Narrow-linewidth frequency-sweeping photoelectric oscillator and system based on space-time symmetry mechanism

Abstract

The invention relates to a narrow linewidth sweep frequency optoelectronic oscillator and system based on a space-time symmetry mechanism, and relates to the technical field of microwave photons. The narrow linewidth sweep frequency optoelectronic oscillator based on the space-time symmetry mechanism comprises a microwave photonic filter, a first long optical fiber, a second optical coupler, a gain branch, a loss branch, an electric power combiner and a second electric power divider, and the output end of the microwave photonic filter is sequentially connected with the first long optical fiber and the second optical coupler; the microwave photon filter is used for outputting a first optical signal which is obtained by modulating and filtering the initial optical signal and is equivalent to intensity modulation; the first long optical fiber is used for performing delay processing on the first optical signal; the output end of the second optical coupler is respectively connected with the input ends of the gain branch and the loss branch; a gain loop corresponding to the gain branch and a loss loop corresponding to the loss branch meet a space-time symmetry constraint condition; the output ends of the gain branch and the loss branch are connected with the input end of the electric power combiner; the output and division output end of the electric power combiner is connected with the input end of the second electric power divider; the first output end of the second electric power divider outputs a narrow-linewidth sweep frequency signal, and the second output end of the second electric power divider is connected with the input end of the microwave photonic filter to form a closed loop. According to the scheme, the quality of the sweep frequency signal can be improved.

Description

Technical Field

[0001] The present disclosure relates to the field of microwave photon technology, and in particular to a narrow-linewidth swept-frequency optoelectronic oscillator and system based on a parity-time symmetry mechanism. Background Art

[0002] In the related technologies, the traditional method of generating swept-frequency microwave signals is mainly based on pure electronic means, including voltage-controlled oscillators, direct digital synthesis, and digital-to-analog conversion. Due to the technical bottleneck of electronics, it is difficult for electronic components to generate high-frequency and high-stability swept-frequency signals. Thanks to the advantages of microwave photonic technology, such as large bandwidth, low loss, fast reconfiguration, and anti-electromagnetic interference, microwave photonic technology has broken through the technical bottleneck of traditional electronic means, and optoelectronic oscillators can generate swept-frequency signals up to tens of GHz. However, the swept-frequency signal is mainly realized based on microwave photonic filters. Since microwave photonic filters have a bandwidth of tens of MHz, the instantaneous linewidth of the generated swept-frequency signal is wide, which still cannot meet the quality requirements for the narrow instantaneous linewidth of the swept-frequency signal. Summary of the invention

[0003] In order to overcome the problems existing in the related art, the present disclosure provides a narrow linewidth swept-frequency optoelectronic oscillator and system based on a parity-time symmetry mechanism.

[0004] According to a first aspect of an embodiment of the present disclosure, a narrow linewidth swept-frequency optoelectronic oscillator based on a parity-time symmetry mechanism is provided, characterized in that it includes a microwave photon filter, a first long optical fiber, a second optical coupler, a gain branch, a loss branch, an electric power combiner, and a second electric power divider, wherein:

[0005] The output end of the microwave photon filter is connected to the first long optical fiber and the second optical coupler in sequence; the microwave photon filter is used to output a first optical signal equivalent to intensity modulation obtained by modulating and filtering the initial optical signal; the first long optical fiber is used to perform delay processing on the first optical signal;

[0006] The output end of the second optical coupler is connected to the input end of the gain branch and the loss branch respectively; the gain branch, the microwave photon filter, the first long optical fiber, the second optical coupler, the electric power combiner and the second electric power divider form a gain loop, and the loss branch, the microwave photon filter, the first long optical fiber, the second optical coupler, the electric power combiner and the second electric power divider form a loss loop; the gain loop and the loss loop meet the parity-time symmetry constraint condition;

[0007] The output ends of the gain branch and the loss branch are both connected to the input end of the electric combiner;

[0008] The output end of the electric power combiner is connected to the input end of the second electric power divider;

[0009] The first output end of the second electric power divider outputs a swept frequency signal with a narrow line width, and the second output end of the second electric power divider is connected to the input end of the microwave photon filter to form a closed loop.

