Temperature-compensated fiber optic external cavity strain sensors and

Abstract

Three types of temperature compensated fiber optic external cavity strain sensors and methods of operation thereof are disclosed as well as an intensity-based fiber optic external cavity sensor and system. The fiber optic external cavity sensors each comprise an input optical fiber and a wire bonded together in spaced axial alignment by a connecting sleeve wherein respective ends of the fiber and the wire face one another and are spaced apart a predetermined distance to define an air gap. The ends of the input fiber and wire form two reflective surfaces. The temperature compensation methods involve either keeping the air gap unchanged with respect to temperature variations or having a temperature sensitive reflector at the tip of the wire. An intensity-based external cavity sensor comprises an input fiber which is a single mode fiber. An optical bandpass filter is deposited at the end of the single mode fiber. A reflector is also provided at the end of the wire. In the intensity-based sensor system, a LED, two couplers and a pair of photodetecters are used. There is also a bandpass filter, which is similar to the one in the sensor, in front of one of the photo-detectors. The spectrum of the return light from the sensor is modified as the air gap changes. The spectral changes are detected by a simple spectral radiometric method, which ratio the signals of the two detectors.