Nokia Bell Labs is an industrial research and scientific development company owned by Finnish company Nokia. Its headquarters are located in New Jersey. Other laboratories are located around the world. Bell Labs has its origins in the complex past of the Bell System. In the late 19th century, the laboratory began as the Western Electric Engineering Department and was located at 463 West Street in New York City. In 1925, after years of conducting research and development under Western Electric, the Engineering Department was reformed into Bell Telephone Laboratories and under the shared ownership of American Telephone & Telegraph Company and Western Electric. Researchers working at Bell Labs are credited with the development of radio astronomy, the transistor, the laser, the photovoltaic cell, the charge-coupled device, information theory, the Unix operating system, the programming languages C, C++, S. Nine Nobel Prizes have been awarded for work completed at Bell Laboratories. In 1880, when the French government awarded Alexander Graham Bell the Volta Prize of 50,000 francs (approximately US$10,000 at that time for the invention of the telephone, he used the award to fund the Volta Laboratory in Washington, D.
C. in collaboration with Sumner Tainter and Bell's cousin Chichester Bell. The laboratory was variously known as the Volta Bureau, the Bell Carriage House, the Bell Laboratory and the Volta Laboratory, it focused on the analysis and transmission of sound. Bell used his considerable profits from the laboratory for further research and education to permit the " diffusion of knowledge relating to the deaf": resulting in the founding of the Volta Bureau, located at Bell's father's house at 1527 35th Street N. W. in Washington, D. C, its carriage house became their headquarters in 1889. In 1893, Bell constructed a new building close by at 1537 35th Street N. W. to house the lab. This building was declared a National Historic Landmark in 1972. After the invention of the telephone, Bell maintained a distant role with the Bell System as a whole, but continued to pursue his own personal research interests; the Bell Patent Association was formed by Alexander Graham Bell, Thomas Sanders, Gardiner Hubbard when filing the first patents for the telephone in 1876.
Bell Telephone Company, the first telephone company, was formed a year later. It became a part of the American Bell Telephone Company. American Telephone & Telegraph Company and its own subsidiary company, took control of American Bell and the Bell System by 1889. American Bell held a controlling interest in Western Electric whereas AT&T was doing research into the service providers. In 1884, the American Bell Telephone Company created the Mechanical Department from the Electrical and Patent Department formed a year earlier. In 1896, Western Electric bought property at 463 West Street to station their manufacturers and engineers, supplying AT&T with their product; this included everything from telephones, telephone exchange switches, transmission equipment. In 1925, Bell Laboratories was developed to better consolidate the research activities of the Bell System. Ownership was evenly split between Western Electric and AT&T. Throughout the next decade the AT&T Research and Development branch moved into West Street.
Bell Labs carried out consulting work for the Bell Telephone Company, U. S. government work, a few workers were assigned to basic research. The first president of research at Bell Labs was Frank B. Jewett who stayed there until 1940. By the early 1940s, Bell Labs engineers and scientists had begun to move to other locations away from the congestion and environmental distractions of New York City, in 1967 Bell Laboratories headquarters was relocated to Murray Hill, New Jersey. Among the Bell Laboratories locations in New Jersey were Holmdel, Crawford Hill, the Deal Test Site, Lincroft, Long Branch, Neptune, Piscataway, Red Bank and Whippany. Of these, Murray Hill and Crawford Hill remain in existence; the largest grouping of people in the company was in Illinois, at Naperville-Lisle, in the Chicago area, which had the largest concentration of employees prior to 2001. There were groups of employees in Indianapolis, Indiana. Since 2001, many of the former locations closed; the Holmdel site, a 1.9 million square foot structure set on 473 acres, was closed in 2007.
