Transfer function estimation device, transfer function estimation method and program

Abstract

This transfer function estimation device comprises: a synthesis transfer function calculation unit that calculates, on the basis of a signal transmitted by an optical transmitter and a signal received by an optical receiver, a synthesis transfer function obtained by synthesizing a transmission transfer function which influences the signal transmitted by the optical transmitter and a reception transfer function which influences the signal received by the optical receiver, at each frequency offset which is the difference between the frequency of a carrier wave inputted to an optical modulation unit in the optical transmitter and the frequency of a carrier wave inputted to an optical demodulation unit in the optical receiver; and a transfer function separation unit that calculates the transmission transfer function and the reception transfer function from the synthesis transfer function on the basis of the dependency of the synthesis transfer function on the frequency offset.

Description

[Technical Field]

[0001] The present invention relates to a transfer function estimation device, a transfer function estimation method, and a program. [Background technology]

[0002] To increase the capacity of optical transmission, there is a demand for improving the accuracy of imperfection compensation in transmitters and receivers. Patent Document 1 discloses a method for estimating the transfer function of a transmitter and receiver using white noise and a known signal sequence. Patent Document 2 discloses a method for reducing the mixing of the receiver's phase characteristics into the transmitter's phase characteristics when estimating the transmitter and receiver's transfer function by averaging the transmitter and receiver transfer functions obtained when changing the frequency offset.

[0003] However, the method disclosed in Patent Document 1 has the drawback of requiring a white noise source separate from the transmitter and receiver to obtain a tentative receiver-side transfer function, and the transmitter-side transfer function is obtained after the tentative receiver-side transfer function is obtained, and then the receiver-side transfer function is precisely estimated, resulting in an increased number of processing steps.Furthermore, even in the method disclosed in Patent Document 2, depending on the phase characteristics on the receiver side, it is difficult to completely separate the phase characteristics on the receiver side from the phase characteristics on the transmitter side. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6428881 [Patent Document 2] Patent No. 6984784 [Non-patent literature]

[0005] [Non-Patent Document 1] Umberto Mengali and Michele Morelli. 1997. "Data-aided frequency estimation for burst digital transmission" IEEE Transactions on Communications 45(1):23 - 25. Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above circumstances, an object of the present invention is to provide a technique for estimating a transfer function on the transmitting side and a transfer function on the receiving side in fewer steps. [Means for solving the problem]

[0007] One aspect of the present invention is a transfer function estimation device that includes a composite transfer function calculation unit that calculates, based on a signal transmitted by an optical transmitter and a signal received by an optical receiver, a composite transfer function that combines a transmission transfer function that affects the signal transmitted by the optical transmitter and a reception transfer function that affects the signal received by the optical receiver, for each frequency offset that is the difference between the frequency of a carrier wave input to an optical modulation unit in the optical transmitter and the frequency of a carrier wave input to an optical demodulation unit in the optical receiver, and a transfer function separation unit that calculates the transmission transfer function and the reception transfer function from the composite transfer function based on the dependency of the composite transfer function on the frequency offset. [Effects of the Invention]

[0008] According to the present invention, the transfer function on the transmitting side and the transfer function on the receiving side can be estimated in fewer steps. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating an example of the configuration of a transmission / reception system 1 according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of a transfer function estimation device 4 according to an embodiment. [Figure 3] 10 is a diagram showing a composite transfer function, a frequency offset, an amplitude characteristic, and a phase characteristic recorded in a storage unit 43. FIG. [Figure 4] 4 is a flowchart showing the operation of the transfer function estimation device 4. [Figure 5] 10 is a diagram showing the amplitude characteristics and phase characteristics of the transmission transfer function and the reception transfer function calculated by the transfer function estimation device 4. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Embodiment) 1 is a diagram showing an example of the configuration of a transmission / reception system 1 according to an embodiment. The transmission / reception system 1 includes an optical transmitter 2, an optical receiver 3, a transfer function estimation device 4, and an optical transmission path 100. In the transmission / reception system 1, the optical transmitter 2 generates an optical modulated signal from input transmission data and outputs the signal to the optical receiver 3 via the optical transmission path 100. The optical receiver 3 generates and outputs reception data from the optical modulated signal. The transfer function estimation device 4 estimates transfer functions used by the optical transmitter 2 and the optical receiver 3.

