Active mode-locked coupled optoelectronic oscillator

Abstract

The application discloses an active mode-locked coupled optoelectronic oscillator, and belongs to the technical field of microwave photonics, in order to solve the problems existing in the prior art, the active mode-locked coupled optoelectronic oscillator comprises a mode-locked laser composed of a laser pumping source, a wavelength division multiplexer, a gain optical fiber, an adjustable optical filter, a double-drive Mach-Zehnder intensity modulator, a polarization controller and an adjustable optical delay line, and an optoelectronic oscillator composed of an optical coupler, a detector, a microwave amplifier, a wideband electric filter and an electric power divider. In the structure of the application, the double-drive Mach-Zehnder intensity modulator is added, the feedback signal and the radio frequency signal are injected into the double-drive Mach-Zehnder intensity modulator, so that the double-tone signal can modulate the intensity of the optical pulse, and the active mode-locked coupled optoelectronic oscillator is realized. The injection locking technology and the phase matching technology can improve the noise suppression performance under the high harmonic state. Meanwhile, the wideband filter is added in the coupled optoelectronic oscillator structure, and the tunable range of the optical pulse output frequency is improved.

Description

Technical Field

[0001] This invention belongs to the field of microwave photonics technology, specifically relating to an intensity-feedforward active mode-locked coupled optoelectronic oscillator. Background Technology

[0002] High-spectral-purity microwave signals are widely used in wireless communication systems, radar signals, and measurement systems. Opto-oscillators can generate microwave signals with low phase noise and high side-mode rejection ratios, offering the advantage of frequency tunability. Traditional active mode-locked lasers, due to high intracavity noise, phase jitter between modes, and mode gain competition, cannot achieve high side-mode rejection ratio single-mode signal oscillation, making it difficult to generate high-frequency-purity single-tone signals. Therefore, combining microwave photonics technology with lasers utilizes phase-matching conditions to achieve stable optical pulse output.

[0003] Traditional high-repetition-rate optical pulse signals are generated by actively mode-locked fiber lasers (AMS), and periodic loss modulation is achieved by changing the frequency of the injected signal to output harmonic signals. Typically, the frequency of the output pulse signal is an integer multiple of the fundamental frequency. However, in harmonic operation, AMS lasers experience supermode noise and mode competition within the cavity, leading to amplitude jitter in the microwave signal. This jitter worsens with increasing mode-locking order, making it impossible to output high signal-to-noise ratio (SNR) microwave signals. Microwave photonics, as an interdisciplinary field of microwave and photonics technologies, offers advantages such as high bandwidth and low loss. Opto-oscillators can achieve stable phase matching of the opto-loop by adjusting the phase of the electrical circuit, maximizing the transmittance of the optical pulse through the modulator and achieving high side-mode rejection ratio (SNR) microwave signal output.

[0004] A typical method to improve spectral purity within an optical cavity is to incorporate a Fabry-Perot filter, as shown in the diagram below. Figure 1As shown, refer to the article "A Scheme for Suppressing Supermode Noise in Fiber Lasers Based on High-Precision Optical Filters" published by Kazi Sarwar Abedin et al. in *Applied Physics Letters*. PUMP (pump source) is a 980nm pump source, WDM (Wavelength division multiplexer) is a wavelength division multiplexer, EDF (Erbium-Doped Fiber) is an erbium-doped gain fiber, OC (Optical Isolator) is an optical coupler, VODL (Variable Optical Delay Line) is a tunable optical delay line, MZM (Mach-Zehnder Modulator) is a Mach-Zehnder modulator, PC (Polarization Controller) is a polarization controller, FP (Fabry Perot) is an optical filter, and RF is a radio frequency signal source. Without affecting the overall cavity length, by adjusting the bandwidth and corresponding gain wavelength of the optical filter, the center wavelength of the transmission spectrum of the comb filter is aligned with a set of modes. At this point, the transmittance of that set of modes within the cavity reaches its maximum, thereby suppressing sidemode noise. However, the transmission peak of the FP filter needs to be constantly aligned with an integer multiple of the laser's fundamental frequency, which introduces a more complex structure outside the cavity. Furthermore, the FP optical filter has a relatively large insertion loss, increasing the loss within the laser cavity, requiring greater optical power to ensure stable pulse output.

