Resonant-cavity-free ultra-short optical pulse source self-starting method for optical sampling analog-to-digital converter

Abstract

The invention relates to the technical field of photoelectricity, in particular to a resonant-cavity-free ultra-short optical pulse source self-starting device for an optical sampling analog-to-digital converter and an implementation method. On the basis of the principle of an optical sampling electric quantization type analog-to-digital converter, by detecting the power difference after down-conversion analog-to-digital conversion of low-frequency and high-frequency signals, the driving parameters of the cavity-free optical pulse source are optimally searched by using an iterative optimization algorithm, and meanwhile, the parameters are controlled in real time without manual adjustment, so that the accuracy and the reliability of the cavity-free optical pulse source are improved. And finally, the one-key power-on self-starting of the resonant-cavity-free ultra-short optical pulse source can be realized.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic technology, and in particular to a resonant cavity-free ultrashort optical pulse self-starting device for an optical sampling analog-to-digital converter and an implementation method thereof. Background Art

[0002] Analog-to-digital converters (ADCs) are key components for converting analog signals into digital signals. In the digital information age, with explosive data growth and increasingly limited electromagnetic spectrum resources, applications such as high-speed wireless communications, radar, and oscilloscope testing are urgently demanding ADCs with higher sampling rates and wider bandwidths. Traditional electronic ADCs are limited by the physical limits of carrier mobility. Single-core ADCs typically operate at low frequencies (on the order of GHz) and low sampling rates (on the order of GS / s). The use of high-mobility semiconductor materials and mobility enhancement techniques can only partially increase the analog bandwidth and sampling rate. Furthermore, due to sampling time jitter, conversion accuracy at high frequencies cannot meet practical requirements. To improve analog bandwidth and conversion accuracy, optical ADCs (optical ADCs), particularly optically sampled and quantized ADCs (OADCs), have been proposed. These optically sample analog signals by applying them to the intensity envelope of ultrashort optical pulses. Quantization and encoding are then performed using sophisticated and flexible quantization techniques, achieving high-bandwidth, high-precision ADCs.

[0003] Optically sampled, quantized analog-to-digital converters use ultrashort optical pulse trains with high repetition rates and low temporal jitter as sampling pulses. The narrower the pulse width of the ultrashort optical pulse source, the wider the spectrum and the larger the optical sampling bandwidth it can support. The lower the temporal jitter, the more accurate the sampling of the input analog signal during the optical sampling process. The higher the repetition rate, the larger the aliasing-free optical sampling bandwidth, enabling optical sampling analog-to-digital conversion with a wider instantaneous bandwidth. Commonly used ultrashort optical pulse sources include passively mode-locked lasers, actively mode-locked lasers, and resonator-free ultrashort optical pulse sources. While passively mode-locked lasers offer extremely low temporal jitter (femtoseconds) and pulse widths (less than 1ps), they are limited by cavity length and struggle to achieve high repetition rates (less than 1GHz). Actively mode-locked lasers can generate picosecond optical pulse trains with repetition rates of tens of GHz, facilitating simultaneous high sampling rates and instantaneous bandwidth in optical sampling. However, they are susceptible to loss of lock due to external perturbations, suffer from poor stability, and are difficult to integrate. The resonant cavity-free ultrashort optical pulse source has the advantages of high repetition rate, low time jitter, stability and easy integration, and is the most ideal optical pulse source for optical sampling analog-to-digital converters.

[0004] Analog-to-digital converters based on resonant-free ultrashort optical pulse sources have the advantages of large bandwidth and high precision. In 2015, UCSD in the United States proposed an optical sampling analog-to-digital converter based on a resonant-free ultrashort optical pulse source (Esman DJ, et al. Highly linear broadband photonic-assisted Q-band ADC [J]. IEEE / OSA Journal of Lightwave Technology, 2015, 33(11): 2256-2262). This scheme uses a distributed feedback laser diode to generate a DC optical carrier, introduces linear chirp and generates a high-repetition-rate optical pulse sequence through a time lens structure composed of a phase modulator and an intensity modulator, and then passes through a dispersion-compensating fiber to compensate for the chirp and compress the pulse width, ultimately generating an ultrashort optical pulse with a repetition frequency of 10 GHz and a pulse width of 3.5 ps. This pulse is used for optical sampling, realizing optical analog-to-digital conversion of RF signals in the 40 GHz frequency range, with an effective bit number of 7 bits.

