Fiber Optics Cable Construction

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Fiber Optic Cable Loose Tube Single Mode / Duct Type

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Fiber Optic Cable Loose Tube Single Mode / Aerial Type

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Fiber Optic Cable Loose Tube Single Mode / Duct Type with Corrugated Steel Armoured

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Fiber Optic Cable Loose Tube Multi Mode / ADSS Type

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Fiber Optic Cable Slotted Core Type

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Fiber Optic Cable Ribbon Type

Above are a few of available design of fiber optics cable construction. It is depends on site environment i.e. oil&gas, power utilities provider etc and design criteria as per clients' requirement.

Propagation of Light Along Fiber Optics (Details)

For those who would like to know in details about the theory on propagation of light along fiber optics. Article taken from this web.

PROPAGATION OF LIGHT ALONG A FIBER

The concept of light propagation, the transmission of light along an optical fiber, can be described by two theories. According to the first theory, light is described as a simple ray. This theory is the ray theory, or geometrical optics, approach. The advantage of the ray approach is that you get a clearer picture of the propagation of light along a fiber. The ray theory is used to approximate the light acceptance and guiding properties of optical fibers. According to the second theory, light is described as an electromagnetic wave. This theory is the mode theory, or wave representation, approach. The mode theory describes the behavior of light within an optical fiber. The mode theory is useful in describing the optical fiber properties of absorption, attenuation, and dispersion. These fiber properties are discussed later in this chapter.

Q.21 Light transmission along an optical fiber is described by two theories. Which theory is used to approximate the light acceptance and guiding properties of an optical fiber?

Ray Theory

Two types of rays can propagate along an optical fiber. The first type is called meridional rays. Meridional rays are rays that pass through the axis of the optical fiber. Meridional rays are used to illustrate the basic transmission properties of optical fibers.

The second type is called skew rays. Skew rays are rays that travel through an optical fiber without passing through its axis.

MERIDIONAL RAYS. - Meridional rays can be classified as bound or unbound rays. Bound rays remain in the core and propagate along the axis of the fiber. Bound rays propagate through the fiber by total internal reflection. Unbound rays are refracted out of the fiber core. Figure 2-10 shows a possible path taken by bound and unbound rays in a step-index fiber. The core of the step-index fiber has an index of refraction n₁. The cladding of a step-index has an index of refraction n₂, that is lower than n₁. Figure 2-10 assumes the core-cladding interface is perfect. However, imperfections at the core-cladding interface will cause part of the bound rays to be refracted out of the core into the cladding. The light rays refracted into the cladding will eventually escape from the fiber. In general, meridional rays follow the laws of reflection and refraction.

Figure 2-10. - Bound and unbound rays in a step-index fiber.

It is known that bound rays propagate in fibers due to total internal reflection, but how do these light rays enter the fiber? Rays that enter the fiber must intersect the core-cladding interface at an angle greater than the critical angle (Θ_c). Only those rays that enter the fiber and strike the interface at these angles will propagate along the fiber.

How a light ray is launched into a fiber is shown in figure 2-11. The incident ray I₁ enters the fiber at the angle Θ_a. I₁ is refracted upon entering the fiber and is transmitted to the core-cladding interface. The ray then strikes the core-cladding interface at the critical angle (Θ _c). I₁ is totally reflected back into the core and continues to propagate along the fiber. The incident ray I₂ enters the fiber at an angle greater than Θ_a. Again, I₂ is refracted upon entering the fiber and is transmitted to the core-cladding interface. I₂ strikes the core-cladding interface at an angle less than the critical angle (Θ_c). I₂ is refracted into the cladding and is eventually lost. The light ray incident on the fiber core must be within the acceptance cone defined by the angle Θ_a shown in figure 2-12.

Angle Θ_a is defined as the acceptance angle. The acceptance angle (Θ_a) is the maximum angle to the axis of the fiber that light entering the fiber is propagated. The value of the angle of acceptance (Θ_a) depends on fiber properties and transmission conditions.

Figure 2-11. - How a light ray enters an optical fiber.

Figure 2-12. - Fiber acceptance angle.

The acceptance angle is related to the refractive indices of the core, cladding, and medium surrounding the fiber. This relationship is called the numerical aperture of the fiber. The numerical aperture (NA) is a measurement of the ability of an optical fiber to capture light. The NA is also used to define the acceptance cone of an optical fiber.

Figure 2-12 illustrates the relationship between the acceptance angle and the refractive indices. The index of refraction of the fiber core is n₁. The index of refraction of the fiber cladding is n₂. The index of refraction of the surrounding medium is n₀. By using Snell's law and basic trigonometric relationships, the NA of the fiber is given by:

Since the medium next to the fiber at the launching point is normally air, n₀ is equal to 1.00. The NA is then simply equal to sin Θ_a.

The NA is a convenient way to measure the light-gathering ability of an optical fiber. It is used to measure source-to-fiber power-coupling efficiencies. A high NA indicates a high source-to-fiber coupling efficiency.

Source-to-fiber coupling efficiency is described in chapter 6. Typical values of NA range from 0.20 to 0.29 for glass fibers. Plastic fibers generally have a higher NA. An NA for plastic fibers can be higher than 0.50.

In addition, the NA is commonly used to specify multimode fibers.

