JP6075057B2 - Coherent optical receiver - Google Patents

Description

  The present invention relates to an optical communication receiver using digital coherent technology, and more particularly to power control of local light used for demodulation of received light.

  With the spread of the Internet, mobile phones and smartphones and the diversification and increase in capacity of services handled, the transmission capacity required for optical communication networks from the metro area to the backbone area is steadily increasing. In these networks, wavelength division multiplexing (WDM) is applied, and a large capacity is realized by multiplexing and demultiplexing a plurality of wavelengths in one optical fiber. The transmission capacity per wavelength is increasing from 2.5 Gbps to 10 Gbps, 40 Gbps, and 100 Gbps year by year, and the applied optical transceiver system is diversifying. In particular, high-speed optical transceivers of 40 Gbps or more are increasingly using coherent technology.

  Coherent technology is a technology that demodulates the signal superimposed on the frequency, phase, etc. by modulating the frequency, phase, etc. of the light with the signal on the transmission side and transmitting it to the local light, which is the reference on the reception side. It is. This technology has been commercialized for a long time in wireless communication, but optical communication with high carrier frequency and modulation speed has had many difficulties in implementation due to device speed and performance constraints. Realized. However, there is still a situation where characteristics as theoretical values cannot be easily obtained, and a technique for optimizing optical reception performance is required.

  In the coherent optical receiver (optical receiver), the received signal received at the signal receiving terminal and the local light output from the variable wavelength light source are combined and photoelectrically converted by the coherent receiver, and then converted to digital by the AD converter. Then, the signal is demodulated by being compared by the digital signal processing circuit.

  In coherent transmission, the received signal input to the coherent receiver and the power of the local light are important. The larger the product of both, the better, but the TIA (Trans impedance Amplifier) installed in the coherent receiver. When the differential current entering becomes large, high-frequency distortion occurs, leading to quality degradation. That is, there is an optimum value of local optical power for the received signal.

  As conventional local light control for improving transmission quality, a configuration is disclosed in which when a transmission error occurs, the power of the local light is changed to the power stored in advance (for example, Patent Document 1). ). Moreover, the structure which controls the frequency of local light is disclosed (for example, patent documents 2 thru | or 4).

JP2011-160146 Japanese Patent Laid-Open No. 5-199186 JP-A-6-29926 JP-A-7-218943

  Since the received light intensity often changes with a change in the state of the transmission path or a change in the path, it is important to secure a resistance against a change in the intensity of the received signal. However, since the conventional coherent optical receiver is configured as described above, the intensity of the local light cannot be optimized when the received signal light intensity changes, and the transmission quality of the received signal (for example, BER) There was a problem that (Bit Error Ratio) was deteriorated.

  It is an object of the present invention to obtain a coherent optical receiver that solves the above problems.

The present invention is a coherent light receiving device, a signal receiving terminal for receiving a received signal, a variable wavelength light source for outputting local light, a signal obtained by combining the received signal and the local light, and performing photoelectric conversion A coherent receiver for outputting the local light, a local light optical level adjuster for adjusting the power of the local light input to the coherent receiver, a control circuit for controlling the local light optical level adjuster, and a signal output from the coherent receiver. And an error rate detection circuit for calculating an error rate based on the reference signal, and the control circuit refers to a table indicating an optimum relationship between the power of the received signal and the local optical power stored in advance, and each of the coherent receivers is referred to So that the local light power is optimal with respect to the received signal power input to the It performs coarse adjustment to control the Le Hikari Mitsumochi level adjuster, the after the coarse adjustment, as the error rate to calculate the error rate detection circuit is minimized, controlling the local Hikari Mitsumochi level adjuster it is obtained to carry out the fine-tuning to be.

  As described above, according to the present invention, the optimum power ratio of the local light with respect to the power of the received signal input to the coherent receiver with reference to the pre-stored optimum power ratio table of the received signal and the local light. Rough adjustment to control the local light optical level adjuster to achieve the ratio, and fine adjustment to control the local light optical level adjuster to minimize the error rate. When the signal light intensity to be changed changes, the intensity of the local light can be optimized to prevent the transmission quality of the received signal from deteriorating.

It is a block diagram of the coherent optical receiver by Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the coherent optical receiver by Embodiment 1 of this invention. It is a block diagram of the coherent optical receiver by Embodiment 2 of this invention. It is a block diagram of the coherent optical receiver by Embodiment 3 of this invention. It is a block diagram of the coherent optical receiver by Embodiment 4 of this invention. It is a block diagram of the coherent optical receiver by Embodiment 5 of this invention.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an optical receiver (coherent optical receiver) in digital coherent transmission. In the figure, an optical receiver includes a control circuit 1, a local light monitor 2, a reception signal monitor 3, an error rate detection circuit 4, a local light optical attenuator 5 (local light optical level adjuster), and a reception signal light. It includes an attenuator 6 (received signal light level adjuster), a variable wavelength light source 7, a signal receiving terminal 8, a coherent receiver 9, and an AD converter 10.

