CN109842444B - Weak signal detection amplification system and method based on photoelectric oscillator - Google Patents

Abstract

The invention provides a weak signal detection amplification system based on a photoelectric oscillator and a detection amplification method thereof, belonging to the technical field of microwave photonics. The weak signal detection and amplification system based on the photoelectric oscillator comprises: the device comprises a laser, a beam splitter, a phase modulator, a high nonlinear optical fiber, a circulator, a photoelectric detector, a power divider, a coupler, an electric amplifier, an intensity modulator, a variable optical attenuator and a radio frequency source; the laser is connected with the beam splitter, the beam splitter is respectively connected with the phase modulator and the intensity modulator, and the phase modulator, the circulator, the photoelectric detector, the power divider, the coupler and the electric amplifier are sequentially connected end to form a loop; the intensity modulator, the adjustable optical attenuator and the circulator are sequentially connected, the radio frequency source is connected to the intensity modulator, and the phase modulator is connected with the circulator through the high nonlinear optical fiber. The invention can realize rapid and high-precision weak signal detection and amplification by adjusting the radio frequency source and the variable optical attenuator.

Description

Weak signal detection and amplification system and method based on photoelectric oscillator

technical field

The invention relates to the technical field of microwave photonics, in particular to a weak signal detection and amplification system and method based on a photoelectric oscillator.

Background technique

Fast frequency measurement is playing an increasingly important role in systems such as radar and electronic stations, but the premise of fast frequency measurement is that the system can distinguish the received signal, especially the detection of weak signals. It is particularly important to detect and amplify the signal with a wide frequency band and high power. For the problem of detection and amplification of weak signals, narrow filters and amplifiers are used in its electronic solution, but the realization of this solution is particularly difficult due to technical development and the noise introduced by the electric amplifier. The microwave photonics method is adopted by more people because of its advantages of large bandwidth, low loss, and anti-interference. However, in the existing method, the weak signal scheme of the multimode photodetector without an electric bandpass filter in the OEO cavity based on the injection locking process can only amplify the signal in the frequency range of 1 to 6 GHz by 8dB, and the detection sensitivity is low. Reaching -83dBm, there are problems that the detection frequency range is small and the amplification effect is not very obvious; the tunable photodetector system based on Bragg grating can detect and amplify the radio frequency signal. The signal is amplified by 10dB, the detection sensitivity reaches -91dBm, and the measurement error of the detection frequency reaches 100MHz. However, the frequency range that can be detected by this method is limited to 5.5GHz by the grating, and the method uses the loss of the first-order phase modulation. The scheme of realizing the conversion from phase modulation to intensity modulation to realize the amplification of weak signals by sidebands has an amplification bottleneck in theory.

In addition, the specific environment is often complex and changeable. The weak signals received are often not single-frequency narrow-band signals, but also wide-bandwidth signals or even multi-frequency signals. Effective detection and amplification is also a very important issue.

SUMMARY OF THE INVENTION

(1) Technical problems to be solved

The present invention provides a weak signal detection and amplification system and method based on a photoelectric oscillator to at least partially solve the above technical problems.

(2) Technical solutions

According to an aspect of the present invention, there is provided a weak signal detection and amplification system based on an optoelectronic oscillator, comprising: a laser (1), a beam splitter (2), a phase modulator (3), and a highly nonlinear optical fiber (4) , circulator (5), photodetector (7), power divider (8), coupler (9), electrical amplifier (10), intensity modulator (11), adjustable optical attenuator (12) and radio frequency source(13);

The laser (1) is connected to the beam splitter (2), which is in turn connected to the phase modulator (3) and the intensity modulator (11), respectively, the phase modulator (3), the circulator (5), the photodetector (7), the power divider (8), the coupler (9) and the electric amplifier (10) are connected end to end to form a loop, the intensity modulator (11) , a tunable optical attenuator (12) and a circulator (5) are connected in sequence, the radio frequency source (13) is connected to the intensity modulator (11), and the high nonlinear optical fiber (4) is connected to the Between the phase modulator (3) and the circulator (5).

