  We present a one-port sensor based on a single diffraction grating delineated
over a planar optical waveguide. Distinctly to previously reported devices, the
grating here is used not only as I/O coupler, but also provides a built-in
reference beam which is basically unaffected by the sensing process as
manifested in changes of the effective refractive index of the waveguide. 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 will translate into a large sensing
dynamic range.
