Automated real-time spectral characterization of phase-change tunable filters using a linear variable filter and IR camera for wide-field MWIR imaging

Actively tunable optical filters based on chalcogenide phase-change materials (PCMs) are an emerging technology with applications across chemical spectroscopy and thermal imaging. The refractive index of an embedded PCM thin film is modulated through an amorphous-to-crystalline phase transition induced through thermal stimulus. Performance metrics include transmittance, passband center wavelength (CWL), and bandwidth; ideally monitored during operation (in situ) or after a set number of tuning cycles to validate real-time operation. Measuring these aforementioned metrics in real-time is challenging. Fourier-transform infrared (IR) spectroscopy provides the gold-standard for performance characterization yet is expensive and inflexible-incorporating the PCM tuning mechanism is not straightforward, hence in situ electro-optical measurements are challenging. In this work, we implement an open-source MATLAB (R)-controlled real-time performance characterization system consisting of an inexpensive linear variable filter (LVF) and mid-wave IR camera, capable of switching the PCM-based filters while simultaneously recording in situ filter performance metrics and spectral filtering profile. These metrics are calculated through pixel intensity measurements and displayed on a custom-developed graphical user interface in real-time. The CWL is determined through spatial position of intensity maxima along the LVF's longitudinal axis. Furthermore, plans are detailed for a future experimental system that further reduces cost, is compact, and utilizes a near-IR camera. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License.

Automated summary

This study introduces actively tunable optical filters based on chalcogenide phase-change materials, which modulate refractive index through thermal stimulus-induced phase transition, enabling real-time monitoring of filter performance metrics during operation.