Wire Grid Polarizers
Wire Grid Polarizers
Wire grid polarizers are a class of polarizers that use fine metal wires to restrict E-field oscillation for s-polarized light. Fine metal wires typically 100 nm to several microns apart are lithographically deposited on substrates depending on the desired wavelength range. For the s-component, the metal grid works like a typical metal surface as electrons are excited along the wire length. As a result, the s-polarization is almost completely reflected. In case of the p-component, electrons can only be excited along with wire width, which is in the sub-micron range. Hence, most of the p-polarized light is transmitted. A wire grid polarizer is typically characterized by the extinction ratio (ER) and polarization efficiency (PE).
Wire grid polarizers offer several advantages over conventional polarizers. For instance, they are suited for applications that require a high ER. They are also inherently broadband and can be designed to operate across UV-Visible-IR by choosing appropriate substrates. Finally, they have greater thermal stability and can operate under high temperature or high flux conditions. These features make them ideal for high quality projection systems, military applications, medical imaging, simulators and even digital cinema. They are commonly used:
- to polarize radiation from an unpolarized source
- to attenuate radiation from a polarized source
- in reflectance accessories for dispersive and FTIR spectrophotometers
- in the study of metal surfaces and crystal structures at grazing incidence
Optometrics manufactures ruled wire grid polarizers on CaF2 (Calcium Fluoride) and ZnSe (Zinc Selenide), together covering a wavelength range from 2.5 to 20 microns and holographic wire grid polarizers on CaF2 (Calcium Fluoride), ZnSe (Zinc Selenide), BaF2 (Barium Fluoride), KRS-5 and Ge (Germanium), covering a wavelength region from 2.5 to 30 microns.
Two polarizers can be used:
- in series to achieve extinction ratios greater than 90,000:1
- in series to polarize and attenuate a source
- in conjunction with a beamsplitter to create a polarizing beamsplitter simply by placing one polarizer in each beam tuned to opposite polarizations