Reconfigurable time-frequency domain mode-locked optoelectronic oscillator

Abstract

The application discloses a reconfigurable time-frequency domain mode-locked optoelectronic oscillator, and belongs to the technical field of microwave photonics. The oscillator comprises a waveform generator, a laser, a modulator, a filter, an adjustable attenuator, an optical fiber, an optoelectronic detector, an electric amplifier and an electric power divider. The waveform generator generates an electric control signal to control the injection current of the laser. The wavelength and power of the continuous light output by the laser change with the amplitude of the electric control signal generated by the waveform generator. The continuous light output by the laser enters the modulator to generate a modulated light signal, and then enters the filter for filtering. The filtered modulated light signal is transmitted through the adjustable attenuator and the optical fiber, and then enters the optoelectronic detector. The optoelectronic detector performs photoelectric conversion to generate a microwave signal. The microwave signal is amplified by the electric amplifier, and then enters the electric power divider. In the electric power divider, the microwave signal is divided into two paths. One path is fed back to the modulator, and the other path is output as the output of the optoelectronic oscillator. The reconfigurable mode-locked optoelectronic oscillator is generated by using the waveform generator, the adjustable attenuator and the fast adjustable microwave photon bandpass filter. Compared with the optoelectronic oscillator which can only work in one mode-locked state, the optoelectronic oscillator of the application can be flexibly switched among the frequency domain mode-locked optoelectronic oscillator, the time domain mode-locked optoelectronic oscillator and the time-frequency domain mode-locked optoelectronic oscillator.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microwave photonics, and particularly relates to a reconfigurable time-frequency domain mode-locked optoelectronic oscillator. BACKGROUND

[0002] With the increasing complexity of the detection target, the modern radar system requires high performance and multifunction to meet the comprehensive detection of the target. This change requires the transmitted radar signal to meet the parameter requirements needed in different detection situations, for example, the pulse repetition frequency and the pulse width of the signal are required to be flexibly tuned to solve the speed ambiguity and the range ambiguity problems encountered in detecting the target; the pulse signal with large time-bandwidth product is required to solve the contradiction between the detection distance and the range resolution; the phase synchronization or coherence between pulses is required to ensure the target velocity measurement, imaging and high anti-clutter interference capability, etc.

[0003] Optoelectronic oscillators (OEOs) have been widely studied due to their ability to generate high-quality microwave signals with low phase noise. In a conventional OEO, it is difficult to achieve stable multi-mode oscillation in the loop due to the random power and phase relationship caused by the competition effect between the oscillation modes. Recently, some mode-locking techniques have been introduced into the OEO structure to achieve fixed power and phase relationship between the oscillation modes to generate complex microwave signals, demonstrating the reconfigurable ability of the OEO. For example, Fourier domain mode-locking technique is introduced into the OEO cavity to generate linearly chirped microwave waveform signals with large pulse width and large time-bandwidth product, to improve the detection distance range and range resolution of the radar. Or time-domain mode-locking technique is introduced into the OEO cavity to generate high-quality microwave pulse signals, for realizing flexible tuning of the pulse repetition frequency and pulse width of the radar signal. In addition, time-domain mode-locking and frequency-domain mode-locking techniques can also be introduced into the OEO to generate linearly chirped microwave waveforms with flexibly tunable pulse width. However, the mode-locked OEOs studied at present only introduce one mode-locking technique and have a complex structure, and it is impossible to realize a simple and reconfigurable mode-locked OEO to output a reconfigurable and tunable microwave signal. Therefore, it is an urgent problem to be solved to study a simple and reconfigurable time-frequency domain mode-locked OEO system. SUMMARY

[0004] The present application aims at the problems in the background art, and provides a reconfigurable time-frequency domain mode-locked optoelectronic oscillator. The reconfigurable time-frequency domain mode-locked optoelectronic oscillator can realize flexible switching among three reconfiguration states of the frequency domain mode-locked OEO state, the time domain mode-locked OEO state and the time-frequency domain mode-locked OEO state, and solves the problem that the mode-locked OEOs at present only work in a single mode-locked state and have a complex system.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] A reconfigurable time-frequency domain mode-locked optoelectronic oscillator, comprising a waveform generator, a laser, a modulator, a filter, an adjustable attenuator, an optical fiber, an optoelectronic detector, an electrical amplifier and an electrical power divider;

