What is the beam splitter?

Beam splitters are optical devices that split a beam of light into two or more beams of light, which is a key part of most interferometers. It is usually composed of a metal film or a dielectric film.

The most common shape is a cube made of two triangular glass prisms glued together on a substrate using polyester, epoxy or urethane adhesives. The thickness of the resin layer is adjusted so that half of a (certain wavelength) of light incident through one "port" (ie, cube-sided) is reflected and the other half is continuously transmitted due to total internal reflection. Polarizing beamsplitters, such as Wollaston prisms, use birefringent material to split light into differently polarized light beams.

Another design is to use a half-silvered mirror, a piece of glass or plastic, a clear, thin metal coating that is now usually aluminum vapor deposited with aluminum. The thickness of the deposit is controlled so that the portion (typically half) of the light that is incident at a 45 degree angle and that is not absorbed by the coating is transmitted and the remaining portion is reflected. Very thin half-silvered mirrors for photography are commonly referred to as pellicle mirrors. In order to reduce the loss of light due to the absorption of the reflective coating, so-called "Swiss Cheese" beamsplitters have been used. Initially, these were perforated, highly polished metal sheets to achieve the desired reflectance and transmittance. Thereafter, the metal is splashed onto the glass to form a discontinuous coating, or a small area of continuous coating is removed by chemical or mechanical action to create a very literally "half-silvered" surface.

Instead of a metal coating, a dichroic optical coating can be used. Depending on its nature, the ratio of reflection to transmission will vary as a function of the wavelength of the incident light. Beamsplitters are used for some elliptical reflector spotlights to disperse unwanted infrared (thermal) radiation and output couplers in the laser structure.

A third type of beamsplitter is a dichroic mirror prism assembly that uses a dichroic optical coating to split an incident beam into a plurality of spectrally distinct output beams. Such devices are used in tri-color tube video cameras and tri-color color film cameras. It is currently used in modern three CCD cameras. The optically similar system is used as a reverse for the beam combiner in a three-LCD projector in which light from three separate monochrome LCD displays is combined into a single full-color image for projection.

Splitters for single-mode fiber for PON networks use single-mode behavior to split the beam. The splitters are "spliced" to X by splitting the two fibers.

Using a single lens and a single exposure point to capture the alignment of the mirrors or prisms of a stereoscopic pair is sometimes referred to as a "beam splitter," but this is an improper use of words because they are actually pairs of periscopes that refract The light is not out of coincidence. In some rare cases of stereo photography attachments, the mirror or prism block performs the opposite function as the beamsplitter, with the overlayed theme allowing direct production of the embossed 3-d image from two different perspective views through a color filter, or by rapidly alternating louvers Order field 3D video.

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