Effect of deposition parameters and semi-empirical relations between non-linear refractive index with linear refractive index and third order susceptibility for a-Ge_20Se_70-xln_10Bi_x thin films

摘要

Present work reports the influence of deposition parameters, i.e., the effect of the type of substrate on the optical properties of a-Ge_(20)Se_(70-x)In_(10)Bi_x (x = 0, 2, 4, 6, 8, and 10) thin films. Optical constants were accurately determined by envelope method using transmission spectra in the wavelength region of 400-1800 nm. The order obtained for the refractive index is n_(mica) > n_(microscope glass) > n(quartz) for different substrates used in the deposition of thin films. The bandgap of the film deposited on mica substrate is smallest as compared to the bandgap of the films deposited on microscopic glass and quartz. To open the possibility of the use of chalcogenide glasses for nonlinear switching, these vitreous systems were studied with respect to their non-linear susceptibility and refractive index. Third-order optical susceptibility (x~3) is evaluated from changes of index of refraction using Wang approximations. We examined the dependence of susceptibility on the absorption edge, thereby showing that the susceptibility rapidly increases with the redshift in absorption edge. Different formulations were used to predict the non-linear behavior of the Ge-Se-In-Bi system. The linear refractive index and Wemple-DiDomenico parameters were used for the determination of nonlinear refractive index in the wavelength region of 400 to 1800nm. The addition of Bi drastically increases the non-linear refractive index. In amorphous materials, maximum optical non-linearity has been predicted at a telecommunication wavelength (～1550nm). Comparison of our results shows a good agreement with values available in the literature at 0.8 eV or 1550 nm. Non-linear refractive indices, three orders higher than silica glass, were obtained in the system under investigation. The obtained results may lead to yield more sensitive optical limiting devices, and these glasses may be used as an optical material for a high speed communication fiber.