A method and device for simultaneously generating microwave signals and optical pulses

Abstract

The present invention discloses a method for simultaneously generating microwave signals and optical pulses, and belongs to the field of microwave photonic technology. The present invention introduces parallel optical or microwave gain and loss channels in a coupled optoelectronic oscillator to realize a parity-time symmetric structure, and controls the energy distribution in the parity-time symmetric structure so that the system reaches a parity-time symmetry breaking state, thereby realizing frequency domain parity-time symmetry in the optoelectronic oscillation loop to improve the signal side mode suppression ratio and suppress phase noise, and realizing time domain parity-time symmetry in the optical oscillation loop to suppress supermodes. The present invention also discloses a device for simultaneously generating microwave signals and optical pulses. Compared with the prior art, the present invention can generate single-frequency microwave signals with high frequency stability, low phase noise, and high side mode suppression ratio, and optical pulses with high repetition rate and low time jitter, and has the advantages of simple system structure, higher adaptability and reliability.

Description

Technical Field

[0001] The invention relates to a method for simultaneously generating microwave signals and optical pulses, belonging to the technical field of microwave photons. Background Art

[0002] Microwaves are an important carrier of modern information transmission, and their spectrum purity directly affects the core performance of the entire RF system. In the fields of wireless communications and radar detection, the quality of microwave signals restricts the communication capacity of the communication system and the sensitivity of the detection system. However, microwave signal sources based on traditional microwave technology are limited by electronic bottlenecks and are difficult to meet the growing frequency and bandwidth requirements.

[0003] Microwave photonic technology, with its extremely large bandwidth and extremely low noise, can achieve the generation of high-frequency, broadband, and low-phase noise microwave signals. The coupled optoelectronic oscillator has an optical oscillation loop and an optoelectronic oscillation loop, which can simultaneously generate high-frequency microwave signals and high-repetition-rate optical pulse signals, and is an effective optical microwave device. However, the coupled optoelectronic oscillator requires the optical oscillation loop and the optoelectronic oscillation loop to be locked at the same time in order to output a stable microwave signal, and the supermode noise in the optical oscillation loop and the side mode in the optoelectronic oscillation loop are very close to the oscillation frequency, and are difficult to filter out through optical filters or narrowband electrical filters, resulting in great difficulty in achieving stable single-frequency microwave and optical pulse output.

[0004] In terms of suppressing supermode noise, researchers have introduced an optical pulse power feedback mechanism in the optical oscillation loop to reduce the probability of supermode generation [Dai Y, Wang R, Yin F, et al. Sidemode suppression for coupled optoelectronic oscillator by optical pulse power feedforward [J]. Optics express, 2015, 23 (21): 27589-27596.] or introduced a nonlinear polarization rotation mirror to achieve saturation absorption of optical pulses to suppress supermodes [Doerr CR, Haus HA, Ippen EP, et al. Additive-pulse limiting [J]. Optics letters, 1994, 19 (1): 31-33.]. However, these methods require the introduction of additional devices or apparatuses in the optical oscillation loop, which makes the optical oscillation loop structure complex, further deteriorates the stability of the optical oscillation loop, and is difficult to be practical.

[0005] In terms of suppressing optoelectronic oscillation modes, researchers have introduced a composite cavity structure based on a polarization-maintaining dual ring into the optical oscillation loop to stabilize the polarization state of the system and achieve the effect of side mode suppression [Onodera N. Supermodebeat suppression in harmonically mode-locked erbium-doped fibre ring lasers with composite cavity structure [J]. Electronics Letters, 1997, 33 (11): 962-963.] or introduced two oscillation loops into the optoelectronic oscillation loop for mutual injection locking to achieve mode competition and achieve the effect of side mode suppression [Dai J, Liu A, Liu J, et al. Supermode noise suppression with mutual injection locking for coupled optoelectronic oscillator [J]. Optics Express, 2017, 25 (22): 27060-27066.]. These methods have achieved the improvement of the side mode suppression ratio of the signal, but the composite cavity structure and the mutual injection structure require the introduction of additional complex structures, and the phase noise performance of the system cannot be guaranteed.

