Glossary

History Of Fiber Optics

Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon and Jacques Babinet in Paris in the early 1840s. John Tyndall included a demonstration of it in his public lectures in London, 12 years later. Tyndall also wrote about the property of total internal reflection in an introductory book about the nature of light in 1870: "When the light passes from air into water, the refracted ray is bent towards the perpendicular... When the ray passes from water to air it is bent from the perpendicular... If the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the ray will not quit the water at all: it will be totally reflected at the surface.... The angle which marks the limit where total reflection begins is called the limiting angle of the medium. For water this angle is 48°27', for flint glass it is 38°41', while for diamond it is 23°42'." Unpigmented human hairs have also been shown to act as an optical fiber.

Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century. Image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. The principle was first used for internal medical examinations by Heinrich Lamm in the following decade. Modern optical fibers, where the glass fiber is coated with a transparent cladding to offer a more suitable refractive index, appeared later in the decade. Development then focused on fiber bundles for image transmission. Harold Hopkins and Narinder Singh Kapany at Imperial College in London achieved low-loss light transmission through a 75 cm long bundle which combined several thousand fibers. Their article titled "A flexible fibrescope, using static scanning" was published in the journal Nature in 1954. The first fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, and Lawrence E. Curtiss, researchers at the University of Michigan, in 1956. In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers; previous optical fibers had relied on air or impractical oils and waxes as the low-index cladding material.

A variety of other image transmission applications soon followed.

In 1880 Alexander Graham Bell and Sumner Tainter invented the Photophone at the Volta Laboratory in Washington, D.C., to transmit voice signals over an optical beam. It was an advanced form of telecommunications, but subject to atmospheric interferences and impractical until the secure transport of light that would be offered by fiber-optical systems. In the late 19th and early 20th centuries, light was guided through bent glass rods to illuminate body cavities. Jun-ichi Nishizawa, a Japanese scientist at Tohoku University, also proposed the use of optical fibers for communications in 1963, as stated in his book published in 2004 in India. Nishizawa invented other technologies that contributed to the development of optical fiber communications, such as the graded-index optical fiber as a channel for transmitting light from semiconductor lasers. The first working fiber-optical data transmission system was demonstrated by German physicist Manfred Börner at Telefunken Research Labs in Ulm in 1965, which was followed by the first patent application for this technology in 1966. Charles K. Kao and George A. Hockham of the British company Standard Telephones and Cables (STC) were the first to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer (dB/km), making fibers a practical communication medium. They proposed that the attenuation in fibers available at the time was caused by impurities that could be removed, rather than by fundamental physical effects such as scattering. They correctly and systematically theorized the light-loss properties for optical fiber, and pointed out the right material to use for such fibers — silica glass with high purity. This discovery earned Kao the Nobel Prize in Physics in 2009.

NASA used fiber optics in the television cameras that were sent to the moon. At the time, the use in the cameras was classified confidential, and only those with sufficient security clearance or those accompanied by someone with the right security clearance were permitted to handle the cameras.

The crucial attenuation limit of 20 dB/km was first achieved in 1970, by researchers Robert D. Maurer, Donald Keck, Peter C. Schultz, and Frank Zimar working for American glass maker Corning Glass Works, now Corning Incorporated. They demonstrated a fiber with 17 dB/km attenuation by doping silica glass with titanium. A few years later they produced a fiber with only 4 dB/km attenuation using germanium dioxide as the core dopant. Such low attenuation ushered in the era of optical fiber telecommunication. In 1981, General Electric produced fused quartz ingots that could be drawn into strands 25 miles (40 km) long.

Attenuation in modern optical cables is far less than in electrical copper cables, leading to long-haul fiber connections with repeater distances of 70–150 kilometers (43–93 mi). The erbium-doped fiber amplifier, which reduced the cost of long-distance fiber systems by reducing or eliminating optical-electrical-optical repeaters, was co-developed by teams led by David N. Payne of the University of Southampton and Emmanuel Desurvire at Bell Labs in 1986. Robust modern optical fiber uses glass for both core and sheath, and is therefore less prone to aging. It was invented by Gerhard Bernsee of Schott Glass in Germany in 1973.

The emerging field of photonic crystals led to the development in 1991 of photonic-crystal fiber, which guides light by diffraction from a periodic structure, rather than by total internal reflection. The first photonic crystal fibers became commercially available in 2000. Photonic crystal fibers can carry higher power than conventional fibers and their wavelength-dependent properties can be manipulated to improve performance.

 

Definitions

Fusion splicing is the act of joining two optical fibers end-to-end using heat. The goal is to fuse the two fibers together in such a way that light passing through the fibers is not scattered or reflected back by the splice, and so that the splice and the region surrounding it are almost as strong as the virgin fiber itself. The source of heat is usually an electric arc, but can also be a laser, or a gas flame, or a tungsten filament through which current is passed.

 

Process

The process of fusion splicing normally involves using localized heat to melt or fuse the ends of two optical fibers together. The splicing process begins by preparing each fiber end for fusion.

