Professional paper for period ending Sep 86,
NAVAL OCEAN SYSTEMS CENTER SAN DIEGO CA
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The first silicon-on-sapphire optical waveguides have been demonstrated. Waveguiding at lambda 1.3 microns has been observed in silicon films 0.95 and 1.5 microns thick and in raised strip structures 1.5 microns thick. Previously, an epitaxial silicon-on-silicon technique was used to construct silicon waveguides for lambda 1.3 or 1.55 microns, but the Si-on-Si technique allows guided light to spread evanescently into the lossy substrate because the refractive index step between substrate and guiding layer is approximately 0.01. However, tighter mode confinement is offered at these wavelengths by silicon-on-insulator SOI structures. This occurs because the Si-to-dielectric compositional change gives a larger index-step than the Si-to-Si doping profile change. Various SOI waveguide structures are possible including silicon-on-SiO, MBE-silicon-on-CAF and silicon-on sapphire SOS. SOS is an attractive candidate structure because of sapphires excellent mechanical, electrical and optical properties and of its development for the electronics industry. Electronic device fabrication on the same chip with the optical waveguide devices optoelectronic integration is possible. Waveguide theory predicts a single TE guided mode of 1.3 micron radiation in an SOS film below 0.22 microns in thickness. The ordinary refractive index of the sapphire substrate is 1.75 and the Si index is 3.50. We obtained SOS films of 0.3, 0.95 and 1.5 microns thickness and for these, theory predicts 2, 5, and 7 TE modes respectively. Evanescent field penetration depths into the sapphire is on the order of 0.1 microns according to calculations.
- Electrical and Electronic Equipment