Abstract

When a tightly focused, high intensity beam is input into a doubling crystal near phase-matching for efficient second harmonic (SH) generation (SHG), quadratic spatial solitons (QSS) can be formed that consist of mutually self-trapped fundamental (FW) and harmonic (SH) optical beams. The mutual beam narrowing that occurs in any nonlinear wave mixing process due to photon exchange, balances diffraction. This effect was predicted back in the mid 1970s and observed for the first time in the mid 1990s.[1,2] Since then QSS’es have been observed in a number of quadratically nonlinear material systems. Of particular interest are periodically poled (PP) ferroelectric media where the PP can lead to phase-matching (QPM) at virtually any wavelength. They represent an important and unique limit of non-critical phase-matching (NCPM). Solitons in periodically poled LiNbO₃ (PPLN) have been reported at very low soliton threshold of 1.5 GW/cm² [3]. That pioneering work established the existence of quadratic solitons in periodically poled media but none of the unique properties associated with a combination of non-critical-phase-matching and QPM were reported.

© 2002 Optical Society of America