Transmitter calibration method, system and medium based on IQ modulator

Abstract

The present invention discloses a transmitter calibration method, system, and medium based on an IQ modulator, belonging to the field of optical communications. The method includes: controlling the transmitter to transmit two multi-tone signals according to a pre-designed number of scanning frequency points, scanning frequency intervals, and multiple beat frequency intervals, so that the IQ modulator modulates the multi-tone signals and outputs corresponding optical signals; performing square detection and DC isolation processing on the optical signals in sequence to obtain low-frequency electrical signals, and separating the I-channel frequency response correlation signal, the Q-channel frequency response correlation signal, and the IQ delay difference correlation signal from the low-frequency electrical signals; using the cosine signal and sine signal of the beat frequency interval, performing calculation processing on the I-channel frequency response correlation signal, the Q-channel frequency response correlation signal, and the IQ delay difference correlation signal, respectively, to obtain the I-channel frequency response, the Q-channel frequency response, and the IQ two-channel delay difference to calibrate the transmitter. This greatly reduces measurement costs and broadens applicable scenarios.

Description

Technical Field

[0001] The present invention belongs to the field of optical communications, and more specifically, relates to a transmitter calibration method, system and medium based on an IQ modulator. Background Art

[0002] To cope with the rapid growth in traffic in modern optical communication systems, higher-order modulation formats and higher symbol rates are being deployed. In high-speed coherent optical transmission scenarios, high-speed signals are highly sensitive to coherent optical transmitter impairments (such as bandwidth limitations, phase response, and IQ delay). Therefore, accurately measuring and compensating for these impairments is crucial. Existing solutions for measuring coherent optical transmitter impairments require expensive equipment, resulting in high costs. Furthermore, impairment calibration is performed before the coherent optical transmitter leaves the factory, making them unsuitable for field calibration.

[0003] Currently, the following methods are commonly used to deal with impairments: transmitting specific signals in related systems; or using digital signal processing (DSP) algorithms for equalization, etc. Among them, the former method requires the use of a coherent receiver to measure the transmitter IQ delay by receiving the transmitted multi-tone signal, which is costly and not suitable for large-scale applications. The latter method calculates the transmission matrix based on the DSP algorithm and separates the transmitter and receiver coefficients to calculate the transmitter IQ delay. However, in practical applications, this method has complex equalization parameter selection problems, and its measurement stability also needs to be improved. Therefore, how to develop a transmitter frequency response and IQ two-way delay difference measurement method that does not require additional hardware structure and has high accuracy and stability is crucial to compensate for impairments.

[0004] Furthermore, existing IQ modulator bias point control methods all rely on linear point stabilization and control schemes, making it difficult to achieve stable control at certain special points (such as π, π, π or π, π, 0). Achieving stable bias control at these special points is also of great research interest. Summary of the Invention

[0005] In response to the defects of the existing technology and the need for improvement, the present invention provides a transmitter calibration method, system and medium based on an IQ modulator, which aims to solve the problems of high cost, poor measurement stability and complex implementation in the existing transmitter frequency response and IQ two-path delay difference measurement.

[0006] To achieve the above objectives, according to one aspect of the present invention, a transmitter calibration method based on an IQ modulator is provided, comprising: S1, controlling a transmitter to transmit two multi-tone signals based on a pre-designed number of scanning frequencies, a scanning frequency interval, and multiple beat frequency intervals, so that the IQ modulator modulates the multi-tone signals and outputs corresponding optical signals; S2, sequentially performing square detection and DC blocking on the optical signals to obtain low-frequency electrical signals, and separating an I-channel frequency response correlation signal, a Q-channel frequency response correlation signal, and an IQ delay difference correlation signal from the low-frequency electrical signals; S3, performing computations on the I-channel frequency response correlation signal, the Q-channel frequency response correlation signal, and the IQ delay difference correlation signal using cosine and sine signals of the beat frequency intervals to obtain an I-channel frequency response, a Q-channel frequency response, and an IQ two-channel delay difference; and S4, calibrating the transmitter using the I-channel frequency response, the Q-channel frequency response, and the IQ two-channel delay difference.

[0007] Furthermore, before S1, the step further includes: designing the number of scanning frequency points, the scanning frequency interval, and the multiple beat frequency intervals according to the following constraints:

[0008] ω m =Nω

[0009] nΔω+ω I ≠nΔω+ω Q ≠ω IQ +ω Q +nΔω≠ω IQ -ω I -nΔω

[0010] Among them, ω m is the target scanning bandwidth range, N is the number of scanning frequency points, ω is the scanning frequency interval, n=1,2,…,N, Δω is the frequency interval growth rate of the multi-tone signal, ω I is the beat frequency interval between two adjacent tones of the I-channel multi-tone signal, ω Q is the beat frequency interval between two adjacent tones of the Q-channel multi-tone signal, ω IQ It is the beat frequency interval between two adjacent tones in the I and Q multi-tone signals.

