A Curvature Sensor Based on Twisted Single-Mode–Multimode–Single-Mode Hybrid Optical Fiber Structure

An optical fiber curvature sensor based on a twisted multimode fiber (MMF) sandwiched between two single-mode fibers (SMF) is proposed and investigated theoretically and experimentally. The measured transmission spectrum exhibits good agreement with theoretical predictions. Compared with a traditional single-mode-multimode-single-mode fiber structure sensor, the proposed configuration offers a higher average curvature sensitivity of -2.42 nm/m-1over a curvature measurement range of 0-1.7390 m-1and -7.09 dB/m-1at an operating wavelength of 1537 nm. The temperature sensitivity of this sensor has been determined as 0.01 nm/°C over a wavelength range of 1535-1550 nm and circa 0.007 dB/°C at the wavelength of 1537 nm, over a measured temperature range of 21-121 °C.