The first silicon -on-sapphire optical waveguides have been demonstrated. Waveguiding at k=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 X= 1.3 or 1.55 micronsl, but the Si -on -Si technique allows guided light to spread evanescentlyinto 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 possible2 including silicon-on -SiO2, MBE-silicon -on-CAF2 and silicon -on-sapphire (SOS). SOS is an attractive candidate structure because of sapphire's 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.

An optically clocked track-and-hold (TH) circuit for improved TH linearity and noise performance is presented. Results with fi.=1.0073 GHz and sample rate f,=1.003 GWs show 11.8 SFDR bits and 9.6 SNR bits.

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