WO2019171587A1

WO2019171587A1 - Optical receiver and optical transmission/reception system

Info

Publication number: WO2019171587A1
Application number: PCT/JP2018/009267
Authority: WO
Inventors: 怜典松本
Original assignee: 三菱電機株式会社
Priority date: 2018-03-09
Filing date: 2018-03-09
Publication date: 2019-09-12
Also published as: JPWO2019171587A1; JP6479278B1

Abstract

An optical receiver (4) is provided with: a distortion amount estimation unit (24b) that estimates, from a pilot signal detected by a pilot signal detection unit (24a) and from a single carrier signal, an amplitude distortion amount of the pilot signal and a phase distortion amount of the pilot signal, respectively; and a distortion correction unit (24e) that corrects an amplitude distortion of the single carrier signal by use of the amplitude distortion amount estimated by the distortion amount estimation unit (24b) and also corrects a phase distortion of the single carrier signal by use of the phase distortion amount estimated by the distortion amount estimation unit (24b).

Description

Optical receiver and optical transmission / reception system

The present invention relates to an optical receiver that demodulates a single carrier signal having signal points on a complex plane having the same phase axis (In-Phase axis: I axis) and a quadrature phase axis (Quadrature-Phase axis: Q axis). And an optical transmission / reception system including an optical receiver that demodulates a single carrier signal.

IEEE 802.3 standardizes a 100G Ethernet passive optical network (hereinafter referred to as “100G-EPON”). IEEE 802.3 is a standard related to Ethernet published by the American Institute of Electrical and Electronics Engineers (IEEE). (Ethernet is a registered trademark)
In 100G-EPON, a coherent passive optical network (hereinafter referred to as “Coherent PON”) is listed as a candidate for achieving a transmission rate of 100 Gbps (Giga Bits Per Second) class.
Coherent PON is a technique for performing digital coherent reception by combining synchronous detection and digital signal processing. An optical receiver that implements Coherent PON can demodulate a multilevel signal with high sensitivity.

However, the performance of digital coherent reception is limited by IQ distortion, which is an imbalance between the I axis and the Q axis. IQ distortion results from imperfections in the transmitting / receiving device.
In particular, low-cost devices used in optical access networks introduce large IQ distortion, so the performance of digital coherent reception results in severe degradation.

Patent Document 1 below discloses a compensation method for compensating IQ imbalance by using known signals modulated respectively to a first carrier frequency and a second carrier frequency in an orthogonal frequency division multiplexed signal. .
Hereinafter, the orthogonal frequency division multiplexing is referred to as OFDM (Orthogonal Frequency Division Multiplexing).

Special table 2014-502816

In the compensation method disclosed in Patent Document 1, when IQ imbalance is compensated, a known signal modulated to each of the first carrier frequency and the second carrier frequency in the OFDM signal is used. However, the compensation method using the known signal has a problem that it cannot compensate for IQ distortion in a single carrier signal in which signal points exist on a complex plane having an I axis and a Q axis.

The present invention has been made to solve the above-described problems, and is an optical receiver capable of compensating for IQ distortion in a single carrier signal in which signal points exist on a complex plane having an I axis and a Q axis. The purpose is to obtain.
Another object of the present invention is to provide an optical transmission / reception system including an optical receiver capable of compensating for IQ distortion in a single carrier signal having signal points on a complex plane having an I axis and a Q axis. .

An optical receiver according to the present invention includes a pilot signal detector that detects a pilot signal included in a single carrier signal in which signal points exist on a complex plane having the same phase axis and a quadrature phase axis, and a pilot signal detection A distortion amount estimation unit for estimating the amplitude distortion amount of the pilot signal and the phase distortion amount of the pilot signal from the pilot signal detected by the monitoring unit and the single carrier signal, and the amplitude distortion amount estimated by the distortion amount estimation unit. A distortion correction unit that corrects the amplitude distortion of the single carrier signal and corrects the phase distortion of the single carrier signal using the phase distortion amount estimated by the distortion amount estimation unit. Thus, the single carrier signal in which each of the amplitude distortion and the phase distortion is corrected is demodulated.

According to the present invention, the distortion amount estimation unit and the distortion amount estimation unit for estimating the amplitude distortion amount of the pilot signal and the phase distortion amount of the pilot signal from the pilot signal and the single carrier signal detected by the pilot signal detection unit, respectively. A distortion correction unit that corrects the amplitude distortion of the single carrier signal using the amplitude distortion amount estimated by the step, and corrects the phase distortion of the single carrier signal using the phase distortion amount estimated by the distortion amount estimation unit. An optical receiver was configured to provide. Therefore, the optical receiver according to the present invention can compensate for IQ distortion in a single carrier signal in which signal points exist on a complex plane having an I axis and a Q axis.

1 is a configuration diagram illustrating an optical transmission / reception system according to Embodiment 1. FIG. 2 is a configuration diagram showing the inside of an IQ distortion compensation unit 24. FIG. 2 is a hardware configuration diagram showing hardware of a digital signal processing unit 13. FIG. It is a hardware block diagram of a computer in case the digital signal processing part 13 is implement | achieved by software or firmware. It is explanatory drawing which shows the frame structure of the single carrier signal containing a pilot signal. It is explanatory drawing which shows the frequency spectrum of the single carrier signal to which IQ distortion is not added, and the frequency spectrum of the single carrier signal to which IQ distortion is added. It is explanatory drawing which shows each simulation result of phase distortion amount (theta) hat and amplitude distortion amount g hat estimated by the distortion amount estimation part 24b. Is an explanatory diagram showing experimental results of bit error rate of a single carrier signal r _n demodulated by the demodulator 25. Figure 9A is an explanatory view showing the arrangement of signal points in the case where compensation processing of the IQ skew in the single-carrier signal r _n is not performed, FIG. 9B, as the optical receiver 4 shown in FIG. 1, the single carrier signal is an explanatory view showing the arrangement of signal points when doing the compensation of the IQ skew in r _n. FIG. 6 is a configuration diagram illustrating an optical transmission / reception system according to a second embodiment. 2 is a configuration diagram showing the inside of an IQ distortion compensation unit 105. FIG. 2 is a hardware configuration diagram showing hardware of a digital signal processing unit 93. FIG. It is explanatory drawing which shows the frame structure of the polarization multiplexing signal with which the 1st single carrier signal and the 2nd single carrier signal are multiplexed.

Hereinafter, in order to explain the present invention in more detail, modes for carrying out the present invention will be described with reference to the accompanying drawings.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram illustrating an optical transmission / reception system according to the first embodiment.
FIG. 2 is a configuration diagram showing the inside of the IQ distortion compensation unit 24.
FIG. 3 is a hardware configuration diagram showing hardware of the digital signal processing unit 13.
1 to 3, the optical transmitter 1 includes a light source 1 a and is connected to an optical receiver 4 through an optical fiber 2.
The optical transmitter 1 transmits a pilot signal to a single carrier signal having signal points on a complex plane having the same phase axis (In-Phase axis: I axis) and a quadrature phase axis (Quadrature-Phase axis: Q axis). include.
The pilot signal included in the single carrier signal by the optical transmitter 1 is a signal equal to a signal obtained by multiplying the complex conjugate signal of the pilot signal by an imaginary unit.
The optical transmitter 1 transmits the single carrier signal to the optical receiver 4 by using the light output from the light source 1 a and outputting the single carrier signal including the pilot signal as an optical signal to the optical fiber 2. To do.

The optical fiber 2 is an optical transmission line having one end connected to the optical transmitter 1 and the other end connected to the optical receiver 4.
The local light source 3 is a light source that outputs a local signal, which is local light, to the optical receiver 4.
The optical receiver 4 includes a photoelectric conversion circuit 11, an A / D converter 12 that is an analog-digital converter, and a digital signal processing unit 13.
The optical receiver 4 is a digital coherent receiver that receives the single carrier signal transmitted from the optical transmitter 1 and demodulates the received single carrier signal.

The photoelectric conversion circuit 11 converts the single carrier signal transmitted from the optical transmitter 1 from an optical signal into an electrical signal, and converts the local signal output from the local light source 3 from an optical signal into an electrical signal.
The photoelectric conversion circuit 11 outputs a single carrier signal that is an electric signal and a local oscillation signal that is an electric signal to the A / D converter 12.
The A / D converter 12 converts the single carrier signal output from the photoelectric conversion circuit 11 from an analog signal to a digital signal, and converts the local signal output from the photoelectric conversion circuit 11 from an analog signal to a digital signal. .
The A / D converter 12 outputs a single carrier signal that is a digital signal and a local signal that is a digital signal to the digital signal processing unit 13.

The digital signal processing unit 13 includes a frame synchronization unit 21, a frequency compensation unit 22, a phase compensation unit 23, an IQ distortion compensation unit 24, and a demodulation unit 25.
The frame synchronization unit 21 is realized by, for example, the frame synchronization circuit 41 illustrated in FIG.
The frame synchronization unit 21 uses the local signal output from the A / D converter 12 to detect the head of the single carrier signal output from the A / D converter 12, and detects the single carrier signal that has detected the head and Each of the local signals is output to the frequency compensation unit 22.