  The signal reception terminal 8 inputs a reception signal from the transmission path. The local light variable wavelength light source 7 outputs local light having a wavelength corresponding to the received signal. The coherent receiver 9 multiplexes the received signal and the local light, and performs photoelectric conversion by a photodiode or the like. The AD converter 10 digitally converts the electrical signal that has been photoelectrically converted, and the error detection circuit 4 calculates the BER. The local wavelength variable wavelength light source 7, the coherent receiver 9, and the AD converter 10 are general devices used in a digital coherent transmission system.

  The reception signal optical attenuator 6 is installed between the signal reception terminal 8 and the coherent receiver 9, and adjusts the power of the reception signal. The local light attenuator 5 is installed between the local light variable wavelength light source 7 and the coherent receiver 9, and adjusts the power of the local light. The reception signal monitor 3 detects the power of the reception signal light input from the signal reception terminal 8 and input to the coherent receiver 9. The local light monitor 2 detects the power of the local light output from the variable wavelength light source 7 and input to the coherent receiver 9. Each monitor uses an element such as a PD that is generally used for optical power detection.

  The control circuit 1 refers to a table of optimal ratios of received signal and local light power stored in advance, and calculates an optimum value of local light power for the received signal. The power detected by the local optical monitor 2 and the received signal monitor 3 and the BER value calculated by the error rate detection circuit 4 are read, the local light optical attenuator 5 and the received signal optical attenuator 6 are controlled, and the received signal And adjust the local light power to the optimum value. Commercially available elements such as VOA are used for each attenuator.

  Next, the operation will be described. FIG. 2 is a control flowchart of the optical receiver of the present invention. First, an initial sequence (coarse adjustment sequence), which is an algorithm when the optical transceiver starts up, will be described. When a reception signal is input from the signal reception terminal 8 (step S11), the reception signal monitor 3 detects the power of the reception signal light (step S12). The control circuit 1 reads the value detected by the reception signal monitor 3, and adjusts the reception signal optical attenuator 6 so that the power of the reception signal becomes a predetermined value (steps S13 and S14). This value is determined from the coherent receiver 9. Next, the control circuit 1 refers to a table of optimum ratios of received signal and local light power stored in advance (step S15), and the local light has an optimum power ratio with respect to the adjusted received signal power. Or the local light optical attenuator 5 is adjusted based on the detection value of the local light monitor 2 so that the local light has an optimal power value calculated based on the received signal power and the optimal power ratio. (Step S16, Step S17).

  When the initial sequence is completed, a fine adjustment sequence (fine adjustment sequence) is executed. In the fine adjustment sequence, the control circuit 1 reads the value of the error rate detection circuit 4 (step S201), and slightly changes the power of the local light by the control of the reception signal optical attenuator 6 and the local light optical attenuator 5. (Step S206, Step S211), the point with the smallest BER value is searched (Step S207, Step S212, Step S213). The amount of power change and the number of executions when changing local light are determined by the performance of each device constituting the receiver, system requirements, operation method, and the like. Whether the fine adjustment sequence is performed periodically with the initial sequence or only the first time is determined is determined from the system requirements and the operation method.

  The operation will be described in detail below. The control circuit 1 reads the BER value calculated by the error rate detection circuit 4 (step S201), and stores the local light power (detected value of the local light monitor 2) at the completion of the initial sequence as P00 (step S202). At the same time, the value of BER is stored as B00 (step S203). Hereinafter, in this fine adjustment sequence, the BER value calculated by the error rate detection circuit 4 and read by the control circuit 1 is simply referred to as “BER value”.

  Next, the local light power is stored as P01 (step S204), and the BER value is stored as B01 (step S205). At the start of the fine adjustment sequence, P01 = P00 and B01 = B00. In step S206, the power of the local light is lowered by adjustment of the local light attenuator 5, and it is determined whether or not the BER value is deteriorated from the stored B01 (step S207). If the BER value does not deteriorate (No in S207), the process returns to S204, where the local light power after S206 adjustment is overwritten and saved as P01 (step S204), and the BER value is overwritten and saved as B01 (step S205). S206 and S207 are repeated.

  In step S207, if the BER value deteriorates (Yes in S207), or even if the BER value does not deteriorate, if the number of repetitions of step S204 to step S207 exceeds the predetermined set number, the process proceeds to step S208. The light power is returned to the stored P00.

  Further, the local light power is stored as P02 (step S209), and the BER value is stored as B02 (step S210). At the start of the fine adjustment sequence, P02 = P00 and B02 = B00. In step S211, the local light power is increased by adjustment of the local light attenuator 5, and it is determined whether or not the BER value is deteriorated from the stored B01 (step S212). If the BER value does not deteriorate (No in S212), the process returns to S209, and the local light power after S211 adjustment is overwritten and saved as P02 (step S209), and the BER value is overwritten and saved as B02 (step S210). S211 and S212 are repeated.

