What is Fiber Optic?

Fiber optic is a very thin transparent glass material, which is widely used in data networks, through which light representing the data to be transmitted is sent.

What is Fiber Optic?

Fiber Optic Cable

The signal of light radiates across the core of the fiber with a reflection angle above the total reflection boundary angle as a function of Snell’s law. Also, the light source can be laser or led.

Fibers are widely used in telecommunications because they allow large amounts of data to be sent over a long distance at speeds similar to radio or wired network structures.

The transmission medium and power are excellent because they are not immune to electromagnetic interference. They are also used for local networks that are required to take advantage of other transmission environments.


The history of fiber communication is based on the production of a test system in the UK a few years after it was installed.

In 1959, as a result of physics studies focused on optics, a new light called laser signal applied to telecommunications was discovered to transmit messages to unusual speeds and long distances.

However, it was very limited due to the lack of pipes and channels suitable for moving electromagnetic waves caused by photon rain from a source called laser.

Scientists specializing in optics then directed them to the production of a pipe or channel known as fiber optic today.

Later, in 1966, the proposal to use an optical fiber guide for communication appeared.

The use of light as an information carrier in this way is an electromagnetic wave with the same structure as radio waves, except that the length of the waves is in the range of micrometers rather than meters or centimeters.

The concept of lightwave communication has been known for many years, but the results of the theoretical work were not published until the mid-1970s.

It was possible to impregnate a light signal to a transparent fiber, thereby providing an optical analog of the wire signal electronically.

The technical problem that had to be solved for the advance of the optical fiber in the fibers was that the fibers that made the process difficult to absorb light.

For practical communication, the optical fiber must be able to transmit light signals for kilometers.

Since the ordinary glass has several meters of the light beam, new very pure glasses have been developed, which are much more transparent than ordinary glass.

These glasses began to be produced in the early 1970s, and this innovation gave impetus to the fiber industry.

Lasers or light-emitting diodes are used as the light source in fiber cables.

Both are further reduced for fiber optic system components that require significant research and development work.

Lasers produce consistent light on an extremely narrow path. Diodes emit inconsistent light.


The fiber cable is a dielectric waveguide operating at optical frequencies, and each filament consists of a central plastic or glass core with a high refractive index, surrounded by a similar layer of material with some refractive index.

When the light reaches a surface bounded by a lower refractive symptom, it is largely reflected, as the difference in indices grows and the angle of incidence increases, the total internal reflection occurs.

Light signals can be reflected on the walls at very wide angles, practically moving along the center, and light signals can be directed losslessly over long distances.

   Stronger Coverage

The coating material of the fiber contains 25% more material than conventional products.

   Double Usage Area

Resistance to water and ultraviolet emissions, resistant coater, and extended environmental performance contributes to greater reliability throughout the life of the fiber.

   More Protection in Damp Places

Moisture penetration into the fiber is combined with multiple layers of protection around the fiber, providing longer lifetime and reliability in wet areas.

   High-Density Packaging

With the smallest possible maximum number of fibers in the diameter, it is faster and easier to twist the cable into sharp bends and tight spaces.

A 72-fiber super-dense structure with a diameter less than that of conventional cables were obtained.



The core consists of silica, molten quartz, or plastic. Optical waves pass through it and diameter 50 or 62.5 µm is used for the multimodal type and 9 µm for the single-mode type.

   Optical Sheath

It generally consists of the same materials as the core but has additives that limit the optical waves in the core.

   Protective Coating

The protective coating is usually made of plastic and provides mechanical protection of the fiber.


   Single-Mode Fiber

Single-mode fiber is the fiber that offers the largest capacity for information transfer. It has a bandwidth of 100 GHz/km and the highest streams are achieved with this type.

It can transmit signals with a path that follows the axis of the fiber, which is why it is named a single mode.

They are fibers whose core diameter is the same size as the wavelength of the optical signals they transmit, i.e. about 5 to 8 mm.

High data transfers are the main advantage of single-mode fibers, but due to their small size, they have precise handling and connection difficulties.

   Gradient Multimode Fiber

Multimode fibers have a data band up to 500 MHz/km. It is based on the reduction of the refractive index inside the core when it is moved to the shell.

Fibers allow the dispersion between diffusion modes different from the core to be reduced.

Multimode fiber with stepped gradient index size 62.5/125 m is normal, but multimode types with graded-index multimode 100/140 mm and gradient index 50/125 mm can be found.

   Multimode Staggered Fiber

Multimode stepped index fibers are made of glass with 30 dB/km attenuation or plastic with 100 dB/km attenuation and have a data band up to 40 MHz/km.

In these fibers, the refractive index of the core is made of a material that is clearly higher than that of the surrounding shell.

Connector Types

Whether it is a transmitter or a receiver, these connector types are responsible for connecting fiber lines. The available connector types are very diverse, but some of them are:

   FC Connector

The FC connector is used in data transmission and telecommunications.

   FDDI Connector

The FDDI connector is used for fiber networks.

