Modeling of Label-Free Optical Waveguide Biosensors with Surfaces Covered Partially by Vertically Homogeneous and Inhomogeneous Films

Figure 1

The structure of the modeled OWLS waveguide chips with inhomogeneous adlayer. The modeled multilayered assembly consists of 4 layers: substrate, waveguide film, adlayer, and cover (see inset c). The adlayer covers the waveguide film surface in a certain percent (see inset b) and it has vertical refractive index distribution: step-index and exponential distribution (see inset a). This vertical distribution is realized in our model calculations by dividing the adlayer into 150 sublayers (not shown in figure) which has the appropriate refractive index of the selected distribution. These layers are implemented in the transfer matrix method where and are the amplitudes of the upward and downward propagating electromagnetic waves (see inset c and equation (4)).