Towards a photonic mid-infrared nulling interferometer in chalcogenide glass

Area of Science:

• Astronomy and astrophysics
• Optical engineering
• Materials science

Background:

• Nulling interferometry aims to detect exoplanets by suppressing host star light.
• The 4 μm wavelength offers favorable star-planet contrast and reduced atmospheric disturbance.
• Integrated optical waveguide devices are desired for robust and stable interferometers.

Purpose of the Study:

• To develop on-chip optical components for nulling interferometry at 4 μm.
• To demonstrate femtosecond laser direct writing of low-loss waveguides in a suitable host material.
• To fabricate key components for a compact, integrated nulling interferometer.

Main Methods:

• Femtosecond laser direct writing with cumulative heating and multiscan techniques.
• Fabrication of single-mode optical waveguides in gallium lanthanum sulphur glass.
• Design and testing of S-bends, Y-splitters, and directional couplers.

Main Results:

• Achieved single-mode waveguides with 0.22 ± 0.02 dB/cm propagation loss at 4 μm.
• Demonstrated polarization-dependent loss < 0.1 dB/cm.
• Fabricated broadband Y-splitters (3.6-4.2 μm) with < 0.5 dB loss and directional couplers.

Conclusions:

• Femtosecond laser writing enables fabrication of essential components for on-chip nulling interferometry.
• The developed components show low loss and broadband operation at 4 μm.
• Projected total intrinsic loss < 1 dB is sufficient for future ground-based exoplanet detection experiments.