Subharmonic Entrainment of Kerr Breather Solitons.

We predict subharmonic entrainment of breather-soliton oscillations to a periodic perturbation at the round-trip time T_{R} in Kerr-nonlinear optical resonators; an integer ratio T_{b}/T_{R}=N≫1 results for breathing period T_{b}. Rigid entrainment is observed with intermediate finesse (F∼30-40) for N up to 20, and we propose a way to realize higher entrainment ratios at higher finesse. This nontrivial synchronization across the widely separated timescales of the photon lifetime and round-trip time points to a new direction for research in this field and may find application, for example, in the measurement of a pulse train repetition rate that is electronically inaccessible.