What is Fiber Optic [Optical Fiber]? – Definition, Features, Types, Pros and Cons

Fiber Optic. It is a transmission medium commonly used in data networks; a fine thread of transparent material, glass or plastic materials, through which pulses of light that represent the data to be transmitted are passed. The beam of light is wholly confined and propagates through the fiber core with a reflection angle above the total reflection limit angle, depending on Snell’s law. The light source can be laser or a led.

Fibers are widely used in telecommunications, as they allow substantial amounts of data to be sent a great distance, with speeds similar to those of radio or cable. They are the transmission medium par excellence because they are immune to electromagnetic interference, they are also used for local networks, where you need to take advantage of the fiber optic advantages over other transmission media

Fiber Optic Definition

The Fiber Optic is a physical means of transmission of information, usually in data networks and telecommunications, which consists of a thin filament of glass or plastic, through which pulses of laser or LED light travel, in which the data to be transmitted

Through the transmission of these light pulses, information can be sent and received at remarkable speeds through a cable run, safe from electromagnetic interference and with rates similar to those of the radio. This makes fiber optic the most advanced cable transmission medium that exists.

The Fiber Optic as such would not enjoy the interest of the engineers until 1950, and in 1970 the first piece would be manufactured, using impurities of titanium on silica, by Robert Maurer, Donald Keck, Peter Schultz, and Frank Zimar. The first transmission of information through this medium was made on April 22, 1977 in Long Beach, California, and in the 1980s it was perfected and began to be implemented internationally.

Fiber Optic Features

Fiber Optic is a dielectric waveguide that operates at optical frequencies. Each filament consists of a central core of plastic or glass (silicon oxide and germanium) with a high refractive index, surrounded by a layer of similar material with a slightly lower refractive index.

When the light reaches a surface that borders a lower refractive index, it is primarily reflected, the higher the difference in indices and the higher the angle of incidence, then there is the talk of total internal reflection.

Inside an Fiber Optic, the light is reflected against the walls at very open angles, so that it practically advances through its center. In this way, the light signals can be guided without loss over long distances.

Throughout the entire creation and development of fiber optics, some of its features have been changing to improve it. The most outstanding features of fiber optic today are:

• Stronger coverage: the cover contains 25% more material than conventional sheets.
• Dual-use (indoor and outdoor): The resistance to water and ultraviolet emissions, the resistant cover, and the extended environmental performance of the Fiber Optic contribute to more excellent reliability during the life of the thread.
• Increased protection in humid places: The intrusion of moisture inside the fiber with multiple layers of security around it is combated, which gives the thread a longer life and reliability in humid places.
• High-density packaging: With the maximum number of fibers in the smallest possible diameter, a faster and easier installation is achieved, where the cable must face sharp bends and narrow spaces. A cord with 72 super dense construction fibers whose diameter is 50% smaller than that of conventional cables has been achieved.

Origin and evolution

The history of fiber optic communication is relatively short. In 1977, a test system was installed in England; Two years later, significant quantities of orders for this material were already produced.

Earlier, in 1959, as a derivation of studies in physics focused on optics, a new use of light was discovered, which was called a laser beam, which was applied to telecommunications for messages to be transmitted to incredible speeds and extensive coverage.

However, this use of the laser was very limited because there were no suitable conduits and channels to travel the electromagnetic waves caused by the rain of photons originating from the source called laser.

It was then that scientists and technicians specialized in optics directed their efforts to the production of a duct or channel, known today as the Fiber Optic. In 1966 the proposal to use an optical guide for communication emerged.

This way of using light as an information carrier can be detailed as follows: It is an electromagnetic wave of the same nature as radio waves, with the only difference that the wavelength is of the order of micrometers instead of meters or centimeters.

Optical Fiber Evolution

The concept of lightwave communications has known for many years.

However, it was not until the mid-1970s that the results of the theoretical work were published. These indicated that it was possible to rely on a light beam in a flexible transparent fiber and thus provide an optical analog of the signaling by wires electronically.

The technical problem that had to be solved for the advance of the Fiber Optic lay in the fibers themselves, which absorbed light that hindered the process. For practical communication, the Fiber Optic must transmit detestable light signals for many kilometers.

Ordinary glass has a light beam of a few meters. New very pure crystals have developed with much greater transparency than regular glass.

These glasses began to be produced in the early seventies. This breakthrough gave impetus to the fiber optic industry. Lasers or light-emitting diodes are used as a light source in the fiber optic cables. Both have to be miniaturized for fiber optic system components, which has required considerable research and development.

Lasers generate intense “coherent” light that remains on an extremely narrow path. The diodes emit “incoherent” light that is neither strong nor concentrated. What should be used depends on the technical requirements to design the given fiber optic circuit.

Components and Types

Fiber optic components

• Core: in silica, molten quartz, or plastic. In it, the optical waves propagate. Diameter: 50 or 62.5  µmfor multimode fiber and 9 µm for a single-mode thread.
• Optical cover: Generally the same materials as the core but with additives that confine the optical waves in the center.
• The protective coating: it is usually made of plastic and ensures the mechanical protection of the fiber.

Types of Fiber Optics

Singlemode fiber: Potentially, this is the fiber that offers the highest information transport capacity. It has a passband of the order of 100  GHz /km. The highest flows are achieved with this fiber, but it is also the most complex to the implant.

The drawing shows that only the rays that have a trajectory that follows the axis of the fiber can be transmitted, so it has earned the name of “single-mode” (propagation mode, or path of the light beam, unique). They are fibers that have the diameter of the core in the same order of magnitude as the wavelength of the optical signals they transmit, that is, about 5 to 8  mm.

