The thesis focuses the design and fabrication of silica-on-silicon multimode interference (MMI) devices for optical communications. Firstly, the relationship between different kinds of multimode interference was established for the first time. This gives a clearer understanding of the multimode interference and helps to design better performance optical MMI devices With the consideration of weak lateral light confinement, different kinds of novel approaches to designing high performance MMI devices are developed. The first new approach is for optimization of silica-on-silicon MMI couplers. It is shown that the length of the multimode section can be varied in a well-defined range to find optimal device performance. The range is linked to the propagation constant spacing of fundamental and higher order modes of the multimode waveguide. The second approach is to introduce a new criterion for designing a MMI coupler with central input. According to overlapping interference analysis, one image space should be left for the adjacent output waveguides because of the lateral distribution of alternatively vanishing and non-vanishing images. This consideration is neglected in previous work and is shown to be important for achieving good uniformity MMI power splitters. Thirdly, a new design of silica-on-silicon multimode interference (MMI) device is proposed. Deeply etched air trenches define the boundaries of the multimode section to achieve strong lateral confinement, resulting in lower loss and imbalance. The access waveguides, however, are buried channel and square core, giving low fibre insertion loss and low polarization dependence. The novel design balanced requirement of the strong lateral confinement of the field in the multimode waveguides and the matching between the fiber and the access waveguides. Then a new approach of designing silica-on-silicon optical switches based on cascaded MMI couplers is presented. The approach combines the transfer matrix method, optimisation of the MMI dimensions, and mode propagation analysis (MPA) for calculation of phase shifts. The feasibility of the large port count switches is also discussed. It is shown that the good performance devices can be realized with a large port count of 32. Finally MMI couplers based on silica-on-silicon optical waveguides were fabricated. The Ge-doped silica waveguides were fabricated by HC-PECVD and RIE. Fabrication processes such as thin film deposition and etching are discussed. Good performance devices have been realized.

A new multihop wavelength-division multiplexed (WDM) optical network designed for uniform traffic with two wavelengths per node that can give the maximum throughput and minimum delay is proposed. It is called a 'Simple Star' multihop optical network. This network has good characteristics in traffic balance and small average number of hops. Moreover, Simple Star can be used together with multiple star couplers to reduce the number of wavelength used. Furthermore, unlike most existing networks, this network does not impose an upper limit to the number of nodes. Another interesting pattern is Simple Star with Center Node (Simple Star CN) particularly for prime numbers of nodes. It can be shown that the average number of hops of Simple Star (normal plus CN) is in between those of Shufflenet and Kautz, but the throughput and delay are better. An associated network called Simple Star Shared Channel (Simple Star SC) for two transceivers per node is also presented and it can be used together with multiple star couplers to reduce the number of wavelengths. An example of a 16-node Simple Star SC shows that the number of wavelengths used can be 8 times less than that in the normal Simple Star network. The Shared Channel simulation model is based on the concept of CSMA/CD (Carrier Sense Multiple Access with Collision Detection).

Ph.D. / Applied Physics & Electronic Science / Direct detection, photon counting receivers for use in optical communication through the clear air, turbulent atmosphere have been examined. In particular, spatial diversity arrays to overcome the effect off adding due to atmospheric turbulence are considered. Experimental results are compared with theoretical results for an optimum receiver structure based upon Bayes criterion of minimum probability of error. In addition, certain suboptimum receivers with simpler structures are derived directly from the optimum receiver. These receivers, along with an adaptive threshold receiver, are considered in order to examine the trade off between performance and complexity. The results indicate that the adaptive threshold receiver is a good compromise for information rates that are high with respect to scintillation frequencies, a relatively unrestrictive condition.

This thesis work researches the theory and application of systems performing omnidirectional, non-direct path optical data communication (ONP systems). Such systems are characterized by 1) the communication involves a local, usually circular area; 2) Obstacles are allowed between a transmitter and the receivers. This is in contrast to the point-to-point and line-of-sight communications performed by almost all existing infrared data communication or transmission systems. The elimination of the point-to-point limitation makes ONP systems suitable for optical local area networking. The feasibility of ONP systems employing infrared LEDs and silicon photo detectors has been analyzed and the performance of such systems predicted. The analysis shows that indoor ONP systems are both feasible and practical. Only a few LEDs are required to cover the entire area of a large room. Efforts have been made in finding rules for optimal design of the ONP systems. A set of design criteria and curves have been established. The theoretical analysis has been verified in a successful experiment done with OptoNet, an ONP infrared datalink for local area networks. This experimental system consists of two identical communication units employing FSK modulation and microprocessor controllers. The experiment has demonstrated that the ONP optical data communications can be realized by relatively simple electronic hardware. / Graduation date: 1991

Many researchers and engineers designing laser drivers for data rates at or above 10 gigabits per second (Gbps) implemented their designs using integrated circuit technologies that provide high bandwidth and good quality passive components such as GaAs, silicon bipolar, and InP. However, in low-cost and high volume short-haul applications at data rates of around 10 Gbps (such as LAN, MAN, and board-to-board interconnection), there has been an increasing interest in commercial CMOS technology for implementing the laser driver. This is because CMOS technology has unique advantages such as low power and low cost of fabrication that are the result of high yield and a high degree of integration. Therefore, the objective of this research in this dissertation is to investigate the possibility of implementing a high-speed CMOS laser driver for these cost sensitive applications. The high-speed CMOS laser drivers designed in this research are of two types. The first type is a low power laser driver for driving a vertical cavity surface emitting laser (VCSEL). The other driver type is a high current laser driver for driving edge-emitting lasers such as double-heterojunction (DH), multiquantum well (MQW), or Febry-Perrot (FP) lasers. The parasitic effects of the layout geometry are crucial in the design of the high-speed laser drivers. Thus, in this research, all simulations contain a complete set of parasitic elements extracted from the layout of the laser driver. To test laser drivers, chip-on-board (COB) technology is employed, and printed circuit boards (PCBs) to test the laser drivers are designed at the same time as the laser drivers themselves and manufactured specifically for these tests. This research makes two significant new contributions to the technology that are reported and described here. One is the first 10 Gbps performance of a differential CMOS laser driver with better than 10-14 bit-error-rate (BER). The second is the first demonstration of a heterogeneous integration method to integrate independently grown and customized thin film lasers onto CMOS laser driver circuits to form an optical transmitter.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 247-259). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 247-259). Also available on the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.