Single-period oscillation microwave signal generation device and method based on frequency shift light injection locking

Abstract

The invention provides a single-period oscillation microwave signal generation device and method based on frequency shift light injection locking, and relates to the technical field of microwave photonics. The device comprises a master laser, a first optical circulator, an optical attenuator, a first polarization controller, a second optical circulator, a slave laser, an optical fiber amplifier, a second polarization controller, a Brillouin ring cavity, a second optical fiber coupler, a photoelectric detector, an optical frequency shifter, an optical filter and a third polarization controller. Light emitted by the master laser is injected into the slave laser to generate a single-period oscillation optical signal, the single-period oscillation optical signal is input into the Brillouin cavity to generate Brillouin laser and is divided into two paths, and one path is subjected to photoelectric conversion to generate a microwave signal; and the other path is injected into the master laser after passing through the optical frequency shifter so as to lock the master laser, and then is injected into the slave laser by the master laser so as to lock the single-cycle oscillation optical signal. According to the invention, a stable single-frequency microwave signal can be output, and the advantages of low phase noise, high side-mode rejection ratio and wide tuning range are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of microwave photonics, and in particular to a single-cycle oscillation microwave signal generation device and method based on frequency-shifted light injection locking. BACKGROUND

[0002] The traditional electronic technology faces great challenges in generating microwave signals, such as high frequency loss, limited Q value, and difficulty in further reducing phase noise. Microwave photonics has great advantages in generating microwave signals due to its large bandwidth, low loss, and resistance to electromagnetic interference. The main methods used in the prior art include direct modulation, external modulation, optical heterodyne, optical phase-locked loop, mode-locked laser, optoelectronic oscillator, and optical injection semiconductor laser. The optical injection method breaks through the limitation of the intrinsic relaxation oscillation frequency of the semiconductor laser and can generate single-frequency signals in the range of several GHz to hundreds of GHz in a single-cycle oscillation state. However, the output signal is not ideal in terms of spectral purity and stability. For example, the inherent spontaneous emission noise of the laser degrades the spectral purity of the generated microwave signal, resulting in a 3 dB line width typically in the wide range of 1-10 MHz. In addition, the fluctuations in the injection light frequency and power can cause frequency jitter in the output microwave signal, with a typical amplitude of about 100 MHz.

[0003] To improve the line width and stability of the single-cycle oscillation of the optical injection semiconductor laser, researchers have proposed a series of improvement methods, mainly including double locking method, optical modulation sideband injection locking method, optical feedback method, optoelectronic feedback method, and PT symmetric method. The double locking method and the optical modulation sideband injection locking method require an additional signal source, and the quality of the generated signal is also limited by the signal source. The microwave line width obtained by the optical feedback method can reach 50 kHz, but it is easily affected by interference, which in turn affects the line width and frequency stability of the generated microwave signal. The optoelectronic feedback method and the PT symmetric method can generate stable low-phase noise microwave signals, but are limited by the electrical devices in the system, with limited microwave bandwidth and complex system. SUMMARY

[0004] The first object of the present application is to provide a single-cycle oscillation microwave signal generation device based on frequency-shifted light injection locking to achieve low phase noise and high spurious suppression ratio. The second object is to provide a single-cycle oscillation microwave signal generation method based on frequency-shifted light injection locking.

[0005] Technical solution: A single-cycle oscillation microwave signal generation device based on frequency-shifted light injection locking, comprising:

[0006] The light injection module comprises a main laser, a first optical circulator, a first polarization controller, a second optical circulator and a slave laser, the main laser generates a continuous light signal, the continuous light signal sequentially passes through the first optical circulator, the first polarization controller and the second optical circulator and then enters the slave laser, and the slave laser outputs a single-cycle oscillation light signal;

[0007] The Brillouin ring cavity module comprises a second polarization controller, a third circulator and a Brillouin ring cavity, the single-cycle oscillation light signal enters the Brillouin ring cavity after passing through the second polarization controller and the third circulator, and the Brillouin ring cavity is stimulated to generate Brillouin laser and output;

[0008] The microwave output module comprises a second optical fiber coupler and a photodetector, the Brillouin laser passes through the second optical fiber coupler and is divided into two paths, one path enters the photodetector, and the other path is output externally;

[0009] The frequency-shifted light injection locking module comprises an optical frequency shifter, an optical filter and a third polarization controller, the optical frequency shifter receives the Brillouin laser output by the second optical fiber coupler, outputs frequency-shifted laser, the frequency-shifted laser passes through the optical filter and outputs an optical component of the same wavelength as the single-cycle oscillation light signal, the optical component passes through the third polarization controller and the first optical circulator and is injected into the main laser, the main laser outputs a light signal containing a single-cycle oscillation light signal component, and the light signal is injected into the slave laser again.