[0005] The main problems with cavity-free ultrashort optical pulse sources in optical sampling analog-to-digital converters are: First, this type of optical pulse source is mainly generated by multi-level electro-optical modulation, and each level of the electro-optical modulator requires an RF signal to drive it. Due to optical delays within the system and inconsistent RF circuit delays, phase differences exist between the multiple RF drive signals. Electronic phase shifters are usually used for manual blind adjustment of phase alignment, which is inefficient and inaccurate. Second, in the actual use of analog-to-digital converters, in order to obtain optical pulses with optimal frequency response within the required frequency range, the position of the electro-optical intensity bias point usually needs to be properly adjusted. Manual adjustment is imprecise, and there is a lack of reasonable criteria for evaluating the optimal optical pulse source for analog-to-digital converter systems. Summary of the Invention

[0006] In view of the shortcomings of the existing technical solutions, the present invention proposes a resonant cavity-free ultrashort optical pulse self-starting device and an implementation method for an optical sampling analog-to-digital converter.

[0007] The technical solution of the present invention is a resonant cavity-free ultrashort optical pulse self-starting device for an optical sampling analog-to-digital converter and an implementation method thereof. The device comprises: a direct current laser (1), a first electro-optical intensity modulator (2), a first phase modulator (3), a second phase modulator (4), a dispersion compensation module (5), an erbium-doped fiber amplifier (6), a polarization controller (7), a second electro-optical intensity modulator (8), a photodetector (9), a low-pass filter (10), an electronic analog-to-digital converter (11), a control program and data processing module (12), a first microwave source and a voltage source (13), a second microwave source (14), a third microwave source (15), a first electrically controlled phase shifter (16), a second electrically controlled phase shifter (17), and a fourth microwave source (18). The invention is characterized in that the components are connected in the following order: the output end of the DC laser (1) is connected to the input end of the first electro-optical intensity modulator (2), the output end of the first electro-optical intensity modulator (2) is connected to the input end of the first phase modulator (3), the output end of the first phase modulator (3) is connected to the input end of the second phase modulator (4), the output end of the second phase modulator (4) is connected to the input end of the dispersion compensation module (5), the output end of the dispersion compensation module (5) is connected to the input end of the erbium-doped fiber amplifier (6), the output end of the erbium-doped fiber amplifier (6) is connected to the input end of the polarization controller (7), the output end of the polarization controller (7) is connected to the input end of the second electro-optical intensity modulator (8), the output end of the second electro-optical intensity modulator (8) is connected to the input end of the photodetector (9), the output end of the photodetector (9) is connected to the input end of the low-pass filter (10), and the low-pass filter (10) is connected to the input end of the low-pass filter (10). The output end of the electronic analog-to-digital converter (11) is connected to the input end of the electronic analog-to-digital converter (11), the digital output end of the electronic analog-to-digital converter (11) is connected to the input end of the control program and data processing module (12), the four output ends of the control program and data processing module (12) are respectively connected to the first microwave source and voltage source (13), the second microwave source (14), the third microwave source (15) and the fourth microwave source (18), the radio frequency output port of the first microwave source and voltage source (13) is connected to the radio frequency input end of the first electro-optical intensity modulator (2), the direct current output port of the first microwave source and voltage source (13) is connected to the direct current port of the first electro-optical intensity modulator (2), the output ports of the second microwave source (14) and the third microwave source (15) are respectively connected to the radio frequency input ports of the first phase modulator (3) and the second phase modulator (4), and the output port of the fourth microwave source (18) is connected to the radio frequency input port of the second electro-optical intensity modulator (8).

[0008] The method for realizing self-start of a resonant cavity-free ultrashort optical pulse for an optical sampling analog-to-digital converter comprises the following steps:

[0009] Step 1: The control program and data processing module (12) controls the first microwave source and the voltage source (13), the second microwave source (14), and the third microwave source (15) to output randomly generated initial parameters, and performs initial random point control on the optical pulse. The first electro-optical intensity modulator (2) has a random bias point, and the radio frequency input signals of the two-stage phase modulators (3) and (4) have random phases.

