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Torsion balance system as a high precision important ultra-small force measurement tool usually requires ultra-highresolution deviation measurement of the torsion angle. Currently, autocollimators are used for the torsion angle deviation measurement. Optical coherence tomography (OCT) is a high-resolution three-dimensional imaging technology, which has the characteristics of real-time imaging of samples with micron or sub-micron resolution at millimeter depth, and is widely used in biomedical research and industrial detection fields. In this work, utilizing the single-mode fiber based common-path OCT system architecture, we design and fabricate a compact probe that consists of four displacement sensing fibers connected to one home-built SD-OCT system with a central wavelength of 840 nm. Each fiber senses the distance between the fiber tip and torsion balance integrated reflection mirror. The distance peaks from each fiber are designed to be distributed along system one A-scan depth which enables simultaneous measurement. With the phase sensitive reconstruction algorithm, tens of pm distance sensing resolution can be achieved. Analyzing the displacement values from four distributed spatial points, the torsion principle surface can be reconstructed for post experiment analysis. We believe our proposed work will be valuable for distributed ultra-high resolution compact and stable displacement sensing.
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