Abstract

Since several decades frequency conversion based on quadratic nonlinearities is a well-established technique in nonlinear optics. In particular, the interest in optical parametric oscillators (OPOs) as tunable light sources with low oscillation thresholds has been renewed. This is mainly due to recent advances in stable pump lasers and nonlinear materials. A considerable reduction of threshold pump power down to a few milliwatts could be achieved in phase-matched, triply resonant OPOs (TROs) [1]. Bistability as well as delayed bifurcation in this configuration could be verified experimentally [1]. In an OPO the high frequency incident photon spontaneously decays into two low frequency photons beyond the threshold. The alternative scenario, viz. intra-cavity frequency up-conversion, has likewise attracted much attention, in particular as far as the degenerate case (second-harmonic generation - SHG) is concerned. Efficient SHG was reported in Ti:LiNbO₃ waveguide resonators a decade ago [2]. More recently a conversion efficiency of 82% in a monolithic MgO:LiNbO₃ resonator with 100 mW input power was achieved [3]. Theoretically, for a high finesse cavity optical bistability was predicted for plane wave solutions [4] whereas different kinds of patterns and solitary waves [5] could be observed if transverse effects were taken into account.

© 1998 Optical Society of America