Epitaxial grown K1−xRbxTiOPO4 films with extremely flat surfaces for waveguiding

Abstract We report on epitaxial {1 0 0} K 1−x Rb x TiOPO 4 waveguide films for the visible spectral range grown on KTiOPO4 substrates by liquid phase epitaxy. Using the m-line technique a refractive index increase of Δnx≈0.007 and Δnz≈0.004 for TM and TE polarisation has been determined for a K0.78Rb0.22TiOPO4 film. Optical transmission and nearfield distribution are comparable to conventional ion-exchanged waveguides. Typical attenuation of about 1 dB/cm for both TM and TE polarisation was obtained at λ=532 and 1064 nm. Energy-dispersive X-ray spectrometry reveals solid-solution films with graded rubidium composition profiles. X-ray rocking curve analyses confirm the epitaxial growth process and indicate perfect and relaxed K1−xRbxTiOPO4 films. Atomic force microscopy investigations reveal regular step structures with step heights Δh