A slim optical fingerprint recognition sensor (OFRS) based on a grating input coupler and a microprism sensing surface is proposed. By using a subwavelength grating coupler, input light is coupled into the planar waveguide and the propagation angle is well engineered to avoid image overlap, thus an undistorted fingerprint is captured. For maintaining a thin structure, a microprism array is utilized to facilitate the breaking of total internal reflection under a large diffraction angle from the grating. The feasibility, efficiency, and image quality of the proposed structure are verified and discussed. The device has the advantages of a slim structure, a high image contrast, and a compact architecture, suitable for mobile devices.