Integrated Ultra-Wideband Tunable Fourier Domain Mode-Locked Optoelectronic Oscillator

Fourier domain mode-locked optoelectronic oscillator (FDML OEO) is a crucial component for the upcoming sixth-generation (6G) communication era, as it can break the limitation of mode building time in the conventional OEO and generate high-quality frequency-tunable microwave signals or waveform such as linearly chirped microwave waveform (LCMW) for millimeter-wave applications thanks to its ultra-low phase noise. However, most FDML OEOs reported thus far are discrete and their operating bandwidth are limited, which makes it difficult to meet the real applications' requirements. Here, we propose and demonstrate the first integrated tunable FDML OEO with the tunable frequency range of 342.5 GHz in the lithium niobate on insulator (LNOI) photonic integrated circuit platform. As examples, we demonstrate the generation of LCMW, quadratic-chirp signal, and triangle waveform with the center frequency covering millimeter-wave band using the proposed FDML OEO. The FDML OEO provides a promising solution for the compact and effective signal generation solution, which breaks the bandwidth limitations and facilitates the realization of extensive applications in the field of radio frequency (RF), including high-precision microwave photonic radar, next-generation wireless communication, and unmanned autonomous driving systems.