Estimation method, optical receiving device, and computer program

Abstract

An estimation method for an optical transmission system which comprises an optical transmitting apparatus and an optical receiving apparatus and performs communication by a digital coherent scheme, the estimation method comprising: performing digital Fourier transformation on a tap coefficient of a digital filter provided in the optical receiving apparatus to obtain a frequency domain signal by the transformation, and thereafter calculating the ratio of the linearly transformed quantity; and estimating, on the basis of amplitude and phase information on the calculated ratio of the linearly transformed quantity, at least the physical quantity related to a response between the optical transmitting apparatus and the optical receiving apparatus.

Description

[Technical Field]

[0001] The present invention relates to an estimation method, an optical receiving device, and a computer program. [Background technology]

[0002] In coherent optical communications, polarization / phase diversity transmission and reception has been realized, and digital signal processing utilizing phase information obtained on the receiving side has been realized (see, for example, Non-Patent Documents 1 and 2). Crosstalk and linear distortion between polarization multiplexed signals are equalized by adaptive coefficient control of a digital filter, typically an FIR filter (Finite Impulse Response Filter). Crosstalk and delay differences between in-phase and quadrature signals of quadrature amplitude modulation (QAM) signals can also be equalized by adaptive coefficient control of an FIR filter (see, for example, Non-Patent Document 3). Furthermore, crosstalk and delay differences between subcarrier signals can also be equalized by coefficient control of a digital filter (see, for example, Non-Patent Document 4). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Seb J. Savory, “Digital filters for coherent optical receivers”, Vol. 16, Issue 2, pp. 804-817 (2008). [Non-patent document 2] Kazuro Kikuchi, “Fundamentals of Coherent Optical Fiber Communications”, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 34, NO. 1, JANUARY 1, 2016. [Non-patent document 3] Wooseok Nam, Heejin Roh, Jungwon Lee and Inyup Kang, “Blind Adaptive I / Q Imbalance Compensation Algorithms for Direct-Conversion Receivers”, IEEE SIGNAL PROCESSING LETTERS, VOL. 19, NO. 8, AUGUST 2012. [Non-patent document 4] Edson Porto da Silva, Darko Zibar, “Widely Linear Blind Adaptive Equalization for Transmitter IQ-Imbalance / Skew Compensation in Multicarrier Systems”, 42nd European Conference and Exhibition on Optical Communications, September 18-22, 2016, Dusseldorf. Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, waveform distortion occurs due to delay differences between the I and Q channels of a QAM signal, as well as amplitude and quadrature errors, degrading signal quality. While it is possible to compensate for waveform distortion using a digital filter, performance improvement through compensation is limited due to limitations on the number of taps and imperfections in coefficient control. Therefore, it is possible to identify the cause of the distortion and directly eliminate it by observing and measuring the physical quantities that cause it. This reduces the amount of compensation required by the digital filter and improves signal quality. However, this method requires separate dedicated measuring instruments to measure the physical quantities, which leads to operational inefficiencies.

[0005] In view of the above circumstances, an object of the present invention is to provide a technique that can efficiently identify the cause of signal quality degradation without performing measurements using dedicated equipment. [Means for solving the problem]

[0006] One aspect of the present invention is an estimation method in an optical transmission system that communicates using a digital coherent method and that includes an optical transmitting device and an optical receiving device, in which tap coefficients of a digital filter included in the optical receiving device are converted into frequency domain signals using a digital Fourier transform, and then a ratio of linearly transformed quantities is calculated, and a physical quantity related to the response between at least the optical transmitting device and the optical receiving device is estimated based on amplitude and phase information of the calculated ratio of the linearly transformed quantities.

[0007] One aspect of the present invention is an optical receiving device in an optical transmission system that communicates using a digital coherent method, the optical receiving device comprising an optical transmitting device and an optical receiving device, the optical receiving device comprising: an adaptive equalization unit that performs adaptive equalization processing using a digital filter; a Fourier transform unit that converts tap coefficients of the digital filter into frequency domain signals by digital Fourier transform; and an estimation unit that calculates a ratio of linearly transformed quantities after conversion into frequency domain signals by the Fourier transform unit, and estimates physical quantities related to at least the response between the optical transmitting device and the optical receiving device based on amplitude and phase information of the calculated ratio of the linearly transformed quantities.

