Abstract: Fiber-optic displacement and vibration sensor are described in a single set up with higher dynamic range. Hard polymer clad silica fiber is used for both transmission and reception of light. The sensor system consists of coherent optical source, transmitting fiber, bi-convex lens, receiving fiber array, detectors and electronic circuitry. Light of $lambda $EQ 980 nm is launched to transmitting fiber and light reflected from the target is received by fiber array and detected by p-i-n diode. Detected power of two adjacent fibers is subtracted by difference amplifier and followed by a level shifter. A mathematical model relating focal length of lens, radius of fiber, spacing between transmitting and receiving fiber, distance of the fiber from optical axis has been developed. The range of linear displacement, and angular displacement using four receiving fiber array is 0 to 1365 $mu@m and 0 degrees to 0.5, respectively. The same concept of measurement is also applied to develop a vibration sensor. The range of measurement of peak to peak amplitude of vibration using three fiber array is obtained as 910 $mu@m. !8
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