[0010] According to a second aspect of an embodiment of the present disclosure, a communication system is provided, comprising using the narrow linewidth swept-frequency optoelectronic oscillator based on the parity-time symmetry mechanism described in any one of the first aspects as a microwave source.

[0011] The technical solution provided by the embodiment of the present disclosure may include the following beneficial effects: the output end of the microwave photon filter is connected to the first long optical fiber and the second optical coupler in sequence; the microwave photon filter is used to output the first optical signal equivalent to intensity modulation obtained after modulating and filtering the initial optical signal; the first long optical fiber is used to delay the first optical signal; the output end of the second optical coupler is respectively connected to the input end of the gain branch and the loss branch; the gain loop corresponding to the gain branch and the loss loop corresponding to the loss branch meet the parity-time symmetry constraint condition; the output ends of the gain branch and the loss branch are both connected to the input end of the electric power combiner; the output end of the electric power combiner is connected to the input end of the second electric power divider; the first output end of the second electric power divider outputs a narrow linewidth swept frequency signal, and the second output end of the second electric power divider is connected to the input end of the microwave photon filter to form a closed loop. By introducing a closed loop that meets the parity-time symmetry condition, the side modes in the swept frequency signal are removed, and the swept frequency signal of the single-mode oscillation with the highest gain is retained, so that a swept frequency signal with a narrow instantaneous linewidth can be obtained, and the quality of the swept frequency signal is improved.

[0012] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0014] Figure 1 It is a schematic structural diagram of a narrow linewidth swept-frequency optoelectronic oscillator based on a parity-time symmetry mechanism according to an exemplary embodiment.

[0015] Figure 2 It is a schematic diagram of a swept-frequency signal output by a single-loop swept-frequency photoelectric oscillation according to an embodiment of the present disclosure.

[0016] Figure 3 It is a schematic diagram of a de-chirp signal output by a single-loop swept-frequency optoelectronic oscillator proposed in an embodiment of the present disclosure.

[0017] Figure 4It is a schematic diagram of a sweep signal output by a dual-loop swept-frequency photoelectric oscillation based on parity-time symmetry proposed in an embodiment of the present disclosure.

[0018] Figure 5 It is a schematic diagram of a de-chirped signal output by a dual-loop swept-frequency optoelectronic oscillator under parity-time symmetry proposed in an embodiment of the present disclosure.

[0019] Figure 6 It is a schematic diagram of a narrow linewidth swept frequency signal proposed in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are merely examples of devices and methods consistent with some aspects of the present invention as detailed in the appended claims.

[0021] The terms used in the disclosed embodiments are only for the purpose of describing specific embodiments, and are not intended to limit the disclosed embodiments. The singular forms "a", "an" and "the" used in the disclosed embodiments and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0022] It should be understood that although the terms first, second, third, etc. may be used to describe various information in the disclosed embodiments, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the disclosed embodiments, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the words "if" and "if" as used herein may be interpreted as "at" or "when" or "in response to determination".

[0023] In addition, various forms of processes shown in the embodiments of the present disclosure may be used to reorder, add or delete steps. For example, the steps described in the present application may be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present disclosure can be achieved, and this document does not limit this.

[0024] In the related technologies, the traditional method of generating swept-frequency microwave signals is mainly based on pure electronic means, including voltage-controlled oscillators, direct digital synthesis, and digital-to-analog conversion. Due to the technical bottleneck of electronics, it is difficult for electronic components to generate high-frequency and high-stability swept-frequency signals. Thanks to the advantages of microwave photonic technology, such as large bandwidth, low loss, fast reconfiguration, and anti-electromagnetic interference, microwave photonic technology has broken through the technical bottleneck of traditional electronic means, and optoelectronic oscillators can generate swept-frequency signals up to tens of GHz. However, the swept-frequency signal is mainly realized based on microwave photonic filters. Since microwave photonic filters have a bandwidth of tens of MHz, the instantaneous linewidth of the generated swept-frequency signal is wide, which still cannot meet the quality requirements for the narrow instantaneous linewidth of the swept-frequency signal.