[0011] Furthermore, the multi-tone signal is:

[0012]

[0013]

[0014] Among them, V I (t), V Q(t) are the multi-tone signals transmitted to the I and Q channels at time t, Δt is the delay difference between the two multi-tone signals, m = N, N-1, ..., 1, a I (ω), They are the amplitude response and phase response at ω of I path, a Q (ω), are the amplitude response and phase response at ω of Q path respectively.

[0015] Furthermore, the I-channel frequency response correlation signal and the I-channel frequency response are respectively:

[0016]

[0017]

[0018]

[0019] Amp_I=5log10(Amp_phase_RI1 2 +Amp_phase_RI2 2 )

[0020]

[0021] in, is the I-channel frequency response correlation signal, a I (ω), are the amplitude response and phase response at ω of channel I, N is the number of scanning frequency points, ω is the scanning frequency interval, n=1, 2, ..., N, Δt is the delay difference between the two multi-tone signals, Δω is the frequency interval growth rate of the multi-tone signal, ω I is the beat frequency interval between two adjacent tones of the I-channel multi-tone signal, Amp_phase_RI1 and Amp_phase_RI2 are the I-channel first phase response associated signal and I-channel second phase response associated signal obtained after the operation, T is the detection period, t is the time, Amp_I and Phase_I are the amplitude response and phase response contained in the I-channel frequency response, respectively, ω m is the target scanning bandwidth range, and unwrap() is the phase angle unwrapping operation.

[0022] Furthermore, the Q-path frequency response correlation signal and the Q-path frequency response are respectively:

[0023]

[0024] Amp_Q=5log10(Amp_phase_RQ1 2 +Amp_phase_RQ2 2 )

[0025]

[0026]

[0027]

[0028] Wherein, Q is the Q-path frequency response correlation signal, a Q (ω), are the amplitude response and phase response at ω on the Q path, N is the number of scanning frequency points, ω is the scanning frequency interval, n=1, 2, ..., N, Δω is the frequency interval growth rate of the multi-tone signal, ω Q is the beat frequency interval between two adjacent tones of the Q-channel multi-tone signal, ω IQ is the beat frequency interval between two adjacent tones in the I and Q two-way multi-tone signals, Amp_phase_RQ1 and Amp_phase_RQ2 are the first amplitude response correlation signal of the Q channel and the second amplitude response correlation signal of the Q channel obtained after the operation, T is the detection period, t is the time, Amp_Q and Phase_Q are the amplitude response and phase response contained in the Q channel frequency response, respectively, ω m is the target scanning bandwidth range, and unwrap() is the phase angle unwrapping operation.

[0029] Furthermore, the IQ delay difference associated signal and the IQ two-path delay difference are respectively:

[0030] IQ=cos((ω IQ +ω Q +nΔω)t-nωΔt)+cos((ω IQ -nΔω-ω I )t-(n(ω+Δω)+ω I )Δt)

[0031]

[0032]

[0033]

[0034]

[0035]

[0036] Wherein, IQ is the IQ delay difference associated signal, skew is the IQ two-way delay difference, n=1,2,…,N, ω is the scanning frequency interval, Δω is the frequency interval growth rate of the multi-tone signal, ω Iis the beat frequency interval between two adjacent tones of the I-channel multi-tone signal, ω Q is the beat frequency interval between two adjacent tones of the Q-channel multi-tone signal, ω IQ is the beat frequency interval between two adjacent tones in the I and Q multi-tone signals, Δt is the delay difference of the two multi-tone signals, FR1, FR2, SR1, and SR2 are the first delay difference associated signal, the second delay difference associated signal, the third delay difference associated signal, and the fourth delay difference associated signal obtained after the operation, respectively. angle() is the phase angle operation, unwrap() is the phase angle unwrapping operation, T is the detection period, and t is the time.

[0037] Furthermore, before S1, it also includes: S01, obtaining a correlation coefficient by injecting a pilot according to the real-time optical power of the IQ modulator, and calculating a bias signal according to the relationship between the correlation coefficient and the bias signal; S02, generating a corresponding control signal according to the bias signal and the injected pilot to perform bias control on the IQ modulator; S03, repeating S01-S02 until the real-time optical power is equal to the target optical power.

