Programmable Mode-Locked Optoelectronic Oscillator for Wideband Arbitrary Microwave Waveforms Generation

We propose and experimentally demonstrate a programmable mode-locked optoelectronic oscillator (PML-OEO) for generating wideband arbitrary microwave waveforms. In the proposed system, a bandpass microwave photonic filter (MPF) is implemented based on phase-modulation to intensity-modulation (PM-IM) conversion, with center frequency controlled via optical carrier wavelength tuning. Upon closing the MPF loop, an optoelectronic oscillator (OEO) is created, where mode locking happens when the period of the wavelength-tuning driving signal matches the round-trip time of the OEO loop. By controlling the driving signal, the proposed PML-OEO can operate in three different mode-locking states, including Fourier-domain mode locking (FDML), active mode locking (AML), and dual mode locking (DML). An experiment is performed, in which wideband arbitrary microwave waveforms, including continuous-wave (CW) microwave signals with reconfigurable modulation patterns, frequency-tunable, and linearly chirped microwave pulses (LCMPs) with customizable duty cycles, are experimentally generated. Particularly noteworthy is the performance of the generated LCMP, exhibiting a bandwidth as broad as 6 GHz, a frequency tuning range of 9 GHz from 12 to 21 GHz, a chirped error as small as 1.95%, and a tunable duty cycle from 20% to 80%. With its unique waveform programmability, the proposed PML-OEO system provides an efficient solution for demanding RF applications spanning from multifunctional radar and high-speed wireless communications to high-resolution electromagnetic imaging.