Applied Nanophotonics, Liquid Crystals and Biomedical Optics

In the field of optical sensing, one-dimensional photonic crystals (1DPhC) are of great interest and seem to be a promising alternative to plasmonic sensors. In this paper, a fast ellipsometric sensor based on the Bloch surface wave (BSW) is demonstrated. The Kretschmann configuration and a pixelated micro-grid polarization camera are used, allowing real-time observation of ellipsometric parameters tanψ and cosΔ. Moreover, this method is improved by utilizing another 1DPhC acting as a spectral filter, leading to the deepening of the BSW dip in the angular domain. Furthermore, ratios between the different measured intensities from the four pixels are shown to reveal a deep narrow dip which can also be used for sensing with high figure of merit. This new approach is experimentally confirmed using a 1DPhC comprising of 6 bilayers of TiO₂/SiO₂ and a termination layer of TiO₂. Sensors based on this concept have the potential to be used in many applications, including real-time chemical or biological analytes detection.