Quadruplicated frequency tunable photoelectric oscillator and method based on stimulated Brillouin scattering

Abstract

The invention discloses a quadruplicated frequency tunable optoelectronic oscillator and method based on stimulated Brillouin scattering, and belongs to the technical field of microwave photonics. Comprising a tunable laser source, a coupler, a circulator, an optical isolator, a high-nonlinearity optical fiber, a polarization controller, an erbium-doped optical fiber amplifier, a Mach-Zehnder modulator, a double-parallel Mach-Zehnder modulator, a photoelectric detector, an electric amplifier, an optical band-pass filter and a spectrum analyzer. The frequency of the output microwave signal is changed by adjusting the wavelength of the tunable laser source, and the frequency tuning range is 35.12 GHz to 37.76 GHz; by controlling the direct-current bias voltage of the dual-parallel Mach-Zehnder modulator, the phase of the output microwave signal can be adjusted, and the phase tuning range is 0-360 degrees. By means of gain-loss compensation of the stimulated Brillouin scattering effect, oscillation signals with the frequency equal to four times of Brillouin frequency shift are achieved.

Description

Technical Field

[0001] The present invention relates to a quadruple-frequency tunable optoelectronic oscillator and method based on stimulated Brillouin scattering, belonging to the technical field of microwave photonics. Background Art

[0002] Microwave photonics technology has significant advantages in the generation of high-frequency microwave signals and is widely used in fields such as radar and communication. Traditional microwave signal generation methods are limited by the electronic bottleneck effect of electronic devices. As the oscillation frequency increases, problems such as increased phase noise and decreased frequency stability will be faced, making it difficult to generate high-quality microwave signals at high frequencies. The optoelectronic oscillator utilizes the low loss, high frequency stability of light, and the long delay characteristics of optical fibers, and can effectively overcome these limitations, providing a new solution for generating high-quality microwave and millimeter-wave signals.

[0003] The prior art CN102751644A discloses a broadband continuously tunable optoelectronic oscillator based on the stimulated Brillouin scattering effect, which is a broadband continuously tunable optoelectronic oscillator. The stimulated Brillouin scattering effect in an optical fiber is used to phase-shift the carrier of the single-sideband modulated optical signal in the optoelectronic oscillator. By beating the carrier of the optical modulation signal with the positive first-order sideband or the carrier with the negative first-order sideband at the photodetector, the change in the phase shift amount of the microwave signal in the optoelectronic oscillator ring cavity is realized. At the same time, with the cooperation of a tunable microwave filter, the broadband continuous tunability of the output signal frequency of the optoelectronic oscillator is finally realized. However, it cannot achieve quadruple-frequency tunable optoelectronic oscillation.

[0004] In specific application scenarios, microwave signals not only need to have high quality, but also require the signal source to have a wide output frequency range and tunability. Therefore, the research on the tunability of microwave signal frequency and phase has significant practical value. Summary of the Invention

[0005] Aiming at the deficiencies in the prior art, the present invention provides a quadruple-frequency tunable optoelectronic oscillator and method based on stimulated Brillouin scattering. On the basis of the traditional optoelectronic oscillator based on stimulated Brillouin scattering, an optical coupler, a circulator, a highly nonlinear optical fiber, an erbium-doped fiber amplifier, and a Mach-Zehnder modulator are used to optically modulate the continuous wave output by a tunable laser to generate four pump lights with the same frequency interval. The four pump lights generate the stimulated Brillouin scattering effect with the carrier-suppressed double-sideband modulation signal generated by the dual-parallel Mach-Zehnder modulator in the highly nonlinear optical fiber. After the gain spectra and loss spectra of the four pump lights interact with each other, only one gain spectrum and one loss spectrum remain, and then one of the sidebands is filtered out by an optical bandpass filter, thereby obtaining a 4-fold frequency signal.

[0006] To achieve the above technical objectives, the present invention discloses a frequency quadrupling tunable optoelectronic oscillator based on stimulated Brillouin scattering, characterized in that: it includes a tunable laser source, which is connected to two inlets of a third coupler in two lines through a first coupler, wherein one line includes a first circulator, a second coupler, a second circulator, and a first erbium-doped fiber amplifier connected in sequence, and the other line is a direct line connection;

[0007] The output of the third coupler is sequentially connected to a fourth coupler and a Mach-Zehnder modulator, a third circulator, and a second highly nonlinear optical fiber; a first photodetector is further connected in parallel between the fourth coupler and the Mach-Zehnder modulator, port 1 of the third circulator is connected to the Mach-Zehnder modulator, and port 2 of the third circulator is connected to the second highly nonlinear optical fiber;

[0008] Port 3 of the first circulator is connected to port 1 of the second circulator via a second coupler, and port 2 of the first circulator is connected to port 2 of the second circulator via a first highly nonlinear optical fiber;

[0009] The second coupler is further connected in sequence to a polarization controller, a second erbium-doped fiber amplifier, and a dual-parallel Mach-Zehnder modulator; wherein the dual-parallel Mach-Zehnder modulator is respectively connected to a fifth coupler and an electrical amplifier and a second photodetector connected in sequence, the second photodetector is connected to three ports of the third circulator, the fifth coupler is respectively connected to an optical isolator and an optical bandpass filter, and the optical isolator is connected to the second highly nonlinear optical fiber;

[0010] The optical bandpass filter is sequentially connected to a third photodetector and a spectrum analyzer.