Stripping the fiber

Stripping is the act of removing the protective polymer coating around optical fiber in preparation for fusion splicing. The splicing process begins by preparing both fiber ends for fusion, which requires that all protective coating is removed or stripped from the ends of each fiber. Fiber optical stripping is usually carried out by a special stripping and preparation unit that uses hot sulphuric acid or a controlled flow of hot air to remove the coating. There are also mechanical tools used for stripping fiber which are similar to copper wire strippers. Fiber optical stripping and preparation equipment used in fusion splicing is commercially available through a small number of specialized companies, which usually also designs machines used for fiber optical recoating.

Cleaning the fiber

The bare fibers are cleaned using alcohol and wipes.

Cleaving the fiber

The fiber is then cleaved using the score-and-break method so that its endface is perfectly flat and perpendicular to the axis of the fiber. The quality of each fiber end is inspected using a microscope. In fusion splicing, splice loss is a direct function of the angles and quality of the two fiber-end faces. The closer to 90 degrees the cleave angle is the lower optical loss the splice will yield.

Splicing the fibers

Fiber spliced, still unprotected

Current fusion splicers are either core or cladding alignment. Using one of these methods the two cleaved fibers are automatically aligned by the fusion splicer[1] in the x,y,z plane, then are fused together. Prior to removing the spliced fiber from the fusion splicer, a proof-test preformed to ensure that the splice is strong enough to survive handling, packaging and extended use. The bare fiber area is protected either by recoating or with a splice protector. A splice protector is a heat shrinkable tube with a strength membrane.

Connector Definitions & Descriptions

 

Connector Part or Type

Description

APC (Angled Physical Contact)

This is a fiber optic polishing style that has an 8 degree angle on the endface. This connector style is typically indicated by a green connector body or green strain relief boot.

Backplane Connector

This is a fiber optic connector that mates the rear of the PCA to the inside back wall of the chassis.

Bulkhead Adapter

This is a plastic or metal housing which allows two fiber-optic connectors to mate. Typically these are located on the front panel or the backplane of a PCA.

Connector

This is a plastic or metal housing located at the end of a fiber-optic cable to connect cables to a transmitter, receiver, or another cable.

Cladding

This is the inside region of the fiber optic endface that is made of a low refractive index glass. This region starts at the outside edge of the core and ends at a diameter of 125 microns.

Core

This is the center most region of the fiber optic endface that carries and guides the majority of the light. The diameter can be 9 microns, 50 microns, or 62.5 microns that depend on fiber type.

Note: Often the core might not be illuminated and is indistinguishable from the cladding.

E2000

This is a fiber optic connector style with a single-fiber 2.5 mm diameter ferrule. This specialized connector uses a metallic ferrule and has a spring-loaded protective shutter. It is offered exclusively by Diamond, Inc.

Endface

This is the mating surface of a fiber optic connector. It consists of a glass core and cladding, surrounded by a ferrule made of either ceramic, plastic, or metal. It is critical to keep this entire area protected from damage at all times.

F3000

This is a fiber optic connector style with a single-fiber 1.25 mm diameter ferrule. This specialized connector uses a metallic ferrule and has a spring-loaded protective shutter. Does not fit into LC ports

FC

A fiber optic connector style with a single-fiber 2.5 mm diameter ferrule. It features a keyed, threaded barrel that is used to mate the connector.

Ferrule

The outside portion of the fiber optic endface that is precisely hollowed out to hold and align the glass cladding and core. It is typically made of an insulative material such as ceramic or plastic. They are available in single-fiber and multi-fiber styles.

LC

This is a fiber optic connector style with a single-fiber diameter ferrule. It features a distinctive plastic latch on the connector 1.25 mm body that provides a positive engagement when mated.

MPO (also known as MTP)

This is a fiber optic connector style with a multi-fiber plastic ferrule.

MU

This is a fiber optic connector style with a single-fiber 1.25 mm diameter ferrule.

Multimode Fiber

This is an optical fiber which transmits or emits multiple modes of light. These fibers usually have a large core, typically 50 or 62.5 microns.

OGI

This is a fiber optic connector style with a multi-fiber plastic ferrule. Manufactured by 3M.

PC (Physical Contact)

This is a fiber optic polishing style that has a convex, domed endface.

Pigtailed Device

This is a packaged optical component with a length of fiber attached to a male connector.

Receptacle Device

This is a packaged optical component with female ports that typically mount flush to the front panel. These may use fiber or optical lenses internally, which depends on the design and/or vendor. SFPs, XFPs, GBICs, XenPAKs, & SFFs are all examples of receptacle transceiver devices.

Ribbon Connector

This is another term for a multi-fiber connector.

SC

This is a fiber optic connector style with a single-fiber 2.5 mm diameter ferrule.

Single Mode Fiber

This is an optical fiber that supports one spatial mode of light propagation. These fibers typically have a 9 micron core.

ST

This is a fiber optic connector style with a single-fiber 2.5 mm diameter ferrule.

UPC (Ultra-polished physical contact)

This is a fiber optic polishing style that has a convex, domed endface. It is highly polished to attain enhanced performance.






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