[0011] The optical transmitter 2 comprises a modulation signal generator 21, a transmission light source 22, and an optical modulator 23. The modulation signal generator 21 converts input transmission data from bit data into a symbol sequence. The modulation signal generator 21 performs digital signal processing on the symbol sequence to generate a transmission waveform sequence s(t). The digital signal processing performed by the modulation signal generator 21 is, for example, spectrum shaping and pre-equalization of the transfer function of the optical transmitter 2 (hereinafter referred to as the transmission transfer function). The transmission transfer function H Tx The transmitted waveform sequence after (f) is expressed by equation (1) using S(f), which is the frequency domain representation (after Fourier transform) of s(t).

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[0012] where S'(f) is the transmission transfer function H TxThe modulation signal generator 21 outputs S(f) to the transfer function estimator 4.

[0013] The modulation signal generator 21 performs digital-to-analog conversion on the digitally processed signal to generate a modulation signal in the baseband region. The optical modulator 23 converts the modulation signal and the frequency f output from the transmission light source 22. sig The optical modulated signal is generated based on the carrier wave of frequency f in the baseband region and output to the optical receiver 3. sig The electric field signal E(f) of the optical modulation signal modulated by the carrier wave is expressed by equation (2).

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[0014] The optical receiver 3 includes a local light source 31, an optical demodulator 32, and a signal processor 33. The optical demodulator 32 demodulates the optical modulated signal received from the optical transmitter 2 via the optical transmission line 100 into a frequency f lo The baseband signal R(f) generated by the optical demodulator 32 is expressed by equation (3).

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[0015] Here, Δf is the frequency offset between the transmitting light source 22 and the local light source 31, and Δf=f sig -f lo The signal processing unit 33 converts the baseband signal from an analog signal to a digital signal and performs digital signal processing. The digital signal processing performed by the signal processing unit 33 is, for example, spectrum shaping and equalization of the transfer function of the optical receiver 3 (hereinafter referred to as the receiving transfer function). The receiving transfer function H Rx R'(f), which is a signal affected by (f), is expressed by equation (4).

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[0016] The signal processing unit 33 estimates Δf from R(f) and S(f). The signal processing unit 33 estimates Δf by, for example, a method disclosed in Non-Patent Document 1, in which a baseband signal is converted from an analog signal to a digital signal and then the frequency offset is estimated from the time change in the phase relationship between r(t) and the transmission signal waveform s(t). Here, r(t) is the inverse Fourier transform of the received signal. The signal processing unit 33 outputs R'(f) to the transfer function estimation device 4. The signal processing unit 33 may also output R'(f) to the outside as received data.

[0017] FIG. 2 is a diagram illustrating an exemplary configuration of a transfer function estimation device 4 according to an embodiment. The transfer function estimation device 4 includes a composite transfer function calculation unit 41, a transfer function separation unit 42, and a storage unit 43. The composite transfer function calculation unit 41 calculates a composite transfer function by varying a frequency offset Δf. These components are implemented by, for example, a hardware processor such as a CPU (Central Processing Unit) executing a program (software). Some or all of these components may be implemented by hardware (including circuitry) such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a GPU (Graphics Processing Unit), or may be implemented by a combination of software and hardware. The program may be stored in advance in a storage device (a storage device having a non-transitory storage medium) such as an HDD (Hard Disk Drive) or a flash memory, or may be stored in a removable storage medium (a non-transitory storage medium) such as a DVD or a CD-ROM, and installed by inserting the storage medium into a drive device.

[0018] A specific calculation method will be described below. The composite transfer function calculation unit 41 acquires the frequency offset Δf from the optical receiver 3. The composite transfer function calculation unit 41 may acquire Δf by estimating Δf using the same method as the signal processing unit 33, or may acquire Δf by receiving Δf estimated by the signal processing unit 33 from the optical receiver 3. The composite transfer function calculation unit 41 compensates for R'(f) using Δf. The composite transfer function calculation unit 41 may also compensate for chromatic dispersion, polarization mode dispersion, and polarization rotation that occur in the optical fiber of the optical transmission line 100. The composite transfer function calculation unit 41 may also compensate for the phase noise of the transmitting light source 22 and the local light source 31. The corrected signal R'(f+Δf) is expressed by equation (5).

