Method and device for generating repetition frequency agile optical pulse with adjustable time domain waveform

Abstract

The invention discloses a method for generating a repetition frequency agile optical pulse with an adjustable time domain waveform. Firstly, an optical pulse signal with the repetition frequency of fr is generated; performing synchronous frequency division on the optical pulse signal by using a pulse pickup method to obtain a frequency division optical pulse signal with a repetition frequency of fr / N, and realizing agility of the repetition frequency of the frequency division optical pulse signal by adjusting a frequency division coefficient N to obtain a repetition frequency agility frequency division optical pulse signal; and finally, adjusting the time domain waveform of the repetition frequency agile frequency division optical pulse signal to obtain a repetition frequency agile optical pulse with an adjustable time domain waveform. The invention further discloses a device for generating the repetition frequency agile optical pulse with the adjustable time domain waveform. Compared with the prior art, the method can effectively generate the repetition frequency agile optical pulse signal with the time domain waveform capable of being flexibly adjusted.

Description

Technical Field

[0001] The present invention relates to a method for generating a pulse repetition frequency agile optical pulse, and particularly to a method and device for generating a pulse repetition frequency agile optical pulse with adjustable time-domain waveform. Background Art

[0002] Pulse repetition frequency agility means that the repetition frequency of a pulse signal can be changed within several pulse repetition periods or within each repetition period. The main advantage of the agility frequency technology is that it can effectively improve the measurement accuracy. Classified according to the frequency conversion method, the existing optical pulse frequency conversion technologies can be divided into two types: external cavity frequency conversion and internal cavity frequency conversion. The advantage of internal cavity frequency conversion is its simplicity in use and small size, but its frequency conversion range and output power are relatively small. And to generate a pulse signal with low time jitter, it is necessary to keep the cavity length fixed. Therefore, it is difficult to generate a low-jitter agile pulse signal based on a single-frequency optical pulse. The advantage of external cavity frequency conversion is that it can flexibly control the frequency conversion range and output power of the laser, but it requires external devices such as nonlinear crystals or optical fibers. And the signal synchronization problem between modulators also limits the speed characteristics and accuracy of arbitrarily adjustable pulse repetition frequency.

[0003] Optical pulse shaping is a technology for generating a desired optical pulse shape by controlling the amplitude, phase, etc. of a laser pulse. The main direction of the existing optical pulse shaping technology is to compress the pulse width of the optical pulse to obtain an ultrashort pulse with a higher peak power. However, for the requirements of a specific pulse shape, the simple pulse compression shaping technology often cannot be satisfied. By reasonably designing parameters such as the refractive index modulation amplitude and chirp coefficient of the fiber grating, different output pulse waveforms can be achieved, but the process of quantitatively designing parameters and fabricating the grating is very complicated.

[0004] The regulation of the repetition frequency of optical pulses and the adjustment of the time-domain waveform have extensive applications in many fields respectively. Especially in radar systems, the optical pulse repetition frequency determines the ranging ability and the maximum unambiguous range of the radar. High-repetition-frequency pulses enable the radar to sample echoes quickly, improving ranging accuracy, but they cause range ambiguity problems; low-repetition-frequency pulses allow the radar to detect farther targets, but the sampling rate decreases and the ranging accuracy deteriorates. The frequency agility of the pulse can avoid blind spots and range ambiguity problems. At the same time, the time-domain waveform of the pulse determines the resolution, penetration ability, and complexity of echo signal processing of the system. The width of the pulse determines the minimum resolvable distance of the radar, so short pulses can improve the system resolution, but the detection distance is limited; increasing the pulse width can increase the energy of the detection signal and broaden the detection distance, but it will sacrifice a certain amount of resolution. Therefore, generating a frequency-agile optical pulse with an adjustable time-domain waveform can flexibly adjust the ranging and resolution performance of the radar in different situations, that is, it can solve range ambiguity in the case of a lower repetition frequency, and at the same time, by adjusting the pulse waveform and narrowing the pulse rising edge, the ranging accuracy can be improved at a higher resolution. However, currently, no technical solution capable of generating a frequency-agile optical pulse with an adjustable time-domain waveform has been publicly disclosed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for generating a frequency-agile optical pulse with an adjustable time-domain waveform, which can effectively generate an optical pulse signal with frequency agility and a flexibly adjustable time-domain waveform.

