Genis, Alan P.
B.S. (Bachelor of Science)
Department of Electrical Engineering
Optical fiber technology has become one of the most important new developments in communications. Telecommunications and broadcast communications have become the most visible applications of fiber optics. The computer terminals in the lab at Northern Illinois University communicate over a fiber optic local area network (LAN). These and many other applications illustrate the utility of fiber optics in electrical engineering. What is it about fiber optics that makes them so useful in communications? How can light transmit a telephone call or a television program? The answers to these questions lies in the fact that light is no different from microwaves and radio waves except for the frequency. In other words, light is another form of electromagnetic energy that can be harnessed. The optical region of the electromagnetic spectrum is from 3*10¹² Hz to 6*10¹⁵ Hz. This is higher than radio frequencies and microwave frequencies. And because light is the carrier in optical communication, it follows that optical systems offer a wider bandwidth than RF and microwave communication systems. In a typical system where the bandwidth is a fraction of the carrier frequency, it is possible to attain bandwidths on the order of 10⁶ Hz. This is why a single optical fiber can carry thousands of telephone and television channels simultaneously. Another advantage of optical communications is the immunity to interference. Because optical fibers are dielectrics, they do not conduct electricity and are thus immune to electrical discharge. The extremely high frequency of optical signals prevents most electromagnetic interference from distorting the signal. Thus, fiber optic telephone lines offer clearer transmission than coaxial cables. A third advantage of fiber optics is that glass fibers offer low attenuation compared to some media. At certain wavelengths it is possible for some fibers to have attenuation as low as 0.5 dBIkrn. This makes it practical to use fiber optics for longdistance communication links. Fiber optic cables have even been laid on the ocean floor to carry telephone channels between Europe and the United States. FIBER OPTIC SENSORS Another more specialized application of fiber optics is in sensors. This project is intended to demonstrate one example of a fiber optic sensor. In this experiment, I will demonstrate a moving-fiber displacement sensor to measure the amplitude and frequency of acoustic signals. This simple sensor is useful for detecting sounds in air or under water. This is one design for a sensor called a hydrophone. It can be used like a microphone to listen under water or to make measurements on sound waves in the water, similar to those performed by sonar. In this report, I will give a brief introduction to fiber optic technology and discuss their application to sensing. I will then talk about the specific components used in this experiment and give a summary of the tests performed. This paper will conclude with a brief discussion of the interferometric sensor concept used on board surface vessels and submarines in the Navy.
Conner, Patrick D., "Fiber optic hydrophone" (1993). Honors Capstones. 538.
iii, 24 pages
Northern Illinois University
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