A single-cycle oscillation microwave signal generation device and method based on frequency-shift light injection locking

Abstract

The application provides a single-cycle 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 photodetector, an optical frequency shifter, an optical filter and a third polarization controller. The light emitted by the master laser is injected into the slave laser to generate a single-cycle oscillation light signal, the single-cycle oscillation light signal is input into the Brillouin cavity to generate Brillouin laser and is divided into two paths, one path is converted into a microwave signal through photoelectric conversion; the other path is injected into the master laser through the optical frequency shifter to realize the locking of the master laser, and then the single-cycle oscillation light signal is locked by the master laser and the slave laser. The application can output stable single-frequency microwave signals, and has the advantages of low phase noise, high side mode suppression ratio and wide tuning range.

Description

Technical Field

[0001] This invention relates to the field of microwave photonics technology, specifically to a device and method for generating single-cycle oscillation microwave signals based on frequency-shifted optical injection locking. Background Technology

[0002] Traditional electronic technologies face significant challenges in generating microwave signals, including high-frequency losses, limited Q values, and difficulties in further reducing phase noise. Microwave photonics technology, however, offers substantial advantages in this area due to its wide optical bandwidth, low loss, and resistance to electromagnetic interference. Existing methods include direct modulation, external modulation, optical heterodyne, optical phase-locked loops, mode-locked lasers, optoelectronic oscillators, and optically injected semiconductor lasers. Optical injection, in particular, overcomes the limitation of the intrinsic relaxation oscillation frequency of semiconductor lasers, enabling the generation of single-frequency signals ranging from several GHz to hundreds of GHz in a single-cycle oscillation state. It also boasts advantages such as simple structure and ease of tuning. However, the output signal suffers from less than ideal 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 relatively wide 3 dB linewidth typically ranging from 1 to 10 MHz. Furthermore, fluctuations in the injected light frequency and power cause frequency jitter in the output microwave signal, with typical amplitudes reaching approximately 100 MHz.

[0003] To improve the linewidth and stability of single-cycle oscillations in optically injected semiconductor lasers, researchers have proposed a series of improvement methods, mainly including the double-locking method, optical modulation sideband injection-locking method, optical feedback method, photoelectric feedback method, and PT symmetry method. Among them, the double-locking method and 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 optical feedback method can achieve a microwave linewidth of up to 50 kHz, but it is susceptible to interference, which in turn affects the linewidth and frequency stability of the generated microwave signal; the photoelectric feedback method and PT symmetry method are not affected by interference and can generate stable microwave signals with low phase noise, but they are limited by the electrical components in the system, resulting in limited microwave bandwidth and system complexity. Summary of the Invention

[0004] Purpose of the invention: The first purpose of the invention is to provide a single-cycle oscillation microwave signal generation device with low phase noise and high side-mode suppression ratio based on frequency-shift optical injection locking; the second purpose is to provide a single-cycle oscillation microwave signal generation method based on frequency-shift optical injection locking.

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

[0006] The optical injection module includes a master laser, a first optical circulator, a first polarization controller, a second optical circulator, and a slave laser. The master laser generates a continuous optical signal, which passes through the first optical circulator, the first polarization controller, and the second optical circulator in sequence before entering the slave laser. The slave laser outputs a single-cycle oscillating optical signal.

[0007] Brillouin ring cavity module: includes a second polarization controller, a third circulator and a Brillouin ring cavity. The single-cycle oscillating optical signal enters the Brillouin ring cavity after passing through the second polarization controller and the third circulator. The Brillouin ring cavity is stimulated to generate Brillouin laser and output it.

[0008] Microwave output module: includes a second fiber coupler and a photodetector. The Brillouin laser is split into two paths after passing through the second fiber coupler, one path is input to the photodetector, and the other path is output to the outside.