The frequency compensation unit 22 is realized by, for example, the frequency compensation circuit 42 illustrated in FIG.
The frequency compensation unit 22 detects a frequency error between the frequency of the single carrier signal output from the frame synchronization unit 21 and the frequency of the local oscillation signal, and performs a process of removing the frequency error included in the frequency of the single carrier signal. carry out.
The frequency compensation unit 22 outputs the single carrier signal from which the frequency error has been removed to the phase compensation unit 23.
The phase compensation unit 23 is realized by, for example, the phase compensation circuit 43 illustrated in FIG.
The phase compensation unit 23 performs a process for removing phase noise included in the phase of the single carrier signal output from the frequency compensation unit 22.
The phase compensation unit 23 outputs the single carrier signal from which the phase noise has been removed to the IQ distortion compensation unit 24.

As shown in FIG. 2, the IQ distortion compensation unit 24 includes a pilot signal detection unit 24a, a distortion amount estimation unit 24b, and a distortion correction unit 24e.
The pilot signal detection unit 24a is realized by, for example, a signal detection circuit 44 illustrated in FIG.
The pilot signal detection unit 24a detects a pilot signal included in the single carrier signal output from the phase compensation unit 23, and performs processing to output the pilot signal to the distortion amount estimation unit 24b.

The distortion amount estimation unit 24b includes a distortion amount estimation processing unit 24c and an averaging processing unit 24d, and is realized by, for example, the distortion amount estimation circuit 45 illustrated in FIG.
The distortion amount estimation unit 24b, from the pilot signal output from the pilot signal detection unit 24a and the single carrier signal, an amplitude distortion amount that is the magnitude of the amplitude distortion of the pilot signal and a phase that is the magnitude of the phase distortion of the pilot signal. A process of estimating the amount of distortion is performed.
The distortion amount estimation unit 24b outputs each of the amplitude distortion amount and the phase distortion amount to the distortion correction unit 24e.

Based on the fact that the pilot signal output from the pilot signal detector 24a is a signal equal to a signal obtained by multiplying the complex conjugate signal of the pilot signal by an imaginary unit, the distortion amount estimation processing unit 24c generates a single carrier signal. A process of decomposing the real part and the imaginary part is performed.
The distortion amount estimation processing unit 24c performs processing of estimating the amplitude distortion amount of the pilot signal from the imaginary part of the single carrier signal and estimating the phase distortion amount of the pilot signal from the real part of the single carrier signal.
The averaging processing unit 24d performs a process of calculating the average amplitude distortion amount by averaging the amplitude distortion amount estimated N times by the distortion amount estimation processing unit 24c.
The averaging processing unit 24d performs a process of calculating the average phase distortion amount by averaging the phase distortion amount estimated N times by the distortion amount estimation processing unit 24c.

The distortion correction unit 24e includes a delay unit 24f and a distortion correction processing unit 24g, and is realized by, for example, the distortion correction circuit 46 illustrated in FIG.
The distortion correction unit 24e performs a process of correcting the amplitude distortion of the single carrier signal using the average amplitude distortion amount calculated by the averaging processing unit 24d.
In addition, the distortion correction unit 24e performs a process of correcting the phase distortion of the single carrier signal using the average phase distortion amount calculated by the averaging processing unit 24d.
The distortion correction unit 24 e outputs a single carrier signal obtained by correcting each of the amplitude distortion and the phase distortion to the demodulation unit 25.

The delay unit 24f is a total time of the processing time of the pilot signal detection unit 24a for detecting the pilot signal and the processing time of the distortion amount estimation unit 24b for calculating each of the average amplitude distortion amount and the average phase distortion amount. A process of delaying the single carrier signal by the amount is performed.
The delay unit 24f outputs the delayed single carrier signal to the distortion correction processing unit 24g.
The distortion correction processing unit 24g performs a process of correcting the amplitude distortion of the single carrier signal output from the delay unit 24f using the average amplitude distortion amount calculated by the averaging processing unit 24d.
Further, the distortion correction processing unit 24g performs a process of correcting the phase distortion of the single carrier signal in which the amplitude distortion is corrected, using the average phase distortion amount calculated by the averaging processing unit 24d.

The demodulator 25 is realized by, for example, a demodulator circuit 47 shown in FIG.
The demodulator 25 performs a process of demodulating the single carrier signal whose amplitude distortion and phase distortion are corrected by the distortion correction processor 24g.

In FIG. 1, a frame synchronization unit 21, a frequency compensation unit 22, a phase compensation unit 23, a pilot signal detection unit 24 a, a distortion amount estimation unit 24 b, a distortion correction unit 24 e, and a demodulation unit 25 that are components of the digital signal processing unit 13. Each is assumed to be realized by dedicated hardware as shown in FIG. That is, it is assumed that the digital signal processing unit 13 is realized by the frame synchronization circuit 41, the frequency compensation circuit 42, the phase compensation circuit 43, the signal detection circuit 44, the distortion amount estimation circuit 45, the distortion correction circuit 46, and the demodulation circuit 47. doing.
The frame synchronization circuit 41, the frequency compensation circuit 42, the phase compensation circuit 43, the signal detection circuit 44, the distortion amount estimation circuit 45, the distortion correction circuit 46, and the demodulation circuit 47 are, for example, a single circuit, a composite circuit, a programmed processor, A parallel-programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof is applicable.
FIG. 4 is a hardware configuration diagram of a computer when the digital signal processing unit 13 is realized by software or firmware.

The components of the digital signal processing unit 13 are not limited to those realized by dedicated hardware, but the digital signal processing unit 13 is realized by software, firmware, or a combination of software and firmware. May be.
Software or firmware is stored as a program in the memory of a computer. The computer means hardware that executes a program, for example, a CPU (Central Processing Unit), a central processing unit, a processing unit, a processing unit, a microprocessor, a microcomputer, a processor, or a DSP (Digital Signal Processor) To do.

When the digital signal processing unit 13 is realized by software or firmware, the frame synchronization unit 21, the frequency compensation unit 22, the phase compensation unit 23, the pilot signal detection unit 24a, the distortion amount estimation unit 24b, the distortion correction unit 24e, and the demodulation unit A program for causing the computer to execute the 25 processing procedures is stored in the memory 52. Then, the computer processor 51 executes the program stored in the memory 52.
FIG. 3 shows an example in which each component of the digital signal processing unit 13 is realized by dedicated hardware, and FIG. 4 shows an example in which the digital signal processing unit 13 is realized by software or firmware. ing. However, some components in the digital signal processing unit 13 may be realized by dedicated hardware, and the remaining components may be realized by software or firmware.

Next, the operation of the optical transmission / reception system shown in FIG. 1 will be described.
The optical transmitter 1 generates a single carrier signal having signal points on a complex plane having an I axis and a Q axis, and includes a pilot signal in the single carrier signal.
Here, FIG. 5 is an explanatory diagram showing a frame configuration of a single carrier signal including a pilot signal.
The frame of the single carrier signal is a burst frame 61.
The burst frame 61 includes a first frame 62 that stores a frame synchronization signal, a second frame 63 that stores a pilot signal, and a third frame 64 that stores a payload of a single carrier signal. . In the burst frame 61, a fourth frame 65 for storing a frame end signal is arranged.

The frame synchronization signal stored in the first frame 62 is a signal set in advance between the optical transmitter 1 and the optical receiver 4.
Each of the pilot signal stored in the second frame 63 and the payload stored in the third frame 64 is modulated using, for example, a quadrature phase shift keying (QPSK).
The pilot signal is a signal set in advance between the optical transmitter 1 and the optical receiver 4 and is a signal equal to a signal obtained by multiplying the complex conjugate signal of the pilot signal by an imaginary unit.
For example, in the n-th sampling, if the pilot signal included in the single carrier signal is s _n , the pilot signal s _n is expressed by the following equation (1). The single carrier signal in the nth sampling is a single carrier signal that the optical transmitter 1 transmits nth.

In Expression (1), j is an imaginary unit, and s _n ^* is a complex conjugate signal of the pilot signal s _n .

The optical transmitter 1 transmits the single carrier signal to the optical receiver 4 by using the light output from the light source 1 a and outputting the single carrier signal including the pilot signal as an optical signal to the optical fiber 2. To do.
The single carrier signal, which is an optical signal, is output to the optical receiver 4 with IQ distortion and additive white Gaussian noise added.
The local light source 3 outputs a local signal, which is local light, to the optical receiver 4.

The photoelectric conversion circuit 11 converts the single carrier signal transmitted from the optical transmitter 1 from an optical signal to an electrical signal, and outputs the single carrier signal, which is an electrical signal, to the A / D converter 12.
The photoelectric conversion circuit 11 converts the local oscillation signal output from the local light source 3 from an optical signal into an electrical signal, and outputs the local oscillation signal, which is an electrical signal, to the A / D converter 12.

When receiving a single carrier signal from the photoelectric conversion circuit 11, the A / D converter 12 converts the single carrier signal from an analog signal to a digital signal, and outputs the single carrier signal, which is a digital signal, to the frame synchronization unit 21.
When receiving the local oscillation signal from the photoelectric conversion circuit 11, the A / D converter 12 converts the local oscillation signal from an analog signal to a digital signal, and outputs the local oscillation signal, which is a digital signal, to the frame synchronization unit 21.

The frame synchronization unit 21 causes the local signal output from the A / D converter 12 to interfere with the single carrier signal output from the A / D converter 12 to thereby convert the signal sequence included in the single carrier signal. Determine.
The frame synchronization unit 21 compares the signal sequence included in the single carrier signal with the frame synchronization signal set in advance between the optical transmitter 1 and the optical receiver 4 to obtain the first The frame synchronization signal stored in the frame 62 is detected.
The frame synchronization unit 21 detects the head of the single carrier signal by detecting the frame synchronization signal stored in the first frame 62.
The frame synchronization unit 21 outputs each of the single carrier signal and the local oscillation signal whose head is detected to the frequency compensation unit 22.

