Novel dual-loop optoelectronic oscillator based on self-polarization-stabilization technique

A novel dual-loop optoelectronic oscillator (OEO) based on self-polarization-stabilization technique has been experimentally demonstrated. The input light in each loop will retrace its path through a 45° Faraday rotator and single mode fiber with different length after reflecting off a 45° Faraday rotator mirror. By this way, the polarization state of the output signal is always rotated by 180° from the polarization state of the input signal in each loop even if the round-trip fiber is perturbed by the mechanical vibration or temperature. Moreover, the required fiber length is cut in half due to the round-trip transmission in each path, resulting in higher system stability and more compacter structure. The experimental results show that in an intensity modulator (IM)-based OEO system, this scheme has better phase noise performance than the traditional polarization multiplexing method. Furthermore, to avoid the DC bias drifting problem of IM, a simple phase modulation to intensity modulation convertor by using a polarization-dependent phase modulator and a polarizer is proposed without the need of expensive optical filters or dispersive devices. Based on this scheme, a novel dual-loop OEO using phase modulator and self-polarization-stabilization technique has been experimentally demonstrated. The phase noise of -114.1 dBc/Hz at 10 kHz away from the carrier (10 GHz) is achieved and the side mode suppression ratio is improved to 63 dB.