The mirrored-glass building was designed by Eero Saarinen. In August 2013, Somerset Development bought the building, intending to redevelop it into a mixed commercial and residential project. A 2012 article expressed doubt on the success of the newly named Bell Works site however several large tenants had announced plans to move in through 2016 and 2017 Bell Laboratories was, is, regarded by many as the premier research facility of its type, developing a wide range of revolutionary technologies, including radio astronomy, the transistor, the laser, information theory, the operating system Unix, the programming languages C and C++, solar cells, the CCD, floating-gate MOSFET, a whole host of optical and wired communications
The micrometre or micrometer commonly known by the previous name micron, is an SI derived unit of length equalling 1×10−6 metre. The micrometre is a common unit of measurement for wavelengths of infrared radiation as well as sizes of biological cells and bacteria, for grading wool by the diameter of the fibres; the width of a single human hair ranges from 10 to 200 μm. The longest human chromosome is 10 μm in length. Between 1 μm and 10 μm: 1–10 μm – length of a typical bacterium 10 μm – Size of fungal hyphae 5 μm – length of a typical human spermatozoon's head 3–8 μm – width of strand of spider web silk about 10 μm – size of a fog, mist, or cloud water droplet Between 10 μm and 100 μm about 10–12 μm – thickness of plastic wrap 10 to 55 μm – width of wool fibre 17 to 181 μm – diameter of human hair 70 to 180 μm – thickness of paper The term micron and the symbol μ were accepted for use in isolation to denote the micrometre in 1879, but revoked by the International System of Units in 1967; this became necessary because the older usage was incompatible with the official adoption of the unit prefix micro-, denoted μ, during the creation of the SI in 1960.
In the SI, the systematic name micrometre became the official name of the unit, μm became the official unit symbol. In practice, "micron" remains a used term in preference to "micrometre" in many English-speaking countries, both in academic science and in applied science and industry. Additionally, in American English, the use of "micron" helps differentiate the unit from the micrometer, a measuring device, because the unit's name in mainstream American spelling is a homograph of the device's name. In spoken English, they may be distinguished by pronunciation, as the name of the measuring device is invariably stressed on the second syllable, whereas the systematic pronunciation of the unit name, in accordance with the convention for pronouncing SI units in English, places the stress on the first syllable; the plural of micron is "microns", though "micra" was used before 1950. The official symbol for the SI prefix micro- is a Greek lowercase mu. In Unicode, there is a micro sign with the code point U+00B5, distinct from the code point U+03BC of the Greek letter lowercase mu.
According to the Unicode Consortium, the Greek letter character is preferred, but implementations must recognize the micro sign as well. Most fonts use the same glyph for the two characters. Metric prefix Metric system Orders of magnitude Wool measurement The dictionary definition of micrometre at Wiktionary
An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include rectangular waveguides. Optical waveguides are used as components in integrated optical circuits or as the transmission medium in local and long haul optical communication systems. Optical waveguides can be classified according to their geometry, mode structure, refractive index distribution and material. Practical rectangular-geometry optical waveguides are most understood as variants of a theoretical dielectric slab waveguide called a planar waveguide; the slab waveguide consists of three layers of materials with different dielectric constants, extending infinitely in the directions parallel to their interfaces. Light may be confined in the middle layer by total internal reflection; this occurs only if the dielectric index of the middle layer is larger than that of the surrounding layers. In practice slab waveguides are not infinite in the direction parallel to the interface, but if the typical size of the interfaces is much much larger than the depth of the layer, the slab waveguide model will be an excellent approximation.
Guided modes of a slab waveguide cannot be excited by light incident from the top or bottom interfaces. Light must be injected with a lens from the side into the middle layer. Alternatively a coupling element may be used to couple light into the waveguide, such as a grating coupler or prism coupler. One model of guided modes is that of a plane wave reflected back and forth between the two interfaces of the middle layer, at an angle of incidence between the propagation direction of the light and the normal, or perpendicular direction, to the material interface is greater than the critical angle; the critical angle depends on the index of refraction of the materials, which may vary depending on the wavelength of the light. Such propagation will result in a guided mode only at a discrete set of angles where the reflected planewave does not destructively interfere with itself; this structure confines electromagnetic waves only in one direction, therefore it has little practical application. Structures that may be approximated as slab waveguides do, sometimes occur as incidental structures in other devices.
