JP6753831B2 - Optical receiver and frequency shift compensation method - Google Patents

Description

The present invention relates to an optical receiver and a frequency shift compensation method.

In an optical communication system, the clocks used by an optical transmitter and an optical receiver are different from each other. Therefore, the optical receiver needs to synchronize the sampling frequency corresponding to the clock of the optical receiver with the sampling frequency corresponding to the clock of the optical transmitter.

FIG. 13 is a diagram showing an example of the configuration of a conventional optical receiver. A conventional optical receiver has a sampling frequency deviation amount monitor that detects a sampling frequency deviation amount (hereinafter referred to as "sampling frequency deviation amount") and a sampling frequency deviation amount compensator that is an individual circuit that compensates for the sampling frequency deviation amount. And.

The sampling frequency deviation monitor detects the sampling frequency deviation of the received signal. The sampling frequency deviation compensation unit compensates for the detected sampling frequency deviation (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2010-268404

As described above, the conventional optical receiver cannot compensate for the sampling frequency deviation unless it is provided with an individual circuit for compensating for the sampling frequency deviation. Therefore, the conventional optical receiver has a problem that the sampling frequency deviation amount cannot be compensated when the circuit scale for compensating the sampling frequency deviation amount is small.

In view of the above circumstances, the present invention provides an optical receiver and a frequency deviation compensation method capable of compensating for the sampling frequency deviation even if the circuit scale for compensating the sampling frequency deviation is small. It is an object.

In one aspect of the present invention, the tap coefficient of the detection unit that detects the deviation amount of the sampling frequency of the main signal output from the frequency domain filter and the circuit that shifts the sample phase in the main signal is updated based on the deviation amount. It is an optical receiver provided with an adaptive equalization unit.

One aspect of the present invention is the above-mentioned optical receiver, and the tap coefficient is a value based on a shift amount of a sample phase.

One aspect of the present invention is the above-mentioned optical receiver, in which the tap coefficient is a value based on the sum of the shift amount of the sample phase and the shift amount of less than the sample phase.

One aspect of the present invention is the above-mentioned optical receiver, which is a phase shift amount acquisition unit that acquires a sample phase shift amount based on the shift amount, and adjusts the clock phase based on the sample phase shift amount. It is further provided with a clock adjusting unit.

One aspect of the present invention is a frequency shift compensation method executed by an optical receiver, in which a step of detecting a shift in the sampling frequency of a main signal output from a frequency domain filter and a sample phase in the main signal are set. This is a frequency shift compensation method including a step of updating the tap coefficient of the shifting circuit based on the shift amount.

According to the present invention, it is possible to compensate for the sampling frequency deviation even if the circuit scale for compensating for the sampling frequency deviation is small.

It is a figure which shows the example of the structure of the optical communication system in 1st Embodiment. It is a figure which shows the 1st example of the structure of the sampling frequency deviation amount monitor in 1st Embodiment. It is a figure which shows the 2nd example of the structure of the sampling frequency deviation amount monitor in 1st Embodiment. It is a figure which shows the 3rd example of the structure of the sampling frequency deviation amount monitor in 1st Embodiment. It is a figure which shows the 4th example of the structure of the sampling frequency deviation amount monitor in 1st Embodiment. It is a figure which shows the example of the update period of the tap coefficient of a phase shift in 1st Embodiment. It is a figure which shows the example of the structure of the clock adjustment device of an optical receiver in 1st Embodiment. It is a flowchart which shows the example of the operation of the optical receiver in 1st Embodiment. It is a figure which shows the example of the structure of the optical communication system in 2nd Embodiment. It is a figure which shows the example of the tap coefficient of a phase shift in 2nd Embodiment. It is a figure which shows the example of the update period of the tap coefficient of a phase shift in 2nd Embodiment. It is a flowchart which shows the example of the operation of the optical receiver in 2nd Embodiment. It is a figure which shows the example of the structure of the conventional optical receiver.