   LC and MT-Array Connector

LC and MT-Array connectors are used for high data density transmissions.

   SC and SC-Duplex Connector

SC and SC-Duplex connectors are used for data transmission.

   ST/BFOC Connector

ST or BFOC are used in building networks and security systems.

   Light Beam Emitters

These devices are responsible for converting the electrical signal into a light signal, emitting the light signal that allows data transmission, these emitters are divided into LEDs and Lasers.

1. LEDs

They use 50 to 100 mA of current, their speed is slow, they can only be used in multimode fibers, but they are easy to use and economical as well as a very long life.

2. Lasers

This type of transmitter uses 5 to 40 mA current, it is very fast and can be used with both single-mode and multi-mode types, but on the contrary, it is difficult to use, its life is long but less.

   Electric Light Current Converters

This type of device converts optical light signals into electrical signals.

Malfunctions are limited to obtaining a current from the modulated light, and this current is proportional to the power received and therefore to the waveform of the modulation signal.

It is based on the inverse phenomenon of recombination, that is, the creation of electron-hole pairs from photons.

The simplest detector type corresponds to a P-N semiconductor connection.

To detect very weak optical signals for a photodetector to fulfill for use in the communication field, the reverse current must be very small, the fast response and the noise level produced by the device itself must be minimal.

There are two types of detectors, a PIN photodiode, and Avalanche photodiode.

1. PIN Photodiode

The PIN photodiode consists of the P-N port, and between this port, there is a new interior (I) zone that increases the efficiency of the detector.

It is generally used in systems that allow easy separation between possible light levels and short distances.

2. Avalanche Photodiode

Avalanche photodiode are photodiodes that apply an inverted high voltage, showing an internal effect of the current gain due to pulse ionization.

The task of these photodiodes is to launch a high-speed electron against an atom so that it can attract another electron.

These detectors are of two types: silicon and germanium.

1. Silicon

They have a low noise level and up to 90% performance and require high supply voltage (200-300 V).

2. Germanium

It is suitable for working with wavelengths between 1000 and 1300 nm and 70% performance.

How Does It Work?

There is a transmitter in the transmission system responsible for converting electromagnetic waves into optical or light energy, which is why it is considered the active component of this process.

When the light signal is transmitted by small fibers, at the third end of the circuit there is a third component called an optical detector or receiver, whose task is to convert the light signal into electromagnetic energy, similar to the original signal.

The basic transmission system consists of this input signal, amplifier, light source, optical corrector, line, attachment, optical corrector, receiver, amplifier, and output signal sequence.

In summary, this works as a means of carrying the light signal produced by the communication process, optical fiber, LEDs, and laser transmitters.

LEDs and laser diodes are suitable sources for transmission, as their outputs can be quickly controlled by deflection current. They are also small in size, brightness, wavelengths, and low-voltage attractive to handle them.

Internal Components

The main blocks of the communication link are the transmitter, receiver, and fiber guide.

The transmitter has an analog or digital interface, a voltage-current converter, a light source, and a light source adapter.

The guide is an ultra-pure glass or plastic cable.

The receiver includes a fiber-light detector connector device, a photodetector, a current-voltage converter, a voltage amplifier, and an analog or digital interface.

In a transmitter, the light source can be modulated with an analog signal or digital, but limited to combine impedances and amplitude of the signal or digital pulses.

The current transducer voltage acts as an electrical interface between the input circuits and the light source.

The light source can be an LED or an ILD laser injection diode, the amount of light emitted is proportional to the excitation current.

Therefore, the voltage to the current converter converts the input signal voltage into a current used to direct the light source.

The connection socket is a mechanical interface, the function of which is to connect the light source with the cable.

Fiberglass or plastic core consists of a jacket and a protective layer, and the combining device of the detector is also a mechanical binder.

The light detector component is usually a PIN diode or an APD.

Both convert light energy into the current. As a result, a current-voltage converter is required that converts the changes in detector current into voltage changes in the output signal.


  1. It has a very wide band that allows very high data transfers.
  2. Small size, therefore takes up little space.
  3. Great flexibility, curvature radius can be less than 1 cm, which greatly facilitates installation.
  4. Very lightweight, the weight is a few grams per kilometer, which is about nine times less than that of a conventional cable.
  5. It is fully powerful against electromagnetic disturbances, which means a very good transmission quality.
  6. Entry to an optical fiber can be easily detected by the weakening of light energy at the reception, in addition, it is useful for applications that require a high level of privacy.
  7. It is insensitive to parasites, a feature used predominantly in annoying industrial environments.
  8. Allows the same cables of non-metallic optical cables to coexist with electrical power cables.
  9. The very small attenuation is independent of frequency, which makes it possible to bridge significant distances without intermediate active elements.
  10. It is resistant to heat, cold, and corrosion.
  11. Thanks to a telemetry-based process, it is easy to locate cuts, which simplifies maintenance by allowing us to quickly locate the place and repair the fault later.