[0025] In order to solve the above problems, the present invention provides a narrow linewidth swept frequency optoelectronic oscillator and system based on the parity-time symmetry mechanism, which are connected to a first long optical fiber and a second optical coupler in sequence through the output end of a microwave photon filter; the microwave photon filter is used to output a first optical signal equivalent to intensity modulation obtained after modulating and filtering an initial optical signal; the first long optical fiber is used to perform delay processing on the first optical signal; the output end of the second optical coupler is respectively connected to the input ends of a gain branch and a loss branch; the gain loop corresponding to the gain branch and the loss loop corresponding to the loss branch meet the parity-time symmetry constraint condition; the output ends of the gain branch and the loss branch are both connected to the input end of an electric power combiner; the output end of the electric power combiner is connected to the input end of a second electric power divider; the first output end of the second electric power divider outputs a narrow linewidth swept frequency signal, and the second output end of the second electric power divider is connected to the input end of the microwave photon filter to form a closed loop. By introducing a closed loop that satisfies the parity-time symmetry condition, the side modes of the swept frequency signal are removed and the swept frequency signal of the single-mode oscillation with the highest gain is retained, so that a swept frequency signal with a narrow instantaneous linewidth can be obtained, thereby improving the quality of the swept frequency signal.

[0026] Figure 1 is a schematic structural diagram of a narrow linewidth swept-frequency optoelectronic oscillator based on a parity-time symmetry mechanism according to an exemplary embodiment, such as Figure 1 As shown, it should be noted that the narrow linewidth swept-frequency optoelectronic oscillator based on the parity-time symmetry mechanism of the embodiment of the present disclosure can be applied to communication systems.

[0027] like Figure 1 As shown, the narrow linewidth swept-frequency optoelectronic oscillator based on the parity-time symmetry mechanism includes a microwave photon filter, a first long optical fiber, a second optical coupler, a gain branch, a loss branch, an electric power combiner and a second electric power divider, wherein:

[0028] The output end of the microwave photon filter is connected to the first long optical fiber and the second optical coupler in sequence; the microwave photon filter is used to output a first optical signal equivalent to intensity modulation obtained after modulating and filtering the initial optical signal; the first long optical fiber is used to perform delay processing on the first optical signal;

[0029] The output end of the second optical coupler is connected to the input end of the gain branch and the input end of the loss branch respectively;

[0030] The gain branch, the microwave photon filter, the first long optical fiber, the second optical coupler, the electric power combiner and the second electric power divider form a gain loop, and the loss branch, the microwave photon filter, the first long optical fiber, the second optical coupler, the electric power combiner and the second electric power divider form a loss loop; the gain loop and the loss loop satisfy the parity-time symmetry constraint condition;

[0031] The output ends of the gain branch and the loss branch are both connected to the input end of the electric combiner;

[0032] The output end of the electric power combiner is connected to the input end of the second electric power divider;

[0033] The first output end of the second electric power divider outputs a swept frequency signal with a narrow line width, and the second output end of the second electric power divider is connected to the input end of the microwave photon filter to form a closed loop.

[0034] In some embodiments of the present disclosure, the first optical coupler is an optical coupler that divides the power of an optical signal into two equal parts for output.

[0035] In one example, the notch filter may be a filter with a 3 dB bandwidth of tens of MHz, and may be any one of a phase-shifted fiber Bragg grating, a microring resonator, a Fabry-Perot cavity, a gas absorption cell, or an optical filter based on stimulated Brillouin scattering effect.

[0036] In one embodiment, the first long optical fiber is used to delay the transmission of the modulated signal output by the microwave photon filter; the second optical coupler divides the optical signal into two paths with equal power, and inputs them into the gain branch and the loss branch respectively. The loops corresponding to the gain branch and the loss branch, that is, the gain loop and the loss loop, meet the conditions required for parity-time symmetry by adjusting the delay line and the optical attenuator; the electric power combiner is used to combine the two electrical signals output by the gain branch and the loss branch into one output; the second electric power divider is used to divide the electrical signal output by the electric power combiner into two parts, one part is used as the output, and the other part is fed back to the phase modulator to form a closed loop of the optoelectronic oscillator.

[0037] In some embodiments of the present disclosure, the parity-time symmetry constraint conditions include: the signal transmission period of the gain loop and the loss loop are the same, and the net gain value of the gain loop is equal to the net loss value of the loss loop, and is greater than or equal to the loop cavity coupling coefficient corresponding to the gain loop and the loss loop.