[0011] Furthermore, the dual parallel Mach-Zehnder modulator includes three Mach-Zehnder modulators and three DC regulated power supplies respectively supplying power, including a main Mach-Zehnder modulator 3 and a sub-Mach-Zehnder modulator 1 and a sub-Mach-Zehnder modulator 2; the sub-Mach-Zehnder modulator 1 and the sub-Mach-Zehnder modulator 2 are respectively arranged on the two arms of the main Mach-Zehnder modulator 3, and the three DC regulated power supplies include a first DC regulated power supply for supplying power to the sub-Mach-Zehnder modulator 1, a second DC regulated power supply for supplying power to the sub-Mach-Zehnder modulator 2, and a third DC regulated power supply for supplying power to the main Mach-Zehnder modulator 3; by adjusting the voltage of the DC regulated power supply, the sub-Mach-Zehnder modulator 1 operates in carrier suppressed double-sideband modulation, the sub-Mach-Zehnder modulator 2 operates at a maximum transmission point when only an optical carrier is allowed to pass through, and the dual parallel Mach-Zehnder modulator operates in a carrier phase shifted double-sideband modulation bias point; the Mach-Zehnder modulator is connected to a fourth DC regulated power supply for supplying power to it;

[0012] The optical wavelength at which the Mach-Zehnder modulator operates is 1525 nm to 1605 nm, and the bandwidth is 40 GHz; the optical wavelength at which the dual-parallel Mach-Zehnder modulator operates is 1525 nm to 1605 nm, and the bandwidth is 40 GHz to 60 GHz; the adjustable range of the output voltage values of the first DC regulated power supply, the second DC regulated power supply, the third DC regulated power supply, and the fourth DC regulated power supply is 1 V to 20 V.

[0013] Further, the lengths of the first highly nonlinear fiber and the second highly nonlinear fiber are the same, both being 1 km, the stimulated Brillouin gain linewidth is 40 MHz, and the stimulated Brillouin frequency shift amount f B is 11 GHz.

[0014] Further, the isolation degree of the optical isolator is greater than 40 dB; the bandwidths of the first photodetector, the second photodetector, and the third photodetector are 60 GHz; the wavelength tuning range of the optical bandpass filter is between 1480 nm and 1620 nm, the tuning accuracy is 5 pm, and the insertion loss is 5 dB; the amplification multiples of the first erbium-doped fiber amplifier and the second erbium-doped fiber amplifier are greater than 25 times; the bandwidth of the spectrum analyzer is 100 GHz.

[0015] A working method of a quadruple-frequency tunable optoelectronic oscillator based on stimulated Brillouin scattering is as follows:

[0016] The light emitted by the tunable laser source is split by the first coupler to form a first branch light and a second branch light. After the first branch light generates the first-order Stokes light and the second-order Stokes light in sequence, it forms a fourth branch light, which is amplified by the first erbium-doped fiber amplifier and then fed into the third coupler. The amplified fourth branch light has the same intensity as the second branch light signal;

[0017] The second branch light is directly fed into the third coupler. After the fourth branch light formed by the second-order Stokes light is combined by the third coupler, it is sent to the fourth coupler for splitting and then respectively input into the first photodetector and the Mach-Zehnder modulator; the electrical signal generated by entering the first photodetector is used to modulate the Mach-Zehnder modulator. By adjusting the voltage of the fourth DC regulated power supply, the Mach-Zehnder modulator operates in the carrier-suppressed double-sideband mode, and the Mach-Zehnder modulator generates four beams of pump light and sends them into the third circulator;

[0018] The third branch light signal is polarization-controlled by the polarization controller and amplified by the second erbium-doped fiber amplifier, and then enters the dual-parallel Mach-Zehnder modulator as the carrier light; the carrier phase-shifted double-sideband signal output by the dual-parallel Mach-Zehnder modulator is split by the fifth coupler. One part is sent to the optical isolator, and the other part is sent to the optical bandpass filter to filter out the optical carrier and the lower sideband to obtain the carrier phase-shifted single-sideband signal;

[0019] Four beams of pump light are input into the second highly nonlinear optical fiber through a third circulator, and interact with the optical signal output by the optical isolator in the second highly nonlinear optical fiber to produce stimulated Brillouin scattering effect to form carrier light. After the carrier light is input into the second photodetector through the third circulator and beats, it is amplified by an electrical amplifier and drives a dual parallel Mach-Zehnder modulator to produce stronger sidebands, and ultimately generates an oscillation signal with a frequency four times the Brillouin frequency shift of the input optical signal; the output signal is beat by a third photodetector connected to an optical band filter and displayed and observed by a spectrum analyzer.

