Tunable optoelectronic oscillator based on a polarization-dependent phase modulator cascaded with a linear chirped FBG

Abstract

A tunable optoelectronic oscillator (OEO) based on polarization controlled frequency response shifting of a dispersion-induced microwave photonic filter (MPF) is proposed and experimentally demonstrated. The MPF consists of a phase modulator (PM), a linear chirped fiber Bragg grating (LCFBG), and polarization multiplexed dual loops. Thanks to the polarization properties of the LiNbO3 crystal, the center frequency of the MPF can be tuned by simply adjusting the polarization state of the optical signal, and a tunable optoelectronic oscillator is established. Compared to the previous structure, the expensive wavelength-tunable laser is not needed in the proposed structure. In addition, the instability of oscillation frequency caused by the bias drifts of the modulator is avoided. A pure oscillation signal with a tunable frequency range from 3.3 to 7.3 GHz is generated. The single-sideband phase noise of the oscillation signal is about −110 dBc/Hz at 10-kHz offset. During more than 30 min observation, the oscillation frequency drift is about 7 kHz.