Optical filter control device, optical receiving device, optical transmission system, and optical receiving method

Abstract

To achieve optimal compensation for waveform distortion of an optical signal by adjusting an optical filter.SOLUTION: An optical filter control device according to the present disclosure includes a compensation characteristic estimation unit that receives a received signal extracted from an optical signal that has passed through an optical filter provided in an optical transmission path and transmitting optical signals of a predetermined frequency setting value, and estimates compensation characteristics that compensate for waveform distortion caused by the transmission path of the received signal, a frequency deviation estimation unit that estimates a frequency deviation between the frequency setting value and a received frequency value obtained from the received signal, and a setting value calculation unit that calculates an optical filter setting value to be set in the optical filter using the compensation characteristic adjusted on the basis of the frequency deviation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an optical filter control device, an optical receiving device, an optical transmission system, and an optical receiving method. [Background technology]

[0002] Patent Document 1 discloses an optical wavelength stabilization system for a wavelength tunable optical filter at the receiving end of optical wavelength division multiplexing communications. This system suppresses temperature fluctuations in the transmission wavelength by electrically controlling the transmission wavelength of the wavelength tunable optical filter in response to ambient temperature fluctuations, thereby obtaining optimal reception characteristics for any wavelength signal that is densely wavelength division multiplexed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-269895 Summary of the Invention [Problem to be solved by the invention]

[0004] In response to the demand for higher capacity optical communication systems, the amount of transmission has increased dramatically with the introduction of digital coherent optical communication technology. Since the introduction of digital coherent optical communication technology, equalization signal processing by digital signal processing has been adopted on the receiving side, such as using a DSP (digital signal processor) to collectively compensate for chromatic dispersion accumulated in the optical transmission line on the receiving side.

[0005] On the other hand, complex digital signal processing requires increased power consumption in optical receivers, even with the benefits of cutting-edge CMOS (Complementary Metal-Oxide-Semiconductor). Therefore, it is expected that improving performance solely in optical receivers equipped with DSPs will become increasingly inefficient. Therefore, while utilizing digital signal processing, it is desirable to optimize waveform distortion compensation for optical signals throughout the entire optical communication system.

[0006] One of these technologies is a method to reduce the load on the DSP by compensating in the optical domain for part of the waveform distortion that was previously compensated for by the DSP.However, when part of the waveform distortion that was previously compensated for by the DSP is offloaded to an optical filter installed in the optical transmission line, there is a problem in that it is difficult to perform high-precision distortion compensation because there is no established method for adjusting the optical filter.

[0007] In view of the above-mentioned problems, an object of the present disclosure is to provide an optical receiving device, an optical communication system, and an optical receiving method that are capable of adjusting an optical filter to optimize compensation for waveform distortion of an optical signal. [Means for solving the problem]

[0008] The optical filter control device according to the present disclosure includes a compensation characteristic estimation unit that receives a received signal extracted from an optical signal that has passed through an optical filter provided in an optical transmission path and that transmits an optical signal of a predetermined frequency setting value, and estimates compensation characteristics that compensate for waveform distortion caused by the transmission path of the received signal; a frequency deviation estimation unit that estimates a frequency deviation between the frequency setting value and a received frequency value obtained from the received signal; and a setting value calculation unit that calculates an optical filter setting value to be set in the optical filter using the compensation characteristic adjusted based on the frequency deviation.

[0009] The optical receiving device according to the present disclosure includes an optical receiver that extracts a received signal from an optical signal that has passed through an optical filter that is provided in an optical transmission path and that transmits optical signals of a predetermined frequency setting value; a compensation characteristic estimation unit that estimates compensation characteristics that compensate for waveform distortion due to the transmission path of the received signal; a frequency deviation estimation unit that estimates a frequency deviation between the frequency setting value and a received frequency value obtained from the received signal; and a setting value calculation unit that calculates an optical filter setting value to be set in the optical filter using the compensation characteristics that have been adjusted based on the frequency deviation.

[0010] An optical transmission system according to the present disclosure comprises an optical transmitting device and an optical receiving device that receives an optical signal output from the optical transmitting device via an optical transmission path, the optical transmission path including an optical filter that transmits an optical signal of a frequency setting value, and the optical receiving device comprises an optical receiver that extracts a received signal from the optical signal that has passed through the optical filter, a compensation characteristic estimator that estimates compensation characteristics that compensate for waveform distortion due to the transmission path of the received signal, a frequency deviation estimator that estimates a frequency deviation between the frequency setting value and a received frequency value obtained from the received signal, and a setting value calculator that calculates an optical filter setting value to be set in the optical filter using the compensation characteristics adjusted based on the frequency deviation.

[0011] The optical receiving method according to the present disclosure includes an optical receiver extracting a received signal from an optical signal that has passed through an optical filter provided in an optical transmission path and that transmits optical signals of a predetermined frequency setting value, a processor estimating a compensation characteristic that compensates for waveform distortion of the received signal due to the transmission path, a frequency deviation estimation unit estimating a frequency deviation between the frequency setting value and a received frequency value obtained from the received signal, and a setting value calculation unit calculating an optical filter setting value to be set in the optical filter using the compensation characteristic adjusted based on the frequency deviation. [Effects of the Invention]

[0012] According to the present disclosure, it is possible to optimize compensation for waveform distortion of an optical signal by adjusting an optical filter. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 illustrates a schematic diagram of a communication system according to the present disclosure. [Figure 2] FIG. 2 is a schematic diagram of an optical filter setting device according to the present disclosure. [Figure 3] FIG. 3 is a block diagram showing the configuration of an optical communication system according to the present disclosure. [Figure 4] FIG. 4 is a diagram illustrating a configuration of a compensation characteristic estimation unit according to the present disclosure. [Figure 5]FIG. 5 shows the ideal spectrum of the received signal, the spectrum of the actually received signal, and the estimated transmission path compensation characteristics when the received LO light from the light source on the receiving side is used as a reference. [Figure 6] FIG. 6 shows the amplitude characteristics of the optical filter when a notch filter is applied. [Figure 7] FIG. 7 shows the optical filter setting values ​​set in the optical filter when a notch filter is superimposed. [Figure 8] FIG. 8 shows the spectrum of the signal received by the optical receiver. [Figure 9] FIG. 9 is a diagram illustrating adjustment of the transmission path compensation characteristics based on a frequency deviation. [Figure 10] FIG. 10 is a flow diagram illustrating the optical receiving method of the present disclosure. [Figure 11] FIG. 11 is a diagram illustrating the setting position of the reference frequency. [Figure 12] FIG. 12 is a flow diagram illustrating another example of the optical receiving method of the present disclosure. [Figure 13] FIG. 13 shows the amplitude characteristics of the optical filter when a bandpass filter is applied. [Figure 14] FIG. 14 shows the spectrum of the signal received by the optical receiver when the bandpass filter shown in FIG. 13 is applied to the optical filter. [Figure 15] FIG. 15 is a block diagram showing a portion of the configuration of an optical communication system according to the present disclosure. [Figure 16] FIG. 16 shows the spectrum of the WDM signal output from the optical filter immediately before it is received by the optical receiving device. [Figure 17] FIG. 17 shows the spectrum of the signal received by the optical receiver of each optical receiving unit. [Figure 18] FIG. 18 shows a state in which a WDM signal is reproduced from the signal received by each optical receiving section. [Figure 19] FIG. 19 shows an example of optical filter setting values ​​calculated by the WDM signal setting value calculation unit over the entire signal band of the WDM signal. [Figure 20] FIG. 20 shows an example of the physical configuration of the optical filter setting unit. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and for clarity of explanation, duplicate explanations will be omitted as necessary.

