Light erasing method for fabricating planar waveguide volume holographic gratings in LiNbO 3 :Fe crystal

The fabrication of volume holographic gratings (VHGs) has been investigated for many years. According to the photorefractive properties of LiNbO₃:Fe crystal, the VHGs with the grating vector normal to c-axis of the crystal are obtained hardly. A new method for fabrication of above gratings in the planar waveguide array (PWA) in LiNbO₃:Fe crystal based on the light erasing effect is presented. This light erasing technique is divided into two steps: the fabrication of PWA and the light recording of VHGs in the PWA. A PWA is formed firstly in the LiNbO₃:Fe crystal through interference field of two red laser beams. The alignment direction of the formed PWA is parallel to c-axis of crystal. Then the VHGs are recorded using periodical erasing to the formed PWA by the bright fringes of interference, here the vector of the kind of gratings can be perpendicular to c-axis of LiNbO₃:Fe crystal. Furthermore, the VHGs with the period of micron order are created in a PWA employing the light erasing method. The experiment results demonstrate that the light erasing method for fabricating VHGs with the grating vector perpendicular to c-axis in LiNbO₃ crystal is feasible.