However, for small core diameters, such as in single mode fibers, the ray theory breaks down. Ray theory describes only the direction a plane wave takes in a fiber. Ray theory eliminates any properties of the plane wave that interfere with the transmission of light along a fiber. In reality, plane waves interfere with each other. Therefore, only certain types of rays are able to propagate in an optical fiber. Optical fibers can support only a specific number of guided modes. In small core fibers, the number of modes supported is one or only a few modes. Mode theory is used to describe the types of plane waves able to propagate along an optical fiber.

SKEW RAYS. - A possible path of propagation of skew rays is shown in figure 2-13.

Figure 2-13, view A, provides an angled view and view B provides a front view.

Skew rays propagate without passing through the center axis of the fiber.

The acceptance angle for skew rays is larger than the acceptance angle of meridional rays. This condition explains why skew rays outnumber meridional rays. Skew rays are often used in the calculation of light acceptance in an optical fiber. The addition of skew rays increases the amount of light capacity of a fiber. In large NA fibers, the increase may be significant.

Figure 2-13. - Skew ray propagation: A. Angled view; B. Front view.

The addition of skew rays also increases the amount of loss in a fiber. Skew rays tend to propagate near the edge of the fiber core. A large portion of the number of skew rays that are trapped in the fiber core are considered to be leaky rays. Leaky rays are predicted to be totally reflected at the core-cladding boundary. However, these rays are partially refracted because of the curved nature of the fiber boundary. Mode theory is also used to describe this type of leaky ray loss.

Advantages of Fiber Optics Cable over Copper Cable

Optical transmission has several advantages over copper wire:

• optical fibre’s high bandwidth means that a lot more data can be transmitted faster.
  A pair of copper wires (which is what most houses in urban areas use for the initial point of access to the Internet can transmit two telephone calls simultaneously, while a single optical fibre can transmit over 80,000;
• glass is cheaper and lighter than copper;
• optical fibre is unaffected by electro-magnetic interference, and so is ideal in electrically “noisy” environments, eg where there is high voltage equipment nearby;
• no electrical current is transmitted down a fibre (glass is a good insulator), so it is suitable in hazardous environments where electrical discharge would dangerous;
• as transmission technology continues to improve, higher and higher bandwidths are possible over the same optical fibre links without having to replace the cables.

Article taken from this web

Principle of Fiber Optics

Principles of Optical Fiber

Optical fiber transmits light. But, what prevents the light from escaping from the fiber? The answer is based on a principle that we experience every day.

While swimming at the beach as a child, have you ever thought that you were safely in shallow water only to be surprised to find that it was too deep to touch the bottom? When you look straight down into a clear lake or puddle, you can see its bottom. However, when you view it at an angle and look off into the distance, the distant scenery is reflected upside down. This is caused by the difference in the index of refraction between the water and air, which you probably learned about in grade school.

Although optical fiber appears to be only a simple thread, it is actually composed 2 structures similar to water and air. The area where light is transmitted is called the core, and the external area is called the clad.

When light enters the area between 2 materials with different indexes of refraction (boundary face), the light will be either entirely reflected or a portion of it will be refracted, depending on the angle. If the light can be kept at an angle where it is entirely reflected, it will become trapped inside and transmitted along the fiber.

Note:
The explanation about looking into a body of water from air above was provided to make the principles of optical fiber easier to understand. Although in explaining the principles of fiber optics, it is opposite, being a more appropriate comparison to look from water (where the index of refraction for water (1.3) is greater) to air (1.0), it was decided that an example of something most people have experienced would be easiest to understand.

Simple explanation on Principle of Optical Fiber is taken from this web

Types of Fiber Optics

There are two main fiber optics type :-

a. Singlemode or in fiber optics term 9/125 micron
b. Multimode or in fiber optics term 50/125 or 62.5/125 micron

What are those fiber optics terms stand for ?





What is the difference between multimode and single mode fiber?

Multimode fiber has a relatively large light carrying core, usually 62.5 microns or larger in diameter. It is usually used for short distance transmissions up to maximum length of 5 kilometers.

Single-mode fiber has a small light carrying core of 8 to 10 microns in diameter. It is normally used for long distance transmissions more than 5 kilometers in length.

How fiber optics are made ?

See interesting documentary video as shown on Discovery Channel recently...



or following article is taken from this web

Making optical fibers requires the following steps:

1. Making a preform glass cylinder
2. Drawing the fibers from the preform
3. Testing the fibers

Making the Preform Blank
The glass for the preform is made by a process called modified chemical vapor deposition (MCVD).

Image courtesy Fibercore Ltd. MCVD process for making the preform blank

In MCVD, oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) and/or other chemicals. The precise mixture governs the various physical and optical properties (index of refraction, coefficient of expansion, melting point, etc.). The gas vapors are then conducted to the inside of a synthetic silica or quartz tube (cladding) in a special lathe. As the lathe turns, a torch is moved up and down the outside of the tube. The extreme heat from the torch causes two things to happen:

Photo courtesy Fibercore Ltd. Lathe used in preparing the preform blank

• The silicon and germanium react with oxygen, forming silicon dioxide (SiO2) and germanium dioxide (GeO2).

• The silicon dioxide and germanium dioxide deposit on the inside of the tube and fuse together to form glass.

The lathe turns continuously to make an even coating and consistent blank. The purity of the glass is maintained by using corrosion-resistant plastic in the gas delivery system (valve blocks, pipes, seals) and by precisely controlling the flow and composition of the mixture. The process of making the preform blank is highly automated and takes several hours. After the preform blank cools, it is tested for quality control (index of refraction).

Drawing Fibers from the Preform Blank
Once the preform blank has been tested, it gets loaded into a fiber drawing tower.

Diagram of a fiber drawing tower used to draw optical glass fibers from a preform blank

The blank gets lowered into a graphite furnace (3,452 to 3,992 degrees Fahrenheit or 1,900 to 2,200 degrees Celsius) and the tip gets melted until a molten glob falls down by gravity. As it drops, it cools and forms a thread.

The operator threads the strand through a series of coating cups (buffer coatings) and ultraviolet light curing ovens onto a tractor-controlled spool. The tractor mechanism slowly pulls the fiber from the heated preform blank and is precisely controlled by using a laser micrometer to measure the diameter of the fiber and feed the information back to the tractor mechanism. Fibers are pulled from the blank at a rate of 33 to 66 ft/s (10 to 20 m/s) and the finished product is wound onto the spool. It is not uncommon for spools to contain more than 1.4 miles (2.2 km) of optical fiber.

Testing the Finished Optical Fiber
The finished optical fiber is tested for the following:

• Tensile strength - Must withstand 100,000 lb/in² or more

• Refractive index profile - Determine numerical aperture as well as screen for optical defects

• 
  Photo courtesy Corning
  Finished spool of optical fiber
  Fiber geometry - Core diameter, cladding dimensions and coating diameter are uniform

• Attenuation - Determine the extent that light signals of various wavelengths degrade over distance

• Information carrying capacity (bandwidth) - Number of signals that can be carried at one time (multi-mode fibers)

• Chromatic dispersion - Spread of various wavelengths of light through the core (important for bandwidth)

• Operating temperature/humidity range

• Temperature dependence of attenuation

• Ability to conduct light underwater - Important for undersea cables

­ Once t­he fibers have passed the quality control, they are sold to telephone companies, cable companies and network providers. Many companies are currently replacing their old copper-wire-based systems with new fiber-optic-based systems to improve speed, capacity and clarity.

What are Fiber Optics

Fiber optics are long, thin strands of very pure glass about the size of diameter of a human hair. They are arranged in bundles called optical cables and used to transmit lightsignals over short or long distances.


Fiber optics consist of following parts :-

• Core - Thin glass center of the fiber where the light travels
• Cladding - Outer optical material surrounding the core that reflects the light back into the core
• Buffer coating - Plastic coating that protects the fiber from damage and moisture

Hundreds or thousands of these optical fibers are arranged in bundles in optical cables. The bundles are protected by the cable's outer covering, called a jacket.

Optical fibers come in two types:

• Single-mode fibers
• Multi-mode fibers

Fiber-Optic Chronology Development

Circa 2500 B.C.: Earliest known glass

Roman Times: Glass is drawn into fibers

1713: Rene de Reaumur makes spun glass fibers

1790s: Claude Chappe invents 'optical telegraph' in France

1841: Daniel Colladon demonstrates light guiding in jet of water Geneva

1842: Jacques Babinet reports light guiding in water jets and bent glass rods Paris

1853: Paris Opera uses Colladon's water jet in the opera Faust

1854: John Tyndall demonstrates light guiding in water jets, duplicating but not acknowledging Colladon

1873: Jules de Brunfaut makes glass fibers that can be woven into cloth

1880: Alexander Graham Bell invents Photophone, Washington

1880: William Wheeler invents system of light pipes to illuminate homes from an electric arc lamp in basement, Concord, Mass.

1884: International Health Exhibition in South Kensington district of London has first fountains with illuminated water jets, designed by Sir Francis Bolton

1887: Charles Vernon Boys draws quartz fibers for mechanical measurements

1887: Royal Jubilee Exhibition in Manchester has illuminated "Fairy Fountains" designed by W. and J. Galloway and Sons

1888: Illuminated fountains at Glasgow and Barcelona fairs

1888: Dr. Roth and Prof. Reuss of Vienna use bent glass rods to illuminate body cavities

1889: Universal Exhibition in Paris shows refined illuminated fountains designed by G. Bechmann

1895: Henry C. Saint-Rene designs a system of bent glass rods for guiding light in an early television scheme (Crezancy, France)

1892: Herman Hammesfahr shows glass dress at Chicago World's Fair

April 25, 1898: David D. Smith of Indianapolis applies for patent on bent glass rod as a surgical lamp

1920s: Bent glass rods used for microscope illumination

June 2, 1926: C. Francis Jenkins applies for U.S. patent on a mechanical television receiver in which light passes along quartz rods in a rotating drum to form an image.

Oct. 15, 1926: John Logie Baird applies for British patent on an array of parallel glass rods or hollow tubes to carry image in a mechanical television. He later built an array of hollow tubes.

December 30, 1926: Clarence W. Hansell outlines principles of the fiber-optic imaging bundle in his notebook at the RCA Rocky Point Laboratory on Long Island. RCA files for U.S. patent Aug. 13, 1927, and later files for British patent.

1930: Heinrich Lamm, a medical student, assembles first bundle of transparent fibers to carry an image (of an electric lamp filament) in Munich. His effort to file a patent is denied because of Hansell's British patent.

December 1931: Owens-Illinois devises method to mass-produce glass fibers for Fiberglas.

1937: Armand Lamesch of Germany applies for U.S. patent on two-layer glass fiber (non-optical)

1939: Curvlite Sales offers illuminated tongue depressor and dental illuminators made of Lucite, a transparent plastic invented by DuPont.

