optic fiber

Optic fiber

A few months ago in my town you are wiring the entire fiber optic network to permanently delete the copper connections, What are they and how these substitutes copper for data transmissions?

The optical fibers, refer to the medium and the technology associated with the transmission of information as pulses of light along a wire or a glass or plastic fiber. A fiber optic cable may contain a variable number of these glass fibers, from a few to a few hundred. Around the fiberglass core there is another layer of glass called coating. One known as a buffer tube layer protects the coating and a coating layer serves as a final protective layer for the single wire.

How does the optical fiber

The optical fibers transmit data in the form of particles of light - or photons – that pulse through a fiber optic cable. The core of glass fiber and the coating each have a different refractive index which bends the incoming light at a certain angle. When the light signals are sent through the fiber optic cable, reflect the core and the coating in a series of rebounds in a zig-zag, adhering to a process called total internal reflection. The light signals do not travel at the speed of light due to the more dense glass layers, reach approximately 70% the speed of light. To renew or strengthen the signal on his journey, the transmission of the optical fiber sometimes requires repeaters to regenerate the optical signal by converting it into an electrical signal, processed and ritrasmettesso as optical signal.

Types of fiber optic cables

The multimode fiber and singlemode fiber are the two main types of fiber optic cable.

Lthe fiber monomodale It is used for longer distances due to the smaller core diameter of glass fiber, which reduces the attenuation of the signal strength. The smallest aperture isolates the light in a single beam, which provides a more direct path and allows the signal to travel a greater distance. The singlemode fiber also has a significantly higher bandwidth compared to multimode fiber. The light source used for the single-mode fiber is typically a laser. The singlemode fiber is usually more expensive because it requires accurate calculations to produce the laser light in a smaller opening.

The multimode fiber It is used for shorter distances because the core of the wider opening allows light signals to bounce and reflect more along the route. The larger diameter allows to send more light pulses through the cable at once, which results in increased data transmission. This also means that there are more chances of loss, reduction or signal interference. The multimode optical fibers typically use an LED to create the light pulse.

While the copper cables were the traditional choice for telecommunications, networks and cable connections for years, the optical fiber has become a common alternative. Most long-distance telephone lines are now made with fiber optic cables. The optical fiber carries more information than the traditional copper wire, thanks to the greater bandwidth and higher speeds. Since glass does not conduct electricity, the optical fibers are not subject to electromagnetic interference and signal losses are reduced to a minimum.

Furthermore, the fiber optic cables can be immersed in water and used in high-risk environments such as undersea cables, They are also more resistant, thinner and lighter than copper cables and should not be subjected to maintenance or replacement. The copper wire is often most economical of the optical fibers, however, and it is already installed in many areas in which the fiber optic cable has not been installed.

Using optical fibers

The computer network is a case of common use of the optical fibers, because of the optical fiber ability to transmit data and provide high bandwidth. Similarly, the optical fibers are frequently used in the transmissions and electronics to provide better connections and performance.

Even the military and space industries use the optical fiber as a medium of communication and signal transfer, in addition to its ability to provide the temperature detection, They are useful due to their lower weight and smaller dimensions.

Optical fibers are frequently used in a variety of medical tools to provide precise lighting. They also help in minimally invasive medical procedures. Since the optical fiber is not subject to electromagnetic interference, It is ideal for various tests such as MRI scans. Other medical applications for optical fibers include the X-ray imaging, endoscopy, light therapy and the surgical microscope.

The use of modern types of fiber optic cables is rooted in the research of the '50s. In those years, Research and development in the transmission of visible images through optical fibers led to some success in the world of medicine, where it was used in lighting instruments and remote viewing. In 1966 Charles Kao and George Hockham proposed the transmission of information on fiberglass and realized that, to make a practical proposal, essential were much lower cable losses. This was the driving force behind the developments to reduce optical losses in the fiber production. Today, those losses are significantly lower than the original target set by Kao and Hockham.

The benefits of fiber optics

Because of the properties at low loss and with a high bandwidth of the fiber-optic cabling, It can be used over greater distances than copper cables. In data networks, sections can be made up to 2 km without the use of repeaters. The light weight and small size also make them ideal for applications where copper cables would be impractical functioning; using multiplexer, a fiber can replace hundreds of copper cables. That's pretty impressive for a small glass filament.

Today there are three standard sizes used in data communications: 50/125, 62,5/125 e 8,3/125. The multimode cables 50/125 e 62,5 / 125 microns are used in data networks; although, recently, the 62.5 It has become the most popular choice,though the 50/125 is the best option for Gigabit Ethernet applications is a telecommunications technology that provides data rates up to 10 billion bits per second .