[0020] Furthermore, the center frequency of the tunable laser source is f c The light is split by the first coupler to form a first branch that is input into the first circulator, and the second branch formed is input into the third coupler; the first branch optical signal is input from port 1 of the first circulator and output from port 2 to the first highly nonlinear optical fiber, where it undergoes stimulated Brillouin scattering effect and generates a frequency of f c -f b The first-order Stokes light is input from port 2 of the first circulator and output from port 3 to the second coupler. After the first-order Stokes light is equally divided by the second coupler, a part of it forms the third branch as the input signal of the dual parallel Mach-Zehnder modulator, and the other part is input from port 1 of the second circulator and output from port 2 to the first highly nonlinear optical fiber, where it undergoes secondary stimulated Brillouin scattering effect, generating a frequency of f c -2f b The second-order Stokes light is input from port 2 of the second circulator and output from port 3 to form a fourth branch and sent to the first erbium-doped fiber amplifier;

[0021] Furthermore, after being polarization-controlled by the polarization controller and amplified by the second erbium-doped fiber amplifier, the third branch optical signal enters the dual parallel Mach-Zehnder modulator as carrier light. The carrier phase-shifted double-sideband signal output by the parallel Mach-Zehnder modulator is split by the fifth coupler, with one portion sent to the optical isolator and the other portion sent to the optical bandpass filter. The optical carrier and lower sideband are filtered out to obtain a carrier phase-shifted single-sideband signal, which is then passed through the third photodetector to obtain an output signal. The frequency of the final output signal can be displayed and observed using a spectrum analyzer.

[0022] Furthermore, the frequency of the fourth branch output is f c -2f b The second-order Stokes optical signal is amplified by the erbium-doped fiber amplifier and has the same intensity as the second branch optical signal. The third coupler combines the two beams and outputs a frequency of f. c -2f b and f cThe combined light is divided equally by the fourth coupler, one part is used as the input signal of the Mach-Zehnder modulator, and the other part enters the first photodetector to generate a frequency of 2f for modulating the Mach-Zehnder modulator. b electrical signals;

[0023] By adjusting the voltage of the fourth DC regulated power supply, the Mach-Zehnder modulator operates in the carrier suppressed double-sideband mode. The output signal of the Mach-Zehnder modulator has the same intensity and the adjacent frequency interval is 2f b The frequencies of the four pump beams are f c -4f b , f c -2f b , f c and f c +2f b , the generated four pump lights are sent to the third circulator.

[0024] Furthermore, four pump beams enter from port 1 of the third circulator and are output from port 2 to the second highly nonlinear optical fiber, where they interact with the optical signal output from the optical isolator to produce stimulated Brillouin scattering. Each pump beam will be emitted at a frequency lower than the pump frequency f. b A gain spectrum is generated at a frequency higher than the pump frequency f b The loss spectrum is generated at the pump light f c -4f b At frequency f c -5f b The gain spectrum is generated at the frequency f c -3f b The loss spectrum is generated at c -2f b At frequency f c -3f b The gain spectrum is generated at the frequency f c -f b The loss spectrum is generated at c At frequency f c -f b The gain spectrum is generated at the frequency f c +f b The loss spectrum is generated at the pump light f c +2f b At frequency f c +f b The gain spectrum is generated at the frequency f c +3f b The loss spectrum is generated at the pump light f c -2f b 、f c and fc +2f b The gain spectrum of c -4f b completely cancels out the pump light f c -2f b and f c The loss spectra, leaving only the pump light f c -4f b The gain spectrum of f c -5f b , and the pump light f c +2f b The loss spectrum of f c +3f b , finally, the pump light after being processed by the stimulated Brillouin scattering effect will significantly amplify the optical signal with a frequency of f c -5f b and attenuate the optical signal with a frequency within f c +3f b ;

[0025] Furthermore, the amplified sideband at f c -5f b , the attenuated sideband at f c +3f b and the carrier light at f c -f b enter the second photodetector through the 3-port of the third circulator for beat frequency, and then are amplified by an electrical amplifier to generate an electrical signal with a frequency of 4f b , and use the generated electrical signal with a frequency of 4f b to drive the dual-parallel Mach-Zehnder modulator to generate stronger sidebands at f c -5f b and f c +3f b ; through positive feedback, the oscillation signal at 4f b will become stronger and stronger until the output frequency of the optoelectronic oscillator loop is stabilized at 4f b of the millimeter-wave signal.

[0026] Beneficial effects: The present invention utilizes optical modulation of the continuous wave output by a tunable laser to achieve gain-loss superposition of stimulated Brillouin scattering, thereby obtaining a 4-fold frequency microwave signal; by using a dual-parallel Mach-Zehnder modulator biased in carrier-suppressed double-sideband modulation, the phase of the output microwave signal is tunable; compared with the prior art of using an optoelectronic oscillator based on stimulated Brillouin scattering to achieve frequency multiplication of the output microwave signal, the present invention utilizes multiple pump lights with a certain frequency interval instead of a single pump light to achieve frequency multiplication. The 4-fold frequency tunable optoelectronic oscillator based on stimulated Brillouin scattering according to claim 1 is characterized in that the wavelength of the optical signal output by the tunable laser is 1510nm to 1620nm, and the corresponding Brillouin frequency shift f b The adjustment range is 8.78GHz to 9.44GHz. The present invention adjusts the frequency f of the tunable laser c The output signal frequency can be adjusted from 35.12 GHz to 37.76 GHz. The output microwave signal phase can be adjusted from 0 degrees to 360 degrees by adjusting the DC bias voltage of Mach-Zehnder modulator 3 in the dual parallel Mach-Zehnder modulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the structure of the stimulated Brillouin scattering based quadruple frequency tunable optoelectronic oscillator of the present invention;

