Integrated frequency-modulated optical parametric oscillator

TL;DR

This paper introduces a novel integrated optical frequency comb generator called FM-OPO, which combines electro-optics and parametric amplification to produce a highly efficient, broadband, frequency-modulated microcomb in a compact platform.

Contribution

The paper presents the first demonstration of an FM-OPO microcomb that maintains high efficiency and broad bandwidth without pulse formation, using integrated thin-film lithium niobate technology.

Findings

Pump to comb internal conversion efficiency exceeds 93%.

Spectral span of approximately 6 THz with about 1,000 modes.

Bandwidth determined by cavity dispersion, enabling broadband operation.

Abstract

Optical frequency combs have revolutionized precision measurement, time-keeping, and molecular spectroscopy. A substantial effort has developed around "microcombs": integrating comb-generating technologies into compact, reliable photonic platforms. Current approaches for generating these microcombs involve either the electro-optic (EO) or Kerr mechanisms. Despite rapid progress, maintaining high efficiency and wide bandwidth remains challenging. Here, we introduce a new class of microcomb -- an integrated optical frequency comb generator that combines electro-optics and parametric amplification to yield a frequency-modulated optical parametric oscillator (FM-OPO). In stark contrast to EO and Kerr combs, the FM-OPO microcomb does not form pulses but maintains operational simplicity and highly efficient pump power utilization with an output resembling a frequency-modulated laser. We outline the working principles of FM-OPO and demonstrate them by fabricating the complete optical system in thin-film lithium niobate (LNOI). We measure pump to comb internal conversion efficiency exceeding 93% (34% out-coupled) over a nearly flat-top spectral distribution spanning approximately 1,000 modes (approximately 6 THz). Compared to an EO comb, the cavity dispersion rather than loss determines the FM-OPO bandwidth, enabling broadband combs with a smaller RF modulation power. The FM-OPO microcomb, with its robust operational dynamics, high efficiency, and large bandwidth, contributes a new approach to the field of microcombs and promises to herald an era of miniaturized precision measurement, and spectroscopy tools to accelerate advancements in metrology, spectroscopy, telecommunications, sensing, and computing.