[0010] Step 2: After the DC light output by the DC laser (1) is modulated by the first electro-optical intensity modulator (2), the initial shaping of the optical pulse is achieved, and a small amount of modulation sidebands are generated in the spectrum. The initial pulse light passes through the two-stage phase modulators (3) and (4). Under the action of phase modulation, an approximately linear positive chirp is introduced at the center of the pulse, the time domain of the pulse light remains unchanged, the spectrum is broadened, and more sidebands are generated. The pulse light with the linear positive chirp enters the dispersion compensation module (5). The linear negative chirp introduced by the dispersion compensation module (5) can achieve chirp compensation, compress the time domain width of the optical pulse, and generate an approximately chirp-free ultrashort optical pulse.

[0011] Step 3: After the ultrashort optical pulse is amplified by the erbium-doped fiber amplifier (6) and the polarization state is adjusted by the polarization controller (7), it enters the second electro-optical intensity modulator (8) biased at the orthogonal point to perform optical down-conversion sampling on the low-frequency and high-frequency radio frequency signals generated by the fourth microwave source (18);

[0012] Step 4: The sampled light pulse enters the photodetector (9) for photoelectric conversion. The converted electric pulse passes through a low-pass filter (10) to filter out interference signals outside the first Nyquist zone. The obtained electric signal is sent to the electronic analog-to-digital converter (11) for analog-to-digital conversion and a real-time Fourier transform (FFT) is performed to calculate the power difference of the baseband signal.

[0013] Step 5: Based on the calculated power difference, the output parameters of the first microwave source and voltage source (13), the second microwave source (14), and the third microwave source (15) are updated according to the particle swarm algorithm iterative formula, that is, the cavity-free optical pulse is iteratively updated to obtain a new cavity-free optical pulse;

[0014] Step 6: Repeat steps 3-5 until the iteration termination condition is met (a certain number of iterations is reached), and a cavity-free optical pulse with a narrow pulse width and a flat spectrum is obtained, completing a search process.

[0015] Step 7: Repeat the full-range parameter search several times to determine a reasonable small range of the independent variable parameter. Repeat steps 1-6 within the small range and perform an iterative search to eventually obtain an ultrashort optical pulse with a narrow pulse width and flat spectrum.

[0016] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0017] (1) The cavity-free light source self-starting method can automatically adjust the bias point of the intensity modulator and the phase alignment of the RF drive signals at each level, thereby achieving automatic adjustment of the cavity-free light pulse, completely avoiding the problems of low efficiency and inaccuracy of manual adjustment and human eye observation;

[0018] (2) The results of sampling different signals by the optical pulse source are used as optimization parameters, so that the optical pulse source has a more reasonable evaluation standard and a larger bandwidth optical sampling analog-to-digital converter can be obtained;

[0019] (3) It can avoid the change of optical pulse waveform caused by temperature change or environmental disturbance, improve the stability of optical sampling analog-to-digital converter, and provide technical support for the practical application of optical sampling analog-to-digital converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the system structure of a resonant cavity-free ultrashort optical pulse self-starting device for an optical sampling analog-to-digital converter of the present invention;

[0021] Figure 2 Schematic diagram of the generation principle of the resonant cavity-free ultrashort optical pulse source;

[0022] Figure 3 Flowchart of the search process for the optimal driving parameters of a light pulse source based on a particle swarm optimization search algorithm, where (a) is the overall iterative idea flow chart, and (b) is the flow chart of a specific search.

[0023] Figure 4 Figure 2 shows the self-starting simulation search process of a resonant-free ultrashort optical pulse source with a repetition rate of 10 GHz. (a) is the full-range search process diagram, and (b) is the small-range search process diagram.

[0024] Figure 5 The simulation results of the self-startup of a resonant-free ultrashort optical pulse source with a repetition rate of 10 GHz are shown in Figure 1. (a) and (b) are the time-domain waveforms and spectra of the optical pulses obtained at the beginning of the iteration, and (c) and (d) are the time-domain waveforms and spectra of the optical pulses obtained at the end of the iteration.

[0025] Figure 6 The self-starting experimental results of a resonant-free ultrashort optical pulse source with a repetition rate of 10.2 GHz. (a) is the spectrum of the light source at the beginning of the iteration, (b) is the spectrum of the optical pulse source generated by the iteration, and (c) is the time domain waveform of the optical pulse source generated by the iteration.

