Propagation of 9.57 (mu)m radiation in epitaxial silicon waveguides
Jennings, John Harold
Wilson, William L.
Master of Science
Waveguides for CO laser wavelengths consisting of high resistivity Si epilayers on low resistivity SI substrates were investigated. The 9.57 ym line of a CO2 laser was used since Si has a lower absorption at this wavelength than at other CO wavelengths. Absorption measurements were made by focusing onto a cleaved edge and detecting the end-fire radiation from the other end. By measuring the transmitted power for different guide lengths, the absorption coefficient could be calculated assuming equal input and output coupling efficiencies. The measured absorption coefficient was compared to the theoretical value derived by assuming only losses due to free carrier absorption and lattice absorption are important. The mode structure of the guide was determined by scanning the far-field radiation pattern. Phase gratings were produced by coating wafers with photo resist and then exposing to two interfering Ar laser beams. Coupling to the guides with photo resist gratings and gratings that were sputter (RF) etched into the waveguide surface were investigated.