[0006] In summary, the existing coupled optoelectronic oscillator has the problem of being difficult to simultaneously generate high supermode noise suppression, low phase noise, high side mode suppression ratio radio frequency signals and high repetition rate and low time jitter optical pulses. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing coupled optoelectronic oscillator, and provide a method and device for simultaneously generating microwave signals and optical pulses. The parity-time symmetry principle is introduced into the traditional coupled optoelectronic oscillator, so that the frequency domain parity-time symmetry is realized in the optoelectronic oscillation loop to improve the signal side mode suppression ratio and suppress phase noise, and the time domain parity-time symmetry is realized in the optical oscillation loop to suppress supermodes, thereby generating a single-frequency microwave signal with high frequency stability, low phase noise and high side mode suppression ratio and an optical pulse with high repetition rate and low time jitter.

[0008] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0009] A method for simultaneously generating microwave signals and optical pulses comprises: constructing at least one parity-time symmetric structure consisting of a signal gain channel and a signal loss channel in parallel and having the same signal transmission delay in at least one of two mutually coupled loops of a coupled optoelectronic oscillator: an optical oscillation loop and an optoelectronic oscillation loop, so as to form a gain oscillation loop and a loss oscillation loop in the loop where the parity-time symmetric structure is located; controlling the signal energy distribution in the parity-time symmetric structure so that the coupled optoelectronic oscillator reaches a parity-time symmetry breaking state, realizing frequency domain parity-time symmetry in the optoelectronic oscillation loop, and realizing time domain parity-time symmetry in the optical oscillation loop, so that the optoelectronic oscillation loop outputs a single-frequency microwave signal, and the optical oscillation loop outputs an optical pulse signal, wherein the frequency of the single-frequency microwave signal is equal to the repetition frequency of the optical pulse signal.

[0010] Preferably, the signal energy distribution in the control parity-time symmetric structure is specifically achieved by adjusting the signal power of the signal gain channel and the signal loss channel so that the gain of the gain oscillation loop is equal to the loss of the loss oscillation loop.

[0011] As one of the preferred solutions, the parity-time symmetric structure is realized by splitting the optical signal power into two paths and adjusting the power division ratio of the optical power divider.

[0012] As another preferred solution, the parity-time symmetric structure is realized by power-splitting the microwave signal into two paths and adjusting the power-splitting ratio of the two power-splitting signals.

[0013] As another preferred solution, the parity-time symmetric structure is achieved by polarization division multiplexing the optical signal into two paths with orthogonal polarization states and adjusting the polarization states of the two polarized optical signals.

[0014] Preferably, the optical oscillation loop is a linear optical oscillation cavity composed of a Fabry-Perot resonant cavity, an optical amplifier device, and an electro-optic modulator shared with the optoelectronic oscillation loop.

[0015] Based on the same inventive concept, the following technical solutions can also be obtained:

[0016] A device for simultaneously generating microwave signals and optical pulses comprises a coupled optoelectronic oscillator having two mutually coupled loops: an optical oscillation loop and an optoelectronic oscillation loop. At least one parity-time symmetric structure consisting of a signal gain channel and a signal loss channel in parallel and having the same signal transmission delay is constructed in at least one of the optical oscillation loop and the optoelectronic oscillation loop, so that a gain oscillation loop and a loss oscillation loop are formed in the loop where the parity-time symmetric structure is located. The signal energy distribution in the parity-time symmetric structure is configured to enable the coupled optoelectronic oscillator to reach a parity-time symmetry breaking state, realize frequency domain parity-time symmetry in the optoelectronic oscillation loop, and realize time domain parity-time symmetry in the optical oscillation loop, so that the optoelectronic oscillation loop outputs a single-frequency microwave signal, and the optical oscillation loop outputs an optical pulse signal, and the frequency of the single-frequency microwave signal is equal to the repetition frequency of the optical pulse signal.

[0017] Preferably, the signal energy distribution in the parity-time symmetric structure is specifically achieved by adjusting the signal power of the signal gain channel and the signal loss channel so that the gain of the gain oscillation loop is equal to the loss of the loss oscillation loop.

