Modulator bias point control method based on double perturbation signal combination and circuit thereof
By using a modulator bias point control method combining dual perturbation signals, the problem of bias point drift in Mach-Zehnder modulators was solved, achieving real-time and stable bias point control and improving the transmission efficiency and reliability of optical communication systems.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHONGQING WEI SI WO TECH CO LTD
- Filing Date
- 2022-10-25
- Publication Date
- 2026-07-03
AI Technical Summary
In the prior art, the bias point of the Mach-Zehnder modulator is easily affected by factors such as temperature and mechanical vibration, which leads to a decrease in the quality of the transmitted signal. Furthermore, the existing automatic control methods are complex, have poor real-time performance, are prone to lockout, and have low system stability.
A modulator bias point control method using a combination of dual perturbation signals is adopted. The bias point control is performed by detecting the phase relationship of the perturbation signals. This includes adding perturbation signals A and B of different frequencies to a DC bias signal, performing gating filtering and envelope detection on the output photocurrent signal, and finally feeding back the bias point signal through multiplication phase detection.
It achieves real-time tracking control of the bias point, reduces circuit and algorithm complexity, improves system real-time performance and stability, and reduces spurious emissions and MCU costs.
Smart Images
Figure CN115913380B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of modulator bias point control, and more specifically to a modulator bias point control method and circuit based on a combination of dual perturbation signals. Background Technology
[0002] The Mach-Zehnder modulator, as the most commonly used external modulator, plays a crucial role in optical communication systems. Utilizing the optical properties of lithium niobate crystals, the Mach-Zehnder modulator converts the input optical signal into an electrical signal, realizing photoelectric conversion. However, the transmission curve of the Mach-Zehnder modulator exhibits periodicity and nonlinearity, such as... Figure 1 As shown, during its operation, due to uncontrollable factors such as external temperature or mechanical vibration, the bias point (quad2) will inevitably drift, resulting in a reduction in the quality of the transmitted signal and a serious impact on the system's transmission efficiency. Therefore, it is necessary to automatically control the modulator bias point.
[0003] The existing mature automatic modulator bias point control circuit mechanism involves adding a low-frequency disturbance signal to the control terminal. Automatic bias point control is achieved by extracting the fundamental frequency and second harmonic signals of the modulated disturbance signal and calculating their amplitude correlation. However, the second harmonic signal is much smaller than the fundamental frequency signal, making its extraction complex. The industry generally uses a digital method, which involves converting the modulated disturbance signal using an analog-to-digital converter (AD converter) and then using a Fast Fourier Transform (FFT) to extract the amplitudes of the fundamental frequency and second harmonic signals. However, the accuracy of FFT calculation is directly proportional to the number of sampling points. Too few sampling points cannot distinguish the second harmonic signal, while increasing the number of sampling points increases the computational load, causing delays, poor system real-time performance, and a tendency to lose lock and reduce stability. Furthermore, the digital method also introduces significant high-frequency noise, resulting in poor spurious performance across the entire link. Summary of the Invention
[0004] In view of the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a modulator bias point control method and circuit based on a combination of dual perturbation signals. The method employs a dual perturbation signal combination modulation and demodulation scheme and automatically controls the bias point by detecting the phase relationship of the perturbation signals after modulation by the modulator.
[0005] The objective of this invention is achieved through the following technical solution:
[0006] The modulator bias point control method based on dual-perturbation signal combination includes the following steps:
[0007] S1. Add and fuse the disturbance signals A and B of different frequencies and the DC bias signal to obtain the bias voltage control signal;
[0008] S2. Apply the bias voltage control signal to the modulator bias control terminal to control the bias point.
[0009] S3, The modulator outputs a photocurrent signal that reflects the optical power;
[0010] S4. The photocurrent signal is converted into a voltage signal reflecting the optical power through photoelectric conversion;
[0011] S5. The voltage signal is gating and filtered to remove the disturbance signal A, and the pilot signal is obtained.
[0012] S6. The pilot signal is converted into an envelope signal;
[0013] S7. Multiply the envelope signal and the disturbance signal A to detect the phase and output the bias point feedback AC signal.
[0014] S8. Condition the AC bias signal feedback to the DC bias signal in step S1.