[0038] Furthermore, the correlation coefficient includes an I-path correlation coefficient, a Q-path correlation coefficient, a P-path first correlation coefficient, and a P-path second correlation coefficient, wherein the P-path second correlation coefficient is:

[0039]

[0040] Among them, CIIQP is the second correlation coefficient of the P path, T is the detection period, t is the time, f1 is the frequency of the pilot signal injected into the I path, f2 is the frequency of the pilot signal injected into the Q path, f3 is the frequency of the pilot signal injected into the P path, and s(t) is the real-time optical power at time t.

[0041] According to another aspect of the present invention, a transmitter calibration system based on an IQ modulator is provided, comprising: a transmission control module for controlling the transmitter to transmit two multi-tone signals based on a pre-designed number of scanning frequencies, a scanning frequency interval, and multiple beat frequency intervals, so that the IQ modulator modulates the multi-tone signals and outputs corresponding optical signals; a detection and separation module for sequentially performing square detection and DC blocking on the optical signals to obtain low-frequency electrical signals, and separating an I-channel frequency response correlation signal, a Q-channel frequency response correlation signal, and an IQ delay difference correlation signal from the low-frequency electrical signals; a processing module for performing computations on the I-channel frequency response correlation signal, the Q-channel frequency response correlation signal, and the IQ delay difference correlation signal using cosine and sine signals at the beat frequency intervals to obtain an I-channel frequency response, a Q-channel frequency response, and an IQ delay difference; and a calibration module for calibrating the transmitter using the I-channel frequency response, the Q-channel frequency response, and the IQ delay difference.

[0042] According to another aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored. When the program is executed by a processor, the IQ modulator-based transmitter calibration method as described above is implemented.

[0043] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0044] (1) A transmitter calibration method based on an IQ modulator is provided. A low-bandwidth photodetector is introduced to measure the optical signal. By utilizing its square detection and low-bandwidth characteristics, a low-frequency signal containing delay information can be directly extracted without the need for additional hardware structure, which reduces costs and broadens the applicable scenarios. In addition, the transmitter delay difference can be obtained by performing a simple correlation expectation operation using a single-tone signal of known frequency, which reduces the computational complexity and makes the solution more feasible.

[0045] (2) By sending multi-tone signals with varying intervals on the I and Q channels, and simultaneously scanning the delay difference and frequency response information of multiple frequency points, the transmitter IQ delay difference and I and Q channel frequency response can be measured in one go, eliminating the need for multiple scans, thereby improving the stability and accuracy of transmitter calibration.

[0046] (3) By establishing a connection between the bias of the I, Q, and P control signals and the I, Q, and P pilot signals, the spectrum analysis in the existing technology is replaced, and the bias control hardware circuit and software resources are reused, thereby expanding the functionality of the coherent optical transmitter system and increasing the integration of the transmitter system;

[0047] (4) During the bias control process, all the correlation coefficients introduced are independent of the RF signal input from the external IQ modulator, making the bias control method applicable to any modulation format; in addition, the introduction of the P-path second correlation coefficient enables the bias control method to achieve stable bias control of any special point. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A flowchart of a transmitter calibration method based on an IQ modulator provided in an embodiment of the present invention;

[0049] Figure 2 A control block diagram of a transmitter calibration method based on an IQ modulator provided in an embodiment of the present invention;

[0050] Figure 3 A structural diagram of an IQ modulator provided in an embodiment of the present invention;

[0051] Figure 4 Spectrum diagram of the transmitted I and Q multi-tone signals provided by an embodiment of the present invention;

[0052] Figure 5 This is a spectrum diagram of the signal received when a low-pass filter with a bandwidth of 2 GHz is used in the simulation system provided by an embodiment of the present invention;

[0053] Figure 6 A time delay measurement curve obtained by calculation and fitting in the simulation system provided by an embodiment of the present invention;

[0054] Figure 7 An amplitude response curve diagram measured by the simulation system provided in an embodiment of the present invention;

[0055] Figure 8 A phase response curve diagram measured by the simulation system provided in an embodiment of the present invention;

[0056] Figure 9 This is a block diagram of a transmitter calibration system based on an IQ modulator provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0057] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0058] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0059] Figure 1 This is a flow chart of a transmitter calibration method based on an IQ modulator provided by an embodiment of the present invention. Figure 1 , combined with Figure 2-Figure 8 The transmitter calibration method based on the IQ modulator in this embodiment is described in detail. The method includes operations S1 to S4. The overall process of the method in this embodiment is as follows: Figure 2 shown.