[0007] The waveform generator generates an electrical control signal to control the injection current of the laser, and the wavelength and power of the continuous light output by the laser vary with the amplitude of the electrical control signal generated by the waveform generator; after the continuous light output by the laser enters the modulator to generate a modulated light signal, the modulated light signal enters the filter to select the center frequency and the oscillation mode; after the filtered modulated light signal is transmitted through the adjustable attenuator and the optical fiber, it enters the optoelectronic detector to generate a microwave signal through photoelectric conversion; after the microwave signal is amplified by the electrical amplifier, it enters the electrical power divider, where it is divided into two paths, one of which is fed back to the modulator to form a closed optoelectronic oscillation loop, and the other of which is output as the output of the optoelectronic oscillator, outputting a reconfigurable tunable microwave signal.

[0008] When the modulator is an electro-optical intensity modulator and the filter is an electrical band-pass filter, the frequency of the electrical control signal generated by the waveform generator is equal to an integer multiple of the inverse of the delay of the optoelectronic oscillation loop, and when the voltage of the tuning electrical control signal and the adjustable attenuator make the maximum gain of the open-loop gain in the optoelectronic oscillation loop greater than 1 and the minimum gain less than 1, the reconfigurable time-frequency domain mode-locked optoelectronic oscillator works in a time-domain mode-locked OEO state, generating a microwave pulse signal, and the center frequency of the generated microwave pulse signal is equal to the center frequency of the electrical band-pass filter, and the number of microwave comb teeth of the generated microwave pulse signal is equal to the number of optoelectronic oscillation modes within the bandwidth of the electrical band-pass filter.

[0009] When the modulator is a phase modulator and the filter is an optical notch filter, the laser, the phase modulator, the optical notch filter and the optoelectronic detector together constitute a microwave photon band-pass filter with adjustable center frequency, and the waveform generator, the adjustable attenuator and the microwave photon band-pass filter constitute a reconfigurable module of the reconfigurable time-frequency domain mode-locked optoelectronic oscillator, which includes three reconfiguration states: a frequency-domain mode-locked OEO state, a time-domain mode-locked OEO state and a time-frequency domain mode-locked OEO state. By controlling the frequency, signal form and voltage of the electrical control signal generated by the waveform generator, and the maximum gain and minimum gain of the open-loop gain, the switching between the three reconfiguration states is realized, so that the optoelectronic oscillator works in different states to generate a microwave signal, and the center frequency of the generated microwave signal is equal to the center frequency of the microwave photon band-pass filter.

[0010] Specifically, when the modulator is a phase modulator and the filter is an optical notch filter, the waveform generator generates an electrical control signal to control the injection current of the laser, so that the wavelength and power of the continuous light output by the laser vary with the amplitude of the electrical control signal generated by the waveform generator; since the center frequency of the microwave photonic bandpass filter is equal to the reciprocal of the difference between the wavelength of the continuous light output by the laser and the notch wavelength of the optical notch filter, the frequency of the microwave signal generated by the optoelectronic oscillator varies with the same wavelength as the laser. When the frequency of the electrical control signal generated by the waveform generator is equal to an integer multiple of the reciprocal of the delay of the optoelectronic oscillator loop, the signal form and voltage of the electrical control signal are controlled to periodically change the center frequency of the output microwave signal, and the maximum gain and minimum gain of the open-loop gain in the optoelectronic oscillator loop are changed by tuning the tunable attenuator, so that the reconfigurable time-frequency domain mode-locked optoelectronic oscillator is switched among three reconfiguration states (frequency domain mode-locked OEO state, time domain mode-locked OEO state and time-frequency domain mode-locked OEO state).

