In this work, we demonstrate the possibility of planar waveguide photonic crystals to be used in general sensing proposes. The electromagnetic performance of photonic crystals obtained by connecting in cascade planar optical waveguides with high index contrast was analysed. 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, an on state can be introduced in the gap. The local defect modifies the optical path, so that the PBG is broken, and the <i>on state </i>appears in the PBG interval. Besides, the on state wavelength 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 single and double sensing channel, are demonstrated.
Refraction index evaluation by means of a quasi-normal incidence technique is presented. The theoretical procedure
involves Fresnel equations as well as a complete statistical algorithm developed for experimental values treatment. The
characteristics of the experimental technique are analyzed in depth and rules for high precision measurements are given.
Refraction indices of soda lime and BK7 substrates were evaluated as function of wavelength. Accuracies of the order of
10<sup>-3</sup> in refraction indices determination were obtained. Finally, and making use of high precision polishing techniques,
the authors are adapting this method for the reproduction of step and graded index profile functions and diffusion depths
of integrated optical waveguides.