In some embodiments, the beam splitter (2) is used to divide the optical signal emitted by the laser (1) into two parts, and a part of the optical signal and the received weak signal are obtained through the phase modulator (3) The positive first-order sideband and the negative first-order sideband, together with another part of the optical signal and the microwave signal emitted by the radio frequency source (13), pass through the intensity modulator (11) to obtain the double-sideband pump light in a highly nonlinear optical fiber ( 4) When the loss spectrum and gain spectrum of the generated stimulated Brillouin scattering coincide, the received weak signal is recovered.

In some embodiments, the laser (1), the beam splitter (2) and the phase modulator (3) are connected by an optical fiber; the circulator (5) and the photodetector (8) are connected by an optical fiber connection; the beam splitter (2), the intensity modulator (11), the adjustable optical attenuator (12), and the circulator (5) are connected by optical fibers.

In some embodiments, between said photodetector (7), power divider (8), coupler (9), electric amplifier (10), phase modulator (3) and said radio frequency source (13) It is connected with the intensity modulator (11) through cables.

In some embodiments, the laser (1) is a narrow linewidth single wavelength laser.

In some embodiments, the laser (1), beam splitter (2), phase modulator (3), highly nonlinear fiber (4), circulator (5), photodetector (7), intensity modulation The device (11) and the radio frequency source (13) together form a microwave photonic filter; the passband of the microwave photonic filter is determined by the wavelength difference between the laser (1) and the gain spectrum or the loss spectrum.

In some embodiments, the change period and signal of the microwave photonic filter are in the phase modulator (3), the high nonlinear fiber (4), the circulator (5), the photodetector (7), the power divider In the loop formed by the coupler (8), the coupler (9) and the electric amplifier (10), the transmission delay of one cycle is matched, and the Fourier domain mode locking condition is satisfied:

nT=Tr

Wherein n is a positive integer, T is the change period of the microwave photonic filter, and Tr is the delay of one cycle of signal transmission in the loop.

In some embodiments, the phase modulator (3), high nonlinear fiber (4), circulator (5), photodetector (7), power divider (8), coupler (9), and electrical The loop formed by the amplifier (10) has zero dispersion so that signals of different frequencies have the same delay in the loop.

In some embodiments, the system further comprises an erbium-doped fiber amplifier; the erbium-doped fiber amplifier is connected between the circulator (5) and the photodetector (7), and is used for monitoring the circulator (5) The output optical signal is amplified.

According to another aspect of the present invention, there is provided a weak signal detection and amplification method using the photoelectric oscillator-based weak signal detection and amplification system provided by the above embodiments, the method comprising:

The optical signal emitted by the laser (1) is divided into two parts by the beam splitter (2), one part is transmitted to the phase modulator (3), and the other part is transmitted to the intensity modulator (11);

The radio frequency source (13) sends out a microwave signal and transmits it to the intensity modulator (11);

The optical signal is subjected to carrier suppression modulation by the microwave source signal in the intensity modulator (11) to generate two first-order sidebands as pump light and transmitted to the adjustable optical attenuator (12);

A tunable optical attenuator (12) adjusts the power of the pump light and transmits the pump light to a highly nonlinear optical fiber (4) through a circulator (5) to generate stimulated Brillouin scattering and distribution in all The loss spectrum and gain spectrum on the left and right sides of the pump light;

The weak signal is transmitted to the phase modulator (3) through the coupler (8) electric amplifier (10);

In the phase modulator (3), the optical signal is phase-modulated by the weak signal, and two sidebands of positive first order and negative first order are generated to enter the highly nonlinear optical fiber (4);

In the highly nonlinear optical fiber (4), the gain spectrum generated by the pump light gains the negative first-order sideband, and the loss spectrum loses the positive first-order sideband, so that the optical signal is converted from phase modulation to Intensity modulation, the new optical signal after gain and loss is transmitted to the beat frequency of the photodetector (7) through the circulator (5);

The photodetector (7) converts the new optical signal into an electrical signal and transmits it to the power divider (8);

The power divider (8) couples the electrical signal output with the received weak signal and feeds it back to the radio frequency port of the phase modulator;

By analyzing the power of the electrical signal output by the power divider (8), the amplified frequency of the weak signal is obtained.

