Two-Dimensional Hole-Array Grating-Coupling-Based Excitation of Bloch Surface Waves for Highly Sensitive Biosensing

In this study, a surface diffraction two-dimensional (2D) grating structure was placed on the topmost layer of distributed Bragg reflectors (DBRs) for biosensing. Bloch surface wave (BSW) resonance was realized by coupling a 2D subwavelength hole-array grating and could be excited at different locations: the surface of 2D-grating layer or the inter-face between the DBR and bio-solution. Material losses in the multilayer dielectric were measured to test the robustness of this scheme. Both the surface diffraction-grating BSW (DG-BSW) and the alternative guided grating-coupled BSW (GC-BSW) configuration showed markedly enhanced angular sensitivity compared to conventional prism-coupled schematics. Exciting these modes using a grating-coupling technique appears to yield different extreme sensitivity modes with a maximum of 1190°/RIU for DG-BSW and 2255°/RIU for GC-BSW. Refractive index sensors with a high figure of merit may be realized via such compact configurations.

Theory of Dispersion Reduction in Plastic Optical Gratings Fiber

In this paper, we have proposed a way for reducing the dispersion level in plastic optical grating fiber by optimizing the grating-coupling strength (ξ) numerically. The effects of average refractive index (δn) and temperature (T) variation on the dispersion properties are investigated. Results show that, for reducing the dispersion level, the ξ parameter should be optimized and the amplitude of the δn needs to be reduced. Also results show that the dispersion due to the wavelength shift induced by the temperature variation will be eliminated by operating at high ξ value.