Cherenkov radiation induced symmetry breaking in counter propagating dissipative Kerr solitons

The process of soliton Cherenkov radiation (also known as dispersive wave emission) in microresonator frequency combs plays a critical role in generating broadband and coherent microcomb spectra. Here, we report the observation of symmetry breaking in the group velocity of counter-propagating dissipative Kerr solitons, induced by polychromatic soliton Cherenkov radiation. Results show that in the presence of higher-order dispersion, the temporal arrangement of a multi-soliton state affects its group velocity, an effect which originates from the interference between multiple radiative tails emitted by individual solitons. Experimentally, we bidirectionally pump a microresonator with laser fields of equal power and frequency, and observe lifting of the degeneracy between the repetition rates of the counter-propagating solitons. The observation of symmetry breaking despite symmetric pumping conditions not only shines new light on the impact of dispersive waves on dissipative Kerr soliton dynamics, but also introduces a novel approach to develop coherent dual-comb spectrometers based on microcombs.