Optically induced photorefractive waveguides in KNSBN:Ce crystal

We present our experiments on fabricating fiber-like and planar photorefractive waveguides in a KNSBN:Ce crystal solely by laser irradiation with the wavelength of 632.8 nm and 532 nm, respectively. The high refractive index regions induced by thin cylindrical beams or thin sheet beams propagating through the crystal are used as waveguide structures. The refractive index changes in the waveguide region are measured by a Mach-Zehnder interferometer using the phase-stepping method, and the refractive index profiles are mapped. The optically induced distributions of refractive index changes observed in our experiments are discussed according to the transport mechanism of the photo-induced charge carriers in the crystal. The asymmetry of the light-induced space charge fields in the absence of external electric field may cause the asymmetry of the refractive index distributions. The guidance of the waveguides fabricated in our experiments shows that the probe beams are trapped in the waveguide regions. It is shown that fabricating photorefractive waveguides by use of light-induced refractive index changes in KNSBN:Ce crystals is feasible.