CN114189286A - Method and system for simultaneously calibrating frequency response and IQ time delay difference of coherent optical transceiver - Google Patents
Method and system for simultaneously calibrating frequency response and IQ time delay difference of coherent optical transceiver Download PDFInfo
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Abstract
The invention discloses a method and a system for simultaneously calibrating frequency response and IQ time delay difference of a coherent optical transceiver, belonging to the field of communication. The invention generates IQ interweaved multi-tone signals at a transmitting end according to the bandwidth characteristics of a coherent optical transceiver, takes the IQ interweaved multi-tone signals as the input of the coherent optical transceiver, uses a coherent optical receiver to receive signals at a receiving end, and can obtain the frequency response and IQ time delay difference of the whole coherent optical transceiver at one time by analyzing the received multi-tone signals. After obtaining the frequency response and the IQ delay difference of the coherent optical transceiver, the transmitter pre-compensates the data to be transmitted to complete the calibration of the coherent optical transceiver, and the receiver performs the IQ delay difference compensation on the received signal to complete the calibration of the coherent optical receiver. The invention can separate IQ time delay difference of a transmitter and a receiver in the coherent optical transceiver to be calibrated by adopting an IQ-based multi-tone signal interleaving method, thereby realizing accurate calibration of the coherent optical transceiver.
Description
Technical Field
The present invention belongs to the field of communications, and more particularly, to a method and system for calibrating frequency response and IQ delay variation of a coherent optical transceiver simultaneously.
Background
High order QAM (Quadrature Amplitude Modulation) signal transmissions in excess of 100GBaud are very sensitive to various impairments (e.g., IQ imbalance, IQ delay variation) in coherent optical transceivers. These defects are more sensitive, especially when the coherent optical transceiver bandwidth is limited. At a receiving end, various powerful equalization technologies can effectively reduce the influence of the damage, but the influence of the residual damage still has a great influence on the high-speed high-order QAM signal. For example, at a bit error rate of 1e-3, a 10GBaud 64QAM signal is less than 5ps tolerant to IQ delay variation, even though a typical butterfly FIR (Finite Impulse Response) equalizer is used. Therefore, in the next generation coherent optical fiber communication system, precise calibration of the coherent optical transceiver is essential.
There are many studies on the calibration of the coherent optical transceiver, for example, the calibration of IQ delay difference and frequency response of the coherent optical transceiver is realized by frequency sweeping. However, the current research can only realize the calibration of the coherent optical transmitter or receiver alone, and the calibration of the coherent optical transceiver still has great challenges. Furthermore, the IQ delay differences of the coherent optical transmitter and the coherent optical receiver have different effects on the signal, and separating the IQ delay differences of the coherent optical transceiver also has a great challenge.
Disclosure of Invention
In view of the above drawbacks and needs of the prior art, the present invention provides a method and system for calibrating frequency response and IQ delay difference of a coherent optical transceiver simultaneously, which aims to measure the frequency response and IQ delay difference of the coherent optical transceiver simultaneously at one time, thereby solving the technical problem of calibrating and separating IQ delay difference of the coherent optical transceiver and the coherent optical receiver simultaneously.
To achieve the above object, in a first aspect, the present invention provides a method for calibrating frequency response and IQ delay difference of a coherent optical transceiver simultaneously, comprising the following steps:
at the transmitting end, two paths of multi-tone electric signals with an interleaving relation in a frequency domain are respectively input into two branches of TI and TQ of a coherent light transmitter, and the method comprises the following steps:
the two paths of input polyphonic signals with the interleaving relation in the frequency domain are respectively expressed as follows:
wherein 2 Δ f represents the frequency interval of two paths of input polyphonic electrical signals having an interleaving relationship in the frequency domain, φnAnd N is a positive integer set according to the calibration bandwidth for a preset known random phase, and the maximum frequency 2N delta f of the two paths of input multi-tone electric signals with an interleaving relation in the frequency domain is covered to the bandwidth of the coherent optical transceiver.
