Nanocrystalline diamond (NCD) thin films are suitable biointerfaces having excellent stability due to their hardness and chemical inertness. NCD coatings on planar waveguides (PWG) in the IR region allow to design optical sensors sensitive to absorbers like proteins or other biomolecules. In this contribution, we present a 2D model of a multi-layer PWG developed under FEM (finite element method) simulation software Comsol Multiphysics. The model is based on the modified wave equation solved in the frequency domain and includes optical absorption in the materials. Prior to these simulations, calculations of optical modes were performed in order to design a suitable single-mode PWG with the NCD/a-Si:H/glass heterostructure. It was found that for the single-mode PWG working in the narrow region of 1550-2000 nm the silicon thickness must be 150-320 nm. Shorter wavelengths are excluded due to the optical absorption of both amorphous silicon and diamond. It was found that in order to keep a reasonable signal attenuation, the NCD film must be prepared with the optical absorption coefficient lower than 10 cm-1, being a technical challenge. Dependencies of the signal attenuation on the NCD film thickness, absorbing layer height, its absorption coefficient and exciting wavelengths are presented.Keywords: nanocrystalline diamond, amorphous silicon, optical waveguides, FEM simulations
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