[0015] Furthermore, step S6 specifically includes the following steps:
[0016] S61. The pilot signal is passed through a detector to detect the envelope, and the envelope signal of the tooth-shaped wave is obtained.
[0017] S62. The envelope signal with tooth-shaped ripples is gating and filtered to obtain a smooth ripple envelope signal.
[0018] Further, in step S62, the tooth-shaped wave envelope signal is gating filtered by the center frequency of the high-Q value perturbation signal A to obtain a smooth wave envelope signal.
[0019] Furthermore, in step S5, the voltage signal is gating filtered at the center frequency of the high-Q disturbance signal B to filter out the disturbance signal A.
[0020] Furthermore, the frequency of the disturbance signal A is less than the frequency of the disturbance signal B.
[0021] Furthermore, the frequency of the disturbance signal B is 8 to 12 times the frequency of the disturbance signal A.
[0022] Furthermore, the voltage of the disturbance signal A is 200–300 mV; the voltage of the disturbance signal B is 200–300 mV.
[0023] Furthermore, the frequency of the disturbance signal A is 0.8~1.2kHz, and the frequency of the disturbance signal B is 8~12kHz.
[0024] The control circuit for the modulator bias point control method based on dual-perturbation signal combination includes:
[0025] The photoelectric conversion unit receives the photocurrent signal reflecting the optical power output by the modulator, converts it into a voltage signal, and outputs it.
[0026] The first filtering unit receives the voltage signal emitted by the photoelectric conversion unit, performs gating filtering to remove the disturbance signal A, obtains the pilot signal, and outputs it.
[0027] The detection unit receives the pilot signal from the first filtering unit, performs envelope detection on the pilot signal, obtains the envelope signal of the tooth-shaped ripple at frequency A of the disturbance signal, and outputs it.
[0028] The second filtering unit receives the envelope signal of the tooth-shaped wave emitted by the detection unit, and selects and filters the envelope signal of the tooth-shaped wave to obtain the envelope signal of the smooth wave and outputs it.
[0029] The disturbance signal A generation unit generates and outputs disturbance signal A;
[0030] The disturbance signal B generation unit generates and outputs the disturbance signal B.
[0031] The phase detection unit receives the smoothed oscillating envelope signal and the disturbance signal A emitted by the second filtering unit, and performs multiplication phase detection on the two received signals to obtain the bias point feedback AC signal and output it.
[0032] The bias generation unit receives the bias point feedback AC signal from the phase detection unit, then conditions the bias point feedback AC signal into a DC bias signal and outputs it.
[0033] The adder unit receives the DC bias signal from the bias generation unit, the disturbance signal A from the disturbance signal A generation unit, and the disturbance signal B from the disturbance signal B generation unit. It then adds and fuses the three received signals to obtain the bias voltage control signal and outputs it to the modulator bias control terminal for bias point control.
[0034] The system for modulator bias point control based on dual-perturbation signal combination includes the control circuit of the modulator bias point control method based on dual-perturbation signal combination described above.
[0035] Because of the adoption of the above technical solution, the present invention has the following advantages:
[0036] A closed-loop control method with real-time feedback is adopted to follow the changing bias point in real time, avoiding the problem that the bias point voltage will drift due to the influence of environmental changes and changes in input optical power, and thus the bias point cannot be adjusted in real time.
[0037] This method adds an additional disturbance signal, eliminates the need for second harmonic amplitude detection, and eliminates the need for AD conversion and Fast Fourier Transform (FFT), thereby reducing the complexity of the circuit and algorithm, improving the real-time performance of the control, and providing a basis for adopting a pure analog circuit scheme.
[0038] This invention can reduce system stray noise, the circuit can be designed without software and has high reliability, the circuit eliminates the need for an MCU, reducing costs, and the circuit system has high real-time performance.
[0039] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description
[0040] The accompanying drawings of this invention are described below:
[0041] Figure 1 This is a diagram showing the electro-optical conversion characteristics of the modulator.
[0042] Figure 2 This is a waveform diagram of the voltage signal after conversion by the photoelectric conversion unit in this embodiment.
[0043] Figure 3 This is a waveform diagram of the pilot signal after the first filtering unit filters out the disturbance signal A in this embodiment.