Embodiments of the present invention will be described in detail with reference to the drawings.
(First Embodiment)
FIG. 1 is a diagram showing an example of the configuration of the optical communication system 1a. The optical communication system 1a includes an optical transmitter 2, a transmission line 3, and an optical receiver 4a. The optical transmitter 2 converts a data signal into an optical signal (optical modulation signal). The optical transmitter 2 transmits an optical signal to the optical receiver 4a via a transmission line 3 such as an optical fiber.

The optical receiver 4a receives an optical signal via the transmission line 3. The optical receiver 4a includes a receiver 40, an ADC 41, a frequency domain filter 42 (FEQ: Frequency domain Equalizer), a sampling frequency shift amount monitor 43, and a time domain filter 44a (adaptive equalizer) (AEQ: Adaptive Equalizer). ) And a decoding unit 45. The optical receiver 4a further includes a phase shift amount calculation unit 46 as one of the functional units of the device (clock adjustment device) that adjusts the phase of the clock.

The receiving unit 40 includes a laser module and a photoelectric converter. The receiving unit 40 causes the optical modulation signal received via the transmission line 3 to interfere with the station light emission output from the laser module. The receiving unit 40 demodulates the optical modulation signal into a baseband signal (electrical signal).

The ADC 41 (analog-to-digital converter) converts the baseband signal into a digital signal in which the number of samples per symbol is (M / N) (sample / symbol). Here, M and N are positive integers, respectively. M is, for example, 4. N is, for example, 3.

The frequency domain filter 42 extracts a main signal (digital signal) in a specific sampling frequency region from the digital signal output from the ADC 41. The frequency domain filter 42 outputs a main signal in a specific sampling frequency region to the frequency domain filter 42 and the sampling frequency deviation amount monitor 43.

The sampling frequency deviation amount monitor 43 (detection unit) detects the sampling frequency deviation amount (sampling frequency shift amount) in the main signal output from the frequency domain filter 42 with respect to a predetermined sampling frequency. The sampling frequency deviation amount monitor 43 outputs information indicating the sampling frequency deviation amount to the frequency domain filter 42.

FIG. 2 is a diagram showing a first example of the configuration of the sampling frequency deviation amount monitor 43. In FIG. 2, the optical receiver 4a has a system in which the main signal is propagated through a resampling function unit that executes resampling, a phase shift unit that executes phase shift of the main signal, and a sampling frequency shift amount monitor 43. It is provided as hardware such as a circuit in a system different from the (main signal line). The sampling frequency deviation amount monitor 43 may operate at an operating speed lower than the operating speed of signal processing applied to the main signal.

FIG. 3 is a diagram showing a second example of the configuration of the sampling frequency deviation amount monitor 43. In FIG. 3, the optical receiver 4a includes a resampling function unit, a phase shift unit, and a sampling frequency shift amount monitor 43 as a processor.

FIG. 4 is a diagram showing a third example of the configuration of the sampling frequency deviation amount monitor 43. In FIG. 4, the optical receiver 4a includes a part of the resample function unit, the phase shift unit, and the sampling frequency shift amount monitor 43 as hardware (preprocessing unit), and the remaining function unit as a processor.

FIG. 5 is a diagram showing a fourth example of the configuration of the sampling frequency deviation amount monitor 43. In FIG. 5, the optical receiver 4a includes a resampling function unit, a phase shift unit, and a sampling frequency shift amount monitor 43 in the main signal line. The optical receiver 4a uses the resampling function unit, the phase shift unit, and the sampling frequency shift amount monitor 43 only when the tap coefficient is updated (at startup).

Returning to FIG. 1, the description of the configuration of the optical communication system 1a will be continued. The time domain filter 44a (adaptive equalization unit) extracts the main signal of a specific time domain from the main signal output from the frequency domain filter 42. The time domain filter 44a includes a phase shift unit 440a, an FIR filter 441, an error detection unit 442, a coefficient update unit 443, and a phase shift unit 444a.

FIG. 6 is a diagram showing an example of the update cycle of the tap coefficient of the phase shift. The phase shift unit 440a applies a sample phase shift, which is a process of shifting the sample phase, to the main signal output from the frequency domain filter 42. The phase shift unit 440a shifts the sample phase of the main signal by the sample phase shift amount, which is the shift amount of the sample phase, so as to compensate for the sampling frequency shift amount. For example, the phase shift unit 440a obtains a symbol of the main signal by performing a downsampling process on the main signal output from the frequency domain filter 42. The phase shift unit 440a outputs a main signal whose sample phase has been shifted to the coefficient update unit 443.

