Silicon-on-Insulator Waveguides

Abstract

While developed for the needs of microelectronics, the silicon-on-insulator (SOI) wafers are excellent substrates for optical waveguides. SOI is a kind of structures formed by a thin layer of crystalline silicon (Si) on an insulating layer, which typically is silicon dioxide (SiO2). SOI optical waveguides possess unique optical properties due to the high transparency of silicon in the infrared spectrum and the large refractive index difference between silicon (guiding layer or core, n = 3.45) and SiO2 (insulator layer or cladding, n = 1.46). This high difference in indices of refraction strongly confines the electromagnetic field into the silicon layer. The widely used SOI waveguides may take the form of a channel waveguide, ridge waveguide, photonic-crystal waveguide, or slot waveguide. The photonic-crystal waveguide is an exceptional option for making SOI waveguides. The refractive indices of different areas of the cladding can be flexibly engineered by varying the diameter of the holes and the lattice constants. These excellent optical properties, as well as compatibility with silicon complimentary-metal-oxide semiconductor (CMOS) integrated technology, enable low-cost and dense optoelectronic integrated circuits. In fact, SOI material has become a main platform for both photonics and VLSI CMOS electronics, with fully compatible processing procedures. This chapter will give a brief review about the principle design, materials selection, and fabrication process of the SOI waveguides. © Springer International Publishing Switzerland 2014.