[0018] As one of the preferred solutions, the parity-time symmetric structure is realized by splitting the optical signal power into two paths and adjusting the power division ratio of the optical power divider.

[0019] As another preferred solution, the parity-time symmetric structure is realized by power-splitting the microwave signal into two paths and adjusting the power-splitting ratio of the two power-splitting signals.

[0020] As another preferred solution, the parity-time symmetric structure is achieved by polarization division multiplexing the optical signal into two paths with orthogonal polarization states and adjusting the polarization states of the two polarized optical signals.

[0021] Preferably, the optical oscillation loop is a linear optical oscillation cavity composed of a Fabry-Perot resonant cavity, an optical amplifier device, and an electro-optic modulator shared with the optoelectronic oscillation loop.

[0022] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0023] The present invention introduces parallel optical or microwave gain and loss channels into a coupled optoelectronic oscillator for the first time to realize a parity-time symmetric structure, and controls the energy distribution in the parity-time symmetric structure so that the system reaches a parity-time symmetry breaking state, thereby realizing frequency domain parity-time symmetry in the optoelectronic oscillation loop to improve the signal side mode suppression ratio and suppress phase noise, and realizing time domain parity-time symmetry in the optical oscillation loop to suppress supermodes, thereby generating single-frequency microwave signals with high frequency stability, low phase noise, and high side mode suppression ratio, and optical pulses with high repetition rate and low time jitter;

[0024] The present invention does not require the introduction of additional complex structures such as optical pulse power feedback mechanism, saturated absorption structure, composite cavity structure and mutual injection structure, and can be implemented based on various existing coupled optoelectronic oscillators. It has the significant advantages of simple system structure, higher adaptability and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural principle block diagram of the technical solution of the present invention;

[0026] Figure 2 It is a structural schematic diagram of a first specific embodiment of the present invention;

[0027] Figure 3 It is a structural schematic diagram of a second specific embodiment of the present invention;

[0028] Figure 4 It is a schematic structural diagram of a third specific embodiment of the present invention;

[0029] Figure 5 It is a structural schematic diagram of a fourth specific embodiment of the present invention;

[0030] Figure 6 This is a comparison diagram of the measured spectrum of the first specific embodiment;

[0031] Figure 7 This is a comparison diagram of the measured phase noise of the first specific embodiment;

[0032] Figure 8 This is a spectrum diagram of the first specific embodiment. DETAILED DESCRIPTION

[0033] In view of the shortcomings of the prior art, the solution of the present invention is to introduce parallel optical or microwave gain and loss channels in a coupled optoelectronic oscillator to realize a parity-time symmetric structure, and control the energy distribution in the parity-time symmetric structure so that the system reaches a parity-time symmetry breaking state, thereby realizing frequency domain parity-time symmetry in the optoelectronic oscillation loop to improve the signal side mode suppression ratio and suppress phase noise, and realizing time domain parity-time symmetry in the optical oscillation loop to suppress supermodes, thereby generating single-frequency microwave signals with high frequency stability, low phase noise, and high side mode suppression ratio and optical pulses with high repetition rate and low time jitter.

[0034] Different from the existing parity-time symmetric optoelectronic oscillator [Zhang J, Yao J. Parity-time–symmetric optoelectronic oscillator [J]. Science advances, 2018, 4 (6): eaar6782.], the present invention forms frequency domain parity-time symmetry in a dual-ring optoelectronic oscillator to perform radio frequency mode selection to improve the side mode suppression ratio. The present invention introduces optical (microwave) gain and loss parallel channels into the optical oscillation loop and / or optoelectronic oscillation loop of the coupled optoelectronic oscillator, controls the energy distribution in the optical (microwave) gain channel and the optical (microwave) loss channel so that the system reaches a parity-time symmetry breaking state, thereby realizing frequency domain parity-time symmetry in the optoelectronic oscillation loop, optimizing the filtering response in the optoelectronic oscillation loop to improve the signal side mode suppression ratio and suppress phase noise; and realizing time domain parity-time symmetry in the optical oscillation loop to suppress supermodes and optimize optical pulse signals.