The frequency compensation unit 22 detects a frequency error Δf between the frequency of the single carrier signal output from the frame synchronization unit 21 and the frequency of the local signal output from the frame synchronization unit 21.
Then, the frequency compensation unit 22 removes the frequency error Δf included in the frequency of the single carrier signal.
Since the frequency error Δf removal process itself is a known technique, a detailed description thereof will be omitted. For example, the removal process of the frequency error Δf is disclosed in Non-Patent Document 1 below.
[Non-Patent Document 1]
“Frequency Estimation in Intradyne Reception” Andreas Leven, Senior Member, IEEE, Noriaki Kaneda, Member, IEEE, Ut-Va Koc, Member, IEEE, and Young-Kai Chen, Fellow, IEEE
The frequency compensation unit 22 outputs a single carrier signal from which the frequency error Δf has been removed to the phase compensation unit 23.

The phase compensation unit 23 removes the phase noise ρ included in the phase of the single carrier signal output from the frequency compensation unit 22. The phase noise ρ is noise generated from the light source 1 a or the local light source 3 of the optical transmitter 1.
Since the process of removing the phase noise ρ itself is a known technique, a detailed description thereof is omitted. For example, the removal process of the phase noise ρ is disclosed in Non-Patent Document 2 below.
[Non-Patent Document 2]
“Nonlinear Estimation of PSK-Modulated Carrier Phase with Application to Burst Digital Transmission” ANDREW J. VITERBI, FELLOW, IEEE, AND AUDREY M. VITERBI, MEMBER, IEEE Abstract
The phase compensation unit 23 outputs a single carrier signal from which the phase noise ρ has been removed to the IQ distortion compensation unit 24.

FIG. 6 is an explanatory diagram showing a frequency spectrum of a single carrier signal to which IQ distortion is not added and a frequency spectrum of a single carrier signal to which IQ distortion is added.
In FIG. 6, reference numeral 71 denotes a frequency spectrum of a single carrier signal to which no IQ distortion is added. The single carrier signal to which no IQ distortion is added is the desired signal itself.
A single carrier signal to which IQ distortion is added includes an interference signal in addition to a desired signal.
Reference numeral 72 denotes the frequency spectrum of the desired signal. The intensity of the frequency spectrum 72 of the desired signal is lower than that of the frequency spectrum 71 due to the influence of IQ distortion.
73 shows the frequency spectrum of the interference signal accompanying IQ distortion.

Here, a desired signal x _n, if the composite signal between the interfering signal and the desired signal x _n is to be y _n, the synthesized signal y _n is represented by the following formula (2).

In the formula (2), g is amplitude distortion of the desired signal _{x n,} theta is the phase distortion of the desired signal _{x _n,} _x ^{n *} is the complex conjugate signal of the desired signal _{x n.}

Pilot signal optical transmitter 1 is included in the single-carrier signal is a pilot signal s _n shown in equation (1). Therefore, when the single-carrier signal from the phase compensation unit 23 is output to the IQ distortion compensator 24 is assumed to be r _n, the single-carrier signal r _n, is expressed by the following equation (3).

In the text of the specification, on the relationship between the electronic filing, the letter "g", can not be denoted by the symbol of the character "θ" on the "^", hereinafter referred to as "g _n hat", "θ _n hat ".
In the formula (3), g _n hat the instantaneous value of the amplitude distortion of the pilot signal s _n at the n-th sampling, theta _n hat is the instantaneous value of the phase distortion of the pilot signal s _n at the n-th sampling.

Pilot signal detection unit 24a receives a single carrier signal r _n from the phase compensation unit 23, detects a pilot signal s _n contained in the single-carrier signal r _n.
Pilot signal s _n is stored in the second frame 63 included in the burst frames 61.
Pilot signal detection unit 24a outputs the detected pilot signal s _n to the distortion amount estimation processing unit 24c.

Distortion amount estimation processing unit 24c, as shown in the following equation (4) and (5), decomposes the single-carrier signal r _n output from the phase compensation unit 23 to the real part Re and imaginary part Im.
Pilot signal s _n output from the pilot signal detection unit 24a is, because it is equal to the signal and the complex conjugate signal s _n ^* to signal the imaginary unit j is multiplied by the single-carrier signal r _n shown in equation (3) is, It can be decomposed into a real part Re and an imaginary part Im.

Distortion amount estimation processing unit 24c estimates the phase distortion amount theta _n hat of a pilot signal s _n from the real part Re of the single-carrier signal r _n, and outputs the phase distortion amount theta _n hat averaging unit 24d.
Further, the distortion amount estimation processing unit 24c estimates and the imaginary part Im of the single-carrier signal r _n, and a phase distortion amount theta _n hat estimated pilot signal s _n the amplitude distortion amount g _n hat, amplitude distortion amount g _{The n} hat is output to the averaging processing unit 24d.
Phase distortion amount theta _n hat of a pilot signal s _n corresponds to phase distortion of a single-carrier signal r _n, an amplitude distortion amount g _n-hat of the pilot signal s _n is equivalent to the amplitude distortion of the single-carrier signal r _n To do.

The averaging processing unit 24d performs an averaging process on each of the phase distortion amount θ _n hat and the amplitude distortion amount g _n hat output from the distortion amount estimation processing unit 24c in order to reduce the influence of white noise or the like.
Specifically, as shown in the following equation (6), the averaging processing unit 24d performs N phase distortion amounts θ _n hat in the first to Nth samplings output from the distortion amount estimation processing unit 24c. Is averaged to calculate the average phase distortion amount θ hat.

The averaging processing section 24d, as shown in the following equation (7), the N amplitude distortion amount g _n-hat of the first ~ N th sampling output from the distortion amount estimating unit 24c averages Thus, the average amplitude distortion amount g hat is calculated.

The averaging processing unit 24d outputs each of the average phase distortion amount θ hat and the average amplitude distortion amount g hat to the distortion correction processing unit 24g.

Delay section 24f in advance, the processing time _{T 1} of the pilot signal detecting unit 24a, is aware of the total time _{_{_{T 3 (= T 1 + T}}} 2) and the processing time _{T 2} of the distortion amount estimating section 24b. For example, the internal memory of the delay section 24f, the total time T ₃ is pre-stored.
Processing time T ₁ of the pilot signal detecting unit 24a is the time required for detection of the pilot signal s _n.
Processing time T ₂ of the distortion amount estimating unit 24b, and calculates the average phase distortion amount θ hat, the average amplitude distortion amount g hat calculated and the time required.
Delay unit 24f receives a single carrier signal r _n from the phase compensation unit 23, only the total time T _3, and outputs the hold the single-carrier signal r _n, the single-carrier signal r _n to the distortion correction processing section 24g .

Distortion correction processing unit 24g, using the average amplitude distortion amount g hat output from the averaging process unit 24d, to correct the amplitude distortion of the single-carrier signal r _n output from the delay section 24f.
Amplitude distortion of the single-carrier signal r _n, for example, multiplication and addition average amplitude distortion amount g hat to the amplitude of the single-carrier signal r _n, or subtracts multiply the average amplitude distortion amount g hat from the amplitude of the single carrier signal r _n This can be corrected.
Further, the distortion correction processing section 24g, using the average phase distortion amount θ hat output from the averaging process unit 24d, corrects the phase distortion of the single-carrier signal r _n the amplitude distortion has been corrected.
Phase distortion of the single-carrier signal r _n, for example, multiplication and addition average phase distortion amount θ hat to the phase of the single-carrier signal r _n obtained by correcting the amplitude distortion, or from the phase of a single carrier signal r _n obtained by correcting the amplitude distortion Correction can be made by multiplying and subtracting the average phase distortion amount θ hat.

Here, the distortion correction processing section 24g is, after correcting the amplitude distortion of the single-carrier signal r _n, shows an example of correcting a phase distortion of the single-carrier signal r _n. However, this is only an example, the distortion correction processing section 24g is also possible to previously correct the phase distortion of the single-carrier signal r _n, correcting the amplitude distortion of the single-carrier signal r _n obtained by correcting the phase distortion Good.
Distortion correction processing unit 24g is a single carrier signal r _n obtained by correcting the respective amplitude distortion and phase distortion, and outputs to the demodulation section 25 as a single-carrier signal r _{n '.}

The demodulation unit 25 performs a demodulation process on the single carrier signal r _n ′ output from the distortion correction processing unit 24g, and extracts signal points existing on a complex plane having the I axis and the Q axis.
Since the demodulation processing itself of the single carrier signal r _n ′ is a known technique, detailed description thereof is omitted.

FIG. 7 is an explanatory diagram illustrating simulation results of the phase distortion amount θ hat and the amplitude distortion amount g hat estimated by the distortion amount estimation unit 24b.
In the simulation of this case, the optical transmitter 1, it is assumed that the single-carrier signal r _n is transmitted at a symbol rate of 32Gb / s.
Further, in the simulation, 50,000 symbols such as the payload contained in the single-carrier signal r _n is, are modulated by the modulation scheme of QPSK, pilot signals of N symbols is included in the single-carrier signal r _n It is supposed to be.
In the simulation, the single-carrier signals r _n which are transmitted from the optical transmitter 1, on the IQ distortion and additive white Gaussian noise is added, it is assumed to be received in the optical receiver 4.
In the simulation, the amplitude distortion in IQ distortion is 4 dB, the phase distortion in IQ distortion is 40 degrees, and the signal-to-noise ratio (Signal to Noise Ratio: SNR) is 11.5 dB.