[0009] Frequency-shifted optical injection locking module: includes an optical frequency shifter, an optical filter, and a third polarization controller. The optical frequency shifter receives the Brillouin laser output from the second fiber coupler and outputs the frequency-shifted laser. After passing through the optical filter, the frequency-shifted laser outputs a light component with the same wavelength as the single-period oscillating light signal. The light component is injected into the main laser after passing through the third polarization controller and the first optical circulator. The main laser outputs an optical signal containing the single-period oscillating light signal component, which is then injected into the slave laser.

[0010] Preferably, the optical injection module further includes an optical attenuator, which is used to change the power of the continuous optical signal by adjusting the optical attenuation.

[0011] Preferably, the Brillouin ring cavity module further includes an optical fiber amplifier, which is used to amplify the intensity of the single-cycle oscillating optical signal to a level higher than the stimulated Brillouin scattering threshold.

[0012] Specifically, the Brillouin ring cavity includes a gain fiber, a first fiber coupler, and an optical isolator. The gain fiber receives a single-cycle oscillating optical signal and generates stimulated Brillouin scattering, outputting Brillouin laser. The first fiber coupler is used to split 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 is used to block residual single-cycle oscillating optical signals.

[0013] Specifically, the photodetector converts the input Brillouin laser into a photoelectric signal and outputs a single-cycle oscillating microwave signal.

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

[0015] Specifically, an optical frequency shifter consists of a modulator and a signal source, and is used to achieve single-sideband modulation with carrier suppression.

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

[0017] Preferably, the optical filter is a narrowband bandpass filter or a dual bandpass filter.

[0018] The present invention also provides a method for generating a single-cycle oscillation microwave signal using the above-mentioned single-cycle oscillation microwave signal generation device based on frequency-shift optical injection locking, comprising the following steps:

[0019] S1. The main laser generates a continuous optical signal, which is then output after adjusting the output power.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] Beneficial effects: Compared with the prior art, the significant effects of the present invention are:

[0027] 1. This invention fully utilizes the filtering and linewidth compression characteristics of the Brillouin ring cavity to give the beat-frequency microwave signal low side-mode noise and extremely narrow linewidth. Furthermore, based on acoustic damping and intracavity feedback, the phase noise of the Brillouin laser is reduced. Since the dual-wavelength signals share a single Brillouin ring cavity, the highly correlated phase noise cancels each other out, ultimately resulting in a low phase noise output microwave signal.

[0028] 2. This invention achieves the locking of the optical signal output from the main laser and the single-cycle signal output from the laser through optical frequency shifting injection locking, that is, a stable single-cycle oscillating optical signal is obtained, which is then converted into a stable microwave signal through a Brillouin ring cavity and photoelectric conversion.

[0029] 3. The present invention has a simple overall structure and is easy to manufacture. By adjusting the injection parameters, a wide range of microwave signal tuning can be achieved. At the same time, thanks to the all-optical signal generation scheme, the microwave bandwidth is only limited by the bandwidth of the photodetector. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of the single-cycle oscillation microwave signal generating device according to Embodiment 1 of the present invention.

[0031] Figure 2 This is the spectrum diagram of the single-frequency microwave signal obtained in Embodiment 2 of the present invention.

[0032] Figure 3 This is the phase noise diagram of the single-frequency microwave signal obtained in Embodiment 2 of the present invention. Detailed Implementation

[0033] A preferred embodiment of the present invention will be further described below with reference to the accompanying drawings.

[0034] Example 1

[0035] Please see Figure 1 As shown, this embodiment provides a single-cycle oscillation microwave signal generation device based on frequency-shift optical injection locking, which, after functional division, includes the following modules:

[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 optical signal, which passes through the first optical circulator 2, the optical attenuator 3, 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.