[0035] In order to facilitate public understanding, the technical solution of the present invention is described in detail below with reference to the accompanying drawings:

[0036] like Figure 1 As shown in FIG. 1 , the device for simultaneously generating microwave signals and optical pulses proposed in the present invention comprises a coupled optoelectronic oscillator having two mutually coupled loops: an optical oscillation loop and an optoelectronic oscillation loop, wherein the optical oscillation loop and the optoelectronic oscillation loop share the same electro-optical conversion module (electro-optical modulator), the input optical signal in the optoelectronic oscillation loop is provided by the optical oscillation loop, and the radio frequency signal in the optical oscillation loop that drives the electro-optical conversion module is provided by the optoelectronic oscillation loop; Figure 1 As shown, in at least one of the optical oscillation loop and the optoelectronic oscillation loop, there is constructed at least one parity-time symmetric structure consisting of a signal gain channel and a signal loss channel in parallel with the same signal transmission delay, that is, Figure 1 The optical gain and loss parallel channels and microwave gain and loss parallel channels in the circuit form a gain oscillation loop and a loss oscillation loop in the circuit where the parity-time symmetric structure is located ( Figure 1 The signal energy distribution in the parity-time symmetric structure is controlled so that the coupled optoelectronic oscillator reaches a parity-time symmetry breaking state, and frequency domain parity-time symmetry is realized in the optoelectronic oscillation loop, and time domain parity-time symmetry is realized in the optical oscillation loop. Then, the optoelectronic oscillation loop outputs a single-frequency microwave signal with high frequency stability, low phase noise, and high side mode suppression ratio, and the optical oscillation loop outputs an optical pulse signal with high repetition rate and low time jitter, and the frequency of the single-frequency microwave signal is equal to the repetition rate of the optical pulse signal.

[0037] Specifically, by adjusting the signal power of the signal gain channel and the signal loss channel so that the gain of the gain oscillation loop is equal to the loss of the loss oscillation loop, the system can reach a parity-time symmetry breaking state, realize frequency domain parity-time symmetry in the optoelectronic oscillation loop, and realize time domain parity-time symmetry in the optical oscillation loop.

[0038] The parity-time symmetric structure can be set only in the optical oscillation loop or the photoelectric oscillation loop, or in both the optical oscillation loop and the photoelectric oscillation loop; wherein the parity-time symmetric structure in the photoelectric oscillation loop can be a microwave gain and loss parallel channel set in the microwave part, or can be an optical gain and loss parallel channel set in the optical part.

[0039] To help understand, first briefly introduce the principle of coupled optoelectronic oscillator:

[0040] In an optical oscillator loop without an active mode-locking structure, due to the gain amplification effect of the erbium-doped fiber, multiple groups of longitudinal modes are continuously excited in the optical oscillator loop. The amplitudes and phases of different groups of longitudinal modes are independent of each other. When a harmonic active mode-locking structure is added to the loop, that is, an electro-optic modulator that injects harmonic signals into the optical oscillator loop, since the harmonic signal is an integer multiple of the longitudinal mode interval, a group of longitudinal modes is phase-locked to the harmonic signal, and after continuous amplification by the erbium-doped fiber, an optical frequency comb with a relatively uniform amplitude is finally formed in the frequency domain; in the time domain, the loss modulation effect of the electro-optic modulator continuously concentrates the time domain energy of the locked longitudinal mode, and finally forms a narrow-band optical pulse in the time domain. Assume that the stable longitudinal mode of the optical oscillator loop in the active mode-locking structure is ω i , with an amplitude of E i , the initial phase is One of the modes has a frequency of ω0 and an initial phase of 0. There is a phase difference α between adjacent frequency combs, and the frequency difference between the frequencies is Δω. Assume that the i-th frequency comb is:

[0041]

[0042] The total optical frequency comb can be expressed as:

[0043]

[0044] =E0cosω0t{1+2cos(Δωt+α)+2cos[2(Δωt+α)]+…2cos[N(Δωt+α)]}

[0045] The RF signal modulated by the electro-optic modulator in the active mode-locking structure can be expressed as:

[0046]

