Germanium-antimony-tellurium alloy-based multilayer periodic, aperiodic, and disordered microcavities

Germanium-antimony-tellurium (GST) alloys are among the most widely investigated phase-change materials because of the large variation of their optical constants accompanying the reversible transition between amorphous and crystalline phases. In this work, the optical response of one-dimensional microcavities incorporating a GST defect layer is theoretically investigated by means of the transfer matrix method. Different microcavity architectures are considered, including periodic photonic crystals, Fibonacci quasicrystals, Thue-Morse aperiodic structures, and disordered multilayers characterized by random thickness fluctuations or random layer permutations. The optical transmission spectra are calculated by employing experimentally measured optical constants of GST in both amorphous and crystalline states, together with the wavelength-dependent refractive indices of silica and alumina. In all investigated configurations, the phase transition of GST induces pronounced modifications of the transmission spectra, including intensity variations, suppression of resonant modes, and changes in the spectral distribution of defect-related resonances. The results demonstrate that the incorporation of GST into ordered, aperiodic, and disordered photonic microcavities provides an effective strategy to realize thermally tunable optical components. The proposed structures may find applications in optical switching, temperature sensing, adaptive photonic filters, and reconfigurable photonic devices.