A novel ultra-low refractive index nanoporous dielectric based aqueous core light waveguide system

This dissertation presents the fabrication of an on-chip waveguide system capable of guiding light through aqueous solutions. The waveguide relies on total internal reflection for light propagation wherein the core of the waveguide consists of the aqueous solution and the cladding is formed by an ultra low refractive index nanoporous dielectric coating. Such waveguides are of great interest in biosensor design as water is the natural medium for any biological processes.;In this dissertation, three types of nanoporous dielectric films have been considered -- the ordered nanoporous silica, nanoporous organosilicate films through porogen extraction and organosilicate nanoparticles based nanoporous films. The organosilicate nanoparticle based films have been developed during the course of this research and these films offer superior properties with respect to formation of crack free films and ultra low refractive index. The hydrophobic nature of the films requires no further surface modification in order to be applied as the cladding material for the aqueous core waveguide system. Because of their unique morphology, these films feature a large surface area and the mechanical strength of these films is higher than similar porosity films formed by porogen extraction. A hypothetical formation mechanism is described for the formation of these films.;Two types of liquid core waveguide designs are considered. In the first design, physical channels are etched in silicon substrates for liquid containment. Low refractive index nanoporous dielectric coatings are deposited in the channels through dip/spin coating techniques. The channels are sealed with a nanoporous dielectric coated glass substrate to form the final device. The presence of surface structures in the substrate presented unique fabrication challenges for the integration of the nanoporous dielectrics. The fabrication challenges are presented along with the description and remedy.;An improved design of the liquid core waveguide is described to overcome the drawbacks of the first design. In the improved design, the requirements of physical channels are eliminated by exploiting the surface tension and capillarity properties of fluids confined to small volumes. Both the designs have been tested for waveguide performance. The waveguide losses have been greatly reduced in the improved design. The fabrication methodology employed is compatible with the standard microfabrication techniques allowing scope for mass production. In addition to these, the waveguide is designed so as to allow easy cleaning to be applied as a reusable system.