Thin Film Removal procedure is one of the production friendly design options of OptiLayer: 

Synthesis --> Thin Film Removal

This procedure allows you to remove thin layers from the obtained design.

The Thin Layer Removal window shows expected merit function values after removing various design layers (MF increase column). Layers in the list box are sorted by their physical thickness values in the ascending order.

In Automatic mode Thin Layer Removal will work until one of termination criteria is fulfilled. Termination criteria include termination on the bases of allowed increase of the merit function value or/and termination when there is no layers thinner than a given value.

Exclude material(s) list allows to exclude some materials from consideration. It is useful if thin metal layers present in the design.

Example. Designing a beamsplitter:

• Spectral range from 620 nm to 680 nm;
• Rs=Rp=50%;
• AOI=45⁰;
• Thin film materials - Nb₂O₅/SiO₂.

A 35-layer design can be easily obtained with the help of the Needle Optimization Technique (see Rp/Rs and refractive index profile at the right panel).

It is seen that design reflectances perfectly approximate target characteristics. At the same time, the design contains several very thin layers. Thin Film Removal can be used to remove thin layers and keep the excellent approximation of target reflectance by design reflectance.

It is seen (left panel) that the design contains 2 layers thinner than 10 nm and 5 layers thinner than 50 nm.

In this example, a low limit for thicknesses of design layers is 40 nm. Of course, it is assumed that the low limit is a reasonable value. Low boundary higher than 50 nm would lead to significant worsening of the merit function.

As a result, a 29-layer design has been obtained. Correspondence between target and design spectral reflectance is still excellent.

At the same time, the thinnest layer is 49.5 nm.