(3) Beneficial effects

As can be seen from the above technical solutions, the present invention has at least one or a part of the following beneficial effects:

(1) The weak signal detection and amplification system and method based on the photoelectric oscillator provided by the present invention, by adopting the radio frequency source whose frequency can be tuned rapidly and continuously, sends out the periodically changing microwave signal, so that the system can realize the single frequency microwave signal, the broadband The high-speed detection of microwave signals and multi-frequency signals makes the detection range of the system larger;

(2) The weak signal detection and amplification system and method based on the photoelectric oscillator provided by the present invention, through the gain characteristics of the Brillouin scattering gain spectrum, and the microwave signal emitted by the radio frequency source and the optical signal emitted by the laser passing through the intensity modulator The two first-order sidebands generated by the modulation are used as pump light, and the double-sideband pumping can more effectively improve the gain effect of the photoelectric oscillator on weak signals;

(3) The weak signal detection and amplification system and method based on the photoelectric oscillator provided by the present invention realizes the detection of weak signals in a more complex detection environment through the selective characteristics of the Brillouin scattering gain spectrum (loss spectrum);

(4) The weak signal detection and amplification system and method based on the photoelectric oscillator provided by the present invention adopts the sideband as the pump light, so that there is a fixed phase relationship between the signal light and the pump light, avoiding the signal light and the pump light. In the case where the pump light is an independent light source, which leads to an error in the wavelength shift of the pump light, the detection of weak signals with high precision can be obtained.

Description of drawings

1 is a schematic structural diagram of a weak signal detection and amplification system based on an optoelectronic oscillator provided by an embodiment of the present invention;

2 is a flowchart of a method for detecting and amplifying weak signals based on an optoelectronic oscillator provided by an embodiment of the present invention;

3A is a schematic diagram of a result of phase modulation of a phase modulator provided by an embodiment of the present invention;

FIG. 3B is a schematic diagram of a result of carrier suppression modulation of an intensity modulator provided by an embodiment of the present invention;

FIG. 3C is a schematic diagram of a microwave photonic filter based on stimulated Brillouin scattering provided by an embodiment of the present invention.

In the above drawings, the meanings of the reference numerals are as follows:

1-laser; 2-beam splitter; 3-phase modulator; 4-high nonlinear fiber; 5-circulator; 6-erbium-doped fiber amplifier; 7-photodetector; 8-power splitter; 9-coupling 10-electric amplifier; 11-intensity modulator; 12-adjustable optical attenuator; 13-radio frequency source.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

According to an aspect of the present invention, a weak signal detection and amplification system based on an optoelectronic oscillator is provided. As shown in FIG. 1 , FIG. 1 is a schematic structural diagram of a weak signal detection and amplification system based on an optoelectronic oscillator provided by an embodiment of the present invention. , the weak signal detection and amplification system based on photoelectric oscillator includes:

Laser 1, beam splitter 2, phase modulator 3, high nonlinear fiber 4, circulator 5, photodetector 7, power splitter 8, coupler 9, electric amplifier 10, intensity modulator 11, adjustable optical attenuation device 12 and radio frequency source 13, wherein:

Laser 1 is connected to beam splitter 2, one port of beam splitter 2 is connected to phase modulator 3, the other port of beam splitter 2 is connected to intensity modulator 11, phase modulator 3, circulator 5, photodetector 7. The power divider 8, the coupler 9 and the electric amplifier 10 are connected end to end to form a loop; the intensity modulator 11, the adjustable optical attenuator 12 and the circulator 5 are connected in sequence; the radio frequency source 13 is connected to the intensity modulator 11 On; the high nonlinear fiber 4 is connected between the phase modulator 3 and the circulator 5.

In this embodiment, the laser 1, the beam splitter 2 and the phase modulator 3 are connected by an optical fiber, and the circulator 5 and the photodetector 8 are connected by an optical fiber. The beam splitter 2, the intensity modulator 11, the adjustable The optical attenuator 12 and the circulator 5 are connected by optical fibers; the photodetector 7, the power divider 8, the coupler 9, the electric amplifier 10, the phase modulator 3 and the radio frequency source 13 and the intensity modulator 10 are connected are connected by cables.

In this embodiment, the weak signal generally refers to a signal whose power is lower than 0 dB.