FIG. 7 shows the relationship between the average filter length and the square error, where (1) represents the estimation error of the amplitude distortion amount g hat, and (2) represents the estimation error of the phase distortion amount θ hat. ing. The average filter length corresponds to the number of samples used for averaging the phase distortion amount θ _n hat and the amplitude distortion amount g _n hat in the averaging processing unit 24d.
Each estimation error in the amplitude distortion amount g hat and the phase distortion amount θ hat is a square error of 10 ⁻² or less in an average filter length of 10 or more, as shown in FIG.
Therefore, the estimation error included in each of the phase distortion amount θ hat and the amplitude distortion amount g hat is a square error of 10 ⁻² or less at an average filter length of 10 or more, and the distortion amount estimation unit 24 b performs high estimation. It can be seen that an accurate distortion amount can be obtained.

8, the bit error rate of a single carrier signal _{r n} demodulated by the demodulator 25: is an explanatory diagram showing experimental results of (Bit Error Ratio BER).
In this case the experiment, the transmission distance of the single-carrier signals r _n which are transmitted from the optical transmitter 1 to the optical receiver 4 is assumed to be 40 km.
In the experiment, has a frame synchronizing signal included in the single-carrier signal _{r n,} the pilot signal, each of the transmission time corresponding to each of the signal length of the payload and frame termination signal 816ns, 10ns, 10495ns, assumed to be 100 ns.
In the simulation, the modulation scheme of a single carrier signal _{r n} is polarization multiplexed 4-level phase modulation 32Gbaud: is assumed to be (Dual Polarization Quadrature Phase Shift Keying DP -QPSK).
In the simulation, it is assumed that the amplitude distortion in IQ distortion is 4 dB, the phase distortion in IQ distortion is 40 degrees, and the average filter length is 20 (in the averaging processing unit 24d, the number of samples used for averaging is N = 20).

Figure 8 shows the relationship between the received optical power and BER of the single-carrier signals r _n which are input to the optical receiver 4.
8, (1) shows the BER of the case where compensation processing of the IQ skew in the single-carrier signal r _n is not performed.
(2), as the optical receiver 4 shown in FIG. 1 shows the BER of the case where performing compensation processing of the IQ skew in the single-carrier signal r _n.
(3) shows an ideal BER in the case where the IQ distortion single carrier signal r _n is not added.

In the optical receiver 4 shown in FIG. 1, as shown in (2) of FIG. 8, the received optical power when the BER is 4.3 × 10 ⁻³ is −31.4 (dBm).
If the compensation processing of the IQ skew in the single-carrier signal _{r n} is not performed, as shown in (1) in FIG. 8, the received optical power when the BER is 4.3 × ^{10 -3} is -27.3 (DBm) received light power.
Accordingly, the optical receiver 4 shown in Figure 1, than if the compensation processing of the IQ skew is not performed in the single-carrier signal r _n, only 4.1 (dB), even at low received optical power, BER is The same 4.3 × 10 ⁻³ , and the reception sensitivity is improved.
In other words, in the optical receiver 4 shown in FIG. 1, if the received optical power is the same, the BER is lower than that in the case _where the IQ distortion compensation processing for the single carrier signal rn is not performed.
If IQ distortion single carrier signal _{r n} is not added, as shown in (3) in FIG. 8, the received optical power when the BER is 4.3 × ^{10 -3} is, -31.7 (dBm) It is.
Accordingly, the optical receiver 4 shown in FIG. 1, as compared with the case where the IQ distortion single carrier signal r _n is not added, the deterioration of the reception sensitivity when the BER is 4.3 × 10 ^-3 is slightly 0 .3 (dBm).

Figure 9 is an explanatory view showing the arrangement of signal points in a single carrier signal _{r n} when received optical power is -29.7 (dBm).
Figure 9A shows an arrangement of signal points in the case where compensation processing of the IQ skew in the single-carrier signal r _n is not performed, FIG. 9B, as the optical receiver 4 shown in FIG. 1, the single carrier signal It shows an arrangement of signal points when doing the compensation of the IQ skew in r _n.
9A and 9B show the respective arrangements at 11 signal points, 10 signal points, 01 signal points, and 00 signal points.
In the optical receiver 4 shown in FIG. 1, since the influence of IQ distortion is removed, the signal points are arranged at appropriate positions as shown in FIG. 9B. Accordingly, the optical receiver 4 shown in FIG. 1, it is possible to prevent the demodulation accuracy of the degradation of a single-carrier signal r _n.
The optical receiver is not performed compensation processing of the IQ skew in the single-carrier signal r _n, the influence of IQ distortion, as shown in FIG. 9A, the arrangement of signal points are shifted from the proper position.
For example, 11 signal points are originally arranged in the vicinity of the position where the I axis is +1 and the Q axis is +1, as shown in FIG. 9B. However, when IQ distortion compensation processing is not performed, among the 11 signal points, as shown in FIG. 9A, there are signal points in which the I axis is arranged on the −1 side from 0, There is a signal point in which the Q axis is arranged on the −1 side from 0.

In the first embodiment, the distortion amount estimation unit 24b that estimates the amplitude distortion amount of the pilot signal and the phase distortion amount of the pilot signal from the pilot signal and the single carrier signal detected by the pilot signal detection unit 24a, The amplitude distortion of the single carrier signal is corrected using the amplitude distortion amount estimated by the distortion amount estimation unit 24b, and the phase distortion of the single carrier signal is corrected using the phase distortion amount estimated by the distortion amount estimation unit 24b. The optical receiver 4 is configured to include the distortion correcting unit 24e. Therefore, the optical receiver 4 can compensate for IQ distortion in a single carrier signal in which signal points exist on a complex plane having the I axis and the Q axis.

The digital signal processing unit 13 illustrated in FIG. 1 illustrates an example including a frequency compensation unit 22 and a phase compensation unit 23.
In place of the digital signal processing unit 13 shown in FIG. 1 including the frequency compensation unit 22 and the phase compensation unit 23, for example, the optical transmitter 1 outputs the phase of the light output from the light source 1a and the output from the local light source 3. A phase synchronization circuit that synchronizes with the phase of the local light to be emitted may be provided.
If the optical transmitter 1 includes the phase synchronization circuit, it is possible to prevent the generation of the frequency error Δf included in the frequency of the single carrier signal and the generation of the phase noise ρ included in the phase of the single carrier signal.
In the phase synchronization circuit, the processing itself for synchronizing the phase of the light output from the light source 1a and the phase of the local light output from the local light source 3 is a known technique, and thus detailed description thereof is omitted. It is also known that the phase synchronization circuit can prevent the occurrence of the frequency error Δf and the generation of the phase noise ρ by performing a process for achieving synchronization.

Embodiment 2. FIG.
In the optical receiver 4 according to the first embodiment, an example is shown in which a single carrier signal in which signal points are present on a complex plane having an I axis and a Q axis is demodulated.
In the second embodiment, an optical receiver 82 that demodulates a first single carrier signal for the first polarization and a second single carrier signal for the second polarization will be described.
The first polarization and the second polarization are polarizations orthogonal to each other. Further, each of the first single carrier signal and the second single carrier signal is a signal on a complex plane having the I axis and the Q axis, similarly to the single carrier signal demodulated by the optical receiver 4 of the first embodiment. It is a single carrier signal in which dots exist.

FIG. 10 is a configuration diagram illustrating an optical transmission / reception system according to the second embodiment.
FIG. 11 is a configuration diagram showing the inside of the IQ distortion compensation unit 105.
FIG. 12 is a hardware configuration diagram showing hardware of the digital signal processing unit 93.
10 to 12, the same reference numerals as those in FIGS. 1 to 3 denote the same or corresponding parts, and thus the description thereof is omitted.
The optical transmitter 81 includes a light source 81 a and is connected to the optical receiver 82 via the optical fiber 2.
The optical transmitter 81 includes the first pilot signal in the first single carrier signal and includes the second pilot signal in the second single carrier signal.
The first pilot signal is a signal equal to a signal obtained by multiplying the complex conjugate signal of the first pilot signal by an imaginary unit.
The second pilot signal is a signal equal to a signal obtained by multiplying the complex conjugate signal of the second pilot signal by an imaginary unit.
The optical transmitter 81 generates a polarization multiplexed signal in which the first single carrier signal and the second single carrier signal are multiplexed.
The optical transmitter 81 transmits the polarization multiplexed signal to the optical receiver 82 by using the light output from the light source 81 a and outputting the polarization multiplexed signal as an optical signal to the optical fiber 2.

The optical receiver 82 includes a photoelectric conversion circuit 91, an A / D converter 92, and a digital signal processing unit 93.
The optical receiver 82 receives the polarization multiplexed signal transmitted from the optical transmitter 81 and separates each of the first single carrier signal and the second single carrier signal from the polarization multiplexed signal.
The optical receiver 82 demodulates each of the first single carrier signal and the second single carrier signal.

The photoelectric conversion circuit 91 converts the polarization multiplexed signal transmitted from the optical transmitter 81 from an optical signal to an electrical signal, and converts the local oscillation signal output from the local light source 3 from an optical signal to an electrical signal.
The photoelectric conversion circuit 91 outputs a polarization multiplexed signal that is an electric signal and a local signal that is an electric signal to the A / D converter 92.
The A / D converter 92 converts the polarization multiplexed signal output from the photoelectric conversion circuit 91 from an analog signal to a digital signal, and converts the local oscillation signal output from the photoelectric conversion circuit 91 from an analog signal to a digital signal. To do.
The A / D converter 92 outputs a polarization multiplexed signal that is a digital signal and a local signal that is a digital signal to the digital signal processing unit 93.