[0008] One aspect of the present invention is a computer program for causing a computer to function as an optical receiving device in an optical transmission system that communicates using a digital coherent method and that includes an optical transmitting device and an optical receiving device, the computer program converting tap coefficients of a digital filter included in the optical receiving device into frequency domain signals using a digital Fourier transform, calculating a ratio of linearly transformed quantities after conversion into frequency domain signals, and estimating physical quantities related to at least the response between the optical transmitting device and the optical receiving device based on amplitude and phase information of the calculated ratio of the linearly transformed quantities. [Effects of the Invention]

[0009] According to the present invention, it is possible to efficiently identify the cause of degradation in signal quality without performing measurements using dedicated equipment. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating a system configuration of an optical transmission system according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of a digital signal processing unit in the first embodiment. [Figure 3] FIG. 2 is a diagram illustrating an example of a digital filter (FIR filter) included in a digital filter unit according to the first embodiment. [Figure 4] FIG. 3 is a diagram illustrating an example of a mathematical model of distortion equalized by a digital filter in the first embodiment. [Figure 5] FIG. 2 is a diagram illustrating an example in which the configuration of the digital filter according to the first embodiment is equivalently converted to match a mathematical model. [Figure 6] FIG. 4 is a diagram for explaining how to obtain the amplitude difference between the I lane and the Q lane in the first embodiment. [Figure 7] 4A and 4B are diagrams for explaining how to obtain a delay difference and an orthogonality error between an I lane and a Q lane in the first embodiment. [Figure 8] 4 is a flowchart showing a flow of processing performed by the optical receiving device according to the first embodiment. [Figure 9] FIG. 10 is a diagram illustrating an example of a digital filter (FIR filter) included in a digital filter unit according to the second embodiment. [Figure 10] FIG. 10 is a diagram showing a relational expression for deriving the relationship of (Equation 4). [Figure 11] FIG. 10 is a diagram showing a relational expression for deriving the relationship of (Equation 4). [Figure 12] FIG. 10 is a diagram for explaining how to obtain the amplitude difference between the I lane and the Q lane in the second embodiment. [Figure 13] 10A and 10B are diagrams for explaining how to obtain a delay difference and an orthogonality error between an I lane and a Q lane in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (overview) In the optical transmission system of the present invention, the tap coefficients of a digital filter provided in an optical receiving device are converted into frequency domain signals by digital Fourier transform, and then the ratio of the linearly transformed quantities is calculated. From the amplitude and phase information, at least physical quantities related to the response between the optical transmitting device and the optical receiving device are estimated. Here, the physical quantities related to the response between the optical transmitting device and the optical receiving device are the delay difference, amplitude difference, and quadrature error between the I channel and the Q channel. This makes it possible to estimate the physical quantities that cause distortion. It becomes possible to efficiently identify the causes of signal quality degradation without performing measurements using dedicated equipment. A specific configuration for realizing the above processing will be described below.

[0012] (First embodiment) In the first embodiment, a case where a single carrier signal is input to an optical receiving device will be described as an example. 1 is a diagram showing the system configuration of an optical transmission system 100 according to the first embodiment. The optical transmission system 100 includes an optical transmitter 10 and an optical receiver 20. The optical transmitter 10 and the optical receiver 20 are connected via an optical transmission path 30. The optical transmission path 30 transmits an optical signal transmitted by the optical transmitter 10 to the optical receiver 20. The optical transmission path 30 is composed of an optical fiber 31 that connects the optical transmitter 10 and the optical receiver 20, and an optical amplifier 32 that amplifies the optical signal. Note that the optical transmission path 30 may have devices such as an optical switch or a regenerative repeater inserted along its path.

[0013] The optical transmitting device 10 includes an optical transmitting unit 11 that transmits a single-carrier optical signal. The optical transmitting unit 11 includes an electrical signal generating unit 12 and an optical signal generating unit 13. The electrical signal generating unit 12 encodes transmission data, which is an information source, and converts the encoded transmission data into an electrical signal waveform to generate and output an electrical signal of the transmission data.

[0014] The optical signal generating unit 13 converts the electrical signal generated by the electrical signal generating unit 12 into an optical signal and transmits the optical signal to the optical receiving device 20 via the optical transmission path 30. The optical signal generating unit 13 includes a digital-to-analog converter, a driver amplifier, a modulator, a laser, etc. The optical signal generating unit 13 generates an optical signal using, for example, a QPSK (Quadrature Phase Shift Keying) modulation method.