[0011] In the process of operating the reconfigurable time-frequency domain mode-locked optoelectronic oscillator in the frequency domain mode-locked OEO state, the amplitude of the electrical control signal generated by the waveform generator varies periodically and continuously in time, for example, the electrical control signal is a triangular wave signal, and the amplitude of the triangular wave signal varies continuously from V1 to V2 over time in one period, where V1 < V2, so that the center frequency of the output microwave signal varies periodically from f1 to f2 in time, where f1 corresponds to the triangular wave signal amplitude V1, and f2 corresponds to the triangular wave signal amplitude V2, so that the periodically varying open-loop gain in the optoelectronic oscillator loop varies periodically from the minimum gain G1 to the maximum gain G2 in time, where the minimum gain G1 corresponds to the triangular wave signal amplitude V1, and the maximum gain G2 corresponds to the triangular wave signal amplitude V2. The frequency of the electrical control signal is controlled to be an integer multiple of the reciprocal of the delay of the optoelectronic oscillator loop, and the minimum gain G1 of the periodically varying open-loop gain in the optoelectronic oscillator loop is greater than 1 by tuning the tunable attenuator, so that the reconfigurable time-frequency domain mode-locked optoelectronic oscillator operates in the frequency domain mode-locked OEO state, and outputs a linearly chirped microwave waveform with a frequency varying periodically from f1 to f2.

[0012] The process that the reconfigurable time-frequency domain mode-locked optoelectronic oscillator works in the time domain mode-locked OEO state is that: the electric control signal generated by the waveform generator is a square wave signal, and there are only two values V1 and V2 in a period, where V1 < V2, so that the center frequency of the output microwave signal periodically jumps f1 and f2, where the square wave signal amplitude corresponding to f1 is V1, and the square wave signal amplitude corresponding to f2 is V2, so that the periodically changing open loop gain in the optoelectronic loop jumps from the minimum gain G1 to the maximum gain G2, where the square wave signal amplitude corresponding to the minimum gain G1 is V1, and the square wave signal amplitude corresponding to the maximum gain G2 is V2. The frequency of the control square wave signal is equal to an integer multiple of the reciprocal of the delay of the optoelectronic oscillation loop, and the minimum gain G1 of the periodically changing open loop gain in the optoelectronic oscillation loop is less than 1 and the maximum gain G2 is greater than 1 by tuning the adjustable attenuator, so that the reconfigurable time-frequency domain mode-locked optoelectronic oscillator works in the time domain mode-locked OEO state, and the output microwave pulse signal has a center frequency equal to f2.

[0013] The process that the reconfigurable time-frequency domain mode-locked optoelectronic oscillator works in the time-frequency domain mode-locked OEO state is that: the amplitude of the electric control signal generated by the waveform generator changes periodically and continuously in time, for example, the electric control signal is a triangular wave signal, and the amplitude of the triangular wave signal changes from V1 to V2 continuously in time in a period, where V1 < V2, so that the center frequency of the output microwave signal changes from f1 to f2 in time, where the triangular wave signal amplitude corresponding to f1 is V1, and the triangular wave signal amplitude corresponding to f2 is V2, so that the periodically changing open loop gain in the optoelectronic loop changes from the minimum gain G1 to the maximum gain G2 in time, where the triangular wave signal amplitude corresponding to the minimum gain G1 is V1, and the triangular wave signal amplitude corresponding to the maximum gain G2 is V2. The amplitude V0 of the triangular wave signal corresponding to the open loop gain equal to 1 and the center frequency f0 of the output microwave signal, where V1 < V0 < V2, f1 < f0 < f2. The frequency of the electric control signal is equal to an integer multiple of the reciprocal of the delay of the optoelectronic oscillation loop, and the minimum gain G1 of the periodically changing open loop gain in the optoelectronic oscillation loop is less than 1 and the maximum gain G2 is greater than 1 by tuning the adjustable attenuator, so that the reconfigurable time-frequency domain mode-locked optoelectronic oscillator works in the time-frequency domain mode-locked OEO state, and the output pulse linearly chirped microwave waveform has a frequency that changes from f0 to f2.

[0014] Further, when the reconfigurable time-frequency domain mode-locked optoelectronic oscillator works in the frequency domain mode-locked OEO state, the bandwidth, repetition frequency and center frequency of the output linearly chirped microwave waveform signal are adjusted by changing the amplitude, frequency of the electric control signal generated by the waveform generator and the bias current of the laser.