[0015] The present disclosure relates to an optical communication system that optimizes compensation for waveform distortion in an optical signal by adjusting the frequency characteristics of an optical filter provided in an optical transmission line. Prior to describing embodiments of the present disclosure, an overview of the present disclosure will be provided. FIG. 1 schematically illustrates a communication system according to the present disclosure. The optical communication system 100 includes an optical filter setting device 10, an optical transmitting device 20, an optical transmission line 30, and an optical receiving device 40.

[0016] The optical transmitting device 20 and the optical receiving device 40 are connected to each other via an optical transmission path 30. The optical receiving device 40 receives the optical signal transmitted from the optical transmitting device 20 via the optical transmission path 30. The optical receiving device 40 extracts a received signal from the optical signal that has passed through an optical filter provided in the optical transmission path 30.

[0017] The optical transmission path 30 includes an optical fiber 31 and an optical filter 32. The optical fiber 31 guides the optical signal transmitted from the optical transmitter 20. The optical filter 32 is a filter having a phase equalization function in addition to an amplitude equalization function. The optical filter 32 may be, for example, a wavelength selective switch (WSS) that can switch an optical signal of a desired wavelength from a wavelength-multiplexed optical signal to an arbitrary path. In other words, the optical filter 32 can selectively transmit an optical signal of a predetermined frequency setting value.

[0018] 2 schematically illustrates an optical filter setting device 10 according to the present disclosure. The optical filter setting device 10 includes a compensation characteristic estimator 11, a frequency deviation estimator 12, and a setting value calculator 13. A received signal is input to the optical filter setting device 10 from an optical receiving device 40.

[0019] The compensation characteristic estimator 11 estimates compensation characteristics that compensate for waveform distortion caused by the transmission path of the received signal. Note that the transmission path may include the optical transmitter 21, the optical receiver 41, etc. in addition to the optical transmission path 30. The frequency deviation estimator 12 estimates the frequency deviation between the frequency setting value of the optical filter 32 and the reception frequency value acquired from the received signal. The setting value calculator 13 calculates the optical filter setting value to be set in the optical filter using the compensation characteristics adjusted based on the frequency deviation. The optical filter setting value to be set in the optical filter 32 is a frequency characteristic parameter that determines the frequency characteristic of the optical filter 32.

[0020] In the present disclosure, by setting the calculated optical filter setting value in the optical filter 32, it is possible to compensate for waveform distortion contained in the received signal in the optical domain. The optical receiving device 40 can perform equalization signal processing using digital signal processing on the received signal whose waveform distortion has been compensated for in the optical domain. In this way, the present disclosure can reduce the load on the optical receiving device 40 due to digital signal processing. Furthermore, the present disclosure makes it possible to optimize waveform distortion compensation of the optical signal in the entire optical communication system including the optical filter 32 and the optical receiving device 40. Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0021] Embodiment 1 3 is a block diagram showing the configuration of an optical communication system 100 according to the present disclosure. The optical communication system 100 includes an optical transmitting device 20, an optical transmission path 30, and an optical receiving device 40. The optical transmitting device 20 and the optical receiving device 40 are connected to each other via the optical transmission path 30. The optical transmitting device 20 converts a signal input from a client side into an optical signal and transmits it to the optical transmission path 30. The optical transmitting device 20 includes an optical transmitter 21 and a light source 22.

[0022] Although not shown here, the optical transmitter 21 may include a framer, a transmission DSP, etc. The framer accommodates a client signal in a transmission frame. The framer is connected to a transmission DSP. The transmission DSP may include an error correction coding processing unit, a signal mapping processing unit, a transmission spectrum shaping processing unit, a DA conversion unit, etc.

[0023] The error correction coding processing unit performs error correction coding processing on the input transmission frame. The signal mapping processing unit maps the signal to a signal point on a constellation according to the set modulation method. The transmission spectrum shaping processing unit equalizes the analog signal waveform input from the signal mapping processing unit in the time and frequency domains to shape it into a form suitable for transmission. The DA conversion unit converts the digital signal input from the transmission spectrum shaping processing unit into an analog electrical signal and outputs it to the optical transmitter 21.

[0024] The light source 22 outputs CW (Continuous wave) light. The light source 22 may be, for example, a laser diode. The frequency of the CW light output by the light source 22 is assumed to be f0. The optical transmitter 21 modulates the CW light output from the light source 22 in accordance with an input analog electrical signal to generate an optical signal. The optical signal generated by the optical transmitter 21 is output to the optical transmission path 30.

[0025] The optical transmission path 30 transmits the optical signal output from the optical transmitting device 20 to the optical receiving device 40. The optical transmission path 30 has an optical fiber 31, an optical filter 32, and an optical amplifier 33. The optical fiber 31 guides the optical signal transmitted from the optical transmitting device 20. The optical amplifier 33 amplifies the optical signal and compensates for propagation loss in the optical fiber 31. The optical amplifier 33 may be, for example, an erbium-doped fiber amplifier (EDFA).

[0026] The optical filter 32 is a filter that has a phase equalization function in addition to an amplitude equalization function. As described above, the optical filter 32 is, for example, a WSS that can switch an optical signal of a desired wavelength from a wavelength-multiplexed optical signal to any path. That is, the optical filter 32 can selectively transmit an optical signal of a predetermined frequency setting value. The frequency setting value of the optical filter is assumed to be f0''. The optical transmission line 30 may include multiple optical amplifiers 33 and multiple optical filters 32.