[0010] Preferably, the light injection module further comprises an optical attenuator, and the optical attenuator is used for adjusting the power of the continuous light signal by adjusting the optical attenuation.

[0011] Preferably, the Brillouin ring cavity module further comprises an optical fiber amplifier, and the optical fiber amplifier is used for amplifying the intensity of the single-cycle oscillation light signal to be higher than a stimulated Brillouin scattering threshold.

[0012] Specifically, the Brillouin ring cavity comprises a gain optical fiber, a first optical fiber coupler and an optical isolator, the gain optical fiber receives the single-cycle oscillation light signal and generates stimulated Brillouin scattering to output Brillouin laser, the first optical fiber coupler is used for dividing the Brillouin laser into two paths, one path is fed back into the Brillouin ring cavity, and the other path is output to the microwave output module, and the optical isolator is used for blocking residual single-cycle oscillation light signals.

[0013] Specifically, the photodetector converts the input Brillouin laser into a single-cycle oscillation microwave signal through photoelectric conversion.

[0014] Preferably, the main laser and the slave laser are distributed feedback semiconductor lasers.

[0015] Specifically, the optical frequency shifter is composed of a modulator and a signal source and is used for realizing carrier-suppressed single-sideband modulation.

[0016] Preferably, the gain optical fiber is a single-mode optical fiber or a nonlinear optical fiber.

[0017] Preferably, the optical filter is a narrow-band bandpass filter or a double-bandpass filter.

[0018] The application also provides a single-cycle oscillation microwave signal generation method using the single-cycle oscillation microwave signal generation device based on frequency-shifted light injection locking.

[0019] S1, the main laser generates a continuous light signal, and outputs after adjusting the output power;

[0020] S2, the continuous light signal is injected into the slave laser through the first optical circulator, the first polarization controller and the second optical circulator, the slave laser excites a dynamic behavior to output a single-cycle oscillation light signal, and the first polarization controller is adjusted to maximize the injection efficiency of the continuous light signal;

[0021] S3, the single-cycle oscillation light signal is input into the Brillouin ring cavity through the second polarization controller and the third optical circulator, the second polarization controller is adjusted to make the Brillouin ring cavity have the maximum Brillouin gain, and the Brillouin ring cavity is stimulated to generate Brillouin laser propagating in the opposite direction of the single-cycle oscillation light signal;

[0022] S4, the Brillouin laser is divided into two paths after passing through the second optical fiber coupler, one path is input into the photodetector for photoelectric conversion and outputs a corresponding microwave signal, and the other path is input into the optical frequency shifter;

[0023] S5, the optical frequency shifter shifts the frequency of the Brillouin laser, the frequency shift size is equal to the Brillouin frequency, the shifted laser contains a light component with the same wavelength as the single-cycle oscillation light signal, and the shifted laser is filtered through the optical filter, the light component with the same wavelength as the single-cycle oscillation light signal is retained and output;

[0024] S6, the light component is injected into the main laser through the third polarization controller and the first optical circulator to realize injection locking of the main laser, the third polarization controller is adjusted to realize the maximum injection efficiency, and the light signal output by the main laser contains a single-cycle oscillation light signal component, which is injected into the slave laser again to realize injection locking of the single-cycle oscillation light signal;

[0025] S7, the steps S1 to S6 are repeated, so that the line width of the single-cycle oscillation light signal is narrowed and the frequency is stabilized, a laser output with a line width lower than a set threshold value and a single-cycle oscillation microwave signal with a phase noise lower than a set threshold value and a side mode suppression ratio higher than a set threshold value are obtained.