[0015] Further, when the reconfigurable time-frequency domain mode-locked optoelectronic oscillator works in the time domain mode-locked OEO state, the duty cycle, the repetition frequency of the square wave signal generated by the waveform generator and the bias current of the laser are changed to realize the adjustment of the pulse width, the repetition frequency and the center frequency of the output microwave pulse signal.

[0016] Further, when the reconfigurable time-frequency domain mode-locked optoelectronic oscillator works in the time-frequency domain mode-locked OEO state, the symmetry, the repetition frequency of the electric control signal generated by the waveform generator and the bias current of the laser are changed to realize the adjustment of the chirp polarity, the repetition frequency, the center frequency and the pulse width of the output pulse linear chirp microwave waveform signal.

[0017] Compared with the prior art, the reconfigurable time-frequency domain mode-locked optoelectronic oscillator has the following beneficial effects:

[0018] 1. The reconfigurable time-frequency domain mode-locked optoelectronic oscillator can generate a reconfigurable mode-locked optoelectronic oscillator by using a waveform generator, an adjustable optical attenuator and a fast adjustable microwave photonic bandpass filter, and can be flexibly switched among a frequency domain mode-locked optoelectronic oscillator, a time domain mode-locked optoelectronic oscillator and a time-frequency domain mode-locked optoelectronic oscillator, compared with an optoelectronic oscillator that can only work in one mode-locked state.

[0019] 2. The reconfigurable time-frequency domain mode-locked optoelectronic oscillator has a simple structure, and can realize flexible switching among three mode-locked states by tuning the open-loop gain and the wavelength of the laser through a waveform generator and an adjustable attenuator, without the need of additional mode-locked devices to switch the mode-locked state, thereby being low in cost and easy to implement.

[0020] 3. The reconfigurable time-frequency domain mode-locked optoelectronic oscillator can generate a wideband, low-phase-noise reconfigurable tunable microwave signal, and the signal format, the bandwidth, the pulse width and the repetition frequency of the microwave signal can be flexibly tuned by using a low-frequency waveform generator, and the center frequency of the reconfigurable tunable microwave signal can be adjusted by using the microwave photonic bandpass filter. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 FIG. 1 is a structural schematic diagram of the reconfigurable time-frequency domain mode-locked optoelectronic oscillator of the embodiment 1 of the present application;

[0022] Figure 2 FIG. 3 is a basic operation schematic diagram of the reconfigurable function of the reconfigurable time-frequency domain mode-locked optoelectronic oscillator of the embodiment 1 of the present application;

[0023] Figure 3 FIG. 5 is an instantaneous frequency schematic diagram of the output signal of the reconfigurable time-frequency domain mode-locked optoelectronic oscillator of the embodiment 1 of the present application working in the time-frequency domain mode-locked OEO state;

[0024] Figure 4 Fig. 1 is a schematic diagram of the instantaneous frequency of the output signal of the reconfigurable time-frequency domain mode-locked optoelectronic oscillator of the present application in the time domain mode-locked OEO state;

[0025] Figure 5 Fig. 1 is a schematic diagram of the instantaneous frequency of the output signal of the reconfigurable time-frequency domain mode-locked optoelectronic oscillator of the present application in the time domain mode-locked OEO state;

[0026] Figure 6 Fig. 2 is a schematic diagram of the structure of the time domain mode-locked optoelectronic oscillator of the present application;

[0027] Figure 7 Fig. 2 is a schematic diagram of the structure of the time domain mode-locked optoelectronic oscillator of the present application; DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application. The technical solutions of the present application will be described in detail below in conjunction with the accompanying drawings and embodiments.