[0015] The optical receiving device 20 includes an optical receiving unit 21 that receives an optical signal. The optical receiving unit 21 includes a coherent optical receiving unit 22 and a digital signal processing unit 23. The coherent optical receiving unit 22 includes a 90-degree optical hybrid circuit, a local oscillator light source, a photodetector, and optical fibers coupled thereto. An analog-to-digital converter may be provided in the coherent optical receiving unit 22, or an analog-to-digital converter may be provided between the coherent optical receiving unit 22 and the digital signal processing unit 23.

[0016] The coherent optical receiver 22 separates the baseband optical signal into two optical signals with orthogonal polarization planes. These optical signals and the local light from the local oscillator light source are input to a 90-degree optical hybrid circuit, which produces a total of four output lights: one set of output lights caused by in-phase and anti-phase interference between the two lights, and another set of output lights caused by orthogonal (90°) and anti-orthogonal (-90°) interference. These output lights are each converted from optical signals to analog electrical signals by photodiodes. An analog-to-digital converter converts the analog signals into digital signals and outputs them to the digital signal processor 23.

[0017] When an optical signal propagates through the optical transmission line 30, the signal waveform is distorted due to a nonlinear optical effect in which the signal phase rotates in proportion to the optical power of the signal. The digital signal processing unit 23 receives the digital signal output by the analog-to-digital converter as a received signal and performs various compensation processes on the received signal.

[0018] 2 is a diagram showing an example of the configuration of the digital signal processing unit 23 in the first embodiment. The digital signal processing unit 23 includes a first signal processing unit 231, a digital filter unit 232, and a second signal processing unit 233.

[0019] The first signal processing unit 231 performs signal processing on the input digital signal. For example, the first signal processing unit 231 compensates for chromatic dispersion that occurs in the optical transmission line 30 in the input digital signal. Note that the signal processing performed by the first signal processing unit 231 is not limited to this, and other signal processing may be performed. For example, the first signal processing unit 231 may perform any signal processing that has conventionally been performed before adaptive equalization processing by the adaptive equalization unit 234.

[0020] The digital filter unit 232 compensates for distortion that occurs in the waveform of the optical signal in the optical transmission path 30. The digital filter unit 232 includes an adaptive equalization unit 234, a Fourier transform unit 235, and an estimation unit 236. The adaptive equalization unit 234 performs adaptive equalization processing using a digital filter such as an FIR filter (finite impulse response filter) according to set tap coefficients.

[0021] The Fourier transform unit 235 performs a digital Fourier transform to convert the tap coefficients of the digital filter into frequency domain signals.

[0022] The estimation unit 236 calculates the ratio of linearly transformed quantities based on the frequency domain signals, and estimates the physical quantity relating to the response between the transmitter and receiver from the amplitude and phase information.

[0023] The second signal processing unit 233 performs signal processing on the digital signal that has been subjected to adaptive equalization processing. For example, the second signal processing unit 233 performs processing to compensate for frequency offsets and phase offsets in the input digital signal, and demodulates and decodes the digital signal. Note that the signal processing performed by the second signal processing unit 233 is not limited to this, and other signal processing may also be performed. For example, the second signal processing unit 233 may perform any signal processing that has conventionally been performed after adaptive equalization processing by the adaptive equalization unit 234.

[0024] 3 is a diagram illustrating an example of a digital filter (FIR filter) included in the digital filter unit 232 according to the first embodiment. 11 represents the tap coefficient In-Phase → In-Phase component (real vector) of the digital filter, and h 12 represents the tap coefficients of the digital filter, Quadrature → In-Phase components (real vector), and h 21 represents the tap coefficients of the digital filter (In-Phase → Quadrature components (real vector)), and h 22 represents the tap coefficients of the digital filter, Quadrature → Quadrature components (real vector). A mathematical model of the distortion equalized by the digital filter in the first embodiment can be expressed as shown in FIG.

