Beam splitter
Encyclopedia
A beam splitter is an optical device
that splits a beam of light
in two. It is the crucial part of most interferometer
s.
In its most common form, a rectangle, it is made from two triangular glass prism
s which are glued together at their base using Canada balsam
. The thickness of the resin layer is adjusted such that (for a certain wavelength
) half of the light incident through one "port" (i.e., face of the cube) is reflected
and the other half is transmitted due to frustrated total internal reflection. Polarizing beam splitters
, such as the Wollaston prism
, use birefringent materials, splitting light into beams of differing polarization.
Another design is the use of a half-silvered mirror
. This is a plate of glass
with a thin coating
of aluminium
(usually deposited from aluminium vapor
) with the thickness of the aluminium coating such that part, typically half, of light incident at a 45-degree angle is transmitted, and the remainder reflected. Instead of a metallic coating, a dielectric
optical coating
may be used. Such mirrors are commonly used as output coupler
s in laser construction
. A half-silvered mirror used in photography
is often called a pellicle mirror
. Depending on the coating that is being used, reflection/transmission ratios may differ in function of the wavelength
.
A third version of the beam splitter is a dichroic mirrored prism
assembly which uses dichroic
optical coating
s to divide an incoming light beam into a number of spectrally distinct output beams. Such a device was used in multi-tube color television cameras, in the three-film Technicolor
movie cameras as well as modern, three-CCD cameras. It is also used in the 3 LCD projectors to separate colors and in ellipsoidal reflector spotlights to eliminate heat radiation.
Beam splitters are also used in stereo photography to shoot stereo photos using a single shot with a non-stereo camera. The device attaches in place of the lens
of the camera. Some argue that "image splitter" is a more proper name for this device.
Beam splitters with single mode fiber for PON networks
use the single mode behavior to split the beam. The splitter is done by physically splicing two fibers "together" as an X.
Optical instrument
An optical instrument either processes light waves to enhance an image for viewing, or analyzes light waves to determine one of a number of characteristic properties.-Image enhancement:...
that splits a beam of light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
in two. It is the crucial part of most interferometer
Interferometry
Interferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...
s.
In its most common form, a rectangle, it is made from two triangular glass prism
Prism (optics)
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 geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...
s which are glued together at their base using Canada balsam
Canada balsam
Canada balsam, also called Canada turpentine or balsam of fir, is a turpentine which is made from the resin of the balsam fir tree of boreal North America...
. The thickness of the resin layer is adjusted such that (for a certain wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
) half of the light incident through one "port" (i.e., face of the cube) is reflected
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
and the other half is transmitted due to frustrated total internal reflection. Polarizing beam splitters
Polarizer
A polarizer is an optical filter that passes light of a specific polarization and blocks waves of other polarizations. It can convert a beam of light of undefined or mixed polarization into a beam with well-defined polarization. The common types of polarizers are linear polarizers and circular...
, such as the Wollaston prism
Wollaston prism
A Wollaston prism is an optical device, invented by William Hyde Wollaston, that manipulates polarized light. It separates randomly polarized or unpolarized light into two orthogonal linearly polarized outgoing beams....
, use birefringent materials, splitting light into beams of differing polarization.
Another design is the use of a half-silvered mirror
Mirror
A mirror is an object that reflects light or sound in a way that preserves much of its original quality prior to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection...
. This is a plate of glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
with a thin coating
Coating
Coating is a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wetability, corrosion resistance, wear resistance, and scratch resistance...
of aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
(usually deposited from aluminium vapor
Vapor
A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point....
) with the thickness of the aluminium coating such that part, typically half, of light incident at a 45-degree angle is transmitted, and the remainder reflected. Instead of a metallic coating, a dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
optical coating
Optical coating
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 coating is an antireflection coating, which reduces unwanted reflections from surfaces, and...
may be used. Such mirrors are commonly used as output coupler
Output coupler
An output coupler is a partially reflective mirror used in lasers to extract a portion of the laser beam from the optical resonator....
s in laser construction
Laser construction
A laser is constructed from three principal parts:*An energy source ,*A gain medium or laser medium, and*Two or more mirrors that form an optical resonator.-Pump source:...
. A half-silvered mirror used in photography
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
is often called a pellicle mirror
Pellicle mirror
right|thumb|The pellicle mirror of the [[Canon EOS RT]]A pellicle mirror is an ultra-thin, ultra-lightweight semi-transparent mirror employed in the light path of an optical instrument, splitting the light beam into two separate beams, both of reduced light intensity...
. Depending on the coating that is being used, reflection/transmission ratios may differ in function of the wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
.
A third version of the beam splitter is a dichroic mirrored prism
Dichroic prism
A dichroic prism is a prism that splits light into two beams of differing wavelength . 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...
assembly which uses dichroic
Dichroism
Dichroism has two related but distinct meanings in optics. A dichroic material is either one which causes visible light to be split up into distinct beams of different wavelengths , or one in which light rays having different polarizations are absorbed by different amounts.The original meaning of...
optical coating
Optical coating
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 coating is an antireflection coating, which reduces unwanted reflections from surfaces, and...
s to divide an incoming light beam into a number of spectrally distinct output beams. Such a device was used in multi-tube color television cameras, in the three-film Technicolor
Technicolor
Technicolor is a color motion picture process invented in 1916 and improved over several decades.It was the second major process, after Britain's Kinemacolor, and the most widely used color process in Hollywood from 1922 to 1952...
movie cameras as well as modern, three-CCD cameras. It is also used in the 3 LCD projectors to separate colors and in ellipsoidal reflector spotlights to eliminate heat radiation.
Beam splitters are also used in stereo photography to shoot stereo photos using a single shot with a non-stereo camera. The device attaches in place of the lens
Photographic lens
A camera lens is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.While in principle a simple convex lens will suffice, in...
of the camera. Some argue that "image splitter" is a more proper name for this device.
Beam splitters with single mode fiber for PON networks
Passive optical network
A passive optical network is a point-to-multipoint, fiber to the premises network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 16-128. A PON consists of an optical line terminal at the service provider's central...
use the single mode behavior to split the beam. The splitter is done by physically splicing two fibers "together" as an X.