[0006] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0007] A method for generating a frequency-agile optical pulse with an adjustable time-domain waveform, first generating an optical pulse signal with a repetition frequency of f r ; then using a pulse picking method to synchronously divide the frequency of the optical pulse signal to obtain a divided-frequency optical pulse signal with a repetition frequency of f r / N, and realizing the frequency agility of the divided-frequency optical pulse signal by adjusting the division coefficient N to obtain a frequency-agile divided-frequency optical pulse signal; finally, adjusting the time-domain waveform of the frequency-agile divided-frequency optical pulse signal to obtain a frequency-agile optical pulse with an adjustable time-domain waveform.

[0008] Preferably, the adjustment of the time-domain waveform of the frequency-agile divided-frequency optical pulse signal is realized by spectral filtering and shaping.

[0009] Further, the frequency-agile divided-frequency optical pulse signal is time-domain broadened before spectral filtering and shaping.

[0010] Preferably, a mode-locked laser is used to generate the optical pulse signal with a repetition frequency of f r .

[0011] Based on the same inventive concept, the following technical solutions can also be obtained:

[0012] A high-repetition-rate frequency-agile optical pulse generation device with adjustable time-domain waveform, comprising:

[0013] An optical pulse generation module for generating an optical pulse signal with a repetition frequency of f r ;

[0014] A high-repetition-rate frequency-agile module for synchronously dividing the frequency of the optical pulse signal by using a pulse picking method to obtain a frequency-divided optical pulse signal with a repetition frequency of f r / N, and realizing the agility of the repetition frequency of the frequency-divided optical pulse signal by adjusting the frequency division coefficient N to obtain a high-repetition-rate frequency-agile frequency-divided optical pulse signal;

[0015] A pulse shaping module for adjusting the time-domain waveform of the high-repetition-rate frequency-agile frequency-divided optical pulse signal to obtain a high-repetition-rate frequency-agile optical pulse with an adjustable time-domain waveform.

[0016] Preferably, the pulse shaping module adjusts the time-domain waveform of the high-repetition-rate frequency-agile frequency-divided optical pulse signal through spectral filtering and shaping.

[0017] More preferably, a programmable optical filter is used for the spectral filtering and shaping.

[0018] Further, the pulse shaping module performs time-domain broadening on the high-repetition-rate frequency-agile frequency-divided optical pulse signal before performing spectral filtering and shaping.

[0019] Preferably, a dispersion module is used for the time-domain broadening.

[0020] Preferably, the optical pulse generation module is a mode-locked laser.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0022] The present invention first synchronously divides the frequency of the optical pulse signal by using a pulse picking method, realizes the agility of the repetition frequency of the frequency-divided optical pulse signal by adjusting the frequency division coefficient, and then adjusts the time-domain waveform of the obtained optical pulse to realize arbitrary adjustment of the time-domain waveform of the output optical pulse signal, so as to finally generate a high-repetition-rate frequency-agile optical pulse with an adjustable time-domain waveform; the synchronous frequency division, high-repetition-rate frequency agility, and pulse shaping schemes adopted by the present invention will not have an adverse impact on the time jitter characteristics of the optical pulse, and can be combined with low-jitter light sources such as mode-locked lasers to generate a high-repetition-rate frequency-agile optical pulse with an adjustable time-domain waveform and low jitter. Description of the Drawings

[0023] Figure 1 is a schematic block diagram of the high-repetition-rate frequency-agile optical pulse generation device with adjustable time-domain waveform of the present invention;

[0024] Figure 2 This is a schematic structural diagram of a specific embodiment of the device for generating a PRF-agile optical pulse with adjustable time-domain waveform according to the present invention;

[0025] Figure 3 This is a schematic diagram of the pulse synchronization and frequency division principle based on an acousto-optic modulator;

[0026] Figure 4 This is an oscilloscope capture diagram of the frequency-divided pulse signal;

[0027] Figure 5 This is the time-domain waveform diagram after shaping the frequency-divided pulse. Specific embodiments

[0028] Aiming at the deficiencies of the prior art, the solution idea of the present invention is to first perform synchronous frequency division on the optical pulse signal by the pulse pick-up method, and achieve the agility of the repetition frequency of the frequency-divided optical pulse signal by adjusting the frequency division coefficient. Then, by adjusting the time-domain waveform of the obtained optical pulse, the time-domain waveform of the output optical pulse signal can be adjusted arbitrarily, so as to finally generate a PRF-agile optical pulse with adjustable time-domain waveform.