Circa 1949: Holger Moller Hansen in Denmark and Abraham C. S. Van Heel at the Technical University of Delft begin investigating image transmission through bundles of parallel glass fibers.

April 11, 1951: Holger Moller Hansen applies for a Danish patent on fiber-optic imaging in which he proposes cladding glass or plastic fibers with a transparent low-index material. Patent claim is denied because of Hansell patent.

October 1951: Brian O'Brien (University of Rochester) suggests to Abraham C. S. Van Heel (Technical University of Delft) that applying a transparent cladding would improve transmission of fibers in his imaging bundle.

July 1952: Harold Horace Hopkins applies for a grant from the Royal Society to develop bundles of glass fibers for use as an endoscope at Imperial College of Science and Technology. Hires Narinder S. Kapany as an assistant when he receives grant.

Spring 1953: Hopkins tell Fritz Zernicke his idea of fiber bundles; Zernicke tells van Heel, who decides to publish quickly

June 12, 1953: van Heel publishes first report of clad fiber in Dutch-language weekly De Ingeneur after submitting brief paper to Nature.

January 2, 1954: Hopkins and Kapany and van Heel publish separate papers in Nature. Hopkins and Kapany report imaging bundles of unclad fibers; van Heel reports simple bundles of clad fibers.

1954: Basil Hirschowitz visits Hopkins and Kapany in London from the University of Michigan

September 1954: American Optical hires Will Hicks to implement develop fiber-optic image scramblers, an idea O'Brien proposed to the Central Intelligence Agency

Summer 1955: Kapany completes doctoral thesis on fiber optics under Hopkins, moves to University of Rochester.

Summer 1955: Hirschowitz and C. Wilbur Peters hire undergraduate student Larry Curtiss to work on their fiber-optic endoscope project.

Summer 1956: Curtiss suggests making glass clad fibers by melting a tube onto a rod of higher-index glass

December 8, 1956: Curtiss makes first glass-clad fibers by rod-in-tube method.

February 1957: Hirschowitz is first to test fiber-optic endoscope in a patient.

1957: Image scrambler project ends after Hicks tells CIA the code is easy to break.

1958: Hicks, Paul Kiritsy and Chet Thompson leave American Optical to form Mosaic Fabrications in Southbridge, Mass., the first fiber-optics company.

1958: Alec Reeves begins investigating optical communications at Standard Telecommunication Laboratories

1959: Working with Hicks, American Optical draws fibers so fine they transmit only a single mode of light. Elias Snitzer recognizes the fibers as single-mode waveguides.

May 16, 1960: Theodore Maiman demonstrates first laser at Hughes Research Laboratories in Malibu.

December 1960: Ali Javan makes first helium-neon laser at Bell Labs, the first laser to emit a steady beam.

Circa 1960: George Goubau at Army Electronics Command Laboratory, Bell Telephone Laboratories and Standard Telecommunication Laboratories begin investigating hollow optical waveguides with regularly spaced lenses

January 1961: Charles C. Eaglesfield proposes hollow optical pipeline made of reflective pipes

May 1961: Elias Snitzer of American Optical publishes theoretical description of single-mode fibers.

1962-63: Alec Reeves at Standard Telecommunications Laboratories in Harlow, UK, commissions a group to study optical waveguide communications under Antoni E. Karbowiak. One system they study is optical fiber.

Autumn 1962: Four groups nearly simultaneously make first semiconductor diode lasers, but they operate only pulsed at liquid-nitrogen temperature. Robert N. Hall's group at General Electric is first.

1963: Karbowiak proposes flexible thin-film waveguide.

December 1964: Charles K. Kao takes over STL optical communication program when Karbowiak leaves to become chair of electrical engineering at the University of New South Wales. Kao and George Hockham soon abandon Karbowiak's thin-film waveguide in favor of single-mode optical fiber.

January 1966: Kao tells Institution of Electrical Engineers in London that fiber loss could be reduced below 20 decibels per kilometer for inter-office communications.

Early 1966: F. F. Roberts starts fiber-optic communications research at British Post Office Research Laboratories

July 1966: Kao and Hockham publish paper outlining their proposal in the Proceedings of the Institution of Electrical Engineers.

July 1966: John Galt at Bell Labs asks Mort Panish and Izuo Hayashi to figure out why diode lasers have high thresholds at room temperature.

September 1966: Alain Werts, a young engineer at CSF in France, publishes proposal similar to Kao's in French-language journal L'Onde Electronique, but CSF does nothing further for lack of funding.

1966: Roberts tells William Shaver, a visitor from the Corning Glass Works, about interest in fiber communications. This leads Robert Maurer to start a small research project on fused-silica fibers.

1966: Kao travels to America early in year, but fails to interest Bell Labs. He later finds more interest in Japan.

Early 1967: British Post Office allocates an extra 12 million pounds to research; some goes to fiber optics.

Early 1967: Shojiro Kawakami of Tohoku University in Japan proposes graded-index optical fibers.

Summer 1967: Corning summer intern Cliff Fonstad makes fibers. Loss is high, but Maurer decides to continue the research using titania-doped cores and pure-silica cladding.

October 1967: Clarence Hansell dies at 68.

Late 1967: Maurer recruits Peter Schultz from Corning's glass chemistry department to help making pure glasses.

