Mono/dual-polarization refractive-index biosensors with enhanced   sensitivity based on annular photonic crystals
  To promote the development of two-dimensional (2D) photonic crystals (PCs) based refractive-index (RI) biosensors, there is an urgent requirement of an effective approach to improve the RI sensitivity of 2D PCs (usually less than 500 nm/RIU). In this work, the photonic band gap (PBG) feature and the corresponding RI sensitivity of the air-ring type 2D annular PCs (APCs) have been studied in detail. Such type of 2D PCs can easily and apparently improve the RI sensitivity in comparison with conventional air-hole type 2D PCs that have been widely studied in previous works. This is because the APCs can naturally exhibit suppressed up edge of PBG that can strongly affect the final RI sensitivity. In general, an enhanced sensing performance of as high as up to 2-3 times RI sensitivity can be obtained from pure 2D APCs. Such high RI sensitivity is also available in three typical waveguides developed from pure 2D APCs. Furthermore, a new conception of dual-polarization RI biosensors has been proposed by defining the RI sensitivity as the difference of crossing relative sensitivity of up-edge PBG between different polarizations. Based on pure 2D APCs, a dual-polarization RI biosensor with high RI sensitivity of around 1190 nm/RIU in infrared range was also presented as an example. 
Liyong Jiang, Hong Wu, We Zhang, and Xiangyin Li
physics.bio-ph physics.optics