A scheme of using CO 2 laser beams to thermally fix layers of photorefractive phase holograms in a single block of LiNbO 3 crystal to fabricate a solid state miniaturized optical system is suggested. Theoretical analysis shows that by the heating with two face to face narrow beams a layer like temperature distribution switable for fixing can be reached. In a primary experiment, a stage of the Gamma network is realized in a single blook of photorefractive LiNbO 3 crystal. It is thus seen that to package and miniaturize a complicated optical system into a single blook of crystal is possible.