Self-phase-locked degenerate femtosecond optical parametric oscillator based on BiB3O6

Degenerate sub-harmonic ultrafast optical parametric oscillators (OPOs) synchronously-pumped by mode-locked femtosecond lasers have drawn special attention in recent years due to their potential for generating broadband frequency combs in the near- to mid-IR spectral regions. Following the first demonstration of the self-phase-locking concept in a degenerate cw OPO by Nabor et al. in 1990, in recent years extensive research has been carried out in femtosecond OPOs, which has now firmly established degenerate sub-harmonic femtosecond OPOs as attractive sources of broadband frequency combs, which are inherently phase-locked to the pump frequency comb. At the same time, successful operation of such OPOs has relied exclusively on engineered quasi-phase-matched (QPM) nonlinear materials, primarily periodically-poled lithium niobate (PPLN), and more recently GaAs, combining the high nonlinear gain and broadband generation under type I (eee) QPM interaction. However, the high cost of PPLN, limited availability of OP-GaAs, and the need for temperature phase-matching may be prohibitive for widespread applications.