[0026] Among them, 1 is a DC laser, 2 is a first electro-optical intensity modulator, 3 is a first phase modulator, 4 is a second phase modulator, 5 is a dispersion compensation module, 6 is an erbium-doped fiber amplifier, 7 is a polarization controller, 8 is a second electro-optical intensity modulator, 9 is a photodetector, 10 is a low-pass filter, 11 is an electronic analog-to-digital converter, 12 is a control program and data processing module, 13 is a first microwave source and a voltage source, 14 is a second microwave source, 15 is a third microwave source, 16 is a first electrically controlled phase shifter, 17 is a second electrically controlled phase shifter, and 18 is a fourth microwave source. DETAILED DESCRIPTION

[0027] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0028] Combine Figure 1 、 2 3. The system principle of the present invention is further explained as follows:

[0029] like Figure 1 and Figure 2 As shown in the figure, the resonant cavity-free ultrashort optical pulse source consists of a continuous wave laser, an intensity modulator, two phase modulators and a dispersion compensation module. The continuous optical signal output by the laser enters the r In the intensity modulator driven by the RF signal, the continuous light is modulated to form a repetition frequency of f r The initial pulse light forms a few modulation sidebands in the spectrum; the initial pulse light passes through a two-stage phase modulator, both of which are composed of a frequency of f r The high-power RF signal is driven by the phase modulator, and the signal is synchronized with the driving signal of the intensity modulator. In order to make the phase modulation introduce the largest linear positive chirp at the center of the pulse, when the intensity modulator is biased at π / 2~π, the relative phase difference between the phase modulated driving signal and the intensity modulated driving signal should be 0. When the intensity modulator is biased at π~3π / 2, the relative phase difference between the phase modulated driving signal and the intensity modulated driving signal should be π. The phase modulator introduces an approximately linear positive chirp into the initial pulse light, the pulse light time domain remains unchanged, the spectrum is broadened, and more sidebands are generated; the pulse light with an approximately linear positive chirp enters the dispersion compensation module, and the linear negative chirp introduced by the dispersion compensation module can realize chirp compensation, compress the time domain width of the optical pulse, and finally produce an approximately chirp-free optical pulse with a repetition frequency of f r ultrashort optical pulses.

[0030] The optimization search principle of ultrashort optical pulse source is as follows Figure 1 As shown. The independent variable parameter of the resonant cavity-free ultrashort optical pulse source is the DC bias voltage V of the intensity modulator. bias and the electronically controlled phase shifter voltage V used for adjusting the phase of the RF signal in the two-stage phase modulator phase1 、V phase2 The ultrashort optical pulses are used to generate low-frequency f low and high frequency f high The RF signal is sampled, and the two signal frequencies must meet f high -f low >f r , let the power response after optical sampling analog-to-digital conversion be P(f), and the response power difference between the two signals be

[0031] P diff =P(f low )-P(f high ) (1)

[0032] The optimization search is performed as the objective function, and the search goal is to minimize the objective function value, which can obtain the optical sampling analog-to-digital converter with the largest bandwidth, and at the same time realize the automatic search of the optimal parameters of the ultrashort optical pulse source. The specific search process is as follows Figure 3 As shown, the search idea is as follows Figure 3 As shown in (a), multiple optimization searches with a small number of iterations are performed on the optimal values ​​of the three independent variable parameters in the entire range to determine a reasonable small search range. Within this small range, an optimization search with a small number of iterations can output the optimal driving parameters of the ultrashort optical pulse. A specific search process is as follows: Figure 3 As shown in (b), the independent variable parameters are randomly initialized within the range and the current response difference P is calculated. diff And update the individual and group optimal values, then iteratively update the independent variable parameters, using the speed update formula in the particle swarm algorithm

[0033]

[0034] Perform iterative search. is the update direction of the next moment, ω is the inertia factor, is the direction at the current moment, c1 is the individual learning factor, which controls the weight of individual learning experience, and pBest i is the current individual optimal value, c2 is the social learning factor, which controls the group learning experience weight, gBest i is the optimal value of the current group, r1 and r2 are random numbers in [0,1], which increase the disturbance and enhance the global search capability. The position is updated with each generation update as the time unit, and the position is the independent variable parameter value. The position update formula is

[0035]

[0036] in, where is the value of the independent variable parameter at the next moment. The iterative search process ends when the maximum number of iterations is met or the objective function value remains unchanged, resulting in a set of driving parameters for the ultrashort optical pulse. The iterative search within this final small range yields the optimal driving parameters for the cavity-free optical pulse source.

