Bragg filter

Bragg filter

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Bragg filter: Optical design

Configuration file
../demo/code/bragg_filter/bragg.wcd

Main window

What do you see?
This example shows transmittance and reflectance spectra of a SiO2/TiO2-superlattice with 20 repetitions of the double layer. The layer stack is deposited on a 1 mm SiO2 substrate.
In the bottom of the window the two optical spectra are shown. The center is filled with color information: For each spectrum the L*, a* and b* values are displayed together with a visualization of the color in the rectangle above the numerical color coordinates. In addition, there is a second rectangle with a fixed L* value of 70 and the same values of a* and b* as the first one. This is useful for colors with low L* values (see below) which appear on most screens completely black. The brightened version with L*=70 and the same a* and b* values then gives still a good impression.
Finally, in the window's top area there are two thickness sliders for SiO2 and TiO2 thickness variations, respectively.

What can you do?
First of all you can and should move the sliders, of course. It's certainly fun to watch how spectra and colors change almost instantly if you vary one of the layer thickness values.

·	Try to investigate how you can influence the width and the position of the strong reflectance peak.

Set the SiO2 thickness close to 70 nm and the TiO2 thickness close to 50 nm. This leads to a L* value of the transmitted radiation below 15 which appears to be completely black (at least on my screen). To get an impression of dark colors like this we have introduced the L*=70 version of the same color.