The evaluation of the refractive indices of bulk and thick polydimethylsiloxane and polydimethyl-diphenylsiloxane elastomers by the prism coupling technique

This paper presents the study of the optical properties of bulk and thin-film samples made from polydimethylsiloxane and polydimethyl-diphenylsiloxane elastomers. The chemical structures of the prepared elastomer samples were characterised by infrared spectroscopy. Also their transmission spectra were measured in the visible and infrared regions. The refractive indices of the samples were measured by the prism coupling technique using dark mode spectroscopy for five wavelengths (473, 632.8, 964, 1311 and 1552 nm). Particular focus was placed on the effect of the dependence of refractive index on the conditions of deposition. It has been found that the changes of refractive indices can be achieved by the modification of deposition conditions (hardening temperature and/or A:B mixed agent ratios). In order to obtain more significant changes of the refractive indices, we recommend using polydimethyl-diphenylsiloxane elastomer as a waveguide layer because of it content of phenyl groups, which lead to an increase in the value of the refractive index.