[0026] Advantages: Compared with the prior art, the significant effect of the application is:

[0027] 1、The present application makes full use of the filtering and linewidth compression characteristics of the Brillouin ring cavity, so that the beat frequency microwave signal has low side mode and extremely narrow linewidth. In addition, based on the acoustic damping and the feedback effect in the cavity, the phase noise of the Brillouin laser is reduced, the double-wavelength signal shares one Brillouin ring cavity, the highly correlated phase noise cancels each other, and finally the output microwave signal has low phase noise.

[0028] 2、The present application realizes the locking of the light signal output by the main laser and the single-period signal output by the slave laser through optical frequency shift injection locking, that is, a stable single-period oscillation light signal is obtained, and then a stable microwave signal is obtained through the Brillouin ring cavity and photoelectric conversion.

[0029] 3、The present application has simple overall structure and is easy to manufacture, and through adjusting the injection parameters, wide-range tuning of the microwave signal can be realized; at the same time, due to the all-optical signal generation scheme, the microwave bandwidth is only limited by the bandwidth of the photoelectric detector. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the overall structure schematic diagram of the single-period oscillation microwave signal generation device of the embodiment 1 of the present application.

[0031] Figure 2 is the frequency spectrum diagram of the single-frequency microwave signal obtained by the embodiment 2 of the present application.

[0032] Figure 3 is the phase noise diagram of the single-frequency microwave signal obtained by the embodiment 2 of the present application. DETAILED DESCRIPTION

[0033] A preferred scheme of the present application will be further described below in combination with the drawings.

[0034] Embodiment 1

[0035] Please refer to Figure 1 , the present embodiment provides a single-period oscillation microwave signal generation device based on frequency shift optical injection locking, which is divided into the following modules based on functions:

[0036] The optical injection module includes a main laser 1, a first optical circulator 2, an optical attenuator 3, a first polarization controller 4, a second optical circulator 5 and a slave laser 6. The main laser 1 generates a continuous light signal, which enters the slave laser 6 after sequentially passing through the first optical circulator 2, the optical attenuator 3, the first polarization controller 4 and the second optical circulator 5. The slave laser 6 outputs a single-period oscillation light signal.

[0037] The Brillouin ring cavity module includes the optical fiber amplifier 7, the second polarization controller 8, the third circulator 9 and the Brillouin ring cavity. After the single-cycle oscillation light signal passes through the optical fiber amplifier 7, the intensity is amplified to be higher than the threshold of stimulated Brillouin scattering, and then the single-cycle oscillation light signal is input into the second polarization controller 8 and the third circulator 9 and then into the Brillouin ring cavity. The Brillouin ring cavity is stimulated to generate Brillouin laser and output. The pump light is the red-shift peak and the regenerative peak components with higher power in the single-cycle oscillation light signal. The two-wavelength signal can stimulate the stimulated Brillouin scattering after amplification. As a preferred scheme, in the embodiment, the Brillouin ring cavity includes the gain optical fiber 10, the first optical fiber coupler 11 and the optical isolator 12. The gain optical fiber 10 receives the single-cycle oscillation light signal to generate the stimulated Brillouin scattering and output the Brillouin laser. The first optical fiber coupler 11 is used to divide the Brillouin laser into two paths. One path is fed back into the Brillouin ring cavity, and the other path is output to the microwave output module. The optical isolator 12 is used to block the residual single-cycle oscillation light signal.

[0038] The microwave output module includes the second optical fiber coupler 13 and the photodetector 14. The Brillouin laser is divided into two paths after passing through the second optical fiber coupler 13. One path is input into the photodetector 14, and the other path is output externally. The photodetector 14 converts the input Brillouin laser into the single-cycle oscillation microwave signal after photoelectric conversion.

[0039] The frequency-shifted light injection locking module includes the optical frequency shifter 15, the optical filter 16 and the third polarization controller 17. The optical frequency shifter 15 receives the Brillouin laser output by the second optical fiber coupler 13 and outputs the frequency-shifted laser. The frequency-shifted laser outputs the light component with the same wavelength as the single-cycle oscillation light signal after passing through the optical filter 16. The light component passes through the third polarization controller 17 and the first optical circulator 2 and is injected into the master laser 1, so that the injection locking of the master laser 1 is completed. The master laser 1 outputs the light signal containing the single-cycle oscillation light signal component, and the single-cycle oscillation light signal is injection locked again by the slave laser 6.

