| Optical fibers are becoming increasingly important for communication systems because of their large bandwidth and low propagation losses. The rapid growth of the fiber-optic industry has resulted in significant research effort being directed towards the development of high-performance, low cost optoelectronic devices, such as diode lasers, modulators and detectors. Traditionally, the fabrication of fiber-coupled devices involves the interruption of the fiber and the insertion of the device. Several drawbacks are associated with this approach, including high insertion loss, mechanical instability, and high packaging costs. In-line fiber devices, in which light is evanescently coupled between single mode fibers and multimode high index waveguides, offer solutions to these problems.; This work focuses on gallium arsenide (GaAs) based in-line devices. GaAs and other compound semiconductors offer advantages over other materials such as lithium niobate, electro-optic polymer and liquid crystal, in that they can be monolithically integrated with lasers and high-speed electronics, thereby reducing fabrication costs. The difficulty in phase-matching the modes of the single mode fiber and the GaAs waveguide, which are made of materials of vastly different refractive indices, is overcome by the use of dielectric mirrors in the semiconductor structure. The demonstrated devices include a filter with a minimum linewidth of 0.5nm, a wavelength selective detector with a linewidth of 1.6nm and a external quantum efficiency of 75%, an intensity modulator with an on/off ratio of 4:1, as well as a resonant light emitter. The theory, design, fabrication and characterization of these novel optoelectronic devices are discussed in detail. |
