Green Light Generated by Frequency-Doubling in LiNbO3 and LiTaO3 Thin Films

Abstract

AbstractThin films of LiNbO3 and LiTaO3 are grown by off-axis magnetron sputtering on A12O3 and LiTaO3 substrates. When stoichiometry is precisely controlled, the films display excellent crystallographic and morphologic properties and have optical losses that are acceptable for frequency-doubling. LiNbO3/A12O3 samples have rocking curve widths as low as Δω = 76 arc sec and rms surface roughnesses less than 1 nm. Rocking curves performed with a resolution of 12 arc sec in 2θ indicate that there is very little tilt to the grains. Most of the width of the standard rocking curve is associated with variations in the interplanar spacing. The LiTaO3 films have similar characteristics. LiNbO3/LiTaO3 samples have rocking curve widths as low as Δω = 28 arc sec. Again, there is very little tilt misalignment to the grains, and the best samples have rms surface roughnesses less than 1 nm. The LiNbO3/LiTaO3 samples are typically 650 nm thick and many have optical losses less than 5 dB/cm. The LiNbO3/A12O3 samples, typically 250 nm thick, have losses of 5–7 dB/cm. The higher modal intensity at the surface of the thinner films increases surface scattering losses.We have generated green light by frequency doubling in LiTaO3 and LiNbO3 thin-film planar waveguides. Phase matching was achieved by both modal dispersion and quasi-phase matching.