[0040] As a preferred scheme, the master laser 1 and the slave laser 6 are distributed feedback semiconductor lasers, and neither of them is provided with an isolator. A laser with a narrower line width can be selected.

[0041] As a preferred scheme, the optical frequency shifter 15 is composed of a modulator and a signal source, and is used to realize the single-sideband modulation of carrier suppression.

[0042] As a preferred scheme, the gain optical fiber 10 is selected from a single-mode optical fiber. A nonlinear optical fiber with a shorter length can also be used to reduce the threshold of stimulating the stimulated Brillouin scattering.

[0043] As a preferred scheme, the optical filter 16 is selected from a narrow-band bandpass filter or a double-bandpass filter to retain the light component required for the injection locking.

[0044] Embodiment 2

[0045] The embodiment provides a single-cycle oscillation microwave signal generation method based on frequency shift light injection locking realized by the single-cycle oscillation microwave signal generation device described in embodiment 1, and the method comprises the following steps.

[0046] S1, a continuous light signal is generated by a master laser, and the light power injected from a slave laser is changed by adjusting an optical attenuator;

[0047] S2, the continuous light signal is injected into the slave laser through a first optical circulator, a first polarization controller and a second optical circulator, a single-cycle oscillation light signal is output by exciting the slave laser, and the injection efficiency of the continuous light signal is maximized by adjusting the first polarization controller;

[0048] S3, after the single-cycle oscillation light signal passes through an optical fiber amplifier, the intensity is amplified to be higher than the preformed stimulated Brillouin scattering, and then the single-cycle oscillation light signal is input into a Brillouin ring cavity as pump light through a second polarization controller and a third optical circulator, the Brillouin ring cavity has the maximum Brillouin gain by adjusting the second polarization controller, the Brillouin ring cavity is stimulated to generate Brillouin laser propagating in the opposite direction of the single-cycle oscillation light signal, the unidirectional propagation of the light signal in the Brillouin ring cavity is ensured through an optical isolator, the Brillouin laser is divided into two paths through a first optical fiber coupler, one path is fed back to the Brillouin ring cavity, and the other path outputs multi-wavelength Brillouin laser;

[0049] S4, the output Brillouin laser is divided into two paths again through a second optical fiber coupler, one path is input into a photodetector to perform photoelectric conversion and output corresponding microwave signals, and the other path is input into an optical frequency shifter;

[0050] S5, the optical frequency shifter performs frequency shift on the Brillouin laser, the frequency shift size is equal to the Brillouin frequency, the frequency-shifted laser contains a light component with the same wavelength as the single-cycle oscillation light signal, and the frequency-shifted laser is filtered through an optical filter, the light component with the same wavelength as the single-cycle oscillation light signal is retained and output;

[0051] S6, the light component is injected into the master laser through a third polarization controller and a first optical circulator, injection locking of the master laser is realized, the maximum injection efficiency is realized by adjusting the third polarization controller, the light signal output by the master laser contains a single-cycle oscillation light signal component, the single-cycle oscillation light signal component is injected into the slave laser again, and injection locking of the single-cycle oscillation light signal is realized;

[0052] S7, after the single-cycle oscillation light signal is injected and locked for the first time, the line width is narrowed, the frequency is stabilized, then the single-cycle oscillation light signal with narrower line width and more stable frequency is obtained through line width compression and frequency shift light injection locking, and the laser output with super-narrow line width and the microwave signal with low phase noise and high side mode suppression ratio are obtained through continuous circulation.

[0053] The technical solution of the embodiment is described below in a specific implementation scenario.