[0027] The optical receiving device 40 receives an optical signal and recovers the transmitted information. It includes an optical receiver 41, a light source 42, and a receiving DSP 43. The light source 42 outputs CW light that serves as local oscillator light. Hereinafter, the light output from the light source 42 is assumed to be received LO light. The frequency of the received LO light output from the light source 42 is assumed to be f0'. The optical receiver 41 uses the CW light output from the light source 42 to perform coherent detection on the optical signal transmitted over the optical transmission line 30 and extracts the received signal.

[0028] The reception DSP 43 is a reception processing unit that demodulates the reception signal and outputs the demodulated signal. Although not shown here, the reception DSP 43 may include an AD conversion unit, a reception spectrum shaping processing unit, a fixed equalization processing unit, an adaptive equalization processing unit, a signal demapping processing unit, an error correction decoding processing unit, a deframer, etc. The AD conversion unit samples the reception signal output from the optical receiver 41 and converts the reception signal into a signal in the digital domain. The reception spectrum shaping processing unit performs spectrum shaping on the digital signal input from the AD conversion unit.

[0029] The fixed equalization processing unit compensates for losses that occur in the optical signal along its transmission path in a fixed manner. The fixed equalization processing unit performs, for example, chromatic dispersion compensation and nonlinear compensation. The fixed equalization processing unit outputs the compensated signal to the adaptive equalization processing unit.

[0030] The adaptive equalization processor adaptively compensates for waveform distortion occurring in the transmission path of the optical signal based on dynamic parameters. Note that in the reception DSP 43, at least the fixed equalization processor and the adaptive equalization processor can be realized by hardware circuits such as a fixed equalization filter and an adaptive equalization filter.

[0031] When a chromatic dispersion compensation filter is used as the fixed equalization filter, the chromatic dispersion compensation filter compensates for waveform distortion caused by, for example, chromatic dispersion in the optical fiber 31. Here, the chromatic dispersion of the optical fiber 31 is usually static unless the optical fiber 31 is switched, and a distortion model is determined depending on the type of optical fiber and the transmission distance. For this reason, the chromatic dispersion compensation filter is treated statically once its filter coefficients are set according to the amount of chromatic dispersion to be compensated.

[0032] The adaptive equalization filter compensates for various distortions contained in the signal whose waveform distortion caused by chromatic dispersion has been compensated for by the fixed equalization filter. The filter coefficients of the adaptive equalization filter are adaptively updated by a coefficient update unit (not shown). The coefficient update unit updates the filter coefficients for each sample or symbol at one time, for example, based on the input signal and output signal of the adaptive equalization filter.

[0033] The coefficient update unit calculates the difference between the output of the adaptive equalization filter and a desired state as a loss function. The coefficient update unit sequentially updates the filter coefficients of the adaptive equalization filter so as to minimize the loss function, for example. Any known algorithm used in digital coherent communication is used for updating the coefficients. Examples of adaptive equalization algorithms that can be used include the constant modulus algorithm (CMA) and the decision-directed least mean square (DD-LMS).

[0034] The signal demapping processor performs a demapping process on the signal output from the adaptive equalization processor to detect symbols and convert them into bit data. The error correction decoding processor performs an error correction process on the signal output from the signal demapping processor to recover the data coded on the transmitting side. The deframer receives the decoded data, converts it into a client signal, and transmits it to a client network.

[0035] 3, the optical receiving device 40 further includes an optical filter setting unit 44. The optical filter setting unit 44 realizes each function of the optical filter setting device 10 of embodiment 1. The optical filter setting unit 44 includes a compensation characteristic estimating unit 1, a frequency deviation estimating unit 2, a setting value calculating unit 3, a filter superimposing unit 4, and an overall control unit 5.

[0036] A received signal extracted from an optical signal by an optical receiver 41 is input to the compensation characteristic estimator 1. The compensation characteristic estimator 1 estimates compensation characteristics that compensate for waveform distortion caused by the transmission path of the optical signal. FIG. 4 is a diagram showing the configuration of the compensation characteristic estimator of the present disclosure. As shown in FIG. 4, the compensation characteristic estimator 1 includes an adaptive equalizer 101 and a coefficient updater 102.

[0037] The adaptive equalizer 101 may be an adaptive equalization filter that compensates for waveform distortion contained in a received signal, and may be configured, for example, by a finite impulse response (FIR) filter or a multi-input multi-output (MIMO) filter.

[0038] The coefficient update unit 102 adaptively updates the filter coefficients of the adaptive equalizer 101. The coefficient update unit 102 sequentially updates the filter coefficients of the adaptive equalization filter so as to minimize the difference between the output signal of the adaptive equalizer 101 and a desired state. The filter coefficients obtained as a result of converging the output signal to a desired signal with high accuracy become compensation characteristics (hereinafter referred to as transmission path compensation characteristics) that most suitably compensate for the characteristics of the transmission path including the optical transmitter 21, the optical transmission line 30, the optical receiver 41, etc. The coefficient update unit 102 updates the coefficients using any known algorithm used in digital coherent communication. Examples of adaptive equalization algorithms that can be used include CMA and DD-LMS.

[0039] In the present disclosure, the compensation characteristic estimator 1 performs ideal adaptive equalization processing based on the received signal and the output signal, and static equalization coefficients are extracted from the obtained equalization coefficients to serve as transmission path compensation characteristics for the optical filter 32 to compensate for waveform distortion due to the transmission path of the optical signal. For example, compensation for band narrowing and group delay ripple occurring in the optical fiber 31 can be offloaded from the receiver DSP 43 to the optical filter 32. This makes it possible to improve the performance of wavelength distortion compensation throughout the optical communication system 100. Furthermore, it is possible to suppress increases in power consumption without increasing the circuit size of the receiver DSP 43.

[0040] Fig. 5 shows the ideal spectrum of the received signal, the spectrum of the actually received signal, and the estimated transmission path compensation characteristics when the received LO light (frequency f0') from the light source 42 on the receiving side is used as a reference. In Fig. 5, the horizontal axis represents the optical frequency, and the vertical axis represents the amplitude. Note that in Fig. 5, the light (frequency f0) from the light source 22 on the transmitting side is the true value. By setting an optical filter setting value in the optical filter 32 according to the transmission path compensation characteristics, it is expected that the waveform distortion of the received signal spectrum will be compensated for, resulting in a spectrum close to the ideal spectrum.