[0037] The feasibility of the present invention is described below with reference to specific embodiments:

[0038] Example 1:

[0039] according to Figure 1 Based on the structure shown in the figure, a cavity-free ultrashort optical pulse self-starting simulation system for optical sampling analog-to-digital converter was established in MATLAB. Among them, the basic parameters of the optical sampling link are set as follows: the RF driving signal frequency of each level of modulator is 10GHz, the bias search range of the intensity modulator is 2π, and the phase search range of the driving signal of the two-stage phase modulator is 2π. By performing optical sampling analog-to-digital conversion on the 0.1GHz low-frequency signal and the 39.9GHz high-frequency signal and performing real-time FFT transformation, the corresponding baseband signal power is calculated, and the power difference between the two signals is used as the objective function for optimization search. The specific search process is as follows Figure 4 As shown, Figure 4 (a) is an example of a full-range search. The power differences corresponding to the first generation are all greater than 8dB. The corresponding optical pulse time domain waveform and spectrum are as follows: Figure 5 As shown in (a) and (b), no symmetrical narrow-pulse-width optical pulses are formed in the time domain. After 12 generations of searching, the corresponding power difference is 1.55 dB; Figure 4 (b) is a small search range determined based on the full-range search. Optimization search is performed within this small range. After 10 generations of search, the corresponding power difference is 1.53 dB. The final time domain and spectrum diagrams of the optical pulse source are shown in Figure 2. Figure 5 As shown in (c) and (d), an ultrashort optical pulse source was finally generated, with a repetition frequency of 10 GHz, a time-domain pulse width of 1.7 ps, and a spectral width of 3.54 nm.

[0040] Example 2:

[0041] according to Figure 1The structure shown in the figure is used in the experiment to establish a resonant cavity-free ultrashort optical pulse source-starting experimental system for optical sampling analog-to-digital converters. In the experiment, the RF driving signal frequency of each level of modulator is 10.2 GHz, and the corresponding optical pulse source repetition frequency is 10.2 GHz. The MATLAB programmable microwave source (R&S SMA100) is used to input a low-frequency signal of 0.8 GHz and a high-frequency signal of 40 GHz into the system respectively. A real-time oscilloscope (R&S RTO1024) is used instead of an electronic analog-to-digital converter to collect digital signals and transmit the collected signals to the data processing module. The optical pulse source is used to optically sample the low-frequency signal of 0.8 GHz and the high-frequency signal of 40 GHz respectively, and two signals with the same frequency but different amplitudes can be obtained. The real-time oscilloscope is used to perform electrical sampling analog-to-digital conversion, and the data acquisition and processing module is used to perform real-time FFT transformation. The power difference between the two signals is used as the objective function for optimization search. The corresponding search process is similar to the simulation. Figure 6 (a) shows the spectral waveform initially generated by the iterative search. Due to phase misalignment, the spectral comb teeth are small and uneven, and no optical pulse is formed. Figure 6 (b) (c) are the optical pulse source spectrum and time domain waveform finally generated by the iterative search. The optical pulse source spectrum is flat, the spectrum width is 3.46nm, the number of comb teeth is 43, and the time domain pulse width of the optical pulse source is 2.3ps.

[0042] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A resonant-less ultrashort optical pulse self-starting device for an optical sampling analog-to-digital converter, characterized by: The invention comprises a direct current laser (1), a first electro-optical intensity modulator (2), a first phase modulator (3), a second phase modulator (4), a dispersion compensation module (5), an erbium-doped fiber amplifier (6), a polarization controller (7), a second electro-optical intensity modulator (8), a photodetector (9), a low-pass filter (10), an electronic analog-to-digital converter (11), a control program and data processing module (12), a first microwave source and a voltage source (13), a second microwave source (14), a third microwave source (15), a first electrically controlled phase shifter (16), a second electrically controlled phase shifter (17), and a fourth microwave source (18); The various devices are connected in the following order: the output end of the DC laser (1) is connected to the input end of the first electro-optical intensity modulator (2), the output end of the first electro-optical intensity modulator (2) is connected to the input end of the first phase modulator (3), the output end of the first phase modulator (3) is connected to the input end of the second phase modulator (4), the output end of the second phase modulator (4) is connected to the input end of the dispersion compensation module (5), the output end of the dispersion compensation module (5) is connected to the input end of the erbium-doped fiber amplifier (6), the output end of the erbium-doped fiber amplifier (6) is connected to the input end of the polarization controller (7), the output end of the polarization controller (7) is connected to the input end of the second electro-optical intensity modulator (8), the output end of the second electro-optical intensity modulator (8) is connected to the input end of the photodetector (9), the output end of the photodetector (9) is connected to the input end of the low-pass filter (10), and the output end of the low-pass filter (10) is connected to the input end of the low-pass filter (10). The first microwave source and the second microwave source (14) are connected to the input end of the electronic analog-to-digital converter (11); the digital output end of the electronic analog-to-digital converter (11) is connected to the input end of the control program and data processing module (12); the four output ends of the control program and data processing module (12) are respectively connected to the first microwave source and the voltage source (13), the second microwave source (14), the third microwave source (15) and the fourth microwave source (18); the radio frequency output port of the first microwave source and the voltage source (13) is connected to the radio frequency input end of the first electro-optical intensity modulator (2); the direct current output port of the first microwave source and the voltage source (13) is connected to the direct current port of the first electro-optical intensity modulator (2); the output ports of the second microwave source (14) and the third microwave source (15) are respectively connected to the radio frequency input ports of the first phase modulator (3) and the second phase modulator (4); and the output port of the fourth microwave source (18) is connected to the radio frequency input port of the second electro-optical intensity modulator (8).

