Near infrared quazi-omnidirectional reflector in chalcogenide glasses

Abstract The quazi-omnidirectional reflector was designed as a planar quarter wave stack consisting of the alternating amorphous chalcogenide Ge25S75 and Sb40Se60 films. Photonic bandgap calculation of the intended reflector predicted ∼240 nm omnidirectional and ∼450 nm normal incidence first-order bandgaps centred near 1.55 μm for appropriate values of the index of refraction and thickness of the films. The TEM and HR-TEM images of the prepared 7.5 pairs reflector verified good periodicity, smooth interface and amorphous structure of the chalcogenide films deposited by thermal and flash evaporation, respectively. The optical reflectivity measurements revealed 98.8% normal incidence stopband of the reflector at 1.55 μm. We also report the ellipsometry study of the prepared reflector. The TEM and ellipsometry studies confirmed the thickness variation of prepared individual layers to be ±7 and ±9 nm, respectively, compared to theoretical predictions.