Fourier domain mode-locked optoelectronic oscillator with an electrically tuned thin-film lithium niobate micro-ring filter

Linearly chirped microwave waveforms (LCMWs) are indispensable in advanced radar systems. Our study introduces and validates, through extensive experimentation, the innovative application of a thin-film lithium niobate (TFLN) photonic integrated circuit (PIC) to realize a Fourier domain mode-locked optoelectronic oscillator (FDML OEO) for generating high-precision LCMW signals. This integrated chip combines a phase modulator (PM) and an electrically tuned notch micro-ring resonator (MRR), which functions as a rapidly tunable bandpass filter, facilitating the essential phase-to-intensity modulation (PM-IM) conversion for OEO oscillation. By synchronizing the modulation period of the applied driving voltage to the MRR with the OEO loop delay, we achieve Fourier domain mode-locking, producing LCMW signals with an impressive tunable center frequency range of 18.55 GHz to 23.59 GHz, an adjustable sweep bandwidth from 3.85 GHz to 8.5 GHz, and a remarkable chirp rate up to 3.22 GHz/μs. Unlike conventional PM-IM based FDML OEOs, our device obviates the need for expensive tunable lasers or microwave sources, positioning it as a practical solution for generating high-frequency LCMW signals with extended sweep bandwidth and high chirp rates, all within a compact and cost-efficient form factor.