Long Range Surface Plasmon Polariton Waveguides for Hydrogen Sensing

Applications that involve the use of hydrogen gas (H-2) have an inherent risk in that hydrogen is combustible in air and hence accurate detection of its concentration is critical for safe operation. Long-Range Surface Plasmon Polaritons (LRSPPs) are optical surface waves that are guided along thin metal films or stripes which are symmetrically cladded by a dielectric and have been demonstrated to be highly sensitive for biological and chemical sensing. The sensor presented here consists of a gold (Au) stripe suspended on an ultrathin Cytop membrane. This architecture is referred to as the membrane waveguide and has previously been demonstrated to support LRSPP propagation. Hydrogen sensing is achieved by overlaying a palladium (Pd) patch on a straight waveguide section, which induces a measureable insertion loss change under the presence of hydrogen. The design and optimization of the sensor through finite element method (FEM) simulation will be discussed. This will include the design of the optimal waveguide geometry along with the design of an integrated grating coupler for broadside light coupling. In addition, details on the fabrication process are presented.