Experimental demonstration of photonic phase correctors based on grating coupler arrays and thermo-optic shifters

TL;DR

This paper demonstrates a silicon photonic chip that uses grating coupler arrays and thermo-optic shifters to coherently combine telescope beamlets into a single-mode fiber, improving astronomical light coupling under atmospheric turbulence.

Contribution

It introduces a novel integrated photonic phase corrector with grating couplers and thermo-optic shifters for adaptive optics applications in astronomy.

Findings

Experimental results show effective beam co-phasing on an AO testbed.

Performance closely matches simulation predictions.

The device enhances coupling efficiency into single-mode fibers.

Abstract

In ground-based astronomy, the ability to couple light into single-mode fibers (SMFs) is limited by atmospheric turbulence, which prohibits the use of many astrophotonic instruments. We propose a silicon-on-insulator photonic chip capable of coherently coupling the out-of-phase beamlets from the subapertures of a telescope pupil into an SMF. The photonic integrated circuit (PIC) consists of an array of grating couplers that are used to inject light from free space into single-mode waveguides on the chip. Metallic heaters modulate the refractive index of a coiled section of the waveguides, facilitating the co-phasing of the propagating modes. The phased beamlets can then be coherently combined to efficiently deliver the light to an output SMF. In an adaptive optics (AO) system, the phase corrector acts as a deformable mirror (DM) commanded by a controller that takes phase measurements from a wavefront sensor (WFS). We present experimental results for the PIC tested on an AO testbed and compare the performance to simulations.