[0029] The technical solution proposed by the present invention is specifically as follows:

[0030] A method for generating a PRF-agile optical pulse with adjustable time-domain waveform, first generating an optical pulse signal with a repetition frequency of f r ; then using the pulse pick-up method to perform synchronous frequency division on the optical pulse signal to obtain a frequency-divided optical pulse signal with a repetition frequency of f r / N, and achieving the agility of the repetition frequency of the frequency-divided optical pulse signal by adjusting the frequency division coefficient N to obtain a PRF-agile frequency-divided optical pulse signal; finally, adjusting the time-domain waveform of the PRF-agile frequency-divided optical pulse signal to obtain a PRF-agile optical pulse with adjustable time-domain waveform.

[0031] A device for generating a PRF-agile optical pulse with adjustable time-domain waveform, comprising:

[0032] An optical pulse generation module for generating an optical pulse signal with a repetition frequency of f r ;

[0033] A PRF-agile module for using the pulse pick-up method to perform synchronous frequency division on the optical pulse signal to obtain a frequency-divided optical pulse signal with a repetition frequency of f r / N, and achieving the agility of the repetition frequency of the frequency-divided optical pulse signal by adjusting the frequency division coefficient N to obtain a PRF-agile frequency-divided optical pulse signal;

[0034] A pulse shaping module for adjusting the time-domain waveform of the PRF-agile frequency-divided optical pulse signal to obtain a PRF-agile optical pulse with adjustable time-domain waveform.

[0035] The optical pulse generation module can adopt various existing pulse light generation technologies; in order to minimize the time jitter of the optical pulse as much as possible, create good synchronization conditions for subsequent pulse frequency division, and facilitate synchronization locking with external synchronization signals, the optical pulse generation module preferably uses a mode-locked laser to generate mode-locked optical pulses with low timing jitter.

[0036] The pulse repetition frequency agile module can synchronously divide the frequency of the optical pulse signal by pulse picking methods such as the electro-optic switch method and the acousto-optic modulator method.

[0037] The function of the pulse shaping module is to adjust the time-domain waveform of the pulse repetition frequency agile divided-frequency optical pulse signal according to the actually required waveform, and methods such as dispersion broadening, spectral filtering and shaping, and chirped pulse amplification can be adopted; in the present invention, the adjustment of the time-domain waveform of the optical pulse is preferably achieved through spectral filtering and shaping, that is, by adjusting parameters such as the phase and intensity of the pulse spectrum, so as to output a time-domain pulse waveform with a specific shape through the inverse Fourier transform relationship from the frequency domain to the time domain.

[0038] For the convenience of public understanding, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and a specific embodiment:

[0039] The device for generating a pulse repetition frequency agile optical pulse with adjustable time-domain waveform according to the present invention has a basic structure as Figure 1 shown, including: an optical pulse generation module, a pulse repetition frequency agile module, and a pulse shaping module; the optical pulse generation module is used to generate an optical pulse signal with a repetition frequency of f r ; the pulse repetition frequency agile module uses the pulse picking method to synchronously divide the frequency of the optical pulse signal to obtain a divided-frequency optical pulse signal with a repetition frequency of f r / N, and realizes the agility of the repetition frequency of the divided-frequency optical pulse signal by adjusting the division coefficient N to obtain a pulse repetition frequency agile divided-frequency optical pulse signal; the pulse shaping module is used to adjust the time-domain waveform of the pulse repetition frequency agile divided-frequency optical pulse signal to obtain a pulse repetition frequency agile optical pulse with an adjustable time-domain waveform.

[0040] The structure of a specific embodiment of the device is as Figure 2 shown, including an optical pulse generation module, a synchronization module, a pulse repetition frequency agile module, and a pulse shaping module.

[0041] Among them, the optical pulse generation module adopts a passive mode-locked laser and is used to output an ultra-narrow low-jitter femtosecond mode-locked optical pulse with a repetition frequency of f r .