The digital signal processing unit 93 includes a frame synchronization unit 101, a polarization separation unit 102, a frequency compensation unit 103, a phase compensation unit 104, an IQ distortion compensation unit 105, and a demodulation unit 106.
The frame synchronization unit 101 is realized by, for example, the frame synchronization circuit 111 illustrated in FIG.
The frame synchronization unit 101 uses the local signal output from the A / D converter 92 and the first single carrier signal and the first signal included in the polarization multiplexed signal output from the A / D converter 92. The head of each of the two single carrier signals is detected.
The frame synchronization unit 101 generates a first detection signal indicating the start detection timing of the first single carrier signal and a second detection signal indicating the start detection timing of the second single carrier signal. To 102.
Also, the frame synchronization unit 101 outputs the polarization multiplexed signal to the polarization separation unit 102 and outputs the local oscillation signal to the frequency compensation unit 103.

The polarization separation unit 102 is realized by, for example, the polarization separation circuit 112 illustrated in FIG.
The polarization separation unit 102 performs signal separation processing on the polarization multiplexed signal at the timing when the first detection signal is output from the frame synchronization unit 101 and the timing at which the second detection signal is output from the frame synchronization unit 101. To implement.
As a method of separating the first single carrier signal for the first polarization and the second single carrier signal for the second polarization, for example, a constant envelope reference algorithm (CMA: Constant Modulus Algorithm) is used. Can be used.
When the polarization separation unit 102 separates the first single carrier signal and the second single carrier signal by performing signal separation processing on the polarization multiplexed signal, the polarization separation unit 102 performs the first single carrier signal and the second single carrier signal. Each of the carrier signals is output to the frequency compensation unit 103.

The frequency compensation unit 103 is realized by, for example, the frequency compensation circuit 113 illustrated in FIG.
The frequency compensator 103 performs a process of detecting a frequency error between the first single carrier signal output from the polarization separator 102 and the frequency of the local signal output from the frame synchronizer 101.
Further, the frequency compensation unit 103 performs a process of detecting a frequency error between the second single carrier signal output from the polarization separation unit 102 and the frequency of the local signal output from the frame synchronization unit 101.
The frequency compensation unit 103 performs a process of removing the frequency error included in the frequency of the first single carrier signal and removing the frequency error included in the frequency of the second single carrier signal.
The frequency compensation unit 103 outputs each of the first single carrier signal from which the frequency error has been removed and the second single carrier signal from which the frequency error has been removed to the phase compensation unit 104.

The phase compensation unit 104 is realized by, for example, the phase compensation circuit 114 illustrated in FIG.
The phase compensator 104 removes phase noise included in the phase of the first single carrier signal output from the frequency compensator 103, and at the same time the phase of the second single carrier signal output from the frequency compensator 103. The process which removes the phase noise contained in is implemented.
The phase compensation unit 104 outputs each of the first single carrier signal and the second single carrier signal from which phase noise has been removed to the IQ distortion compensation unit 105.

As shown in FIG. 11, the IQ distortion compensation unit 105 includes a pilot signal detection unit 105a, a distortion amount estimation unit 105b, and a distortion correction unit 105e.
The pilot signal detection unit 105a is realized by, for example, a signal detection circuit 115 illustrated in FIG.
The pilot signal detection unit 105a detects a first pilot signal included in the first single carrier signal output from the phase compensation unit 104, and outputs the first pilot signal to the distortion amount estimation unit 105b. To implement.
Pilot signal detection section 105a detects the second pilot signal included in the second single carrier signal output from phase compensation section 104, and outputs the second pilot signal to distortion amount estimation section 105b. Perform the process.

The distortion amount estimation unit 105b includes a distortion amount estimation processing unit 105c and an averaging processing unit 105d, and is realized by, for example, the distortion amount estimation circuit 116 illustrated in FIG.
The distortion amount estimation unit 105b uses the first pilot signal and the first single carrier signal to calculate the first amplitude distortion amount that is the magnitude of the amplitude distortion of the first pilot signal and the phase distortion of the first pilot signal. The first phase distortion amount that is the size of each is estimated.
The distortion amount estimation unit 105b calculates a second amplitude distortion amount that is the magnitude of the amplitude distortion of the second pilot signal and the phase distortion of the second pilot signal from the second pilot signal and the second single carrier signal. A process of estimating the second phase distortion amount that is the magnitude of each of the first and second phase distortions is performed.
The distortion amount estimation unit 105b outputs each of the first amplitude distortion amount, the second amplitude distortion amount, the first phase distortion amount, and the second phase distortion amount to the distortion correction unit 105e.

The distortion amount estimation processing unit 105 c performs processing for decomposing each of the first single carrier signal and the second single carrier signal output from the phase compensation unit 104 into a real part and an imaginary part.
The decomposition processing of the first single carrier signal uses that the first pilot signal is a signal equal to a signal obtained by multiplying the complex conjugate signal of the first pilot signal by an imaginary unit.
The decomposition processing of the second single carrier signal uses that the second pilot signal is a signal equal to a signal obtained by multiplying the complex conjugate signal of the second pilot signal by an imaginary unit.
The distortion amount estimation processing unit 105c estimates the first amplitude distortion amount of the first pilot signal from the imaginary part of the first single carrier signal, and calculates the first pilot signal from the real part of the first single carrier signal. A process of estimating the first phase distortion amount is performed.
The distortion amount estimation processing unit 105c estimates the second amplitude distortion amount of the second pilot signal from the imaginary part of the second single carrier signal, and calculates the second pilot signal from the real part of the second single carrier signal. A process of estimating the second phase distortion amount is performed.

The averaging processing unit 105d performs a process of calculating the first average amplitude distortion amount by averaging the first amplitude distortion amount estimated N times by the distortion amount estimation processing unit 105c.
The averaging processing unit 105d performs a process of calculating the first average phase distortion amount by averaging the first phase distortion amount estimated N times by the distortion amount estimation processing unit 105c.
The averaging processing unit 105d performs a process of calculating the second average amplitude distortion amount by averaging the second amplitude distortion amount estimated N times by the distortion amount estimation processing unit 105c.
The averaging processing unit 105d performs a process of calculating the second average phase distortion amount by averaging the second phase distortion amount estimated N times by the distortion amount estimation processing unit 105c.

The distortion correction unit 105e includes a delay unit 105f and a distortion correction processing unit 105g, and is realized by, for example, the distortion correction circuit 117 illustrated in FIG.
The distortion correction unit 105e performs a process of correcting the amplitude distortion of the first single carrier signal using the first average amplitude distortion amount calculated by the averaging processing unit 105d.
In addition, the distortion correction unit 105e performs a process of correcting the phase distortion of the first single carrier signal using the first average phase distortion amount calculated by the averaging processing unit 105d.
The distortion correction unit 105e performs a process of correcting the amplitude distortion of the second single carrier signal using the second average amplitude distortion amount calculated by the averaging processing unit 105d.
In addition, the distortion correction unit 105e performs a process of correcting the phase distortion of the second single carrier signal using the second average phase distortion amount calculated by the averaging processing unit 105d.
The distortion correction unit 105e outputs each of the corrected first single carrier signal and the corrected second single carrier signal to the demodulation unit 106.

Delay unit 105f, only the total time _{_{_{T 6 (= T 4 + T}}} 5) worth of processing time _{T 5} of the processing time _{T 4} and distortion amount estimating section 105b of the pilot signal detecting unit 105a, a first single-carrier signal and the A process of delaying each of the two single carrier signals is performed.
Processing time T ₄ of the pilot signal detecting unit 105a includes a detection of the first pilot signal is detected and the time required for the second pilot signal.
Processing time T ₅ of the strain amount estimating unit 105b, a calculation of the first average amplitude distortion amount, the calculation of the second average amplitude distortion amount, the calculation of the first average phase distortion amount, a second average phase This is the time required to calculate the amount of distortion.
The delay unit 105f outputs each of the delayed first single carrier signal and the delayed second single carrier signal to the distortion correction processing unit 105g.

The distortion correction processing unit 105g performs a process of correcting the amplitude distortion of the first single carrier signal output from the delay unit 105f using the first average amplitude distortion amount calculated by the averaging processing unit 105d. .
Further, the distortion correction processing unit 105g performs a process of correcting the phase distortion of the first single carrier signal in which the amplitude distortion is corrected, using the first average phase distortion amount calculated by the averaging processing unit 105d. .
The distortion correction processing unit 105g performs a process of correcting the amplitude distortion of the second single carrier signal output from the delay unit 105f using the second average amplitude distortion amount calculated by the averaging processing unit 105d. .
Further, the distortion correction processing unit 105g performs a process of correcting the phase distortion of the second single carrier signal in which the amplitude distortion is corrected, using the second average phase distortion amount calculated by the averaging processing unit 105d. .

The demodulation unit 106 is realized by, for example, a demodulation circuit 118 illustrated in FIG.
The demodulation unit 106 performs a process of demodulating the first single carrier signal in which each of the amplitude distortion and the phase distortion is corrected by the distortion correction processing unit 105g.
The demodulation unit 106 performs a process of demodulating the second single carrier signal in which each of the amplitude distortion and the phase distortion is corrected by the distortion correction processing unit 105g.

