Narrow linewidth swept photo-oscillator and system based on parity-time symmetry mechanism

Abstract

The present disclosure relates to a narrow-line-width swept photoelectric oscillator and system based on the time-reversal symmetry mechanism, and relates to the field of microwave photonics. The narrow-line-width swept photoelectric oscillator based on the time-reversal symmetry mechanism comprises a microwave photonics filter, a first long optical fiber, a second optical coupler, a gain branch, a loss branch, an electrical combiner, and a second electrical power divider. The output end of the microwave photonics filter is connected with the first long optical fiber and the second optical coupler in sequence. The microwave photonics filter is used to output a first optical signal which is equivalent to an intensity-modulated signal 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 connected with the input end of the gain branch and the loss branch, respectively. The gain loop corresponding to the gain branch and the loss loop corresponding to the loss branch satisfy the time-reversal symmetry constraint condition. The output end of the gain branch and the loss branch is connected with the input end of the electrical combiner. The output end of the electrical combiner is connected with the input end of the second electrical power divider. The first output end of the second electrical power divider outputs a narrow-line-width swept signal. The second output end of the second electrical power divider is connected with the input end of the microwave photonics filter, forming a closed loop. The present scheme can improve the quality of the swept signal.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of microwave photonics, and in particular to a narrow linewidth swept optical-electrical oscillator and system based on the mechanism of time-reversal symmetry. BACKGROUND

[0002] In the related art, the generation of a conventional swept microwave signal is mainly based on pure electronic means, including a voltage-controlled oscillator, direct digital synthesis, digital-to-analog conversion, etc. Due to the technical bottleneck of electronics, it is difficult for electronic components to generate a high-frequency and high-stability swept signal. Thanks to the advantages of microwave photonics, such as large bandwidth, low loss, fast reconfigurability, and anti-electromagnetic interference, microwave photonics has broken through the technical bottleneck of traditional electronic means, and an optical-electrical oscillator can generate a swept signal of up to several tens of GHz. However, the swept signal is mainly realized based on a microwave photonics filter. Since the microwave photonics filter has a bandwidth of several tens of MHz, the instantaneous linewidth of the generated swept signal is relatively wide, and it still cannot meet the quality requirements for narrow instantaneous linewidth of the swept signal. SUMMARY

[0003] To overcome the problems in the related art, the present disclosure provides a narrow linewidth swept optical-electrical oscillator and system based on the mechanism of time-reversal symmetry.

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

[0005] The output end of the microwave photonics filter is connected with the first long optical fiber and the second optical coupler in sequence; the microwave photonics filter is configured to output a first optical signal which is equivalent to intensity modulation after modulating and filtering an initial optical signal; and the first long optical fiber is configured to perform delay processing on the first optical signal.

[0006] The output end of the second optical coupler is connected with the input end of the gain branch and the loss branch, respectively; the gain branch and the loss branch, together with the microwave photonics filter, the first long optical fiber, the second optical coupler, the electrical combiner, and the second electrical power divider, form a gain loop and a loss loop, respectively; and the gain loop and the loss loop satisfy a time-reversal symmetry constraint condition.

[0007] The output end of the gain branch and the loss branch is connected with the input end of the electrical combiner.

[0008] The output end of the electrical combiner is connected with the input end of the second electrical power divider.

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

[0010] According to a second aspect of the embodiments of the present disclosure, a communication system is provided, which comprises the narrow line width sweep optoelectronic oscillator based on the time-reversal symmetry mechanism as the microwave source.