Returning to FIG. 1, the description of the configuration of the optical communication system 1a will be continued. The FIR filter 441 (finite impulse response filter) acquires the main signal output from the frequency domain filter 42. The FIR filter 441 acquires the tap coefficient from the phase shift unit 444a. The FIR filter 441 performs FIR filter processing on the main signal according to the tap coefficient acquired from the phase shift unit 444a. The FIR filter 441 outputs the main signal subjected to the FIR filter processing to the decoding unit 45.

The error detection unit 442 detects the difference (error) between the symbol position of the main signal and the reference position of the main signal output from the FIR filter 441. The reference position is defined in a modulation scheme standard such as Quadrature Phase Shift Keying (QPSK), for example. The difference between the symbol position of the main signal and the reference position is expressed by, for example, the phase difference on the IQ plane. The difference between the symbol position of the main signal and the reference position may be expressed by, for example, the difference in the amplitude of the main signal. Further, the difference between the symbol position of the main signal and the reference position may be calculated based on the subtraction result of the complex number. The error detection unit 442 outputs information indicating the difference between the symbol position of the main signal and the reference position to the coefficient updating unit 443.

The coefficient update unit 443 acquires the main signal whose sample phase has been shifted from the phase shift unit 440a. The coefficient updating unit 443 acquires information indicating the difference between the symbol position of the main signal and the reference position from the error detecting unit 442. The coefficient updating unit 443 determines the tap coefficient applied to the phase shift unit 444a so that the difference between the symbol position of the main signal and the reference position is small. Here, the coefficient updating unit 443 performs averaging using the step size μ. The coefficient updating unit 443 outputs the tap coefficient applied to the phase shift unit 444a to the phase shift unit 444a.

The phase shift unit 444a acquires the tap coefficient updated by the coefficient update unit 443 from the coefficient update unit 443. The phase shift unit 444a acquires information representing the sampling frequency deviation amount from the sampling frequency deviation amount monitor 43. The phase shift unit 444a shifts the sample phase based on the tap coefficient acquired from the coefficient update unit 443 and the information representing the sampling frequency shift amount. The phase shift unit 444a outputs the tap coefficient obtained as a result of shifting the sample phase to the FIR filter 441. The decoding unit 45 decodes the main signal output from the time domain filter 44a.

The description of the time domain filter 44a can be supplemented as follows. The phase shift unit 440a phase shifts the received signal so that the sampling frequency shift of the received signal is eliminated. The error detection unit 422 acquires, as an error value, the difference between the received signal that has passed through the FIR filter 441 and has no sampling frequency deviation and the ideal signal. The coefficient updating unit 443 updates the tap coefficient based on the phase-shifted received signal and the error value. By updating the tap coefficient, the coefficient updating unit 443 acquires the FIR tap coefficient for the FIR filter 441 to output the received signal (main signal) without sampling frequency deviation. The phase shift 444a shifts the tap coefficient of the FIR filter 441 so as to eliminate the deviation of the sampling frequency of the received signal input from the frequency domain filter 42 to the FIR filter 441. As a result, the time domain filter 44a can compensate for the deviation of the sampling frequency and the waveform distortion of the received signal to be compensated by the FIR filter 441.

FIG. 7 is a diagram showing an example of the configuration of the clock adjusting device of the optical receiver 4a. The optical receiver 4a includes an ADC 41, a sampling frequency shift amount monitor 43, a phase shift amount calculation unit 46, a FIFA 47, a sample shift unit 48, a clock generation unit 49, and a clock adjustment unit 50 as clock adjustment devices. To be equipped. The phase shift amount calculation unit 46 may be provided in the coefficient update unit 443 of the time domain filter 44a.

The phase shift amount calculation unit 46 (phase shift amount acquisition unit) calculates the phase shift amount based on the sampling frequency shift amount detected by the sampling frequency shift amount monitor 43. The phase shift amount calculation unit 46 feeds back the phase shift amount to the clock generation unit 49 or the clock adjustment unit 50 to adjust the phase of the clock output from the clock generation unit 49 so that the sampling frequency shift amount becomes small. ..

