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Fiber Optics | Basics | Construction | Advantages

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Fiber optics is a relatively recent development in the electronics world and has met widespread acceptance. Fiber optics, as it is used in the electronics field, is the controlled transmission of light as a signal. Look at Figure 1.

The AM signal is converted to light and transmitted through the fiber-optics cable. At the cable destination, the fluctuating light signal is converted back to an AM signal.

You have already learned that copper wire as a conductor will accomplish the same goal. Let’s look at some of the reasons why optics fibers might be a better medium.

The fiber-optic system converts electrical signals to light signals and then back to electrical signals.

Figure 1. The fiber-optics system converts electrical signals to light signals and then back to electrical signals.

Fiber Optics Advantages

It may seem like extra work to convert an electronic signal to light and then convert it back again to an electronic signal. One could question why the use of copper wire, where these conversions are unnecessary, would not be more efficient.

There are quite a number of reasons a fiber-optics transmission medium might be chosen over another conductor.

  • Fiber-optics cable is lightweight and very small in diameter.
  • Fiber-optics cable is corrosion and water resistant.
  • Fiber-optics cable provides data security.
  • Fiber-optics cable is immune to electromagnetic interference.
  • Fiber-optics cable provides a great deal of safety from fire and explosion
  • The fiber-optics transmission has a wide bandwidth

Weight and size

Fiber-optics cables are exceptionally lightweight when compared to traditional copper wiring systems. This is important in general wiring applications but a much greater advantage is gained when it is used in applications where weight is a critical factor. Some of these uses are in aircraft and ships.

The lighter the weight of the plane or ship, the more cargo it can carry. Fiber-optics cables are approximately 1/10th the weight of a comparable copper wiring system.

Fiber-optics cable also has a smaller overall diameter than conventional cable systems. This is extremely important when running communication lines.

Many more communication lines can be provided in the same conduit using a fiber-optics cable. In telephone lines, over 1000 fiber-optics lines can easily fit into space where a system of 100 conventional cables once resided.

Corrosion and water resistance

The very nature of glass or plastic makes it resistant to most corrosives. Water does not affect the light conduction capabilities of a properly installed cable system. Fiber-optics cables have been run under all of the world’s oceans and are expected to last for many, many years.

Security

In today’s society, information is profitable and, in some cases, a priceless commodity. It is so important in business, industry, and in military applications that it must be protected against unethical people who would seek to gain from stealing it.

It is virtually impossible to tap into a fiber-optics cable without being detected on a secure communication line.

Any cut made into the cable or cladding will disturb the light signal. Cutting into the cable completely disrupts the transmission of the signal. Removal of any of the cladding results in a loss of signal strength.

At the present, fiber-optics lines are secure. However, many systems throughout history have been viewed as virtually impenetrable only to be compromised later.

It should be emphasized that applied creative human intellect can develop methods to compromise even the best security system. But for now, the fiber-optics cable is far more secure than copper cable.

Immunity to electromagnetic energy

Most of us have the annoying experience of having our television or radio signals interfered with by lightning strikes or the operation of an electric motor nearby.

 Fiber-optics cable conducts light instead of electricity. This makes it immune to the electromagnetic interference generated by motors, radio signals, lighting, and other sources of electromagnetic energy.

The conventional copper cable must be shielded to prevent electromagnetic interference. Adding shielding to cable results in a cable that is much more expensive to produce, much larger in overall diameter, and a lot heavier.

The military has a large investment in fiber optics and began research in the field many years ago. The detonation of nuclear weapons creates a powerful magnetic field. This magnetic field is strong enough to destroy communication systems based on copper wire. The destruction caused by this magnetic field can occur many miles from an actual nuclear explosion area.

Since fiber-optics cable can withstand the electromagnetic field generated by even a nuclear weapon, military communications could remain intact through its use.

Safety

Fiber optics can be installed near explosive vapors and dust such as in petroleum factories or food processing plants. This use eliminates the fear of an electrical spark caused by a shorted or grounded circuit using conventional conductors.

