A fiber sensor for different curvature measurement based on nano-erbium-ytterbium co-doped fiber cascade structure as both source and sensor

Abstract

A fiber sensing system based on Nano-Erbium-Ytterbium co-doped fiber (Nano-EYDF) is proposed and demonstrated, where it works as both source and sensor. Especially, a fiber curvature sensor based on Mach-Zehnder interferometer is fabricated in a Nano-EYDF, which is a cascaded structure composed of single-mode fiber (SMF), Nano-EYDF and SMF. Based on the principle of evanescent wave coupling, the light transmitted in the SMF core can be coupled into the Nano-EYDF cladding. Therefore, the Nano-EYDF core mode and cladding mode that satisfy the phase matching conditions can couple evanescent waves to form a double-beam interference. When the external environment changes, the interference spectrum will change, so the curvature sensing can be realized by observing the wavelength shift. The experimental results show when the length of the Nano-EYDF is 20 mm and 25 mm, the transmission spectrum of the sensor appears blue shift in the downforce curvature range of 0–1.76 m−1, and the curvature sensitivity is −9.763 nm/m−1 and −12.787 nm/m−1 respectively. In the propulsion curvature range of 0–0.94 m−1, the transmission spectrum exhibits blue shift, and the curvature sensitivity can be up to −9.261 nm/m−1 and −9.411 nm/m−1, respectively. The sensor is easily fabricated and has high sensitivity, and demonstrates good application prospects in curvature measurement fields such as 3D shape reconstruction and geological monitoring.