Waveguide are used in Augmented reality glasses, there are 2 technologies: diffractive waveguides and reflective waveguides. Augmented reality systems guru Karl Guttag compared the optics of diffractive waveguides against the competing technology, reflective waveguides. A strip waveguide is a strip of the layer confined between cladding layers; the simplest case is a rectangular waveguide, formed when the guiding layer of the slab waveguide is restricted in both transverse directions rather than just one. Rectangular waveguides are used in laser diodes, they are used as the basis of such optical components as Mach–Zehnder interferometers and wavelength division multiplexers. The cavities of laser diodes are constructed as rectangular optical waveguides. Optical waveguides with rectangular geometry are produced by a variety of means by a planar process; the field distribution in a rectangular waveguide cannot be solved analytically, however approximate solution methods, such as Marcatili's method, Extended Marcatili's method and Kumar's method, are known.
A rib waveguide is a waveguide in which the guiding layer consists of the slab with a strip superimposed onto it. Rib waveguides provide confinement of the wave in two dimensions. Optical waveguides maintain a constant cross-section along their direction of propagation; this is for example the case of rib waveguides. However, waveguides can have periodic changes in their cross-section while still allowing lossless transmission of light via so-called Bloch modes; such waveguides are referred as photonic crystal waveguides. Optical waveguides find their most important application in photonics. Configuring the waveguides in 3D space provides integration between electronic components on a chip and optical fibers; such waveguides may be designed for a single mode propagation of infrared light at telecommunication wavelengths, configured to deliver optical signal between input and output locations with low loss. One of the methods for constructing such waveguides utilizes photorefractive effect in transparent materials.
An increase in the refractive index of a material may be induced by nonlinear absorption of pulsed laser light. In order maximize the increase of the refractive index, a short laser pulses are used, focused with a high NA microscope objective. By translating the focal spot through a bulk transparent material the waveguides can be directly written. A variation of this method uses a low NA microscope objective and translates the focal spot along the beam axis; this improves the overlap between the focused laser beam and the photorefractive material, thus reducing power needed from the laser. When transparent material is exposed to an unfocused laser beam of sufficient brightness to initiate photorefractive effect, the waveguides may start forming on their own as a result of an accumulated self-focusing; the formation of such waveguides leads to a breakup of the laser beam. Continued exposure results in a buildup of the refractive index towards the centerline of each waveguide, collapse of the mode field diameter of the propagating light.
Such waveguides remain permanently in the glass and can be pho
Quantum tunnelling or tunneling is the quantum mechanical phenomenon where a subatomic particle passes through a potential barrier that it cannot surmount under the provision of classical mechanics. Quantum tunnelling plays an essential role in several physical phenomena, such as the nuclear fusion that occurs in main sequence stars like the Sun, it has important applications in the tunnel diode, quantum computing, in the scanning tunnelling microscope. The effect was predicted in the early 20th century, its acceptance as a general physical phenomenon came mid-century. Fundamental quantum mechanical concepts are central to this phenomenon, which makes quantum tunnelling one of the novel implications of quantum mechanics. Quantum tunneling is projected to create physical limits to the size of the transistors used in microprocessors, due to electrons being able to tunnel past them if the transistors are too small. Tunnelling is explained in terms of the Heisenberg uncertainty principle that the quantum object can be known as a wave or as a particle in general.
Quantum tunnelling was developed from the study of radioactivity, discovered in 1896 by Henri Becquerel. Radioactivity was examined further by Marie Curie and Pierre Curie, for which they earned the Nobel Prize in Physics in 1903. Ernest Rutherford and Egon Schweidler studied its nature, verified empirically by Friedrich Kohlrausch; the idea of the half-life and the possibility of predicting decay was created from their work. In 1901, Robert Francis Earhart, while investigating the conduction of gases between spaced electrodes using the Michelson interferometer to measure the spacing, discovered an unexpected conduction regime. J. J. Thomson commented. In 1911 and 1914, then-graduate student Franz Rother, employing Earhart's method for controlling and measuring the electrode separation but with a sensitive platform galvanometer, directly measured steady field emission currents. In 1926, using a still newer platform galvanometer of sensitivity 26 pA, measured the field emission currents in a "hard" vacuum between spaced electrodes.