At the receiving end, receive two routes output multitone electrical signals simultaneously from two branches RI and RQ respectively, obtain the amplitude response and the phase response of TI and TQ and each branch of RI and RQ, include:
the two paths of output multi-tone signals received from the coherent optical receiver are represented as:
where RI (t) and RQ (t) respectively represent polyphonic electrical signals received by the two branches of the coherent optical receiver RI and RQ, obviously RI (t) includes the transmission of the branch of the coherent optical transmitter TIThe emission signal and the crosstalk signal of the TQ branch, RQ (t) comprises the emission signal of the coherent optical transmitter TQ branch and the crosstalk signal of the TI branch; theta represents a phase difference between the signal light and the local oscillation light, alphaXY,nIndicating the amplitude of the nth frequency bin of the received multi-tone signal,
and the phase of the nth frequency point of the received multi-tone signal is shown, and X, Y is I, Q. Obtaining the amplitude response and the phase response of each branch of the coherent optical transceiver by performing Fourier transform on RI (t) and RQ (t):
αXY(f)＝abs(FFT(RX(t)))|XY
where abs () represents taking the absolute value, angle () represents taking the angle, FFT () represents the Fourier transform, phinIs a preset known random phase. For example, abs (FFT (RI (t)))IQMeans RI (t) is subjected to Fourier transform to obtain polyphonic signals contained in the frequency spectrum, and polyphonic signals belonging to Q branch transmission are extracted to obtain absolute value to obtain corresponding alpha of amplitudeIQ(f)。
After the frequency response and the IQ delay difference of the coherent optical transceiver are obtained from the amplitude response and the phase response of each branch, pre-compensating the data to be transmitted at the transmitting end according to the frequency response, and compensating the IQ delay difference at the receiving end, comprising:
the IQ time delay difference between the coherent optical transmitter and the coherent optical receiver is:
frequency response H of I branch and Q branch of coherent optical transceiverI(f)、HQ(f) Can be expressed as:
after obtaining the frequency response H (f) and IQ time delay difference of the coherent optical transceiver, calibrating at the transmitting end according to the frequency response of the coherent optical transceiver, i.e. making the transmitted data of the TI branch pass through a mode of
The filter of (1) passing the transmission data of the TQ branch in a form of
The filter can compensate amplitude and phase distortion caused by bandwidth limitation of a coherent optical transceiver and IQ delay difference TX at a transmitting end caused by inconsistent length of a radio frequency wire at the end of the coherent optical transceiverskew。
At the receiving end, according to the measured IQ delay difference RX of the receiving endskewThe electric signal received by the coherent optical receiver is calibrated, and IQ time delay difference caused by inconsistent length of the radio frequency line of the receiving end can be compensated.
In a second aspect, the present invention provides a system for calibrating both frequency response and IQ delay difference of a coherent optical transceiver, comprising: a computer-readable storage medium and a processor;
the computer-readable storage medium is used for storing executable instructions;
the processor is configured to read executable instructions stored in the computer-readable storage medium, and execute the method for simultaneously calibrating the frequency response and the IQ delay difference of the coherent optical transceiver according to the first aspect of the present invention.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:
1. the method for calibrating the frequency response and the IQ delay difference of the coherent optical transceiver simultaneously realizes the simultaneous measurement of the frequency response and the IQ delay difference of the coherent optical transceiver, wherein the IQ delay difference comprises the IQ delay difference of the coherent optical transceiver and the IQ delay difference of the coherent optical transceiver;
2. the method for calibrating the frequency response and the IQ time delay difference of the coherent optical transceiver simultaneously realizes the simultaneous measurement of the IQ time delay difference of the coherent optical transmitter and the IQ time delay difference of the coherent optical receiver;
3. the method for calibrating the frequency response and the IQ delay difference of the coherent optical transceiver simultaneously can pre-compensate the data to be transmitted according to the measured frequency response of the coherent optical transceiver, and can pre-compensate the signal distortion caused by the bandwidth limitation of the coherent optical transceiver and the IQ delay difference of the coherent optical transmitter; the received data can be post-compensated according to the measured IQ time delay difference of the coherent optical receiver, and signal distortion caused by the IQ time delay difference of the coherent optical receiver can be compensated.