[0041] However, as shown in the lower part of Figure 5, the frequency setting value f0" of the optical filter 32 may be different from the frequency f0' of the received LO light. If the optical filter 32 is set based on the transmission path compensation characteristics estimated from the received signal without taking this frequency difference into consideration, the characteristics set for the optical filter 32 will be different in the direction of the optical frequency axis (the left-right direction in Figure 5). This may result in a decrease in the accuracy of waveform distortion compensation, making it impossible to expect improvement in transmission characteristics.

[0042] Therefore, in the present disclosure, highly accurate waveform distortion compensation is achieved by taking into consideration the deviation between the frequency setting value f0'' of the optical filter 32 and the frequency f0' of the received LO light. The frequency deviation estimation unit 2 estimates the frequency deviation between the frequency setting value of the optical filter 32 and the reception frequency value obtained from the received signal.

[0043] The filter superimposing unit 4 generates a notch filter used to detect frequency deviation and superimposes it on the transmission path compensation characteristic. The notch filter, for example, blocks optical signals of a predetermined reference frequency of the optical filter 32 and transmits optical signals of frequencies other than the reference frequency. In other words, the filter superimposing unit 4 can also be called a reference frequency setting unit.

[0044] FIG. 6 shows the amplitude characteristics of the optical filter 32 when a notch filter is applied. In FIG. 6, the horizontal axis represents the optical frequency based on the frequency setting value f0'' of the optical filter 32, and the vertical axis represents the intensity of the optical signal. In the example shown in FIG. 6, the reference frequency is set to f1'', and the optical signal of frequency f1'' is blocked, forming a notch portion.

[0045] FIG. 7 shows the optical filter setting values ​​set in the optical filter 32 when a notch filter is superimposed. In FIG. 7, the horizontal axis represents the optical frequency based on the frequency setting value f0'' of the optical filter 32, and the vertical axis represents the amplitude of the optical signal. As shown in FIG. 7, a notch portion is formed at a position corresponding to the reference frequency f1'' of the optical filter setting value of the optical filter 32.

[0046] When the optical filter setting values ​​shown in FIG. 7 are applied to the optical filter 32, a notch portion is formed in the received signal when the optical signal that has passed through the optical filter 32 is received by the optical receiver 41. FIG. 8 shows the spectrum of the received signal received by the optical receiver 41. The horizontal axis represents the optical frequency when the received LO light (f0') from the light source 42 is used as a reference, and the vertical axis represents the intensity of the received signal. As shown in FIG. 8, the frequency f1' of the notch portion observed in the received signal corresponds to the reference frequency f1'' set in the optical filter 32. The frequency f1' is defined as the frequency in the received signal that corresponds to the reference frequency f1''.

[0047] The frequency deviation estimator 2 can estimate the frequency deviation Δf from the difference between the reference frequency f1″ and the notch portion (corresponding frequency f1′) observed in the received signal based on the received LO light. That is, the frequency deviation Δf is expressed by the following equation (1). Δf=f1''-f1' (1)

[0048] The setting value calculation unit 3 adjusts the transmission path compensation characteristics based on the frequency shift estimated by the frequency shift estimation unit 2, and calculates an optical filter setting value to be set in the optical filter 32 using the adjusted transmission path compensation characteristics. Fig. 9 is a diagram explaining the adjustment of the transmission path compensation characteristics based on the frequency shift. As shown in Fig. 9, the estimated transmission path compensation characteristics are shifted by the frequency shift Δf, and the optical filter setting value to be set in the optical filter 32 is calculated.

[0049] The overall control unit 5 controls each function of the optical filter setting unit 44. For example, the overall control unit 5 can cause each functional component of the optical filter setting unit 44 to execute an optical receiving method described below.

[0050] (First example of optical receiving method) Here, the optical receiving method of the present disclosure will be described with reference to Fig. 10. Fig. 10 is a flow diagram illustrating the optical receiving method of the present disclosure. The method shown in Fig. 10 is a flow for setting the reference frequency of the notch filter within the signal band. This flow can be performed, for example, at system startup.

[0051] In the example shown in Fig. 10, the optical receiving method includes three phases: (1) a transmission path compensation characteristic estimation phase, (2) a frequency deviation estimation phase, and (3) an optical filter setting phase. First, the parameters of each block are initialized (S10). For example, the compensation characteristic estimation unit 1 does not calculate the transmission path compensation characteristic for compensating for waveform distortion from the received signal, but sets it to a flat characteristic. Furthermore, the frequency deviation estimation unit 2 sets the frequency deviation Δf = 0. Then, the transmission path compensation characteristic estimation phase is performed.

[0052] In the traditional path compensation characteristic estimation phase, a predetermined frequency setting value is set in the optical filter 32 (S11). At this time, the filter superimposing unit 4 does not superimpose the characteristics of the notch filter on the frequency setting value. Then, the compensation characteristic estimating unit 1 estimates the transmission path compensation characteristic from the received signal based on the optical signal that has passed through the optical filter 32, and stores it in a memory or the like (not shown) (S12).

[0053] In the frequency deviation estimation phase, the filter superimposing unit 4 superimposes a notch filter characteristic that forms a notch portion in a reference frequency on a predetermined frequency setting value set in the optical filter 32 (S13). Then, the frequency deviation estimating unit 2 detects the notch portion that appears in the received signal and estimates the frequency deviation (Δf) (S14). Specifically, the frequency deviation estimating unit 2 calculates the difference between the reference frequency set in the filter superimposing unit 4 and the frequency of the notch portion detected in the received signal as Δf. Note that the order of the transmission path compensation characteristic estimation phase and the frequency deviation estimation phase may be reversed.

[0054] In the optical filter optimization phase, the setting value calculation unit 3 calculates the optical filter setting value from the transmission path compensation characteristic obtained in S12, taking into account the estimated frequency deviation (Δf) (S15). Specifically, the setting value calculation unit 3 can obtain the optical filter setting value by translating the transmission path compensation characteristic in the optical frequency axis direction according to the frequency deviation (Δf).

[0055] Then, the optical filter setting value adjusted based on the frequency deviation Δf is set in the optical filter 32 (S16). After that, normal optical signal reception is performed using the optical filter 32 with the optical filter setting value set. Note that during normal operation, the filter superimposing unit 4 does not superimpose a notch filter on the optical filter setting value.