[0038] In some embodiments of the present disclosure, the net gain value is the difference between the optical signal power value of the gain loop and the oscillation threshold of the gain loop; the net loss value is the difference between the oscillation threshold of the loss and the optical signal power value of the loss loop.

[0039] As an example, the conditions that must be satisfied for parity-time symmetry based on are:

[0040] T g =T Y

[0041] I g -I 01 =I 02 -I γ

[0042] Among them, I g is the optical signal power of the optoelectronic oscillator gain loop, I 01 is the oscillation threshold of the optoelectronic oscillator gain loop, I γ is the optical signal power of the optoelectronic oscillator gain loop, I 02 is the oscillation threshold of the optoelectronic oscillator gain loop, I g -I 01 Represents the net gain value, I 02 -I γ Indicates the net loss value.

[0043] In one example, the physical properties of the components used in the gain loop and the loss loop can be ensured to be almost the same, so as to ensure that the transmission period T of the signal in the two loops is g =T γ , and ensure that the oscillation thresholds of the gain loop and the loss loop are equal.

[0044] In addition, if there is a slight difference in the transmission period of the gain loop and the loss loop of the order of ps or in the loop length of the order of mm, it will not affect the implementation result.

[0045] It should be noted that the oscillation threshold is the optical power input to the photodetector measured when the gain loop and the loss loop are just about to oscillate and generate a microwave signal.

[0046] In addition, in the optoelectronic oscillator, the center frequency of the signal is the main mode of oscillation or the mode with the highest gain, referred to as the main mode. In the frequency domain of the signal, a mode will appear at every inverse of the ring cavity period. These modes are called side modes, referred to as side modes. In the optoelectronic oscillator, the main mode and the side mode will oscillate simultaneously, which results in a wider 3dB bandwidth or instantaneous linewidth of the signal.

[0047] In addition, the coupling coefficient is the coupling coefficient between the loop cavity of the gain loop and the loss loop, which is a fixed value determined by the system structure and will not change with changes in system parameters.

[0048] Therefore, when the net gain value and the net loss value are both smaller than the coupling coefficient of the two loop cavities (that is, the loop cavity of the gain loop and the loop cavity of the loss loop), the oscillation mode will split, that is, the main mode and the side mode will appear, that is, two oscillation signals with close frequencies will appear at the same time; when the net gain value and the net loss value are both equal to the coupling coefficient of the two loop cavities, it is a transition point for the split oscillation mode to be converted into a main oscillation mode; when the net gain value and the net loss value are both greater than the coupling coefficient of the two loop cavities, paired amplification and attenuation modes will be generated in each cavity, and the amplification mode passes through the transition point to break the parity-time symmetry and oscillate, and other oscillation modes will be suppressed, which plays a role in mode selection. In the amplification mode, only the mode oscillation with the highest gain is retained, and finally the instantaneous single-mode oscillation of the swept frequency signal is realized, so that a swept frequency signal with a narrow instantaneous linewidth can be obtained, thereby improving the quality of the swept frequency signal.

[0049] For example, Figure 2 It is a swept frequency signal within one cycle of the swept frequency optoelectronic oscillator output in the traditional mode (i.e. single loop). Since the bandwidth of the microwave photon filter in the swept frequency optoelectronic oscillator is tens or even hundreds of MHz, multiple modes will oscillate simultaneously in the system at any time, which leads to a wider instantaneous linewidth of the swept frequency signal. Figure 3 The de-chirped signal is output by a conventional single-loop swept-frequency optoelectronic oscillator, and its frequency is f0. It can be observed that the 3dB bandwidth of the signal is relatively wide (the 3dB bandwidth is the width of the signal after the peak value of the signal power drops by 3dB).

[0050] Figure 4 It is a frequency sweep signal within one cycle of the dual-loop (including gain loop and loss loop) frequency sweep photoelectric oscillation output based on parity-time symmetry. Since parity-time symmetry has a mode selection effect, it selects the oscillation mode with the highest gain, that is, suppresses the oscillation of other modes, so that the frequency sweep signal has a narrower instantaneous linewidth. Figure 5 The dual-loop frequency-swept optoelectronic oscillator under parity-time symmetry is Figure 1The de-chirped signal (that is, the single-frequency difference frequency signal proposed in some embodiments of the present disclosure) outputted by output 2 corresponding to the midpoint mixer has a frequency of f0, and it can be observed that the 3dB bandwidth of the signal is relatively narrow (the 3dB bandwidth is the width of the signal after the peak value of the signal power drops by 3dB).