[0047] Among them, Vm ,ω m , are the amplitude, angular frequency and initial phase of the signal respectively. Under the signal injection, the output optical signal of the modulator is:

[0048]

[0049] Assume that the optical signal input to the modulator is The optical signal output after the modulator is:

[0050]

[0051] Where β = πV m / V π , J n (*) represents the first-order Bessel function of nth order, so after one modulation, multiple high-order harmonic components are generated, and the harmonic component interval is ω m For the convenience of analysis, only the first-order case is considered here:

[0052]

[0053] It can be seen that the longitudinal mode ω0 generates two frequencies ω0-ω after passing through the modulator m With ω0+ω m After the two new sidebands are injected into adjacent longitudinal modes, the initial phase difference of adjacent modes is consistent. After multiple cycles, the initial phases of all modes within the gain bandwidth are suppressed, achieving phase locking.

[0054] From the above process, we can know that the light signal in the optical oscillation loop is separated by a beam of light through the coupler and enters the photodetector for beat frequency, which can be obtained:

[0055]

[0056] Where ρ is the responsivity of the photodetector. Due to the limitation of the response bandwidth of the photodetector, the high-frequency component is suppressed, so the electrical signal output by the photodetector is:

[0057]

[0058] Where x and y are integers and R is the output resistance of the photodetector.

[0059] Due to the use of microwave narrowband filters in the optoelectronic oscillation loop, only the difference frequency component obtained by any adjacent longitudinal mode beat frequency exists in the optoelectronic oscillation loop, so the obtained single-frequency electrical signal can be expressed as:

[0060]

[0061] The single-frequency signal is also the signal injected into the optical oscillation loop.

[0062] In the present invention, at least one parity-time symmetric structure consisting of a signal gain channel and a signal loss channel in parallel with the same signal transmission delay is constructed in the optical oscillation loop and the optoelectronic oscillation loop of the coupled optoelectronic oscillator, so that a gain oscillation loop and a loss oscillation loop are formed in the loop where the parity-time symmetric structure is located. It is assumed that the gain oscillation loop and the loss oscillation loop have the same loop length, and there is a coupling exchange of energy between the two loops. The coupled system can describe the nth intrinsic oscillation mode in the parity-time symmetric system by a coupled mode equation.

[0063]

[0064] Among them, a n and b n are the nth eigenmodes of the two loops respectively; ω n is the angular frequency of the nth eigenmode, g an and g bn are the gain coefficients of the two eigenmodes, κ n is the coupling coefficient of the two loops.

[0065] By solving the above coupled mode equation, we can obtain the angular frequency of the nth eigenmode in the parity-time symmetric system as shown below.

[0066]

[0067] When the gain factor in the gain loop is adjusted to be equal to the loss factor in the loss loop, i.e. g an =-g bn =g n , the system reaches a state of symmetry breaking. At this time, the above formula can be written as:

[0068]

[0069] It can be seen from the above formula that when the gain coefficient of the parity-time symmetric system is equal to the coupling coefficient, the system has a singular point. When the gain coefficient is greater than the coupling coefficient, the system realizes a pair of conjugate gain mode and loss mode. The frequency mode pair will have frequency degeneracy, which can produce single-mode oscillation. At this time, the signal mode is in a parity-time symmetry breaking state. At this time, the optoelectronic oscillation loop of the coupled optoelectronic oscillator has a symmetry breaking state. In this state, there is a unique set of signal modes that realize the conjugate mode, and other modes will have mode splitting, realizing parity-time symmetry in the frequency domain, thereby optimizing the filtering response in the optoelectronic oscillation loop. When the gain coefficient is less than the coupling coefficient, any pair of eigenmodes will undergo bounded neutral oscillation, and the mode will experience mode splitting. At this time, the signal mode is in a parity-time symmetry non-breaking state. Therefore, according to the above explanation, in the parity-time symmetric coupled optoelectronic oscillator system, only when the gain of the gain loop is equal to the loss of the loss loop, and the gain coefficient is greater than the coupling coefficient, the main mode is in a parity-time symmetry breaking state. At this time, a pair of conjugated mode pairs appear in the system, and the mode pair will have frequency degeneracy and produce single-mode oscillation. Since the gain coefficient of other modes is less than the coupling coefficient, they are in a parity-time symmetry non-breaking state. These modes will undergo boundary neutral oscillation and frequency splitting, and thus will be suppressed. At this time, the parity-time symmetric coupled optoelectronic oscillator system achieves single-mode oscillation and optimizes the side mode suppression ratio and phase noise of the output signal.

