Evanescent field analysis of air-silica microstructure waveguides [for biosensing applications]

A comprehensive analytical and numerical study of the fraction of evanescent modal power and the fraction of modal power in the holes has been presented for air-silica microstructures. It was shown for the 4-layer structures, that when the waveguide half width was kept constant and a was varied between 0 and s/2, the fraction of modal power in regions 2 and 4 was greater in the case of the periodic waveguide than the waveguide with the core region. This was a result of the core region have a confining effect on the mode. It was also determined that by adding another air-silica layer to the 4-layer structure, the fraction of evanescent power and power in the holes was increased for all values of a So, the ideal waveguide characteristics of a periodic 6-layer air-silica microstructure that maximises the power in the holes and evanescent power for biosensing applications is to have a as large as mechanically possible (i.e. large holes).