[0051] In some embodiments of the present disclosure, the frequency sweep period T of the microwave photon filter is s The delay T of the gain loop g and the loss loop delay T γ corresponding;

[0052] Among them, T s , T g and T γ The following Fourier domain mode locking conditions are met:

[0053] N*T s =T g =T γ (N∈N+)

[0054] Where N is a positive integer, T s is the frequency sweep period of the microwave photon filter, T s The same as the sweep period of the swept laser, T g T is the time it takes for the signal to propagate through the gain loop. γ The time it takes for a signal to travel around a lossy loop.

[0055] In some embodiments of the present disclosure, the microwave photon filter includes a swept-frequency laser, a phase modulator, and a notch filter, wherein the swept-frequency laser is connected to the first input end of the phase modulator and the notch filter in sequence; the swept-frequency laser is used to output an initial optical signal; the second input end of the phase modulator is connected to the second output end of the second electric power divider; the phase modulator is used to modulate the initial optical signal with the narrow linewidth swept-frequency signal output by the second electric power divider to obtain a modulated signal including a positive-order sideband and a negative-order sideband of the swept-frequency optical carrier; the notch filter is used to filter out any one of the positive-order sideband and the negative-order sideband to obtain an optical signal equivalent to an intensity modulated signal; and the output end of the notch filter is connected to the first long optical fiber.

[0056] It should be noted that the speed of the time-frequency variation of the swept signal output by the narrow-linewidth swept optoelectronic oscillator based on the parity-time symmetry mechanism is determined by the sweep speed of the swept laser, and the phase of the swept signal is continuous.

[0057] In one example, the center frequency of the microwave photonic filter is equal to the difference between the optical carrier of the swept laser and the center frequency of the notch filter.

[0058] It can be understood that the swept-frequency laser is used to generate an initial optical signal of continuous frequency; the phase modulator is used to modulate the swept-frequency optical signal (that is, the initial optical signal) generated by the swept-frequency laser and the electrical signal output by the second electrical power divider to generate a modulated signal including a swept-frequency optical carrier, a positive-order sideband and a negative-order sideband; the notch filter is used to filter out any one of the positive-order sideband and the negative-order sideband of the modulated signal output by the phase modulator, and output an optical signal equivalent to intensity modulation, thereby realizing the conversion from phase modulation to intensity modulation.

[0059] In some embodiments of the present disclosure, the bandwidth of the swept frequency signal is tuned by adjusting the swept frequency range of the swept frequency laser.

[0060] In some embodiments of the present disclosure, the center frequency of the swept frequency signal is tuned by adjusting the center wavelength of the swept frequency laser.

[0061] In some embodiments of the present disclosure, the microwave photonic filter further includes a polarization controller, wherein the polarization controller is connected to a line between the frequency-sweeping laser and the phase modulator to adjust the polarization state of the initial optical signal.

[0062] It should be noted that the polarization controller is used to adjust the polarization state of the initial optical signal so as to minimize the optical polarization loss of the initial optical signal reaching the phase modulator.

[0063] In some embodiments of the present disclosure, the gain branch includes a first adjustable optical attenuator, a first adjustable delay line, and a first photodetector, and the loss branch includes a second adjustable optical attenuator, a second adjustable delay line, and a second photodetector, wherein:

[0064] An input end of the first adjustable optical attenuator is connected to a first output end of the second optical coupler;

[0065] An output end of the first adjustable optical attenuator is connected in sequence to a first adjustable delay line, a first photodetector and a first input end of the electric combiner;

[0066] An input end of the second adjustable optical attenuator is connected to a second output end of the second optical coupler;

[0067] The output end of the second adjustable optical attenuator is connected to the second adjustable delay line, the second photodetector and the second input end of the electric combiner in sequence; the delay corresponding to the first adjustable delay line is the same as the delay corresponding to the second adjustable delay line.