[0054] In the present scenario, the main laser generates a continuous optical signal when it is free running, with a power of 6.84 dBm, and the slave laser outputs an optical signal with a power of 4.06 dBm when it is free running, and the frequency difference between the two is 14.7 GHz. The optical signal output by the main laser is injected into the slave laser through the first polarization controller and the second circulator, so that the slave laser is excited to output a single-periodic signal, and the first polarization controller is adjusted to maximize the injection efficiency. The output power of the optical fiber amplifier is set to 23 dBm, and the single-periodic oscillation optical signal is amplified by the optical fiber amplifier and then input into the Brillouin ring cavity as pump light through the second polarization controller and the third circulator. The frequency difference between the Brillouin laser and the pump light is 10.850 GHz, and the second polarization controller is adjusted to achieve maximum Brillouin gain in the gain fiber. The propagation directions of the pump light and the excited Brillouin laser in the Brillouin ring cavity are opposite, and the Brillouin laser propagates counterclockwise due to the blocking of the optical isolator and the third optical circulator, and is output through one port of the first optical fiber coupler. The light at the other port is fed back to the Brillouin ring cavity to continue participating in the resonance. The output Brillouin laser is also divided into two paths after passing through the second optical fiber coupler, one of which is input into the photodetector for photoelectric conversion to output a microwave signal, and the other of which is input into the optical frequency shifter, with the frequency shift size set to the Brillouin frequency, i.e., 10.850 GHz. At this time, the frequency-shifted laser contains an optical component with the same wavelength as the pump light. Subsequently, the frequency-shifted laser is filtered by the optical filter to retain the optical component with the same wavelength as the single-periodic oscillation signal. The filtered light passes through the third polarization controller and the first optical circulator and is first injected into the main laser to achieve injection locking of the main laser. The third polarization controller is adjusted to achieve maximum injection efficiency. Since the optical signal output by the main laser contains a single-periodic oscillation optical signal component, the single-periodic oscillation optical signal can be injection locked by being injected into the slave laser again. Thus, the single-periodic oscillation optical signal after the first frequency-shifted injection locking has a narrowed linewidth and a stable frequency. Subsequently, the single-periodic oscillation optical signal with a narrower linewidth and a more stable frequency is obtained through linewidth compression and frequency-shifted light injection locking, and the cycle continues until the super-narrow-linewidth laser output and the low-phase-noise, high-side-mode-suppression-ratio microwave signal generation are finally achieved. Please refer to Figure 2 As shown in the figure, the microwave signal output after photoelectric conversion is 29.339 GHz, and the spectrum has very low side modes, with a side mode suppression ratio of more than 65 dB. Please refer to Figure 3 As shown in the figure, the phase noise at a frequency offset of 10 kHz in the phase noise diagram is -105.3 dBc / Hz (lower than -100 dBc / Hz), which proves that the single-periodic oscillation microwave signal obtained by the present application has extremely high frequency stability.

Claims

1. A single-cycle oscillation microwave signal generation device based on frequency-shift optical injection locking, characterized in that, include: The optical injection module includes a main laser (1), a first optical circulator (2), a first polarization controller (4), a second optical circulator (5), and a slave laser (6). The main laser (1) generates a continuous optical signal, which passes through the first optical circulator (2), the first polarization controller (4), and the second optical circulator (5) in sequence before entering the slave laser (6). The slave laser (6) outputs a single-cycle oscillating optical signal. Brillouin ring cavity module: includes a second polarization controller (8), a third circulator (9) and a Brillouin ring cavity. The single-cycle oscillating optical signal enters the Brillouin ring cavity after passing through the second polarization controller (8) and the third circulator (9). The Brillouin ring cavity is stimulated to generate Brillouin laser and output it. Microwave output module: includes a second fiber coupler (13) and a photodetector (14). The Brillouin laser is split into two paths after passing through the second fiber coupler (13), one path is input to the photodetector (14), and the other path is output to the outside. Frequency-shifting optical injection locking module: includes an optical frequency shifter (15), an optical filter (16) and a third polarization controller (17). The optical frequency shifter (15) receives the Brillouin laser output from the second fiber coupler (13) and outputs the frequency-shifted laser. The frequency-shifted laser passes through the optical filter (16) and outputs a light component with the same wavelength as the single-cycle oscillating light signal. The light component passes through the third polarization controller (17) and the first optical circulator (2) and is injected into the main laser (1). The main laser (1) outputs an optical signal containing the single-cycle oscillating light signal component and injects it into the slave laser (6) again.

2. The single-cycle oscillation microwave signal generation device based on frequency-shifted optical injection locking according to claim 1, characterized in that: The optical injection module also includes an optical attenuator (3), which is used to change the power of the continuous optical signal by adjusting the optical attenuation.

