LINEAR AND NONLINEAR-OPTICAL PROPERTIES OF KNBO3 RIDGE WAVE-GUIDES

Ridged channel waveguides in KNbO3 were produced using He+ ion implant ation, photolithographic masking, and subsequent Ar+ ion sputtering. W e investigated the linear and nonlinear optical characteristics of the waveguides. The effective mode indices are derived from the refractiv e index profiles using the effective index method. The losses are inve stigated as a function of wavelength and of the geometrical parameters channel width and ridge height. A minimum loss of 2 dB cm(-1) is meas ured at a wavelength of 0.633 mu m. We investigated the power handling capabilities at visible and near-infrared wavelengths. Second-harmoni c generation in these waveguides is studied both theoretically and exp erimentally with regard to its dependence on the guide fabrication par ameters. Phase-matching configurations for blue light second-harmonic generation are evaluated on the basis of the dispersion of the effecti ve mode indices. Overlap integrals are calculated on the basis of the field distributions derived from the refractive index profiles. The mi nimum effective guide cross section is 25 mu m(2). A continuous-wave s econd-harmonic output power of 14 mW at 438 nm was obtained with an in -coupled fundamental power of 340 mW in a 0.73 cm long waveguide, yiel ding a normalized internal conversion efficiency of 25% W-1 cm(-2) (13 % W-1). This corresponds to an improvement by a factor of 3 compared t o the best results reported for KNbO3 waveguides up to now. (C) 1998 A merican Institute of Physics.