[0068] In one embodiment, the conditions required for parity-time symmetry can be met by adjusting the first adjustable delay line, the second adjustable delay line, the first adjustable optical attenuator, and the second adjustable optical attenuator.

[0069] In some embodiments of the present disclosure, the second optical coupler is an optical coupler that divides the power of the optical signal into two equal parts for output.

[0070] In some embodiments of the present disclosure, the narrow linewidth swept-frequency optoelectronic oscillator based on the parity-time symmetry mechanism further includes a first optical coupler and a first electrical power divider, wherein:

[0071] The first optical coupler is connected to the line between the first long optical fiber and the second optical coupler;

[0072] An output end of the first optical coupler is connected to the second long optical fiber, the third photodetector and the input end of the electric mixer in sequence; the first long optical fiber and the second long optical fiber have different lengths;

[0073] The first electric power divider is connected to the line between the electric power combiner and the second electric power divider, and an output end of the first electric power divider is connected to the input end of the electric mixer; the output end of the electric mixer outputs a single-frequency difference frequency signal for displaying the instantaneous linewidth characteristics of the swept frequency signal.

[0074] In one example, both the first long optical fiber and the second long optical fiber may be energy storage elements with a loss as low as 0.2 dB / km.

[0075] In one embodiment of the present disclosure, a first optical coupler divides an optical signal into two paths of equal power, one of which is an oscillation loop of an optoelectronic oscillator, and the other enters a second long optical fiber. The optical signal is converted into a swept-frequency microwave signal by a third photodetector, and enters an electrical mixer together with the swept-frequency microwave signal from the first electrical power divider. The two signals experience different time delays, and the electrical mixer outputs a single-frequency difference frequency signal or a de-chirped signal. This process is a de-chirp process, and the instantaneous linewidth characteristics of the swept-frequency signal can be reflected by observing the linewidth of the single-frequency de-chirped signal (that is, the above-mentioned single-frequency difference frequency signal).

[0076] It can be understood that the line width of the chirp signal will directly reflect the instantaneous characteristics of the swept frequency signal. The narrower the measured line width of the de-chirp signal is, the narrower the instantaneous line width of the swept frequency signal is, and the better the quality of the swept frequency signal is.

[0077] It should be noted that de-chirping refers to removing the chirp effect of a signal. Chirp is a term in communication technology, which refers to the linear increase or decrease of the carrier frequency of a signal within the duration of a pulse. This effect causes the frequency of the signal to change. The process of de-chirping is to adjust the signal through specific technical means to keep its frequency stable and eliminate frequency changes.

[0078] For example, if Figure 6 As shown, Figure 6 The solid line in Figure 1The difference between the start frequency and the end frequency of the sweep signal output by output 1 is the sweep signal bandwidth B, and the period of the sweep signal is T, which is equal to the ring cavity delay time. After the sweep signal passes through the second longest optical fiber, the delay time is △t, such as Figure 6 The electrical mixer mixes the solid sweep signal in the loop with the dashed sweep signal that passes through the second long optical fiber. Figure 1 The output port 2 outputs two difference frequency signals after mixing, with frequencies f1 and f2 respectively. The frequency of f1 can be expressed as BΔt / T, and the frequency of f2 can be expressed as B(T-△t) / T.

[0079] In some embodiments of the present disclosure, the narrow linewidth swept-frequency optoelectronic oscillator based on the parity-time symmetry mechanism further includes an optical amplifier, wherein the optical amplifier is connected to the line between the microwave photon filter and the first long optical fiber.

[0080] In one embodiment, the optical amplifier may be any one of a semiconductor optical amplifier and a fiber amplifier, and the optical amplifier is used to compensate for the loss of the optoelectronic oscillator loop to reduce the difficulty of system oscillation starting.

[0081] In some embodiments of the present disclosure, the narrow linewidth swept-frequency optoelectronic oscillator based on the parity-time symmetry mechanism further includes an electrical amplifier, wherein:

[0082] The electric amplifier is connected to the line between the electric power combiner and the second electric power divider; or,

[0083] The electric amplifier is connected to an output terminal of the second electric power divider.

[0084] In some embodiments of the present disclosure, the first adjustable optical attenuator and the second adjustable optical attenuator have the same structure and performance; the first photodetector and the second photodetector have the same structure and performance; the first adjustable delay line and the second adjustable delay line have the same structure and performance.

