Optical sensor for hydrogen gas based on a palladium-coated polymer microresonator

Abstract

We report an integrated optical sensor of hydrogen (H2) gas employing an SU-8 polymer microdisk resonator coated with a palladium (Pd) layer and coupled to a single-mode optical waveguide. The sensing mechanism relies on the expansion in the Pd lattice due to palladium hydride formation in the presence of H2. Strain induced in the microresonator then causes a red shift of the spectral positions of the resonator whispering gallery modes (WGMs) which is monitored using a tunable laser coupled to the waveguide. H2 concentrations below the flammable limit (4%) down to 0.3% could be detected in nitrogen atmosphere at room temperature. For H2 concentrations between 0.3 and 1%, WGM spectral positions shifted linearly with H2 concentration at a rate of 32pm/% H2. Average response time of the devices was measured to be 50s for 1% H2. The proposed device concept can also be used to detect different chemical gases by using appropriate sensing layers.