Integrated astrophotonic phase control for high resolution optical interferometry

TL;DR

This paper presents a novel integrated astrophotonic chip for high-resolution optical interferometry, enabling precise phase control and beam combination to overcome atmospheric turbulence effects in ground-based telescopic arrays.

Contribution

The work introduces a silicon photonic chip with multiple channels and microheaters for dynamic phase correction, offering a compact, cost-effective alternative to traditional adaptive optics systems.

Findings

Successful fabrication of a 4.7x10mm silicon photonic chip with 2 to 32 channels.

Effective phase measurement using off-chip artificial guide star signals.

Coherent on-chip beam combination demonstrated for optical interferometry.

Abstract

Long baseline optical interferometry and aperture synthesis using ground-based telescopes can enable unprecedented angular resolution astronomy in the optical domain. However, atmospheric turbulence leads to large, dynamic phase errors between participating apertures that limit fringe visibility using telescopes arrays or subaperture configurations in a single large telescope. Diffraction limited optics or adaptive optics can be used to ensure coherence at each aperture, but correlating the phase between apertures requires high speed, high stroke phase correction and recombination that is extremely challenging and costly. As a solution, we show an alternative phase correction and beam combination method using a centimeter-scale silicon astrophotonic chip optimized for H-band operation. The 4.7x10mm silicon photonic chip is fabricated using electron beam lithography with devices with 2 up to 32 independent channels. Light is coupled into the chip using single mode fiber ribbons. An array of microheaters is used to individually tune the effective index of each spiral delay waveguides. Narrowband spectral splitters at each spatial channel divert a modulated digital reference signal from an artificial guide star off-chip for phase measurement. Science light from other wavelengths is coherently combined using on-chip beam combiners and outputted to a single waveguide. We described the role, design, fabrication and characterization of the photonic chip. This photonic phase control scheme can be applied in astronomical interferometry or optical satellite communications.