Fiber optic cables offer a number of disadvantages compared to other transmission environments, the most important of which are:

  1. Fibers have high fragility.
  2. Requires more expensive transmitters and receivers.
  3. The connections between the fibers are difficult to make especially in the field and make repairs difficult in case of a cable break.
  4. You cannot transmit power to intermediate repeaters.
  5. In many cases, it requires the need to perform electrical-optical conversion processes.
  6. This cable cannot transmit high power.

The cost of fiber optic cables can only be high when large bandwidth capacity and low attenuation are required. For low bandwidth, copper may be a much more expensive solution than a conductor.

The optical fiber cable does not conduct electrical energy, which requires power from the power supply to the receiving terminal and power must be provided by separate conductors.

Hydrogen molecules can penetrate silicon fibers and cause changes in weakening. Since the water corrodes the glass surface, the service life of the cables may decrease.

There are international regulations regarding some aspects of transmission quality and testing.

Where Are Fiber Cables Used?

The usage areas of fiber optic cables can be used for digital communication, sensors, and decorative designs such as Christmas trees, night lights, and other similar elements.

It is especially used in single fiber applications, submarine, and intercity network connection.

   Internet Area

It is the biggest factor providing high data transfer and reliability in the Internet connection services.

To surf the global network, you need the Internet, not only a computer, modem and some programs, but also a large structure.

The user can spend a few minutes waiting for a page to load, or several hours trying to download a program to their computer from the Internet.

This is because of the various tools that millions of users use to connect to the Internet.

It makes it possible to surf the Internet at two million bps compared to the traditional system, where the majority of users connect at 28,000 or 33,600 bps.

   Computer Networks Area

In computer networks, the optical cable is increasingly used because light signals have a high frequency, and the information-carrying ability of a signal increases with frequency. Also, laser systems are used in communication networks.

Many optical cables for long-distance communication are operating in computer networks today, offering intercontinental and transoceanic connections.

One advantage of these systems is the large distance that a signal can travel before it needs a repeater to restore its intensity.

Optical cable repeaters have distances of approximately 100 km from each other in electrical systems compared to about 1.5 km.

Amplifiers can further increase this distance, and another popular application is local area networks.

Unlike long-distance communication, these systems connect to central equipment such as a set of computers or printers.

This system improves equipment performance and allows new users to easily join the network.

The development of new electro-optics and integrated optical components will further increase the capacity of these systems.

Computers on the local network are separated by distances up to several kilometers and are often used in offices or university campuses.

LAN provides fast and efficient information transfer within a group of users and reduces operating costs. Other computing resources connected are Wide Area Networks (WAN) or Private PBXs.

WANs are similar to LANs but connect computers that are separated at greater distances in different parts of a country or in different countries.

PBXs provide continuous computer connections for private data transfer, such as phone transmissions, but are not suitable for spreading and receiving short-lived data increases used by most computer applications.

   Telephone Networks Area

Due to the standardization of existing interfaces, transmission systems for public telecommunications network levels are available in wide application but differ from subscriber network systems.

It is fully sufficient with existing copper conductors for a telephone connection.

The use of fiber will become necessary with the provision of broadband services such as video conferencing, video telephony.

An extensive experience was achieved with BIGFON (Integrated Urban Fiber Optic Broadband Telecommunication Network).

According to the developed strategy, broadband services will be expanded later with radio and television distribution services in an integrated broadband telecommunications network (IBFN).

   Sensor Area

Optical fibers can be used as sensors to measure tension, temperature, pressure, and other parameters.

The small size and the lack of electrical current provide some advantages over the electrical sensor.

It is used as a hydrophone for earthquake or sonar applications. Hydroponic systems with more than 100 sensors have been developed using optical cables.

Hydrophones are used by the oil industry and the navies of some countries.

These sensors can operate at higher temperatures than semiconductor sensors.

Another use as a sensor is in optical gyroscope and hydrogen micro-sensors used by Boeing 767.

   Lighting Area

Another area of ​​use is to illuminate any area. Due to the advantages this type of lighting represents in recent years, it has been widely used.

The absence of electricity and heat is that the fiber has the ability to transmit only light signals and the lamp that illuminates the fiber does not come into direct contact with it.

You can change the color of the lighting without having to change the lamp. This is because any color can carry the light beam regardless of the color of the fiber.

With a lamp, you can make a wider illumination through the fiber. This is because you can illuminate several fibers with a lamp and place them in different places.

It can be used as a waveguide in medical or industrial applications where a beam of light should be directed to a target that is not within the field of view.

Fiber optic cables can be used as a sensor to measure stress, temperature, pressure, and other parameters.

Patch cords can be used with lenses to make long and thin imaging devices called endoscopes.

Endoscopes are used in medicine to visualize objects through a small hole.

Industrial endoscopes are used for similar purposes, such as inspecting the inside of turbines.

Optical fibers have also been used for decorative uses, including lighting, Christmas trees.

It is also used to fool the sensory taxi system, which causes the taximeter not to mark the true cost of the trip.

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