Optical Properties of Clad And Unclad Sapphire Fiber

Single-crystal sapphire fibers have been grown, using the laser heated pedestal technique, with losses as low as 0.7 dB/m and with lengths up to 150 cm. We have applied polymer and sol- gel coatings to the fibers and we have evaluated the performance of these coatings as optical cladding. The best coating seems to be teflon AF even though the coatings are reasonably thin and low temperature.

Single crystal layers of formula have been epitaxially grown on formula and sapphire substrates using metallic Zn and Se. A nozzle for the Se flow was placed at about 1 cm in front of the substrate, and this arrangement resulted in much less Se consumption than in the case when the nozzle was further separated from the substrate. The epitaxial conditions were investigated as a function of the source and substrate temperatures. When the substrate temperature and one of the source temperatures were fixed, the growth rate increased with the other source temperature and then saturated. Below the saturation point, the growth rate is proportional to the flow rate and the vapor pressure of each source material. Dependence on substrate temperature of growth rate is shown to be surface‐controlled phenomenon below 770°C and is one of mass transfer controlled phenomena above 770°C. The epitaxial growth on Formula substrates occurred in the substrate temperature range of 650°–880°C with a growth rate ranging from 1 to 30 μm/hr. The resistivity of the as‐grown layer was too high (106 Ω · cm) to be useful for LED application.


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