In this embodiment, the beam splitter 2 is used to divide the optical signal emitted by the laser 1 into two parts, one part of the optical signal and the received weak signal passing through the phase modulator 3 to obtain a positive first-order sideband and a negative first-order sideband The sideband, the loss spectrum and the gain spectrum of stimulated Brillouin scattering generated in the highly nonlinear fiber 4 by the double-sideband pump light obtained by passing through the intensity modulator 11 with another part of the optical signal and the microwave signal from the radio frequency source 13 When coincident, the received weak signal is recovered.

Specifically, a part of the optical signal is modulated by the weak signal received by the phase modulator 3 to obtain the positive first-order sideband and the negative first-order sideband, and the other part of the optical signal is transmitted through the intensity modulator by the microwave emitted by the radio frequency source 13. After the signal is subjected to carrier suppression modulation, the obtained two first-order sidebands enter the highly nonlinear fiber 4 as pump light to generate stimulated Brillouin scattering. When the loss spectrum and gain spectrum of excimer Brillouin scattering coincide with the first-order sideband obtained in the phase modulator, the conversion of the optical carrier from phase modulation to intensity modulation is realized, and the received weak signal is recovered. Among them, the laser 1 is a narrow linewidth single-wavelength laser; the radio frequency source 13 is a radio frequency source whose frequency can be adjusted rapidly and continuously; the high nonlinear fiber 4 is a high-Q microwave energy storage element with optical nonlinearity, and its length is several meters to tens of thousands Meter.

In this embodiment, the adjustable optical attenuator 12 controls the gain of the sideband by controlling the optical power of the pump light, so that weak signals can be detected and amplified. The tunable optical attenuator 12 can also be connected between the high nonlinear fiber 4 and the circulator 5 .

The weak signal detection and amplification system based on the photoelectric oscillator provided by the present invention, by using a radio frequency source whose frequency can be tuned rapidly and continuously, the emitted microwave signal can change periodically, so the system can realize high-speed detection of broadband microwave signals and multi-frequency signals , so that the detection range of the system is larger; through the gain characteristics of the Brillouin scattering gain spectrum and the double-sideband pumping obtained by the carrier suppression modulation of the optical signal emitted by the laser and the microwave signal emitted by the radio frequency source, it can be more effective. The gain effect of the photoelectric oscillator on weak signals is improved; the weak signals can be detected in a more complex detection environment through the selective characteristics of the Brillouin scattering gain spectrum (loss spectrum).

In this embodiment, the laser 1, the beam splitter 2, the phase modulator 3, the highly nonlinear optical fiber 4, the circulator 5, the photodetector 7, the intensity modulator 11 and the radio frequency source 13 together form a microwave photonic filter; The passband of the microwave photonic filter is determined by the wavelength difference between the swept frequency laser 1 and the gain spectrum or loss spectrum. in:

The change period of the microwave photonic filter and the signal are transmitted for one cycle in the loop formed by the phase modulator 3, the high nonlinear fiber 4, the circulator 5, the photodetector 7, the power divider 8, the coupler 9 and the electric amplifier 10. The delays are matched to satisfy the Fourier domain mode-locking condition:

nT=Tr

Wherein n is a positive integer, T is the change period of the microwave photonic filter, and Tr is the delay of one cycle of signal transmission in the loop.

In this embodiment, the dispersion of the loop formed by the phase modulator 3, the high nonlinear fiber 4, the circulator 5, the photodetector 7, the power divider 8, the coupler 9 and the electric amplifier 10 is controlled to zero, so that the Signals of different frequencies have the same delay in this loop.

In this embodiment, the weak signal detection and amplification system based on the photoelectric oscillator may further include an erbium-doped fiber amplifier 5, which is connected between the circulator 4 and the photodetector 6, and is used to detect the light output from the circulator 4. signal is amplified.

In this embodiment, the power divider 8 is used to divide the electrical signal converted by the photodetector 7 from the optical signal into two parts, one part is used for output, and the other part is transmitted to the coupler 9 and coupled with the weak signal to transmit the electrical signal Amplifier 10.

The weak signal detection and amplification system based on the photoelectric oscillator provided by the present invention adopts the sideband as the pump light, so that there is a fixed phase relationship between the signal light and the pump light, avoiding that the signal light and the pump light are independent In the case of the wavelength drift of the pump light resulting in errors, the detection of weak signals with high precision can be obtained.

