Optical Propagation

Optical transit through the centimeter-scale three-layer stack is described as nanosecond-scale propagation latency. The angular spectrum method is used instead of the Fresnel approximation to avoid an additional paraxial approximation on spatial frequencies. Propagation is modeled using monochromatic scalar wave optics. Free-space propagation is treated as a linear operator under the scalar wave model. The scalar diffraction model may fail when vectorial effects, anisotropy, or polarization-dependent responses become important.