Photonic generation of frequency-switchable microwave signals exploiting polarization-induced spectrum splitting in fiber grating-based Fabry–Perot filters

Frequency-switchable microwave signals are optically generated using a dual-wavelength single-longitudinal-mode erbium-doped fiber ring laser. The splitting of the resonance peak is observed in fiber grating-based Fabry–Perot (F–P) filters depending on the injected light polarization states. Choosing two different resonance peaks of the grating-based F–P filter and using a variable saturable absorber formed by a section of incompletely transparent erbium-doped fiber, wavelength-switchable dual-wavelength single longitudinal-mode operation is achieved in the fiber ring laser. Microwave frequency switched among 8.75, 21.25 and 25.4 GHz is implemented by feeding the output laser to a high-speed photodetector.