According to another aspect of the present invention, a weak signal detection and amplification method based on an optoelectronic oscillator is proposed, as shown in FIG. 2 . FIG. 2 is a weak signal detection and amplification system based on an optoelectronic oscillator provided by an embodiment of the present invention. Signal detection and amplification method, the method includes the following steps:

Step S101, the optical signal emitted by the laser is divided into two parts by the beam splitter, one part is transmitted to the phase modulator, and the other part is transmitted to the intensity modulator.

Before step S101, the method further includes: adjusting the photoelectric oscillator to a threshold state.

Step S102, the radio frequency source sends out a microwave signal and transmits it to the intensity modulator.

Preferably, the radio frequency source is a radio frequency source whose frequency can be adjusted rapidly and continuously, so the frequency of the microwave signal emitted by the radio frequency source changes periodically.

In step S103, the optical signal is subjected to carrier suppression modulation by the microwave signal in the intensity modulator, and two first-order sidebands are generated as pump light and transmitted to the adjustable optical attenuator. As shown in FIG. 3B , FIG. 3B is a schematic diagram of the carrier suppression modulation result of the intensity modulator.

The double-sideband pump light can better improve the gain effect of the photoelectric oscillator on weak signals.

Step S104, the adjustable optical attenuator adjusts the power of the pump light and transmits the pump light to the highly nonlinear fiber through the circulator to generate stimulated Brillouin scattering to obtain the loss spectrum and gain distributed on the left and right sides of the pump light. spectrum.

Specifically, after the pump light is excited in a highly nonlinear fiber, stimulated Brillouin scattering is generated, and at the same time, a loss spectrum and a gain spectrum with a bandwidth of about tens of megahertz distributed on the left and right sides of the pump light are generated. Among them, the frequencies corresponding to the gain spectrum and the loss spectrum of the pump light and the stimulated Brillouin scattering region differ by about 10 GHz.

Step S105, the weak signal is transmitted to the radio frequency port of the phase modulator through the coupler and the electric amplifier.

Step S106, in the phase modulator, the optical signal is phase-modulated by the weak signal, and two sidebands of positive first order and negative first order are generated to enter the highly nonlinear optical fiber. As shown in FIG. 3A , FIG. 3A is a schematic diagram of the modulation result of the phase modulator.

In step S107, the gain spectrum generated by the pump light in the highly nonlinear optical fiber gains a negative first-order sideband, and the loss spectrum loses a positive first-order sideband, so that the optical signal is converted from phase modulation to intensity modulation, and the new value after gain and loss is converted into intensity modulation. The optical signal is transmitted to the photodetector beat frequency through the circulator. The weak signal received at this time is recovered.

Specifically, by periodically and rapidly tuning the center frequency of the microwaves emitted by the radio frequency source, the change period of the microwave photonic filter in the photoelectric oscillator is matched with the one-cycle delay of the signal in the photoelectric oscillator loop, and the Fourier frequency is satisfied. Leaf domain mode-locking conditions:

nT=Tr

Among them, n is a positive integer, T is the change period of the microwave photonic filter, and Tr is the delay of one cycle of signal transmission in the photoelectric oscillator loop. Thus, a Fourier domain mode-locked photoelectric oscillator can be realized, which can generate a frequency sweep microwave signal. In the process of frequency sweeping, when the loss spectrum of the gain spectrum subject to Brillouin scattering just coincides with the negative and positive first-order sidebands of the received weak signal phase-modulated optical signal, the gain spectrum of stimulated Brillouin scattering The loss spectrum can gain the negative and positive first-order sidebands generated by the gain loss phase modulator modulation, and the modulated signal after the gain spectrum gain loss spectrum loss subjected to excimer Brillouin scattering is shown in Figure 3C. The size of the positive and negative first-order sidebands is no longer equal, and the gain loss effect of the gain spectrum loss spectrum on the sidebands is controlled by adjusting the adjustable optical attenuator, so the phase modulation is converted into an intensity modulation.

The weak signal detection and amplification method based on the photoelectric oscillator provided by the invention can more effectively improve the gain effect of the photoelectric oscillator on the weak signal through the gain characteristics of the Brillouin scattering gain spectrum and double-sideband pumping; The selective characteristic of the Brillouin scattering loss spectrum enables the detection of weak signals in a more complex detection environment.

In step S108, the photodetector converts the new optical signal into an electrical signal and transmits it to the power divider.