[0011] The technical scheme provided by the embodiments of the present disclosure can have the following beneficial effects: the output end of the microwave photon filter is connected with a first long optical fiber and a second optical coupler in sequence; the microwave photon filter is used to output a first optical signal which is equivalent to intensity modulation after the initial optical signal is modulated and filtered; 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 with the input end of a gain branch and a loss branch respectively; the gain loop corresponding to the gain branch and the loss loop corresponding to the loss branch satisfy a time-reversal symmetry constraint condition; the output end of the gain branch and the output end of the loss branch are connected with the input end of an electric power combiner; the output end of the electric power combiner is connected with the input end of a second electric power divider; the first output end of the second electric power divider outputs a narrow line width sweep signal, and the second output end of the second electric power divider is connected with the input end of the microwave photon filter to form a closed loop. By introducing the closed loop satisfying the time-reversal symmetry condition, the side mode in the sweep signal is removed, the sweep signal of the single mode oscillation with the highest gain is reserved, and thus a sweep signal with a relatively narrow instantaneous line width can be obtained, and the quality of the sweep signal is improved.

[0012] It should be understood that the foregoing general description and the following detailed description are only exemplary and explanatory, and cannot limit the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0013] The accompanying drawings, which are incorporated into and form part of the specification, illustrate an embodiment consistent with the present disclosure and, together with the specification, serve to explain the principles of the present disclosure.

[0014] Figure 1 FIG. 1 is a structural schematic diagram of a narrow line width sweep optoelectronic oscillator based on a time-reversal symmetry mechanism according to an exemplary embodiment.

[0015] Figure 2 FIG. 2 is a schematic diagram of a sweep signal output by a single loop sweep optoelectronic oscillator according to an embodiment of the present disclosure.

[0016] Figure 3 FIG. 3 is a schematic diagram of a de-chirped signal output by a single loop sweep optoelectronic oscillator according to an embodiment of the present disclosure.

[0017] Figure 4is a schematic diagram of a sweep signal output by a double-loop sweep photoelectric oscillator based on time-reversal symmetry according to an embodiment of the present disclosure.

[0018] Figure 5 is a schematic diagram of a dechirped signal output by a double-loop sweep photoelectric oscillator under time-reversal symmetry according to an embodiment of the present disclosure.

[0019] Figure 6 is a schematic diagram of a sweep signal with a narrow linewidth according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] The illustrative examples described herein will be explained more fully with reference to the accompanying drawings, in which specific details of certain embodiments are shown. However, specific structural and functional details disclosed herein are not to be interpreted as limiting but merely as a representative basis for teaching one skilled in the art to variously employ the present application. As such, the terms "exemplary," and / or "illustrative" used throughout this detailed description, specify and describe possible embodiments only and should not be construed as limiting the scope of the present disclosure.

[0021] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0022] It will be understood that, although the terms first, second, third, etc. can be used herein to describe various information, the information should not be limited by these terms. These terms are only used to distinguish one piece of information from another. For example, a first information could be termed a second information, and, similarly, a second information could be termed a first information without departing from the scope of the present disclosure. As used herein, the term "if' can be construed to mean "when" or "upon" or "in response to determining" terms that indicate a sufficiency of a certain condition.

[0023] Moreover, the steps recited in the various forms of flow diagrams shown in the present disclosure can be reordered, added, or removed. For example, the steps recited in the present disclosure can be executed in parallel, in series, or in a different order, as long as the desired results of the present disclosure are achieved, and the present disclosure is not limited herein.

[0024] In the related art, the generation of a traditional swept microwave signal is mainly based on pure electronic means, including voltage-controlled oscillators, direct digital synthesis, digital-to-analog conversion, etc. Due to the technical bottleneck of electronics, it is difficult for electronic components to generate a high-frequency and high-stability swept signal. Thanks to the advantages of microwave photonics, such as large bandwidth, low loss, fast reconfigurability, and anti-electromagnetic interference, microwave photonics has broken through the technical bottleneck of traditional electronics, and an optoelectronic oscillator can generate a swept signal of up to several tens of GHz. However, the swept signal is mainly realized based on a microwave photonics filter. Since the microwave photonics filter has a bandwidth of several tens of MHz, the instantaneous linewidth of the generated swept signal is relatively wide, and it still cannot meet the quality requirements for narrow instantaneous linewidth of the swept signal.