[0029] Embodiment 1

[0030] As shown in Fig. 1, the present embodiment provides a schematic diagram of the structure of a reconfigurable time-frequency domain mode-locked optoelectronic oscillator, which includes a waveform generator 1, a laser 2, a phase modulator 3, an optical wave filter 4, an adjustable optical attenuator 5, an optical fiber 6, an optoelectronic detector 7, an electrical amplifier 8, and an electrical power divider 9. Figure 1 The waveform generator 1 generates an electrical control signal to control the injection current of the laser 2, and the wavelength and power of the continuous light output by the laser 2 vary with the amplitude of the electrical control signal generated by the waveform generator; the continuous light output by the laser 2 enters the phase modulator 3 to generate a double-sideband modulated light signal, which includes a carrier and two positive and negative first-order light sidebands with equal amplitude and opposite phase; the optical wave filter 4 filters one sideband of the double-sideband modulated light signal to generate a single-sideband modulated light signal; the generated single-sideband modulated light signal is transmitted through the adjustable optical attenuator 5 and the optical fiber 6 and then is optoelectronically converted by the optoelectronic detector 7 to generate a microwave signal; the optoelectronically converted microwave signal is amplified by the electrical amplifier 8 and then enters the electrical power divider 9; the electrical power divider 9 divides the amplified microwave signal into two paths, one of which outputs to close the optoelectronic oscillation loop in the phase modulator 3, and the other of which outputs a reconfigurable tunable microwave signal.

[0031]

[0032] ​The laser 2, the phase modulator 3, the optical notch filter 4 and the photodetector 7 jointly constitute a fast adjustable microwave photonic bandpass filter, the center frequency of the microwave photonic bandpass filter is equal to the reciprocal of the difference between the wavelength of the continuous light output by the laser 2 and the notch wavelength of the optical notch filter; the frequency of the reconfigurable tunable microwave signal output by the electrical power divider 9 is equal to the center frequency of the microwave photonic bandpass filter.

[0033] The waveform generator 1, the adjustable optical attenuator 5 and the fast adjustable microwave photonic bandpass filter constitute a reconfigurable module of the reconfigurable time-frequency domain optoelectronic oscillator provided in the embodiment. The embodiment can realize flexible switching among three reconfiguration states, including a frequency domain mode-locked OEO state, a time domain mode-locked OEO state and a time-frequency domain mode-locked OEO state, by changing the parameters of the reconfigurable module, as shown in Figure 2 The periodic amplitude change of the electrical control signal generated by the waveform generator 1 causes the wavelength and the power of the continuous light output by the laser 2 to have the same periodic change. The periodic change of the wavelength of the continuous light output by the laser 2 causes the center frequency of the microwave photonic bandpass filter to have the same periodic change, and the frequency of the output microwave signal has the same periodic change, that is, changing the amplitude of the electrical control signal generated by the waveform generator 1 causes the frequency of the output microwave signal to have the same change. Changing the amplitude change of the electrical control signal generated by the waveform generator 1 causes the power of the continuous light output by the laser 2 to have periodic change, so that the open loop gain in the optoelectronic loop has periodic change. When the frequency of the electrical control signal generated by the waveform generator 1 is equal to an integer multiple of the reciprocal of the delay of the optoelectronic loop, the oscillation mode in the optoelectronic loop is constrained by the periodic change of the wavelength and the power of the continuous light output by the laser 2, the oscillation mode is locked to obtain fixed power and phase relationship, and the frequency domain mode-locked and time domain mode-locked technologies are introduced in the loop. By controlling the signal form and voltage of the electrical control signal generated by the waveform generator 1 and changing the maximum gain and minimum gain of the open loop gain in the loop through the adjustable optical attenuator 5, the reconfigurable time-frequency domain mode-locked optoelectronic oscillator provided in the embodiment can be flexibly switched among the three reconfiguration states.

[0034] The process that the reconfigurable time-frequency domain mode-locked optoelectronic oscillator provided in the embodiment works in the frequency domain mode-locked OEO state is as follows: the waveform generator 1 generates a triangular wave signal, the amplitude of the triangular wave signal continuously changes from -18.8 mV to 18.8 mV over a period, so that the center frequency of the output microwave signal periodically changes from 6 GHz to 14 GHz over time, wherein 6 GHz corresponds to the triangular wave signal amplitude of -18.8 mV, and 14 GHz corresponds to the triangular wave signal amplitude of 18.8 mV, so that the periodically changing open-loop gain in the optoelectronic loop periodically changes from the minimum gain G1 to the maximum gain G2 over time, wherein the minimum gain G1 corresponds to the triangular wave signal amplitude of -18.8 mV, and the maximum gain G2 corresponds to the triangular wave signal amplitude of 18.8 mV. The frequency of the triangular wave signal is controlled to be 19.69 kHz, which is equal to the reciprocal of the delay of the optoelectronic loop of 50.79 μs, and the adjustable optical attenuator 5 is controlled so that the minimum gain G1 of the periodically changing open-loop gain in the optoelectronic loop is greater than 1. The reconfigurable time-frequency domain mode-locked optoelectronic oscillator provided in the embodiment is in the frequency domain mode-locked OEO state, and outputs a linearly chirped microwave waveform, the frequency of which periodically changes from 6 GHz to 14 GHz, and the schematic diagram of the instantaneous frequency of the output linearly chirped microwave waveform is as shown in Figure 3 .