[0060] See Figure 3 The IQ modulator consists of two sub-Mach-Zehnder modulators (MZMs) and a phase shifter P (or phase delay device). The I-channel MZM modulator (MZM_I) and the Q-channel MZM modulator (MZM_Q) can modulate the phases of the optical carrier signals loaded onto the I and Q channels, respectively, while the phase shifter P ensures that the phases of the two optical carriers remain orthogonal when they are combined.

[0061] Before performing operations S1 to S4, the bias point of the IQ modulator needs to be configured to a suitable state. The bias control method of the IQ modulator can be used to control the bias of the IQ modulator.

[0062] The embodiment of the present invention provides a better method for bias control of an IQ modulator, specifically including operations S01 to S03, which can be implemented by designing a signal acquisition module, a function selection module, a frequency source, a power monitoring module, a correlation integration module, a feedback control module, and a coupling unit.

[0063] Operation S01 : According to the real-time optical power of the IQ modulator, a correlation coefficient is obtained by injecting a pilot signal, and a bias signal is calculated according to the relationship between the correlation coefficient and the bias signal.

[0064] The signal acquisition module acquires the real-time optical power of the IQ modulator. This module, which includes a fiber coupler, a photodetector, and an analog-to-digital converter, connects to the IQ modulator's output fiber and converts the real-time optical signal into a digital signal. A signal separation unit can also be included to separate the DC and AC signals, amplify them, and then digitize them. A frequency source outputs a pilot signal to the IQ modulator. A hardware frequency source converts the pilot signal into a digital signal using an analog-to-digital converter, generating a stable pilot signal. A software frequency source uses a digital-to-analog converter and a direct digital frequency synthesizer algorithm to generate the pilot signal, saving electronic components, reducing the size of the control system, and accelerating computational speed.

[0065] Specifically, operation S01 includes sub-operations S01A-S01C.

[0066] In sub-operation S01A, the signal acquisition module obtains the real-time optical power s(t) of the IQ modulator, and the power monitoring module calculates the DC optical power according to s(t). The frequency source sends out a pilot signal.

[0067] The pilot signals sent by the frequency source include: I-channel MZM pilot signal Asin(2πf1t) with frequency f1, Q-channel MZM pilot signal Asin(2πf2t) with frequency f2, and P-channel MZM pilot signal Asin(2πf3t) with frequency f3. Among them, the amplitude A is 1% V π ~10%V π ; V π is the half-wave voltage of the IQ modulator. The detection period T is usually 0.2ms to 0.5ms to ensure accurate calculation of the DC optical power and to avoid the impact of a long detection period on real-time control.

[0068] In sub-operation S01B, a pilot signal is injected to obtain correlation coefficients, which include an I-channel correlation coefficient CII, a Q-channel correlation coefficient CIQ, a P-channel first correlation coefficient CIIQ, and a P-channel second correlation coefficient CIIQP:

[0069]

[0070]

[0071]

[0072]

[0073] Wherein, f1 is the frequency of the pilot signal injected into path I, f2 is the frequency of the pilot signal injected into path Q, f3 is the frequency of the pilot signal injected into path P, and s(t) is the real-time optical power at time t. Preferably, the pilot frequency is 1 kHz to 10 kHz.

[0074] In sub-operation S01C, the feedback control module calculates the bias signal according to CII, CIQ, CIIQ and CIIQP. The bias signal includes the bias V of the I-way control signal. I , Q-way control signal bias V Q and P-way control signal bias V P .

[0075] The relationship between the correlation coefficient and the bias signal is:

[0076]

[0077]

[0078]

[0079]

[0080] Among them, J1() is the first-order Bessel function, V πI is the half-wave voltage of MZM I, V πQ is the half-wave voltage of the Q-path MZM, V πP is the half-wave voltage of the P-circuit MZM.

[0081] Operation S02 : generating a corresponding control signal according to the bias signal and the injected pilot to perform bias control on the IQ modulator.

[0082] The coupling unit outputs V according to the feedback control module. I 、V Q and V P And each pilot signal generates an I-way control signal V' I , Q-path control signal V′ Q and P-way control signal V' P :

[0083] V′ I =V I +Asin(2πf1t)

[0084] V′ Q =V Q +Asin(2πf2t)

[0085] V′ P =V P +Asin(2πf3t)

[0086] V′ I Input I-channel MZM modulator, V′ Q Input Q-channel MZM modulator, V′ P Input phase delay P to bias the IQ modulator.

[0087] Operation S03 : Repeat operations S01 to S02 until the real-time optical power is equal to the target optical power.

[0088] During the bias control process, the real-time optical power s(t) of the IQ modulator is:

[0089]

[0090] The optical power signal I(t) of the I-channel MZM modulator and the optical power signal Q(t) of the Q-channel MZM modulator satisfy:

[0091]

[0092]

[0093]

[0094]

[0095] Operation S01 to operation S02 are repeatedly performed multiple times, thereby achieving automatic control of the bias point of the IQ modulator.