January 1968: Donald Keck starts work for Maurer as the first full-time fiber developer at Corning. The team also includes Frank Zimar, who draws fiber in a high-temperature furnace he built

1968: Kao and M. W. Jones measure intrinsic loss of bulk fused silica at 4 decibels per kilometer, the first evidence of ultratransparent glass, prompting Bell Labs to seriously consider fiber optics.

August 1968: Dick Dyott of British Post Office picks up suggestion for pulling clad optical fibers from molten glass in a double crucible.

1969: Martin Chown of STL demonstrates fiber-optic repeater at Physical Society exhibition.

April 1970: STL demonstrates fiber optic transmission at Physics Exhibition in London.

Spring 1970: First continuous-wave room-temperature semiconductor lasers made in early May by Zhores Alferov's group at the Ioffe Physical Institute in Leningrad (now St. Petersburg) and on June 1 by Mort Panish and Izuo Hayashi at Bell Labs.

June 30, 1970: AT&T introduces Picturephone in Pittsburgh. The telephone monopoly plans to install millimeter waveguides to provide the needed extra capacity.

Summer 1970: Maurer, Donald Keck, Peter Schultz, and Frank Zimar at Corning develop a single-mode fiber with loss of 17 dB/km at 633 nanometers by doping titanium into fiber core.

September 30, 1970: Maurer announces results at London conference devoted mainly to progress in millimeter waveguides.

November 1970: Measurements at British Post Office and STL confirm Corning results.

Late Fall 1970: Charles Kao leaves STL to teach at Chinese University of Hong Kong; Murray Ramsay heads STL fiber group.

1970-1971: Dick Dyott at Post Office and Felix Kapron of Corning separately find pulse spreading is lowest at 1.2 to 1.3 micrometers.

May 1971: Murray Ramsay of Standard Telecommunication Labs demonstrates digital video over fiber to Queen Elizabeth at the Centenary of the Institution of Electrical Engineers.

October 13, 1971: Alec Reeves dies in London.

1971-1972: Unable to duplicate Corning's low loss, Bell Labs, the University of Southampton, and CSIRO in Australia experiment with liquid-core fibers.

1971-1972: Focus shifts to graded-index fibers because single-mode offers few advantages and many problems at 850 nanometers.

June 1972: Maurer, Keck and Schultz make multimode germania-doped fiber with 4 decibel per kilometer loss and much greater strength than titania-doped fiber.

Late 1972: STL modulates diode laser at 1 Gbit/s; Bell Labs stops its last work on hollow light pipes.

December 1972: John Fulenwider proposes a fiber-optic communication network to carry video and other signals to homes at International Wire and Cable Symposium.

1973: John MacChesney develops modified chemical vapor deposition process for fiber manufacture at Bell Labs.

Mid-1973: Diode laser lifetime reaches 1000 hours at Bell Labs.

Spring 1974: Bell Labs settles on graded-index fibers with 50- to 100 micrometer cores.

December 7, 1974: Heinrich Lamm dies at 66

February 1975: Bell completes installation of 14 kilometers of millimeter waveguide in New Jersey. After tests, Bell declares victory and abandons the technology.

June 1975: First commercial continuous-wave semiconductor laser operating at room temperature offered by Laser Diode Labs.

September 1975: First non-experimental fiber-optic link installed by Dorset (UK) police after lightning knocks out their communication system

October 1975: British Post Office begins tests of millimeter waveguide; like Bell it declares the tests successful, but never installs any.

1975: Dave Payne and Alex Gambling at University of Southampton calculate pulse spreading should be zero at 1.27 micrometers.

January 13, 1976: Bell Labs starts tests of graded-index fiber-optic system transmitting 45 million bits per second at its Norcross, Georgia plant. Laser lifetime is main problem.

Early 1976: Valtec launches Communications Fiberoptics division.

Early 1976: Masaharu Horiguchi (NTT Ibaraki Lab) and Hiroshi Osanai (Fujikura Cable) make first fibers with low loss -- 0.47 decibel per kilometer -- at long wavelengths, 1.2 micrometers.

March 1976: Japan's Ministry for International Trade and Industry announces plans for Hi-OVIS fiber-optic "wired city" experiment involving 150 homes.

Spring 1976: Lifetime of best laboratory lasers at Bell Labs reaches 100,000 hours (10 years) at room temperature.

Summer 1976: Horiguchi and Osanai open third window at 1.55 micrometers.

July 1976: Corning sues ITT alleging infringement of American patents on communication fibers.

Late 1976: J. Jim Hsieh makes InGaAsP lasers emitting continuously at 1.25 micrometers.

Spring 1977: F. F. Roberts reaches mandatory retirement age of 60; John Midwinter becomes head of fiber-optic group at British Post Office.

April 1, 1977: AT&T sends first test signals through field test system in Chicago's Loop district.

April 22, 1977: General Telephone and Electronics sends first live telephone traffic through fiber optics, 6 Mbit/s, in Long Beach, California.

May 1977: Bell System starts sending live telephone traffic through fibers at 45 Mbit/s fiber link in downtown Chicago.

June 1977: British Post Office begins sending live telephone traffic through fibers in underground ducts near Martlesham Heath.

June 29, 1977: Bell Labs announces one-million hours (100-year) extrapolated lifetime for diode lasers.

Summer 1977: F. F. Roberts dies of heart attack.

