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

TL;DR

This paper introduces a novel one-port planar waveguide sensor utilizing a diffraction grating that acts both as an input/output coupler and a reference beam source, enabling dual-scale sensing with high sensitivity and large dynamic range.

Contribution

The device uniquely combines a diffraction grating for both coupling and reference beam generation, enabling simultaneous measurement of angle and phase changes for enhanced sensing performance.

Findings

Demonstrated dual-scale sensing with high sensitivity.

Achieved large dynamic range through combined angle and phase measurements.

Validated the sensor's capability to detect effective refractive index changes.

Abstract

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.