A novel differential thermal measuring system using optical fiber sensors is proposed. A Michelson interferometer composed of an optical fiber coupler is applied to maintain a thermally symmetrical configuration. An optical sensing fiber is connected to each out-put arm of the coupler and each fiber end is coated with aluminum to reflect the signal light. One of these fibers is wound around a cup containing a sample material and the other is wound around the other cup containing a reference material, for the purpose of sensing its temperature difference. In order to immune from fluctuations of the light source and the amplifier, a pseudo-heterodyne detection scheme is adopted and the phase difference proportional to the temperature difference between the cups can be extracted with good stability. A rotating-phase measuring circuit is proposed to measure over a wide dynamic range of phase difference. As a result, the temperature sensing sensitivity of 250πrad/K can be obtained.
First, in this paper, the advantages of the Michelson Interferometer using optical fiber couplers are mentioned. Next, a newly-developed pseudo-heterodyne detection scheme and a rotating phase measuring circuit designed for the system are described. Finally, the experimental results are shown and the errors of the system are discussed.

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