[0085] In some embodiments of the present disclosure, a narrow linewidth swept-frequency optoelectronic oscillator based on a parity-time symmetric mechanism can be applied to radar detection or communication systems.

[0086] According to the narrow linewidth swept frequency optoelectronic oscillator of the parity-time symmetry mechanism proposed in the embodiment of the present disclosure, the output end of the microwave photon filter is connected to the first long optical fiber and the second optical coupler in sequence; the microwave photon filter is used to output the first optical signal equivalent to intensity modulation obtained after modulating and filtering the initial optical signal; the first long optical fiber is used to delay the first optical signal; the output end of the second optical coupler is respectively connected to the input ends of the gain branch and the loss branch; the gain loop corresponding to the gain branch and the loss loop corresponding to the loss branch meet the parity-time symmetry constraint condition; the output ends of the gain branch and the loss branch are both connected to the input end of the electric power combiner; the output end of the electric power combiner is connected to the input end of the second electric power divider; the first output end of the second electric power divider outputs a narrow linewidth swept frequency signal, and the second output end of the second electric power divider is connected to the input end of the microwave photon filter to form a closed loop. By introducing a closed loop that satisfies the parity-time symmetry condition, the side modes of the frequency sweep signal are removed, and the frequency sweep signal of the single-mode oscillation with the highest gain is retained, so that a frequency sweep signal with a narrow instantaneous line width can be obtained, and the quality of the frequency sweep signal is improved. The present invention generates a frequency sweep microwave signal with a narrow line width and tunable bandwidth and frequency without the need for high-frequency electronic devices. The present invention can be used as a high-quality microwave signal source, can be used in radar detection and communication systems, and can improve the accuracy of radar detection.

[0087] In a second aspect, the present disclosure further provides a communication system, which uses the narrow linewidth swept-frequency optoelectronic oscillator based on the parity-time symmetry mechanism described in any of the above embodiments as a swept-frequency microwave signal source.

[0088] In the foregoing description of the embodiments, the description with reference to the terms "one embodiment", "an implementation", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0089] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present disclosure, "plurality" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0090] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present disclosure is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed in the present disclosure. The description and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0091] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism, characterized in that: The device comprises a microwave photon filter, a first long optical fiber, a second optical coupler, a gain branch, a loss branch, an electric power combiner and a second electric power divider, wherein: The output end of the microwave photon filter is connected to the first long optical fiber and the second optical coupler in sequence; the microwave photon filter is used to output a first optical signal equivalent to intensity modulation obtained by modulating and filtering the initial optical signal; the first long optical fiber is used to perform delay processing on the first optical signal; The output end of the second optical coupler is connected to the input end of the gain branch and the loss branch respectively; the gain branch, the microwave photon filter, the first long optical fiber, the second optical coupler, the electric power combiner and the second electric power divider form a gain loop, and the loss branch, the microwave photon filter, the first long optical fiber, the second optical coupler, the electric power combiner and the second electric power divider form a loss loop; the gain loop and the loss loop meet the parity-time symmetry constraint condition; The output ends of the gain branch and the loss branch are both connected to the input end of the electric combiner; The output end of the electric power combiner is connected to the input end of the second electric power divider; The first output end of the second electric power divider outputs a swept frequency signal with a narrow line width, and the second output end of the second electric power divider is connected to the input end of the microwave photon filter to form a closed loop.

2. The narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism according to claim 1, characterized in that: The microwave photon filter includes a frequency-sweeping laser, a phase modulator, and a notch filter, wherein: The frequency sweeping laser is connected to the first input end of the phase modulator and the notch filter in sequence; the frequency sweeping laser is used to output the initial optical signal; The second input end of the phase modulator is connected to the second output end of the second electric power divider; the phase modulator is used to modulate the initial optical signal with the narrow linewidth swept frequency signal output by the second electric power divider to obtain a modulated signal including a positive-order sideband and a negative-order sideband of the swept frequency optical carrier; the notch filter is used to filter out any one of the positive-order sideband and the negative-order sideband to obtain an optical signal equivalent to an intensity modulated signal; The output end of the notch filter is connected to the first long optical fiber.