When the phase shift amount exceeds a certain value, the FIFO 47 skips the sample phase at a phase of a constant size. As a result, the FIFO 47 can absorb the amount of sample phase shift. For example, when the phase shift amount is ± 128 samples, the sample phase in the main signal is shifted in units of 128 samples.

The sample shift unit 48 shifts the sample phase of the main signal output from the FIFA 47 in units of ± 1 sample. That is, when the phase shift amount exceeds a certain value, the sample shift unit 48 skips the sample phase at a phase of a constant size. For example, when the phase shift amount is ± 0.5 sample, the sample phase in the main signal is shifted in units of one sample. As a result, the sample shift unit 48 can absorb the amount of deviation of the sample phase. The sample shift unit 48 outputs the main signal whose sample phase has been shifted to the FIR filter 441 of the time domain filter 44a.

The clock generation unit 49 outputs a clock to the clock adjustment unit 50. The clock adjustment unit 50 acquires information representing the phase shift amount from the phase shift amount calculation unit 46. The clock adjusting unit 50 adjusts the phase of the clock so that the sampling frequency shift amount in the main signal becomes small according to the information representing the phase shift amount (sample phase shift amount).

Next, an example of the operation of the optical receiver 4a will be described.
FIG. 8 is a flowchart showing an example of the operation of the optical receiver 4a (operation including phase shift to clock adjustment). The sampling frequency deviation amount monitor 43 detects the sampling frequency deviation amount. The sampling frequency shift amount monitor 43 or the phase shift amount calculation unit 46 calculates the phase shift amount based on the sampling frequency shift amount (step S101). In the first embodiment, the phase shift amount is equal to the sampling phase shift amount.

The coefficient updating unit 443 applies the tap coefficient associated with the phase shift amount to the phase shift unit 444a. The phase shift unit 444a outputs the tap coefficient obtained as a result of shifting the sample phase to the FIR filter 441 (step S102).

The phase shift amount calculation unit 46 determines whether or not the phase shift amount exceeds the range of ± 0.5 samples (step S103). When the phase shift amount does not exceed the range of ± 0.5 samples (step S103: NO), the phase shift amount calculation unit 46 returns the process to step S101. When the phase shift amount exceeds the range of ± 0.5 samples (step S103: YES), the sample shift unit 48 shifts the sample phase of the main signal output from the FIFA 47 in units of ± 1 sample (step S103: YES). Step S104).

The phase shift amount calculation unit 46 determines whether or not the phase shift amount exceeds the range of the number of samples (for example, ± 128 samples) corresponding to one clock (step S105). When the phase shift amount does not exceed the range of ± 1 clock (step S105: NO), the phase shift amount calculation unit 46 returns the process to step S101. When the phase shift amount exceeds the range of ± 1 clock (step S105: YES), the FIFA 47 shifts the sample phase of the main signal output from the FIFO 47 in units of ± 1 clock (= ± 128 samples). (Step S106).

The clock adjusting unit 50 adjusts the phase of the clock according to the phase shift amount. The phase shift amount calculation unit 46 may feed back the phase shift amount to the phase of the clock generated by the clock generation unit 49 (step S107).

As described above, the optical receiver 4a of the first embodiment includes a sampling frequency deviation amount monitor 43 as a detection unit and a time domain filter 44a as an adaptive equalization unit. The sampling frequency deviation amount monitor 43 detects the deviation amount of the sampling frequency of the main signal output from the frequency domain filter. The time domain filter 44a updates the tap coefficient of the circuit that shifts the sample phase in the main signal based on the amount of deviation. As a result, the optical receiver 4a of the first embodiment can compensate for the sampling frequency deviation even if the circuit scale for compensating for the sampling frequency deviation is small. The tap coefficient is a value based on the shift amount of the sample phase.

When the optical receiver 4a of the first embodiment updates the tap coefficient in the time domain filter (adaptive equalization unit), the sampling frequency deviation amount based on the clock is convoluted and corrected. As a result, the optical receiver 4a of the first embodiment can reduce the circuit scale as compared with the case where a circuit (functional block) for compensating for the sampling frequency deviation amount is separately added. Further, the optical receiver 4a of the first embodiment can suppress an increase in power consumption.