[0056] As described above, according to the first embodiment, it is possible to calculate the optical filter setting value from the transmission path compensation characteristics estimated from the received signal, taking into consideration the frequency deviation between the received signal and the frequency setting value of the optical filter, thereby enabling wavelength distortion compensation with higher accuracy.

[0057] In the present disclosure, the optical filter setting unit 44 compensates for the quasi-static characteristics of the transmission path while correcting the discrepancy between the frequency of the light source 42 and the frequency setting value of the optical filter 32. Unlike the reception DSP 43, the optical filter setting unit 44 does not regenerate data encoded on the transmission side. Therefore, the optical filter setting unit 44 does not require high-speed processing by hardware. For example, there is no restriction on the time required for the compensation characteristic estimation unit 1 to estimate the compensation characteristic, and the optical filter 32 may be controlled in units of several seconds to several days.

[0058] The optical filter setting unit 44 may be configured as, for example, a device having a processor and a memory. Some of the functions of each unit in the optical filter setting unit 44 may be realized in software by the processor executing instructions stored in the memory. By implementing the compensation characteristic estimating unit 1 in software, it becomes possible to obtain highly accurate compensation characteristic estimation results, although this takes time. Note that the optical filter setting unit 44 may also be configured as hardware.

[0059] (Second example of optical receiving method) Furthermore, when blocking an optical signal having the reference frequency of the optical filter 32, the filter superimposing unit 4 may set the reference frequency outside the signal band of the optical signal. For example, if the signal input from the client side is a WDM signal in which multiple wavelengths are multiplexed, the reference frequency may be set in a guard band between adjacent signal bands in the WDM signal, as shown in Fig. 11. In other words, the notch portion may be formed in a band where the signal intensity is at the noise floor level.

[0060] Fig. 12 is a flow diagram illustrating another example of the optical receiving method of the present disclosure. The method shown in Fig. 12 is a flow when the reference frequency of the notch filter is set outside the signal band. This flow can be applied not only at system startup but also during normal optical signal receiving operation.

[0061] In the example shown in Fig. 12, the optical receiving method includes three phases: (1) a transmission path compensation characteristic estimation phase, (2) a frequency deviation estimation phase, and (3) an optical filter setting phase. First, the parameters of each block are initialized (S20). For example, the compensation characteristic estimation unit 1 does not calculate the transmission path compensation characteristic for compensating for waveform distortion from the received signal, but sets it to a flat characteristic. Furthermore, the frequency deviation estimation unit 2 sets the frequency deviation Δf = 0.

[0062] Thereafter, the transmission path compensation characteristic estimation phase is carried out. First, the filter superimposing unit 4 sets a notch filter in which a notch portion is formed at a reference frequency outside the signal band (S21). Then, a predetermined frequency setting value is set in the optical filter 32 (S22). The compensation characteristic estimating unit 1 estimates the transmission path compensation characteristic from the received signal based on the optical signal that has passed through the optical filter 32, and stores it in a memory or the like (not shown) (S23).

[0063] In the frequency deviation estimation phase, the frequency deviation estimation unit 2 detects a notch that appears in the received signal and estimates the frequency deviation (Δf) (S24). Specifically, the difference between the reference frequency set by the filter superimposition unit 4 and the frequency of the notch that is detected in the received signal is calculated as Δf. Note that the order of the transmission path compensation characteristic estimation phase and the frequency deviation estimation phase may be reversed.

[0064] In the optical filter optimization phase, the setting value calculation unit 3 calculates the optical filter setting value from the transmission path compensation characteristic obtained in S23, taking into account the estimated frequency deviation (Δf) (S25). Then, the optical filter setting value adjusted based on the frequency deviation Δf is set in the optical filter 32 (S26).

[0065] In this way, when the reference frequency is set outside the signal band of the optical signal, the frequency deviation can be estimated while normal reception is being performed. The flow shown in Fig. 12 may be repeatedly performed during normal reception of the optical signal. That is, while the reception DSP 43 is demodulating the received signal, the optical filter setting unit 44 can sequentially perform a loop in which the optical filter setting unit 44 adjusts the estimated transmission path compensation characteristics based on the frequency deviation, calculates the optical filter setting value, and sets the optical filter setting value in the optical filter 32. This makes it possible to deal with fluctuations in the frequency deviation due to environmental changes, etc.

[0066] The filter superimposing unit 4 may generate a bandpass filter (BPF) instead of the above-mentioned notch filter and superimpose it on the transmission path compensation characteristic. The bandpass filter transmits an optical signal of a predetermined reference frequency of the optical filter 32 and attenuates optical signals of frequencies other than the reference frequency.

[0067] FIG. 13 shows the amplitude characteristics of the optical filter 32 when a bandpass filter is applied. In FIG. 13, the horizontal axis represents the optical frequency based on the frequency setting value f0'' of the optical filter 32, and the vertical axis represents the intensity of the optical signal. In the example shown in FIG. 13, the reference frequency is set to f1'', so that optical signals of frequency f1'' are transmitted and optical signals of frequencies other than f1'' are blocked.

[0068] 14 shows the spectrum of the received signal received by the optical receiver 41 when the bandpass filter shown in FIG. 13 is applied to the optical filter 32. The horizontal axis shows the optical frequency when the received LO light (f0') from the light source 42 is used as a reference, and the vertical axis shows the intensity of the received signal. As shown in FIG. 14, the frequency f1' component observed in the received signal corresponds to the reference frequency f1'' set in the optical filter 32.

[0069] In the above description, the adaptive equalization processing unit and the compensation characteristic estimating unit 1 are provided separately in the reception DSP 43, but it is also possible to use the adaptive equalization processing unit provided in the reception DSP 43 as the compensation characteristic estimating unit 1. The optical filter setting value may be calculated using the compensation characteristic calculated in the adaptive equalization processing unit in the reception DSP 43 for adaptively compensating for waveform distortion occurring in the transmission path of the optical signal.

[0070] Embodiment 2 Fig. 15 is a block diagram showing a portion of the configuration of an optical communication system 100A according to the present disclosure. The optical communication system 100A is a WDM optical transmission system using a digital coherent scheme. Fig. 15 shows an example of the optical communication system 100A that receives a three-wave WDM signal. The optical communication system 100A includes an optical receiving device 40. Although not shown in Fig. 15, the optical communication system 100A may also include the optical transmitting device 20 and the optical transmission line 30 shown in Fig. 3.

