Analysis of Rugates
Rugates option allows you to analyze socalled rugate coatings. Rugate coatings are described by analytical expression giving dependence of the refractive index on the coating thickness. In OptiLayer the dependence of the refractive index is described with the help of fraction function on the basis of Changeable Composite material. Example: Refractive index profile, transmittance and formula representation of the rugate presented in B.H. Southwell, "Extendedbandwidth reflector designs by using wavelets", Appl. Opt., 1997, Vol. 36 

\(n(x)=n_a+0.5 n_p A(x) \sin\left(\displaystyle\frac{4\pi x}{\lambda_0}\right)\) \(A(x)=10 t^315 t^4+6 t^5 \) \(t=\displaystyle\frac{2x}{TOT},\;\;\mbox{ if}\;\; x<\frac{TOT}{2} \) \(t=\displaystyle\frac{2(TOTx)}{TOT},\;\;\mbox{ if}\;\; x>\frac{TOT}{2}\) Here x is thickness coordinate, TOT is total optical thickness.

Design of Rugates
Rugate filters are optical coatings with the refractive index which is varied continuously. In comparison with conventional multilayer structures, rugate filters provide some special potentials:

Example: designed beam splitter with the help of rugate filter design option. 
For a theoretical analysis, a rugate coating structure can be approximated by a refractive index profile with a larger number of steps. Therefore, design of rugates requires an efficient method to specify the structure, calculate spectral characteristics and optimize the structures. OptiLayer allows you fast and effective designing rugate filters. The details of our expertise in rugate coatings analysis and design has been published:
