Abstract

Photorefractive waveguides (PRW) are of prime interest for applications in integrated optics such as optical switching, resonant filtering or holographic memories. Therefore, investigations are to date extensively increasing to search new efficient methods of PRW’s fabrication Among the potential optical materials, lithium niobate (LiNbO₃) has been subjected to extensive development, especially because crystals of good optical quality are commercially available. Comparatively to other known and mostly used methods of PRW’s elaboration in LiNbO₃, the very new method of combined proton and copper exchange seems to present some interesting advantages [1,2]. This ionic exchange process enables to control easily and precisely the photorefractive response parameters since the copper concentration as well as the ratio Cu⁺/Cu²⁺ can be varied gradually in a wide range [1]. Moreover, it allows to reach an extremely high holographic sensitivity [2]. However, an undesired feature of the proton-exchanged waveguides is that the electrooptical coefficients are reduced significantly [2]. In contrast, no degradation of the latter is observed in ion-implanted waveguides [3]. Therefore, to elaborate the LiNbO₃ waveguides with improved photorefractive properties, we have used a new two-step techique : First, the optical waveguides are formed by implantation of He⁺-ions at room temperature under a fluence of 2×10¹⁶ ions/cm² and with an energy of 1 MeV, and second, the photorefractive sensitivity of the waveguides are increased by using the combined proton and copper exchage process, but conducted in specific conditions, i.e. when the proton exchange is minima, not sufficient to induce both an essential degradation of the electrooptical effect and a marked change of the effective refractive index.

© 1998 IEEE