[0035] The process that the reconfigurable time-frequency domain mode-locked optoelectronic oscillator provided in the embodiment works in the time domain mode-locked OEO state is as follows: the waveform generator 1 generates an electrically controlled signal in the form of a square wave signal, and there are only two values of -20 mV and 20 mV in a period, so that the center frequency of the output microwave signal periodically jumps between 18.5 GHz and 10 GHz, wherein 18.5 GHz corresponds to the square wave signal amplitude of -20 mV, and 10 GHz corresponds to the square wave signal amplitude of 20 mV, so that the periodically changing open-loop gain in the optoelectronic loop periodically jumps from the minimum gain G1 to the maximum gain G2, wherein the minimum gain G1 corresponds to the square wave signal amplitude of -20 mV, and the maximum gain G2 corresponds to the square wave signal amplitude of 20 mV. The frequency of the square wave signal is controlled to be 19.69 kHz, which is equal to the reciprocal of the delay of the optoelectronic loop of 50.79 μs, the adjustable optical attenuator 5 is controlled so that the minimum gain G1 of the periodically changing open-loop gain in the optoelectronic loop is less than 1, and the maximum gain G2 is greater than 1. The reconfigurable time-frequency domain mode-locked optoelectronic oscillator provided in the embodiment is in the time domain mode-locked OEO state, and outputs a microwave pulse signal, the center frequency of which is equal to 10 GHz, and the schematic diagram of the instantaneous frequency of the output microwave pulse signal is as shown in Figure 4 .

[0036] The process that the reconfigurable time-frequency domain mode-locked optoelectronic oscillator provided in the embodiment works in the time-frequency domain mode-locked OEO state is as follows: the waveform generator 1 generates a triangular wave signal, the amplitude of the triangular wave signal continuously changes from -29.7 mV to 29.7 mV over time in a period, so that the center frequency of the output microwave signal periodically changes from 19 GHz to 7 GHz over time, wherein 19 GHz corresponds to the triangular wave signal amplitude of -29.7 mV, and 7 GHz corresponds to the triangular wave signal amplitude of 29.7 mV, so that the open-loop gain periodically changes from the minimum gain G1 to the maximum gain G2 in the optoelectronic loop over time, wherein the minimum gain G1 corresponds to the triangular wave signal amplitude of -29.7 mV, and the maximum gain G2 corresponds to the triangular wave signal amplitude of 29.7 mV. The open-loop gain equal to 1 corresponds to the triangular wave signal amplitude of 0 mV and the center frequency of the output microwave signal of 13 GHz. The frequency of the triangular wave signal is controlled to be 19.69 kHz, which is equal to the reciprocal of the delay of the optoelectronic loop of 50.79 μs, and the adjustable optical attenuator 5 is controlled to make the minimum gain G1 of the open-loop gain periodically changing in the optoelectronic loop less than 1 and the maximum gain G2 greater than 1. The reconfigurable time-frequency domain mode-locked optoelectronic oscillator provided in the embodiment is in the time-frequency domain mode-locked OEO state, and outputs a pulsed linearly chirped microwave waveform, the frequency of which periodically changes from 7 GHz to 13 GHz, and a schematic diagram of the instantaneous frequency of the output pulsed linearly chirped microwave waveform is as shown in FIG. 6. Figure 5

