Phase-change material based actively tunable MWIR thin-film bandpass filters

Tunable mid-wave infrared (MWIR) filters are highly desirable in a wide variety of imaging and spectroscopic applications; with the waveband containing numerous invaluable spectral absorption signatures. We demonstrate spectrally-tunable, all solid-state, thin-film bandpass filters operating across the MWIR by utilizing the phase-change material (PCM) Ge2Sb2Te5 as a tunable cavity medium between two Bragg mirrors. The induced PCM refractive index modulation increases the cavity’s optical path length, thereby tuning the filter passband. Our filters have 300 nm spectral tunability, ~70% transmission efficiencies, and ~60 nm passbands. We further show multispectral thermal imaging and dynamic CO2 gas plume sensing using the filters.