Multilayer As₂Se₃/GeS₂ quarter wave structures for photonic applications

Abstract

The optical properties of single layers from As2Se3 and GeS2, double-layered stack and quarter-wave multilayer structure consisting of alternating layers from both materials are investigated. For modelling of multilayer coating the thickness dependence of the refractive index of single coatings from both materials is studied. The particularities and scope of application of different spectrophotometric methods for calculation of optical parameters of thin chalcogenide layers are discussed for film thickness, d, in the range λ/25–1.5λ (λ being the operating wavelength). Having acquired the knowledge of optical parameters (refractive index, n, and extinction coefficient, k) of the single layers, we designed and produced a one-dimensional photonic crystal with fundamental reflection band at λ = 850 nm. It was shown that the photoinduced changes of the refractive index of thin chalcogenide films can be used for enhancement of the optical contrast of both materials.

Thin Chalcogenide Films for Photonic Applications

“…The chalcogenide layers were deposited by thermal evaporation at deposition rate of 0.5 -0.7 nm/s. The X-ray microanalysis showed that the film composition is close to that of the bulk samples (Todorov et al, 2010b).…”

“…Combinations of Ge-S / Sb-Se (Kohoutek et al 2009) with optical contrast of more than 1 and exposed As 2 Se 3 / GeS 2 with optical contrast more than 0.8 have been already realized. (Todorov et al 2010b). …”

“…8 for modelling of double-and multilayered structures. The reflectance spectrum of a double layered coating from As 2 Se 3 and GeS 2 (BK-7/As 2 Se 3 /GeS 2 ) was discussed in (Todorov et al 2010b). Having determined the optical parameters and thickness of the single layers we calculated the theoretical reflectance spectrum of the complex structure using the equations from section 3.1.…”

Optical properties of porous chalcogenide films for sensor application

“…The comparison for the refractive indices, n for wavelength λ = 1550 nm, optical band gap and slope parameter B for thin film prepared on rotated substrates and obliquely deposited films at angle 75˚ is given in table 1. Significant variation of the band gap when changing the angle of incidence of the vapours is observed for thin As 10 Ge 30 S 60 layer. The lower values of B for the thin films with columnar structure are due to larger structural disorder.…”

“…The program used to calculate n will determine it to an accuracy of  0.5 % for an error in the transmittance of  0.1 % [10]. In figure 2 a comparison is given of the dispersions of the refractive index of thin films deposited normally or obliquely at 75° angle of The reflectance and transmittance spectra wеre used for calculation of the linear absorption coefficient, α and optical band gap, E g through the equations: …”