October 1977: Valtec "acquires" Comm/Scope, but Comm/Scope owners soon gain control of Valtec.

Late 1977: AT&T and other telephone companies settle on 850 nanometer gallium arsenide light sources and graded-index fibers for commercial systems operating at 45 million bits per second.

1977-1978: Low loss at long wavelengths renews research interest in single-mode fiber.

May 22-23, 1978: Fiber Optic Con, first fiber-optic trade show, held in Boston. (This document copyright Jeff Hecht, jeff@jeffhecht.com)

July 1978: Optical fibers begin carrying signals to homes in Japan's Hi OVIS project.

August 1978: NTT transmits 32 million bits per second through a record 53 kilometers of graded-index fiber at 1.3 micrometers.

September 1978: Richard Epworth reports modal noise problems in graded-index fibers.

September 1978: France Telecom announces plans for fiber to the home demonstration in Biarritz, connecting 1500 homes in early 1983.

1978: AT&T, British Post Office and STL commit to developing a single mode transatlantic fiber cable, using the new 1.3-micrometer window, to be operational by 1988. By the end of the year, Bell Labs abandons development of new coaxial cables for submarine systems.

Late 1978: NTT Ibaraki lab makes single-mode fiber with record 0.2 decibel per kilometer loss at 1.55 micrometers.

January 1980: AT&T asks Federal Communications Commission to approve Northeast Corridor system from Boston to Washington, designed to carry three different wavelengths through graded-index fiber at 45 Mbit/s.

Winter 1980: Graded-index fiber system carries video signals for 1980 Winter Olympics in Lake Placid, New York, at 850 nanometers.

February 1980: STL and British Post Office lay 9.5 km submarine cable in Loch Fyne, Scotland, including single-mode and graded-idex fibers

1980: Bell Labs publicly commits to single-mode 1.3-micrometer technology for the first transatlantic fiber-optic cable, TAT-8.

September 1980: With fiber optics hot on the stock market, M/A Com buys Valtec for $224 million in stock.

July 27, 1981: ITT signs consent agreement to pay Corning and license Corning communication fiber patents.

1981: Commercial second-generation systems emerge, operating at 1.3 micrometers through graded-index fibers.

1981: British Telecom transmits 140 million bits per second through 49 kilometers of single-mode fiber at 1.3 micrometers, starts shifting to single-mode.

Late 1981: Canada begins trial of fiber optics to homes in Elie, Manitoba.

1982: British Telecom performs field trial of single-mode fiber, changes plans abandoning graded-index in favor of single-mode.

December 1982: MCI leases right of way to install single-mode fiber from New York to Washington. The system will operate at 400 million bits per second at 1.3 micrometers. This starts the shift to single-mode fiber in America.

Late 1983: Stew Miller retires as head of Bell Labs fiber development group.

January 1, 1984: AT&T undergoes first divestiture, splitting off its seven regional operating companies, but keeping long-distance transmission and equipment manufacture.

1984: British Telecom lays first submarine fiber to carry regular traffic, to the Isle of Wight.

1985: Single-mode fiber spreads across America to carry long-distance telephone signals at 400 million bits per second and up.

Summer 1986: All 1500 homes connected to Biarritz fiber to the home system.

October 30, 1986: First fiber-optic cable across the English Channel begins service.

1986: AT&T sends 1.7 billion bits per second through single-mode fibers originally installed to carry 400 million bits per second.

1987: Dave Payne at University of Southampton develops erbium-doped fiber amplifier operating at 1.55 micrometers.

1988: Linn Mollenauer of Bell Labs demonstrates soliton transmission through 4000 kilometers of single-mode fiber.

December 1988: TAT-8 begins service, first transatlantic fiber-optic cable, using 1.3-micrometer lasers and single-mode fiber.

February 1991: Masataka Nakazawa of NTT reports sending soliton signals through a million kilometers of fiber.

February 1993: Nakazawa sends soliton signals 180 million kilometers, claiming "soliton transmission over unlimited distances."

February 1993: Linn Mollenauer of Bell Labs sends 10 billion bits through 20,000 kilometers of fibers using a simpler soliton system.

February 1996: Fujitsu, NTT Labs, and Bell Labs all report sending one trillion bits per second through single optical fibers in separate experiments using different techniques.

Copyright: JeffHecht

A Short History of Fiber Optics

Reproduced from Fiber Optics Technician's Handbook, by Jim Hayes, Delmar Publishers, Albany, New York.

Optical communication systems date back two centuries, to the "optical telegraph" that French engineer Claude Chappe invented in the 1790s. His system was a series of semaphores mounted on towers, where human operators relayed messages from one tower to the next. It beat hand-carried messages hands down, but by the mid-19th century was replaced by the electric telegraph, leaving a scattering of "Telegraph Hills" as its most visible legacy.

Alexander Graham Bell patented an optical telephone system, which he called the Photophone, in 1880, but his earlier invention, the telephone, proved far more practical. He dreamed of sending signals through the air, but the atmosphere didn't transmit light as reliably as wires carried electricity. In the decades that followed, light was used for a few special applications, such as signalling between ships, but otherwise optical communications, like the experimental Photophone Bell donated to the Smithsonian Institution, languished on the shelf.

