Multichannel tunable narrowband mid-infrared optical filter based on phase-change material Ge₂Sb₂Te₅ defect layers

The defect mode, which exists at the defect layer of a one-dimensional photonic crystal (1DPhC) heterostructure, provides the possibility of realizing narrowband transmission owing to its strong electromagnetic field localized effects. In this study, we numerically investigate the single- and multichannel narrowband filters in the mid-infrared region based on the defect mode by adding the monolayer and multilayer phase-change material Ge₂Sb₂Te₅ (GST) defect layer in 1DPhC. It can provide a promising avenue to tune the transmission spectra by changing the crystallization fraction X of the GST defect layer. The remarkable narrowband transmission enhancement can be acquired for both TM and TE polarizations in spite of the large oblique incident angle. Such a defect-mode-based 1DPhC heterostructure enables tunable operating wavelength by adjusting geometrical parameters to realize the spectral selectivity of the filter in the mid-infrared region. The significant improvement and tunability of the designed single- or multichannel filters can be applied to biochemical sensing and material characterization.