We propose a structure of a photorefractive polymer device. An electric field is applied to the device in plane so as to coincide with the direction of a grating formed by two writing beams. This structure permits us to fabricate a thick photorefractive polymer device with a high optical gain. The maximum thickness we fabricated was 600 μm. We investigate the device performance using a two-beam coupling experiment and demonstrate high-beam-coupling gain in the thick device. We also describe position dependence of the photorefractive effect for an apical electrode structure.