Drawings
FIG. 1 is a scheme flow diagram of the present invention;
FIG. 2 is a diagram of an exemplary back-to-back coherent optical communication system;
FIG. 3 is a diagram of the spectrum of an input multi-tone signal at the I branch of a coherent optical transmitter;
FIG. 4 is a diagram of a coherent optical transmitter Q branch input multi-tone signal spectrum;
FIG. 5 is a diagram of an IQ-interleaved multitone signal spectrum transmitted by a coherent optical transmitter;
FIG. 6 is a spectrum diagram of an I-branch received signal of a coherent optical receiver;
fig. 7 is a spectrum diagram of a Q-branch received signal of a coherent optical receiver.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The present invention provides a method for calibrating frequency response and IQ delay difference of a coherent optical transceiver simultaneously, as shown in fig. 1, comprising:
at the transmitting end, two paths of multi-tone electric signals with an interleaving relation in a frequency domain are respectively input into two branches TI and TQ of a coherent light transmitter.
A typical back-to-back coherent optical communication system is shown in fig. 2, and typical frequency spectrums of nodes a-e are shown in fig. 3-7. According to the bandwidth characteristics of the coherent optical transceiver, the frequency interval of the IQ interleaved multi-tone signal and the maximum frequency of the single-tone signal are determined.
The IQ-interleaved multi-tone signal can be expressed as:
where 2 Δ f represents the frequency interval, φ, of the I, Q multitone signalnFor a preset known random phase, N is a positive integer set according to the calibration bandwidth, and the maximum frequency 2N delta f of the two paths of input multi-tone signals with the interleaving relation in the frequency domain is covered to the bandwidth of the coherent optical transceiver.
The generated TI (t), TQ (t) are interleaved in the frequency domain, as shown in fig. 3 and 4, TI (t), TQ (t) are used as input signals of the coherent optical transmitter TI branch and TQ branch. The IQ interleaved multi-tone signal during transmission is shown in fig. 5.
At a receiving end, two paths of electric signals are simultaneously received from an RI branch and an RQ branch of the coherent optical receiver. Due to the aliasing effect of coherent optical transmission, the received electrical signal will carry the entire transceiver transmission impairment characteristics. Thus, the amplitude response and phase response of each branch of TI and TQ and RI and RQ can be obtained, including:
in the case of back-to-back optical and using a homologous laser, the electrical signal obtained by the receiving end through the coherent optical receiver is as shown in fig. 6 and 7, regardless of the influence of the laser frequency offset, which can be expressed as:
where ri (t), rq (t) respectively represent the electrical signals received by the two branches of the coherent optical receiver I, Q, θ represents the phase difference between the signal light and the local oscillator light, and α representsXY,nRepresenting the amplitude of the nth frequency point of the signal in the received multi-tone signal,
and the phase of the nth frequency point in the received multi-tone signal is shown, and X, Y is I, Q. The amplitude response and phase response of each branch (TI to RI, TI to RQ, TQ to RI, and TQ to RQ) of the coherent optical transceiver are obtained by fourier transform of RI (t), RQ (t):
αXY(f)＝abs(FFT(RX(t)))|XY
where abs () represents taking the absolute value, angle () represents taking the angle, FFT () represents the fourier transform, and φ n is a preset known random phase. For example, abs (FFT (RI (t)))IQMeans RI (t) is subjected to Fourier transform to obtain polyphonic signals contained in the frequency spectrum, and polyphonic signals belonging to Q branch transmission are extracted to obtain absolute value to obtain corresponding alpha of amplitudeIQ(f)。
After the frequency response and the IQ delay difference of the coherent optical transceiver are obtained from the amplitude response and the phase response of each branch, pre-compensating the data to be transmitted at the transmitting end according to the frequency response, and compensating the IQ delay difference at the receiving end, comprising:
the IQ delay difference between the coherent optical transmitter and the coherent optical receiver may be:
frequency response H of I branch and Q branch of coherent optical transceiverI(f)、HQ(f) Expressed as:
after obtaining the frequency response H (f) and IQ time delay difference of the coherent optical transceiver, calibrating at the transmitting end according to the frequency response of the coherent optical transceiver, i.e. making the transmitted data of the TI branch pass through a mode of
The filter of (1) passing the transmission data of the TQ branch in a form of
Can compensate for bandwidth limitations of coherent optical transceiversAmplitude and phase distortion caused by modulation, and IQ delay difference TX at transmitting end caused by inconsistent length of radio frequency line at coherent light transmitting endskew。
At the receiving end, according to the corresponding IQ delay difference RX of the receiving endskewThe electric signal received by the coherent optical receiver is calibrated, and IQ time delay difference caused by inconsistent length of the radio frequency line of the receiving end can be compensated.