[0044] Figure 4 This is a schematic diagram of the detection effect after the detection unit performs envelope detection in this embodiment.
[0045] Figure 5 This is a schematic diagram of the smooth envelope signal effect after filtering by the second filtering unit in this embodiment.
[0046] Figure 6 This is the bias voltage waveform after the adder units are fused in this embodiment.
[0047] Figure 7 This is a circuit diagram of the control circuit for the modulator bias point control method based on the combination of dual perturbation signals in this embodiment. Detailed Implementation
[0048] The present invention will be further described below with reference to the accompanying drawings and embodiments.
[0049] Example:
[0050] The modulator bias point control method based on dual-perturbation signal combination includes the following steps:
[0051] S1. Add and fuse the disturbance signals A (1kHz, 200-300mV) and B (10kHz, 200-300mV) of different frequencies and the DC bias signal to obtain the bias voltage control signal.
[0052] S2. Apply the bias voltage control signal to the modulator bias control terminal to control the bias point.
[0053] S3, After the bias voltage signal is applied to the modulator, according to Figure 1 As shown in the electro-optic conversion characteristic diagram of the modulator, the output optical power will change according to the magnitude of the bias signal, and the modulator back-probe PD will convert this optical power change into photocurrent.
[0054] S4. The photocurrent signal is converted into a voltage signal reflecting the optical power via photoelectric conversion; the converted voltage signal is as follows: Figure 1 As shown in the curve, the waveform at this time contains 1KHz and 10KHz signals;
[0055] S5. The voltage signal undergoes high-Q gating filtering at a center frequency of 10kHz. The resulting pilot signal is as follows: Figure 3 As shown in the curve, after filtering out the 1kHz disturbance signal, the amplitude of the 10kHz signal changes with the envelope of the 1kHz signal.
[0056] S6. The filtered 10kHz pilot signal is subjected to envelope detection by a detector, and the detection effect is as follows: Figure 4 The continuous toothed lines at the top of the middle section represent the 1kHz envelope signal, which still has some glitches and requires further filtering and smoothing.
[0057] The tooth-shaped undulating envelope signal is then passed through a high-Q center frequency 1kHz gating filter to obtain a smooth undulating envelope signal.
[0058] S7. Multiply the smoothed oscillation envelope signal and the disturbance signal A to detect the phase, and output the bias point feedback AC signal.
[0059] S8. Condition the AC bias signal feedback to the DC bias signal in step S1.
[0060] The control circuit for the modulator bias point control method based on dual-perturbation signal combination is shown in the figure, including:
[0061] The photoelectric conversion unit receives the photocurrent signal reflecting the optical power output by the modulator, converts it into a voltage signal, and outputs it.
[0062] The first filtering unit receives the voltage signal emitted by the photoelectric conversion unit, performs gating filtering to remove the disturbance signal A, obtains the pilot signal, and outputs it.
[0063] The detection unit receives the pilot signal from the first filtering unit, performs envelope detection on the pilot signal, obtains the envelope signal of the tooth-shaped ripple at frequency A of the disturbance signal, and outputs it.
[0064] The second filtering unit receives the envelope signal of the tooth-shaped wave emitted by the detection unit, and selects and filters the envelope signal of the tooth-shaped wave to obtain the envelope signal and outputs it.
[0065] The disturbance signal A generation unit generates and outputs disturbance signal A;
[0066] The disturbance signal B generation unit generates and outputs the disturbance signal B.
[0067] The phase detection unit receives the envelope signal and disturbance signal A from the second filtering unit, performs multiplication phase detection on the two received signals, obtains the bias point feedback AC signal, and outputs it.
[0068] The bias generation unit receives the bias point feedback AC signal from the phase detection unit, then conditions the bias point feedback AC signal into a DC bias signal and outputs it.
[0069] The adder unit receives the DC bias signal from the bias generation unit, the disturbance signal A from the disturbance signal A generation unit, and the disturbance signal B from the disturbance signal B generation unit. It then adds and fuses the three received signals to obtain the bias voltage control signal and outputs it to the modulator bias control terminal for bias point control.
[0070] The system for modulator bias point control based on dual-perturbation signal combination includes a control circuit or control module for modulator bias point control based on dual-perturbation signal combination, and a storage medium.
