Broadband pulse generator based on a self-injection-locked Fourier domain mode-locked optoelectronic oscillator

Abstract

A novel broadband pulse generator based on a Fourier domain mode-locked optoelectronic oscillator (FDML-OEO) is proposed and experimentally demonstrated. The system consists of a dual-loop self-injection-locked OEO with an on-off keying (OOK) bias-controlled Mach–Zehnder modulator (MZM) as an optical switch. By applying a square-wave voltage onto the bias port of the MZM the broadband pulses are directly generated by slicing the outputs of the FDML-OEO. The duty cycle can be easily changed by just tuning that of the square wave. Different microwave pulses with the duty cycles of 1:1, 1:10 and 1:100 are demonstrated. In particular, the tunability of the central frequency and the bandwidth of the generated signal is also displayed. Furthermore, the amplitude coherence superposition of 8 pulses is increased by ∼16 times and the frequency modulated pulse with different central frequencies are also demonstrated. The proposed broadband microwave signal pulse generator based on the injection-locked FDML-OEO can generate signals with large time bandwidth product (TBWP), and the linearly chirped microwave waveforms (LCMWs) are widely used in modern radar systems to achieve high-resolution detection and imaging.