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[0019] The composite transfer function calculation unit 41 divides R'(f+Δf) by S(f) to obtain H Rx (f+Δf)H Tx (f) is the composite transfer function H TRx The frequency offset Δf can be changed by changing the frequency setting value of either or both of the transmitting light source 22 and the local light source 31. The value of the frequency offset Δf is changed by a computer or a user, and the composite transfer function calculation unit 41 calculates a composite transfer function that differs depending on Δf. For example, when the value of Δf is Δf1, Δf2, ... Δf n When the composite transfer function calculation unit 41 calculates the composite transfer function H TRx (f, Δf1), H TRx (f, Δf2), H TRx (f, Δf n The composite transfer function calculation unit 41 records the calculated composite transfer function in the storage unit 43 in association with the frequency offset.

[0020] The transfer function separation unit 42 separates the composite transfer function H TRx Based on the dependence of the frequency offset Δf on (f, Δf), the synthetic transfer function H TRx (f, Δf) is the transmission transfer function H Tx(f) and the receiving transfer function H Rx The estimated value of (f) is calculated. The specific separation method is explained below.

[0021] The transfer function separating unit 42 includes an amplitude characteristic calculating unit 421, a phase characteristic calculating unit 422, an amplitude characteristic separating unit 423, a phase characteristic separating unit 424, an optical transmitter transfer function calculating unit 425, and an optical receiver transfer function calculating unit 426. The amplitude characteristic calculating unit 421 calculates a composite transfer function H TRx (f, Δf1), H TRx (f, Δf2), H TRx (f, Δf n The phase characteristic calculation unit 422 calculates the amplitude characteristic of the composite transfer function H TRx (f, Δf1), H TRx (f, Δf2), H TRx (f, Δf n ) and calculates the phase characteristic of the frequency offset Δf. The amplitude characteristic calculation unit 421 records the calculated amplitude characteristic in the storage unit 43, and the phase characteristic calculation unit 422 records the calculated phase characteristic in the storage unit 43. FIG. 3 is a diagram showing the composite transfer function, frequency offset, amplitude characteristic, and phase characteristic recorded in the storage unit 43. The storage unit 43 records the amplitude characteristic and phase characteristic for different frequency offsets Δf.

[0022] The amplitude characteristic A(f) and the phase characteristic φ(f) are defined by the transfer function H(f) as shown in equations (6) and (7).

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[0023] Equation (6) and H TRx (f, Δf)=H Rx (f+Δf)H Tx Since (f), H TRx Amplitude characteristics A of (f, Δf) TRx (f, Δf) is H Rx Amplitude characteristic A of (f+Δf) Rx (f+Δf) and H Tx (f) Amplitude characteristic ATx It is expressed by equation (8) using (f).

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[0024] Furthermore, equation (7) and H TRx (f, Δf)=H Rx (f+Δf)H Tx Since (f), φ TRx Phase characteristic φ of (f, Δf) TRx (f, Δf) is H Rx Phase characteristic φ of (f+Δf) Rx (f+Δf) and H Tx (f) Phase characteristic φ Tx It is expressed by equation (9) using (f).

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[0025] Equation (8) shows that the amplitude characteristics of the composite transfer function depend only on the amplitude characteristics of the receiver transfer function with respect to changes in Δf. Equation (9) shows that the phase characteristics of the composite transfer function depend only on the phase characteristics of the receiver transfer function with respect to changes in Δf.

[0026] The amplitude characteristic separator 423 generates a composite transfer function H TRx (f, Δf1), H TRx (f, Δf2), H TRx (f, Δf n ) amplitude characteristic A TRx (f, Δf1), A TRx (f, Δf2), ···A TRx (f, Δf n ) on Δf, the amplitude characteristic A of the transmission transfer function Tx (f) and amplitude characteristic A of the receiving transfer function Rx The amplitude characteristic separating unit 423 calculates, for example, A TRx (f, Δf) is polynomial-fitted to Δf using equation (10).

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[0027] The amplitude characteristic separation unit 423 separates the amplitude characteristic A recorded in the storage unit 43. TRx (f, Δf1), A TRx (f, Δf2), ···A TRx (f, Δf n ) is used. The amplitude characteristic separating unit 423 calculates at least a0(f) and a1(f) using equation (10).

[0028] In equation (10), a1(f) is a partial differential about Δf=0 and is expressed by equation (11).

