Temperature-Insensitive Mechanical Sensor Using Multi-Modal Behavior of Antiresonant Hollow-Core Fibers

We present the first report on a compact, temperature-insensitive, multi-axial mechanical force sensor based on a single-core antiresonant hollow-core fiber (ARHCF). Single-core antiresonant fibers are inherently few-moded in a short length and show characteristic multimode interference pattern in their transmission spectrum. We report here a simple technique that enhances the interaction between the interfering modes in these fibers, giving rise to up to four-fold increase in the peak-to-peak amplitude of the interference pattern. The enhanced interference pattern is shown to be responsive to external mechanical forces, like longitudinal and transverse strain and curvature, with distinguishable linear responses. Transverse and longitudinal mechanical forces affect different attributes of the interference pattern, making the proposed sensor suitable for their simultaneous sensing. The temperature sensitivity of the sensor is found to be 3.3 pm/°C suggesting negligible thermal crosstalk while measuring the effect of mechanical forces. The sensor has a compact configuration and is inherently insensitive to polarization of light used.