[0042] The synchronization module includes a rubidium clock and is used to generate a stable synchronization reference signal.

[0043] The pulse repetition frequency agile module includes an arbitrary waveform generator, a driver, and an acousto-optic modulator. The arbitrary waveform generator generates a modulated electrical sampling gate signal s(t) with a gate signal width of τ. After being amplified by the driver, it is used as a modulation signal to input into the acousto-optic modulator for pulse picking. The output optical pulse is down-converted to f r / N, where N is the frequency division coefficient. By adjusting the frequency division coefficient, the agility of the optical pulse repetition frequency can be achieved. The optical signal generated by the optical pulse generation module and the electrical modulation gate signal generated by the arbitrary waveform generator of the pulse repetition frequency agile module are both synchronized to the reference signal to ensure the frequency stability of the optical pulse and the pulse synchronization and alignment during the frequency division process.

[0044] The pulse shaping module includes a dispersion module, a programmable optical filter, and an optical amplifier. The role of the dispersion module is to broaden the optical pulse in the time domain through dispersion, facilitating subsequent spectral filtering and shaping. The programmable optical filter is used to adjust the time-domain waveform of the optical pulse through pulse spectral filtering and shaping. The optical amplifier is used to compensate for the optical power attenuated due to dispersion and spectral filtering and shaping.

[0045] Specifically, first, an optical pulse signal with low time jitter is generated by a passively mode-locked laser. The time interval of the optical pulse is inversely proportional to the pulse repetition frequency, i.e., T = 1 / f r 。To obtain a frequency-divided pulse signal with a low repetition frequency, an arbitrary signal generator is used to generate a programmable electrical sampling modulation gate signal to control the acousto-optic modulator to select some pulses to pass through. The arbitrary waveform generator generates a modulated electrical sampling gate signal s(t) with a gate signal width of τ. After being amplified by the driver, it is used as a modulation signal to input into the acousto-optic modulator for pulse picking. The width of the gate signal is set to be less than or equal to the period of a single pulse. Since only the optical pulse signal within the gate signal width can pass through, ultimately only one pulse out of every N pulses in the incident pulse train can pass through the acousto-optic modulator, and the repetition frequency of the pulse sequence is reduced to 1 / N of the original. The repetition frequency f s of the frequency-divided optical pulse is an integer division of the repetition frequency of the mode-locked laser, determined by the frequency division coefficient N, i.e., f s = f r / N, and the repetition period is T = N / f r 。By adjusting the duty cycle of the modulation gate signal of the acousto-optic modulator, i.e., adjusting the frequency division coefficient, the agility of the optical pulse repetition frequency can be achieved.

[0046] The matching and synchronization of the pulses depend on accurately triggering the acousto-optic modulator to achieve electro-optic delay and time-domain pulse synchronization, and its principle is as Figure 3 shown. To stably achieve the generation of a long pulse train, it is necessary to achieve the precise locking of the optical pulse repetition period and the electrical pulse, i.e., T must be exactly equal to N / f r。If there is an error time ΔT between the two, after k pulse periods, the time error between the sampled electrical pulse and the optical pulse will expand to kΔT. When this error accumulates to a certain extent, it will cause system errors. By synchronizing the rubidium clock signal with an arbitrary waveform generator and the output optical pulse signal, the error time ΔT can be eliminated, enabling the generation of long-duration pulse trains.

[0047] A programmable optical filter is a device for dynamically regulating the spectrum. Its core principle is to selectively modulate the amplitude and phase of an optical signal using spectral filtering to achieve spectral shaping, thereby adjusting the time-domain waveform of the output optical signal. According to the Fourier transform, the time-domain waveform of any optical pulse can be regarded as the inverse Fourier transform of its spectrum:

[0048]

[0049] where E(t) is the time-domain expression of the optical pulse. The programmable optical filter can change the amplitude A(ω) of the spectrum, selectively filter specific frequencies, and form pulses with a specific envelope shape through the inverse Fourier transform; or adjust the phase φ(ω) to introduce a second-order phase, i.e., chirp, and control the broadening or compression of the pulse through the inverse Fourier transform.

