A reusable all-polymer coupler using gratings and tapers for vertical light coupling to single-mode planar waveguides is demonstrated. Numerical simulations are performed to optimize the tapers and gratings to increase the coupling efficiency. A hot-embossing replication technique is used for the fabrication of waveguide sensors and gratings, which is adaptable to mass production, such as roll-to-roll processes. The external grating is reversibly bonded to the waveguide via van der Waals forces, and the thus realized re-usability reduces the fabrication costs. The utility of the structure is shown by using these grating couplers for testing of asymmetric Mach-Zehnder interferometers.