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Abstract: A 2x2 multimode interference structure with parabolic down tapering has been proposed and realized by using silica waveguides with silicon oxinitride (SiON) core for the reduction of coupling length. The coupling behavior and dependence of fabrication tolerances on power imbalance of the proposed tapered structure have been compared with those of other tapered MMI structures having both down and up tapering by using a mathematical model based on sinusoidal modes. It has been found both theoretically and experimentally that the beat length (Lπ) of the proposed tapered MMI coupler with Δn=5% is ∼ half that of conventional MMI coupler and the deviation of power imbalance from its minimum value with fabrication tolerances (± ∂w values) for the proposed tapered structure is more than that of other tapered structures. [Copyright &y& Elsevier]

Abstract: In this paper we report on the design and fabrication of an Evanescent Optical Waveguide Sensor (EOWS) using silicon oxynitride (SiON) as the core layer on silica-silicon wafer and its implementation for rapid detection of adulterant traces in pure petrol incorporating composite planar waveguide geometry. The embedded waveguide of length ∼ 10,000μm and core width ∼ 50μm was fabricated using standard Plasma Enhanced Chemical Vapour Deposition (PECVD) technologies and Reactive Ion Etching (RIE) technique. The main aim of this work is to encompass an abrupt choice to the time-consuming existing adulteration detection methods which generally requires some time to give the consequence. Using Simple Effective Index Method (SEIM), the theoretical predictions and experimental results at wavelength 632.8nm are analyzed and presented, which demonstrated that the sensitivity of the proposed EOWS is ∼40 times more than that of the existing planar waveguide sensors and also 20 times more than that of asymmetric waveguide structure thereby allowing rapid detection of adulterant traces in pure petrol without involving the use of chemicals. It is found that the sensor structure is polarization independent and advantages include high sensitivity, easy fabrication and more importantly, requirement of very minimal amount of sample volume for detecting adulteration. [Copyright &y& Elsevier]