Optical fiber temperature sensor based on phase shift by aluminum thermal expansion

The method of using aluminum tube wound by single-mode fiber as a temperature sensor is proposed. The optical source of this temperature sensing system is a 2-frequency He-Ne laser. When the temperature of fiber on aluminum is changed, a phase shift in optical signal will appear. By using electronic circuits, this phase shift can be detected and compared with a reference signal which is obtained directly from the laser source. Then one can obtain information on temperature according to the difference of phases between these two signals. Two experiments have been performed in the laboratory. In the first experiment the aluminum tube is 12 cm in diameter, 8 cm in height, and 2 mm in thickness, with a fiber length about 60 m wounded 155 turns. The sensitivity is 2.1/spl times/10/sup -2/ rad//spl deg/C-m. In the second experiment, the tube is 7.5 cm in diameter and height, and 2 mm in thickness, with a fiber about 10 m length wounded in 21 turns. The sensitivity is 4.9/spl times/10/sup -2/ rad//spl deg/C-m. The temperature from 5/spl deg/C to 80/spl deg/C is measured with this design.<
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