Technical Issues - Index Limits

This page illustrates the steps required for optimizing with index limits. Our goal is to design our 450-750 BBAR coating using the design 100M 200H 100L (physical thickness in nm) with all three indices varied. Each film material to be optimized is represented by a dispersive index function in the Film Indices dialog. Here the simple function N is utilized.

Next, each material is specified as an optimization variable. This is accomplished by entering the negative value displayed under Index in the Var column. Here layer thickness values are kept fixed, so there are no positive variable numbers.

The final step is entering limits in the Index Limits dialog. Editable numeric cells are white and since index function N has only one coefficient (A = n) all entries are in the A column. (For this screen snapshot we hid columns B-G by clicking <F3> to hide C-G and manually eliminating column B.) Check the box in the Use column to enable limits for each variable. Note that $ is omitted from the function name.

Final results are nL = 1.402, nH = 2.102 and nM = 1.776. Disabling limits and optimizing further gives much better results, but material properties become unrealistic (nL ~ 1.2).

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