[0025] 4 is a diagram showing an example of a mathematical model of distortion equalized by the digital filter in the first embodiment. The symbols shown in FIG. 4 represent the following: I(t): Time domain representation of the baseband signal, I-phase component (real scalar) Q(t): Time-domain representation of the baseband signal, Q component (real scalar) G I : Gain coefficient of the baseband signal, phase I component (real scalar) G Q : Gain coefficient Q-phase component of baseband signal (real scalar) ·τ I : Time-delayed I-phase component of the baseband signal (real scalar) ·τ Q : Time-delayed Q-phase component of the baseband signal (real scalar) φ I : Phase rotation I component of baseband signal (real scalar) φ Q : Phase rotation Q-phase component of baseband signal (real scalar)

[0026] The output s(t) shown in FIG. 4 is expressed as the following (Equation 1).

[0027]

number

[0028] Here, the configuration of a commonly implemented digital filter shown in FIG. 3 differs from the mathematical model shown in FIG. 4, and therefore equivalent conversion is required as shown in FIG. 5. FIG. 5 is a diagram showing an example in which the configuration of the digital filter in the first embodiment is equivalently converted to match the mathematical model. In FIG. 5, the input signal is a real number, and the coefficients are complex numbers. By equivalently converting the configuration of the digital filter to match the mathematical model, the tap coefficients a1 and a2 of the digital filter are converted to complex numbers by the equivalent configuration. For example, the tap coefficients a1 and a2 of the digital filter in FIG. 5 are expressed as shown in the following (Equation 2).

[0029]

number

[0030] The Fourier transform unit 235 performs a digital Fourier transform on the tap coefficients a1 and a2 of the digital filter to convert the tap coefficients a1 and a2 of the digital filter into frequency domain signals A1(ω) and A2(ω). After that, the estimation unit 236 calculates the ratio (A2(ω) / A1(ω)) of the quantities A1(ω) and A2(ω) converted into frequency domain signals, and estimates physical quantities such as amplitude difference, delay difference, and quadrature error from the amplitude and phase information of the calculated ratio. Note that A1(ω) is the frequency domain signal (A IA2(ω) represents the frequency domain signal (A Q (also written as "(or (or (( ...

[0031] FIG. 6 is a diagram for explaining how to obtain the amplitude difference between the I lane and the Q lane in the first embodiment. I ,A Q is expressed as follows (Equation 3).

[0032]

number

[0033] Then, the estimation unit 236 calculates A I ,A Q Calculate the ratio of the amounts and set the amplitude ratio to 20log 10 (A Q / A I The estimation unit 236 estimates the calculated amplitude ratio value as the amplitude difference between the I lane and the Q lane.

[0034] 7 is a diagram for explaining how to calculate the delay difference and the quadrature error between the I lane and the Q lane in the first embodiment. As shown in FIG. 7, the estimation unit 236 calculates the delay difference and the quadrature error between the I lane and the Q lane. I ,A Q The phase difference is calculated as arg(A Q / A I The estimation unit 236 calculates the calculated (A Q / A I ) is estimated as the delay difference between the I lane and the Q lane, and (A Q / A I ) is estimated as the quadrature error between the I lane and the Q lane.

[0035] FIG. 8 is a flowchart showing the flow of processing by the optical receiving device 20 in the first embodiment. The coherent optical receiving unit 22 receives an optical signal transmitted from the optical transmitting device 10 (step S101). The optical signal received by the coherent optical receiving unit 22 is converted into an electrical signal, and then converted from an analog signal to a digital signal by an analog-to-digital converter and input to the digital signal processing unit 23.

[0036] First signal processing unit 231 performs first signal processing on the input digital signal (step S102). First signal processing unit 231 outputs the digital signal that has been subjected to the first signal processing to digital filter unit 232. Adaptive equalization unit 234 included in digital filter unit 232 performs adaptive equalization processing on the digital signal that has been subjected to the first signal processing and that has been output from first signal processing unit 231 (step S103).

[0037] The Fourier transform unit 235 converts the tap coefficients set in the adaptive equalization unit 234 during adaptive equalization processing into a frequency domain signal by digital Fourier transform (step S104). The estimation unit 236 estimates the amplitude difference, delay difference, and quadrature error based on the frequency domain signal from the Fourier transform unit 235 (step S105). Specifically, as described with reference to FIGS. 6 and 7, the estimation unit 236 estimates the amplitude difference, delay difference, and quadrature error of the frequency domain signal A in the I lane. I and frequency domain signal A in the Q lane Q The amplitude difference, delay difference, and quadrature error are estimated by calculating the ratio of the amounts of the above and determining the amplitude ratio and phase difference.

