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Optical Filters

Definition: devices with a wavelength-dependent transmission or reflectance

German: optische Filter

Category: photonic devices

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An optical filter is usually meant to be a component with a wavelength-dependent (actually frequency-dependent) transmittance or reflectance, although there are also filters where the dependence is on polarization or spatial distribution, or some uniform level of attenuation is provided. Filters with particularly weak wavelength dependence of the transmittance are called neutral density filters.

Types of Optical Filters

There are many different types of optical filters, based on different physical principles. Some examples of optical filters are:

Concerning the shape of the transmission curve, there are

  • bandpass filters, transmitting only a certain wavelength range
  • notch filters, eliminating light of a certain wavelength range, e.g. by reflecting it
  • edge filters, transmitting only wavelengths above or below a certain value (high-pass and low-pass filters)
edge filter
Figure 1: Wavelength-dependent reflectance of a dielectric edge filter with high transmission below 980 nm and high reflectance above 1030 nm. Starting from an analytically formulated design, the performance has been further optimized numerically (using the software RP Coating). Such a filter can be used for injecting pump light into the ytterbium-doped crystal of a laser.


Some examples for the many applications of optical filters are:


The RP Photonics Buyer's Guide contains 221 suppliers for optical filters. Among them:

See also: neutral density filters, rugate filters, tunable optical filters, volume Bragg gratings, acousto-optic tunable filters, hot mirrors, cold mirrors, wavelength tuning, gain equalization, optical fiber communications
and other articles in the category photonic devices

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