A Defective 1-D Photonic Crystal-Based Chemical Sensor in Total Internal Reflection Geometry.

In this paper, we introduce and analytically demonstrate a novel chemical sensor based on defective 1-D photonic crystals in total internal reflection geometry, where a gradient refractive index (GRIN) defect layer is located at the end of the structure. This configuration creates an open sensing interface for real-time detection with ultrahigh sensitivity. Using the GRIN lens in the structure not only helps to tune the resonance wavelength to a desired value but also as a consequence of its special refractive index distribution function, a ring-shaped reflectance distribution appears on the output plane of the structure that plays a key role in finding the optimized refractive index of the defect layer and achieving the best resonance of the cavity modes. The resonance angle of the cavity modes is highly sensitive to the effective refractive index of the fluid flowing above the sensor. The refractive index variation of \Delta nF=10^{-8}RIU that causes \Delta \theta =3.2\times 10^-6 degrees shift at the resonance angle can be detected by this sensor. [ABSTRACT FROM PUBLISHER]