Fabrication and characterisation of zinc sulfide optical waveguides using thermoelectrically cooled substrate holder

• Main Author: Saafie Salleh
• Format: Thesis
• Language: English; English
• Published: 2010
• Subjects: TP200-248 Chemicals: Manufacture, use, etc.
• Online Access: https://eprints.ums.edu.my/id/eprint/3705/1/24%20PAGES.pdf; https://eprints.ums.edu.my/id/eprint/3705/2/FULLTEXT.pdf; https://eprints.ums.edu.my/id/eprint/3705/
• Institution: Universiti Malaysia Sabah

This study describes the fabrication and the characterisation of zinc sulfide optical waveguides produced by thermal evaporation technique at low substrate temperatures. The substrate temperature of particular interest was -500 ( because of lowest propagation loss as reported in literature. A novel thermoelecrically cooled substrate holder was designed and constructed for substrate cooling. In the first instance, a series of ambient deposited ZnS waveguide with the nominal thicknesses of 0.15 μm, 0.50 μm and 0.80 μm were fabricated on oxidised silicon wafer. The propagation modes of these samples are measured with a prism coupler. The propagation modes were analysed to verify the thicknesses and to determine the refractive index. The thicknesses from the modal analyses were found matching well with both nominal thicknesses and measured thicknesses. The refractive index of ambient deposited ZnS waveguide were increased with the increase of sample thicknesses. Based on these introductory experiments, the fabrication of 0.50 IJm thick ZnS waveguides were performed at ambient temperature (25°C) and cold substrate temperature (-50°C). The ambient deposited ZnS waveguide was microcrystalline with the preferred plane of (111) whereas the cold deposited ZnS waveguide was amorphous. The grain size of the ambient deposited ZnS waveguide was about three times bigger than the cold deposited ZnS waveguide. The AFM images of the waveguides revealed that the growth mechanism of ZnS thin films was through island growth. The surface images of ZnS waveguides were obtained with an atomic force microscopy. The surface of cold deposited ZnS waveguide was rougher than ambient deposited ZnS waveguide. The propagation losses of ZnS waveguides were determined by a scattering detection method. Propagation losses of cold deposited ZnS waveguide were 20.41, 11.35, 3.51 and 2.30 dB/cm measured the wavelengths of 633, 986, 1305 and 1540 nm, respectively. Propagation losses of ambient deposited ZnS waveguide were 131.50, 47.99, 4.43 and 2.74 dB/cm measured the wavelengths of 633, 986, 1305 and 1540 nm, respectively. The wavelength dependence of propagation losses analyses were done to establish the loss mechanisms in ZnS waveguides. The results showed that the propagation loss of ambient deposited ZnS waveguide had a ƛ-4.6 dependence and the propagation loss of cold depOSited ZnS waveguide had a ƛ-2.5 dependence. The propagation loss of the ambient depOSited ZnS waveguide was dominated by bulk scattering (Rayleigh scattering) whereas the propagation loss of the cold deposited ZnS waveguide was dominated by surface scattering.