A high response polyimide fiber optic sensor for distributed humidity measurements

The humidity induced strain response along a length of optical fiber coated with polyimide layers of varying thickness up to 1.3 mm was characterized using Optical Frequency Domain Reflectometry. The measured strain response to humidity increased with coating thickness, and response values up to 38.5 ± 1.9 με/% RH were observed. This is far higher than in previous studies of polyimide coated optical fibers, where thinner coatings were applied. The response time, hysteresis and temperature response characteristics of the fiber are also reported. High coating thickness polyimide coated optical fibers with similar properties to those demonstrated here could be suitable for application in cost effective distributed humidity sensing systems.