[0071] The optical transmitting device 20 converts a signal input from the client side into a WDM optical signal (hereinafter referred to as optical signal) in which multiple wavelengths are multiplexed, and transmits the signal to the optical transmission line 30. The optical transmitting device 20 may include multiple optical transmitters 21 and a multiplexer. The multiple optical transmitters 21 each generate coherently modulated optical signals of different wavelengths. The multiplexer wavelength-multiplexes the multiple optical signals generated by the optical transmitters 21 to generate a WDM optical signal, and transmits the WDM optical signal to the optical transmission line 30. Here, the WDM optical signal includes optical signals of three channels. The optical filter 32 can transmit optical signals of multiple frequency setting values ​​corresponding to the frequencies of the multiple channels in the WDM optical signal.

[0072] 15, the optical receiving device 40A includes a demultiplexer 50, three optical receiving units (a first optical receiving unit 45A, a second optical receiving unit 45B, and a third optical receiving unit 45C), and a WDM signal setting value calculation unit 51. The first optical receiving unit 45A, the second optical receiving unit 45B, and the third optical receiving unit 45C are collectively referred to as the optical receiving unit 45. Note that the number of optical receiving units 45 is just an example and is not limited to this example.

[0073] The demultiplexer 50 demultiplexes the WDM optical signal received from the optical fiber transmission line 103 into optical signals of a single wavelength. Each optical receiving unit 45 receives the optical signal output from the demultiplexer 50 and recovers the transmitted information.

[0074] Each optical receiving unit 45 may have the same configuration as the optical receiving device 40 shown in FIG. 3. That is, the optical receiving device 40A includes multiple optical receiving units 45, each combining an optical receiver 41, a light source 42, a receiving DSP 43, a compensation characteristic estimator 1, a frequency offset estimator 2, and a setting value calculator 3, for each optical signal having a plurality of frequency setting values. The light output from the light source 42 of the first optical receiving unit 45A is assumed to be reception LO1 light. The light output from the light source 42 of the second optical receiving unit 45B is assumed to be reception LO2 light. The light output from the light source 42 of the third optical receiving unit 45C is assumed to be reception LO3 light. Note that the filter superposition unit 4 and the overall control unit 5 are omitted in FIG. 15. Each optical receiving unit 45 may further include a filter superposition unit 4 and an overall control unit 5.

[0075] Each optical receiving unit 45 can calculate an optical filter setting value from the transmission path compensation characteristics estimated from the received signal, taking into account the frequency deviation between the received signal and the frequency setting value of the optical filter. Note that the function of each block of the optical receiver 41 is the same as that of the corresponding block in embodiment 1, and redundant explanations will be omitted. The WDM signal setting value calculation unit 51 uses the optical filter setting values ​​calculated respectively by the multiple optical receiving units 45 to calculate the optical filter setting value to be set in the optical filter 32 over the entire signal band of the wavelength division multiplexed optical signal.

[0076] FIG. 16 shows the spectrum of the WDM signal output from the optical filter 32 immediately before it is received by the optical receiving device 40. The horizontal axis represents optical frequency, and the vertical axis represents intensity. Here, the WDM optical signal includes optical signals of three channels. The optical signals of the three channels are designated CH1, CH2, and CH3, respectively. The frequencies (true values) of each channel are assumed to be f01, f02, and f03. The reference frequencies of the notch filters are assumed to be set in the guard bands between adjacent channels in the WDM signal. As shown in FIG. 16, the frequency of the notch portion on the left side of channel CH1 is assumed to be fnotch01, the frequency of the notch portion between channels CH1 and CH2 is assumed to be fnotch12, the frequency of the notch portion between channels CH2 and CH3 is assumed to be fnotch23, and the frequency of the notch portion on the right side of channel CH3 is assumed to be fnotch34.

[0077] 16 also shows the reception frequency bands of the optical receivers 41 of the first optical receiving unit 45A, the second optical receiving unit 45B, and the third optical receiving unit 45C. The reception frequency bands indicate the regions cut out by the receiver bands and mixing with the reception LO light (reception LO1 light, reception LO2 light, reception LO3 light) of each optical receiver 41.

[0078] As shown in Figure 16, ideally, the intervals between the frequencies (true values) of each channel are equal. However, each channel of the WDM signal has offsets on the left and right of the true value due to the light source frequency offsets of the transmit and receive LO light and the receive LO light. The right offsets for frequencies f01, f02, and f03 are respectively Δf1tx, Δf2tx, and Δf3tx, and the left offsets are respectively Δf1rx, Δf2rx, and Δf3rx.

[0079] The reception frequency band of each of the optical receivers 41 in the first optical receiving unit 45A, the second optical receiving unit 45B, and the third optical receiving unit 45C is wider than the signal band. Therefore, the first optical receiving unit 45A, the second optical receiving unit 45B, and the third optical receiving unit 45C can observe the spectral valleys due to the notch filters for detecting frequency deviations arranged in the guard bands. In other words, the reception frequency bands of the two optical receivers 41 receiving adjacent channels overlap each other at the common notch portion.

[0080] 17 shows the spectrum of the received signal received by the optical receiver 41 of each optical receiving unit 45. The horizontal axis represents the optical frequency based on the received LO light (received LO1 light, received LO2 light, received LO3 light) of each light source 42, and the vertical axis represents the intensity of the received signal. The frequency f12' of the notch portion observed by the first optical receiving unit 45A corresponds to the frequency f12' of the notch portion observed by the second optical receiving unit 45B. Furthermore, the frequency f23' of the notch portion observed by the second optical receiving unit 45B corresponds to the frequency f23' of the notch portion observed by the third optical receiving unit 45C.

[0081] Fig. 18 shows the state in which WDM signals are reproduced from the signals received by each optical receiving unit 45. If the frequency characteristics obtained by the three optical receiving units 45 are shifted and correctly positioned so that the corresponding notch portions described above coincide, it is possible to correctly reproduce the relative positions of the WDM signals at the receiving end, as shown in Fig. 18.

[0082] Fig. 19 shows an example of optical filter setting values ​​across the entire signal band of a WDM signal, calculated by the WDM signal setting value calculation unit 51. As in Fig. 18, by shifting and correctly arranging the transmission path compensation characteristics obtained by the compensation characteristic estimation unit 1 of each optical receiving unit 45, it becomes possible to collectively set the optical filter setting values ​​for three waves to be set in the optical filters 32.