In addition, light for illumination can be directly transmitted through fiber optics in place of conventional lamps. When using electrical lamps for illumination in hazardous industries, the lamp fixtures must be a very expensive, explosion-resistant type. Fiber-optics lamps are safer and cheaper.

Bandwidth

The bandwidth available on a fiber-optics cable has superior merit when compared to copper. Light is transmitted at a much higher frequency than typical electrical signals.

More signals can be transmitted at one time with fiber optics than with wire cable systems. Conventional cable systems have limitations and losses due to inductive reactance.

Copper cables lose their conduction capabilities at extremely high frequencies. Fiber-optics cable can handle high frequencies with little to no problem.

The Nature of Light

There are two main theories of light. One theory addresses light as a wave, and the other treats light as a particle.

When light energy is traveling through air, water, or a vacuum, its nature is explained in terms of waves, similar to the electromagnetic waves of radio and TV.

When light interacts with a solid, it is explained as a particle and is referred to as a photon. The correct theory remains to be seen.

For now, the best of both theories are used to explain the phenomena of light and its interaction with the surrounding world we live in.

Look at Figure 2. As you can see light is described in terms of wavelength. Light is usually measured in nanometers (nm). Visible light has wavelengths between 390 nm and 770 nm.

Below visible light, larger wavelengths such as UHF and VHF television waves, and radar waves exist. Above visible light rays are the much shorter wavelength X-rays, gamma rays, and cosmic rays.

The actual spectrum of visible light is quite small when compared to all other forms of electromagnetic radiation.

Most fiber-optics systems use infrared wavelengths between 850 and 1500 nm. At these wavelengths, there is less loss of signal. A typical LED has a wavelength that is between 800 and 900 nm or 1250 and 1350 nm.

Visible light is only a small part of the total electromagnetic wave spectrum.

Figure 2. Visible light is only a small part of the total electromagnetic wave spectrum.

Fiber-Optics Cable Construction

A fiber-optics cable serves as a waveguide for light. The construction of a fiber-optics cable is simple. Look at Figure 3.

The fiber-optics cable is composed of a glass or plastic core surrounded by a cladding. The glass or plastic core is the medium for the movement or transfer of the light energy. The cladding keeps the light wave contained to the core.

The cladding surrounds the entire core and causes the transmitted light to remain in the core. Without the cladding on the core, the light would be lost through the sides of the core material.

The cladding and core are surrounded by a buffer area. The buffer is wrapped around the core and cladding to provide physical protection.

A fiber-optic cable is constructed of a glass or plastic core surrounded by a reflective cladding.

Figure 3. A fiber-optics cable is constructed of a glass or plastic core surrounded by a reflective cladding.

In addition to the buffer area, waterproofing materials can be inserted under the cable sheath. The cable sheath is similar to the insulated jacket on typical conductors.

The outer sheath construction and materials used depend on the environment in which the fiber-optics cable will be installed.

Some sheaths are designed to be oil or water resistant. Other sheaths are designed to be installed in salt water or buried directly in the earth. Some cables are installed in a building plenum area.

A plenum is an airspace above a drop ceiling or under a raised floor, such as those in computer rooms. See Figure 4.

Figure 4. The plenum area of a building structure is located above the dropped ceiling and under a raised floor.

When the fiber-optics cable is installed in plenum areas, the installation usually falls under the jurisdiction of the National Electrical Code. The NEC has strict regulations about the type of insulation that can be used on the outer covering of fiber-optics cables installed in plenum areas.

Fumes produced if this covering were to burn in a fire can be dangerous to personnel in the building. In many buildings, the plenum area also contains the air-conditioning system. This ducting would make fumes and vapors present in the plenum area harmful to personnel throughout the building.

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About Ahmad Faizan

Mr. Ahmed Faizan Sheikh, M.Sc. (USA), Research Fellow (USA), a member of IEEE & CIGRE, is a Fulbright Alumnus and earned his Master’s Degree in Electrical and Power Engineering from Kansas State University, USA.