3. The single-cycle oscillation microwave signal generation device based on frequency-shifted optical injection locking according to claim 1, characterized in that: The Brillouin ring cavity module also includes an optical fiber amplifier (7), which is used to amplify the intensity of the single-cycle oscillating optical signal to a level higher than the stimulated Brillouin scattering threshold.

4. The single-cycle oscillation microwave signal generation device based on frequency-shifted optical injection locking according to claim 1, characterized in that: The Brillouin ring cavity includes a gain fiber (10), a first fiber coupler (11), and an optical isolator (12). The gain fiber (10) receives a single-cycle oscillating optical signal and generates stimulated Brillouin scattering, outputting Brillouin laser. The first fiber coupler (11) is used to split the Brillouin laser into two paths, one of which is fed back into the Brillouin ring cavity, and the other is output to the microwave output module. The optical isolator (12) is used to block residual single-cycle oscillating optical signals.

5. The single-cycle oscillation microwave signal generation device based on frequency-shift optical injection locking according to claim 1, characterized in that: The photodetector (14) outputs a single-cycle oscillating microwave signal after photoelectric conversion of the input Brillouin laser.

6. The single-cycle oscillation microwave signal generation device based on frequency-shift optical injection locking according to claim 1, characterized in that: The master laser (1) and slave laser (6) are distributed feedback semiconductor lasers.

7. The single-cycle oscillation microwave signal generation device based on frequency-shifted optical injection locking according to claim 1, characterized in that: The optical frequency shifter (15) consists of a modulator and a signal source, and is used to achieve single-sideband modulation with carrier suppression.

8. The single-cycle oscillation microwave signal generation device based on frequency-shifted optical injection locking according to claim 4, characterized in that: The gain fiber (10) is a single-mode fiber or a nonlinear fiber.

9. The single-cycle oscillation microwave signal generation device based on frequency-shifted optical injection locking according to claim 1, characterized in that: The optical filter (16) is a narrowband bandpass filter or a dual bandpass filter.

10. A method for generating a single-cycle oscillation microwave signal using the single-cycle oscillation microwave signal generation device based on frequency-shift optical injection locking as described in any one of claims 1 to 9, characterized in that, Includes the following steps: S1. The main laser generates a continuous optical signal, which is then output after adjusting the output power. S2. After passing through the first optical circulator, the first polarization controller, and the second optical circulator, the continuous optical signal is injected into the laser. The laser excites dynamic behavior to output a single-cycle oscillating optical signal. The first polarization controller is adjusted to maximize the injection efficiency of the continuous optical signal. S3. The single-cycle oscillating optical signal is input into the Brillouin ring cavity after passing through the second polarization controller and the third optical circulator. The second polarization controller is adjusted to make the Brillouin ring cavity have the maximum Brillouin gain. The Brillouin ring cavity is stimulated to generate Brillouin laser in the opposite direction to the propagation direction of the single-cycle oscillating optical signal. S4. After passing through the second fiber coupler, the Brillouin laser is split into two paths. One path is input to a photodetector for photoelectric conversion and outputs a corresponding microwave signal. The other path is input to an optical frequency shifter. S5. The optical frequency shifter shifts the Brillouin laser by a magnitude equal to the Brillouin frequency. The frequency-shifted laser contains a light component with the same wavelength as the single-period oscillating light signal. After the frequency-shifted laser is filtered by an optical filter, the light component with the same wavelength as the single-period oscillating light signal is retained and output. S6. The optical component is injected into the main laser after passing through the third polarization controller and the first optical circulator to achieve injection lock of the main laser. The maximum injection efficiency is achieved by adjusting the third polarization controller. The optical signal output by the main laser contains a single-period oscillating optical signal component, which is then injected into the slave laser to achieve injection lock of the single-period oscillating optical signal. S7. Repeat steps S1 to S6 to narrow the linewidth and stabilize the frequency of the single-cycle oscillating optical signal, thereby obtaining a laser output with a linewidth lower than the set threshold and a single-cycle oscillating microwave signal with phase noise lower than the set threshold and side-mode suppression ratio higher than the set threshold.

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