In this work, a simple and low cost technique for studying thermal expansion in a sub-micrometer thin film is presented. The system consists of two silica fibers kept in the coupled state. One of the fibers is coated with the thin film. The input fiber has a light source at one end and an optoelectronic detector at the other end. As the film thermally expands, separation between the fibers increases. This affects the exchange of optical power between the two fibers. This leads to the change in photocurrent. The system is found to be miniature, sensitive and capable of detecting thermal expansion of the order of few nm, in the film.
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