[0083] As described above, according to the second embodiment, it is possible to calculate a wideband optical filter setting value by combining transmission path compensation characteristics estimated in a plurality of optical receiving units 45 while taking frequency deviation into consideration. This allows the optical filter 32 to be set collectively across the wideband of the WDM signal, thereby simplifying filter adjustment.

[0084] In the above-described embodiments, an example has been described in which the light source 42 includes the optical filter setting unit 44. However, the present disclosure is not limited to this. The optical filter setting unit 44 may be configured as a separate device independent of the optical receiving device 40. In other words, the optical filter setting unit 44 does not necessarily have to configure a part of the optical receiving device 40, and the optical receiving device 40 and the optical filter setting unit 44 may be separate devices that are physically separated.

[0085] Furthermore, in the above embodiment, the optical filter setting unit 44 may be configured as any digital signal processing circuit or device. Fig. 20 shows an example of the physical configuration of the optical filter setting unit 44. The optical filter setting unit 44 includes one or more processors 201 and one or more memories 202. The processor 201 can realize the functions of each of the above-mentioned units in software by reading and executing a program stored in the memory 202.

[0086] The program includes instructions (or software code) that, when loaded into a processor, cause the processor to perform one or more functions described in the embodiments. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, compact disc (CD)-ROM, digital versatile disc (DVD), Blu-ray disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals.

[0087] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0088] Each drawing is merely an example for describing one or more embodiments. Each drawing may relate not only to one particular embodiment, but also to one or more other embodiments. As will be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings to create, for example, an embodiment not explicitly shown or described. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

[0089] A part or all of the above-described embodiments can be described as, but not limited to, the following supplementary notes. (Appendix A1) a compensation characteristic estimating unit that receives a received signal extracted from an optical signal that has passed through an optical filter that is provided in an optical transmission line and that transmits an optical signal having a predetermined frequency setting value, and that estimates compensation characteristics that compensate for waveform distortion of the received signal due to the transmission path; a frequency deviation estimation unit that estimates a frequency deviation between the frequency setting value and a reception frequency value acquired from the reception signal; a setting value calculation unit that calculates an optical filter setting value to be set in the optical filter using the compensation characteristic adjusted based on the frequency deviation; Equipped with Optical filter control device. (Appendix A2) a reference frequency setting unit that, when detecting the frequency deviation, blocks optical signals of a predetermined reference frequency of the optical filter and transmits optical signals of frequencies other than the reference frequency, or transmits optical signals of the predetermined reference frequency of the optical filter and attenuates optical signals of frequencies other than the reference frequency; the frequency deviation estimation unit estimates the frequency deviation based on a difference between the reference frequency and a corresponding frequency in the received signal that corresponds to the reference frequency. 10. The optical filter control device according to claim 1, (Appendix A3) When blocking an optical signal of the reference frequency of the optical filter, the reference frequency setting unit sets the reference frequency to a frequency outside a signal band of the optical signal. 10. The optical filter control device according to claim A2. (Appendix B1) an optical receiver that extracts a received signal from an optical signal that has passed through an optical filter that is provided in an optical transmission line and that transmits an optical signal having a predetermined frequency setting value; a compensation characteristic estimation unit that estimates compensation characteristics for compensating for waveform distortion due to a transmission path of the received signal; a frequency deviation estimation unit that estimates a frequency deviation between the frequency setting value and a reception frequency value acquired from the reception signal; a setting value calculation unit that calculates an optical filter setting value to be set in the optical filter using the compensation characteristic adjusted based on the frequency deviation; Equipped with Optical receiving device. (Appendix B2) the optical signal is a wavelength division multiplexed optical signal, the optical filter transmits optical signals having a plurality of frequency setting values, The optical receiving device a plurality of optical receiving units each combining the optical receiver, the compensation characteristic estimating unit, the frequency deviation estimating unit, and the setting value calculating unit for each of optical signals having a plurality of frequency setting values; an overall setting value calculation unit that calculates optical filter setting values ​​over the entire signal band of the wavelength division multiplexed optical signal to be set in the optical filter using the optical filter setting values ​​respectively determined by the plurality of optical receiving units; Including, 10. The optical receiving device according to claim 8, wherein the optical receiving device is a (Appendix B3) a reference frequency setting unit that, when detecting the frequency deviation, blocks optical signals of a predetermined reference frequency of the optical filter and transmits optical signals of frequencies other than the reference frequency, or transmits optical signals of the predetermined reference frequency of the optical filter and attenuates optical signals of frequencies other than the reference frequency; the frequency deviation estimation unit estimates the frequency deviation based on a difference between the reference frequency and a corresponding frequency in the received signal that corresponds to the reference frequency. 10. The optical receiving device according to claim 8, wherein the optical receiving device is a (Appendix B4) the optical signal is a wavelength division multiplexed optical signal, when blocking the optical signal of the reference frequency of the optical filter, the reference frequency setting unit sets the reference frequency to a guard band between adjacent signal bands in the wavelength division multiplexed optical signal. 10. The optical receiving device according to claim B3. (Appendix B5) a reception processing unit that demodulates the received signal and outputs the demodulated signal; when the reference frequency is set outside the signal band of the optical signal, a loop is sequentially performed in which the compensation characteristic is adjusted based on the frequency deviation, the optical filter setting value is calculated, and the optical filter setting value is set in the optical filter while the reception processing unit is demodulating the reception signal. An optical receiving device according to claim B4. (Appendix B6) a reception processing unit that demodulates the received signal and outputs the demodulated signal; the compensation characteristic estimation unit is provided in the reception processing unit and is used when generating the demodulated signal. An optical receiving device according to any one of appendices B1 to B5. (Appendix C1) an optical transmitter; and an optical receiver that receives an optical signal output from the optical transmitter via an optical transmission line; the optical transmission path includes an optical filter that transmits an optical signal having a frequency setting value; The optical receiving device an optical receiver that extracts a received signal from the optical signal that has passed through the optical filter; a compensation characteristic estimation unit that estimates compensation characteristics for compensating for waveform distortion due to a transmission path of the received signal; a frequency deviation estimation unit that estimates a frequency deviation between the frequency setting value and a reception frequency value acquired from the reception signal; a setting value calculation unit that calculates an optical filter setting value to be set in the optical filter using the compensation characteristic adjusted based on the frequency deviation; Equipped with Optical transmission system. (Appendix D1) The optical receiver extracts a received signal from an optical signal that has passed through an optical filter that is provided in the optical transmission line and that transmits an optical signal having a predetermined frequency setting value; The processor: a process of estimating compensation characteristics for compensating for waveform distortion due to a transmission path of the received signal; a frequency deviation estimation unit estimating a frequency deviation between the frequency setting value and a reception frequency value acquired from the reception signal; a setting value calculation unit calculating an optical filter setting value to be set in the optical filter using the compensation characteristic adjusted based on the frequency deviation; To execute Optical receiving method.