In FIG. 10, the frame synchronization unit 101, the polarization separation unit 102, the frequency compensation unit 103, the phase compensation unit 104, the pilot signal detection unit 105a, the distortion amount estimation unit 105b, and the distortion correction unit, which are components of the digital signal processing unit 93. It is assumed that each of 105e and demodulator 106 is realized by dedicated hardware as shown in FIG. That is, the digital signal processing unit 93 includes a frame synchronization circuit 111, a polarization separation circuit 112, a frequency compensation circuit 113, a phase compensation circuit 114, a signal detection circuit 115, a distortion amount estimation circuit 116, a distortion correction circuit 117, and a demodulation circuit 118. It is assumed that it will be realized.
The frame synchronization circuit 111, the polarization separation circuit 112, the frequency compensation circuit 113, the phase compensation circuit 114, the signal detection circuit 115, the distortion amount estimation circuit 116, the distortion correction circuit 117, and the demodulation circuit 118 are, for example, a single circuit or a composite circuit. , A programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof.

The components of the digital signal processing unit 93 are not limited to those realized by dedicated hardware, but the digital signal processing unit 13 is realized by software, firmware, or a combination of software and firmware. May be.
When the digital signal processing unit 93 is realized by software or firmware, the frame synchronization unit 101, polarization separation unit 102, frequency compensation unit 103, phase compensation unit 104, pilot signal detection unit 105a, distortion amount estimation unit 105b, distortion A program for causing the computer to execute the processing procedures of the correction unit 105e and the demodulation unit 106 is stored in the memory 52 shown in FIG. Then, the computer processor 51 executes the program stored in the memory 52.
12 shows an example in which each component of the digital signal processing unit 93 is realized by dedicated hardware, and FIG. 4 shows an example in which the digital signal processing unit 93 is realized by software or firmware. ing. However, some components in the digital signal processing unit 93 may be realized by dedicated hardware, and the remaining components may be realized by software, firmware, or the like.

Next, the operation of the optical transmission / reception system shown in FIG. 10 will be described.
The optical transmitter 81 generates a first single carrier signal having signal points on a complex plane having the I axis and the Q axis, and includes the first pilot signal in the first single carrier signal.
The optical transmitter 81 generates a second single carrier signal having signal points on a complex plane having the I axis and the Q axis, and includes the second pilot signal in the second single carrier signal.
The first single carrier signal is a single carrier signal for the first polarization, and the second single carrier signal is a single carrier signal for the second polarization.
The first polarization and the second polarization are polarizations that are orthogonal to each other.
The optical transmitter 81 generates a polarization multiplexed signal in which the first single carrier signal and the second single carrier signal are multiplexed.

Here, FIG. 13 is an explanatory diagram showing a frame configuration of a polarization multiplexed signal in which the first single carrier signal and the second single carrier signal are multiplexed.
The frame of the polarization multiplexed signal is a burst frame 121.
In the burst frame 121, a first frame 122 that stores a frame synchronization signal and a second frame 123 that stores a polarization separation sequence for separating the first polarization and the second polarization are arranged. Has been.
The burst frame 121 includes a third frame 124 that stores the first and second pilot signals, and a fourth frame 125 that stores the payloads of the first and second single carrier signals. Is arranged.
Further, in the burst frame 121, a fifth frame 126 for storing the frame end signal is arranged.

The frame synchronization signal stored in the first frame 122 is a signal set in advance between the optical transmitter 81 and the optical receiver 82.
The polarization separation sequence stored in the second frame is a processing procedure for separating the first single carrier signal for the first polarization and the second single carrier signal for the second polarization. Etc. are described. Since the polarization separation sequence itself is known, detailed description thereof is omitted.
Each of the first and second pilot signals stored in the third frame 124 and the payload stored in the fourth frame 125 is modulated using, for example, a four-level phase modulation method.
The first pilot signal is a signal set in advance between the optical transmitter 81 and the optical receiver 82, and is equal to a signal obtained by multiplying the complex conjugate signal of the first pilot signal by an imaginary unit. Signal.
For example, in the n-th sampling, when the first pilot signal included in the first single carrier signal is s _{1, n} , the first pilot signal s _{1, n} is expressed by the following equation (8). .

In Equation (8), s _{1, n} ^* is a complex conjugate signal of the first pilot signal s _{1, n} .

The second pilot signal is a signal set in advance between the optical transmitter 81 and the optical receiver 82, and is equal to a signal obtained by multiplying the complex conjugate signal of the second pilot signal by an imaginary unit. Signal.
For example, in the n-th sampling, when the second pilot signal included in the second single carrier signal is s _{2, n} , the second pilot signal s _{2, n} is expressed by the following equation (9). .

In Equation (9), s _{2, n} ^* is a complex conjugate signal of the second pilot signal s _{2, n} .

The optical transmitter 81 transmits the polarization multiplexed signal to the optical receiver 82 by using the light output from the light source 81 a and outputting the polarization multiplexed signal as an optical signal to the optical fiber 2.
The polarization multiplexed signal, which is an optical signal, is output to the optical receiver 82 after adding IQ distortion and additive white Gaussian noise.
The local light source 3 outputs a local signal, which is local light, to the optical receiver 82.

The photoelectric conversion circuit 91 converts the polarization multiplexed signal transmitted from the optical transmitter 81 from an optical signal to an electrical signal, and outputs the polarization multiplexed signal that is an electrical signal to the A / D converter 92.
The photoelectric conversion circuit 91 converts the local signal output from the local light source 3 from an optical signal into an electrical signal, and outputs the local signal, which is an electrical signal, to the A / D converter 92.

Upon receiving the polarization multiplexed signal from the photoelectric conversion circuit 91, the A / D converter 92 converts the polarization multiplexed signal from an analog signal to a digital signal, and outputs the polarization multiplexed signal, which is a digital signal, to the frame synchronization unit 101. To do.
When the A / D converter 92 receives the local oscillation signal from the photoelectric conversion circuit 91, the A / D converter 92 converts the local oscillation signal from an analog signal to a digital signal, and outputs the local oscillation signal which is a digital signal to the frame synchronization unit 101.

The frame synchronization unit 101 causes the local oscillation signal output from the A / D converter 92 to interfere with the polarization multiplexed signal output from the A / D converter 92, so that the signal included in the polarization multiplexed signal Determine the column.
The frame synchronization unit 101 compares the signal sequence included in the polarization multiplexed signal with the frame synchronization signal set in advance between the optical transmitter 81 and the optical receiver 82, thereby The frame synchronization signal stored in the frame 122 is detected.
The frame synchronization unit 101 detects each of the first single carrier signal and the second single carrier signal included in the polarization multiplexed signal by detecting the frame synchronization signal stored in the first frame 122. Detect the beginning.
Since the processing itself for detecting the head of each of the first single carrier signal and the second single carrier signal is a known technique, detailed description thereof is omitted.
The frame synchronization unit 101 generates a first detection signal indicating the start detection timing of the first single carrier signal and a second detection signal indicating the start detection timing of the second single carrier signal. To 102.
Also, the frame synchronization unit 101 outputs the polarization multiplexed signal to the polarization separation unit 102 and outputs the local oscillation signal to the frequency compensation unit 103.

The polarization separation unit 102 performs signal separation processing of the polarization multiplexed signal at the timing when the first detection signal is output from the frame synchronization unit 101.
In addition, the polarization separation unit 102 performs signal separation processing of the polarization multiplexed signal at the timing when the second detection signal is output from the frame synchronization unit 101.
For example, CMA can be used as the signal separation process for the polarization multiplexed signal, but the signal separation process itself is a known technique, and thus detailed description thereof is omitted.
Further, as the signal separation processing of the polarization multiplexed signal, the polarization separation sequence stored in the second frame 123 may be used. Since the signal separation process itself using the polarization separation sequence is a known technique, a detailed description thereof will be omitted.
When the polarization separation unit 102 separates the first single carrier signal and the second single carrier signal by performing signal separation processing on the polarization multiplexed signal, the polarization separation unit 102 performs the first single carrier signal and the second single carrier signal. Each of the carrier signals is output to the frequency compensation unit 103.

The frequency compensation unit 103 detects a frequency error Δf1 between the first single carrier signal output from the polarization separation unit 102 and the frequency of the local signal output from the frame synchronization unit 101.
Further, the frequency compensation unit 103 detects a frequency error Δf2 between the second single carrier signal output from the polarization demultiplexing unit 102 and the frequency of the local signal output from the frame synchronization unit 101.
The frequency compensation unit 103 removes the frequency error Δf1 included in the frequency of the first single carrier signal and removes the frequency error Δf1 included in the frequency of the second single carrier signal.
The frequency compensation unit 103 outputs each of the first single carrier signal from which the frequency error Δf1 has been removed and the second single carrier signal from which the frequency error Δf2 has been removed to the phase compensation unit 104.
The frequency error removal processing itself by the frequency compensation unit 103 is the same as the frequency error removal processing by the frequency compensation unit 22 shown in FIG. 1, and is disclosed in Non-Patent Document 1, for example.

The phase compensator 104 removes the phase noise ρ1 included in the phase of the first single carrier signal output from the frequency compensator 103, and the second single carrier signal output from the frequency compensator 103. The phase noise ρ2 included in the phase is removed. The phase noises ρ1 and ρ2 are noises generated from the light source 1a or the local light source 3 of the optical transmitter 1.
The phase compensation unit 104 outputs each of the first single carrier signal from which phase noise has been removed and the second single carrier signal from which phase noise has been removed to the IQ distortion compensation unit 105.
The phase noise removal processing itself by the phase compensation unit 104 is the same as the phase noise removal processing by the phase compensation unit 23 illustrated in FIG. 1, and is disclosed in Non-Patent Document 2, for example.