Step S109, the power divider outputs the electrical signal, couples with the received weak signal through the coupler, and feeds back to the radio frequency port of the phase modulator.

In step S1010, the amplified frequency of the weak signal is obtained by analyzing the power of the electrical signal output by the power divider.

Specifically, by monitoring in real time whether the power change of the frequency sweep signal generated by the system is abnormal, when the weak signal enters the system, it is detected and amplified by the system. At this time, the power is increased because a new signal is generated. The corresponding relationship can quickly obtain the frequency f of the corresponding radio frequency source at this time, f'=ff ₀ is the frequency of the weak signal we receive, where f ₀ is the size of the Brillouin frequency shift, generally about 10GHz.

The weak signal detection and amplification method based on the photoelectric oscillator provided by the present invention can recover and amplify the received single-frequency, multi-frequency and broadband weak signals by using a radio frequency source whose frequency can be tuned rapidly and continuously, so that the detection and amplification of the system can be achieved. The range is larger; and because there is a fixed phase relationship between the signal light and the pump light, it avoids the situation that the signal light and the pump light are independent and causes errors in the wavelength drift of the pump light, and can obtain higher Accurate detection results.

Further, since no electrical filter is required in the proposed optoelectronic oscillator loop, the frequency of the microwave signal generated by the loop only depends on the difference between the emission wavelength of the tunable laser and the wavelength corresponding to stimulated Brillouin scattering, Therefore, broadband tuning of microwave signals can be achieved.

In addition, the above definitions of each element and method are not limited to various specific structures, shapes or manners mentioned in the embodiments, and those of ordinary skill in the art can simply and familiarly replace the structures, for example: two The other two gain spectral loss spectra generated by one pump light that do not contribute to filtering are filtered out, only one sideband is used as the pump light, and the electrical amplifier is replaced by a fiber amplifier to provide gain to the entire loop; it is also directly in the optical path. An optical amplifier is added to amplify the signal, and an optical isolator is added between the phase modulator and the highly nonlinear light. Also, the attached drawings are simplified and used as examples. The number, shape and size of the devices shown in the drawings may be modified according to the actual situation, and the configuration of the devices may be more complicated.

It should be noted that the ordinal numbers such as "first", "second", "third" and other terms used in the description and the claims are used to modify the corresponding elements, which do not mean or represent that the elements have Any ordinal numbers do not represent the order of a certain element and another element, or the order of the manufacturing method, and the use of these ordinal numbers is only used to enable an element with a certain name to be compatible with another element with the same name. make a clear distinction.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in further detail. It should be understood that the above are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principle of the present invention, any modifications, equivalent replacements, improvements, etc. made should be included within the protection scope of the present invention.

Claims (10)

1. A weak signal detection amplification method of a weak signal detection amplification system based on a photoelectric oscillator is characterized by comprising the following steps:

an optical signal emitted by the laser (1) is divided into two parts by the beam splitter (2), one part is transmitted to the phase modulator (3), and the other part is transmitted to the intensity modulator (11);

the radio frequency source (13) sends out a microwave signal to be transmitted to the intensity modulator (11);

the optical signal is subjected to carrier suppression modulation by the microwave signal in an intensity modulator (11), and two first-order sidebands are generated and transmitted to an adjustable optical attenuator (12) as pump light;

the variable optical attenuator (12) adjusts the power of the pump light and transmits the pump light to the high nonlinear optical fiber (4) through the circulator (5) to generate stimulated Brillouin scattering so as to obtain a loss spectrum and a gain spectrum distributed on the left side and the right side of the pump light;

the weak signal is transmitted to the phase modulator (3) through the coupler (8) and the electric amplifier (10);

the optical signal is phase-modulated by the weak signal at the phase modulator (3) to generate two sidebands of a positive first order and a negative first order to enter the high nonlinear optical fiber (4);

gain spectrum generated by the pump light in the high nonlinear optical fiber (4) gains the negative first-order sideband, loss spectrum loses the positive first-order sideband, so that the optical signal is converted from phase modulation to intensity modulation, and a new optical signal after gain and loss is obtained and transmitted to a photoelectric detector (7) for beat frequency through a circulator (5);

the photoelectric detector (7) converts the new optical signal into an electric signal and transmits the electric signal to the power divider (8);

the power divider (8) couples the electric signal output with the received weak signal and feeds the coupled signal back to a radio frequency port of the phase modulator;

and obtaining the frequency of the weak signal after amplification by analyzing the power of the electric signal output by the power divider (8).