[0037] Further, when the reconfigurable time-frequency domain mode-locked optoelectronic oscillator provided in the embodiment works in the frequency domain mode-locked OEO state, the amplitude, frequency of the triangular wave signal generated by the waveform generator 1 and the bias current of the laser 2 are changed, so that the bandwidth, repetition frequency and center frequency of the output linearly chirped microwave waveform signal can be flexibly adjusted;

[0038] Further, when the reconfigurable time-frequency domain mode-locked optoelectronic oscillator provided in the embodiment works in the time domain mode-locked OEO state, the duty cycle, repetition frequency of the square wave signal generated by the waveform generator 1 and the bias current of the laser 2 are changed, so that the pulse width, repetition frequency and center frequency of the output microwave pulse signal can be flexibly tuned;

[0039] Further, when the reconfigurable time-frequency domain mode-locked optoelectronic oscillator provided in the embodiment works in the time-frequency domain mode-locked OEO state, the symmetry, repetition frequency of the triangular wave signal generated by the waveform generator 1, the bias current of the laser 2 and the adjustable optical attenuator are changed, so that the chirp polarity, repetition frequency, center frequency and pulse width of the output pulsed linearly chirped microwave waveform signal can be flexibly tuned.

[0040] Embodiment 2

[0041] As Figure 6 ​As shown in the figure, the structure of the time-domain mode-locked optoelectronic oscillator provided in the embodiment includes a waveform generator 1, a laser 2, an electro-optical intensity modulator 3, an adjustable optical attenuator 4, an optical fiber 5, an optoelectronic detector 6, an electrical amplifier 7, an electrical band-pass filter 8, and an electrical power divider 9.

[0042] The waveform generator 1 generates an electrical control signal to control the injection current of the laser 2, and the wavelength and power of the continuous light output by the laser 2 vary with the amplitude of the electrical control signal generated by the waveform generator; the continuous light output by the laser 2 enters the electro-optical intensity modulator 3 and is intensity-modulated by the feedback signal; the intensity-modulated optical carrier is transmitted through the adjustable optical attenuator 4 and the optical fiber 5, and then is optoelectronically converted by the optoelectronic detector 6 to generate a microwave signal; the optoelectronically converted microwave signal is amplified by the electrical amplifier 7, and then the center frequency of the microwave signal is selected by the electrical band-pass filter 8. After the filtered microwave signal enters the electrical power divider 9, it is divided into two paths, one of which is output to the electro-optical intensity modulator 3 to close the optoelectronic oscillation loop, and the other of which is output as a microwave pulse signal.

[0043] In the above process, the frequency of the electrical control signal generated by the waveform generator 1 is equal to an integer multiple of the reciprocal of the delay of the optoelectronic oscillation loop, the voltage of the electrical control signal is tuned, and the adjustable attenuator is adjusted so that the maximum gain of the open-loop gain in the optoelectronic oscillation loop is greater than 1 and the minimum gain is less than 1, so that the gain of the optoelectronic oscillation loop is periodically loss-modulated, the oscillation mode is locked to obtain a fixed phase relationship, the microwave pulse signal is generated by the coherent superposition of the oscillation modes, and the basic operation is as shown in the figure. Figure 7

[0044] The above description of the disclosed embodiments enables one skilled in the art to make or use the application. Various modifications to the embodiments will be apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.​

Claims

1. A reconfigurable time-frequency domain mode-locked opto-electronic oscillator, characterized in that, The apparatus comprises a waveform generator, a laser, a modulator, a filter, an adjustable attenuator, an optical fiber, a photodetector, an electrical amplifier and an electrical power divider. The waveform generator generates an electrical control signal to control the injection current of the laser, and the wavelength and power of the continuous light output by the laser vary with the amplitude of the electrical control signal generated by the waveform generator; the continuous light output by the laser enters the modulator to generate a modulated light signal, and then enters the filter to select the center frequency and oscillation mode; the modulated light signal filtered by the filter is transmitted through the adjustable attenuator and the optical fiber, and then enters the photodetector to generate a microwave signal through photoelectric conversion; the microwave signal is amplified by the electrical amplifier and then enters the electrical power divider, which divides the microwave signal into two paths, one of which is fed back to the modulator to form an optoelectronic oscillation loop, and the other of which is output as the output of the optoelectronic oscillator. When the modulator is a phase modulator, the filter is an optical notch filter, the frequency of the electrical control signal generated by the waveform generator is equal to an integer multiple of the reciprocal of the delay of the optoelectronic oscillation loop, and the signal form and voltage of the electrical control signal are controlled to make the center frequency of the output microwave signal periodically change, the maximum gain and minimum gain of the open-loop gain in the optoelectronic oscillation loop are changed by tuning the adjustable attenuator, and the switching between the frequency-domain mode-locked OEO state, the time-domain mode-locked OEO state and the time-frequency-domain mode-locked OEO state of the reconfigurable time-frequency-domain mode-locked optoelectronic oscillator is realized.

