Propagation, loss and free-carrier effects in silicon waveguide structures

This research explores silicon as an integrated optical material. A variety of material systems have been investigated for integrated optic applications, including lithium niobate, GaAs, glass, and polymers. However, silicon, the backbone of the microelectronics industry, has largely been ignored. Yet, silicon's role as the dominant electronic material can be taken advantage of for integrated optics, particularly optoelectronic applications. Low-loss optical waveguides and optical modulators are the two important components of integrated optical circuits investigated for silicon in this thesis.; Attention is directed towards silicon-on-insulator (SOI) material, currently generating excitement for submicron VLSI electronic integration due to its numerous advantages and processing compatibility. Not only could SOI material lead the push towards next generation microelectronic circuits, but it can also act as an optical waveguide. SOI waveguiding properties are fully studied and characterized. Specifically, optical attenuation measurements are presented on SOI material formed by the SIMOX (Separation by IMplantation of OXygen) and BESOI (Bond-and-Etchback Silicon-On-Insulator) processes using a fiber-optic scanning technique. In addition, waveguiding parameters (silicon refractive index, thickness, and grating depth) are determined and grating input coupling efficiency is addressed.; First-order perturbative scattering theories are extended and applied to investigate the source of the measured optical attenuation in SOI waveguides. A separation of the measured optical loss due to scattering from interface roughness and refractive index fluctuations is possible by interpretating the dependence of loss on the mode number (TE{dollar}sb0{dollar} and TE{dollar}sb1{dollar}). Both scattering components play a role in the observed attentuation. The scattering theory is further used to model the physical surface and volume irregularities. Moreover, interesting interference effects are predicted in the calculated loss as a function of waveguide thickness as well as a strong sensitivity of SOI waveguides to surface roughness and refractive-index inhomogeneities compared with other semiconductor waveguides.; Integrated optical modulators find application in optical communication and signal processing. To determine the electrically-induced, free-carrier, refractive-index changes possible in silicon, a silicon Schottky diode structure supporting a surface plasmon mode is employed. The strong overlap of the injected free carriers and optical mode provide a useful change in the refractive index of silicon at a very low current density. The interplay of free-carrier and thermal effects is also examined.