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Abstract

We present an experimental and a theoretical analysis of the
operation characteristics of a femtosecond optical parametric
oscillator (OPO) based on periodically poled LiNbO3 (PPLN). It
provides bright visible pulses through second-harmonic
generation (SHG) of the signal and sum-frequency generation
(SFG) between the signal and the pump, simultaneously with the
parametric oscillation in the near IR. Using a duty cycle of
the poling period of approximately 56%, we achieved strong
enhancement of even-order quasi-phase-matched (QPM) SHG and
SFG, whereas the reduction in the efficiencies of odd-order QPM
processes is negligible. Femtosecond pulses with output powers
of up to 14 mW in the blue, 12 mW in the green, and 18 mW in
the red were obtained for a pump power of only 480 mW. The
tuning ranges extended from 460 nm to 500 nm and from 520 nm to
660 nm for SFG between the pump and signal and SHG of the
signal, respectively, with at least 2-mW output power. Our work
demonstrates that proper choice of the duty cycle of the poling
period allows exploitation of higher-order QPM for intracavity
SHG and SFG processes in PPLN OPOs. (C) 2002 Optical Society of
America.