Relative humidity sensing using micro-cavities produced by the catastrophic fuse effect

Abstract

Air humidity is a parameter with relevant interest to a wide variety of areas, both in industry or in domestic processes. Due to the growing demand on air humidity monitors, especially relative humidity, the development of sensors to assess this parameter has been increasing. Moreover, in the last years, the optical fibre based technology has been overcoming some disadvantages and limitations presented by the solutions based on the conventional technologies. Its limitations and/or restrictions make them unsuitable for explosive or dangerous environments, high electromagnetic interference environments, or where remote monitoring is required. However, the production of optical monitoring solutions still involves a complex and expensive experimental apparatus. In this work, a cost effective solution to produce optical fibre relative humidity sensors based on Fabry-Perot interferometer micro-cavities is proposed. The device is manufactured by the recycling of optical fibres destroyed through the catastrophic fuse effect, which considerably reduces the manufacturing costs. The micro-cavities were filled with an organo-silica hybrid material, called di-ureasil, allowing the sensing of relative humidity. A sensitivity and resolution of (17.1 +/- 1.7) pm/% RH and 0.06 % RH (in the 15-85 % RH range), respectively, were achieved.