  In step S212, if the BER value deteriorates (Yes in S212), or even if the BER value does not deteriorate, the process proceeds to step S213 if the number of repetitions of steps S209 to S212 exceeds the predetermined set number. In step S213, the stored BER values B00, B01, and B02 are compared, and the local light power corresponding to the minimum BER value (any one of the stored P00, P01, and P02) is obtained. The power of the local light is set by the local light attenuator 5 (step S213). The local light power set in S213 is stored as L00 (step S214), and the fine adjustment sequence is terminated.

  In this way, by executing the initial sequence and the fine adjustment sequence, the characteristic variation of the TIA of the coherent receiver 9, the laser of the variable wavelength light source 7 for local light, and the PD of the received signal monitor 2 and the local light monitor 3 is absorbed. Thus, it is possible to control the power of the received signal and the local light at a ratio that provides the best BER.

  As described above, since the optical receiver according to the first embodiment operates, even when the power of the received signal light changes due to the aging of the network, the change of the transmission path, etc., the power of the received signal and the local light By optimizing both, it is possible to minimize the BER of the received signal.

  A configuration in which one or both of the local light optical attenuator 5 and the received signal optical attenuator 6 is an optical amplifier is also possible. Such an optical receiver can be adapted to systems that require adjustment by amplification rather than attenuation of light.

  Further, in order to adjust the power of the local light, it is possible to control the driving current of the variable wavelength light source 7 instead of using the local light attenuator. Such an optical receiver can omit one optical attenuator while maintaining the same control accuracy.

  Further, as an alternative to the error rate detection circuit 4, other reception performance can be used.

Embodiment 2. FIG.
FIG. 3 shows a configuration diagram of an optical receiver according to the second embodiment of the present invention. The basic configuration is the same as that of the optical receiver shown in FIG. 1, and the difference is that the local light monitor 2 is omitted. By omitting the local light monitor 2, in the initial sequence, the control circuit 1 adjusts the local light so that the local light has an optimum power ratio with respect to the adjusted received signal power. The local light optical attenuator 5 is adjusted based on the output value (initial value) of the local light variable wavelength light source 7 stored in advance instead of the power of the local light. The operation of the fine adjustment sequence is almost the same as that of the first embodiment, but since there is no local light monitor 2, instead of storing the local power, the adjustment value of the local light optical attenuator 5 is set to P00, P01, The local light power is set using the adjustment value corresponding to the minimum BER value stored as P02.

  As described above, since the optical receiver of the second embodiment operates, the control accuracy is somewhat lower than that of the first embodiment. However, depending on the conditions of the applied optical communication system, the power of the received signal light changes. However, the object of the invention of minimizing the BER of the received signal by optimizing the power of the received signal and the local light can be achieved. Further, compared with the first embodiment, the detection of the power of the local light by the local light monitor is omitted, so that the control is simplified.

Embodiment 3 FIG.
FIG. 4 shows a configuration diagram of an optical receiver according to the third embodiment of the present invention. The basic configuration is the same as that of the optical receiver shown in FIG. 1, and the difference is that the received signal optical attenuator 6 is omitted. By omitting the reception signal optical attenuator 6, the power of the reception signal is not adjusted to a predetermined value in the initial sequence. The control circuit 1 refers to a table of optimum ratios of received signal and local light power stored in advance so that the local light has an optimum power ratio with respect to the value detected by the received signal monitor 3. The local light attenuator 5 is adjusted based on the detection value of the monitor 2 for the light source. The operation of the fine adjustment sequence is the same as that in the first embodiment.

  As described above, since the optical receiver of the third embodiment operates, the control accuracy is somewhat lower than that of the first embodiment. However, depending on the conditions of the applied optical communication system, the power of the received signal light changes. In addition, the object of the present invention can be achieved by optimizing the power of the local light to prevent the deterioration of the BER of the received signal. Further, compared to the first embodiment, control of the received signal power by the received signal optical attenuator is omitted, so that control is simplified.

Embodiment 4 FIG.
FIG. 5 shows a configuration diagram of an optical receiver according to the fourth embodiment of the present invention. The basic configuration is the same as that of the optical receiver shown in FIG. 1, and the difference is that the local light monitor 2 and the received signal optical attenuator 6 are omitted. By omitting the local light monitor 2 and the reception signal optical attenuator 6, the power of the reception signal is not adjusted to a predetermined value in the initial sequence. The control circuit 1 refers to a table of optimum ratios of received signal and local light power stored in advance so that the local light has an optimum power ratio with respect to the value detected by the received signal monitor 3. The optical attenuator 5 is adjusted. At this time, the power adjustment of the local light is performed based on the output value (initial value) of the variable wavelength light source 7 for local light stored in advance, not the power of the actually detected local light.