[0037] The Brillouin ring cavity module includes an optical fiber amplifier 7, a second polarization controller 8, a third circulator 9, and a Brillouin ring cavity. After passing through the optical fiber amplifier 7, the intensity of the single-cycle oscillating optical signal is amplified to above the stimulated Brillouin scattering threshold. This amplified signal is then input as pump light into the second polarization controller 8 and the third circulator 9 before entering the Brillouin ring cavity. The Brillouin ring cavity generates and outputs Brillouin laser light under stimulation. The pump light consists of the high-power redshift peak and regenerated peak components of the single-cycle oscillating optical signal. Both of these dual-wavelength signals can be amplified to stimulate stimulated Brillouin scattering. In a preferred embodiment, the Brillouin ring cavity includes a gain fiber 10, a first optical fiber coupler 11, and an optical isolator 12. The gain fiber 10 receives the single-cycle oscillating optical signal and generates stimulated Brillouin scattering, outputting Brillouin laser light. The first optical fiber coupler 11 splits the Brillouin laser light 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 blocks any residual single-cycle oscillating optical signal.

[0038] Microwave output module: includes a second fiber coupler 13 and a photodetector 14. After passing through the second fiber coupler 13, the Brillouin laser is split into two paths. One path is input to the photodetector 14, and the other path is output to the outside. The photodetector 14 converts the input Brillouin laser into a single-cycle oscillating microwave signal through photoelectric conversion.

[0039] Frequency-shifting optical injection locking module: includes optical frequency shifter 15, optical filter 16 and third polarization controller 17. Optical frequency shifter 15 receives Brillouin laser output from second fiber coupler 13 and outputs frequency-shifted laser. After passing through optical filter 16, the frequency-shifted laser outputs a light component with the same wavelength as the single-cycle oscillating optical signal. The light component passes through third polarization controller 17 and first optical circulator 2 and is injected into main laser 1 to complete the injection locking of main laser 1. Main laser 1 outputs an optical signal containing the single-cycle oscillating optical signal component, which is then injected into slave laser 6 to achieve injection locking of the single-cycle oscillating optical signal.

[0040] As a preferred option, both the master laser 1 and the slave laser 6 are distributed feedback semiconductor lasers, and neither isolator is installed. Lasers with narrower linewidths can be selected.

[0041] As a preferred embodiment, the optical frequency shifter 15 consists of a modulator and a signal source, used to achieve single-sideband modulation with carrier suppression.

[0042] As a preferred option, the gain fiber 10 is a single-mode fiber, but a shorter nonlinear fiber can also be used to reduce the threshold for exciting the stimulated Brillouin.

[0043] As a preferred option, the optical filter 16 is a narrowband bandpass filter or a dual bandpass filter to retain the optical component required for injection locking.

[0044] Example 2

[0045] This embodiment provides a method for generating a single-cycle oscillating microwave signal based on frequency-shift optical injection locking, implemented using the single-cycle oscillation microwave signal generating device described in Embodiment 1, including the following steps:

[0046] S1. The main laser generates a continuous optical signal, and the optical power injected into the slave laser is changed by adjusting the optical attenuator.

[0047] 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.

[0048] S3. After the single-period oscillating optical signal passes through the fiber amplifier, its intensity is amplified to a level higher than that of the stimulated Brillouin scattering pre-fabrication. Then, it is used as pump light and 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-period oscillating optical signal. The optical isolator ensures the unidirectional propagation of the optical signal in the Brillouin ring cavity. The Brillouin laser is split into two paths through the first 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 split into two paths again after passing through the second fiber coupler. One path is input to the photodetector for photoelectric conversion and outputs the corresponding microwave signal. The other path is input to the optical frequency shifter.

[0050] 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.

[0051] 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.

[0052] S7. After the first frequency-shifting injection locking, the linewidth of the single-cycle oscillating optical signal narrows and the frequency is stabilized. Then, after linewidth compression and frequency-shifting injection locking, a single-cycle oscillating optical signal with even narrower linewidth and more stable frequency is obtained. This cycle continues to achieve ultra-narrow linewidth laser output and obtain microwave signals with low phase noise and high side-mode rejection ratio.

[0053] The technical solution of this embodiment will be described below in a specific implementation scenario.

