In this work, we present robust and easy-to-fabricate optical gas and vapor sensors based on optical fiber resonators (OFR) coated with palladium (Pd) thin films, Pd micro-particles and polymer brushes (PB). Pd based sensors are used for hydrogen (H2) gas detection in concentration range of 0% to 1% and polymer brush-coated OFR are used for detection of vapor in concentration range of 0 to 25%. Sensing mechanism of these sensors is based on spectral shift of resonance wavelength which are called whispering gallery modes (WGMs). This spectral shift is due to volume expansion of the sensing material. Tapered fiber is used in order to excite WGMs in coated OFRs. Good sensitivity and repeatability results are obtained for all three types of sensors.
Optical fiber resonator (OFR) sensor is presented for bulk liquid refractive index (RI) sensing. The sensing mechanism relies on the spectral shifts of whispering gallery modes (WGMs) of OFRs which are excited using a tapered fiber. OFR liquid RI sensor is fully characterized using water solutions of ethanol and ethylene glycol (EG). A good agreement is achieved between the analytical calculations and experimental results for both TE and TM polarizations. The detection limit for bulk RI is calculated to be between 2.7 – 4.7 × 10<sup>−5</sup> refractive index unit (RIU). The OFR sensor provides a robust, easy-to-fabricate and sensitive liquid refractive index sensor which can be employed in lab-on-a-chip applications.
An SU-8 polymer microdisk resonator coated with a palladium (Pd) layer and coupled to a single-mode optical waveguide is used to as a hydrogen (H<sub>2</sub>) gas sensor. In the presence of H<sub>2</sub>, a red shift is observed in the spectral positions of the microdisk whispering gallery modes (WGMs) due to the expansion in the Pd lattice. H<sub>2</sub> concentrations below the flammable limit (4%) down to 0.3% could be detected in nitrogen atmosphere at room temperature. For H<sub>2 </sub>concentrations between 0.3 − 1%, WGM spectral positions shifted linearly with H2 concentration at a rate of 32 pm/%H<sub>2</sub>. Average response time of the devices was measured to be 50 s for 1% H<sub>2</sub>. The proposed device concept can also be used to detect different chemical gases by using appropriate sensing layers.