  The operation of the fine adjustment sequence is almost the same as that of the first embodiment, but since there is no local light monitor 2, instead of storing the local power, the adjustment value of the local light optical attenuator 5 is set to P00, P01, The local light power is set using the adjustment value corresponding to the minimum BER value stored as P02.

  As described above, since the optical receiver of the fourth embodiment operates, the control accuracy is somewhat lower than that of the first embodiment, but the power of the received signal light changes depending on the conditions of the applied optical communication system. In addition, the object of the present invention can be achieved by optimizing the power of the local light to prevent the deterioration of the BER of the received signal. Further, compared with the first embodiment, the detection of the local light power by the local light monitor and the control of the received signal power by the received signal optical attenuator are omitted, so that the control is simplified.

Embodiment 5. FIG.
FIG. 6 shows a configuration diagram of an optical receiver according to the fifth embodiment of the present invention. The basic configuration is the same as that of the optical receiver shown in FIG. 1, and the difference is that the local light monitor 2 and the received signal monitor 3 are omitted. By omitting the local light monitor 2 and the reception signal monitor 3, in the initial sequence, the control circuit 1 refers to the table of the optimum ratio of the reception signal and local light power stored in advance and inputs them to the coherent receiver 9. The local light optical attenuator 5 is adjusted so that the local light power has an optimum power ratio with respect to the power of the received signal. At this time, the power of the received signal is a numerical value based on a notification from a control monitoring device (not shown). Further, the power adjustment of the local light is performed based on the output value (initial value) of the local light variable wavelength light source 7 stored in advance, instead of the actually detected local light power.

  The operation of the fine adjustment sequence is almost the same as that of the first embodiment, but since there is no local light monitor 2, instead of storing the local power, the adjustment value of the local light optical attenuator 5 is set to P00, P01, The local light power is set using the adjustment value corresponding to the minimum BER value stored as P02.

  As described above, since the optical receiver of the fifth embodiment operates, the control accuracy is somewhat lower than that of the first embodiment, but the power of the received signal light changes depending on the conditions of the applied optical communication system. In addition, the object of the present invention can be achieved by optimizing the power of the received signal and the local light to prevent the deterioration of the BER of the received signal. Further, compared to the first embodiment, the detection of the local light power by the local light monitor and the detection of the received signal power by the reception signal monitor are omitted, so that the control is simplified.

1 control circuit, 2 local light monitor, 3 received signal monitor,
4 error rate detection circuit, 5 optical level attenuator (regulator) for local light,
6 Optical level attenuator (regulator) for received signal, 7 Variable wavelength light source,
8 signal receiving terminals, 9 coherent receivers

Claims (5)

A signal receiving terminal for inputting the received signal,
Variable wavelength light source that outputs local light,
A coherent receiver that inputs the received signal and the local light, combines and outputs a photoelectrically converted signal;
An optical level adjuster for local light that adjusts the power of the local light input to the coherent receiver;
A control circuit that controls the optical level adjuster for local light, and an error rate detection circuit that calculates an error rate based on a signal output from the coherent receiver;
The control circuit refers to a table indicating the optimum relationship between the power of the received signal and the local optical power stored in advance, and the power of the local light with respect to the power of the received signal input to the coherent receiver, respectively. so that the optimum value, the make coarse adjustment to control the local Hikari Mitsumochi level adjuster, after performing the coarse adjustment, as the error rate to calculate the error rate detection circuit is minimized, the local coherent optical receiver and performs fine adjustment for controlling the Hikari Mitsumochi level adjuster. The fine adjustment is performed by comparing the error rate value at the completion of the coarse adjustment with the error rate value calculated by controlling the optical level adjuster for local light after the coarse adjustment. Controlling the optical level adjuster for local light so as to be the power of local light corresponding to the value;
  The coherent optical receiver according to claim 1. A reception signal monitor for detecting the power of the reception signal input to the coherent receiver;
The control circuit performs rough adjustment for controlling the light level adjuster for local light so that the power of local light becomes an optimum value with respect to a detection value of the monitor for received signal. The coherent optical receiver according to 1 or 2. A monitor for local light that detects the power of the local light input to the coherent receiver;
4. The coherent light according to claim 3, wherein the control circuit performs coarse adjustment to control the local light light level adjuster so that a detection value of the local light monitor becomes the optimum value. 5. Receiver device. A reception signal optical level adjuster for adjusting the power of the reception signal input to the coherent receiver;
The control circuit controls the optical level adjuster for the received signal so that the power of the received signal input to the coherent receiver becomes a predetermined value determined by the coherent receiver. The coherent optical receiver according to any one of the above.

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