Optical EngineeringModeling and fabrication of evanescent waveguide-based optical sensor for sensitivity enhancement using silicon oxynitride technology
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An evanescent waveguide–based optical sensor incorporating composite planar waveguide geometry using silicon oxynitride as core layer has been designed and developed. The proposed waveguide of length ∼10,000 μm and core width ∼50 μm was embedded on silica/silicon wafer and tailored for sensing glucose concentration in aqueous solution with high waveguide sensitivity ∼0.95 , as an evidence of the design and development. We derived the dispersion relation from the wave equation of the structure for estimating the propagation constants of transverse electric and transverse magnetic modes and then modeled the sensor response to the change of the sensing layer refractive index. The enhancement of waveguide sensitivity is shown by using simple effective index method based on sinusoidal modes. The sensor structure is polarization independent. The theoretical results are in good agreement with the results obtained experimentally. The experimental results have revealed strong enhancement in terms of waveguide sensitivity which is ∼10 times more than that of the existing planar waveguide sensors and five times more than asymmetric waveguide sensor. This proposed waveguide sensor requiring minimal sample volume has the potential to realize for online monitoring of blood glucose levels in the near future.