[0025] To solve the above problems, the present disclosure provides a narrow-linewidth swept optoelectronic oscillator and system based on the time-reversal symmetry mechanism. The output end of the microwave photonics filter is connected with the first long optical fiber and the second optical coupler in sequence. The microwave photonics filter is used to output the first optical signal which is equivalent to intensity modulation after 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 with the input end of the gain branch and the loss branch respectively. The gain loop corresponding to the gain branch and the loss loop corresponding to the loss branch satisfy the time-reversal symmetry constraint condition. The output ends of the gain branch and the loss branch are connected with the input end of the electrical combiner. The output end of the electrical combiner is connected with the input end of the second electrical power divider. The first output end of the second electrical power divider outputs the narrow-linewidth swept signal, and the second output end of the second electrical power divider is connected with the input end of the microwave photonics filter, forming a closed loop. By introducing the closed loop satisfying the time-reversal symmetry condition, the side mode of the swept signal is removed, the single-mode oscillation swept signal with the highest gain is retained, and thus a swept signal with a relatively narrow instantaneous linewidth can be obtained, thereby improving the quality of the swept signal.

[0026] Figure 1 FIG. 1 is a structural schematic diagram of a narrow-linewidth swept optoelectronic oscillator based on the time-reversal symmetry mechanism according to an example embodiment. As shown in FIG. 1, it should be noted that the narrow-linewidth swept optoelectronic oscillator based on the time-reversal symmetry mechanism in the embodiment of the present disclosure can be applied to a communication system. Figure 1

[0027] As shown in FIG. 1, the narrow-linewidth swept optoelectronic oscillator based on the time-reversal symmetry mechanism includes a microwave photonics filter, a first long optical fiber, a second optical coupler, a gain branch, a loss branch, an electrical combiner, and a second electrical power divider. Figure 1

[0028] ​​The output end of the microwave photon filter is connected with the first long optical fiber and the second optical coupler in sequence; the microwave photon filter is used for outputting a first optical signal which is equivalent to intensity modulation after the initial optical signal is modulated and filtered; and the first long optical fiber is used for performing delay processing on the first optical signal.

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

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

[0031] The output end of the gain branch and the loss branch is connected with the input end of the electrical coupler.

[0032] The output end of the electrical coupler is connected with the input end of the second electrical power divider.

[0033] The first output end of the second electrical power divider outputs a narrow-line-width sweep signal, and the second output end of the second electrical power divider is connected with the input end of the microwave photon filter, thereby constituting a closed loop.

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

[0035] In one example, the notch filter can be a filter with a 3dB bandwidth of tens of MHz, and can be any one of a phase-shifted fiber Bragg grating, a micro-ring 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 for performing delay processing on 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 the two paths into the gain branch and the loss branch respectively; the gain branch and the loss branch each correspond to a loop, i.e., the gain loop and the loss loop, which are adjusted by a delay line and an optical attenuator to meet the required conditions of parity-time symmetry; the electrical coupler is used for synthesizing two electrical signals output by the gain branch and the loss branch into one output; and the second electrical power divider is used for dividing the electrical signal output by the electrical coupler into two parts, one part being output and the other part being fed back to the phase modulator, thereby constituting a closed loop of the optoelectronic oscillator.

[0037] In some embodiments of the present disclosure, the parity-time symmetry constraint condition comprises: 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.

[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 value of the gain loop; and the net loss value is the difference between the oscillation threshold value of the loss loop and the optical signal power value of the loss loop.

[0039] As an example, the condition to be satisfied based on the parity-time symmetry is:

[0040]

[0041]

[0042] wherein, is the optical signal power value of the gain loop of the optoelectronic oscillator, is the oscillation threshold value of the gain loop of the optoelectronic oscillator, is the optical signal power value of the gain loop of the optoelectronic oscillator, is the oscillation threshold value of the gain loop of the optoelectronic oscillator, represents the net gain value, represents the net loss value.

[0043] In an example, the physical properties of the devices used in the gain loop and the loss loop can be ensured to be almost the same, so as to ensure that the signal transmission period of the gain loop is the same as that of the loss loop , and the oscillation threshold value of the gain loop is equal to that of the loss loop.

