Temporal Walk-off Induced Dissipative Quadratic Solitons

Abstract

A plethora of applications have recently motivated extensive efforts on the generation of low noise Kerr solitons and coherent frequency combs in various platforms ranging from fiber to whispering gallery and integrated microscale resonators. However, the Kerr (cubic) nonlinearity is inherently weak, and in contrast, strong quadratic nonlinearity in optical resonators is expected to provide an alternative means for soliton formation with promising potential. Here, we demonstrate formation of a dissipative quadratic soliton via non-stationary optical parametric amplification in the presence of significant temporal walk-off between pump and signal leading to half-harmonic generation accompanied by a substantial pulse compression (exceeding a factor of 40) at low pump pulse energies (∼ 4 picojoules). The bright quadratic soliton forms in a low-finesse cavity in both normal and anomalous dispersion regimes, which is in stark contrast with bright Kerr solitons. We present a route to significantly improve the performance of the demonstrated quadratic soliton when extended to an integrated nonlinear platform to realize highly-efficient extreme pulse compression leading to formation of few-cycle soliton pulses starting from ultra-low energy picosecond scale pump pulses that are widely tunable from ultra-violet to mid-infrared spectral regimes.Formation of dissipative solitons in nonlinear resonators has become a versatile mechanism for stable femtosecond sources [1,2]. In the frequency domain it corresponds to a broadband frequency comb which, when self-referenced, leads to a myriad of applications in precision measurements spanning from spectroscopy [3,4], astro-combs [5,6], atomic clocks [7], ranging [8,9], and imaging [10], to name a few. Recently, the ambit of frequency combs has expanded to cover promising avenues including massively parallel data communication [11], and realization of machine learning accelerators [12]. To cater to this increasing list of technologically important applications, there lies the outstanding challenges of attaining low-power operation [13], high pump to soliton conversion efficiency [14-18], broadband (octave-spanning and widely tunable) comb formation in a compact platform [19,20], reliable fabrication and operation of high-Q resonators which need to be addressed.

High‐Power Mid‐IR Few‐Cycle Frequency Comb from Quadratic Solitons in an Optical Parametric Oscillator

“…Recently, there has been increasing interest in realization of purely dissipative cavity solitons [32,33] with the promise of frequency comb sources outside the well-developed near-IR region. The temporal simulton, a special form of quadratic solitons characterized by the generation of simultaneous bright-dark solitons of the signal at ω and the pump at 2ω [34,35], has emerged as a novel state of operation in OPOs [36,37].…”