[0054] In this scenario, the master laser generates a continuous optical signal with a power of 6.84 dBm during free-running operation, while the slave laser outputs a power of 4.06 dBm during free-running operation. The detuning frequency between the two is 14.7 GHz. The optical signal output from the master laser is injected into the slave laser through a first polarization controller and a second circulator, causing the slave laser to excite a single-cycle signal. The first polarization controller is adjusted to maximize the injection efficiency. The output power of the fiber amplifier is set to 23 dBm. After being amplified by the fiber amplifier, the single-cycle oscillating optical signal is used as pump light and then input into the Brillouin ring cavity after passing through a second polarization controller and a third circulator. The frequency difference between the Brillouin laser and the pump light is 10.850 GHz. The second polarization controller is adjusted to achieve the maximum Brillouin gain in the gain fiber. In the Brillouin ring cavity, the pump light and the excited Brillouin laser propagate in opposite directions. Due to the obstruction of the optical isolator and the third optical circulator, the Brillouin laser propagates counterclockwise and is output through one port of the first fiber coupler, while the light from the other port is fed back into the Brillouin ring cavity to continue participating in resonance. The output Brillouin laser is also split into two paths after passing through the second fiber coupler. One path is input to a photodetector for photoelectric conversion, outputting a microwave signal; the other path is input to an optical frequency shifter, with the frequency shift set to the Brillouin frequency, i.e., 10.850 GHz. At this point, the frequency-shifted laser contains a light component with the same wavelength as the pump light. Subsequently, the frequency-shifted laser is filtered by an optical filter to retain the light component with the same wavelength as the single-cycle oscillation signal. The filtered light is then injected into the main laser after passing through the third polarization controller and the first optical circulator, achieving injection lock-in of the main laser. The injection efficiency is maximized by adjusting the third polarization controller. Since the optical signal output by the main laser contains a single-cycle oscillation light signal component, it can be injected back into the slave laser to achieve injection lock-in of the single-cycle oscillation light signal. Thus, after the first frequency-shift injection locking, the linewidth of the single-cycle oscillating optical signal narrows and its frequency stabilizes. Subsequent linewidth compression and frequency-shift injection locking result in an even narrower linewidth and more stable single-cycle oscillating optical signal. This cycle continues until ultra-narrow linewidth laser output and low phase noise, high side-mode rejection ratio microwave signal generation are achieved. Please refer to [reference needed]. Figure 2 As shown, the output microwave signal after photoelectric conversion is 29.339 GHz, with a very low side-mode rejection ratio exceeding 65 dB. Please refer to [reference needed]. Figure 3 As shown, 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), proving that the single-cycle oscillating microwave signal obtained by this invention 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), 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 optical signal, which passes through the first optical circulator (2), the optical attenuator (3), the first polarization controller (4), and the second optical circulator (5) in sequence before entering the slave laser (6). The optical attenuator (3) is adjusted to change the optical power injected into the slave laser (6), and the first polarization controller (4) is adjusted to maximize the injection efficiency. The slave laser (6) outputs a dual-wavelength single-cycle oscillating optical signal containing a redshift peak and a regeneration peak. 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 redshift peak and regenerated peak components in the single-cycle oscillating optical signal are simultaneously excited in the Brillouin ring cavity as pump light, so that the phase noise of the redshift peak and regenerated peak components suppress each other, generating Brillouin laser and outputting 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. The photodetector (14) outputs a single-cycle oscillating microwave signal after photoelectric conversion of the input Brillouin laser. 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 optical 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 optical signal component, which is then injected into the slave laser (6) to form an injection locking loop for the single-cycle oscillating optical signal output from the slave laser (6). This stabilizes the single-cycle oscillating optical signal and narrows its linewidth, so that the photodetector (14) outputs a single-cycle oscillating microwave signal with lower phase noise and higher side-mode suppression ratio.

2. 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.

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 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.

4. 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.

5. The single-cycle oscillation microwave signal generation device based on frequency-shift 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.

6. The single-cycle oscillation microwave signal generation device based on frequency-shifted optical injection locking according to claim 3, characterized in that: The gain fiber (10) is a single-mode fiber or a nonlinear fiber.

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

8. 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 7, 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-cycle oscillating light signal. After the frequency-shifted laser is filtered by an optical filter, the light component with the same wavelength as the single-cycle 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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