Quantum tunneling was first noticed in 1927 by Friedrich Hund when he was calculating the ground state of the double-well potential and independently in the same year by Leonid Mandelstam and Mikhail Leontovich in their analysis of the implications of the new Schrödinger wave equation for the motion of a particle in a confining potential of a limited spatial extent. Its first application was a mathematical explanation for alpha decay, done in 1928 by George Gamow and independently by Ronald Gurney and Edward Condon; the two researchers solved the Schrödinger equation for a model nuclear potential and derived a relationship between the half-life of the particle and the energy of emission that depended directly on the mathematical probability of tunnelling. After attending a seminar by Gamow, Max Born recognised the generality of tunnelling, he realised that it was not restricted to nuclear physics, but was a general result of quantum mechanics that applies to many different systems. Shortly thereafter, both groups considered the case of particles tunnelling into the nucleus.
The study of semiconductors and the development of transistors and diodes led to the acceptance of electron tunnelling in solids by 1957. The work of Leo Esaki, Ivar Giaever and Brian Josephson predicted the tunnelling of superconducting Cooper pairs, for which they received the Nobel Prize in Physics in 1973. In 2016, the quantum tunneling of water was discovered. Quantum tunnelling falls under the domain of quantum mechanics: the study of what happens at the quantum scale; this process cannot be directly perceived, but much of its understanding is shaped by the microscopic world, which classical mechanics cannot adequately explain. To understand the phenomenon, particles attempting to travel between potential barriers can be compared to a ball trying to roll over a hill. Classical mechanics predicts that particles that do not have enough energy to classically surmount a barrier will not be able to reach the other side. Thus, a ball without sufficient energy to surmount the hill would roll back down.
Or, lacking the energy to penetrate a wall, it would bounce back or in the extreme case, bury itself inside the wall. In quantum mechanics, these particles can, with a small probability, tunnel to the other side, thus crossing the barrier. Here, the "ball" could, in a sense, borrow energy from its surroundings to tunnel through the wall or "roll over the hill", paying it back by making the reflected electrons more energetic than they otherwise would have been; the reason for this difference comes from the treatment of matter in quantum mechanics as having properties of waves and particles. One interpretation of this duality involves the Heisenberg uncertainty principle, which defines a limit on how the position and the momentum of a particle can be known at the same time; this implies that there are no solutions with a probability of zero, though a solution may approach infinity if, for example, the calculation for its position was taken as a probability of 1, the other, i.e. its speed, would have to be infinity.
Hence, the probability of a given particle's existence on the opposite side of an intervening barrier is non-zero, such particles will appear on the'other' side with a relative frequency proportional to this probability. The wave function of a particle summarises everything that can be known about a physical s
A collimated beam of light or other electromagnetic radiation has parallel rays, therefore will spread minimally as it propagates. A collimated light beam, with no divergence, would not disperse with distance; such a beam cannot be created, due to diffraction. Light can be collimated by a number of processes, for instance by means of a collimator. Collimated light is sometimes said to be focused at infinity. Thus, as the distance from a point source increases, the spherical wavefronts become flatter and closer to plane waves, which are collimated. Other forms of electromagnetic radiation can be collimated. Collimation of X-rays is important in radiology. Reducing the size of the beam by collimation reduces the volume of the patient's tissue, irradiated, reduces intensity in the periphery of the beam. Peripheral x-rays can be absorbed by the patient's tissues and can generate scattered photons, which travel in many directions and cause film fog, reducing the quality of the x-ray image; the word "collimate" comes from the Latin verb collimare, which originated in a misreading of collineare, "to direct in a straight line".
Laser light from gas or crystal lasers is collimated because it is formed in an optical cavity between two parallel mirrors which constrain the light to a path perpendicular to the surfaces of the mirrors. In practice, gas lasers can use flat mirrors, or a combination of both; the divergence of high-quality laser beams is less than 1 milliradian, can be much less for large-diameter beams. Laser diodes emit less-collimated light due to their short cavity, therefore higher collimation requires a collimating lens. Synchrotron light is well collimated, it is produced by bending relativistic electrons around a circular track. When the electrons are at relativistic speeds, the resulting radiation is collimated, a result which does not occur at lower speeds; the light from stars arrives at Earth collimated, because stars are so far away they present no detectable angular size. However, due to refraction and turbulence in the Earth's atmosphere, starlight arrives uncollimated at the ground with an apparent angular diameter of about 0.4 arcseconds.