[0005] Another method to suppress supermode noise within the optical cavity is to utilize the nonlinear effects (self-phase modulation, cross-phase modulation) and dispersion effects of optical fibers. This is achieved by adding a polarization controller and a polarization-dependent isolator within the optical cavity of the photoelectric oscillator, thus realizing polarization-dependent filtering. A diagram of the device is shown below. Figure 2 As shown. See IEEE Photonics Technology Letters, where Li Yuhua et al. published a paper titled "A Supermode Noise Suppression Method Based on Nonlinear Polarization Rotation". PUMP (Pump source) is a 980nm pump source, WDM (Wavelength Division Multiplexer) is a wavelength division multiplexer, EDF (Erbium-Doped Fiber) is an erbium-doped gain fiber, OC (Optical Isolator) is an optical coupler, VODL (Variable Optical Delay Line) is a tunable optical delay line, MZM (Mach-Zehnder Modulator) is a Mach-Zehnder modulator, PC (Polarization Controller) is a polarization controller, FP (Fabry Perot) is an optical filter, and RF is a radio frequency signal source.

[0006] The pump light within the cavity is elliptically polarized. After passing through a polarization-dependent isolator, the elliptically polarized light becomes linearly polarized. A nonlinear phase shift accumulates through a polarization controller, generating a polarization rotation effect. This causes the second light pulse passing through the polarization controller to undergo polarization-dependent loss modulation. Therefore, this all-optical-domain method utilizing passive mode-locking can improve the side-mode suppression ratio (NPR). However, NPR based on birefringence is susceptible to environmental influences, exhibiting weak resistance to interference, and requires the introduction of long optical fibers with precise control over their dynamic length. Thus, existing methods for suppressing supermode noise within optical ring cavities suffer from structural complexity, instability, and high intracavity loss. Summary of the Invention

[0007] To address the problems of large time jitter, low side-mode rejection ratio, and poor frequency stability of high repetition frequency optical pulses in existing fiber lasers due to the lack of an intensity feedback structure, this invention proposes an active mode-locked coupled opto-oscillator. A dual-drive Mach-Zehnder intensity modulator is added to the coupled opto-oscillator structure, and feedback and radio frequency signals are injected into the dual-drive Mach-Zehnder intensity modulator. This allows the two-tone signal to modulate the intensity of the optical pulse, thus realizing an active mode-locked coupled opto-oscillator.

[0008] The solution to the technical problem of this invention is:

[0009] An active mode-locked coupled optoelectronic oscillator comprises a laser pump source, a wavelength division multiplexer, a gain fiber, an optical isolator, a first tunable optical delay line, a 90:10 optical coupler, a polarization controller, a dual-drive Mach-Zehnder intensity modulator, a 98:2 optical coupler, a tunable optical filter, an RF signal source, a second tunable optical delay line, a photodetector, a tunable electrical gain amplifier, a broadband electrical filter, an electrical phase shifter, and a power divider.

[0010] The laser pump source is connected to end a of the wavelength division multiplexer. The wavelength division multiplexer and the pump source work together to provide a stable pump source for the active mode-locked laser. After passing through the wavelength division multiplexer, the pump light is output from end c and connected to the gain fiber. The gain fiber acts as a gain medium to provide gain for the optical pulses generated by active mode-locking. The other end of the gain fiber is connected to the input end of the optical isolator. The optical isolator has very low loss for forward-propagating light but high loss for reverse-propagating light, ensuring unidirectional transmission of optical circulation within the cavity. The other end of the optical isolator is connected to the first adjustable optical delay line. The output end of the first adjustable optical delay line is connected to end d of the 90:10 optical coupler. The e end of the 90:10 coupler is connected to the polarization controller. The other end of the polarization controller is connected to the optical intensity modulator. The optical intensity modulator receives the radio frequency signal and the signal generated by the optoelectronic oscillator and achieves stable active mode-locking. The other end of the dual-drive Mach-Zehnder intensity modulator enters the input of a 98:2 optical coupler. One output of the 98:2 coupler enters a tunable optical filter, and the output of the tunable optical filter enters the b-terminal of a wavelength division multiplexer, forming a mode-locked laser structure. The tunable optical filter can suppress longitudinal mode competition in the laser, enabling flexible wavelength selection.