Propagation of light

The light travels along a fiber cable by means of a process called total internal reflection ; This is made possible by the use of two types of glass that have different refractive indices. The inner core has a high refractive index and the outer coating has a low index. This is the same principle of the reflection you see when you look in a pond. The water in the pond has a higher refractive index than air, and if you look sideways, you will see a reflection of the surrounding area; however, If you look directly into the water, you can see the bottom of the pond.

For a specific angle between these two points of view, the light stops to reflect on the water surface and passes through the air-water interface, allowing you to see the bottom of the pond.


In multimode fibers, come suggers the name, there are multiple modes of propagation for the light rays. These range from low order modes, taking the most direct route right in the middle, the high-order mode, that take the longest route, while they are bouncing from one side along the entire fiber. This has the effect of spreading the signal because the rays of a light pulse coming end at different times; this is known as intermodal dispersion , sometimes referred to as the differential mode delay o DMD. To ease the problem, They have been developed fibers with graded index. A difference of the types of fiber optic cables that have a barrier between the core and the coating, these have a high refractive index at the center which gradually reduces to a low refractive index at the periphery. This slows down the methods of lower order, allowing the rays to approach farther, reducing the intermodal dispersion and improving the shape of the signal.

A brief history of fiber optics

Ever since Roman times, the glass has been transformed into fibers. In 1790 the brothers Chappe invented the first “optical telegraph”. It was a system consisting of a series of lights mounted on towers where operators would transmit a message from one tower.

In 1954, the “maser” It was developed by Charles Townes and his colleagues at Columbia University. Maser is going to “microwave amplification by stimulated emission of radiation”.

The laser was introduced in 1958 as an efficient source of luce.Il concept was introduced by Charles Townes and Arthur Schawlow to show that masers could be made to operate in the optical and infrared regions. Basically, the light is reflected back and forth in a medium energized to generate amplified light than gas excited molecules amplified to generate radio waves, as in the case of the maser. Laser stands for “amplification of the light emission by stimulated emission of radiation”.

A laser gas helio-neon (O-Ne) It is tested in a laboratory environment. The laser tube is made of lead glass, the same glass used in neon signs.

In 1960, the first to helium-neon gas continuously operating laser was invented and tested. In the same year it was invented an operable laser which used a pink synthetic ruby ​​crystal as a means and producing a pulse of light.

In 1970 Morton Panish e Izuo Hayashi dei Bell Laboratories, along with a group Body Ioffe Institute in Leningrad, They have shown a semiconductor laser diode capable of emitting continuous wave at room temperature.

Military scientists used laser technology for a variety of military applications.

In 1973, Bell Laboratories has developed a modified chemical vapor deposition process that heats the chemical vapor and oxygen to form an ultra-transparent glass that can be produced in series in fiber low-loss optical. This process remains the standard for the production of fiber optic cables.

The fiber amplifier doped with erbium, which has reduced the cost of long-distance fiber systems by eliminating the need for optical-electrical-optical repeaters, It was invented in 1986 by David Payne of the University of Southampton and Emmanuel Desurvire at Bell Labratories. Based on the laser amplifier technology optimized Desurvire, the first transatlantic telephone cable is put into operation in 1988.

The first fiber optic cable, TPC-5, which uses optical amplifiers it has been installed in the Pacific Ocean 1996. The following year the connection optical fiber Around the Globe (FLAG) It became the longest in single cable network in the world and provided the infrastructure for the next generation of Internet applications.

Recently in top of the range Samsung TV, is a tiny fiber optic cable c was added toon the potential for transfer of 12,5 GBPS and an outer diameter of 1,8mm (almost invisible), capable of carrying all the information needed to display images in 4K 3D audio over.

Capable of keeping up to 15m away all the TV inputs to put that does not change the aesthetics of the room in place.

The in submarine optical fiber cables now provide 99,8% all intercontinental communications as Principal arteries of the Internet The rest is history of our giormi.




1 reply
  1. gvsoft
    gvsoft says:

    always accurate, Amilcare
    But I think I used the fiber optic connections even in years 90 to connect to a central computer a series of terminals (PC with terminal function). The connection started from the system via LAN and was part of a LAN / FIBER converter in the head at the end of another fiber cable FIBER / LAN converter. With this system could connect distant terminal groups hundreds of meters from the system and without any slowdown in the responses to and from the system.


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