The Tactile Sensing with Light Propagation in a Four-Layer Slab Waveguide for Breast Tumor Detection

Light propagation in a 4 layer slab waveguide is considered. The supported modes are of higher orders than zero, with a larger node concentration toward the layers with larger refractive index. Additionally, we consider the geometric optics approximation to describe very thick waveguides. Light can be coupled from LED by direct focusing with a lens, and coupling can be optimized by introducing a transverse displacement in order to focus it on the layers with larger refractive index. Further optimization can be done by tilting the lens and bringing in some degree of coma aberrations.