2. A weak signal detection amplification system based on an optoelectronic oscillator for implementing the weak signal detection amplification method of claim 1, comprising:

the device comprises a laser (1), a beam splitter (2), a phase modulator (3), a high nonlinear optical fiber (4), a circulator (5), a photoelectric detector (7), a power divider (8), a coupler (9), an electric amplifier (10), an intensity modulator (11), an adjustable optical attenuator (12) and a radio frequency source (13);

the laser (1) is connected with the beam splitter (2), the beam splitter (2) is respectively connected with the phase modulator (3) and the intensity modulator (11), the phase modulator (3), the circulator (5), the photoelectric detector (7), the power divider (8), the coupler (9) and the electric amplifier (10) are sequentially connected end to form a loop, the intensity modulator (11), the adjustable optical attenuator (12) and the circulator (5) are sequentially connected, the radio frequency source (13) is connected to the intensity modulator (11), and the high nonlinear optical fiber (4) is connected between the phase modulator (3) and the circulator (5).

3. The weak signal detection and amplification system based on the optoelectronic oscillator according to claim 2, wherein the beam splitter (2) splits the optical signal emitted from the laser (1) into two parts, wherein a part of the optical signal and the positive first-order sideband and the negative first-order sideband obtained by the received weak signal passing through the phase modulator (3) coincide with a loss spectrum and a gain spectrum of stimulated brillouin scattering generated in the high nonlinear optical fiber (4) by the other part of the optical signal and the double-sideband pump light obtained by the microwave signal emitted from the radio frequency source (13) passing through the intensity modulator (11).

4. The weak signal detection and amplification system based on the optoelectronic oscillator as claimed in claim 2, wherein the laser (1), the beam splitter (2) and the phase modulator (3) are connected through optical fibers; the circulator (5) is connected with the photoelectric detector (7) through an optical fiber; the beam splitter (2), the intensity modulator (11), the adjustable optical attenuator (12) and the circulator (5) are connected through optical fibers.

5. The weak signal detection and amplification system based on the optoelectronic oscillator as claimed in claim 2, wherein the optoelectronic detector (7), the power divider (8), the coupler (9), the electrical amplifier (10), the phase modulator (3) and the radio frequency source (13) and the intensity modulator (11) are connected by cables.

6. The weak signal detection amplification system based on optoelectronic oscillator of claim 2, characterized in that the laser (1) is a narrow linewidth single wavelength laser.

7. The weak signal detection and amplification system based on the optoelectronic oscillator as claimed in claim 2, wherein the laser (1), the beam splitter (2), the phase modulator (3), the high nonlinear optical fiber (4), the circulator (5), the photodetector (7), the intensity modulator (11) and the radio frequency source (13) together form a microwave photonic filter; the passband of the microwave photonic filter is determined by the wavelength difference between the laser (1) and the gain or loss spectrum.

8. The weak signal detection and amplification system based on the optoelectronic oscillator according to claim 7, wherein the variation period of the microwave photonic filter is matched with the delay of one signal transmission cycle in the loop formed by the phase modulator (3), the high nonlinear fiber (4), the circulator (5), the photodetector (7), the power divider (8), the coupler (9) and the electrical amplifier (10), and a Fourier domain mode locking condition is satisfied:

nT＝Tr

wherein n is a positive integer, T is the variation period of the microwave photon filter, and Tr is the delay of one cycle of signal transmission in the loop.

9. The weak signal detection amplification system based on the optoelectronic oscillator according to claim 2, wherein the dispersion of the loop formed by the phase modulator (3), the high nonlinear optical fiber (4), the circulator (5), the optoelectronic detector (7), the power divider (8), the coupler (9) and the electrical amplifier (10) is zero, so that signals of different frequencies have the same delay in the loop.

10. The optoelectronic oscillator based weak signal detection amplifying system according to claim 2, further comprising an erbium doped fiber amplifier; the erbium-doped fiber amplifier is connected between the circulator (5) and the photoelectric detector (7) and is used for amplifying the optical signal output by the circulator (5).

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