Tunable narrow-linewidth photo-generated microwave source based on polarization control

A tunable narrow-linewidth photo-generated microwave source based on polarization control, comprising:

• a high-reflectivity fiber grating, a high-gain fiber, a low-reflectivity polarization-maintaining fiber grating, a stress adjusting device, an optical wavelength division multiplexer, a single-mode semiconductor pump laser, a polarization beam splitter, a polarization controller, an optical coupler, and a photoelectric detector;
• wherein the high-reflectivity fiber grating, the high-gain fiber, and the low-reflectivity polarization-maintaining fiber grating together form a resonant cavity of the laser, the high-gain fiber serves as a gain medium of the resonant cavity of the laser, and the high-reflectivity fiber grating and the low-reflectivity polarization-maintaining fiber grating form front and rear cavity mirrors of the resonant cavity, which are respectively connected with two ends of the high-gain fiber, so that a signal laser oscillates in the resonant cavity, and a first end of the optical wavelength division multiplexer is connected with the resonant cavity;
• an output end of the single-mode semiconductor pump laser is connected with a second end of the optical wavelength division multiplexer, and a pump laser is injected into the resonant cavity through the optical wavelength division multiplexer;
• due to birefringence in the low-reflectivity polarization-maintaining fiber grating, two reflection peaks with different polarization modes and different central wavelengths exist, so that the laser is enabled to realize orthogonal dual-frequency narrow-linewidth optical fiber laser output through the wavelength division multiplexer;
• an input end of the polarization beam splitter is connected with an output end of the optical wavelength division multiplexer to divide two lasers with different frequencies and different polarizations output by the optical wavelength division multiplexer into fast-axis laser and slow-axis laser;
• an output end of the polarization beam splitter is respectively connected with the polarization controller and the optical coupler, and an output of the optical coupler is connected with the photoelectric detector;
• a polarization state of the slow-axis laser is adjusted by the polarization controller to change an orthogonal relationship between the slow-axis laser and the fast-axis laser, is coupled with the fast-axis laser through the optical coupler and injected into the photoelectric detector, and a narrow-linewidth microwave signal is generated by a beat-frequency technology;
• and
• the stress adjusting device is arranged on the low-reflectivity polarization-maintaining fiber grating, changes birefringence distribution in the grating by changing a stress magnitude applied to the low-reflectivity polarization-maintaining fiber grating, controls output laser frequencies under different polarization modes, and outputs a tunable narrow-linewidth photo-generated microwave signal.