Integrated optical gas sensing with silicon –on –insulator (SOI) chips

1. Integrated opticalgas sensing with silicon –on –insulator (SOI) chips • N. A. Yebo, D. Taillaert , J. Roels , D. Lahem, M. Debliquy, P. Lommens , Z. Hens, R. Baets mailto:nyebo@intec.ugent.be SOI Integrated optical gas sensors • SOI optical structures provide a promising platform for the realization of sensors with interesting features. • Very compact , CMOS compatible, suitable for remote sensing and multiplexing of sensor arrays , low power consuming , safe • Low power consuming , reasonably sensitive , reliable , compact , inexpensive and robust sensors are of a high interest in several gas sensing applications such as air quality and explosion monitoring, breath analysis , and industrial process control. SOI microring resonators (MRRs) with porous sensitive coatings for gas sensing application • Microring resonators (MRRs) fabricated on SOI technology are attractive structures for gas sensing applications • While being highly compact ( less than 5µm in radius) ,they provide enhanced optical response to the surrounding changes owing to the repeated light circulation in the ring • Sensing with the resonance shift of the MRRs facilitates multiplexing of sensor arrays and provides freedom from input power noise • Appropriate gas sensitive coatings on SOI ring resonators would lead to enhanced sensitivity and gas selectivity • Porous ( mesoporous ) coatings provide large surface area for adsorption of gas molecules • Functional groups can be attached to the pores for selective gas sensing • Ethanol vapor and Hydrogen gas sensors based on MRRs coated with metal oxides : Experimental Results • Metal oxides have been extensively used in electrical gas sensors due to their sensitivity, inexpensiveness and stable operation. Metal oxides such as ZnO and WO3 are optically transparent in VIS and NIR regions ,enabling optical applications. We demonstrate the suitability of porous metal oxide films on MRRs for integrated optical gas sensing. Ethanol vapor sensor via evanescent field interaction • Hydrogen gas sensor via thermo-optic effect • Porous film on an SOI MRR is prepared from a colloidal ZnOnanoparticle suspension . • Ethanol vapor adsorption leads to change in the ZnO film refractive index • The MRR resonance red shifts through evanescent field interaction • Very low ethanol concentrations are detected due to efficient vapor adsorption on the porous film. • Pt doped tungsten oxide (WO3) hydrogen sensitive catalytic film is coated on a silica-clad SOI MRR • The catalytic film facilitates an exothermic reaction between hydrogen and the surrounding oxygen molecules at vey low hydrogen concentrations. • The resulting heat is conducted to the MRR to change the effective index via thermo-optic effect, leading to red shift in the resonance wavelength. • High sensitivity to hydrogen is achieved due to the significant thermo-optic coefficient (1.8 10-4 )of Si Experimental Setup • Q ≈ 25000 • 1.2nm resonance shift measured at 3% hydrogen in air ( below the Lower Explosion Limit) • Linear sensitivity of 480pm/%H2 • 220pm resonance shift is measured at 120ppm ethanol vapor concentration • Detection limit below 25ppm ethanol is estimated Conclusion • Reasonably sensitive and highly compact integrated optical gas sensors are demonstrated using metal oxide coatings on SOI MRRs. • With future progresses in thin film micro-patterning techniques , several gas selective films can effectively be coated on MRRs for multiplexed multi-gas sensing on a photonic chip Acknowledgement Nebiyu A. Yebo acknowledges Gent University for funding this research through the ‘Methusalem Smart Photonic Chips ‘ project mailto:First.Author@intec.UGent.be