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Frequency Comb Generation via Cascaded Second-Order Nonlinearities in Microresonators

: Szabados, Jan; Puzyrev, Danila N.; Minet, Yannick; Reis, Luis; Buse, Karsten; Villois, Alberto; Skryabin, Dmitry V.; Breunig, Ingo


Physical review letters 124 (2020), Nr.20, Art. 203902
ISSN: 0031-9007
ISSN: 1079-7114
Fraunhofer IPM ()
nonlinear optics; optical microcavities; Whispering Gallery Mode Resonators; Frequency Comb Generation; Second Order Nonlinearities; microresonators

Optical frequency combs are revolutionizing modern time and frequency metrology. In the past years, their range of applications has increased substantially, driven by their miniaturization through microresonator-based solutions. The combs in such devices are typically generated using the third-order χ(3) nonlinearity of the resonator material. An alternative approach is making use of second-order χ(2) nonlinearities. While the idea of generating combs this way has been around for almost two decades, so far only few demonstrations are known, based either on bulky bow-tie cavities or on relatively low-Q waveguide resonators. Here, we present the first such comb that is based on a millimeter-sized microresonator made of lithium niobate, that allows for cascaded second-order nonlinearities. This proof-of-concept device comes already with pump powers as low as 2 mW, generating repetition-rate-locked combs around 1064 and 532 nm. From the nonlinear dynamics point of view, the observed combs correspond to Turing roll patterns.