3. The narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism according to claim 1, characterized in that: The gain branch includes a first adjustable optical attenuator, a first adjustable delay line, and a first photodetector, and the loss branch includes a second adjustable optical attenuator, a second adjustable delay line, and a second photodetector, wherein: The input end of the first adjustable optical attenuator is connected to the first output end of the second optical coupler; The output end of the first adjustable optical attenuator is connected to the first adjustable delay line, the first photodetector and the first input end of the electric combiner in sequence; The input end of the second adjustable optical attenuator is connected to the second output end of the second optical coupler; The output end of the second adjustable optical attenuator is connected to the second adjustable delay line, the second photodetector and the second input end of the electric combiner in sequence; the delay corresponding to the first adjustable delay line is the same as the delay corresponding to the second adjustable delay line.

4. The narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism according to claim 1, characterized in that: The parity-time symmetry constraint condition includes: the signal transmission period of the gain loop is the same as that of the loss loop, and the net gain value of the gain loop is equal to the net loss value of the loss loop, and is greater than or equal to the loop cavity coupling coefficient corresponding to the gain loop and the loss loop.

5. The narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism according to claim 4, characterized in that: The net gain value is the difference between the optical signal power value of the gain loop and the oscillation threshold of the gain loop; the net loss value is the difference between the oscillation threshold of the loss and the optical signal power value of the loss loop.

6. The narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism according to claim 1, characterized in that: It also includes a first optical coupler and a first electric power divider, wherein: The first optical coupler is connected to the line between the first long optical fiber and the second optical coupler; An output end of the first optical coupler is connected to the second long optical fiber, the third photodetector and the input end of the electric mixer in sequence; the first long optical fiber and the second long optical fiber have different lengths; The first electric power divider is connected to the line between the electric power combiner and the second electric power divider, and an output end of the first electric power divider is connected to the input end of the electric mixer; the output end of the electric mixer outputs a single-frequency difference frequency signal for displaying the instantaneous linewidth characteristics of the swept frequency signal.

7. The narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism according to claim 1, characterized in that: The microwave photon filter further comprises a polarization controller, wherein: The polarization controller is connected to the line between the frequency-sweeping laser and the phase modulator to adjust the polarization state of the initial optical signal.

8. The narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism according to claim 1, characterized in that: Also included is an optical amplifier, wherein The optical amplifier is connected to the line between the microwave photon filter and the first long optical fiber.

9. The narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism according to claim 1, characterized in that: Also included is an electrical amplifier, wherein The electric amplifier is connected to the line between the electric power combiner and the second electric power divider; or, The electric amplifier is connected to an output end of the second electric power divider.

10. The narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism according to claim 3, characterized in that: The first adjustable optical attenuator and the second adjustable optical attenuator have the same structure and performance; the first photodetector and the second photodetector have the same structure and performance; the first adjustable delay line and the second adjustable delay line have the same structure and performance.

11. The narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism according to claim 1, characterized in that: The frequency sweep period T of the microwave photon filter s The delay T of the gain loop g and the delay T of the loss loop γ corresponding; Among them, T s , T g and T γ The following Fourier domain mode locking conditions are met: N*T s =T g =T γ (N∈N+) Where N is a positive integer, T s is the frequency sweep period of the microwave photon filter, T s The same as the sweep period of the swept laser, T g T is the time it takes for the signal to propagate through the gain loop. γ It is the time it takes for the signal to propagate once in the lossy loop.

12. The narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism according to claim 1, characterized in that: The bandwidth of the frequency sweeping signal is tuned by adjusting the frequency sweeping range of the frequency sweeping laser.

13. The narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism according to claim 1, characterized in that: The center frequency of the frequency sweeping signal is tuned by adjusting the center wavelength of the frequency sweeping laser.

14. The narrow linewidth swept-frequency optoelectronic oscillator based on parity-time symmetry mechanism according to claim 3, characterized in that: The first optical coupler and the second optical coupler are both optical couplers that equally divide the optical signal power into two parts for output.

15. A communication system, characterized in that: The invention comprises adopting the narrow linewidth swept frequency optoelectronic oscillator based on the parity-time symmetry mechanism as claimed in any one of claims 1 to 14 as a microwave source.

Images