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[0029] Equation (11) is derived from equation (8). The amplitude characteristic separator 423 integrates a1(f) with frequency f to obtain A Rx Calculate (f) (equation (12)).

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[0030] In equation (12), C is an integral constant. The amplitude characteristic separator 423 may be, for example, A Rx By assuming an integral constant C so that the constraint (0) = 0 is satisfied, A Rx This corresponds to the constraint that the amplitude of the DC component does not change in the optical receiver 3.

[0031] The amplitude characteristic separator 423 separates a0(f) and A Rx Based on (f) A Tx Calculate (f). A Tx (f) is expressed by equation (13).

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[0032] The amplitude characteristic separating unit 423 may calculate the integral constant C by assuming a change in the amplitude of the DC component in the optical transmitter 2. In addition, since the relative relationship between frequencies is important for the amplitude characteristic, it is assumed that the integral constant C=0, and A Tx (f) and A Rx After (f), add C1 and C2 to each and A Tx (f) + C1 and A Rx (f)+C2, and the amplitude characteristics may be calculated under the constraint that the amplitude of the DC component does not change in the optical receiver 3 and the optical transmitter 2. Tx (f) and A Rx (f) can be calculated.

[0033] The phase characteristic separation unit 424 is A Tx (f) and A Rx Similarly to (f), the phase characteristic φ Tx (f) and φ Rx The phase characteristic separation unit 424 calculates the composite transfer function H TRx (f, Δf1), H TRx (f, Δf2), H TRx (f, Δf n ) phase characteristic φ TRx (f, Δf1), φ TRx (f, Δf2), φ TRx (f, Δf n ) on Δf, the phase characteristic φ of the transmission transfer function Tx (f) and the amplitude characteristic φ of the receiving transfer function Rx The phase characteristic separation unit 424 calculates, for example, φ TRx (f, Δf) is polynomial-fitted to Δf using equation (14). Note that the phase characteristic is φ TRx (f, Δf1), φ TRx (f, Δf2), φ TRx (f, Δf n ) is unwrapped and then polynomial fitted.

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[0034] The phase characteristic separation unit 424 separates the phase characteristic φ TRx (f, Δf1), φ TRx (f, Δf2), φ TRx (f, Δf n The phase characteristic separation unit 424 calculates at least b0(f) and b1(f) using equation (14).

[0035] In equation (14), b1(f) is a partial differential around Δf=0 and is expressed by equation (15).

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[0036] Equation (15) is derived from equation (9). The phase characteristic separation unit 424 integrates b1(f) with frequency f to obtain φ Rx Calculate (f) (equation (16)).

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[0037] In equation (16), D is an integral constant. The phase characteristic separation unit 424 calculates b0(f) and φ Rx Based on (f), φ Tx (f) is calculated using equation (17).

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[0038] Therefore, the phase characteristic separation unit 424 calculates φ by equation (18) based on equations (16) and (17). Tx Calculate (f).

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[0039] The phase characteristic separation unit 424 separates the phase characteristic by φ since the DC component of the phase characteristic is zero in the baseband domain in both the transmitter and the receiver. Tx (0) = 0, φTx D is determined so as to satisfy (0)=0. As a result, the phase characteristic separation unit 424 determines φ Tx (f) and φ Rx (f) can be calculated.

[0040] The optical transmitter transfer function calculation unit 425 calculates A Tx (f) and φ Tx Based on (f), the transmission transfer function H Tx Calculate (f).

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[0041] The optical receiver transfer function calculation unit 426 calculates A Rx (f) and φ Rx Based on (f), the transfer function H of the optical receiver is calculated using equation (20). Rx Calculate (f).

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[0042] 4 is a flowchart showing the operation of the transfer function estimation device 4. First, the composite transfer function calculation unit 41 acquires S(f) from the optical transmitter 2 and acquires R'(f+Δf) from the optical receiver 3 (step S11). The composite transfer function calculation unit 41 acquires the frequency offset Δf from the optical receiver 3 (step S12). The composite transfer function calculation unit 41 calculates a composite transfer function by dividing S(f) from R'(f+Δf), and records the result in the storage unit 43 (step S13). The amplitude characteristic calculation unit 421 calculates the amplitude characteristic of the composite transfer function, and the phase characteristic calculation unit 422 calculates the phase characteristic of the composite transfer function, and records the calculated amplitude characteristic and phase characteristic (step S14). When the number of composite transfer functions that differ due to the frequency offset Δf recorded in the storage unit 43 is less than a predetermined number (step S15: NO), the frequency f of the carrier wave output from the transmission light source 22 is calculated. sig and the frequency f of the carrier wave output from the local light source 31 loThe frequency offset Δf is changed by adjusting the frequency offset Δf (step S16). The adjustment of the frequency offset may be controlled by a computer or by the user.