Direct rays of light from the Sun arrive at the Earth uncollimated by one-half degree, this being the angular diameter of the Sun as seen from Earth. During a solar eclipse, the Sun's light becomes collimated as the visible surface shrinks to a thin crescent and a small point, producing the phenomena of distinct shadows and shadow bands. A perfect parabolic mirror will bring parallel rays to a focus at a single point. Conversely, a point source at the focus of a parabolic mirror will produce a beam of collimated light creating a Collimator. Since the source needs to be small, such an optical system cannot produce much optical power. Spherical mirrors are easier to make than parabolic mirrors and they are used to produce collimated light. Many types of lenses can produce collimated light from point-like sources; this principle is used in full flight simulators, that have specially designed systems for displaying imagery of the Out-The-Window scene to the pilots in the replica aircraft cabin. In aircraft where two pilots are seated side by side, if the OTW imagery were projected in front of the pilots on a screen, one pilot would see the correct view but the other would see a view where some objects in the scene would be at incorrect angles.
To avoid this, collimated optics are used in the simulator visual display system so that the OTW scene is seen by both pilots at a distant focus rather than at the focal distance of a projection screen. This is achieved through an optical system that allows the imagery to be seen by the pilots in a mirror that has a vertical curvature, the curvature enabling the image to be seen at a distant focus by both pilots, who see the same OTW scene without any distortions. Since the light arriving at the eye point of both pilots is from different angles to the field of view of the pilots due to different projection systems arranged in a semi-circle above the pilots, the entire display system cannot be considered a collimated display, but a display system that uses collimated light. "Collimation" refers to all the optical elements in an instrument being on their designed optical axis. It refers to the process of adjusting an optical instrument so that all its elements are on that designed axis. With regards to a telescope, the term refers to the fact that the optical axis of each optical component should be centered and parallel, so that collimated light emerges from the eyepiece.
Most amateur reflector telescopes need to be re-collimated every few years to maintain optimum performance. This can be done by simple visual methods such as looking down the optical assembly with no eyepiece to make sure the components are lined up, by using a Cheshire eyepiece, or with the assistance of a simple laser collimator or autocollimator. Collimation can be tested using a shearing interferometer, used to test laser collimation. "Decollimation" is any mechanism or process which causes a beam with the minimum possible ray divergence to diverge or converge from parallelism. Decollimation may be deliberate for systems reasons, or may be caused by many factors, such as refractive index inhomogeneities, scattering, diffraction and refraction. Decollimation must be accounted for to treat many systems such as radio, radar and optical communications. Autocollimation Schlieren photography Pfister, J. & Kneedler, J. A.. A guide to lasers in the OR
In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. At least two of the flat surfaces must have an angle between them; 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, in colloquial use "prism" refers to this type; some types of optical prism are not in fact in the shape of geometric prisms. Prisms can be made from any material, transparent to the wavelengths for which they are designed. Typical materials include glass and fluorite. A dispersive prism can be used to break light up into its constituent spectral colors. Furthermore, prisms can be used to reflect light, or to split light into components with different polarizations. Light changes speed; this speed change causes the light to enter the new medium at a different angle. The degree of bending of the light's path depends on the angle that the incident beam of light makes with the surface, on the ratio between the refractive indices of the two media.
The refractive index of many materials varies with the wavelength or color of the light used, a phenomenon known as dispersion. This causes light of different colors to be refracted differently and to leave the prism at different angles, creating an effect similar to a rainbow; this can be used to separate a beam of white light into its constituent spectrum of colors. A similar separation happens with iridescent materials, such as a soap bubble. Prisms will disperse light over a much larger frequency bandwidth than diffraction gratings, making them useful for broad-spectrum spectroscopy. Furthermore, prisms do not suffer from complications arising from overlapping spectral orders, which all gratings have. Prisms are sometimes used for the internal reflection at the surfaces rather than for dispersion. If light inside the prism hits one of the surfaces at a sufficiently steep angle, total internal reflection occurs and all of the light is reflected; this makes a prism a useful substitute for a mirror in some situations.