[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.
Claims
1. A modulator bias point control method based on a combination of dual perturbation signals, characterized in that, Includes the following steps: S1. Add and fuse the disturbance signals A and B of different frequencies and the DC bias signal to obtain the bias voltage control signal; S2. Apply the bias voltage control signal to the modulator bias control terminal to control the bias point. S3, The modulator outputs a photocurrent signal that reflects the optical power; S4. The photocurrent signal is converted into a voltage signal reflecting the optical power through photoelectric conversion; S5. The voltage signal is gating and filtered to remove the disturbance signal A, and the pilot signal is obtained. S6. The pilot signal is converted into an envelope signal; S7. Multiply the envelope signal and the disturbance signal A to detect the phase and output the bias point feedback AC signal. S8. Condition the AC bias signal feedback to the DC bias signal in step S1.
2. The modulator bias point control method based on dual-perturbation signal combination according to claim 1, characterized in that, Step S6 specifically includes the following steps: S61. The pilot signal is passed through a detector to detect the envelope, and the envelope signal of the tooth-shaped wave is obtained. S62. The envelope signal with tooth-shaped ripples is gating and filtered to obtain a smooth ripple envelope signal.
3. The modulator bias point control method based on dual perturbation signal combination according to claim 2, characterized in that, In step S62, the envelope signal with tooth-shaped ripples is gating filtered at the center frequency of the high-Q perturbation signal A to obtain a smoothed envelope signal.
4. The modulator bias point control method based on dual perturbation signal combination according to claim 1, characterized in that, In step S5, the voltage signal is gating filtered at the center frequency of the high-Q disturbance signal B to filter out the disturbance signal A.
5. The modulator bias point control method based on dual-perturbation signal combination according to claim 1, characterized in that, The frequency of the disturbance signal A is less than the frequency of the disturbance signal B.
6. The modulator bias point control method based on dual-perturbation signal combination according to claim 1, characterized in that, The frequency of the disturbance signal B is 8 to 12 times the frequency of the disturbance signal A.
7. The modulator bias point control method based on dual perturbation signal combination according to claim 1, characterized in that, The voltage of the disturbance signal A is 200–300 mV; the voltage of the disturbance signal B is 200–300 mV.
8. The modulator bias point control method based on dual perturbation signal combination according to claim 1, characterized in that, The frequency of the disturbance signal A is 0.8~1.2kHz, and the frequency of the disturbance signal B is 8~12kHz.
9. A control circuit comprising the modulator bias point control method based on a combination of dual perturbation signals as described in any one of claims 1 to 8, characterized in that, include: The photoelectric conversion unit receives the photocurrent signal reflecting the optical power output by the modulator, converts it into a voltage signal, and outputs it. The first filtering unit receives the voltage signal emitted by the photoelectric conversion unit, performs gating filtering to remove the disturbance signal A, obtains the pilot signal, and outputs it. The detection unit receives the pilot signal from the first filtering unit, performs envelope detection on the pilot signal, obtains the envelope signal of the tooth-shaped ripple at frequency A of the disturbance signal, and outputs it. The second filtering unit receives the envelope signal of the tooth-shaped wave emitted by the detection unit, and selects and filters the envelope signal of the tooth-shaped wave to obtain the envelope signal of the smooth wave and outputs it. The disturbance signal A generation unit generates and outputs disturbance signal A; The disturbance signal B generation unit generates and outputs the disturbance signal B. The phase detection unit receives the smoothed oscillation envelope signal and the disturbance signal A emitted by the second filtering unit, and performs multiplication phase detection on the two received signals to obtain the bias point feedback AC signal and output it. The bias generation unit receives the bias point feedback AC signal from the phase detection unit, then conditions the bias point feedback AC signal into a DC bias signal and outputs it. The adder unit receives the DC bias signal from the bias generation unit, the disturbance signal A from the disturbance signal A generation unit, and the disturbance signal B from the disturbance signal B generation unit. It then adds and fuses the three received signals to obtain the bias voltage control signal and outputs it to the modulator bias control terminal for bias point control.
10. A system for modulator bias point control based on a combination of dual perturbation signals, characterized in that, The control circuit includes the modulator bias point control method based on the combination of dual perturbation signals as described in claim 9.