# Fabrication tolerant chalcogenide mid-infrared multimode interference coupler design with application for Bracewell nulling interferometry

## TL;DR

This paper presents a design for a fabrication-tolerant chalcogenide mid-infrared multimode interference coupler that achieves high extinction ratios, enabling effective nulling interferometry for exoplanet imaging.

## Contribution

It introduces a novel, fabrication-tolerant planar chalcogenide photonic chip design with three multimode interference couplers for nulling interferometry in the mid-infrared.

## Key findings

- Exceeds 60 dB extinction ratio in double nulling mode
- Achieves up to 40 dB in single nulling mode
- Operates effectively across 3.9 to 4.2 microns wavelength range

## Abstract

Understanding exoplanet formation and finding potentially habitable exoplanets is vital to an enhanced understanding of the universe. The use of nulling interferometry to strongly attenuate the central starlight provides the opportunity to see objects closer to the star than ever before. Given that exoplanets are usually warm, the 4 microns Mid-Infrared region is advantageous for such observations. The key performance parameters for a nulling interferometer are the extinction ratio it can attain and how well that is maintained across the operational bandwidth. Both parameters depend on the design and fabrication accuracy of the subcomponents and their wavelength dependence. Via detailed simulation it is shown in this paper that a planar chalcogenide photonic chip, consisting of three highly fabrication tolerant multimode interference couplers, can exceed an extinction ratio of 60 dB in double nulling operation and up to 40 dB for a single nulling operation across a wavelength window of 3.9 to 4.2 microns. This provides a beam combiner with sufficient performance, in theory, to image exoplanets.

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Source: https://tomesphere.com/paper/1702.00468