Microresonator frequency combs offer the promise of precision time and frequency metrology that is integral to applications such as optical atomic clocks in a compact and low-power format that is amenable for deployment outside of a lab.
At the heart of such combs is the physics of a damped, driven, and dispersive Kerr nonlinear resonator. Such systems can support a wide variety of states, including phase-stable single soliton states, in which an input continuous wave laser is transformed into a solitary pulse circulating around the microresonator. The soliton regime in microresonator combs has been widely pursued due to its suitability for low-noise and phase-coherent applications, including in optical frequency synthesis and division.
In a recent work, led by Gregory Moille and in collaboration with Yanne Chembo (also at UMD), we have demonstrated how to broaden the bandwidth of a soliton microcomb through application of a second input continuous wave laser. This second laser introduces a new nonlinear process to the system, that of four-wave mixing Bragg scattering, which we have previously studied in the context of frequency conversion of quantum states. Here, four-wave mixing Bragg scattering acts to spectrally translate soliton comb teeth to both the low frequency and high frequency sides of the spectrum, ulitmately resulting in a spectrum that is 60 % broader than a singly pumped soliton microcomb in this system. We outline the key criteria associated with being able to realize the two intracavity nonlinear processes of soliton formation and four-wave mixing Bragg scattering spectral translation, and present data indicative of its possible metrological potential.
This work has also been highlighted by NIST and phys.org. Please have a look for a beautiful video depicting soliton generation and soliton spectral translation made by Sean Kelley at NIST!
Moille, G., E. F. Perez, J. R. Stone, A. Rao, X. Lu, T. Sami Rahman, Y. K. Chembo, and K. Srinivasan, "Ultra-broadband Kerr microcomb through soliton spectral translation", Nature Communications, vol. 12, pp. 7275, Dec, 2021.