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

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

[0046] In addition, in the optoelectronic oscillator, the center frequency of the signal is the main mode or the mode with the highest gain, which is referred to as the main mode. In the frequency domain of the signal, there is a mode every interval of the reciprocal of the loop cavity period, which is referred to as the side mode. In the optoelectronic oscillator, the main mode and the side mode oscillate at the same time, which leads to a relatively wide 3dB bandwidth or instantaneous linewidth of the signal.

[0047] In addition, the coupling coefficient is a coupling coefficient between the loop cavity of the gain loop and the loop cavity of the loss loop, is a fixed value, and does not change with the change of system parameters.

[0048] Therefore, when the net gain value and the net loss value are both less than the coupling coefficient of the two loop cavities (i.e., the loop cavity of the gain loop and the loop cavity of the loss loop), splitting of the oscillation mode occurs, that is, the main mode and the side mode occur simultaneously, that is, two frequency close oscillation signals occur simultaneously; when the net gain value and the net loss value are both equal to the coupling coefficient of the two loop cavities, the transition point from the split oscillation mode to the 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, a pair of amplification and attenuation modes are generated in each cavity, the amplification mode passes through the transition point to break the parity-time symmetry and oscillate, and other oscillation modes are suppressed, thereby playing a mode selection role. In the amplified mode, only the mode with the highest gain is allowed to oscillate, and finally the instantaneous single-mode oscillation of the sweep signal is realized, so that the sweep signal with a narrow instantaneous line width can be obtained, and the quality of the sweep signal is improved.

[0049] For example, Figure 2 For the sweep signal in one period of the sweep photoelectric oscillation output in the traditional mode (i.e., single loop), because the bandwidth of the microwave photon filter in the sweep photoelectric oscillator is tens or even hundreds of MHz, at any time, the system will have multiple modes oscillating simultaneously, thereby resulting in a relatively wide instantaneous line width of the sweep signal. Figure 3 For the de-chirped signal of the traditional single-loop sweep photoelectric oscillator, the frequency is f0, and the 3dB bandwidth of the signal is wide (the 3dB bandwidth is the width of the signal after the peak value of the power of the signal decreases by 3dB).

[0050] Figure 4 For the sweep signal in one period of the sweep photoelectric oscillation output based on the double loop (including the gain loop and the loss loop) of the parity-time symmetry, because the parity-time symmetry has a mode selection effect, the oscillation mode with the highest gain is selected, that is, the oscillation of other modes is suppressed, so that the sweep signal has a narrower instantaneous line width. Figure 5 For the de-chirped signal of the double-loop sweep photoelectric oscillator under the parity-time symmetry in Figure 1 The de-chirped signal (i.e., the single-frequency difference frequency signal proposed in some embodiments of the present disclosure) of the output 2 output of the midpoint mixer corresponds to the output 2, the frequency is f0, and the 3dB bandwidth of the signal is narrow (the 3dB bandwidth is the width of the signal after the peak value of the power of the signal decreases by 3dB).

[0051] In some embodiments of the present disclosure, the sweep period of the microwave photon filter The delay of the gain loop And the delay of the loss loop corresponding;

[0052] wherein, 、 and satisfy the following Fourier domain mode-locking condition:

[0053]

[0054] wherein, is a positive integer, is a sweeping period of the microwave photonic filter, is the same as the sweeping period of the sweeping laser, is a time for the signal to travel one round in the gain loop, is a time for the signal to travel one round in the loss loop.

[0055] In some embodiments of the present disclosure, the microwave photonic filter comprises a sweeping laser, a phase modulator, and a notch filter, wherein the sweeping laser is connected with the first input end of the phase modulator and the notch filter in sequence; the sweeping laser is configured to output an initial optical signal; the second input end of the phase modulator is connected with the second output end of the second electrical power divider; the phase modulator is configured to modulate the initial optical signal with the narrow-linewidth sweeping signal output by the second electrical power divider to obtain a modulated signal comprising a sweeping optical carrier and positive and negative order sidebands; the notch filter is configured to filter out any one of the positive and negative order sidebands to obtain an optical signal equivalent to an intensity modulated signal; and the output end of the notch filter is connected with the first long optical fiber.

