Back-reflecting interferometeric sensor based on a single grating on a planar waveguide

We present and analyze a one-port sensor based on a single diffraction grating delineated over a planar optical waveguide. Distinct to previously reported devices, the grating we use here is used not only as I/O coupler, but also provides a built-in reference beam that is basically unaffected by the sensing process. The sensing process causes two effects simultaneously: a change in the angle of the out-coupled beam and a change in the phase accumulated by that beam. Both changes can be determined by their conjunction with the reference beam back-diffracted directly by the grating. These two effects are expected to have despair sensitivities, the angle changing effect being coarse and the interferometric phase-change effect being highly sensitive. Sensing simultaneously at two different scales enlarges to a great extent the sensing dynamic range. Theoretical analysis and simulations of a specific implementation example of the device are presented.