In the intervening years, a new technology slowly took root that would ultimately solve the problem of optical transmission, although it was a long time before it was adapted for communications. It depended on the phenomenon of total internal reflection, which can confine light in a material surrounded by other materials with lower refractive index, such as glass in air. In the 1840s, Swiss physicist Daniel Collodon and French physicist Jacques Babinet showed that light could be guided along jets of water for fountain displays. British physicist John Tyndall popularized light guiding in a demonstration he first used in 1854, guiding light in a jet of water flowing from a tank. By the turn of the century, inventors realized that bent quartz rods could carry light, and patented them as dental illuminators. By the 1940s, many doctors used illuminated plexiglass tongue depressors.

Optical fibers went a step further. They are essentially transparent rods of glass or plastic stretched so they are long and flexible. During the 1920s, John Logie Baird in England and Clarence W. Hansell in the United States patented the idea of using arrays of hollow pipes or transparent rods to transmit images for television or facsimile systems. However, the first person known to have demonstrated image transmission through a bundle of optical fibers was Heinrich Lamm, than a medical student in Munich. His goal was to look inside inaccessible parts of the body, and in a 1930 paper he reported transmitting the image of a light bulb filament through a short bundle. However, the unclad fibers transmitted images poorly, and the rise of the Nazis forced Lamm, a Jew, to move to America and abandon his dreams of becoming a professor of medicine.

In 1951, Holger Møller [or Moeller, the o has a slash through it] Hansen applied for a Danish patent on fiber-optic imaging. However, the Danish patent office denied his application, citing the Baird and Hansell patents, and Møller Hansen was unable to interest companies in his invention. Nothing more was reported on fiber bundles until 1954, when Abraham van Heel of the Technical University of Delft in Holland and Harold. H. Hopkins and Narinder Kapany of Imperial College in London separately announced imaging bundles in the prestigious British journal Nature.

Neither van Heel nor Hopkins and Kapany made bundles that could carry light far, but their reports the fiber optics revolution. The crucial innovation was made by van Heel, stimulated by a conversation with the American optical physicist Brian O'Brien. All earlier fibers were "bare," with total internal reflection at a glass-air interface. van Heel covered a bare fiber or glass or plastic with a transparent cladding of lower refractive index. This protected the total-reflection surface from contamination, and greatly reduced crosstalk between fibers. The next key step was development of glass-clad fibers, by Lawrence Curtiss, then an undergraduate at the University of Michigan working part-time on a project to develop an endoscope to examine the inside of the stomach with physician Basil Hirschowitz, physicist C. Wilbur Peters. (Will Hicks, then working at the American Optical Co., made glass-clad fibers at about the same time, but his group lost a bitterly contested patent battle.) By 1960, glass-clad fibers had attenuation of about one decibel per meter, fine for medical imaging, but much too high for communications.

Meanwhile, telecommunications engineers were seeking more transmission bandwidth. Radio and microwave frequencies were in heavy use, so they looked to higher frequencies to carry loads they expected to continue increasing with the growth of television and telephone traffic. Telephone companies thought video telephones lurked just around the corner, and would escalate bandwidth demands even further. The cutting edge of communications research were millimeter-wave systems, in which hollow pipes served as waveguides to circumvent poor atmospheric transmission at tens of gigahertz, where wavelengths were in the millimeter range.

Even higher optical frequencies seemed a logical next step in 1958 to Alec Reeves, the forward-looking engineer at Britain's Standard Telecommunications Laboratories who invented digital pulse-code modulation before World War II. Other people climbed on the optical communications bandwagon when the laser was invented in 1960. The July 22, 1960 issue of Electronics magazine introduced its report on Theodore Maiman's demonstration of the first laser by saying "Usable communications channels in the electromagnetic spectrum may be extended by development of an experimental optical-frequency amplifier."

Serious work on optical communications had to wait for the continuouswave helium-neon laser. While air is far more transparent at optical wavelengths than to millimeter waves, researchers soon found that rain, haze, clouds, and atmospheric turbulence limited the reliability of long-distance atmospheric laser links. By 1965, it was clear that major technical barriers remained for both millimeter-wave and laser telecommunications. Millimeter waveguides had low loss, although only if they were kept precisely straight; developers thought the biggest problem was the lack of adequate repeaters. Optical waveguides were proving to be a problem. Stewart Miller's group at Bell Telephone Laboratories was working on a system of gas lenses to focus laser beams along hollow waveguides for long-distance telecommunications. However, most of the telecommunications industry thought the future belonged to millimeter waveguides.

Optical fibers had attracted some attention because they were analogous in theory to plastic dielectric waveguides used in certain microwave applications. In 1961, Elias Snitzer at American Optical, working with Hicks at Mosaic Fabrications (now Galileo Electro-Optics), demonstrated the similarity by drawing fibers with cores so small they carried light in only one waveguide mode. However virtually everyone considered fibers too lossy for communications; attenuation of a decibel per meter was fine for looking inside the body, but communications operated over much longer distances, and required loss no more than 10 or 20 decibels per kilometer.

One small group did not dismiss fibers so easily -- a team at Standard Telecommunications Laboratories initially headed by Antoni E. Karbowiak, which worked under Reeves to study optical waveguides for communications. Karbowiak soon was joined by a young engineer born in Shanghai, Charles K. Kao.