2. The reconfigurable time-frequency domain mode-locked optoelectronic oscillator of claim 1, wherein, When the amplitude of the electrical control signal generated by the waveform generator varies periodically and continuously in time, the frequency of the electrical control signal is equal to an integer multiple of the reciprocal of the delay of the optoelectronic oscillation loop, and the minimum gain of the periodically varying open-loop gain in the optoelectronic oscillation loop is greater than 1 by tuning the adjustable attenuator, the reconfigurable time-frequency-domain mode-locked optoelectronic oscillator works in the frequency-domain mode-locked OEO state, and a linearly chirped microwave waveform is output. When the electrical control signal generated by the waveform generator is a square wave signal, the frequency of the square wave signal is equal to an integer multiple of the reciprocal of the delay of the optoelectronic oscillation loop, and the minimum gain of the periodically varying open-loop gain in the optoelectronic oscillation loop is less than 1 and the maximum gain is greater than 1 by tuning the adjustable attenuator, the reconfigurable time-frequency-domain mode-locked optoelectronic oscillator works in the time-domain mode-locked OEO state, and a microwave pulse signal is output. When the amplitude of the electrical control signal generated by the waveform generator varies periodically and continuously in time, the frequency of the electrical control signal is equal to an integer multiple of the reciprocal of the delay of the optoelectronic oscillation loop, and the minimum gain of the periodically varying open-loop gain in the optoelectronic oscillation loop is less than 1 and the maximum gain is greater than 1 by tuning the adjustable attenuator, the reconfigurable time-frequency-domain mode-locked optoelectronic oscillator works in the time-frequency-domain mode-locked OEO state, and a pulsed linearly chirped microwave waveform is output.

3. The reconfigurable time-frequency domain mode-locked optoelectronic oscillator of claim 1, wherein, When the reconfigurable time-frequency-domain mode-locked optoelectronic oscillator works in the frequency-domain mode-locked OEO state, the bandwidth, repetition frequency and center frequency of the output linearly chirped microwave waveform signal are adjusted by changing the amplitude and frequency of the electrical control signal generated by the waveform generator and the bias current of the laser. When the reconfigurable time-frequency domain mode-locked optoelectronic oscillator works in the time domain mode-locked OEO state, the pulse width, the repetition frequency and the center frequency of the output microwave pulse signal are adjusted by changing the duty cycle and the repetition frequency of the square wave signal generated by the waveform generator and the bias current of the laser. When the reconfigurable time-frequency domain mode-locked optoelectronic oscillator works in the time-frequency domain mode-locked OEO state, the chirp polarity, the repetition frequency, the center frequency and the pulse width of the output pulse linear chirp microwave waveform signal are adjusted by changing the symmetry and the repetition frequency of the electric control signal generated by the waveform generator and the bias current of the laser.

4. The reconfigurable time-frequency domain mode-locked optoelectronic oscillator of claim 1, wherein, When the phase modulator is replaced by an electro-optic intensity modulator and the filter is replaced by an electrical band-pass filter, the reconfigurable time-frequency domain mode-locked optoelectronic oscillator works in the time domain mode-locked OEO state and outputs a microwave pulse signal when the frequency of the electric control signal generated by the waveform generator is equal to an integer multiple of the inverse of the delay of the optoelectronic oscillation loop, the voltage of the electric control signal is tuned and the adjustable attenuator is tuned so that the maximum gain of the open-loop gain in the optoelectronic oscillation loop is greater than 1 and the minimum gain is less than 1.

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