[0096] In operation S1 , the transmitter is controlled to transmit two multi-tone signals according to the pre-designed number of scanning frequency points, scanning frequency intervals, and multiple beat frequency intervals, so that the IQ modulator modulates the multi-tone signals and outputs corresponding optical signals.

[0097] According to an embodiment of the present invention, before performing operation S1, the method further includes: designing the number of scanning frequency points, the scanning frequency interval, and the multiple beat frequency intervals according to the following constraints:

[0098] ω m =Nω

[0099] nΔω+ω I ≠nΔω+ω Q ≠ω IQ +ω Q +nΔω≠ω IQ -ω I -nΔω

[0100] Among them, ω m is the target scanning bandwidth range, N is the number of scanning frequency points, ω is the scanning frequency interval, n=1,2,…,N, Δω is the frequency interval growth rate of the multi-tone signal, ω I is the beat frequency interval between two adjacent tones of the I-channel multi-tone signal, ω Q is the beat frequency interval between two adjacent tones of the Q-channel multi-tone signal, ω IQ It is the beat frequency interval between two adjacent tones in the I and Q multi-tone signals.

[0101] Right I 、ω Q 、ω IQ , Δω are designed to fit the bandwidth of the photodetector used for optical power measurement. Beat frequency interval ω I 、ω Q 、ω IQ , Δω must be much smaller than ω. It is important to pay attention to the trade-off between N and ω. For a fixed setting of ω m The larger the value of N, the more frequency points are scanned and the higher the calculation accuracy. However, ω needs to be appropriately reduced at this time, which is not conducive to satisfying the condition that the beat frequency interval must be much smaller than ω, and will also affect the accuracy of delay measurement and frequency response.

[0102] According to an embodiment of the present invention, the two multi-tone signals transmitted by the control transmitter are respectively:

[0103]

[0104]

[0105] Among them, V I (t), V Q (t) are the multi-tone signals transmitted to the I and Q channels at time t, Δt is the delay difference between the two multi-tone signals, m = N, N-1, ..., 1, a I (ω), They are the amplitude response and phase response at ω of I path, a Q (ω), are the amplitude response and phase response at ω of Q path respectively.

[0106] In this embodiment, the designed I and Q multi-tone signals will scan the information of 2*N frequency points within the bandwidth range, stagger the frequency intervals to avoid frequency aliasing, and avoid repeated frequency scanning, so as to measure the delay difference and frequency response in the entire frequency band at one time.

[0107] Operations S01 to S03 stabilize the bias points of the IQ MZMs at the linear point. Then, the phase delay is set to 0° or 180°. Finally, the modulated signal can be expressed as:

[0108]

[0109]

[0110] In operation S2 , square detection and DC blocking are performed on the optical signal in sequence to obtain a low-frequency electrical signal, and an I-channel frequency response correlation signal, a Q-channel frequency response correlation signal, and an IQ delay difference correlation signal are separated from the low-frequency electrical signal.

[0111] At the receiving end, a low-bandwidth photodetector is used to receive and square the optical signal to obtain the electrical signal S(t):

[0112]

[0113] Since a low-bandwidth photodetector is used, the high-frequency signal is filtered out, and after DC isolation processing, a low-frequency electrical signal is obtained. The remaining low-frequency signal can be expressed as:

[0114]

[0115]

[0116]

[0117] Separate the I-channel frequency response correlation signal I, the Q-channel frequency response correlation signal Q, and the IQ delay difference correlation signal IQ from the remaining low-frequency signal:

[0118]

[0119]

[0120] IQ=I1Q2+I2Q1

[0121] =cos((ω IQ +ω Q +nΔω)t-nωΔt)+cos((ω IQ -nΔω-ω I )t-(n(ω+Δω)+ω I )Δt)

[0122] In operation S3, the I-channel frequency response correlation signal, the Q-channel frequency response correlation signal, and the IQ delay difference correlation signal are respectively processed using the cosine signal and the sine signal of the beat frequency interval to obtain the I-channel frequency response, the Q-channel frequency response, and the IQ delay difference.

[0123] According to an embodiment of the present invention, the amplitude response Amp_I and the phase response Phase_I included in the obtained I-channel frequency response are respectively:

[0124]

[0125]

[0126] Amp_I=5log10(Amp_phase_RI1 2 +Amp_phase_RI2 2 )

[0127]

[0128] Among them, Amp_phase_RI1 and Amp_phase_RI2 are the first phase response correlation signal of I channel and the second phase response correlation signal of I channel obtained after calculation, T is the detection period, t is the time, Amp_I and Phase_I are the amplitude response and phase response contained in the frequency response of I channel, respectively. m is the target scanning bandwidth range, and unwrap() is the phase angle unwrapping operation.