[0028] Figure 2 Schematic diagram of the structure of the dual parallel Mach-Zehnder modulator in the present invention;

[0029] Figure 3 Schematic diagram of spectrum processing of a frequency quadrupled tunable optoelectronic oscillator based on stimulated Brillouin scattering in an embodiment of the present invention;

[0030] Figure 4 This is a diagram of the output signal spectrum of the tunable laser when it is tuned from 1510 nm to 1620 nm with a step size of 10 nm in an embodiment of the present invention;

[0031] Figure 5 This is a spectrum diagram of the output signal of the tunable laser when the wavelength is 1550nm in an embodiment of the present invention;

[0032] Figure 6 This is a phase noise spectrum diagram of the optoelectronic oscillator when the tunable laser is set to 1550nm in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the accompanying drawings:

[0034] like Figure 1As shown in the figure, the present invention discloses a quadruple-frequency tunable optoelectronic oscillator based on stimulated Brillouin scattering, which includes a tunable laser source, a coupler, a circulator, an optical isolator, a highly nonlinear optical fiber, a polarization controller, an erbium-doped fiber amplifier, a Mach-Zehnder modulator, a dual-parallel Mach-Zehnder modulator, a photodetector, an electrical amplifier, an optical band-pass filter, and a spectrum analyzer.

[0035] The optical signal output by the tunable laser source with a central frequency of f c is split by the first coupler. The optical signal is divided into two optical signals of the first branch and the second branch and respectively output to the first circulator and the third coupler. The optical signal of the first branch is input from port 1 of the first circulator and output from port 2, and enters the first highly nonlinear optical fiber to generate the stimulated Brillouin scattering effect, generating the first-order Stokes light with a frequency of f c -f b , as shown in (1) of Figure 3 . The optical signal f c -f b is input from port 2 of the first circulator and output from port 3, enters the second coupler and is divided into two parts. One part is used as the input signal of the dual-parallel Mach-Zehnder modulator, and the other part is input from port 1 of the second circulator and output from port 2, and enters the first highly nonlinear optical fiber to generate the second-order Stokes light with a frequency of f c -2f b , as shown in (2) of Figure 3 . The optical signal f c -2f b is input from port 2 of the second circulator and output from port 3, and is sent to the erbium-doped fiber amplifier through the fourth branch.

[0036] After the polarization control by the polarization controller and the amplification by the second erbium-doped fiber amplifier, the optical signal of the third branch enters the dual-parallel Mach-Zehnder modulator as the carrier light. As shown in Figure 2As shown, the dual-parallel Mach-Zehnder modulator consists of three Mach-Zehnder modulators, two of which are named Mach-Zehnder modulator 1 and Mach-Zehnder modulator 2, located on each arm of the main Mach-Zehnder modulator 3. The three Mach-Zehnder modulators are powered by a first DC regulated power supply, a second DC regulated power supply, and a third DC regulated power supply, respectively. By adjusting the voltage of the DC regulated power supply, Mach-Zehnder modulator 1 operates in carrier-suppressed double-sideband modulation, Mach-Zehnder modulator 2 operates at the maximum transmission point where only the optical carrier is allowed to pass, and the dual-parallel Mach-Zehnder modulator operates at the bias point of carrier-phase-shifted double-sideband modulation. The carrier-phase-shifted double-sideband signal output by the dual-parallel Mach-Zehnder modulator is split by a fifth coupler, with one portion sent to an optical isolator and the other to an optical bandpass filter. The optical carrier and lower sideband are filtered out to obtain a carrier-phase-shifted single-sideband signal. The output signal is then obtained by beating the signal with a third photodetector. The frequency of the final output signal can be displayed and observed using a spectrum analyzer.

[0037] The frequency of the fourth branch output is f c -2f b The second-order Stokes optical signal is amplified by the erbium-doped fiber amplifier and has the same intensity as the second branch optical signal. The third coupler combines the two beams and the output frequency is f c -2f b and f c The optical signal, such as Figure 3 As shown in (3) in the figure. The combined light is split by the fourth coupler, one part of which is used as the input signal of the Mach-Zehnder modulator, and the other part enters the first photodetector to generate a frequency of 2f for modulating the Mach-Zehnder modulator. b By adjusting the voltage of the fourth DC regulated power supply, the Mach-Zehnder modulator operates in the carrier suppressed double-sideband mode. The output signal of the Mach-Zehnder modulator has the same intensity and the adjacent frequency interval is 2f b Four pump beams f c -4f b , f c -2f b , f c and f c +2f b ,like Figure 3 As shown in (4), the generated four pump beams are sent to the third circulator;

