A fiber optic sensing system with an intensity sensor and an RF modulated source has been shown to have sensitivity and resolution much higher than a comparable system employing low modulating frequencies or DC mode of operation. Also the RF modulation with an appropriate configuration of the sensing system provides compensation for the unwanted intensity losses. This paper describes the basic principles and applications of a fiber optic sensing system employing an RF modulated source. In addition the paper discusses various configurations of the system itself, its components, and modulation and detection schemes. Experimental data are also presented.
A detection technique for intensity type fiberoptic sensors is described. It employs a multimode fiber interferometer, with the sensor in one arm, excited by an LED modulated at RF frequencies fo and 2fo. Sensor induced changes in intensity result in corresponding changes in the ratio of the detected fo and 2fo signals, thus eliminating various common mode effects. Results obtained with a displacement sensor and preliminary results from a pressure sensor illustrate the capabilities of this technique.
NASA Lewis together with John Carroll University has worked for the last several years to develop wavelength-multiplexed digital position transducers for use in aircraft control systems. A prototype rotary encoder is being built for a demonstration program involving the control of a commercial transport''s turbofan engine. This encoder has eight bits of resolution a 90 degree range and is powered by a single LED. A compact electro-optics module is being developed to withstand the extremely hostile gas turbine environment.
Techniques for the quantitative determination of shock position in supersonic flows using direct and indirect methods is presented. A description of an experimental setup is also presented, different configurations of shock position sensing systems are explained, and some experimental results are given. All of the methods discussed are analyzed to determine the ease of technology transfer from the laboratory to in-flight operation.