Abstract
Optical switches that reflect light through the process of total internal reflection offer many advantages when compared with other systems such as interferometric and resonant devices as compact structures can be produced with a wavelength- and polarization-independent response. As well as these benefits, they are immune to temperature variations and tolerant to imperfections which can be imparted into a structure from the manufacturing process. To reflect light efficiently requires the creation of an abrupt change in refractive index which is difficult to achieve in silicon based material systems operating through carrier injection due to the long diffusion length of carriers. The aim of this project was to design, fabricate and test a carrier injection reflective optical switch in the silicon-on-insulator material system for routing applications within a telecommunication network. To achieve the objective, a reflective optical switch design has been developed which consists of a symmetric Y-branch rib waveguide with twin p-i-n diode arrangement. A confinement barrier is incorporated into the structure which is created by the standard CMOS process of creating a deep isolation trench that prevents carriers from diffusing outside the modulation region and at the same time allows the passage of a propagating mode. Computer simulations have predicted the devices are capable of attaining low TE/TM crosstalk values of -20dB for a power consumption below 22.5mW. Models of the ultrathin oxide barrier which is used in the deep isolation trench for electrical isolation have indicated that a layer with a thickness of 2nm can achieve the lowest TE/TM losses of 0.05 and 1.77dB, respectively. Prototype devices have been successfully constructed by using equipment typically found in academia cleanroom environments. Processing was undertaken by using techniques such as chemical mechanical polishing and cryogenic reactive ion etching. The ultrathin oxide has been formed in nitric acid for the confinement barrier. Testing has demonstrated the prototypes are capable of directing light from an input port to a particular output port by applying a forward bias to one of the modulation regions.