[0038] The optical transmission system 100 configured as described above makes it possible to efficiently identify the cause of signal quality degradation without performing measurements using dedicated equipment. Specifically, the optical receiving device 20 converts the tap coefficients of the digital filter into frequency domain signals using a digital Fourier transform, calculates the ratio of the linearly transformed quantities, and estimates physical quantities related to the response between the optical transmitting device 10 and the optical receiving device 20 from the resulting amplitude and phase information. This eliminates the need for measurements using dedicated equipment and does not affect operations. Therefore, it becomes possible to efficiently identify the cause of signal quality degradation without performing measurements using dedicated equipment.

[0039] Furthermore, in the optical transmission system 100, by remotely monitoring the changes over time in the physical quantities of the analog devices provided in each of the optical transmitting device and optical receiving device in the optical transmission system, it is possible to reduce OPEX (Operating Expenditure) such as responding to malfunctions.

[0040] Furthermore, by reflecting the physical quantity estimated by the optical receiving device 20 in an analog device, it becomes possible to further improve the signal quality that can be achieved only by waveform equalization using a digital filter.

[0041] (Second embodiment) In the second embodiment, a case where a multiple carrier (multicarrier) signal is input to an optical receiving device will be described as an example. The configuration of the second embodiment is basically the same as that of the first embodiment, but the configuration of the digital filter is different. Furthermore, the processing in the digital filter unit 232 differs from that of the first embodiment. The differences from the first embodiment will be described below.

[0042] 9 is a diagram showing an example of a digital filter (FIR filter) included in the digital filter unit 232 in the second embodiment. The digital filter shown in FIG. 9 is a digital filter that compensates for crosstalk between subcarriers (see, for example, Non-Patent Document 4). In FIG. 9, a 11represents the tap coefficient r1→r1 component (complex vector) of the digital filter, and a 12 represents the tap coefficient r2 → r1 component (complex vector) of the digital filter, and a 21 represents the tap coefficient r1→r2 component (complex vector) of the digital filter, and a 22 represents the tap coefficient r2 → r2 component (complex vector) of the digital filter.

[0043] Here, the relationship between the input and output of the digital filter in FIG. 9 is expressed as the following (Equation 4).

[0044]

number

[0045] The symbols in (Equation 4) represent the following: A 11 (ω),A 12 (ω),A 21 (ω),A 22 (ω): Tap coefficient a of the digital filter 11 , a 12 , a 21 , a 22 The digital Fourier transform value of ω c : Carrier angular frequency of the subcarrier signal (real number) H(ω), G(ω): Fourier transform values ​​of h(k) and g(k) (complex numbers) ·S1(ω), ~S2(ω) (~ is above S2): Fourier transform values ​​(complex numbers) of two subcarrier signals arranged symmetrically around frequency zero

[0046] Here, the relational equations for deriving the relationship in (Equation 4) are shown in Figures 10 and 11. In Figures 10 and 11, s1(t) and s2(t) represent two subcarrier signals (complex numbers) arranged with frequency zero as the target, h(k) and g(k) represent the time domain responses (complex numbers) of the I / Q lanes, and l(k) represents an ideal low-pass filter (complex number).

[0047] The Fourier transform unit 235 calculates the tap coefficients a of the digital filter. 11 , a 12 , a 21 , a 22 By performing a digital Fourier transform on 11 , a 12 , a 21 , a 22 A 11 (ω),A 12 (ω),A 21 (ω),A 22 Then, the estimation unit 236 converts the converted frequency domain signal A 11 (ω),A 12 (ω),A 21 (ω),A 22 The ratio of quantities based on (ω) is calculated, and physical quantities such as amplitude difference, delay difference, and quadrature error are estimated from the amplitude and phase information of the calculated ratio.

[0048] 12 is a diagram for explaining how to obtain the amplitude difference between the I lane and the Q lane in the second embodiment. 11 (ω),A 12 (ω),A 21 (ω),A 22 The amplitude ratio based on (ω) is calculated based on the following (Equation 5): The estimation unit 236 estimates the calculated amplitude ratio value as the amplitude difference between the I lane and the Q lane.

