Oscillatory motion of a counterpropagating Kerr soliton dimer

Counterpropagating (CP) solitons generated in high-Q microcavities not only offer useful dual-comb sources, but also provide a new platform to study soliton interactions. Here, we demonstrate and theoretically explain a manifestation of soliton trapping that occurs between CP solitons in a silica microcavity introducing a Kerr soliton dimer. In conventional soliton trapping, the group velocities of two solitons can be synchronized by a Kerr-effect-mediated interaction. The solitons can then copropagate with a fixed temporal delay. However, as shown here, when counterpumping a microcavity using slightly detuned pump frequencies and in the presence of backscattering, the group velocities of clockwise and counterclockwise solitons undergo periodic modulation instead of being locked to a constant velocity. Upon emission from the microcavity, the solitons feature a relative oscillatory motion around a locked average relative displacement with an amplitude that can be larger than the soliton pulse width. This relative motion introduces a sideband fine structure into the optical spectrum of the CP solitons. Our observation provides insights on coherently pumped soliton dimers in microcavities.

Automated summary

This study demonstrates the phenomenon of soliton trapping between counterpropagating solitons in a silica microcavity due to counterpumping, where the group velocities undergo periodic modulation instead of being locked to a constant velocity. The solitons exhibit relative oscillatory motion upon emission from the microcavity, introducing a sideband fine structure into the optical spectrum. This observation provides insights on coherently pumped soliton dimers in microcavities.