High-Accuracy Thermal Expansion Coefficient Measurement Based on Fiber-Optic EFPIs With Automatic Temperature Compensation

This article reports a fiber-optic instrument for the coefficient of thermal expansion (CTE) measurement with high accuracy, based on extrinsic Fabry–Perot interferometers (EFPIs) with novel automatic temperature compensation. The prototype CTE measurement instrument consists of two parallel EFPIs mounted on a quartz base. The first EFPI is formed between the endface of an optical fiber and the mirror attached to the endface of a short bar. The second EFPI is fashioned between endface of another optical fiber and the mirror attached to the endface of a long bar. The sensing elements are the short and long bars with the same material, cross Section for bars, and optical fibers. When the instrument is subjected to temperature rise, bars with two different lengths will extend, leading to relatively significant EFPIs’ cavity length variation. CTE of the bars’ material can be determined by the difference between two bars’ length changes, temperature change, difference between two bars’ lengths, and the CTE of the quartz base. The difference between two length changes eliminates temperature impact from the remaining elements, thus providing automatic temperature compensation. For experimental validation, the CTE of three types of samples is characterized in the temperature range from 20 °C to 80 °C. A resolution of
$\pm 0.0032\times 10^{-{6}} /^{\circ }\text{C}$
and an accuracy of
$\pm 0.0758\times 10^{-{6}} /^{\circ }\text{C}$
of CTE are achieved, respectively. Experimental results reveal that the proposed instrument is a practical and effective tool for materials’ CTE measurement, with the advantages of high resolution, simple-to-manufacture, low cost, and high accuracy, which will have the potential to be applied in the fields of material sciences.