Integrated frequency-modulated optical parametric oscillator.

Stokowski, Hubert S; Dean, Devin J; Hwang, Alexander Y; Park, Taewon; Celik, Oguz Tolga; McKenna, Timothy P; Jankowski, Marc; Langrock, Carsten et al. · Nature · 2024

basic_science · Level V

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Abstract

Optical frequency combs have revolutionized precision measurement, time-keeping and molecular spectroscopy<sup>1-7</sup>. A substantial effort has developed around 'microcombs': integrating comb-generating technologies into compact photonic platforms<sup>5,7-9</sup>. Current approaches for generating these microcombs involve either the electro-optic<sup>10</sup> or Kerr mechanisms<sup>11</sup>. Despite rapid progress, maintaining high efficiency and wide bandwidth remains challenging. Here we introduce a previously unknown class of microcomb-an integrated device that combines electro-optics and parametric amplification to yield a frequency-modulated optical parametric oscillator (FM-OPO). In contrast to the other solutions, it does not form pulses but maintains operational simplicity and highly efficient pump power use with an output resembling a frequency-modulated laser<sup>12</sup>. We outline the working principles of our device and demonstrate it by fabricating the complete optical system in thin-film lithium niobate. We measure pump-to-comb internal conversion efficiency exceeding 93% (34% out-coupled) over a nearly flat-top spectral distribution spanning about 200 modes (over 1 THz). Compared with an electro-optic comb, the cavity dispersion rather than loss determines the FM-OPO bandwidth, enabling broadband combs with a smaller radio-frequency modulation power. The FM-OPO microcomb offers robust operational dynamics, high efficiency and broad bandwidth, promising compact precision tools for metrology, spectroscopy, telecommunications, sensing and computing.