Dichroic prism
A dichroic prism is an optical prism that splits a light beam into two beams of different spectra or colors . It is usually made of glass, with certain surfaces provided with dichroic mirrors that reflect or transmit light depending on its wavelength.
Function and application
One application is in color video cameras with three CCD sensors , in the so-called 3-chip CCD process . Two dichroic prisms are used here, as shown in the adjacent figures, to split the light into red, green and blue components, and these are each fed to an assigned image sensor (CCD).
The light beam enters the first prism (A). The blue component is reflected by the dichroic filter (F 1 ), while longer wavelengths can pass. These enter the second prism (B) and are divided by a second filter (F 2 ), which reflects the red component of the light. The remaining green part comes out at the back. The angles of the prisms are chosen so that the blue and red components are deflected by means of total reflection in the prism. There is also a small air gap between prisms (A) and (B) for this purpose. Other filters are often used to improve the color characteristics.
Conversely, dichroic prisms can also be used to combine light of different wavelengths. In some video projectors , separate modulators are used for red, green and blue components, which combine light via dichroic prisms in order to be projected through a lens. The arrangement mainly used here is called the X-Cube .