[0070] In order to help the public fully understand the technical solution of the present invention, several specific embodiments are further described below:

[0071] Embodiment 1:

[0072] like Figure 2 As shown, the device for simultaneously generating microwave signals and optical pulses in this embodiment includes an erbium-doped fiber amplifier, an optical isolator, an optical filter, an adjustable optical delay line, an optical coupler, a polarization controller, an electro-optic modulator, a polarization beam splitter, a balanced photodetector, a microwave amplifier, and a microwave narrowband filter, wherein the erbium-doped fiber amplifier, the optical isolator, the optical filter, the adjustable optical delay line, the optical coupler, the polarization controller, and the electro-optic modulator constitute an optical oscillation loop, and the polarization controller, the electro-optic modulator, the polarization beam splitter, the balanced photodetector, the microwave amplifier, and the microwave narrowband filter constitute an optoelectronic oscillation loop. In this structure, the polarization controller, the polarization beam splitter, and the balanced photodetector constitute a parallel gain-loss channel to realize a parity-time symmetric structure. In this structure, by regulating the polarization state of the polarization controller, and then controlling the optical power of the two loops in different polarization states, the gain of the gain loop in the two loops is equal to the loss of the loss loop, so that the system reaches a parity-time symmetry breaking state, and the frequency mode in the system is selected.

[0073] Embodiment 2:

[0074] like Figure 3 As shown, the device for simultaneously generating microwave signals and optical pulses in this embodiment includes an erbium-doped fiber amplifier, an optical isolator, an optical filter, an adjustable optical delay line, an optical coupler, a polarization controller, an electro-optic modulator, a polarization beam splitter, a photodetector, a microwave amplifier, a microwave narrowband filter, an optical circulator, etc., wherein the erbium-doped fiber amplifier, the optical isolator, the optical filter, the adjustable optical delay line, the optical coupler, the polarization controller, and the electro-optic modulator constitute an optical oscillation loop, and the polarization controller, the electro-optic modulator, the polarization beam splitter, the optical coupler, the optical circulator, the photodetector, the microwave amplifier, and the microwave narrowband filter constitute an optical-electrical oscillation loop. In this structure, the optical coupler, the polarization controller, the polarization beam splitter, and the optical circulator constitute a parallel gain-loss channel to realize a parity-time symmetric structure. In this structure, the polarization states of the two polarization controllers are regulated to control the optical power in different polarization states in two directions, so that the gain of the gain loop in the two loops is equal to the loss of the loss loop, so that the system reaches a parity-time symmetry breaking state and the frequency mode in the system is selected.

[0075] Embodiment 3:

[0076] like Figure 4 As shown, the device for simultaneously generating microwave signals and optical pulses in this embodiment includes an erbium-doped fiber amplifier, an optical isolator, an optical filter, an adjustable optical delay line, an optical coupler, a polarization controller, an electro-optic modulator, a polarization beam splitter, a photodetector, a microwave amplifier, a microwave narrowband filter, etc., wherein the erbium-doped fiber amplifier, an optical isolator, an optical filter, an adjustable optical delay line, an optical coupler, a polarization controller, a polarization beam splitter, and an electro-optic modulator constitute an optical oscillation loop, and the electro-optic modulator, an optical coupler, a photodetector, a microwave amplifier, and a microwave narrowband filter constitute an optoelectronic oscillation loop. In this structure, four polarization controllers, polarization beam splitters, and two optical isolators constitute a parallel gain-loss channel to realize a parity-time symmetric optical oscillation loop. In this structure, by regulating the polarization state of the polarization controller, and then controlling the optical power of the two loops in different polarization states, the gain of the gain loop in the two loops is equal to the loss of the loss loop, so that the system reaches a parity-time symmetry breaking state, and the frequency mode in the system is selected.

