ABSTRACT
The optimum value has to be determined to some extent by trial and error. Nevertheless, this description does provide an understanding of how the absentee layer works and an approximate value of its refractive index. The principles of gradient-index antireflection are based on the idea that a gradual transition in refractive index will produce a smaller reflection compared to a sharp boundary. Gradient-index layers can be produced by continuously altering the refractive index of a thin film during deposition. The principles of converting a tapered structure to a tapered-refractive-index profile are done using the effective medium theory. Unlike the case with discrete thin films, it is difficult to formulate an expression for the reflection coefficient from a gradient-index structure. However, it can be easily calculated using the transfer matrix method.
