New method to fabricate ZnS optical waveguides using thermoelectric devices

This work describes a new method to fabricate ZnS thin films using the thermal evaporation technique with a low substrate temperature. This work also was undertaken to establish that cold substrate evaporation using thermo electric coolers could be utilised to produce ZnS waveguides. A thermoelectric device which could be used to both heat and cool the substrates was designed and employed to deposit ZnS thin films on polished glass and silicon wafers. The heating and cooling were important factors to ensure that the ZnS films deposited on cold substrates show low loss waveguide characteristics. Optimizing this polycrystalline waveguide fabrication was a considerable challenge compared to the established, conventional waveguide fabrication. Propagation mode and power loss measurement were done by a commercial prism coupling method which is fitted with He-Ne laser and diode lasers. The transverse electric mode (TE) and loss decrease when the wavelength is increased. These observations agree well with a Rayleigh scattering model of the loss mechanism. The lowest loss of polycrystalline ZnS waveguide is 2.23 dB/cm measured a wavelength of 1540 nm