Optical wavefront phase-tilt measurement using Si-photonic waveguide grating couplers

TL;DR

This paper introduces silicon photonic wavefront sensors using grating couplers that measure wavefront tilt and phase variation directly on-chip, enabling compact, arrayable sensors for adaptive optics and optical communication.

Contribution

The paper presents two novel silicon photonic wavefront sensors utilizing grating couplers for tilt and phase measurement, eliminating bulk optics and enabling miniaturized, scalable arrays.

Findings

Achieved 7 dB/degree sensitivity in tilt measurement.

Demonstrated phase variation detection with ~2 degree fringe resolution.

Sensors are less than 60 micrometers across, suitable for array integration.

Abstract

Silicon photonic wavefront phase-tilt sensors for wavefront monitoring using surface coupling grating arrays are demonstrated. The first design employs the intrinsic angle dependence of the grating coupling efficiency to determine local wavefront tilt, with a measured sensitivity of 7 dB/degree. A second design connects four gratings in an interferometric waveguide circuit to determine incident wavefront phase variation across the sensor area. In this device, one fringe spacing corresponds to approximately 2 degree wavefront tilt change. These sensor elements can sample a wavefront incident on the chip surface without the use of bulk optic elements, fiber arrays, or imaging arrays. Both sensor elements are less than 60 um across, and can be combined into larger arrays to monitor wavefront tilt and distortion across an image or pupil plane in adaptive optics systems for free space optical communications, astronomy and beam pointing applications.