[0043] If the number of composite transfer functions that differ due to the frequency offset Δf stored in the storage unit 43 is equal to or greater than a predetermined number (step S15: NO), the amplitude characteristic separation unit 423 calculates the amplitude characteristics of the transmitting transfer function and the receiving transfer function by polynomial fitting the amplitude characteristics of the composite transfer function (step S17). Furthermore, the phase characteristic separation unit 424 calculates the phase characteristics of the transmitting transfer function and the receiving transfer function by polynomial fitting the phase characteristics of the composite transfer function (step S18). The optical transmitter transfer function calculation unit 425 calculates the transmitting transfer function from the amplitude characteristics and phase characteristics of the transmitting transfer function, and the optical receiver transfer function calculation unit 426 calculates the receiving transfer function from the amplitude characteristics and phase characteristics of the receiving transfer function (step S19).

[0044] In the above flowchart, the transfer function separation unit 42 calculates the transmission transfer function and the reception transfer function when the number of composite transfer functions that differ due to the frequency offset Δf recorded in the storage unit 43 is equal to or greater than a predetermined number, but the transfer function separation unit 42 may calculate the transmission transfer function and the reception transfer function regardless of the number of composite transfer functions that differ due to the frequency offset Δf recorded in the storage unit 43. Furthermore, the transfer function separation unit 42 may update the transmission transfer function and the reception transfer function by changing the frequency offset after calculating the transmission transfer function and the reception transfer function, calculating a new composite transfer function, the amplitude characteristic of the composite transfer function, and the phase characteristic of the composite transfer function, and then calculating the transmission transfer function and the reception transfer function again based on the newly calculated amplitude characteristic of the composite transfer function and the phase characteristic of the composite transfer function.

[0045] (Experimental example) The optical transmitter 2 digitally converted the digitally processed signal using a digital-to-analog converter with a sampling rate of 120 GSa / s, generating and outputting an optically modulated signal using a modulation signal with a modulation rate of 120 GBaud. The optical receiver 3 converted the signal received via the optical transmission line 100 using a 256 GSa / s analog-to-digital converter and then converted it to a sampling rate of 120 GSa / s using digital signal processing. The frequency offset Δf was varied from -3000 MHz to 3000 MHz in 500 MHz increments to calculate composite transfer functions that varied depending on Δf, and then the transmitter transfer function and receiver transfer function were calculated. The digital-to-analog converter of the optical transmitter 2 has a cutoff at approximately 50 GHz in the amplitude characteristic, while the analog-to-digital converter of the optical receiver 3 has a sufficiently wide frequency band and linear phase characteristic. Figure 5 shows the amplitude and phase characteristics of the transmitter transfer function and receiver transfer function calculated by the transfer function estimator 4. A cutoff near 50 GHz can be seen in the amplitude characteristic of the transmitter transfer function. Furthermore, the amplitude characteristics of the receiver transfer function are roughly constant at 50 GHz, which is the cutoff frequency for the transmit signal, and the phase characteristics are linear. From the above, it can be seen that the transmitter transfer function and receiver transfer function can be calculated separately.

[0046] As described above, the transfer function estimation device 4 can estimate the transmission transfer function and the reception transfer function without a white noise source, unlike conventional methods. Also, unlike conventional techniques, there is no need to calculate a temporary reception-side transfer function, and the transmission transfer function and the reception transfer function can be estimated in fewer steps, thereby shortening the estimation time. Furthermore, since the amplitude and phase characteristics of the composite transfer function depend only on the amplitude and phase characteristics of the receiver with respect to changes in the frequency offset Δf, it is possible to prevent the phase characteristics of the transmitting transfer function and the receiving transfer function from being mixed together.