[0129] According to an embodiment of the present invention, the amplitude response Amp_Q and the phase response Phase_Q included in the obtained Q-path frequency response are respectively:

[0130] Amp_Q=5log10(Amp_phase_RQ1 2 +Amp_phase_RQ2 2 )

[0131]

[0132]

[0133]

[0134] Among them, Amp_phase_RQ1 and Amp_phase_RQ2 are the first amplitude response correlation signal of the Q channel and the second amplitude response correlation signal of the Q channel obtained after the calculation, respectively. Amp_Q and Phase_Q are the amplitude response and phase response included in the Q channel frequency response, respectively.

[0135] According to an embodiment of the present invention, the obtained IQ two-path delay skew is:

[0136]

[0137]

[0138]

[0139]

[0140]

[0141] Among them, FR1, FR2, SR1, and SR2 are the first delay difference correlation signal, the second delay difference correlation signal, the third delay difference correlation signal, and the fourth delay difference correlation signal obtained after the operation, respectively, and angle() is the phase angle operation.

[0142] In this embodiment, the angle between FR1 and FR2 is calculated and a linear fit is performed to obtain the slope, thereby obtaining the IQ delay difference. Similarly, the operation is performed on SR1 and SR2 to obtain the IQ delay. After averaging the two delays, the IQ delay solution can be made more accurate.

[0143] In operation S4, the transmitter is calibrated using the I-path frequency response, the Q-path frequency response, and the I / Q-path delay difference.

[0144] Specifically, the I frequency response (Amp_I and Phase_I), Q frequency response (Amp_Q and Phase_Q), and IQ skew are transmitted to the transmitter. The transmitter can perform frequency response and delay compensation based on the calibrated I and Q frequency responses and IQ skew to complete the calibration.

[0145] Delay compensation can be achieved by applying an additional phase to the I branch in the frequency domain to compensate for the delay between the transmitter I and Q paths. Frequency response compensation can be achieved by multiplying the signal with a complex matrix. This process can be expressed as:

[0146]

[0147] Among them, A I (ω) -1 is the frequency response A I The bandwidth limit can be obtained by multiplying A I (ω) -1 Boosting the high-frequency portion of the signal can alleviate this problem, but since the power of the lower-frequency signal decreases accordingly, the relevant compensation parameters should be optimized to achieve better transmission performance. In this compensation method, the compensation bandwidth is limited to (1 + α)·B / 2, where α is the roll-off factor of the matched filter and B is the bandwidth of the baseband signal. In addition, the normalization factor β, which controls the compensation level, is fixed at 0.6.

[0148] The following Figure 4-Figure 8 The simulation data and experimental results are shown to illustrate the characteristics of the transmitter calibration method based on the IQ modulator in the embodiment of the present invention. The simulation system parameters are shown in Table 1.

[0149] Table 1

[0150] parameter Numerical parameter Numerical Number of transmitted signal tones 30 Sampling rate (MSa / s) 250 Tone frequency spacing (MHz) 500 Received signal-to-noise ratio (dB) 20 Calibration frequency interval (kHz) 1.25～4 Low-pass filter bandwidth (GHz) 2

[0151] The spectrum of the transmitted I and Q multi-tone signals is as follows: Figure 4 The spectrum of the received signal when using a low-pass filter with a bandwidth of 2GHz is shown in Figure 5 As shown, it can be seen that the corresponding 30 single-tone signals are received.

[0152] The delay measurement curve obtained by calculation and fitting in the simulation system is as follows: Figure 6 As shown, the slope of the fitted curve is 6.3e-12. After conversion by t_skew = slope / 2π, the measured delay is equal to 1.0027ps, which is consistent with the 1ps set in the simulation.

[0153] Figure 7 and Figure 8Represents the amplitude response curve and phase response curve respectively. The transmitter simulation setting nominal 3dB bandwidth is 23GHz. Figure 7 and Figure 8 Compared with the nominal frequency response curve of the simulation setting, the amplitude response measurement error is less than 0.5dB, and the phase response measurement error is less than 5°.

[0154] pass Figure 4-Figure 8 From the simulation data and experimental results shown, it can be seen that the method shown in the embodiment of the present invention reduces the measurement cost and the computational complexity, thereby improving the measurement efficiency while ensuring the measurement accuracy and achieving one-time measurement.