[0077] Embodiment 4:

[0078] like Figure 5As shown, the device for simultaneously generating microwave signals and optical pulses in this embodiment includes a semiconductor optical amplifier, an optical filter, an optical coupler, a polarization controller, an electro-optic modulator, a polarization beam splitter, a balanced photodetector, a microwave amplifier, a microwave narrowband filter, etc., wherein the semiconductor optical amplifier, the optical filter, the electro-optic modulator, and the optical reflector constitute a Fabry-Perot resonant cavity, and the polarization controller, the electro-optic modulator, the polarization beam splitter, the balanced photodetector, the microwave amplifier, and the microwave narrowband filter constitute a photoelectric oscillation loop. In this structure, the polarization controller, the polarization beam splitter, and the balanced photodetector constitute a parallel gain-loss channel to realize a parity-time symmetric structure. In this structure, by regulating the polarization state of the polarization controller, the optical power of the two loops in different polarization states is controlled, so that the gain of the gain loop in the two loops is equal to the loss of the loss loop, so that the system reaches a parity-time symmetry breaking state, and the frequency mode in the system is selected. Different from various existing coupled optoelectronic oscillator structures, this embodiment further replaces the traditional ring optical oscillator cavity with a linear optical oscillator cavity composed of a Fabry-Perot resonant cavity (FP cavity), an optical amplifier device, and an electro-optical modulator shared with the optoelectronic oscillation loop. Compared with the ring optical oscillation loop, the linear optical resonant cavity can form multi-longitudinal mode optical signals with equal mode intervals by reflecting the light signal amplified in the cavity back and forth, thereby achieving the same effect as the ring optical resonant cavity, and this method has a simpler structure and is more convenient to operate.

[0079] In order to verify the technical effect of the present invention, actual tests were carried out based on the device of Example 1. When the gain loop output optical power is kept unchanged and the loss loop is disconnected, the system is equivalent to a single-loop coupled optoelectronic oscillator (COEO for short), and the microwave signal spectrum output by it is as follows: Figure 6 As shown by the dotted line in the middle, it can be seen that there are many side modes that cannot be filtered out in the system output signal; when the loss loop is connected, the two loops have gain and loss respectively (called PT-COEO). When the polarization controller is adjusted so that the loss in the loss loop is equal to the gain in the gain loop, the loop is in a parity-time symmetry breaking state, and the output microwave signal spectrum is as follows: Figure 6 Indicated by the solid line; Figure 6 The comparison of the mid-frequency spectrum shows that the symmetry breaking state has a good mode selection effect on the output single-frequency signal. When the output optical power of the gain loop is kept unchanged and the loss loop is disconnected, the system is equivalent to a single-loop COEO, and the phase noise spectrum of its output signal is as follows: Figure 7 As shown by the dashed line in the middle; the loss loop is connected. At this time, the two loops have gain and loss respectively (called PT-COEO). When the polarization controller is adjusted so that the loss in the loss loop is equal to the gain in the gain loop, the loop is in a parity-time symmetry breaking state, and the phase noise spectrum of its output signal is as follows: Figure 7As shown by the solid line in the middle, it can be seen that the phase noise of the output signal under PT-COEO is significantly better than the phase noise of the RF signal output by traditional COEO. Figure 8 The output spectrum signal of COEO (i.e. PT-COEO) with parity-time symmetry is shown in Figure 8 It can be seen that the optical frequency comb output by the PT-COEO structure has a wide wavelength distance and a high frequency comb teeth suppression ratio, from which it can be seen that the quality of the optical pulse signal output by the structure is excellent.

Claims

1. A method for simultaneously generating microwave signals and optical pulses, characterized in that: At least one parity-time symmetric structure consisting of a signal gain channel and a signal loss channel which are parallel and have the same signal transmission delay is constructed in at least one of two mutually coupled loops of a coupled optoelectronic oscillator: an optical oscillation loop and a photoelectric oscillation loop, so that a gain oscillation loop and a loss oscillation loop are formed in the loop where the parity-time symmetric structure is located; the signal energy distribution in the parity-time symmetric structure is controlled so that the coupled optoelectronic oscillator reaches a parity-time symmetry breaking state, frequency domain parity-time symmetry is realized in the photoelectric oscillation loop, and time domain parity-time symmetry is realized in the optical oscillation loop, so that the photoelectric oscillation loop outputs a single-frequency microwave signal, and the optical oscillation loop outputs an optical pulse signal, and the frequency of the single-frequency microwave signal is equal to the repetition frequency of the optical pulse signal.

