Dichroic prism

A dichroic prism is an optical prism which splits a light beam into two beams having different spectra and color. It is usually made ​​of glass, with certain surfaces are provided with dichroic mirrors, the light of which wavelength reflect or transmit dependent.

Function and application

An application can be found in color video cameras using three CCD sensors, the so-called 3-chip CCD method. Here are two dichroic prisms are used as shown in the adjacent images to split the light into red, green and blue components, and this ever an associated image sensor ( CCD) supplied.

The light beam enters the first prism (A). The blue component is reflected by the dichroic filter (F1), while longer wavelengths can happen. These are entering the second prism (B ) and by a second filter (F2 ) divided, which reflects the red portion of the light. The remaining amount of green emerges from behind. The angles of the prisms are selected such that blue and red component is deflected by total reflection in the prism. For this purpose a small air gap between the prisms ( A) and ( B) is present. In order to improve the color characteristics often even more filters.

Conversely, dichroic prisms can be used to combine light of different wavelengths. In some projectors separate modulators are used for red, green, and blue components, the light via dichroic prisms combined to be projected by a lens. The arrangement mainly used here is referred to as X -Cube.