HIGH 2ND-HARMONIC CONVERSION EFFICIENCY OF QUASI-PHASE-MATCHED LITAO3 WAVE-GUIDES PUMPED BY SINGLE-MODE PULSED ALGAAS LASER-DIODES

We show that the averaged second-harmonic conversion efficiency of quasi-phase-matched LiTaO3 waveguides can be increased by a factor larger than 15 with the use of single-mode pulsed AlGaAs laser diodes as the optical sources. The proton exchange followed by thermal annealing is used both to periodically change the sign in d(33) nonlinear coefficient and to fabricate the waveguides. Laser pulses are produced by strong rf modulation of the diode current while single-mode operation is achieved with a grating-tuned external cavity. The averaged conversion efficiency is found to linearly increase with peak power of pulses even in the case of pulses whose spectral width is larger than the spectral acceptance of LiTaO3 waveguides. Experimental results are in agreement with calculated ones. The conversion efficiency of 450 %/W presently reached at optimum (i.e., 1% for 2.2 mW pump and 1 cm interaction length) is among the highest performances reported to date for frequency doubling of laser diodes. (C) 1995 American Institute of Physics.