Optical Sensing Properties of Planar Integrated Optical Waveguides in Cascade

Optical sensing properties of cascade planar optical waveguides with high index contrast are demonstrated first time. The electromagnetic performance of photonic crystals obtained by connecting in cascade planar optical waveguides with high index contrast was analyzed. In our case, the periodicity of the lattice is obtained in the substrate, instead of in the guiding region, as in conventional waveguide photonic crystals. The theoretical model involves a new generalized scattering matrix concept, together with the generalized telegraphist equations formulism and the modal matching technique. The implementation of the pattern waveguide photonic crystals was carried out by connecting abruptly planar optical waveguides. To get the periodic lattice, we use the substrate refractive index as lattice periodic parameter, and the waveguide lengths as lattice constant. Photonic band gaps and photonic windows were obtained. In all cases the power conservation was excellent. If a local defect is introduced in the PBG structure, on states can be introduced in the gap. The local defect modifies the optical path, so that the PBG is broken, and on states appear in the PBG interval. Besides, the on state wavelengths can be tuned if the optical path of the defect is modified: changing the physical length or/and the refraction index of the defect. In this way, planar waveguide photonic crystals could be used for sensing applications when a specimen modifies refraction index lattice site. Sensing properties of planar waveguide photonic crystals, with one, two and three sensing channels, are demonstrated.