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

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

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

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

[0061] In some embodiments of the present disclosure, the microwave photon filter further comprises a polarization controller, wherein the polarization controller is connected to the line between the sweep laser and the phase modulator, for adjusting 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 that the optical polarization loss of the initial optical signal reaching the phase modulator is minimized.

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

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

[0065] 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 electrical power combiner in sequence;

[0066] The input end of the second adjustable optical attenuator is connected to the 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 electrical power combiner in sequence; the corresponding delay time of the first adjustable delay line is the same as that of the second adjustable delay line.

[0068] In one embodiment, the conditions required for the time-reversal 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 equally divides the optical signal power into two parts for output.

[0070] In some embodiments of the present disclosure, the narrow-line-width sweep optoelectronic oscillator based on the time-reversal symmetry mechanism further comprises a first optical coupler and a first electrical power combiner, wherein,

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

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

[0073] The first power divider is connected on the line between the power combiner and the second power divider. One output terminal of the first power divider is connected to the input terminal of the electric mixer. The output terminal of the electric mixer outputs a single-frequency difference signal to display the instantaneous linewidth characteristics of the sweep signal.

[0074] In one example, both the first and second long optical fibers can be energy storage elements with losses as low as 0.2 dB / km.

[0075] In one embodiment of this disclosure, a first optical coupler splits an optical signal into two paths of equal power. One path is the oscillation loop of a photoelectric oscillator, and the other path enters a second long optical fiber. After passing through a third photodetector, the optical signal is converted into a swept-frequency microwave signal, which enters an electrical mixer together with the swept-frequency microwave signal from the first power divider. The two signals experience different time delays, and the electrical mixer outputs a single-frequency difference signal, or dechirped signal. This process is called dechirping. By observing the linewidth of the single-frequency dechirped signal (i.e., the aforementioned single-frequency difference signal), the instantaneous linewidth characteristics of the swept-frequency signal can be reflected.

[0076] It is understandable that the linewidth of the chirped signal directly reflects the instantaneous characteristics of the sweep signal. The narrower the measured linewidth of the dechirped signal, the narrower the instantaneous linewidth of the sweep signal, and the better the quality of the sweep signal.

[0077] It's important to note that dechirping refers to removing the chirp effect from a signal. Chirp is a term in communication technology that refers to the linear increase or decrease of a signal's carrier frequency over the duration of a pulse, causing a change in the signal's frequency. Dechirping involves adjusting the signal using specific techniques to stabilize its frequency and eliminate these frequency variations.

[0078] For example, such as Figure 6 As shown, Figure 6 The solid line in the middle is Figure 1 The sweep frequency signal output from output 1 has a bandwidth B equal to the difference between its start and end frequencies. The period of the sweep frequency signal is T, which is equal to the loop cavity delay time. After passing through the second long optical fiber, the delay time of the sweep frequency signal is... ,like Figure 6 The signal is indicated by the dashed line in the middle. The electric mixer mixes the solid sweep signal in the loop with the dashed sweep signal passing through the second long optical fiber. Figure 1 The output ports 2 output two difference frequency signals after mixing, with frequencies f1 and f2 respectively. The magnitude of frequency f1 can be expressed as B. The frequency of f2 can be expressed as B(T) ) / T.

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

[0080] In one embodiment, the optical amplifier can 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 starting the system.

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

[0082] The electrical amplifier is connected to a line between the electrical hybrid coupler and the second electrical power divider; or,

[0083] The electrical amplifier is connected to an output terminal of the second electrical 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; and 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, the narrow linewidth swept optoelectronic oscillator based on the mechanism of time-reversal symmetry can be applied to a radar detection or a communication system.

