Dichroic prism

Dichroic prism
A trichroic prism assembly

A dichroic prism is a prism that splits light into two beams of differing wavelength (colour). They are usually constructed of one or more glass prisms with dichroic optical coatings that selectively reflect or transmit light depending on the light's wavelength. That is, certain surfaces within the prism act as dichroic filters. These are used as beam splitters in many optical instruments. (See dichroism for the etymology of the term.)

One common application of dichroic prisms is in some camcorders and high-quality digital cameras. A trichroic prism assembly is a combination of two dichroic prisms which are used to split an image into red, green, and blue components so they can be separately detected on three CCD arrays.

A possible layout for the device is shown in the diagram. A light beam enters the first prism (A) and the blue component of the beam is reflected from a low-pass filter coating (F1) that reflects blue light (high-frequency), but transmits longer wavelengths (lower frequencies). The blue beam undergoes total internal reflection from the front of prism A and exits it through a side face. The remainder of the beam enters the second prism (B) and is split by a second filter coating (F2) that reflects red light but transmits shorter wavelengths. The red beam is also totally internally reflected due to a small air-gap between prisms A and B. The remaining green component of the beam travels through prism C.

The trichroic prism assembly can be used in reverse to combine red, green and blue beams into a coloured image, and is used in this way in some projector devices. Assemblies with more than 3 beams are possible.

Contents

Advantages of dichroic prism color separation

When used for color separation in an imaging system this method has some advantages over other methods, like a Bayer filter. Most of those characteristics derive from the usage of dichroic filters and are in common with those.

  • No light is absorbed, all light being directed to one of the output beams.
  • Better color separation than with most other filters.
  • Easy to fabricate for any combination of pass bands.

Disadvantages of dichroic prism color separation

  • Since a dichroic prism uses dichroic filters, the exact bandpass of each filter depends on the light incidence angle.
  • Maximum lens numerical aperture might be restricted due to the geometry of the optical path inside the assembly.
  • The exact bandpass depends on the lens numerical aperture, since this factor changes the average light incidence angle in the filters.
  • Since some of the glass surfaces are at an angle against the incident beam some polarization by reflection effects can result.


See also

External links


Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • Dichroic filter — Dichroic filters A dichroic filter, thin film filter, or interference filter is a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, dichroic mirrors and dichroic… …   Wikipedia

  • Prism (optics) — For other uses, see Prism (disambiguation). A plastic prism In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional… …   Wikipedia

  • Dichroism — Dichroic redirects here. For the filter, see dichroic filter. For the glass, see dichroic glass. Lampworked dichroic glass bead Dichroism has two related but distinct meanings in optics. A dichroic material is either one which causes visible… …   Wikipedia

  • Thin-film optics — Dichroic filters are created using thin film optics. A pattern …   Wikipedia

  • Filter (optics) — Coloured and Neutral Density filters Optical filters are devices which selectively transmit light of different wavelengths, usually implemented as plane glass or plastic devices in the optical path which are either dyed in the mass or have… …   Wikipedia

  • List of optical topics — Probably some Wikipedia articles on topics in optics are not yet listed on this page. If you cannot find the topic you are interested in on this page, the article may nonetheless exist; you can try to find it using the Search box, or look in and… …   Wikipedia

  • Index of optics articles — Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it.[1] Optics usually describes the behavior of visible,… …   Wikipedia

  • Optical coating — Optically coated mirrors and lenses. An optical coating is one or more thin layers of material deposited on an optical component such as a lens or mirror, which alters the way in which the optic reflects and transmits light. One type of optical… …   Wikipedia

  • Digital cinematography — Arriflex D 21 Panavision Genesis …   Wikipedia

  • Image sensor — A CCD image sensor on a flexible circuit board …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”