An optical humidity sensor: A compact photonic chip integrated with artificial opal

Abstract

A novel, miniaturized and easy-to-use optical sensor enabling accurate humidity measurement in real-time has been proposed in current study. This is achieved by the compact integration of a photonic chip with an artificial opal layer. The III-nitride chip with a size of 1 × 1 × 0.21 mm3 simultaneously provides two essential functions, i.e., photoemission and photodetection. The integrated opal film is comprised of silica powders with a hydrophilic nature, and its humidity-dependent light reflection can be precisely monitored by the on-chip detector without any aids of external optics. The optical sensing device shows a highly linear response in the relative humidity (RH) range of 3.8–90% and a sensitivity of 0.046–0.051 μA/%RH. The real-time monitoring function of the sensor has been demonstrated by mounting it on a facial mask which is used under various human breathing conditions. With the advantages of its compact size, ease of operation, high linearity and repeatability, large dynamic range, and fast response time, this cost-effective chip-scale optical sensor shows great potential in a wide range of practical humidity-sensing applications.