The invention also provides a system for calibrating the frequency response and IQ delay difference of the coherent optical transceiver simultaneously, which comprises: a computer-readable storage medium and a processor;
the computer-readable storage medium is used for storing executable instructions;
the processor is used for reading the executable instructions stored in the computer readable storage medium and executing the method for simultaneously calibrating the frequency response and the IQ delay difference of the coherent optical transceiver.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. A method for calibrating frequency response and IQ delay difference of a coherent optical transceiver simultaneously, which is applied in a coherent optical transmitter at a transmitting end and a coherent optical receiver at a receiving end, comprising:
at a transmitting end, two paths of input multi-tone electric signals with an interweaving relation in a frequency domain are respectively input into a TI branch and a TQ branch;
at a receiving end, two paths of output multi-tone electric signals are simultaneously received from an RI branch and an RQ branch respectively to obtain an amplitude response and a phase response of the TI and the TQ as well as the RI and the RQ branches;
and after the frequency response and the IQ delay difference of the coherent optical transceiver are obtained through the amplitude response and the phase response of each branch, pre-compensating data to be transmitted at a transmitting end according to the frequency response, and performing IQ delay difference compensation at a receiving end.
2. The method of claim 1, wherein the two input polyphonic signals having an interleaving relationship in the frequency domain are respectively represented as:
wherein 2 Δ f represents the frequency interval of two paths of input polyphonic electrical signals having an interleaving relationship in the frequency domain, φnAnd N is a positive integer set according to the calibration bandwidth for a preset known random phase, and the maximum frequency 2N delta f of the two paths of input multi-tone electric signals with the interleaving relation in the frequency domain is covered to the bandwidth of the coherent optical transceiver.
3. The method of claim 2, wherein the received two output polyphonic signals are represented as:
where θ represents a phase difference between the signal light and the local oscillation light, and αXY,nRepresenting the amplitude of the nth frequency point of the signal in the received two paths of output polyphonic signals,
and the phase of the nth frequency point in the received two paths of output polyphonic signals is shown, and X and Y are I and Q.
4. A method according to claim 3, wherein the amplitude response and phase response of each branch are as follows:
αXY(f)＝abs(FFT(RX(t)))|XY
where abs () represents taking the absolute value, angle () represents taking the angle, FFT () represents the Fourier transform, phinF represents the frequency for a preset known random phase.
5. The method of claim 3, wherein the IQ delay differences are IQ delay differences of a coherent optical transmitter and a coherent optical receiver, respectively, and are:
wherein,
which indicates the phase response of the coherent optical transceiver, X, Y is I, Q, f is frequency.
6. The method of claim 3, wherein the frequency response H of the coherent optical transceiverI(f)、HQ(f) Expressed as:
wherein alpha isXY(f) For the amplitude response and the phase response of each branch,
for the phase response of the coherent optical transceiver, X, Y is I, Q.
7. The method of claim 6, wherein the pre-compensating the data to be transmitted at the transmitting end according to the frequency response and the IQ delay difference compensation at the receiving end specifically comprise:
at the transmitting end, the TI branch of the data to be transmitted is processed into the form of
Filtering of (1); the TQ branch of the data to be transmitted is processed into a form of
Filtering of (1);
at the receiving end, the IQ time delay difference RX of the coherent optical receiver is obtained according to the measurementskewThe signal received by the coherent optical receiver is calibrated.
8. A system for simultaneously calibrating frequency response and IQ delay variation of a coherent optical transceiver, comprising: a computer-readable storage medium and a processor;
the computer-readable storage medium is used for storing executable instructions;
the processor is configured to read executable instructions stored in the computer readable storage medium and execute the method for simultaneously calibrating the frequency response and the IQ delay difference of the coherent optical transceiver according to any one of claims 1 to 7.
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