Photonic Generation of Phase-Coded Microwave Signals Based on Fourier Domain Mode Locking

Abstract

We report a novel photonic scheme to generate binary phase-coded microwave signals by using two cascaded phase modulators (PMs) based on a Fourier domain mode-locked (FDML) optoelectronic oscillator (OEO). The first PM is driven by a series of electrical coding signals to modulate the phase of the optical carrier. The second PM is a construction of the FDML OEO, which realizes phase-modulation to intensity-modulation conversion together with a phase-shifted fiber Bragg grating. Phase-coded microwave signals can be generated when the period of the electrical coding signal matches with the round-trip time of the OEO. A π phase shift of the phase-coded microwave signals can be achieved by properly adjusting the level of the electrical coding signal. The key point of our work is that phase-coded microwave signals can be generated directly from the FDML OEO cavity. Besides, the proposed system has great reconfigurability in terms of center frequency and bit rate. Our scheme is theoretically analyzed and experimentally verified. Phase-coded microwave signals with a bit rate of 420 Mb/s and center frequency of 9.3 GHz, as well as with a bit rate of 2 Gb/s and center frequency of 12.7 GHz are successfully generated in the experiment.