Thermal Expansion of a Sub-Micrometer Thin Film Detected by Fiber Optics

Thinner structures influence a thin film's structural and other mechanical properties. The objective of the present work is to develop, a simple and low-cost technique for studying thermal expansion in a sub-micrometer thin film. The system designed in this work consists of two silica fibers having one of the fibers coated with a thin film. They are in the coupled state. The input fiber has a light source at one end and an optoelectronic detector at the other end. As the film thermally expands, the separation between the fibers increases. Due to this, the amount of power exchanged between the fibers changes and is also that carried by the input fiber. This leads to the change in photocurrent and the thermal expansion is detected. The system is found to be miniature, sensitive, and capable of detecting thermal expansion of the order of a few nanometers in the film.