[0155] Figure 9 A block diagram of a transmitter calibration system based on an IQ modulator according to an embodiment of the present invention. Figure 9 The IQ modulator-based transmitter calibration system 900 includes a transmission control module 910 , a detection and separation module 920 , an operation processing module 930 and a calibration module 940 .

[0156] The transmission control module 910, for example, performs operation S1 to control the transmitter to transmit two multi-tone signals according to the pre-designed number of scanning frequency points, scanning frequency intervals, and multiple beat frequency intervals, so that the IQ modulator modulates the multi-tone signals and outputs corresponding optical signals.

[0157] The detection and separation module 920 performs operation S2 to perform square detection and DC blocking on the optical signal in sequence to obtain a low-frequency electrical signal, and separates an I-channel frequency response correlation signal, a Q-channel frequency response correlation signal, and an IQ delay difference correlation signal from the low-frequency electrical signal.

[0158] The operation processing module 930, for example, performs operation S3 to respectively perform operation processing on the I-channel frequency response correlation signal, the Q-channel frequency response correlation signal, and the IQ delay difference correlation signal using the cosine signal and the sine signal separated by the beat frequency interval to obtain the I-channel frequency response, the Q-channel frequency response, and the IQ delay difference.

[0159] The calibration module 940, for example, performs operation S4 to calibrate the transmitter using the I-path frequency response, the Q-path frequency response, and the IQ-path delay difference.

[0160] The transmitter calibration system 900 based on IQ modulator is used to perform the above Figures 1-8 The transmitter calibration method based on IQ modulator in the embodiment shown. Figures 1-8 The transmitter calibration method based on the IQ modulator in the illustrated embodiment will not be described in detail here.

[0161] The embodiment of the present invention further provides a computer readable storage medium on which a computer program is stored. When the program is executed by a processor, the following is achieved: Figures 1-8 The transmitter calibration method based on the IQ modulator in the illustrated embodiment will not be described in detail here.

[0162] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A transmitter calibration method based on an IQ modulator, characterized in that: include: S1, controlling the transmitter to transmit two multi-tone signals according to the pre-designed number of scanning frequency points, scanning frequency intervals, and multiple beat frequency intervals, so that the IQ modulator modulates the multi-tone signals and outputs corresponding optical signals; S2, performing square detection and DC blocking processing on the optical signal in sequence to obtain a low-frequency electrical signal, and separating an I-channel frequency response correlation signal, a Q-channel frequency response correlation signal, and an IQ delay difference correlation signal from the low-frequency electrical signal; S3, using the cosine signal and the sine signal of the beat frequency interval, respectively performing calculations on the I-channel frequency response correlation signal, the Q-channel frequency response correlation signal, and the IQ delay difference correlation signal to obtain the I-channel frequency response, the Q-channel frequency response, and the IQ delay difference; S4, calibrating the transmitter using the I-path frequency response, the Q-path frequency response, and the IQ-path delay difference; The multi-tone signal is: Among them, V I (t), V Q (t) are the multi-tone signals transmitted to the I channel and the Q channel at time t, n = 1, 2, ..., N, N is the number of scanning frequency points, ω is the scanning frequency interval, Δω is the frequency interval growth rate of the multi-tone signal, ω I is the beat frequency interval between two adjacent tones of the I-channel multi-tone signal, Δt is the time delay difference between the two multi-tone signals, ω IQ is the beat frequency interval between two adjacent tones in the I and Q multi-tone signals, ω Q is the beat frequency interval between two adjacent tones of the Q-channel multi-tone signal, m=N,N-1,…,1, a I (ω), They are the amplitude response and phase response at ω of I path, a Q (ω), are the amplitude response and phase response at ω of Q path respectively.

2. The transmitter calibration method based on an IQ modulator according to claim 1, wherein: Before S1, the method further includes: designing the number of scanning frequency points, the scanning frequency interval, and the multiple beat frequency intervals according to the following constraints: oh m =No nD+w I ≠nΔω+ω Q ≠ω IQ +oh Q +nΔω≠ω IQ -oh I -nSee Among them, ω m Scan the bandwidth range for the target.

3. The transmitter calibration method based on an IQ modulator according to claim 1, wherein: The I-channel frequency response correlation signal and the I-channel frequency response are respectively: Amp_I=5log10(Amp_phase_RI1 2 +Amp_phase_RI2 2 ) in, is the I-channel frequency response correlation signal, Amp_phase_RI1 and Amp_phase_RI2 are the I-channel first phase response correlation signal and I-channel second phase response correlation signal obtained after the operation, T is the detection period, t is the time, Amp_I and Phase_I are the amplitude response and phase response contained in the I-channel frequency response, respectively, ω m is the target scanning bandwidth range, angle() is the phase angle operation, and unwrap() is the phase angle unwrapping operation.