The first pilot signal included in the first single carrier signal by the optical transmitter 81 is the first pilot signal s _{1, n} shown in Expression (8). Therefore, if the first single carrier signal output from the phase compensation unit 104 to the IQ distortion compensation unit 105 is r _{1, n} , the first single carrier signal r _{1, n} is _expressed by the following equation (10): It is represented by

In Equation (10), g _{1, n} hat is an instantaneous value of amplitude distortion of the first pilot signal s _{1, n in} the n-th sampling, and θ _{1, n} hat is the first pilot in the n-th sampling. This is an instantaneous value of the phase distortion of the signals s _{1 and n} .

The second pilot signal included in the second single carrier signal by the optical transmitter 81 is the second pilot signal s2 _{, n} shown in Expression (9). Therefore, if the second single carrier signal output from the phase compensation unit 104 to the IQ distortion compensation unit 105 is r _{2, n} , the second single carrier signal r _{2, n} is _expressed by the following equation (11). It is represented by

In Expression (11), g _{2, n} hat is an instantaneous value of amplitude distortion of the second pilot signal s _{2, n in} the n-th sampling, and θ _{2, n} hat is a second pilot in the n-th sampling. This is an instantaneous value of the phase distortion of the signals s _{2 and n} .

Upon receiving the _first single carrier signal r _{1, n} from the phase compensation unit 104, the pilot signal detection unit 105a receives the first pilot signal s _{1, n} included in the _first single carrier signal r _{1, n.} Is detected.
Upon receiving the _second single carrier signal r _{2, n} from the phase compensation unit 104, the pilot signal detection unit 105a receives the second pilot signal s _{2, n} included in the _second single carrier signal r _{2, n.} Is detected.
Each of the first pilot signals s _{1, n} and the second pilot signals s _{2, n} is stored in a third frame 124 included in the burst frame 121.
The pilot signal detection unit 105a outputs each of the first pilot signals s _{1, n} and the second pilot signals s _{2, n} to the distortion amount estimation processing unit 105c.

As shown in the following formulas (12) and (13), the distortion amount estimation processing unit 105c converts the first single carrier signal r1 _{, n} output from the pilot signal detection unit 105a into a real part Re and an imaginary part. Decomposes into Im.
Since the first pilot signal s _{1, n} is equal to the signal obtained by multiplying the complex conjugate signal s _{1, n} ^* by the imaginary unit j, the first single carrier signal r _1, shown in Equation (10) is used. _n can be decomposed into a real part Re and an imaginary part Im.

As shown in the following formulas (14) and (15), the distortion amount estimation processing unit 105c converts the second single carrier signal r2 _{, n} output from the pilot signal detection unit 105a into a real part Re and an imaginary part. Decomposes into Im.
Since the second pilot signal s _{2, n} is a signal equal to the signal obtained by multiplying the complex conjugate signal s _{2, n} ^* by the imaginary unit j, the second single carrier signal r _2, shown in Equation (11) is used. _n can be decomposed into a real part Re and an imaginary part Im.

The distortion amount estimation processing unit 105c estimates the first phase distortion amount θ _{1, n} hat of the first pilot signals s _{1, n} from the real part Re of the first single carrier signal r _{1, n} , and the first Of the phase distortion θ _{1, n} is output to the averaging processing unit 105d.
Further, the distortion amount estimation processing unit 105c generates the first pilot signal s _1, from the imaginary part Im of the first single carrier signal r _{1, n} and the estimated first phase distortion amount θ _{1, n} hat _. estimating a first amplitude distortion amount _{g 1, n} hat _n.
The distortion amount estimation processing unit 105c outputs the first amplitude distortion amount g _{1, n} hat to the averaging processing unit 105d.
The first phase distortion amount theta _{1, n} hat of the first pilot signal _{s 1, n} corresponds to the phase distortion of the first single-carrier signals _{r 1, n,} the first pilot signal _{s 1, n} The first amplitude distortion amount g _{1, n} hat corresponds to the amplitude distortion amount of the first single carrier signal r _{1, n} .

The distortion amount estimation processing unit 105c estimates the second phase distortion amount θ _{2, n} hat of the second pilot signal s _{2, n} from the real part Re of the second single carrier signal r _{2, n} , Of phase distortion θ _{2, n} is output to the averaging processing unit 105d.
Further, the distortion amount estimation processing unit 105c generates the second pilot signal s _2, from the imaginary part Im of the second single carrier signal r _{2, n} and the estimated second phase distortion amount θ _{2, n} hat _. second amplitude distortion amount of _n _{g 2,} estimates the _n hat.
The distortion amount estimation processing unit 105c outputs the second amplitude distortion amount g2 _{, n} hat to the averaging processing unit 105d.
The second phase distortion amount theta _{2, n-hat} of the second pilot signal _{s 2, n} corresponds to phase distortion amount of the second single-carrier signal _{r 2, n,} the second pilot signal _{s 2, n} The second amplitude distortion amount g _{2, n} hat corresponds to the amplitude distortion amount of the second single carrier signal r _{2, n} .

The averaging processing unit 105d outputs the first phase distortion amount θ _{1, n} hat, the first amplitude distortion amount g _{1, n} hat, and the second phase distortion amount θ _2, output from the distortion amount estimation processing unit 105c _{. An} averaging process is performed for each of the _n hat and the second amplitude distortion amount g _{2 and the n} hat.
Specifically, the averaging processing unit 105d performs the N first phase distortion amounts in the first to Nth samplings output from the distortion amount estimation processing unit 105c as shown in the following equation (16). The first average phase distortion amount θ ₁ hat is calculated by averaging θ _{1, n} hat.

As shown in the following equation (17), the averaging processing unit 105d outputs the N first amplitude distortion amounts g _{1, n} hat in the first to N-th samplings output from the distortion amount estimation processing unit 105c. Is averaged to calculate the _first average amplitude distortion amount g ₁ hat.

As shown in the following formula (18), the averaging processing unit 105d outputs N second phase distortion amounts θ _{2, n} hat in the first to N-th samplings output from the distortion amount estimation processing unit 105c. Is averaged to calculate the _second average phase distortion amount θ ₂ hat.

As shown in the following equation (19), the averaging processing unit 105d outputs the N second amplitude distortion amounts g _{2, n} hat in the first to Nth samplings output from the distortion amount estimation processing unit 105c. Is averaged to calculate the _second average amplitude distortion amount g ₂ hat.

The averaging processing unit 105d includes a first average phase distortion amount θ ₁ hat, a first average amplitude distortion amount g ₁ hat, a second average phase distortion amount θ ₂ hat, and a second average amplitude distortion amount g ₂ hat. Are output to the distortion correction processing unit 105g.

Delay unit 105f in advance to, knows the total time _{_{_{T 6 (= T 4 + T}}} 5) and the processing time _{T 5} of the processing time _{T 4} and distortion amount estimating section 105b of the pilot signal detecting unit 105a.
Processing time _{T 4} of the pilot signal detecting unit 105a includes a detection of the first pilot signal _{s 1, n,} a second pilot signal _{s 2, n} of the detection and the time required.
Processing time T ₅ of the strain amount estimating unit 105b, a calculation of the first average amplitude distortion amount g ₁ hat, the calculation of the second average amplitude distortion amount g ₂ hat, the first average phase distortion amount theta ₁ hat And the calculation of the second average phase distortion amount θ ₂ hat.
When receiving the first single carrier signal r _{1, n} and the second single carrier signal r _{2, n} from the phase compensation unit 104, the delay unit 105f receives the first single carrier signal r for a total time T _6. _{1, n} and the second single carrier signal r _{2, n} are held.
Delay unit 105f is output to each of the first single-carrier signals _{r 1, n} and a second single carrier signal _{r 2, n} holding only the total time _{T 6} was held for a total time _{T 6} the distortion correction processing section 105g To do.

Distortion correction processing unit 105g uses the first amplitude distortion amount g ₁ hat output from the averaging process unit 105d, the amplitude distortion of the first single-carrier signals r _{1, n} output from the delay unit 105f to correct.
Further, the distortion correction processing unit 105g uses the second amplitude distortion amount g ₂ hat output from the averaging process unit 105d, the amplitude of the second single-carrier signal r _{2, n} output from the delay unit 105f Correct distortion.
The amplitude distortion correction processing itself by the distortion correction processing unit 105g is the same as the amplitude distortion correction processing by the distortion correction processing unit 24g shown in FIG.

The distortion correction processing unit 105 g corrects the phase distortion of the first single carrier signals r _{1 and n} in which the amplitude distortion is corrected, using the _first phase distortion amount θ ₁ hat output from the averaging processing unit 105 d. .
In addition, the distortion correction processing unit 105 g uses the second phase distortion amount θ ₂ hat output from the averaging processing unit 105 d to calculate the phase distortion of the second single carrier signals r _{2 and n} corrected for amplitude distortion. to correct.
The phase distortion correction processing itself by the distortion correction processing unit 105g is the same as the phase distortion correction processing by the distortion correction processing unit 24g shown in FIG.

