Chapter 9: Optical Glass Waveguides

Overview

Optical waveguides are micron size channels that can be used to guide light. Although optical fiber is actually one special type of waveguides, usually waveguides refer to optical integrated circuits on substrates. The concept of optical waveguide came out in early 1960s. However, the first widely successfully used waveguide is semiconductor diode laser, where the device was etched to channels and sandwiched between p-type and n-type semiconductor materials with a little lower refractive index. Therefore, light is well confined in a thin gain layer and as the result, power threshold to achieve laser action was drastically reduced.

Glass waveguides are important devices. In the past 20 years, with the rapid development of optical communication systems, requirement for compact, high density optical devices increased tremendously. Especially after the wavelength division multiplexing (WDM) technique was widely accepted as a new generation of optical communication standard platform, many new device concepts were proposed, devices with excellent performance were put into market with vast quantities.

An optical waveguide is actually a three or more layer thin film assembly, consists basically a substrate, a lower buffer layer, a guiding layer and a top cladding layer. Glass materials for waveguides fabrication can be categorized to silica glass, multi-component glass and polymeric glass materials. Various methods were developed in the past 40 years to fabricate waveguide films, these methods include chemical vapor deposition (CVD), ion-exchange, flame-hydrolysis deposition (FHD), Sol-gel, etc.

Conventional glass waveguides are used simply to guide and split light, just like electric current wires...