? Infrared filter, generally, belong to one of two categories. The simplest, physically, is the absorptive filter, while the latter category, that of interference or dichroic filters, can be quite complex. Selective optical transmission infrared filter has a certain property (usually, a specific range of wavelengths, that is, the color range of light), while blocking the rest.
? Infrared filter are usually made from glass to which various inorganic or organic compounds have been added. These compounds absorb some wavelengths of light while transmitting others. The compounds can also be added to plastic (often polycarbonate or acrylic) to produce gel filters, which are lighter and cheaper than glass-based filters. Infrared filter of the etalons are another variation: transparent cubes or fibers whose polished ends form mirrors tuned to resonate with specific wavelengths. These are often used to separate channels in telecommunications networks that use wavelength division multiplexing on long-haul optic fibers.