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Optoelectronics
^ Fiber Optic Sensors for Force Measurement
S. L. Chuang,* G. Liu
Association of American Railroads

Researchers will develop fiber optic sensors for force measurement applications. One important application is the detection of a flat spot on a defective wheel. Due to internal cracks, manufacturing defects, or long-term wear, rail car wheels can become geometrically deformed, which can cause possible train derailment. A time-domain measurement of the optical transmission through the fiber-optic sensor placed below the wheel of rail will be developed and tested based on a previous design of weigh-in-motion sensors. The approach is to use a fiber optic sensor to measure force. The sensor will detect an abnormal force response due to defective wheel and rail interaction. The defective wheel can be detected while the train passes the sensor. This fiber optic sensor will offer a fast and cost-effective method to detect the deformities in rail car wheels, particularly flat spots.

^ Fiber Optical Sensors for High-Speed Rail Applications
S. L. Chuang,* C. Barkan,* A. Hsu, E. Young
National Academy of Science, Transportation Research Board, NAS 101 TASK NO1

A multimode fiber buckling sensor with a differential signal technique will be designed. It will be used to monitor crucial information for the safety of high-speed rail tracks and railroad crossings. The sensor will detect rail breaks and buckles, as well as the location and speed of a train. It is an integrated, low-cost warning system and an alternative to conventional track circuits. Both laboratory tests at the University of Illinois and field tests at the Transportation Technology Center, Inc., Association of American Railroads in Colorado, will be performed. The potential impact of this project is that optical fiber sensors are more robust than strain gauges, being immune to electromagnetic interference. Consequently, the applications of the optical fibers as sensors in high-speed rails offer a novel technology for railroad crossing safety and infrastructure integrity inspection. The payoff for practice is that fiber optical sensors provide a potential high-speed response at a much lower cost than conventional designs.

^ High-Speed Modulation of Novel Optoelectronic Devices
S. L. Chuang,* X. Jin
University of Illinois, Research Board

Information technology requires ultra-high-speed optoelectronic devices such as semiconductor lasers for telecommunications systems. The purpose of this research is to investigate the ultimate limit of the high-speed performance of novel edge-emitting lasers, integrated electroabsorption modulator-lasers, and selectively oxidized VCSELs. Linewidth broadening and carrier transport combine to impose an upper limit on the modulation frequency of the devices. A new scheme based on injection locking will be applied to probe the intrinsic bandwidth limit of these devices. Experiments will be performed to isolate and measure the effects of relative intensity noise and other high-speed phenomena. Theoretical models will be developed and compared to the measured data in an attempt to ascertain the interrelations of important optoelectronic device parameters and provide new device designs.

^ Modeling of Vertical-Cavity Surface-Emitting Lasers
S. L. Chuang,* G. Liu, A. Hsu
Science Applications International Corporation (SAIC)

The goal of this project is to develop a numerical model for vertical-cavity surface-emitting lasers (VCSELs) in order to support the effort of SAIC to develop PCAD-integrated simulation tools. An electromagnetic frequency-domain model for cavity eigenmode simulations, employing the Beam Propagation Method (BPM) with scalar electric fields, has been developed. Results obtained from this code will be tested and validated against other numerical results, such as the results from finite-difference time-domain method. Also, researchers will perform experiments including laser characterization and near-field measurements from VCSELs for validation of the theoretical model.

^ Smart Fiber Optics System for Condition Monitoring of Railway Bridges
J. Ghaboussi,* D. Foutch,* S. L. Chuang*
National Science Foundation, CMS 99-08651

The main objective of the proposed research is to develop and test a system for continuous condition monitoring of railway bridges under service loads using computational intelligence methods and fiber optics. The proposed system will be capable of continuous condition monitoring of the instrumented and remotely sensed railway bridges under normal train traffic loading. The proposed research will be conducted in three stages. In the first stage, the computational intelligence based smart condition monitoring methodology will be further expanded and improved and the associated software will be developed. The development and testing of fiber optic detection systems will take place in the second stage of the proposed research. In the last phase of the proposed research, the smart condition monitoring system and fiber optics system will be tested in the structural laboratory on a scale model of a railway.


Summary of Engineering Research