[0011] The light output from the 90:10 optical coupler enters the second adjustable optical delay line. This line adjusts the optical delay of the light signal entering the coupled opto-oscillator, ensuring that the time delay from the intensity modulator output point to the optical delay output point equals the transmission delay of the oscillating signal from the opto-oscillator to the intensity modulator. The photodetector, connected to the second adjustable optical delay line, detects the generated optical pulse signal. An adjustable gain amplifier amplifies the optical pulse signal generated by the detector. A broadband electrical filter selects the oscillation frequency of the coupled opto-oscillator structure. An electrical phase shifter adjusts the phase of the microwave signal generated by the coupled opto-oscillator. Connected to the electrical filter, the signal generated by the oscillation is input to another port of the dual-drive Mach-Zehnder intensity modulator via a power divider. By adjusting the gain of the adjustable gain amplifier, the intensity of the feedback signal can be controlled.

[0012] The beneficial effects of this invention are as follows: This invention employs microwave photonics technology, effectively reducing structural complexity and improving the frequency stability and side-mode suppression ratio of the optical pulse signal. By injecting the feedback signal output from the opto-oscillator and the microwave source signal together into a dual-drive Mach-Zehnder intensity modulator, injection locking of the two-tone signal is achieved. Furthermore, the optical delay in the fiber laser and the electrical delay in the opto-oscillator can be flexibly adjusted to achieve precise phase matching, thereby suppressing supermode noise in harmonic states.

[0013] 1. The all-fiber laser, which consists of a pump source, wavelength division multiplexer, gain fiber, tunable filter, dual-drive Mach-Zehnder intensity modulator, polarization controller, and tunable delay line, has a relatively short overall cavity length, less influence from stray frequency modes, and higher side-mode suppression ratio.

[0014] 2. Active mode-locking is achieved by utilizing the dual-tone injection locking characteristic of a dual-drive Mach-Zehnder intensity modulator, reducing the transmittance of spurious modes and suppressing supermode noise in higher harmonic states. This improves the single-sideband phase noise output characteristics of the actively mode-locked coupled optoelectronic oscillator.

[0015] 3. A broadband electrical filter is added to the active mode-locked coupled optoelectronic oscillator to ensure that the output signal has a large frequency tunable range. The frequency tunability is achieved through an adjustable optical delay line and an electrical phase shifter. Attached Figure Description

[0016] Figure 1 This is a typical structural diagram of a fiber laser device designed to improve the side-mode suppression ratio.

[0017] Figure 2 This is a structural diagram of a fiber laser based on nonlinear polarization rotation;

[0018] Figure 3 This is a structural diagram of the active mode-locked coupled optoelectronic oscillator of the present invention, wherein the optical loop is connected by solid lines and the electrical loop is connected by dashed lines.

[0019] Figure 4 This is a schematic diagram of the principle of suppressing supermode noise in the cavity of an active mode-locked coupled optoelectronic oscillator, where (a) is the optical frequency mode generated by the oscillation of the mode-locked laser; (b) is the radio frequency signal frequency generated by the beat frequency of the photodetector; (c) is the oscillation frequency of the active mode-locked coupled optoelectronic oscillator; (d) is the optical pulse signal generated by the feedback of the active mode-locked coupled optoelectronic oscillator; and (e) is the radio frequency signal finally output by the active mode-locked coupled laser.

[0020] Figure 5 This is a spectrum generated by a traditional coupled optoelectronic oscillator;

[0021] Figure 6 This is a spectrum diagram of a tunable single-tone signal generated by an active mode-locked coupled optoelectronic oscillator.

[0022] Figure 7 This is a comparison chart of the phase noise of an active mode-locked coupled optoelectronic oscillator and a conventional coupled optoelectronic oscillator.

