Cs⁺-K⁺ Exchange in Z-Cut KTiOPO₄ Crystal Covered with Chromium Masking Layer

Cs⁺--K⁺ ion exchanges are performed on z-cut KTiOPO₄ crystals with chromium coating covered. The temperature of ion exchange is 430°C, and the time range from 15min to 30min. The dark mode spectra of the samples are measured by the prism coupling method. The channel structures on the samples are observed by a microscope and the near field pattern of the channel waveguides are measured by the end-fire coupling method. The refractive index of the samples increases and the increments at surface are modulated due to the existence of Cr film. In the region covered by Cr film, the refractive index of the samples at the surface increases dramatically in a shallow layer. The results of energy dispersive x-ray spectra indicate that in the region covered with Cr film, Cr ions participate in the ion exchange process, and enhance the refractive index. The results may provide a possibility that achieves index enhancement and Cr doping synchronically.