The paper deals with considerations concerning planar waveguide structures, in which the polymer SU8 is used as the waveguide layer. The results of numerical calculations of the distribution of the field concerning structures of various thicknesses have been presented, and photos taken in the course of investigating the surface by means of a microscope of atomic forces. The results of calculations of sensitivity in relation to the refractive index of the cover layer at various thicknesses of the layer have been presented, too.