Ray angle deviation and dispersion through a prism can be determined by tracing a sample ray through the element and using Snell's law at each interface. For the prism shown at right, the indicated angles are given by θ 0 ′ = arcsin θ 1 = α − θ 0 ′ θ 1 ′ = arcsin θ 2 = θ 1 ′ − α. All angles are positive in the direction shown in the image. For a prism in air n 0 = n 2 ≃ 1. Defining n = n 1, the deviation angle δ is given by δ = θ 0 + θ 2 = θ 0 + arcsin − α If the angle of incidence θ 0 and prism apex angle α are both small, sin θ ≈ θ and arcsin x ≈ x if the angles are expressed in radians; this allows the nonlinear equation in the deviation angle δ to be approximated by δ ≈ θ 0 − α + = θ 0 − α + n α − θ 0 = α
Total internal reflection
Total internal reflection is the phenomenon that makes the water-to-air surface in a fish-tank look like a silvered mirror when viewed from below the water level. Technically, TIR is the total reflection of a wave incident at a sufficiently oblique angle on the interface between two media, of which the second medium is transparent to such waves but has a higher wave velocity than the first medium. TIR occurs not only with electromagnetic waves such as light waves and microwaves, but with other types of waves, including sound and water waves. In the case of a narrow train of waves, such as a laser beam, we tend to speak of the total internal reflection of a "ray". Refraction is accompanied by partial reflection; when a wavetrain is refracted from a medium of lower propagation speed to a medium of higher propagation speed, the angle of refraction is greater than the angle of incidence. Hence, as the angle of incidence approaches a certain limit, called the critical angle, the angle of refraction approaches 90°, at which the refracted ray becomes tangential to the interface.
As the angle of incidence increases beyond the critical angle, the conditions of refraction can no longer be satisfied. In an isotropic medium such as air, water, or glass, the ray direction is the direction normal to the wavefront. If the internal and external media are isotropic with refractive indices n1 and n2 the critical angle is given by θ c = arcsin , is defined if n2 ≤ n1. For example, for visible light, the critical angle is about 49° for incidence from water to air, about 42° for incidence from common glass to air. Details of the mechanism of TIR give rise to more subtle phenomena. Unlike partial reflection between transparent media, total internal reflection is accompanied by a non-trivial phase shift for each component of polarization, the shifts vary with the angle of incidence. While total reflection, by definition, involves no continuing transfer of power across the interface, the external medium carries a so-called evanescent wave, which travels along the interface with an amplitude that falls off exponentially with distance from the interface.
The "total" reflection is indeed total if the external medium is lossless, of infinite extent, but can be conspicuously less than total if the evanescent wave is absorbed by a lossy external medium, or diverted by the outer boundary of the external medium or by objects embedded in that medium. The phase shifts in TIR are utilized by a polarization-modifying device called the Fresnel rhomb; the efficiency of the reflection is exploited by optical fibers, by reflective prisms, such as erecting prisms for binoculars. Although total internal reflection can occur with any kind of wave that can be said to have oblique incidence, including microwaves and sound waves, it is most familiar in the case of light waves. Total internal reflection of light can be demonstrated using a semicircular-cylindrical block of common glass or acrylic glass. In Fig. 3, a "ray box" projects a narrow beam of light radially inward. The semicircular cross-section of the glass allows the incoming ray to remain perpendicular to the curved portion of the air/glass surface, thence to continue in a straight line towards the flat part of the surface, although its angle with the flat part varies.
Where the ray meets the flat glass-to-air interface, the angle between the ray and the normal to the interface is called the angle of incidence. If this angle is sufficiently small, the ray is reflected but transmitted, the transmitted portion is refracted away from the normal, so that the angle of refraction is greater than the angle of incidence. For the moment, let us call the angle of incidence θi and the angle of refraction θt; as θi increases and approaches a certain "critical angle", denoted by θc, the angle of refraction approaches 90°, the refracted ray becomes fainter while the reflected ray becomes brighter. As θi increases beyond θc, the refracted ray disappears and only the reflected ray remains, so that all of the energy of the incident ray is reflected. In brief: If θi < θc, the incident ray is split, being reflected and refracted. The critical angle is the smallest angle of incidence. For light waves and other electromagnetic waves in isotropic media, there is a well-known formula for the critical angle in terms of the refractive indices.
For some other types of waves, it is more convenient to think in terms of propagation velocities rather than refractive indices. The latter approach is more direct and more general, will therefore be discussed first; when a wavefront is refracted from one medium to another, the incident and refracted portions of the wavefront meet at a common line on the