A Relative Humidity Sensor Based on Non-Adiabatic Tapered Optical Fiber for Remote Measurement in Power Cable Tunnel

Abstract

To solve the power supply, signal communication, and lifetime problems in the humidity sensing in power cable tunnel, an intrinsic non-adiabatic tapered optical fiber (NATOF) relative humidity (RH) sensor without functional film was proposed in this article. The sensing principle based on multimode interference and refractive index (RI) sensitivity was introduced. The relationship between humidity sensitivity and the waist diameter of NATOF was theoretically analyzed to improve the sensor sensitivity. It is found that high relative humidity sensitivity detection can be achieved by taking advantage of the NATOF’s high sensitivity near the dispersion turning point (DTP). The test-obtained trends of the humidity sensitivity at different waist diameters were consistent with the theoretical results. The proposed NATOF sensor with a waist diameter of 2.39 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> had a linear response in the range of 35%–90% RH, a detection distance of over 10 km, a relative humidity sensitivity of −47 pm/% RH, and an accuracy of ±4.6% RH. Based on the different response sensitivities to humidity and temperature of different dips, a sensing matrix was established to solve the temperature cross-sensitivity issue of the relative humidity sensor.