[0050] To verify the technical effects of the present invention, the following experiments were conducted:

[0051] Adopt Figure 2 The architecture shown was used to build a device for generating a train of optical pulses with variable repetition frequency and adjustable time-domain waveform. A mode-locked laser was used to generate mode-locked optical pulses with a repetition frequency of 80 MHz, and the optical pulses were locked to an external rubidium clock signal with a frequency of 10 MHz. Then, the mode-locked optical pulses were passed through a module for variable repetition frequency to perform pulse frequency division. By designing the waveform of the electrical modulation gate signal generated by an AWG, an acousto-optic modulator was driven to obtain a continuous train of optical pulses with variable repetition frequency that switched continuously between 1 MHz, 2 MHz, and 3 MHz, as shown in Figure 4 shown. After pulse shaping, the frequency-divided pulses were shaped into square-wave pulse signals with a pulse width of 6.1 ns in the time domain, and the oscilloscope capture diagram is as shown in Figure 5 shown.

[0052] In summary, based on the realization of the control of the repetition frequency of mode-locked optical pulses, the technical solution of the present invention can achieve frequency reconstruction and agility by adjusting the frequency division coefficient; through time-frequency mapping and spectral shaping, the time-domain shaping of the pulses can be realized, and finally, the output of low-jitter optical pulses with variable repetition frequency and adjustable time-domain waveform can be achieved.

Claims

1. A method for generating a PRF-agile optical pulse with adjustable time-domain waveform, characterized in that First, generate an optical pulse signal with a repetition frequency of f r ; then, use the pulse picking method to synchronously divide the frequency of the optical pulse signal to obtain a divided-frequency optical pulse signal with a repetition frequency of f r / N, and achieve agile tuning of the repetition frequency of the divided-frequency optical pulse signal by adjusting the division coefficient N to obtain a divided-frequency optical pulse signal with agile repetition frequency; finally, adjust the time-domain waveform of the divided-frequency optical pulse signal with agile repetition frequency to obtain a re-frequency agile optical pulse with adjustable time-domain waveform.

2. The method for generating a PRF-agile optical pulse with adjustable time-domain waveform according to claim 1, wherein The time-domain waveform of the PRF-agile frequency-divided optical pulse signal is adjusted through spectral filtering and shaping.

3. The method for generating a PRF-agile optical pulse with adjustable time-domain waveform according to claim 2, wherein Before spectral filtering and shaping, the PRF-agile frequency-divided optical pulse signal is temporally broadened.

4. The method for generating a PRF-agile optical pulse with adjustable time-domain waveform according to claim 1, characterized in that, Generate the optical pulse signal with the repetition frequency of f using a mode-locked laser r .

5. A PRF-agile optical pulse generation device with an adjustable time-domain waveform, characterized by comprising: An optical pulse generation module for generating an optical pulse signal with a repetition frequency of f r ; A PRF agile module is used to synchronously divide the optical pulse signal by using a pulse pick-up method to obtain a divided optical pulse signal with a repetition frequency of f r / N, and the agility of the repetition frequency of the divided optical pulse signal is realized by adjusting the division coefficient N to obtain a PRF agile divided optical pulse signal; A pulse shaping module for adjusting the time-domain waveform of the PRF-agile frequency-divided optical pulse signal to obtain a PRF-agile optical pulse with an adjustable time-domain waveform.

6. The time-domain waveform adjustable PRF agile optical pulse generating device according to claim 5, characterized in that, The pulse shaping module adjusts the time-domain waveform of the PRF-agile frequency-divided optical pulse signal through spectral filtering and shaping.

7. The time-domain waveform adjustable PRF agile optical pulse generating device according to claim 6, characterized in that The spectral filtering and shaping is performed using a programmable optical filter.

8. The time-domain waveform adjustable PRF agile optical pulse generating device according to claim 6, wherein, Before performing spectral filtering and shaping, the pulse shaping module temporally broadens the PRF-agile frequency-divided optical pulse signal.

9. The PRF-agile optical pulse generation device with an adjustable time-domain waveform according to claim 8, characterized in that The temporal broadening is performed using a dispersion module.

10. The time-domain waveform adjustable PRF agile optical pulse generating device according to claim 5, wherein The optical pulse generation module is a mode-locked laser.

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