[0086] The narrow-line-width sweep-frequency photoelectric oscillator based on the time-reversal symmetry mechanism according to the embodiment of the present disclosure is connected with a first long optical fiber and a second optical coupler in sequence at the output end of a microwave photon filter; the microwave photon filter is used to output a first optical signal which is equivalent to intensity modulation after the initial optical signal is modulated and filtered; 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 with the input end of a gain branch and a loss branch respectively; the gain loop corresponding to the gain branch and the loss loop corresponding to the loss branch satisfy the time-reversal symmetry constraint condition; the output end of the gain branch and the output end of the loss branch are connected with the input end of an electrical combiner; the output end of the electrical combiner is connected with the input end of a second electrical power divider; the first output end of the second electrical power divider outputs a narrow-line-width sweep-frequency signal, and the second output end of the second electrical power divider is connected with the input end of the microwave photon filter to form a closed loop. By introducing the closed loop satisfying the time-reversal symmetry condition, the side mode of the sweep-frequency signal is removed, the sweep-frequency signal of the single-mode oscillation with the highest gain is reserved, and thus the sweep-frequency signal with a relatively narrow instantaneous line width can be obtained, and the sweep-frequency signal quality is improved. Without the aid of high-frequency electronic devices, the present disclosure generates a narrow-line-width sweep-frequency microwave signal with adjustable bandwidth and frequency, and the present application 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-line-width sweep-frequency photoelectric oscillator based on the time-reversal symmetry mechanism as a sweep-frequency microwave signal source.

[0088] In the foregoing embodiment description, the description of the terms "one embodiment", "an embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present disclosure. In the present description, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present description and the features of the different embodiments or examples without contradiction.

[0089] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present disclosure, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0090] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the application being indicated by the following claims.

[0091] It is to be understood that the application is not limited to the precise construction hereinafter described and as shown in the attached drawings, and that various changes in form and detail can be made therein without departing from the scope thereof. The scope of the application should only be limited by the appended claims.

Claims

1. A narrow linewidth swept optical electric oscillator based on the mechanism of time-reversal symmetry, characterized in that, The microwave photon filter, the first long optical fiber, the second optical coupler, the gain branch, the loss branch, the electrical combiner and the second electrical power splitter are connected in series. The output end of the microwave photon filter is connected with the first long optical fiber and the second optical coupler in sequence; the microwave photon filter is used for outputting the first optical signal which is equivalent to an intensity modulation signal after the initial optical signal is modulated and filtered; the first long optical fiber is used for delaying the first optical signal. The output end of the second optical coupler is connected with the input end of the gain branch and the loss branch respectively; the gain branch and the microwave photon filter, the first long optical fiber, the second optical coupler, the electrical combiner and the second electrical power splitter form a gain loop; the loss branch and the microwave photon filter, the first long optical fiber, the second optical coupler, the electrical combiner and the second electrical power splitter form a loss loop; the gain loop and the loss loop satisfy the parity-time symmetry constraint condition. The output end of the gain branch and the loss branch is connected with the input end of the electrical combiner. The output end of the electrical combiner is connected with the input end of the second electrical power splitter. The first output end of the second electrical power splitter outputs a narrow line width sweep signal; the second output end of the second electrical power splitter is connected with the input end of the microwave photon filter, forming a closed loop. The first optical coupler and the first electrical power splitter are further included, wherein, The first optical coupler is connected on the line between the first long optical fiber and the second optical coupler. One output end of the first optical coupler is connected with the second long optical fiber, the third photodetector and the input end of the electrical mixer in sequence; the length of the first long optical fiber is different from that of the second long optical fiber. The first electrical power splitter is connected on the line between the electrical combiner and the second electrical power splitter; one output end of the first electrical power splitter is connected with the input end of the electrical mixer; the output end of the electrical mixer outputs a single frequency difference frequency signal for displaying the instantaneous line width characteristic of the sweep signal.