[0038] Four pump beams enter from port 1 of the third circulator and are output from port 2 to the second highly nonlinear optical fiber. They interact with the optical signal output from the isolator in the second highly nonlinear optical fiber to produce stimulated Brillouin scattering effect. At this time, each pump light will be lower than the pump frequency f bA gain spectrum is generated at a certain point, and a loss spectrum is generated at a frequency higher than the pump frequency f b A loss spectrum is generated at a certain point, that is, the pump light f c -4f b At the frequency f c -5f b A gain spectrum is generated at a certain point, and a loss spectrum is generated at the frequency f c -3f b A loss spectrum is generated at a certain point; the pump light f c -2f b At the frequency f c -3f b A gain spectrum is generated at a certain point, and a loss spectrum is generated at the frequency f c -f b A loss spectrum is generated at a certain point; the pump light f c At the frequency f c -f b A gain spectrum is generated at a certain point, and a loss spectrum is generated at the frequency f c +f b A loss spectrum is generated at a certain point, the pump light f c +2f b At the frequency f c +f b A gain spectrum is generated at a certain point, and a loss spectrum is generated at the frequency f c +3f b A loss spectrum is generated at a certain point, as shown in (5) of Figure 3 Since the frequency between two pump lights at adjacent frequencies is equal to twice the value of the Brillouin frequency shift 2f b , so the pump light f c -2f b , f c and f c +2f b The gain spectra can completely cancel out the loss spectra of the pump lights f c -4f b , f c -2f b and f c Only the gain spectrum of the pump light f c -4f b remains, and the loss spectrum of the pump light f c -5f b , and the loss spectrum of the pump light f c +2f b The loss spectrum of the light signal at the frequency f c +3f b . Therefore, the pump light after being processed by the stimulated Brillouin scattering effect will significantly amplify the optical signal with a frequency of f c -5f b while attenuating the optical signal with a frequency at f c +3f b ;

[0039] At f c-5f b The amplified sideband at f c +3f b The attenuation sideband at f c -f b The carrier light at the position passes through the 3-port of the third circulator and enters the second photodetector. After the beat frequency is amplified by the electric amplifier, the frequency is 4f b The electrical signal is then generated using a frequency of 4f b The electrical signal drives the dual parallel Mach-Zehnder modulator at f c -5f b and f c +3f b Through positive feedback, 4f b The oscillation signal at the position will become stronger and stronger until the output frequency of the optoelectronic oscillator loop stabilizes and oscillates to 4f b millimeter wave signals.

[0040] By adjusting the frequency f of the tunable laser c , the frequency of the output signal of the quadruple frequency tunable optoelectronic oscillator based on stimulated Brillouin scattering can be adjusted in the range of 35.12 GHz to 37.76 GHz.

[0041] By adjusting the DC bias voltage of the Mach-Zehnder modulator 3 in the dual parallel Mach-Zehnder modulator, the phase of the output microwave signal can be adjusted within the range of 0 degrees to 360 degrees.

[0042] Example 1: Santec's TSL-510 tunable laser is selected as the tunable laser, with a wavelength range of 1510nm to 1630nm, which can be tuned according to the frequency of the output signal. The Mach-Zehnder modulator is Oclaro's AM-40, with a bandwidth of up to 40GHz and a half-wave voltage V πis 4.9V; the dual parallel Mach-Zehnder modulator is Mach-40086 of COVEGA; the first DC regulated power supply, the second DC regulated power supply, the third DC regulated power supply, and the fourth DC regulated power supply are GPS-4303C of GW Instek, with an output voltage amplitude of 1V to 20V; the first circulator, the second circulator, and the third circulator are CIR-3-1550-900um-1m-FC / APC of Shenzhen Zhiyuan Optical Communication Technology Co., Ltd.; the first photodetector, the second photodetector, and the third photodetector are XPDV2120RA produced by Finisar, with a bandwidth of 60GHz and a rate of 40Gbps; the first highly nonlinear fiber and the second highly nonlinear fiber are 1km highly nonlinear fibers of Changfei Technologies Co., Ltd.; the tunable optical filter is XTM-50U, with a wavelength tuning range of 1480nm to 1620nm, a tuning accuracy of 5pm, a bandwidth tuning accuracy of 1pm, and an insertion loss of 5dB; the first erbium-doped fiber amplifier and the second erbium-doped fiber amplifier have a working wavelength range of 1530nm to 1560nm and a gain greater than 25 times; the first coupler, the second coupler, the third coupler, the fourth coupler, and the fifth coupler are FBT Fiber Optic Splitter / FBT Fiber of Snow-Sea Company; the polarization controller is a polarization controller of Sichuan Light Source Optoelectronic Technology Co., Ltd.; the optical isolator is an optical isolator of FiberPro Optoelectronic Technology (Shenzhen) Co., Ltd., with an isolation greater than 40dB; the spectrum analyzer is E5052B of Agilent together with the upconverter E5053 of Agilent, and the measured signal range bandwidth is 10MHz to 110GHz.