[0023] Figure 8 It measures the phase noise and frequency jitter of an active mode-locked coupled optoelectronic oscillator. Detailed Implementation

[0024] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0025] like Figure 3 As shown, the active mode-locked coupled optoelectronic oscillator includes: a mode-locked laser consisting of a laser pump source 1, a wavelength division multiplexer 2, a gain fiber 3, an optical isolator 4, a first tunable optical delay line 5, a 90:10 optical coupler 6, a polarization controller 7, a dual-drive Mach-Zehnder intensity modulator 8, a 98:2 optical coupler 9, a tunable optical filter 10, and an RF signal source 11; and an optoelectronic oscillator consisting of a second tunable optical delay line 12, a photodetector 13, a tunable electrical gain amplifier 14, a broadband electrical filter 15, an electrical phase shifter 16, and a power divider 17.

[0026] The wavelength of the laser pump source 1 is 980nm.

[0027] The wavelength division multiplexer 2 is a 980 / 1550nm wavelength division multiplexer.

[0028] The gain fiber 3 is composed of two segments of gain fiber spliced ​​together, with the first segment having a length of 5m and the second segment having a length of 3m.

[0029] The laser pump source 1 is connected to the a-end of the wavelength division multiplexer 2. The wavelength division multiplexer 2 and the pump source 1 work together to provide a stable pump source for the mode-locked laser. The pump light is output through the c-end of the wavelength division multiplexer 2 and connected to the gain fiber 3. The gain fiber 3 acts as a gain medium to provide gain for the optical pulses generated by active mode-locking. The other end of the gain fiber 3 is connected to the input end of the optical isolator 4. The optical isolator 4 has very low loss for forward-propagating light but high loss for reverse-propagating light, ensuring unidirectional transmission of optical circulation within the cavity. The other end is connected to the first tunable optical delay line 5. The output of the first tunable optical delay line 5 is connected to the d-end of the 90:10 optical coupler 6. The e-end of the 90:10 optical coupler 6 is connected to the polarization controller 7. The other end of the polarization controller 7 is connected to the dual-drive Mach-Zehnder intensity modulator 8. The RF signal source 11 transmits RF signals and the feedback signal output from the power divider 17 to the RF input port of the dual-drive Mach-Zehnder intensity modulator 8 to provide a stable reference signal for the optical pulse and achieve stable active mode locking. The other end of the intensity modulator 8 enters the input of the 98:2 optical coupler 9. One of the outputs of the 98:2 optical coupler 9 enters the tunable optical filter 10. The other output of the tunable optical filter 10 is connected to the b-port of the wavelength division multiplexer, forming a mode-locked laser structure. The tunable optical filter 10 can suppress longitudinal mode competition of the laser and achieve flexible wavelength selection.

[0030] The light output from the f-terminal of the 90:10 optical coupler 6 enters the second adjustable optical delay line 12. The first adjustable optical delay line 5 and the second adjustable optical delay line 12 can adjust the optical delay of the optical signal entering the photoelectric oscillator, so that the time delay of the optical pulse signal from the output point of the intensity modulator to the output point of the optical delay is equal to the transmission delay of the oscillation signal in the photoelectric oscillator to the intensity modulator. By modulating the matching degree between the optical delay and the electrical delay, the optical pulse can be synchronously modulated by the feedback, intensity-adjustable microwave signal. The photodetector 13 is connected to the output terminal of the second adjustable optical delay line 12 to detect the generated optical pulse signal. The output terminal of the photodetector 13 is connected to the input terminal of the adjustable electrical gain amplifier 14, which is used to amplify the optical pulse signal generated by the detector. The output terminal of the adjustable electrical gain amplifier 14 is connected to the input terminal of the broadband electrical filter 15, which can select the oscillation frequency of the active-coupled photoelectric oscillator structure. The output of the broadband electrical filter 15 is connected to the input of the electrical phase shifter 16. The electrical phase shifter 16 can adjust the phase of the microwave signal generated by the active mode-locked coupled optoelectronic oscillator. The output of the electrical phase shifter 16 is connected to the input of the power divider 17. The signal output by the power divider 17 is input to the RF port of the dual-drive Mach-Zehnder intensity modulator 8 to realize the closed loop of the electrical circuit.