Here, the distortion correction processing section 105g is shows an example in which after correcting the amplitude distortion of the first single-carrier signals r _{1, n,} to correct the phase distortion of the first single-carrier signals r _{1, n} . However, this is only an example, the distortion correction processing section 105g is, earlier the phase distortion of the first single-carrier signals r _{1, n} is corrected, the first single-carrier signals r _{1, n} obtained by correcting the phase distortion The amplitude distortion may be corrected.
Similarly, the distortion correction processing section 105g is, the phase distortion of the second single-carrier signal r _{2, n} is corrected earlier, correct the amplitude distortion of the second single-carrier signal r _{2, n} obtained by correcting the phase distortion You may make it do.
The distortion correction processing unit 105g outputs the first single carrier signal r _{1, n} obtained by correcting the amplitude distortion and the phase distortion to the demodulation unit 106 as the _first single carrier signal r _{1, n} ′.
In addition, the distortion correction processing unit 105g outputs the second single carrier signal r2 _{, n} obtained by correcting each of the amplitude distortion and the phase distortion to the demodulation unit 106 as the _second single carrier signal r2 _{, n} '.

The demodulation unit 106 performs demodulation processing on the first single carrier signal r _{1, n} ′ output from the distortion correction processing unit 105g, and obtains signal points existing on the complex plane having the I axis and the Q axis. Extract.
The demodulator 106 performs a demodulation process on the second single carrier signal r _{2, n} ′ output from the distortion correction processor 105g, and obtains signal points existing on the complex plane having the I axis and the Q axis. Extract.
Since the single carrier signal demodulation process itself is a known technique, a detailed description thereof will be omitted.

Embodiment 2 described above shows the optical receiver 82 that demodulates the first single carrier signal for the first polarization and the second single carrier signal for the second polarization. Similar to the optical receiver 4 shown in FIG. 1, the optical receiver 82 can compensate IQ distortion in a single carrier signal in which signal points exist on a complex plane having an I axis and a Q axis.

In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

The present invention is suitable for an optical receiver that demodulates a single carrier signal having a signal point on a complex plane having an I axis and a Q axis.
The present invention is also suitable for an optical transmission / reception system including an optical receiver that demodulates a single carrier signal in which signal points exist on a complex plane having an I axis and a Q axis.

1 optical transmitter, 1a light source, 2 optical fiber, 3 local light source, 4 optical receiver, 11 photoelectric conversion circuit, 12 A / D converter, 13 digital signal processing unit, 21 frame synchronization unit, 22 frequency compensation unit, 23 phase compensation unit, 24 IQ distortion compensation unit, 24a pilot signal detection unit, 24b distortion amount estimation unit, 24c distortion amount estimation processing unit, 2d averaging processing unit, 24e distortion correction unit, 24f delay unit, 24g distortion correction processing unit 25 demodulator, 41 frame synchronization circuit, 42 frequency compensation circuit, 43 phase compensation circuit, 44 signal detection circuit, 45 distortion amount estimation circuit, 46 distortion correction circuit, 47 demodulation circuit, 51 processor, 52 memory, 61 burst frame, 62 1st frame, 63 2nd frame, 64 3rd frame, 65 4 frame, 71 frequency spectrum of single carrier signal without IQ distortion, 72 frequency spectrum of desired signal, 73 frequency spectrum of interference signal, 81 optical transmitter, 81a light source, 82 optical receiver, 91 photoelectric conversion circuit , 92 A / D converter, 93 digital signal processing unit, 101 frame synchronization unit, 102 polarization separation unit, 103 frequency compensation unit, 104 phase compensation unit, 105 IQ distortion compensation unit, 105a pilot signal detection unit, 105b distortion amount Estimator, 105c distortion amount estimation processor, 105d averaging processor, 105e distortion correction unit, 105f delay unit, 105g distortion correction processor, 106 demodulator, 111 frame synchronization circuit, 112 polarization separation circuit, 113 frequency compensation circuit 114 phase compensation circuit, 1 5 signal detection circuit, 116 distortion amount estimation circuit, 117 distortion correction circuit, 118 demodulation circuit, 121 burst frame, 122 first frame, 123 second frame, 124 third frame, 125 fourth frame, 126th 5 frames.

Claims

A pilot signal detector that detects a pilot signal included in a single carrier signal in which a signal point exists in a complex plane having the same phase axis and a quadrature phase axis;
A distortion amount estimation unit for estimating an amplitude distortion amount of the pilot signal and a phase distortion amount of the pilot signal from the pilot signal detected by the pilot signal detection unit and the single carrier signal;
The amplitude distortion of the single carrier signal is corrected using the amplitude distortion amount estimated by the distortion amount estimation unit, and the phase distortion of the single carrier signal is corrected using the phase distortion amount estimated by the distortion amount estimation unit. A distortion correction unit for correcting
An optical receiver comprising: a demodulator that demodulates a single carrier signal in which each of amplitude distortion and phase distortion is corrected by the distortion correction unit.
The distortion amount estimation unit is based on the fact that the pilot signal detected by the pilot signal detection unit and the signal obtained by multiplying the complex conjugate signal of the pilot signal by an imaginary unit are the same signal. 2. The light according to claim 1, wherein an amplitude distortion amount of the pilot signal is estimated from the imaginary part, and a phase distortion amount of the pilot signal is estimated from the real part. Receiver.
The distortion correction unit
For the total time of the processing time of the pilot signal detection unit for detecting the pilot signal and the processing time of the distortion amount estimation unit for estimating each of the amplitude distortion amount and the phase distortion amount, Delay single carrier signal,
Using the amplitude distortion amount, the amplitude distortion of the delayed single carrier signal is corrected, and using the phase distortion amount, the phase distortion of the single carrier signal in which the amplitude distortion is corrected, or the phase The phase distortion of the delayed single carrier signal is corrected using a distortion amount, and the amplitude distortion of the single carrier signal whose phase distortion is corrected is corrected using the amplitude distortion amount. The optical receiver according to 1.
Each of the first single carrier signal for the first polarization and the second single carrier signal for the second polarization orthogonal to the first polarization are signal points on the complex plane. Is a single carrier signal that exists,
Signal separation processing of a polarization multiplexed signal in which the first single carrier signal and the second single carrier signal are multiplexed is performed to separate the first single carrier signal and the separated first single carrier signal. A polarization separation unit that outputs two single carrier signals to the pilot signal detection unit;
The pilot signal detection unit detects a first pilot signal included in the separated first single carrier signal and a second pilot signal included in the separated second single carrier signal. Detect
The distortion amount estimator includes a first amplitude distortion amount of the first pilot signal and a first of the first pilot signal from the first pilot signal and the separated first single carrier signal. The phase distortion amount is estimated, and the second amplitude distortion amount of the second pilot signal and the second pilot signal of the second pilot signal are calculated from the second pilot signal and the separated second single carrier signal. 2 estimate the amount of phase distortion,
The distortion correction unit corrects the amplitude distortion of the separated first single carrier signal using the first amplitude distortion amount, and uses the first phase distortion amount to separate the separated first first carrier signal. The phase distortion of the single carrier signal is corrected, the amplitude distortion of the separated second single carrier signal is corrected using the second amplitude distortion amount, and the separation is performed using the second phase distortion amount. Corrected phase distortion of the second single carrier signal,
The demodulation unit demodulates the first single carrier signal in which each of the amplitude distortion and the phase distortion is corrected by the distortion correction unit, and the second that the amplitude distortion and the phase distortion are corrected by the distortion correction unit. 2. The optical receiver according to claim 1, wherein a single carrier signal is demodulated.
An optical transmitter that includes a pilot signal in a single carrier signal in which signal points exist on a complex plane having the same phase axis and a quadrature phase axis, and transmits the single carrier signal including the pilot signal;
An optical receiver that receives a single carrier signal transmitted from the optical transmitter and demodulates the received single carrier signal;
The optical receiver is:
A pilot signal detector for detecting a pilot signal included in the received single carrier signal;
A distortion amount estimation unit for estimating an amplitude distortion amount of the pilot signal and a phase distortion amount of the pilot signal from the pilot signal detected by the pilot signal detection unit and the received single carrier signal;
The amplitude distortion amount of the received single carrier signal is corrected using the amplitude distortion amount estimated by the distortion amount estimation unit, and the received single carrier is corrected using the phase distortion amount estimated by the distortion amount estimation unit. A distortion correction unit for correcting the phase distortion of the signal;
An optical transmission / reception system comprising: a demodulator that demodulates a single carrier signal in which each of amplitude distortion and phase distortion is corrected by the distortion correction unit.
6. The optical transmission / reception system according to claim 5, wherein the optical transmitter includes a pilot signal included in the single carrier signal equal to a signal obtained by multiplying a complex conjugate signal of the pilot signal by an imaginary unit.
The optical transmitter is
Generating a burst frame in which a first frame storing a frame synchronization signal, a second frame storing a pilot signal, and a third frame storing a payload of a single carrier signal are arranged;
6. The optical transmission / reception system according to claim 5, wherein a single carrier signal of the burst frame is transmitted to the optical receiver.
The optical transmitter modulates each of the pilot signal and the payload of the single carrier signal by a quaternary phase modulation method, stores the modulated pilot signal in the second frame, and transmits the modulated payload to the third payload. 8. The optical transmission / reception system according to claim 7, wherein the optical transmission / reception system is stored in a frame.
The optical receiver is:
A frame synchronization unit that detects the head of a single carrier signal transmitted from the optical transmitter using local light output from a local light source;
A frequency compensation unit that detects a frequency error between the frequency of the single carrier signal whose head is detected by the frame synchronization unit and the frequency of the local light, and removes the frequency error included in the frequency of the single carrier signal When,
6. The optical transmission / reception system according to claim 5, further comprising: a phase compensation unit that removes phase noise included in a phase of a single carrier signal whose head is detected by the frame synchronization unit.