We are happy to answer any questions that you may have about the functionality and use of wire grid polarizers. As a start, we list below some of the typical questions that a customer may have:
1. What are the main uses of wire grid polarizer products?
Free-standing wire grid polarizers are used as low-loss polarizing elements for millimetre and sub-millimetre wavelength radiation (e.g. in the far-infrared wavelength or terahertz frequency region). Typical applications include use as linear polarizers of mid-IR to mm wavelength radiation, beam splitters or dividers in polarizing interferometers, couplers for long-wavelength radiation, and variable attenuators or variable reflectors. Note that because they are polarizing elements, their use as an attenuator, reflector, or coupler will introduce a polarization preference in the system.
2. What is a free-standing wire grid polarizer?
A free-standing wire grid polarizer consists of an array of thin parallel conductive wires (typically 5 to 50 microns in diameter) supported by a frame around the circumference. This wire grid array will reflect incoming radiation where the electric field is polarized parallel to the wires, and transmit radiation where the electric field is polarized orthogonal to the wires. In this way, a wire grid acts as a polarizing element both in transmission and reflection.
3. What is the theory behind how a free-standing polarizer works?
This question is addressed thoroughly in the literature and for a more detailed answer you should refer to, for instance, Hecht (1987). The underlying principal of how a free-standing wire grid polarizer works is based on how the incident electromagnetic radiation interacts with the wire grid depending on the electric field polarization plane relative to the grid orientation.
For the situation where the electric field is polarized parallel to the conductive wire elements of the wire grid, the incident radiation will cause free electrons in the wire to oscillate along its length. This interaction leads to re-radiation and some dissipation of energy though joule heating. The re-radiated wave in the forward direction acts to cancel the transmitted wave, and the re-radiated wave in the reverse direction appears as reflected radiation. In this way the parallel component of the incident wave is stripped out of the transmitted radiation, and appears as a reflected wave.
Given the small diameter of the wires, the orthogonal polarization component of the incident radiation does not interact with the wire grid in the same manner given the inability to cause free electrons to flow in this direction. The orthogonal polarization component is thus completely transmitted by the grid, in the absence of any reflection.
For this process to work efficiently the space between the wires must be less than the wavelength of the radiation. In this way the wire spacing places a limit on the lower wavelength performance of a wire-grid polarizer, and there is some wavelength dependence of a wire-grid polarizer’s performance.
4. Why is tungsten wire used for wire grid polarizers?
Of the materials that are available on a commercial basis, tungsten wire is seen to offer favourable characteristics for use in wire grid polarizers – principally, that it has:
- High tensile strength, which allows the wire to be held firmly in place across the support frame
- Good conductivity, which is a necessary prerequisite for polarization selectivity of a wire grid,
- Excellent corrosion resistance, which allows the polarizer to continue working over an acceptable period of time.
Hecht, E. (1987). Optics, 2nd Ed, Addison Wesley.