The time domain filter (adaptive equalization unit) is an indispensable configuration for the optical receiver in order to correct the distortion generated in the received signal in the transmission line. The optical receiver 4a of the first embodiment compensates for a sampling frequency shift amount based on different clocks by a time domain filter for signal equalization, which is an essential configuration for the optical receiver. As a result, the optical receiver 4a of the first embodiment can combine the FIR circuits applied to the main signal into a time domain filter.

In the optical receiver 4a of the first embodiment, the FIR circuit in the conventional sampling frequency deviation amount compensation unit can be deleted. In the optical receiver 4a of the first embodiment, the operating speed of the FIR filter for applying the phase filter to the signal input to the coefficient update unit 443 is used only when updating the tap coefficient, and therefore the main signal. It is slower than the operating speed of the signal processing applied to. Therefore, the power consumption of the FIR filter for applying the phase filter to the signal input to the coefficient update unit 443 is small.

(Second Embodiment)
The second embodiment is different from the first embodiment in that each phase shift portion of the time domain filter shifts the phase of the sample with a phase less than the sample phase (hereinafter referred to as “fractional phase shift”). In the second embodiment, only the differences from the first embodiment will be described.

FIG. 9 is a diagram showing an example of the configuration of the optical communication system 1b. The optical communication system 1b includes an optical transmitter 2, a transmission line 3, and an optical receiver 4b. The optical transmitter 2 transmits an optical signal to the optical receiver 4b via a transmission line 3 such as an optical fiber.

The optical receiver 4b receives an optical signal via the transmission line 3. The optical receiver 4b includes a receiving unit 40, an ADC 41, a frequency domain filter 42, a sampling frequency deviation amount monitor 43, a time domain filter 44b (fractional AEQ), and a decoding unit 45. The optical receiver 4b further includes a phase shift amount calculation unit 46 as one of the functional units of the device (clock adjustment device) that adjusts the phase of the clock.

The time domain filter 44b extracts a main signal in a specific time domain from the main signal output from the frequency domain filter 42. The time domain filter 44b operates at an oversampling rate that is a non-integer multiple. The time domain filter 44b includes a phase shift unit 440b, an FIR filter 441, an error detection unit 442, a coefficient update unit 443, and a phase shift unit 444b. The time domain filter 44b includes a phase shift unit 440b and a phase shift unit 444b as functional blocks for executing the fractional phase shift.

The sample phase shift amount is pre-folded into the tap coefficient of the fractional phase shift. That is, the phase shift amount of the tap coefficient is the sum of the fractional phase shift amount and the sample phase shift amount. As a result, the phase shift unit 440b and the phase shift unit 444b can execute the fractional phase shift including the sample phase shift. Since the functional block that executes the fractional phase shift executes the fractional phase shift including the sample phase shift, the time domain filter 44b does not need to be separately provided with a circuit for the sample phase shift.

The coefficient update unit 443 stores a data table in which tap coefficients are registered for each phase shift amount. The coefficient update unit 443 selects the tap coefficient from the data table according to the phase shift amount, which is the sum of the sample phase shift amount and the fractional phase shift amount.

FIG. 10 is a diagram showing an example of the tap coefficient of the phase shift. The coefficient update unit 443 selects a tap coefficient from the data table based on the phase shift amount calculated by the coefficient update unit 443 or the phase shift amount calculation unit 46.

FIG. 11 is a diagram showing an example of an update cycle of the tap coefficient of the phase shift. The coefficient update unit 443 may independently update the update cycle of the tap coefficient of the phase shift and the update cycle of the tap for adaptation equalization. The coefficient update unit 443 determines the update cycle of the tap coefficient of the phase shift according to the sampling frequency shift amount detected by the sampling frequency shift amount monitor 43. The coefficient update unit 443 may change the update cycle of the tap coefficient of the phase shift.