[0031] The working process of the active mode-locked coupled optoelectronic oscillator is as follows: The pump light generated by the pump source 1 passes through the gain fiber 3 and generates a corresponding signal light. The signal light continuously oscillates and accumulates energy in the fiber cavity via the optical loop. Due to the randomness of the phase of the optical signal, stable interference cannot be formed in the cavity. Therefore, stable optical pulses cannot be generated without an externally injected radio frequency signal. Thus, an optoelectronic oscillation loop needs to be introduced. By adjusting the first adjustable optical delay line 8, the second adjustable optical delay line 15, and the electrical phase shifter 16, the optical signal delay and electrical signal delay can be continuously changed, so that a certain frequency mode in the optical cavity is aligned with the frequency mode of the electrical signal, achieving mode matching. Under the condition of phase matching, the center wavelength of the optical filter 10 can be changed to achieve switching between different gain wavelengths. Since the delay amounts of different wavelengths are not the same, the output frequency can be tunable. To further stabilize the frequency of the coupled optoelectronic oscillator, the RF signal source 11 needs to be turned on, and the frequency of the injected signal needs to be adjusted to satisfy an integer multiple relationship with the cavity fundamental frequency of the active mode-locked coupled optoelectronic oscillator loop. Then, the injected signal and the RF signal are fed into the dual-drive Mach-Zehnder intensity modulator. When the phase difference between the feedback signal and the reference signal is 180°, the modulation signal in the dual-drive Mach-Zehnder modulator 8 is the difference frequency signal between the two. Referring to formula (1), it can be found that the optical signal with a frequency close to the reference signal has the least loss and the highest optical gain when passing through the dual-drive Mach-Zehnder modulator 8, while the optical signal with other frequencies will have increased loss when passing through the dual-drive Mach-Zehnder modulator 8. In this way, the first adjustable optical delay line 5, the second adjustable optical delay line 12, and the electrical phase shifter 16 are adjusted again so that the oscillation time of the optical signal in the mode-locked fiber laser is equal to the transmission delay of the oscillation signal from the active mode-locked coupled optoelectronic oscillator to the intensity modulator, so that the phase of the optical pulse is consistent with the phase of the electrical signal generated by the active mode-locked coupled optoelectronic oscillator. Precise phase matching conditions act as a bandpass filter, so that the optical pulses generated by the active mode-locked coupled optoelectronic oscillation are synchronously modulated by the microwave signal generated by feedback, suppressing supermode noise and giving the signal in the spectrum a high sidemode rejection ratio.

[0032] In implementing this invention, the bias point of the dual-drive Mach-Zehnder intensity modulator 8 needs to be considered. When the bias is in a suitable position, the intensity of the light pulse can be modulated in reverse through the feedback signal of the photoelectric oscillator. In general implementation, it is necessary to adjust the intensity and phase of the output signal of the microwave source 11 so that the modulator works at the quadrature bias point. At this time, the power transfer curve of the modulator 8 can be expressed by formula (1).

[0033]

[0034] Where T represents the transmission function of the output optical pulse, Vπ It is the half-wave voltage of MZM, V RF and V PIFF These are the radio frequency signals input to the upper and lower ports of the MZM, representing the microwave source signal and the signal generated by the photoelectric oscillator, respectively. V RF and V PIFF It can be expressed by formula (2)

[0035]

[0036] Where f is the microwave source driving frequency, ρ(t) is the electrical pulse intensity output by the photodetector PD, t is time, A is the amplitude of the RF microwave sinusoidal signal, and B is the amplification intensity of the signal generated by the photoelectric oscillator.

