Single-frequency refractive index sensor based on a finite one-dimensional photonic crystals with two defects

A numerical analysis by means of transfer matrix method has been performed on finite one-dimensional photonic. crystals consisting of two-layer repeated cells and two non-identical defect cells for the normal incident transverse electric (TE) wave. The study reveals a remarkable new feature showing that the variation of a photonic pass-band transmittance can be induced by varying the refractive index of one of the defect layer at practically the same peak frequency, which offers the potential application for single frequency sensing. The result further demonstrates the flexibility of tailoring the system parameters for application in the desired range of refractive index at the required sensitivity. It is also shown that the photonic pass-band (PPB) peak transmittance is generally less than unity in the index range considered, except for the case with the grating segment lengths (M, N, L) satisfying the condition N = M + L. This peculiar feature is explained qualitatively in this work.