels;
    A photodiode array that includes two photodiodes provided for each channel, converts the optical signal separated by the planar lightwave circuit into an input photocurrent signal, and outputs the input photocurrent signal;
    For each channel, a transimpedance amplifier IC that differentially amplifies two input photocurrent signals output from the photodiode corresponding to the channel and outputs a received voltage signal,
    The transimpedance amplifier IC includes a power supply control unit that individually controls the operation power supply to the photodiodes for each photodiode according to a control signal input from the outside.
    The power supply controller is
    Provided for each photodiode, a variable resistance element having one end commonly connected to the operating power supply and the other end connected to the cathode terminal of the photodiode;
    By controlling the resistance value of the variable resistance element specified by the control signal among the variable resistance elements, the resistance value at the time of supplying, stopping, and supplying the operating power to the photodiode is controlled. And an optical receiver for coherent communication.
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