Planar quarter wave stacks prepared from chalcogenide Ge–Se and polymer polystyrene thin films

Planar quarter wave stacks based on amorphous chalcogenide Ge–Se alternating with polymer polystyrene (PS) thin films are reported as Bragg reflectors for near-infrared region. Chalcogenide films were prepared using a thermal evaporation (TE) while polymer films were deposited using a spin-coating technique. The film thicknesses, d∼165 nm for Ge25Se75 (n=2.35) and d∼250 nm for polymer film (n=1.53), were calculated to center the reflection band round 1550 nm, whose wavelengths are used in telecommunication. Optical properties of prepared multilayer stacks were determined in the range 400–2200 nm using spectral ellipsometry, optical transmission and reflection measurements. Total reflection for normal incidence of unpolarized light was observed from 1530 to 1740 nm for 8 Ge–Se+7 PS thin film stacks prepared on silicon wafer. In addition to total reflection of light with normal incidence, the omnidirectional total reflection of TE-polarized light from 8 Ge–Se+7 PS thin film stacks was observed. Reflection band maxima shifted with varying incident angles, i.e., 1420–1680 nm for 45° deflection from the normal and 1300–1630 nm for 70° deflection from the normal.