Interferometric Noise Reduction in Optoelectronic Oscillator with Roundtrip Optical Delay Line

Abstract

A roundtrip optical delay line can double the time delay so that it can be used in optoelectronic oscillators (OEOs) to halve the length of the optical fiber. But in bidirectional optical links, the interferometric intensity noise is much higher than that in unidirectional optical link. The intensity noise will be converted to microwave phase noise via amplitude-to-phase conversion at photodetector. In this paper, we built an OEO using a roundtrip optical delay line and suppress the interferometric intensity noise by sweeping the frequency of the optical carrier realized by direct modulating the laser diode. In case of 100kHz modulation, the reduction of phase noise at 1kHz offset frequency is 26dB, and the phase noise of the generated 10GHz signal is -118dBc/Hz @ 1kHz and -136dBc/Hz @ 10kHz. In addition, The OEO was stabilized by injection and phase locked to a stable reference signal.