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The phase shifted vertical side wall gratings are designed and numerically simulated on a submicron SOI waveguide to obtain the performance characteristics needed for an integrated refractive index sensor. The gratings are designed to obtain narrow band width, high transmittivity and sharp line shape in the resonant transmission so that the sensor sensitivity can be improved. The proposed sensor is easy to fabricate and will provide a linear response over a wide wavelength range with a compact structure dimension which is suitable for label free biosensing applications. The detection limit of the sensor is investigated through both wavelength shift and intensity measurement method and the performance parameter is compared with other silicon based structures like Mach-Zehnder interferometer, ring resonator and surface corrugated Bragg grating.

The sensitivity of the fiber polarimetric system for smart structure applications depends on various parameters such as pre-stress, input azimuth, fiber turns etc. The presence of the smart structure modifies the output characteristics of the highly birefringent (HiBi) fiber due to elastic properties of the structure. This differential lateral strain will produce a change in the birefringence of the fiber over this length, which manifests as the state of polarization change in the fiber output. These concepts are used in the defect detection of smart composite structures. Experimental procedures are repeated for bow-tie HiBi fibers with different optical configurations. A parameter sensitivity factor 'Q' is proposed to characterize defects. A significant variation in Q-factor can be attributed to the presence of defects/delamination. This paper deals with the on-line defect detection of smart composites based on such concepts.