**2. Full Vectorial FEM**

82 Photonic Crystals – Innovative Systems, Lasers and Waveguides

holes that extend along the whole fiber length (Ferrando et al. 2000). The discovery of PCFs has led to several possibilities, ranging from guidance of light in vacuum, to achieving unusual dispersion properties, from enhancing non-linear effects to high confinement of light and minimizing the same non-linear effects through very large mode area single mode fibers (Ademgil et al. 2009). These unusual properties of PCFs have led to an increasing interest in their application in areas such as sensing, signal processing and optical

This chapter presents the numerical analysis of a novel sensitive PCF SPR biosensor optimised for operation in aqueous environments. The proposed sensor, shown in Fig. 1, consists of two metalized micro fluidic slots, air holes for light guidance and a small central air hole to facilitate phase matching between guided and plasmon modes. The proposed PCF SPR sensor incorporates extra air holes between the main air holes as a means of reducing the propagation

It will be shown that the proposed PCF SPR sensor can be optimised to achieve a sensitivity of 4000 nm/RIU with regards to spectral interrogation, which is much higher than the 1000 nm/RIU and 3000 nm/RIU reported by (Hautakorpi, Mattinen, and Ludvigsen 2008) and

With regards to fabrication, the proposed structure should be relatively easy to fabricate due to the notably large micro fluidic slots. Deposition of metal layers inside of the micro fluidic slots can be performed either with the high-pressure chemical vapour deposition technique (Sazio 2006) or electroless plating techniques used in fabrication of metalized hollow waveguides and microstructures (Harrington 2000; Takeyasu, Tanaka, and Kawata 2005).

losses whilst ensuring efficient coupling between the core guided and plasma modes.

Fig. 1. Cross section of the proposed PCF SPR biosensor showing various sections.

A full – vectorial Finite Element Method (FEM) with perfectly matched layers (PML) is employed to investigate the variation of key performance parameters such as sensitivity and

communication systems (Ferrando et al. 2000; Ademgil et al. 2009).

(Hassani and Skorobogatiy 2006) respectively.

The finite element method (FEM) can be applied to waveguides in general and PCFs in particular to investigate propagation characteristics of modes. In the case of PCFs, the fibre cross section is divided into homogeneous subspaces where Maxwell's equations are solved by accounting for the adjacent subspaces. These subspaces are triangles which give good approximation of circular structures (Saitoh and Koshiba 2001).

In order to allow the study of fibers with arbitrary air filling fraction and refractive index contrast, a full vector formulation is required. A full vector FEM formulation based on anisotropic perfectly matched layers (PMLs) is able to calculate as many modes as desired in a single run without setting any iterative procedure (Saitoh and Koshiba 2001; Koshiba and Saitoh 2001).