[0047] (Other embodiments) The composite transfer function calculation unit 41 calculates the composite transfer function H TRx (f, Δf) as H Rx (f+Δf)H Tx(f) is calculated, but this is not limited to this. For example, H is calculated by using Equation (4) and S(f-Δf). Rx (f)H Tx (f-Δf) may be calculated as the composite transfer function. TRx (f, Δf) as H Rx (f)H Tx When calculating (f-Δf), the amplitude characteristics of the composite transfer function depend only on the amplitude characteristics of the transfer function of the transmitter with respect to changes in Δf, and the phase characteristics of the composite transfer function depend only on the phase characteristics of the transfer function of the transmitter with respect to changes in Δf. Therefore, the transfer function separation unit 42 similarly performs polynomial fitting. Tx After calculating (f), A Rx Calculate (f) and φ Tx After calculating (f), φ Rx (f) is calculated, and H Tx (f) and H Rx Calculate (f). [Explanation of symbols]

[0048] 1 Transmission and reception system, 2 Optical transmitter, 21 Modulation signal generation unit, 22 Transmission light source, 23 Optical modulation unit, 3 Optical receiver, 31 Local light source, 32 Optical demodulation unit, 33 Signal processing unit, 4 Transfer function estimation device, 41 Composite transfer function calculation unit, 42 Transfer function separation unit, 421 Amplitude characteristic calculation unit, 422 Phase characteristic calculation unit, 423 Amplitude characteristic separation unit, 424 Phase characteristic separation unit, 425 Optical transmitter transfer function calculation unit, 426 Optical receiver transfer function calculation unit, 43 Memory unit

Claims

1. a composite transfer function calculation unit that calculates a composite transfer function obtained by combining a transmission transfer function that affects the signal transmitted by the optical transmitter and a reception transfer function that affects the signal received by the optical receiver, for each frequency offset that is the difference between the frequency of a carrier wave input to an optical modulation unit in the optical transmitter and the frequency of a carrier wave input to an optical demodulation unit in the optical receiver, based on the signal transmitted by the optical transmitter and the signal received by the optical receiver; a transfer function separation unit that calculates the transmission transfer function and the reception transfer function from the composite transfer function based on the dependency of the composite transfer function on the frequency offset; A transfer function estimation device comprising:

2. The transfer function separation unit an amplitude characteristic calculation unit that calculates the amplitude characteristic of the composite transfer function; a phase characteristic calculation unit that calculates the phase characteristic of the composite transfer function; an amplitude characteristic separation unit that calculates the amplitude characteristic of the transmission transfer function and the amplitude characteristic of the reception transfer function based on the dependency of the amplitude characteristic of the composite transfer function on the frequency offset; a phase characteristic separation unit that calculates a phase characteristic of the transmission transfer function and a phase characteristic of the reception transfer function based on a dependency of the phase characteristic of the composite transfer function on the frequency offset; an optical transmitter transfer function calculation unit that calculates the transmission transfer function based on the amplitude characteristic and the phase characteristic of the transmission transfer function; an optical receiver transfer function calculation unit that calculates the receiver transfer function based on the amplitude characteristic and phase characteristic of the receiver transfer function; The transfer function estimating device according to claim 1 , comprising:

3. the amplitude characteristic separation unit calculates the amplitude characteristic of the transmission transfer function and the amplitude characteristic of the reception transfer function by polynomial fitting the amplitude characteristic of the composite transfer function to the frequency offset; the phase characteristic separation unit calculates the phase characteristic of the transmission transfer function and the phase characteristic of the reception transfer function by polynomial fitting the phase characteristic of the composite transfer function to the frequency offset. The transfer function estimation device according to claim 2 .

4. a composite transfer function calculation step of calculating, based on a signal transmitted by an optical transmitter and a signal received by an optical receiver, a composite transfer function obtained by combining a transmission transfer function that affects the signal transmitted by the optical transmitter and a reception transfer function that affects the signal received by the optical receiver, for each frequency offset that is the difference between the frequency of a carrier wave input to an optical modulation unit in the optical transmitter and the frequency of a carrier wave input to an optical demodulation unit in the optical receiver; a transfer function separation step of calculating the transmit transfer function and the receive transfer function from the composite transfer function based on the dependency of the composite transfer function on the frequency offset; 1. A computer-implemented transfer function estimation method comprising:

5. A program that causes a computer to operate as the transfer function estimation device according to claim 1.

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