The coefficient update unit 443 may determine the update period of the tap coefficient of the phase shift based on the number of parallel lanes in the circuit. The number of parallel lanes in the circuit is, for example, 128. In FIG. 11, the coefficient updating unit 443 updates the tap coefficient of the phase shift at a cycle of 128 samples. The coefficient update unit 443 updates the tap coefficient in a sample cycle that is a multiple of 128, so that the tap coefficient is not changed in the middle of the clock. The time domain filter 44b can reduce the circuit scale.

In FIG. 11, the coefficient updating unit 443 multiplies h _A , which is the initial value of the tap coefficient for digital signal equalization, by the tap coefficient r _A for phase shift, thereby h _{A (} tap coefficient for digital signal equalization _{). 1)} Obtain (= h _A * r _A ). Phase shifting unit 440b, by multiplying tap digital signal equalizing coefficient _{h A (1)} to the sample _{S 1,} obtain received symbols _{S A1} is a digital signal.

In FIG. 11, the coefficient updating unit 443 multiplies h _B , which is the initial value of the tap coefficient for digital signal equalization, by the tap coefficient r _B for phase shift, thereby h _{B (} tap coefficient for digital signal equalization _{). 1)} Obtain (= h _B * r _B ). Phase shifting unit 440b, by multiplying tap digital signal equalizing coefficient _{h B (1)} to the sample _{S 2,} obtain received symbols _{S B1} is a digital signal.

In Figure 11, the phase shifter 440b skips sample _{S 3.} The coefficient update unit 443 multiplies h _C , which is the initial value of the tap coefficient for digital signal equalization, by the tap coefficient r _C for phase shift, thereby h _{C (1)} (= _), which is the tap coefficient for digital signal equalization. h _C * r _C ) is obtained. Phase shifting unit 440b, by multiplying tap digital signal equalizing coefficient _{h C (1)} to the sample _{S 4,} obtain received symbols _{S C1} is a digital signal.

The phase shift unit 444b acquires the tap coefficient updated by the coefficient update unit 443 from the coefficient update unit 443. The phase shift unit 444b acquires information representing the sampling frequency deviation amount from the sampling frequency deviation amount monitor 43. The phase shift unit 444b shifts the sample phase and the fractional phase based on the tap coefficient acquired from the coefficient update unit 443 and the information representing the sampling frequency shift amount. The phase shift unit 444b outputs the tap coefficient obtained as a result of shifting the sample phase and the fractional phase to the FIR filter 441.

Next, an example of the operation of the optical receiver 4b will be described.
FIG. 12 is a flowchart showing an example of the operation of the optical receiver 4b (operation including phase shift to clock adjustment). The sampling frequency deviation amount monitor 43 detects the sampling frequency deviation amount in the main signal output from the frequency domain filter 42 (step S201).

The coefficient update unit 443 or the phase shift amount calculation unit 46 determines the fractional phase shift amount for each sample of the received signal based on the sampling frequency shift amount (step S202). In the second embodiment, the phase shift amount is equal to the sum of the sampling phase shift amount and the fractional phase shift amount. The coefficient update unit 443 or the phase shift amount calculation unit 46 obtains the phase shift amount as a result of adding the sample phase shift amount and the fractional phase shift amount (step S203).

The coefficient update unit 443 applies the tap coefficient associated with the phase shift amount in the data table as shown in FIG. 10 to the phase shift unit 444b. The phase shift unit 444b outputs the tap coefficient obtained as a result of shifting the sample phase and the fractional phase to the FIR filter 441 (step S204).

The phase shift amount calculation unit 46 determines whether or not the phase shift amount exceeds the range of ± 0.5 samples (step S205). When the phase shift amount does not exceed the range of ± 0.5 samples (step S205: NO), the phase shift amount calculation unit 46 returns the process to step S201. When the phase shift amount exceeds the range of ± 0.5 samples (step S205: YES), the sample shift unit 48 shifts the sample phase of the main signal output from the FIFA 47 in units of ± 1 sample (step S205: YES). Step S206).

The phase shift amount calculation unit 46 determines whether or not the phase shift amount exceeds the range of ± 1 clock (for example, 128 samples) (step S207). When the phase shift amount does not exceed the range of ± 1 clock (step S207: NO), the phase shift amount calculation unit 46 returns the process to step S201. When the phase shift amount exceeds the range of ± 1 clock (step S207: YES), the FIFO 47 shifts the sample phase of the main signal output from the FIFA 47 in units of ± 1 clock (= ± 128 samples). (Step S208).

