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OptiLayer:  Your Partner in Design and Post-Production Characterization of Optical Coatings


Analysis of Rugates

Rugates option allows you to analyze so-called 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, "Extended-bandwidth reflector designs by using wavelets", Appl. Opt., 1997, Vol. 36

Rugate filters

reflector designs

\(n(x)=n_a+0.5 n_p A(x) \sin\left(\displaystyle\frac{4\pi x}{\lambda_0}\right)\)

\(A(x)=10 t^3-15 t^4+6 t^5 \)

\(t=\displaystyle\frac{2x}{TOT},\;\;\mbox{ if}\;\;  x<\frac{TOT}{2} \)

\(t=\displaystyle\frac{2(TOT-x)}{TOT},\;\;\mbox{ if}\;\;  x>\frac{TOT}{2}\)

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:

  • A sinusoidal oscillation of the refractive index can create an isolated peak in the reflectance and suppress reflectance ripples outside of high reflectance zone.
  • It is possible to linearly superimpose multiple oscillations of the refractive index in order to combine multiple reflection features.
  • Rugate filters have also been reported to have substantially higher laser-induced damage thresholds, compared with conventional multilayers.
Rugate coating
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:

  1. A. V. Tikhonravov, M. K. Trubetskov, T. V. Amotchkina, M. A. Kokarev, N. Kaiser, O. Stenzel, S. Wilbrandt, and D. Gäbler, "New optimization algorithm for the synthesis of rugate optical coatings," Appl. Opt. 45, 1515-1524 (2006).
  2. V. Pervak, A. V. Tikhonravov, M. K. Trubetskov, J. Pistner, F. Krausz, and A. Apolonski, "Band filters: two-material technology versus rugate," Appl. Opt. 46, 1190-1193 (2007).
  3. V. Janicki, S. Wilbrandt, O. Stenzel, D. G&aumbler, N.Kaiser, A. Tikhonravov, M.Trubetskov, T. Amotchkina. Hybrid optical coating design for omnidirectional antireflection purposes, Journal of Optics A: Pure and Applied Optics 7, L1-L14 (2005).

Easy to start

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