### Polarizers

 Polarizers are optical filters that pass radiation of a specified polarization and blocks radiation of other polarization. Thin-film linear polarizers are glass substrates with specially designed and deposited optical coatings (polarizers). The thin film polarizer can either be parallel, working at a particular incidence angle, or a wedge of glass that is cemented to a second wedge to form a polarization cube with the optical coating cutting diagonally across the center. Example: A 50-layer thin film polarizer designed by OptiLayer for the spectral range from 780 nm to 820 nm and the incidence angle of 45 degrees. Materials: Nb2O5 and SiO2; Thinnest layer is 64 nm. Ratio $$T_s/T_p=400$$. You can design such a filter in several seconds. In order to specify the desired specifications, special (user-defined targets) can be used. You can reduce the number of layers step by step (for example, removing neighbor pairs of layer H and L) and make the refinement and obtain a  structure  with a smaller number of layers. With the of Digitize option you can control the ratio between Ts and Tp and achieve a balance between the required ratio as well as acceptable number of layers.

### Polarizing Beamsplitters

 The main difference between a polarizer and a polarizing beamsplitter: In the polarizer only one polarized beam is required; In the polarizing beamsplitter both beams are to be utilized. A polarizing beamsplitter can be used as a polarizer. The performance in transmission or reflection of both devices is usually characterized by their degree pf polarization or by the extinction ratio ER: $ER=\frac{T_{desired}}{T_{undesired}}$ In a polarizing beamsplitter a high degree of polarization is required in both beams and it is more difficult to achieve. In order to specify the desired specifications, special (user-defined targets) can be used. Example: 21-layer polarizing beamsplitter for the spectral range from 520 nm to 560 nm and incidence angle of 45 degrees. Incidence Medium is Glass and Substrate is Glass. The coating is cemented between two Glass substrates. Extinction ratio is more than 3000.