Example 2. Optimization of coating total thickness

Using the new type of targets Thick/Stress you can optimize total thickness of the coating. Consider the same design problem of the edge filter as in Example 1.

Typical total thicknesses of edge filter designs is 3.5-4.2 μm. It may be required to limit the design total thickness by 3 μm. In this case, Thick/Stress target can be specified as it is shown in Fig. 1:

\[ \alpha_1\Sigma_{TiO_2}+\beta_1\Sigma_{SiO_2}<3000μm,\]

\(\alpha_1=1, \beta_1=1\). Target value is 3000 that corresponds to 3000 nm.

Qualifier B indicates that total thickness must be less than 3000 nm.

minimization coating thickness

Fig. 1. Thick/Stress target specification in the case when total coating thickness is to be optimized.

One of the edge filters obtained by optimizing combined merit function is shown Figs. 2 and 3. Total design thickness is less than 3000 nm. At the same time, approximation of the target reflectance in the range 583-683 nm is getting a little bit worse since the thickness is smaller. 

edge filters with minimized thickness

Fig. 2. Spectral performance of the 25-layer edge filter design. Total thickness is 2916 nm.

dichroic filter minimized thickness Fig. 3. Refractive index profile of the 25-layer edge filter.


The new option is very flexible. Obviously, with the help of this option you can not only minimize thickness of one material or/and reduce the total thickness. You can increase or limit thickness of materials or even separate layers.

In order to increase thicknesses you need to specify A qualifier.

To limit thicknesses of layers you need to specify not one but two targets, one with A and another one with B qualifier.

Go to Example 1. Optimization of total thickness of one coating material

Go to Example 3. Reducing of stress using alignment of thicknesses of materials on front and back sides

Go to Example 4. Alignment of stresses caused by front- and backside coatings

Go to Example 5. Designing a beamsplitter maintaining optical flatness after coatings (OIC Design Contest 2013)

Auxiliary information for stress-targets specification