[0049]

number

[0050] 13 is a diagram for explaining how to obtain the delay difference and quadrature error between the I lane and the Q lane in the second embodiment. As shown in FIG. 13, the estimation unit 236 estimates the A signal converted into a frequency domain signal. 11 (ω),A 12 (ω),A 21 (ω),A 22The phase difference based on (ω) is calculated based on the following (Equation 6): The estimation unit 236 estimates the slope of the frequency characteristic (phase) of the phase difference as the delay difference between the I lane and the Q lane, and estimates the intercept of the frequency characteristic (phase) of the phase difference as the orthogonality error between the I lane and the Q lane.

[0051]

number

[0052] According to the optical transmission system 100 of the second embodiment configured as above, even when a multi-carrier signal is received by the optical receiving device 20, it is possible to obtain the same effects as those of the first embodiment.

[0053] Some of the functions of the optical receiving device 20 in the above-described embodiment may be implemented by a computer. In this case, a program for implementing these functions may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed. Note that the term "computer system" as used herein includes hardware such as an operating system (OS) and peripheral devices. Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, read-only memories (ROMs), and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, the term "computer-readable recording medium" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within a computer system serving as a server or client. The program may be for implementing some of the above-described functions, or may be capable of implementing the above-described functions in combination with a program already stored in the computer system, or may be implemented using a programmable logic device such as a field-programmable gate array (FPGA).

[0054] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Industrial Applicability]

[0055] The present invention can be applied to optical transmission system technology that performs equalization processing using a digital filter. [Explanation of symbols]

[0056] 10...optical transmitting device, 11...optical transmitting unit, 12...electrical signal generating unit, 13...optical signal generating unit, 20...optical receiving device, 21...optical receiving unit, 22...coherent optical receiving unit, 23...digital signal processing unit, 30...optical transmission path, 31...optical fiber, 32...optical amplifier, 231...first signal processing unit, 232...digital filter unit, second signal processing unit, 234...adaptive equalization unit, 235...Fourier transform unit, 236...estimation unit

Claims

1. An estimation method in an optical transmission system that performs communication by a digital coherent system and includes an optical transmitting device and an optical receiving device, converting the complex-numbered tap coefficients of the digital filter, which are represented by converting the tap coefficients of the digital filter included in the optical receiving device, into frequency domain signals by digital Fourier transform, and then calculating a ratio between the frequency-converted frequency domain signal in I lane and the frequency domain signal in Q lane; An estimation method for estimating physical quantities related to the response between at least the optical transmitting device and the optical receiving device based on amplitude and phase information of the calculated ratio between the frequency-converted frequency domain signal in the I lane and the frequency domain signal in the Q lane.

2. a delay difference between an I channel and a Q channel is estimated as a physical quantity related to a response between the optical transmitting device and the optical receiving device; The estimation method according to claim 1 .

3. an amplitude difference between an I channel and a Q channel is estimated as a physical quantity related to a response between the optical transmitting device and the optical receiving device; The estimation method according to claim 1 .

4. A quadrature error between the I channel and the Q channel is estimated as a physical quantity relating to the response between the optical transmitting device and the optical receiving device. The estimation method according to claim 1 .

5. An optical receiving device in an optical transmission system for performing communication by a digital coherent system, the optical receiving device including an optical transmitting device and an optical receiving device, an adaptive equalization unit that performs adaptive equalization processing using a digital filter; a Fourier transform unit that converts the tap coefficients of the digital filter into complex numbers and converts the complex numbered tap coefficients of the digital filter into frequency domain signals by digital Fourier transform; an estimation unit that calculates a ratio between the frequency domain signal in the I lane that has been converted into a frequency domain signal by the Fourier transform unit and the frequency domain signal in the Q lane, and estimates a physical quantity related to at least a response between the optical transmitting device and the optical receiving device based on amplitude and phase information of the calculated ratio between the frequency domain signal in the I lane that has been frequency converted and the frequency domain signal in the Q lane; An optical receiving device comprising:

6. A computer program for causing a computer to function as an optical receiving device in an optical transmission system for performing communication by a digital coherent system, the optical receiving device including an optical transmitting device, the computer program comprising: A computer program for converting the tap coefficients of a digital filter provided in the optical receiving device into complex numbers, into frequency domain signals using a digital Fourier transform, calculating a ratio between the frequency domain signal in an I lane that has been frequency converted after the conversion into the frequency domain signal and the frequency domain signal in a Q lane, and estimating a physical quantity related to at least the response between the optical transmitting device and the optical receiving device based on amplitude and phase information of the calculated ratio between the frequency domain signal in the I lane and the frequency domain signal in the Q lane.

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