A peanut-shaped structure fiber optic sensor for curvature sensing via intermodal interference

Abstract This paper presents and experimentally demonstrates a curvature sensor utilizing intermodal interference. The sensor is constructed by splicing a no-core fiber (NCF) between 2 single-mode fibers (SMFs) and incorporating several peanut-shaped (P-S) structures. While adding multiple P-S structures enhances the excitation of high-order cladding modes, thereby influencing both curvature sensitivity and measurement range. The research results reveal that a 1 P-S structure yields a maximum curvature sensitivity of -31.95 nm/m-1. In comparison, the sensitivity decreases by 3.43 nm/m-1 with 2 P-S structures and by 17.5 nm/m-1 when the number increases to 3, with a corresponding reduction in sensing range of 0.467 m-1. Temperature tests reveal a sensitivity of 0.058 nm/°C and a temperature-induced curvature crosstalk of 0.0018 m-1/°C for the single-structure sensor. By adjusting the number of the peanut-shaped structures in the sensor, the sensitivity and detection range can be tailored for specific applications, such as extreme environment detection and deep-sea exploration.