Soliton bursts and deterministic dissipative Kerr soliton generation in auxiliary-assisted microcavities

Abstract

Dissipative Kerr solitons in resonant frequency combs offer a promising route for ultrafast mode-locking, precision spectroscopy and time-frequency standards. The dynamics for the dissipative soliton generation, however, are intrinsically intertwined with thermal nonlinearities, limiting the soliton generation parameter map and statistical success probabilities of the solitary state. Here, via use of an auxiliary laser heating approach to suppress thermal dragging dynamics in dissipative soliton comb formation, we demonstrate stable Kerr soliton singlet formation and soliton bursts. First, we access a new soliton existence range with an inverse-sloped Kerr soliton evolution—diminishing soliton energy with increasing pump detuning. Second, we achieve deterministic transitions from Turing-like comb patterns directly into the dissipative Kerr soliton singlet pulse bypassing the chaotic states. This is achieved by avoiding subcomb overlaps at lower pump power, with near-identical singlet soliton comb generation over twenty instances. Third, with the red-detuned pump entrance route enabled, we uncover unique spontaneous soliton bursts in the direct formation of low-noise optical frequency combs from continuum background noise. The burst dynamics are due to the rapid entry and mutual attraction of the pump laser into the cavity mode, aided by the auxiliary laser and matching well with our numerical simulations. Enabled by the auxiliary-assisted frequency comb dynamics, we demonstrate an application of automatic soliton comb recovery and long-term stabilization against strong external perturbations. Our findings hold potential to expand the parameter space for ultrafast nonlinear dynamics and precision optical frequency comb stabilization.

Nonlinear optics: Keeping solitons warm and stable

Ultrafast optical states called solitons can be prevented from thermally breaking down by carefully heating them with a laser, researchers in the US and China show. Solitons are optical fields that exist in isolation, like smoke rings in air or bubbles in water, and they could greatly improve precision laser measurements and spectroscopy. However, it is difficult to maintain robust soliton states due to nonlinear thermal effects that cause them to break down. Heng Zhou at UESTC, Chee Wei Wong at UCLA, and co-workers generated solitons by directing a ‘frequency comb’ source (comprising discrete, equally-spaced laser lines) onto a silicon nitride optical microcavity. Crucially, they employed a second laser to provide heating to the system and suppress the thermal nonlinearities. This enabled smooth transitions between useful soliton states, while avoiding chaotic intermediate states.