4/4/2014 Beam splitter - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Beamsplitter 1/2

Schematic illustration of a beam splitter

cube.

1 - Incident light

2 - 50% Transmitted light

3 - 50% Reflected light

In practice, the reflective layer absorbs

some light.

BeamsplittersAluminum coated beam splitter.

Beam splitterFrom Wikipedia, the free encyclopedia

(Redirected from Beamsplitter)

See also: Diffractive beam splitter

A beam splitter is an optical device that splits a beam of lightin two. It is the crucial part of most interferometers.

In its most common form, a cube, it is made from two triangularglass prisms which are glued together at their base usingpolyester, epoxy, or urethane-based adhesives. The thicknessof the resin layer is adjusted such that (for a certain wavelength)half of the light incident through one "port" (i.e., face of thecube) is reflected and the other half is transmitted due tofrustrated total internal reflection. Polarizing beam splitters, suchas the Wollaston prism, use birefringent materials, splitting lightinto beams of differing polarization.

Another design is the use of a half-silvered mirror, a sheet ofglass or plastic with a transparently thin coating of metal, nowusually aluminium deposited from aluminium vapor. Thethickness of the deposit is controlled so that part (typically half)

of the light which isincident at a 45-degree angle and notabsorbed by thecoating is transmitted,and the remainder isreflected. A very thinhalf-silvered mirrorused in photographyis often called apellicle mirror. Toreduce loss of lightdue to absorption by the reflective coating, so-called "swiss cheese"

beam splitter mirrors have been used. Originally, these were sheets of highly polished metal perforated withholes to obtain the desired ratio of reflection to transmission. Later, metal was sputtered onto glass so as to forma discontinuous coating, or small areas of a continuous coating were removed by chemical or mechanical actionto produce a very literally "half-silvered" surface.

Instead of a metallic coating, a dichroic optical coating may be used. Depending on its characteristics, the ratioof reflection to transmission will vary as a function of the wavelength of the incident light. Dichroic mirrors areused in some ellipsoidal reflector spotlights to split off unwanted infrared (heat) radiation, and as output couplersin laser construction.

A third version of the beam splitter is a dichroic mirrored prism assembly which uses dichroic optical coatings todivide an incoming light beam into a number of spectrally distinct output beams. Such a device was used inthree-pickup-tube color television cameras and the three-strip Technicolor movie camera. It is currently used inmodern three-CCD cameras. An optically similar system is used in reverse as a beam-combiner in three-LCDprojectors, in which light from three separate monochrome LCD displays is combined into a single full-colorimage for projection.

4/4/2014 Beam splitter - Wikipedia, the free encyclopedia

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pixel=130

Beam splitters with single mode fiber for PON networks use the single mode behavior to split the beam. Thesplitter is done by physically splicing two fibers "together" as an X.

Arrangements of mirrors or prisms used as camera attachments to photograph stereoscopic image pairs withone lens and one exposure are sometimes called "beam splitters", but that is a misnomer, as they are effectively apair of periscopes redirecting rays of light which are already non-coincident. In some very uncommonattachments for stereoscopic photography, mirrors or prism blocks similar to beam splitters perform theopposite function, superimposing views of the subject from two different perspectives through color filters toallow the direct production of an anaglyph 3D image, or through rapidly alternating shutters to record sequentialfield 3D video.

Phase shift

A beam splitter which consists of a glass plate with a reflector on one side, gives a

180 degree phase shift depending on the input used (see figure).[1] Waves which arenot reflected has no phase shift. Waves which enters from the reflector side (red), thereflection is shifted . Waves which enter from the glass side (blue) have no phaseshift. According to Fresnel equations there is only a phase shift if n2 > n1 (n =refractive index). This is the case in the transition of air to reflector, but not from glassto reflector.

References

1. ^ Zetie, K P; S F Adams and R M Tocknell, How does a MachZehnder interferometer work?(https://www.cs.princeton.edu/courses/archive/fall06/cos576/papers/zetie_et_al_mach_zehnder00.pdf),retrieved 13 February 2014

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