Kao took a long, hard look at fiber attenuation. He collected samples from fiber makers, and carefully investigated the properties of bulk glasses. His research convinced him that the high losses of early fibers were due to impurities, not to silica glass itself. In the midst of this research, in December 1964, Karbowiak left STL to become chair of electrical engineering at the University of New South Wales in Australia, and Kao succeeded him as manager of optical communications research. With George Hockham, another young STL engineer who specialized in antenna theory, Kao worked out a proposal for long-distance communications over single-mode fibers. Convinced that fiber loss should be reducible below 20 decibels per kilometer, they presented a paper at a London meeting of the Institution of Electrical Engineers. The April 1, 1966 issue of Laser Focus noted Kao's proposal:

"At the IEE meeting in London last month, Dr. C. K. Kao observed that short-distance runs have shown that the experimental optical waveguide developed by Standard Telecommunications Laboratories has an information-carrying capacity ... of one gigacycle, or equivalent to about 200 tv channels or more than 200,000 telephone channels. He described STL's device as consisting of a glass core about three or four microns in diameter, clad with a coaxial layer of another glass having a refractive index about one percent smaller than that of the core. Total diameter of the waveguide is between 300 and 400 microns. Surface optical waves are propagated along the interface between the two types of glass."

"According to Dr. Kao, the fiber is relatively strong and can be easily supported. Also, the guidance surface is protected from external influences. ... the waveguide has a mechanical bending radius low enough to make the fiber almost completely flexible. Despite the fact that the best readily available low-loss material has a loss of about 1000 dB/km, STL believes that materials having losses of only tens of decibels per kilometer will eventually be developed."

Kao and Hockham's detailed analysis was published in the July 1966 Proceedings of the Institution of Electrical Engineers. Their daring forecast that fiber loss could be reduced below 20 dB/km attracted the interest of the British Post Office, which then operated the British telephone network. F. F. Roberts, an engineering manager at the Post Office Research Laboratory (then at Dollis Hill in London), saw the possibilities, and persuaded others at the Post Office. His boss, Jack Tillman, tapped a new research fund of 12 million pounds to study ways to decrease fiber loss.

With Kao almost evangelically promoting the prospects of fiber communications, and the Post Office interested in applications, laboratories around the world began trying to reduce fiber loss. It took four years to reach Kao's goal of 20 dB/km, and the route to success proved different than many had expected. Most groups tried to purify the compound glasses used for standard optics, which are easy to melt and draw into fibers. At the Corning Glass Works (now Corning Inc.), Robert Maurer, Donald Keck and Peter Schultz started with fused silica, a material that can be made extremely pure, but has a high melting point and a low refractive index. They made cylindrical performs by depositing purified materials from the vapor phase, adding carefully controlled levels of dopants to make the refractive index of the core slightly higher than that of the cladding, without raising attenuation dramatically. In September 1970, they announced they had made single-mode fibers with attenuation at the 633-nanometer helium-neon line below 20 dB/km. The fibers were fragile, but tests at the new British Post Office Research Laboratories facility in Martlesham Heath confirmed the low loss.

The Corning breakthrough was among the most dramatic of many developments that opened the door to fiber-optic communications. In the same year, Bell Labs and a team at the Ioffe Physical Institute in Leningrad (now St. Petersburg) made the first semiconductor diode lasers able to emit continuouswave at room temperature. Over the next several years, fiber losses dropped dramatically, aided both by improved fabrication methods and by the shift to longer wavelengths where fibers have inherently lower attenuation.

Early single-mode fibers had cores several micrometers in diameter, and in the early 1970s that bothered developers. They doubted it would be possible to achieve the micrometer-scale tolerances needed to couple light efficiently into the tiny cores from light sources, or in splices or connectors. Not satisfied with the low bandwidth of step-index multimode fiber, they concentrated on multi-mode fibers with a refractive-index gradient between core and cladding, and core diameters of 50 or 62.5 micrometers. The first generation of telephone field trials in 1977 used such fibers to transmit light at 850 nanometers from gallium-aluminum-arsenide laser diodes.

Those first-generation systems could transmit light several kilometers without repeaters, but were limited by loss of about 2 dB/km in the fiber. A second generation soon appeared, using new InGaAsP lasers which emitted at 1.3 micrometer, where fiber attenuation was as low as 0.5 dB/km, and pulse dispersion was somewhat lower than at 850 nm. Development of hardware for the first transatlantic fiber cable showed that single-mode systems were feasible, so when deregulation opened the long-distance phone market in the early 1980s, the carriers built national backbone systems of single-mode fiber with 1300-nm sources. That technology has spread into other telecommunication applications, and remains the standard for most fiber systems.

However, a new generation of single-mode systems is now beginning to find applications in submarine cables and systems serving large numbers of subscribers. They operate at 1.55 micrometers, where fiber loss is 0.2 to 0.3 dB/km, allowing even longer repeater spacings. More important, erbium-doped optical fibers can serve as optical amplifiers at that wavelength, avoiding the need for electro-optic regenerators. Submarine cables with optical amplifiers can operate at speeds to 5 gigabits per second, and can be upgraded from lower speeds simply to changing terminal electronics. Optical amplifiers also are attractive for fiber systems delivering the same signals to many terminals, because the fiber amplifiers can compensate for losses in dividing the signals among many terminals.

The biggest challenge remaining for fiber optics is economic. Today telephone and cable television companies can cost-justify installing fiber links to remote sites serving tens to a few hundreds of customers. However, terminal equipment remains too expensive to justify installing fibers all the way to homes, at least for present services. Instead, cable and phone companies run twisted wire pairs or coaxial cables from optical network units to individual homes. Time will see how long that lasts.