[0037] Example:

[0038] Measurements show that the total optical cavity length of the active mode-locked coupled optoelectronic oscillator is 10m. It consists of an all-fiber structure including a wavelength division multiplexer 2, a gain fiber 3, an optical isolator 4, a first tunable optical delay line 5, a 90:10 optical coupler 6, a polarization controller 7, a dual-drive Mach-Zehnder intensity modulator 8, a 98:2 optical coupler 9, and a tunable optical filter 10. The corresponding free spectral range is 10MHz. The tuning range of the tunable optical filter 10 can reach 100nm. The 3dB spectral width is 0.16nm. The pump power of the laser pump source 1 is 26dBm. The output optical power of the 98:2 optical coupler 9 is -1dBm. The RF microwave signal frequency of the microwave source 11 is 1.42GHz, and the RF signal power is 10dBm.

[0039] By adjusting the tunable optical filter 10 and the first tunable optical delay line 5 to change the output wavelength and corresponding optical delay of the active mode-locked coupled optoelectronic oscillator, and simultaneously adjusting the electrical phase shifter 16 to change the delay of the electrical loop, the phase matching condition of the active mode-locked coupled optoelectronic oscillator is satisfied when a certain frequency mode within the optical cavity is aligned with the frequency mode of the electrical signal. Using a spectrum analyzer to measure the spectral characteristics of the optical pulse, without external RF signal injection, the optical pulse exhibits severe jitter, with frequency jitter exceeding 100kHz, generating supermode noise with a 10MHz interval within the spectrum, and a supermode noise suppression ratio of 40dB. Figure 5As shown. When an external RF source is injected into the active mode-locked coupled opto-oscillator, to verify the spectral characteristics of the active mode-locked coupled opto-oscillator, the output port of the microwave source 11 is opened, and the strength and frequency of the RF signal output by the microwave source 11 are changed to achieve injection locking. The output frequency ranges from 1.37 GHz to 1.47 GHz, corresponding to the 137th to 147th harmonic mode-locking states of the active coupled opto-oscillator, respectively. The output signal strength is stabilized at 10 dBm. The phase shifter 16 can simultaneously change the phase difference between the feedback signal and the RF signal. When the phase difference between the two-tone signals reaches 180 degrees, the modulation signal of the dual-drive Mach-Zehnder intensity modulator 8 is the difference frequency signal between the two. At this time, the driving voltage is changed so that the dual-drive Mach-Zehnder intensity modulator 8 operates at the quadrature operating point. The feedback signal frequency, which is equal to the frequency mode of the reference signal, obtains the maximum transmittance. The output microwave signal achieves a side-mode rejection ratio of over 70 dB, and the overmode noise suppression is improved by more than 30 dB. The spectrum diagram is shown below. Figure 6 As shown. Due to the short fiber length, spurious frequency noise is suppressed, and the phase noise is below -108.6 dBc / Hz at a 10 kHz frequency offset, such as... Figure 7 As shown. The phase noise and frequency changes of the output signal within a short period of time are as follows. Figure 8 As shown. Frequency jitter is less than 10Hz.

[0040] Considering that the adjustment range of the first adjustable light delay 5 and the second adjustable light delay 12 is 0-300ps, the adjustment range of the electric phase shifter 16 is 360° / 1GHz, and the range of the broadband electric filter 15 is 1370-1470MHz, the frequency tunable range will be controlled by all three.

[0041] The above output characteristics show that the active mode-locked coupled optoelectronic oscillator proposed in this invention can obtain stable optical pulse output, with a side-mode rejection ratio of over 70dB. The generated signal has good spectral purity and frequency jitter of less than 10Hz, further improving the noise suppression performance and stability under high-order harmonic operation.

[0042] Figure 4 A diagram illustrating the principle of noise suppression within the cavity of an actively mode-locked coupled optoelectronic oscillator is shown below. Figure 4 As shown, (a) is the optical frequency mode generated by the mode-locked laser oscillation; (b) is the radio frequency signal frequency generated by the photodetector beat frequency; (c) is the oscillation frequency of the active mode-locked coupled photoelectric oscillator; (d) is the optical frequency signal generated by the active mode-locked coupled photoelectric oscillator; and (d) is the radio frequency signal finally output by the active mode-locked coupled photoelectric oscillator.