[0043] According to Figure 1 Connect the corresponding instruments and equipment. The central frequency output by the tunable laser source is f c The light is split by the first coupler. The optical signal of the first branch undergoes stimulated Brillouin scattering effect in the first highly nonlinear fiber, generating the first-order Stokes light with a frequency of f c -f b The returned first-order Stokes light f c -f bIt is divided into two parts by the second coupler. One part enters the dual-parallel Mach-Zehnder modulator as the carrier light after passing through the polarization controller for polarization control and being amplified by the second erbium-doped fiber amplifier through the third branch. By adjusting the first DC regulated power supply, the second DC regulated power supply, and the third DC regulated power supply, the dual-parallel Mach-Zehnder modulator operates at the carrier phase-shift double-sideband modulation bias point. The output carrier phase-shift double-sideband signal is split by the fifth coupler. One part is sent to the optical isolator, and the other part is sent to the optical band-pass filter. The other branch optical signal output by the second coupler enters the first highly nonlinear fiber to generate the second-order stimulated Brillouin scattering effect, generating the second-order Stokes light with a frequency of f c -2f b which is sent to the erbium-doped fiber amplifier through the fourth branch;

[0044] The second-order Stokes optical signal with a frequency of f c -2f b output from the fourth branch has the same intensity as the optical signal of the second branch after being amplified by the erbium-doped fiber amplifier. The two paths of light are combined by the third coupler, and the output optical signal has frequencies of f c -2f b and f c . The combined light is split by the fourth coupler. One part serves as the input signal of the Mach-Zehnder modulator, and the other part enters the first photodetector to generate an electrical signal with a frequency of 2f b for modulating the Mach-Zehnder modulator. By adjusting the voltage of the fourth DC regulated power supply, the Mach-Zehnder modulator operates in the carrier-suppressed double-sideband mode. The output signal of the Mach-Zehnder modulator is four pump lights with the same intensity and adjacent frequency intervals of 2f b f c -4f b , f c -2f b , f c and f c +2f b . The generated four pump lights are sent to the third circulator;

[0045] The four pump lights interact with the optical signal output from the isolator in the second highly nonlinear fiber to generate the stimulated Brillouin scattering effect. Each pump light will respectively generate a gain spectrum at a frequency lower than the pump frequency f b and a loss spectrum at a frequency higher than the pump frequency f b . Since the frequency between two adjacent-frequency pump lights is equal to twice the value of the Brillouin frequency shift 2f b , so the pump lights f c -2f b , f c and f c +2fb The gain spectrum of c -4f b can completely cancel out the pump light f c -2f b and the loss spectrum of f c , leaving only the gain spectrum of the pump light f c -4f b f c -5f b , and the loss spectrum of the pump light f c +2f b f c +3f b ;

[0046] At f c -5f b , the amplified sideband, at f c +3f b , the attenuated sideband, and at f c -f b , the carrier light enter the second photodetector for beat frequency, and after being amplified by an electrical amplifier, an electrical signal with a frequency of 4f b is generated. Then, it is used to modulate the dual-parallel Mach-Zehnder modulator to generate stronger sidebands at f c -5f b and f c +3f b . Through positive feedback, the oscillation signal at 4f b will become stronger and stronger until the optoelectronic oscillator loop remains stable. The carrier phase-shifted double-sideband signal output by the dual-parallel Mach-Zehnder modulator is split by the fifth coupler. A part of it is filtered by an optical bandpass filter to remove the optical carrier and the lower sideband to obtain a carrier phase-shifted single-sideband signal. The carrier phase-shifted single-sideband signal is sent to a spectrum analyzer after beat frequency by the third photodetector, and the frequency of the final output signal can be displayed and observed.

[0047] Since the Brillouin frequency shift depends on the wavelength of the pump light, the frequency of the microwave signal output by the optoelectronic oscillator can be tuned by tuning the wavelength of the tunable laser source. When the wavelength of the tunable laser source is adjusted from 1620 nm to 1510 nm with a step size of 10 nm, the Brillouin frequency shift f b increases from 8.78 GHz to 9.44 GHz, and the tuning range of the output millimeter-wave signal frequency is 35.12 GHz to 37.76 GHz, as Figure 4 shown.

[0048] When the wavelength of the tunable laser source is set to 1550 nm, the Brillouin frequency shift f b is 9.2 GHz, and the output microwave signal of the optoelectronic oscillator at 36.8 GHz is obtained as Figure 5As shown, the phase noise at a 10 kHz offset is -110.74 dBc / Hz, as Figure 6 shown.