2. The narrow linewidth swept optical photo-oscillator based on the mechanism of time-reversal symmetry, according to claim 1, characterized in that, The microwave photon filter includes a sweep laser, a phase modulator and a notch filter, wherein, The sweep laser is connected with the first input end of the phase modulator and the notch filter in sequence; the sweep laser is used for outputting the initial optical signal; The second input end of the phase modulator is connected with the second output end of the second electrical power splitter; the phase modulator is used for modulating the initial optical signal and the narrow line width sweep signal output by the second electrical power splitter, obtaining a modulation signal including sweep optical carrier positive order sideband and negative order sideband; the notch filter is used for filtering out any one of the positive order sideband and the negative order sideband, obtaining an optical signal equivalent to an intensity modulation signal; The output end of the notch filter is connected with the first long optical fiber.

3. The narrow linewidth swept optical photo-oscillator based on the CPT 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; 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 with the first output end of the second optical coupler; The output end of the first adjustable optical attenuator is connected with the first adjustable delay line, the first photodetector and the first input end of the electrical hybrid coupler in sequence. The input end of the second adjustable optical attenuator is connected with the second output end of the second optical coupler. The output end of the second adjustable optical attenuator is connected with the second adjustable delay line, the second photodetector and the second input end of the electrical hybrid coupler in sequence.

4. The narrow linewidth swept optical photo-oscillator based on the CPT mechanism according to claim 1, characterized in that, The CPT symmetry constraint condition comprises that 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 optical photo-oscillator based on the CPT 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 value of the gain loop; and the net loss value is the difference between the oscillation threshold value of the loss loop and the optical signal power value of the loss loop.

6. The narrow linewidth swept optical photo-oscillator based on the CPT mechanism according to claim 2, characterized in that, The microwave photonic filter further comprises a polarization controller, wherein The polarization controller is connected on the line between the swept-frequency laser and the phase modulator, for adjusting the polarization state of the initial optical signal.

7. The narrow linewidth swept optical photo-oscillator based on the CPT mechanism according to claim 1, characterized in that, Further comprising an optical amplifier, wherein The optical amplifier is connected on the line between the microwave photonic filter and the first long optical fiber.

8. The narrow linewidth swept optical photo-oscillator based on the CPT mechanism according to claim 1, characterized in that, Further comprising an electrical amplifier, wherein The electrical amplifier is connected on the line between the electrical hybrid coupler and the second electrical power splitter; or The electrical amplifier is connected with one output end of the second electrical power splitter.

9. The narrow linewidth swept optical photo-oscillator based on the CPT mechanism according to claim 3, characterized in that, The first adjustable optical attenuator and the second adjustable optical attenuator are the same in structure and performance; the first photodetector and the second photodetector are the same in structure and performance; and the first adjustable delay line and the second adjustable delay line are the same in structure and performance.

10. The narrow linewidth swept optical photo-oscillator based on the CPT mechanism according to claim 2, characterized in that, The sweep period of the microwave photonic filter corresponding to the delay of the gain loop and the delay of the loss loop ​ wherein , and satisfy the following Fourier domain mode-locking condition: wherein, is a positive integer, is a sweep period of the microwave photonic filter, is the same as the sweep period of the swept laser, is a time for a signal to travel one round in the gain loop, is a time for a signal to travel one round in the loss loop.

11. The narrow linewidth swept optical photo-oscillator based on the CPT mechanism according to claim 2, characterized in that, The bandwidth of the swept-frequency signal is tuned by adjusting the swept-frequency range of the swept-frequency laser.

12. The narrow linewidth swept optical photo-oscillator based on the CPT mechanism according to claim 2, characterized in that, The center frequency of the swept-frequency signal is tuned by adjusting the center wavelength of the swept-frequency laser.

13. The narrow linewidth swept optical photo-oscillator based on the CPT mechanism according to claim 3, characterized in that, The first optical coupler and the second optical coupler are optical couplers that equally divide the optical signal power into two parts for output.

14. A communication system, characterized by The narrow-line-width swept optical electrical oscillator based on the CPT symmetry mechanism is used as a microwave source.

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