[0090] Some or all of the elements (e.g., configurations and functions) described in Appendix A2 to Appendix A3 and Appendix B2 to Appendix B6, which are dependent on Appendix A1 and Appendix B1, may also be dependent on Appendix C1 and Appendix D1 in a similar dependent relationship. Some or all of the elements described in any appendix may be applied to various hardware, software, recording means for recording software, systems, and methods. [Explanation of symbols]

[0091] 1 Compensation characteristic estimation section 2 Frequency deviation estimation section 3 Setting value calculation section 4. Filter superposition section 5 Overall control unit 10 Optical filter setting device 11 Compensation characteristic estimation section 12 Frequency deviation estimation unit 13 Setting value calculation section 20 Optical transmitter 21 Optical transmitter 22 Light source 30 Optical transmission line 31 Optical Fiber 32 Optical Filter 33 Optical Amplifier 40 Optical receiving device 40A Optical Receiver 41 Optical receiver 42 Light source 43 Receive DSP 44 Optical filter setting section 45 Optical receiver 45A First optical receiver 45B Second optical receiver 45C Third optical receiver 50 duplexer 51 WDM signal setting value calculation section 100 Optical Communication System 100A Optical Communication System 101 Adaptive Equalizer 102 Coefficient update unit 201 processor 202 memory

Claims

1. a compensation characteristic estimating unit that receives a received signal extracted from an optical signal that has passed through an optical filter that is provided in an optical transmission line and that transmits an optical signal having a predetermined frequency setting value, and that estimates compensation characteristics that compensate for waveform distortion of the received signal due to the transmission path; a frequency deviation estimation unit that estimates a frequency deviation between the frequency setting value and a reception frequency value acquired from the reception signal; a setting value calculation unit that calculates an optical filter setting value to be set in the optical filter using the compensation characteristic adjusted based on the frequency deviation; Equipped with Optical filter control device.

2. a reference frequency setting unit that, when detecting the frequency deviation, blocks optical signals of a predetermined reference frequency of the optical filter and transmits optical signals of frequencies other than the reference frequency, or transmits optical signals of the predetermined reference frequency of the optical filter and attenuates optical signals of frequencies other than the reference frequency; the frequency deviation estimation unit estimates the frequency deviation based on a difference between the reference frequency and a corresponding frequency in the received signal that corresponds to the reference frequency.

2. The optical filter control device according to claim 1.

3. When blocking an optical signal of the reference frequency of the optical filter, the reference frequency setting unit sets the reference frequency to a frequency outside a signal band of the optical signal.

3. The optical filter control device according to claim 2.

4. an optical receiver that extracts a received signal from an optical signal that has passed through an optical filter that is provided in an optical transmission line and that transmits an optical signal having a predetermined frequency setting value; a compensation characteristic estimation unit that estimates compensation characteristics for compensating for waveform distortion due to a transmission path of the received signal; a frequency deviation estimation unit that estimates a frequency deviation between the frequency setting value and a reception frequency value acquired from the reception signal; a setting value calculation unit that calculates an optical filter setting value to be set in the optical filter using the compensation characteristic adjusted based on the frequency deviation; Equipped with Optical receiving device.

5. the optical signal is a wavelength division multiplexed optical signal, the optical filter transmits optical signals having a plurality of frequency setting values, The optical receiving device a plurality of optical receiving units each combining the optical receiver, the compensation characteristic estimating unit, the frequency deviation estimating unit, and the setting value calculating unit for each of optical signals having a plurality of frequency setting values; an overall setting value calculation unit that calculates optical filter setting values ​​over the entire signal band of the wavelength division multiplexed optical signal to be set in the optical filter using the optical filter setting values ​​respectively determined by the plurality of optical receiving units; Including, 5. The optical receiving device according to claim 4.

6. a reference frequency setting unit that, when detecting the frequency deviation, blocks optical signals of a predetermined reference frequency of the optical filter and transmits optical signals of frequencies other than the reference frequency, or transmits optical signals of the predetermined reference frequency of the optical filter and attenuates optical signals of frequencies other than the reference frequency; the frequency deviation estimation unit estimates the frequency deviation based on a difference between the reference frequency and a corresponding frequency in the received signal that corresponds to the reference frequency.

5. The optical receiving device according to claim 4.

7. the optical signal is a wavelength division multiplexed optical signal, when blocking the optical signal of the reference frequency of the optical filter, the reference frequency setting unit sets the reference frequency to a guard band between adjacent signal bands in the wavelength division multiplexed optical signal.

7. The optical receiving device according to claim 6.

8. a reception processing unit that demodulates the received signal and outputs the demodulated signal; when the reference frequency is set outside the signal band of the optical signal, a loop is sequentially performed in which the compensation characteristic is adjusted based on the frequency deviation, the optical filter setting value is calculated, and the optical filter setting value is set in the optical filter while the reception processing unit is demodulating the reception signal.

8. The optical receiving device according to claim 7.

9. an optical transmitter; and an optical receiver that receives an optical signal output from the optical transmitter via an optical transmission line; the optical transmission path includes an optical filter that transmits an optical signal having a frequency setting value; The optical receiving device an optical receiver that extracts a received signal from the optical signal that has passed through the optical filter; a compensation characteristic estimation unit that estimates compensation characteristics for compensating for waveform distortion due to a transmission path of the received signal; a frequency deviation estimation unit that estimates a frequency deviation between the frequency setting value and a reception frequency value acquired from the reception signal; a setting value calculation unit that calculates an optical filter setting value to be set in the optical filter using the compensation characteristic adjusted based on the frequency deviation; Equipped with Optical transmission system.

10. The optical receiver extracts a received signal from an optical signal that has passed through an optical filter that is provided in the optical transmission line and that transmits an optical signal having a predetermined frequency setting value; The processor: a process of estimating compensation characteristics for compensating for waveform distortion due to a transmission path of the received signal; a frequency deviation estimation unit estimating a frequency deviation between the frequency setting value and a reception frequency value acquired from the reception signal; a setting value calculation unit calculating an optical filter setting value to be set in the optical filter using the compensation characteristic adjusted based on the frequency deviation; To execute Optical receiving method.

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