Claims

1. A frequency quadrupled tunable optoelectronic oscillator based on stimulated Brillouin scattering, characterized in that: It includes a tunable laser source, which is connected to two inlets of a third coupler through two lines by a first coupler. One line includes a first circulator, a second coupler, a second circulator, and a first erbium-doped fiber amplifier connected in sequence, and the other line is directly connected; The output of the third coupler is sequentially connected with a fourth coupler, a Mach-Zehnder modulator, a third circulator, and a second highly nonlinear fiber; A first photodetector is also connected in parallel between the fourth coupler and the Mach-Zehnder modulator. The port 1 of the third circulator is connected to the Mach-Zehnder modulator, and the port 2 of the third circulator is connected to the second highly nonlinear fiber; The port 3 of the first circulator is connected to the port 1 of the second circulator through a second coupler, and a first highly nonlinear fiber is connected between the port 2 of the first circulator and the port 2 of the second circulator; The second coupler is also sequentially connected with a polarization controller, a second erbium-doped fiber amplifier, and a dual-parallel Mach-Zehnder modulator; The dual-parallel Mach-Zehnder modulator is respectively connected with a fifth coupler, and an electrical amplifier and a second photodetector connected in sequence. The second photodetector is connected to the port 3 of the third circulator. The fifth coupler is respectively connected with an optical isolator and an optical bandpass filter. The optical isolator is connected to the second highly nonlinear fiber; The optical bandpass filter is sequentially connected with a third photodetector and a spectrum analyzer.

2. The quadruple-frequency tunable optoelectronic oscillator based on stimulated Brillouin scattering according to claim 1, characterized in that: The dual-parallel Mach-Zehnder modulator includes three Mach-Zehnder modulators and three DC regulated power supplies powered respectively, including a main Mach-Zehnder modulator 3 and sub-Mach-Zehnder modulators 1 and 2; The sub-Mach-Zehnder modulator 1 and the sub-Mach-Zehnder modulator 2 are respectively arranged on two arms of the main Mach-Zehnder modulator 3. The three DC regulated power supplies include a first DC regulated power supply for powering the sub-Mach-Zehnder modulator 1, a second DC regulated power supply for powering the sub-Mach-Zehnder modulator 2, and a third DC regulated power supply for powering the main Mach-Zehnder modulator 3; By adjusting the voltage of the DC regulated power supply, the sub-Mach-Zehnder modulator 1 works in carrier-suppressed double-sideband modulation, the sub-Mach-Zehnder modulator 2 works at the maximum transmission point when only allowing the optical carrier to pass through, and the dual-parallel Mach-Zehnder modulator works at the carrier-phase-shifted double-sideband modulation bias point; The Mach-Zehnder modulator is connected with a fourth DC regulated power supply for powering it; The optical wavelength at which the Mach-Zehnder modulator works is 1525 nm to 1605 nm, and the bandwidth is 40 GHz; The optical wavelength at which the dual-parallel Mach-Zehnder modulator works is 1525 nm to 1605 nm, and the bandwidth is 40 GHz to 60 GHz; The adjustable range of the output voltage values of the first DC regulated power supply, the second DC regulated power supply, the third DC regulated power supply, and the fourth DC regulated power supply is 1 V to 20 V.

3. The stimulated Brillouin scattering-based quadruple frequency tunable optoelectronic oscillator according to claim 1, characterized in that: The first highly nonlinear fiber and the second highly nonlinear fiber have the same length of 1 km, the stimulated Brillouin gain linewidth is 40 MHz, and the stimulated Brillouin frequency shift amount f B is 11 GHz.

4. The quadruple-frequency tunable optoelectronic oscillator based on stimulated Brillouin scattering according to claim 1, characterized in that: The isolation of the optical isolator is greater than 40 dB; the bandwidths of the first photodetector, the second photodetector, and the third photodetector are 60 GHz; the wavelength tuning range of the optical bandpass filter is from 1480 nm to 1620 nm, the tuning accuracy is 5 pm, and the insertion loss is 5 dB; the amplification factors of the first erbium-doped fiber amplifier and the second erbium-doped fiber amplifier are greater than 25 times; the bandwidth of the spectrum analyzer is 100 GHz.

5. A working method of the four - frequency - doubling tunable optoelectronic oscillator based on stimulated Brillouin scattering according to claim 1, characterized in that, The steps are as follows: The light emitted by the tunable laser source is split by the first coupler into a first branch light and a second branch light. The first branch light generates a first-order Stokes light and a second-order Stokes light in sequence and then forms a fourth branch light. After being amplified by the first erbium-doped fiber amplifier, the fourth branch light is fed into the third coupler, and the amplified fourth branch light has the same intensity as the second branch light signal. The second branch light is directly fed into the third coupler. The fourth branch light formed by the second-order Stokes light is combined by the third coupler and then sent to the fourth coupler for splitting, and then is respectively input into the first photodetector and the Mach-Zehnder modulator. The signal entering the first photodetector generates an electrical signal for modulating the Mach-Zehnder modulator. By adjusting the voltage of the fourth DC regulated power supply, the Mach-Zehnder modulator operates in the carrier-suppressed double-sideband mode, and the Mach-Zehnder modulator generates four pump lights and sends them into the third circulator. The third branch light signal is polarization-controlled by the polarization controller and amplified by the second erbium-doped fiber amplifier, and then enters the dual-parallel Mach-Zehnder modulator as the carrier light. The carrier phase-shifted double-sideband signal output by the dual-parallel Mach-Zehnder modulator is split by the fifth coupler. One part is sent to the optical isolator, and the other part is sent to the optical bandpass filter. The optical carrier and the lower sideband are filtered out to obtain the carrier phase-shifted single-sideband signal. The four pump lights are input into the second highly nonlinear fiber through the third circulator and interact with the optical signal output by the optical isolator in the second highly nonlinear fiber to generate the stimulated Brillouin scattering effect to form the carrier light. The carrier light is input into the second photodetector through the third circulator for beat frequency, and then is amplified by the electrical amplifier to drive the dual-parallel Mach-Zehnder modulator to generate stronger sidebands, and finally generate an oscillation signal with a Brillouin frequency shift four times that of the input optical signal. The output signal is beat-frequency detected by the third photodetector connected to the optical bandpass filter and then displayed and observed through the spectrum analyzer.