The clock adjusting unit 50 adjusts the phase of the clock according to the phase shift amount. The phase shift amount calculation unit 46 may feed back the phase shift amount to the phase of the clock generated by the clock generation unit 49 (step S209).

As described above, the optical receiver 4b of the second embodiment includes a sampling frequency deviation amount monitor 43 as a detection unit and a time domain filter 44b as an adaptive equalization unit. The sampling frequency deviation amount monitor 43 detects the deviation amount of the sampling frequency of the main signal output from the frequency domain filter. The time domain filter 44b updates the tap coefficient of the circuit that shifts the sample phase in the main signal based on the amount of deviation. As a result, the optical receiver 4b of the second embodiment can compensate for the sampling frequency deviation even if the circuit scale for compensating for the sampling frequency deviation is small. The tap coefficient is a value based on the sum of the shift amount of the sample phase and the shift amount of less than the sample phase (fractional phase).

At least a part of the optical receiver and the optical communication system in the above-described embodiment may be realized by a computer. In that case, the program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read by the computer system and executed. The “computer system” mentioned here includes an OS and hardware such as peripheral devices. The "computer-readable recording medium" refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, or a storage device such as a hard disk built in a computer system. Further, a "computer-readable recording medium" is a communication line for transmitting a program via a network such as the Internet or a communication line such as a telephone line, and dynamically holds the program for a short period of time. It may also include a program that holds a program for a certain period of time, such as a volatile memory inside a computer system that serves as a server or a client in that case. Further, the above program may be for realizing a part of the above-mentioned functions, and may be further realized for realizing the above-mentioned functions in combination with a program already recorded in the computer system. It may be realized by using a programmable logic device such as FPGA (Field Programmable Gate Array).

The embodiment of the present invention has been described in detail above with reference to the drawings, but the specific configuration is not limited to this embodiment, and includes a design and the like within a range not departing from the gist of the present invention.

The present invention is applicable to optical receivers and optical communication systems.

1a, 1b ... Optical communication system, 2 ... Optical transmitter, 3 ... Transmission path, 4a, 4b ... Optical receiver, 40 ... Receiver, 41 ... ADC, 42 ... Frequency domain filter, 43 ... Sampling frequency shift amount monitor, 44a, 44b ... Time domain filter, 45 ... Decoding unit, 46 ... Phase shift amount calculation unit, 47 ... FIFA, 48 ... Sample shift unit, 49 ... Clock generation unit, 50 ... Clock adjustment unit, 440a, 440b ... Phase shift unit , 441 ... FIR filter, 442 ... Error detection unit, 443 ... Coefficient update unit, 444a, 444b ... Phase shift unit

Claims (5)

A detector that detects the amount of deviation in the sampling frequency of the main signal output from the frequency domain filter,
It is provided with an adaptive equalization unit that updates the tap coefficient of the circuit that shifts the sample phase in the main signal based on the deviation amount .
The adaptive equalization unit determines the update period of the tap coefficient of the phase shift based on the number of parallel lanes in the circuit.
Optical receiver. The optical receiver according to claim 1, wherein the tap coefficient is a value based on a shift amount of the sample phase. The optical receiver according to claim 1, wherein the tap coefficient is a value based on the sum of the shift amount of the sample phase and the shift amount of less than the sample phase. A phase shift amount acquisition unit that acquires a sample phase shift amount based on the deviation amount,
The optical receiver according to any one of claims 1 to 3, further comprising a clock adjusting unit that adjusts the phase of the clock based on the shift amount of the sample phase. It is a frequency shift compensation method executed by the optical receiver.
The step of detecting the deviation amount of the sampling frequency of the main signal output from the frequency domain filter, and
It has a step of updating the tap coefficient of the circuit for shifting the sample phase in the main signal based on the deviation amount.
In the updating step, the updating period of the tap coefficient of the phase shift is determined based on the number of parallel lanes in the circuit.
Frequency deviation compensation method.

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