Surface Loading Sensitivity Characterization of a Resonant Planar Optical Waveguide Stack

Detuning of a coupled planar waveguide pair through surface loading of the top waveguide that is in contact with the analyte serves as a transducer for a Stacked Planar Affinity-Regulated Resonant Optical Waveguide (SPARROW) sensor. Here we investigate the surface loading detection sensitivity of a SPARROW transducer composed of a stack of two planar alumina waveguides grown using ion beam assisted e-beam deposition. Using a sucrose analyte solution introduced to the stack surface in a poly-di-methyl-siloxane (PDMS) microfluidic channel, the change in optical output power through the coupled waveguide pair as a function of sucrose analyte solution concentration was experimentally determined. Based on the analyte in the evanescent field penetration depth volume, the effective minimum detectable surface loading of the stack was determined to be 20 with a bulk index sensitivity of 5.6 refractive index units (RIU) for this stack configuration and experimental setup.