  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 spectroscopy (FTIR) 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-controlled real-time performance characterization system consisting of
an inexpensive linear variable filter (LVF) and mid-wave infrared 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-infrared camera.