6. The working method according to claim 5, characterized in that, The central frequency of the tunable laser source is f c The light of is split by the first coupler and the first branch is input into the first circulator, and the second branch is input into the third coupler; the optical signal of the first branch is input from port 1 of the first circulator and output from port 2 to the first highly nonlinear optical fiber to generate stimulated Brillouin scattering effect, generating a frequency of f c -f b of the first-order Stokes light; the first-order Stokes light is then input from port 2 of the first circulator and output from port 3 to the second coupler. After the first-order Stokes light is equally divided by the second coupler, a part forms the third branch as the input signal of the dual-parallel Mach-Zehnder modulator, and the other part is input from port 1 of the second circulator and output from port 2 to the first highly nonlinear optical fiber to generate a second-order stimulated Brillouin scattering effect, generating a frequency of f c -2f b of the second-order Stokes light. The second-order Stokes light is input from port 2 of the second circulator and output from port 3 to form the fourth branch and sent to the first erbium-doped fiber amplifier.

7. The working method according to claim 6, characterized in that: The third branch light signal is polarization-controlled by the polarization controller and amplified by the second erbium-doped fiber amplifier, and then enters the dual-parallel Mach-Zehnder modulator as the carrier light. The carrier phase-shifted double-sideband signal output by the parallel Mach-Zehnder modulator is split by the fifth coupler. One part is sent into the optical isolator, and the other part is sent into the optical bandpass filter. The optical carrier and the lower sideband are filtered out to obtain the carrier phase-shifted single-sideband signal. After beat-frequency detection by the third photodetector, the output signal is obtained, and the frequency of the final output signal can be displayed and observed by the spectrum analyzer.

8. The working method according to claim 7, characterized in that: The frequency output by the fourth branch is f c -2f b The second-order Stokes optical signal of is amplified by an erbium-doped fiber amplifier and has the same intensity as the optical signal of the second branch. The two paths of light are combined by the third coupler, and the output frequency is f c -2f b and f c The combined light is equally divided by the fourth coupler. One part is used as the input signal of the Mach-Zehnder modulator, and the other part enters the first photodetector to generate an electrical signal with a frequency of 2f for modulating the Mach-Zehnder modulator b ; The Mach-Zehnder modulator is operated in the carrier-suppressed double-sideband mode by adjusting the voltage of the fourth DC regulated power supply. The output signal of the Mach-Zehnder modulator is four pump beams with the same intensity and adjacent frequency intervals of 2f b The frequencies of the four pump beams are f c - 4f b , f c - 2f b , f c and f c + 2f b respectively. The four generated pump beams are sent into the third circulator.

9. The working method according to claim 8, characterized in that, Four pump beams enter from port 1 of the third circulator and are output from port 2 to the second highly nonlinear optical fiber. They interact with the optical signal output from the optical isolator in the second highly nonlinear optical fiber to produce stimulated Brillouin scattering effect. Each pump beam will be separately at a frequency lower than the pump frequency f b A gain spectrum is generated at a frequency higher than the pump frequency f b The loss spectrum is generated at the pump light f c -4f b At frequency f c -5f b The gain spectrum is generated at the frequency f c -3f b The loss spectrum is generated at c -2f b At frequency f c -3f b The gain spectrum is generated at the frequency f c -f b The loss spectrum is generated at c At frequency f c -f b The gain spectrum is generated at the frequency f c +f b The loss spectrum is generated at the pump light f c +2f b At frequency f c +f b The gain spectrum is generated at the frequency f c +3f b The loss spectrum is generated at the pump light f c -2f b 、f c and f c +2f b The gain spectrum of the pump light f c -4f b , f c -2f b and f c The loss spectrum of the pump light f c -4f b The gain spectrum f c -5f b , and the pump light f c +2f b The loss spectrum f c +3f b Finally, the pump light after the stimulated Brillouin scattering effect will significantly amplify the frequency f c -5f b The optical signal is attenuated at the frequency f c +3f b The optical signal at .

10. The working method according to claim 9, characterized in that: At f c -5f b the amplified sideband, at f c +3f b the attenuated sideband, and the carrier light at f c -f b enter the 3-port of the third circulator and are beat in the second photodetector, and then amplified by an electrical amplifier to generate an electrical signal with a frequency of 4f b . The generated electrical signal with a frequency of 4f b is used to drive a dual-parallel Mach-Zehnder modulator to generate stronger sidebands at f c -5f b and f c +3f b . Through positive feedback, the oscillation signal at 4f b will become stronger and stronger until the output frequency of the optoelectronic oscillator loop is stabilized at 4f b mm-wave signal.

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