2. The method for simultaneously generating microwave signals and optical pulses according to claim 1, characterized in that: The signal energy distribution in the control parity-time symmetric structure is specifically achieved by adjusting the signal power of the signal gain channel and the signal loss channel so that the gain of the gain oscillation loop is equal to the loss of the loss oscillation loop.

3. The method for simultaneously generating microwave signals and optical pulses according to claim 1 or 2, characterized in that: The parity-time symmetric structure is realized by dividing the optical signal power into two paths and adjusting the power division ratio of the optical power divider.

4. The method for simultaneously generating microwave signals and optical pulses according to claim 1 or 2, characterized in that: The parity-time symmetric structure is realized by dividing the microwave signal power into two paths and adjusting the power division ratio of the two power division signals.

5. The method for simultaneously generating microwave signals and optical pulses according to claim 1 or 2, characterized in that: The parity-time symmetric structure is realized by polarization-division multiplexing an optical signal into two paths with orthogonal polarization states and adjusting the polarization states of the two polarized optical signals.

6. The method for simultaneously generating microwave signals and optical pulses according to claim 1 or 2, characterized in that: The optical oscillation loop is a linear optical oscillation cavity composed of a Fabry-Perot resonant cavity, an optical amplifier device, and an electro-optic modulator shared with the optoelectronic oscillation loop.

7. A device for simultaneously generating microwave signals and optical pulses, characterized in that: The invention comprises a coupled optoelectronic oscillator having two mutually coupled loops: an optical oscillation loop and an optoelectronic oscillation loop. At least one parity-time symmetric structure consisting of a signal gain channel and a signal loss channel which are in parallel and have the same signal transmission delay is constructed in at least one of the optical oscillation loop and the optoelectronic oscillation loop, so that a gain oscillation loop and a loss oscillation loop are formed in the loop where the parity-time symmetric structure is located. The signal energy distribution in the parity-time symmetric structure is configured so that the coupled optoelectronic oscillator can reach a parity-time symmetry breaking state, realize frequency domain parity-time symmetry in the optoelectronic oscillation loop, and realize time domain parity-time symmetry in the optical oscillation loop. Then, the optoelectronic oscillation loop outputs a single-frequency microwave signal, and the optical oscillation loop outputs an optical pulse signal. The frequency of the single-frequency microwave signal is equal to the repetition frequency of the optical pulse signal.

8. The device for simultaneously generating microwave signals and optical pulses as claimed in claim 7, characterized in that: The signal energy distribution in the parity-time symmetric structure is specifically achieved by adjusting the signal power of the signal gain channel and the signal loss channel so that the gain of the gain oscillation loop is equal to the loss of the loss oscillation loop.

9. The device for simultaneously generating microwave signals and optical pulses according to claim 7 or 8, characterized in that: The parity-time symmetric structure is realized by dividing the optical signal power into two paths and adjusting the power division ratio of the optical power divider.

10. The device for simultaneously generating microwave signals and optical pulses according to claim 7 or 8, characterized in that: The parity-time symmetric structure is realized by dividing the microwave signal power into two paths and adjusting the power division ratio of the two power division signals.

11. The device for simultaneously generating microwave signals and optical pulses according to claim 7 or 8, characterized in that: The parity-time symmetric structure is realized by polarization-division multiplexing an optical signal into two paths with orthogonal polarization states and adjusting the polarization states of the two polarized optical signals.

12. The device for simultaneously generating microwave signals and optical pulses according to claim 7 or 8, characterized in that: The optical oscillation loop is a linear optical oscillation cavity composed of a Fabry-Perot resonant cavity, an optical amplifier device, and an electro-optic modulator shared with the optoelectronic oscillation loop.

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