Flexible Platicon Generation via Random Backscattering in Ultra-High-Q Microresonators

Microcombs generated in microresonators with normal group velocity dispersion (GVD) which are referred to as platicons, are promising due to the high conversion efficiency and less efforts on dispersion engineering. Unlike solitons in anomalous GVD raesonators that can be pumped at a wide wavelength range, platicons can only be generated close to the resonance with avoided mode crossings (AMX), which are typically derived from intermodal couplings [1] or synthetic reflections in photonic crystal resonators [2]. These AMXs are usually limited in number, separated by specific wavelengths and thus restrict the tunability of pump wavelength for platicon generation. Although tunable microcombs have been proposed utilizing auxiliary ring heating [3], the use of heaters complicates fabrication and requires strict thermal stabilization. Recently, microresonators with ultra-high Q factor reaching hundreds of millions can be fabricated [4]. Those ultra-high Q devices are more prone to fabrication imperfections, which result in randomly distributed mode splitting caused by coupling between clockwise (CW) and counterclockwise (CCW) propagating light due to Rayleigh backscattering. Although such mode splittings are generally considered undesirable, they can be harnessed to facilate flexible pumping for platicon generation within ultra-high-Q microresonators, where the CW-CCW mode splitting becomes more pronounced. In this work, we show the feasibility of flexible platicon generation via random backscattering in an ultra-high-Q microresonator.