4. The transmitter calibration method based on an IQ modulator according to claim 1, wherein: The Q-path frequency response correlation signal and the Q-path frequency response are respectively: Amp_Q=5log10(Amp_phase_RQ1 2 +Amp_phase_RQ2 2 ) Wherein, Q is the Q-path frequency response correlation signal, Amp_phase_RQ1 and Amp_phase_RQ2 are the Q-path first amplitude response correlation signal and the Q-path second amplitude response correlation signal obtained after the operation, T is the detection period, t is the time, Amp_Q and Phase_Q are the amplitude response and phase response contained in the Q-path frequency response, respectively, ω m is the target scanning bandwidth range, angle() is the phase angle operation, and unwrap() is the phase angle unwrapping operation.

5. The transmitter calibration method based on an IQ modulator according to claim 1, wherein: The IQ delay difference associated signal and the IQ two-path delay difference are respectively: IQ=cos((ω) IQ +oh Q +nΔω)t-nωΔt)+cos((ω IQ -nGive-oh I )t-(n(ω+Dω)+ω I )Δt) Among them, IQ is the IQ delay difference associated signal, skew is the IQ two-path delay difference, FR1, FR2, SR1, and SR2 are the first delay difference associated signal, the second delay difference associated signal, the third delay difference associated signal, and the fourth delay difference associated signal obtained after the operation, respectively. angle() is the phase angle operation, unwrap() is the phase angle unwrapping operation, T is the detection period, and t is the time.

6. The transmitter calibration method based on an IQ modulator according to any one of claims 1 to 5, characterized in that: The S1 also includes: S01, obtaining a correlation coefficient by injecting a pilot signal according to the real-time optical power of the IQ modulator, and calculating a bias signal according to a relationship between the correlation coefficient and the bias signal; S02, generating a corresponding control signal according to the bias signal and the injected pilot to perform bias control on the IQ modulator; S03, repeatedly executing S01-S02 until the real-time optical power is equal to the target optical power.

7. The transmitter calibration method based on an IQ modulator according to claim 6, wherein: The correlation coefficients include an I-path correlation coefficient, a Q-path correlation coefficient, a P-path first correlation coefficient, and a P-path second correlation coefficient. The P-path second correlation coefficient is: Among them, CIIQP is the second correlation coefficient of the P path, T is the detection period, t is the time, f1 is the frequency of the pilot signal injected into the I path, f2 is the frequency of the pilot signal injected into the Q path, f3 is the frequency of the pilot signal injected into the P path, and s(t) is the real-time optical power at time t.

8. A transmitter calibration system based on an IQ modulator, characterized in that: include: A transmission control module is used to control the transmitter to transmit two multi-tone signals according to the pre-designed number of scanning frequency points, scanning frequency intervals and multiple beat frequency intervals, so that the IQ modulator modulates the multi-tone signals and outputs corresponding optical signals; a detection and separation module, configured to sequentially perform square detection and DC blocking processing on the optical signal to obtain a low-frequency electrical signal, and separate an I-channel frequency response correlation signal, a Q-channel frequency response correlation signal, and an IQ delay difference correlation signal from the low-frequency electrical signal; an operation processing module, configured to perform operation processing on the I-channel frequency response correlation signal, the Q-channel frequency response correlation signal, and the IQ delay difference correlation signal respectively using the cosine signal and the sine signal of the beat frequency interval, to obtain the I-channel frequency response, the Q-channel frequency response, and the IQ two-channel delay difference; a calibration module, configured to calibrate the transmitter using the I-path frequency response, the Q-path frequency response, and the IQ two-path delay difference; The multi-tone signal is: Among them, V I (t), V Q (t) are the multi-tone signals transmitted to the I channel and the Q channel at time t, n = 1, 2, ..., N, N is the number of scanning frequency points, ω is the scanning frequency interval, Δω is the frequency interval growth rate of the multi-tone signal, ω I is the beat frequency interval between two adjacent tones of the I-channel multi-tone signal, Δt is the time delay difference between the two multi-tone signals, ω IQ is the beat frequency interval between two adjacent tones in the I and Q multi-tone signals, ω Q is the beat frequency interval between two adjacent tones of the Q-channel multi-tone signal, m=N,N-1,…,1, a I (ω), They are the amplitude response and phase response at ω of I path, a Q (ω), are the amplitude response and phase response at ω of Q path respectively.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the IQ modulator-based transmitter calibration method according to any one of claims 1 to 7 is implemented.

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