Claims

1. An active mode-locked coupled optoelectronic oscillator, characterized in that its... include: Laser pump source (1), wavelength division multiplexer (2), gain fiber (3), optical isolator (4), first tunable optical delay line (5), 90:10 optical coupler (6), polarization controller (7), dual-drive Mach-Zehnder intensity modulator (8), 98:2 optical coupler (9), tunable optical filter (10), RF signal source (11), second tunable optical delay line (12), photodetector (13), tunable electrical gain amplifier (14), broadband electrical filter (15), electrical phase shifter (16), and power divider (17). The laser pump source (1) is connected to the a-end of the wavelength division multiplexer (2). The pump light is output from the c-end of the wavelength division multiplexer (2) and connected to the gain fiber (3). The other end of the gain fiber (3) is connected to the input end of the optical isolator (4). The other end of the optical isolator (4) is connected to the first adjustable optical delay line (5). The output end of the first adjustable optical delay line (5) is connected to the d-end of the 90:10 optical coupler (6). The e-end of the 90:10 optical coupler (6) is connected to the output end of the polarization controller (7). The other end of the polarization controller (7) is connected to the dual-drive motor. The input of the Herzondel intensity modulator (8) is connected to the RF signal source (11) and the feedback signal output by the power divider (17) are transmitted to the RF input port of the dual-drive Mach-Zehnder intensity modulator (8); the other end of the dual-drive Mach-Zehnder intensity modulator (8) is connected to the input of the 98:2 optical coupler (9), one of the outputs of the 98:2 optical coupler (9) is connected to the tunable filter (10), and the output of the other end of the tunable filter (10) is connected to the b port of the wavelength division multiplexer (2) to form a mode-locked laser structure. The light output from the f-end of the 90:10 optical coupler (6) enters the second adjustable optical delay line (12). The first adjustable optical delay line (5) and the second adjustable optical delay line (12) adjust the optical delay of the light signal entering the photoelectric oscillator. The input end of the photodetector (13) is connected to the output end of the second adjustable optical delay line (12) to detect the generated light pulse signal. The output end of the photodetector (13) is connected to the input end of the adjustable electric gain amplifier (14). The output end of the adjustable electric gain amplifier (14) is connected to the input end of the broadband electric filter (15). The output end of the broadband electric filter (15) is connected to the input end of the electric phase shifter (16). The output end of the electric phase shifter (16) is connected to the input end of the power divider (17). The signal output by the power divider (17) is input to the RF port of the dual-drive Mach-Zehnder intensity modulator (8) to form a photoelectric oscillator structure.

2. The active mode-locked coupled optoelectronic oscillator according to claim 1, characterized in that, The wavelength of the laser pump source (1) is 980nm.

3. The active mode-locked coupled optoelectronic oscillator according to claim 1, characterized in that, The wavelength division multiplexer (2) is a 980 / 1550nm wavelength division multiplexer.

4. The active mode-locked coupled optoelectronic oscillator according to claim 1, characterized in that, The gain fiber (3) is made up of two segments of gain fiber spliced ​​together. The first segment is 5m long and the second segment is 3m long.

5. The active mode-locked coupled optoelectronic oscillator according to claim 1, characterized in that, The broadband electrical filter (15) selects the oscillation frequency of the active mode-locked coupled optoelectronic oscillator structure.

6. The active mode-locked coupled optoelectronic oscillator according to claim 1, characterized in that, Adjust the RF signal source (11) and the first adjustable optical delay line (5) so that the frequency of the microwave signal provided by the RF signal source (11) satisfies an integer multiple relationship with the cavity fundamental frequency of the active mode-locked coupled optoelectronic oscillation loop.

7. The active mode-locked coupled optoelectronic oscillator according to claim 1, characterized in that, Before the reference signal generated by the RF signal source (11) and the output oscillation signal are injected into the dual-drive Mach-Zehnder intensity modulator (8), the phase difference between the two signals is guaranteed to be 180°.

8. The active mode-locked coupled optoelectronic oscillator according to claim 1, characterized in that, The difference frequency signal between the oscillation signal output by the power divider (17) and the reference signal generated by the RF signal source (11) is injected into the dual-drive Mach-Zehnder intensity modulator (8).

Images