Abstract
Frequency combs have applications that extend from the ultra-violet into the mid-infrared bands. Microcombs, a miniature and often semiconductor-chip-based device, can potentially access most of these applications, but are currently more limited in spectral reach. Here, we demonstrate mode-locked silica microcombs with emission near the edge of the visible spectrum. By using both geometrical and mode-hybridization dispersion control, devices are engineered for soliton generation while also maintaining optical Q factors as high as 80 million. Electronics-bandwidth-compatible (20 GHz) soliton mode locking is achieved with low pumping powers (parametric oscillation threshold powers as low as 5.4 mW). These are the shortest wavelength soliton microcombs demonstrated to date and could be used in miniature optical clocks. The results should also extend to visible and potentially ultra-violet bands.
Highlights
Frequency combs have applications that extend from the ultra-violet into the mid-infrared bands
Microcomb optical clocks based on the D1 transition (795 nm) and the two-photon clock transition[21] (798 nm) in rubidium have been proposed[9,22]
It is possible that these shorter wavelength systems could be applied in optical coherence tomography systems[24,25,26]
Summary
Frequency combs have applications that extend from the ultra-violet into the mid-infrared bands. The diameter of allresonators in this work (and the assumed diameter in all simulations) is 3.2 mm, which corresponds to a free spectral range (FSR) of approximately 20 GHz, and the resonator thickness is controlled to obtain net anomalous dispersion at the design wavelengths, as described in detail below.
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