2. The method for self-starting a resonant cavity-free ultrashort optical pulse for an optical sampling analog-to-digital converter according to claim 1, characterized in that: The following steps are involved: Step 1: The control program and data processing module (12) controls the first microwave source and the voltage source (13), the second microwave source (14), and the third microwave source (15) to output randomly generated initial parameters, and performs initial random point control on the optical pulse. The first electro-optical intensity modulator (2) has a random bias point, and the radio frequency input signals of the two-stage phase modulators (3) and (4) have random phases. Step 2: The DC light output by the DC laser (1) is modulated by the first electro-optical intensity modulator (2) to achieve the initial shaping of the optical pulse, and a small amount of modulation sidebands are generated in the spectrum. The initial pulse light passes through the two-stage phase modulator (3) and (4). Under the action of phase modulation, an approximately linear positive chirp is introduced at the center of the pulse, the time domain of the pulse light remains unchanged, the spectrum is broadened, and more sidebands are generated. The pulse light with linear positive chirp enters the dispersion compensation module (5). The linear negative chirp introduced by the dispersion compensation module (5) can achieve chirp compensation, compress the time domain width of the optical pulse, and generate an approximately chirp-free ultrashort optical pulse; Step 3: After the ultrashort optical pulse is amplified by the erbium-doped fiber amplifier (6) and the polarization state is adjusted by the polarization controller (7), it enters the second electro-optical intensity modulator (8) biased at the orthogonal point to perform optical down-conversion sampling on the low-frequency and high-frequency radio frequency signals generated by the fourth microwave source (18); Step 4: The sampled light pulse enters the photodetector (9) for photoelectric conversion. The converted electric pulse passes through a low-pass filter (10) to filter out interference signals outside the first Nyquist zone. The obtained electric signal is sent to the electronic analog-to-digital converter (11) for analog-to-digital conversion and a real-time Fourier transform (FFT) is performed to calculate the power difference of the baseband signal. Step 5: Based on the calculated power difference, the output parameters of the first microwave source and voltage source (13), the second microwave source (14), and the third microwave source (15) are updated according to the particle swarm algorithm iterative formula, that is, the cavity-free optical pulse is iteratively updated to obtain a new cavity-free optical pulse; Step 6: Repeat steps 3-5 until the iteration termination condition is met (a certain number of iterations is reached), completing a search process. Step 7: Repeat the full-range parameter search several times to determine a reasonable small range for the independent variable parameter. Repeat steps 1-6 within this small range and perform an iterative search to ultimately obtain an ultrashort optical pulse with the narrowest pulse width and the flattest spectrum.

3. A method for implementing the resonant cavity-free ultrashort optical pulse self-starting device for an optical sampling analog-to-digital converter according to claim 2, characterized in that: The resonant cavity-free ultrashort optical pulse self-starting device is the resonant cavity-free ultrashort optical pulse self-starting device according to claim 1 .

4. A method for realizing a resonant cavity-free ultrashort optical pulse self-starting device for an optical sampling analog-to-digital converter according to any one of claims 2-3, characterized in that: The resonant cavity-free ultrashort optical pulse self-starting device for an optical sampling analog-to-digital converter is the resonant cavity-free ultrashort optical pulse self-starting device for an optical sampling analog-to-digital converter according to claim 1.

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