If the core is made up of a material whose refractive index is very different from that of the roof, then we speak of single-mode stepped fibers. The high flows that can be achieved constitute the main advantage of single-mode threads since their small dimensions imply delicate handling and entail connection difficulties that are still poorly dominated.

• Multimode gradual gradient index fiber: Multimode continuous gradient index fibers have a passband that reaches up to 500  MHz/ km. Its principle is based on the fact that the index of refraction inside the core is not unique and decreases when it moves from the center to the roof.

The light rays are focused towards the fiber axis, as can be seen in the drawing. These fibers allow reducing the dispersion between the different propagation modes through the fiber core. The multimode fiber of gradual gradient index of size 62.5 / 125  m (core diameter/shell diameter) is standardized, but other types of threads can be found:

• Multimode stepped index 100/140  mm.
• Multimode of gradient gradient index 50/125  mm.

Multimode stepped index fiber: Multimode stepped index fibers are made of glass, with an attenuation of 30  dB / km, or plastic, with an attenuation of 100  dB / km. They have a passing band that reaches 40   MHz / km

In these fibers, the core is constituted by a uniform material whose refractive index is higher than that of the surrounding shell. The passage from the nucleus to the deck, therefore, implies a brutal variation of the index, hence its stepped index name.

Connector types

These elements are responsible for connecting the fiber lines to a component, whether it is a transmitter or a receiver. The types of connectors available are very varied, among which we can find  the following:

• FC, which is used in data transmission and telecommunications.
• FDDI is used for fiber-optic networks.
• LC and MT-Array that are used in high-density data transmissions.
• SC and SC-Duplex are used for data transmission.
• 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 beam that allows data transmission, these emitters can be of two types:

1. LEDs They use a current of 50 to 100  mA, its speed is slow, it can only be used in multimode fibers, but its use is natural and its lifetime is considerable, in addition to being economical.
2. Lasers This type of transmitter uses a current of 5 to 40  mA, they are very fast, it can be used with both types of fiber, single-mode and multimode, but on the contrary its use is complicated, its lifetime is long but shorter than the of the LEDs and they are also much more expensive.

• Electric light-current converters. These types of devices convert the light signals that come from the Fiber Optic into electrical signals. They are limited to obtaining a current from the incident modulated light, this current is proportional to the power received, and therefore, to the waveform of the modulating signal.

It is based on the opposite phenomenon to recombination, that is, the generation of electron-hollow pairs from photons. The simplest type of detector corresponds to a PN semiconductor junction. The conditions that a photodetector must meet for its use in the field of communications are the following:

1. The reverse current (in the absence of light) must be minimal, to detect weak optical signals (high sensitivity).
2. Fast response (large bandwidth).
3. The noise level generated by the device itself must be minimal.

There are two types of detectors: PIN photodiodes and APD avalanche.

1. PIN detectors: Its name comes from the fact that they are composed of a PN junction and between that junction, a new zone of natural material (I) is inserted, which improves the efficiency of the detector. It is mainly used in systems that allow easy discrimination between possible light levels and over short distances.
2. APD detectors: Avalanche photodiodes are photodetectors that show, by applying a high reverse voltage, an internal current gain effect (approximately 100), due to impact ionization (avalanche effect). The mechanism of these detectors consists in launching an electron at high speed (with sufficient energy), against an atom so that it can tear out another electron.

These detectors can be classified into three types:

1. Silicon: they have a low noise level and a performance of up to 90% working in the first window. They require a high supply voltage (200-300  V).
2. Germanium: suitable for working with wavelengths between 1000 and 1300 nm and with a yield of 70%.

Fiber Optic Function process

In a fiber optic transmission system, there is a transmitter that is responsible for transforming electromagnetic waves into optical or light energy, which is why it is considered the active component of this process. Once the light signal is transmitted by the tiny fibers, at another end of the circuit, there is a third component called the optical detector or receiver, whose mission is to transform the light signal into electromagnetic energy, similar to the original message.

The primary transmission system is composed in this order of input signal, amplifier, light source, optical corrector, fiber optic line (first section), splicing, fiber optic line (second section), optical corrector, receiver, amplifier and output signal.

In summary, it can be said that this communication process, the Fiber Optic works as a means of transporting the light signal, generated by the transmitter of LED’S (light-emitting diodes) and laser.

Light-emitting diodes and laser diodes are suitable sources for fiber optic transmission because their output can be quickly controlled using a polarization current. Also, their small size, brightness, wavelength, and low voltage needed to handle them are attractive features.

Devices implicit in this process

The main blocks of a fiber optic communications link are a transmitter, receiver, and fiber guide. The antenna consists of an analog or digital interface, a voltage to current converter, a light source and light to fiber source adapter.

The fiber guide is an ultra-pure glass or a plastic cable. The receiver includes a fiber-to-light detector connector device, a photodetector, a current-to-voltage converter, a voltage amplifier, and an analog or digital interface. In a fiber optic transmitter, the light source can be modulated by an analog signal or digital.

Coupling impedances and limiting the amplitude of the signal or in digital pulses. The voltage to current converter serves as an electrical interface between the input circuits and the light source.

The light source can be an LED light-emitting diode or an ILD laser injection diode; the amount of light emitted is proportional to the excitation current. Therefore the voltage to current converter converts the input signal voltage into a flow that is used to direct the light source. The source to fiber connection is a mechanical interface whose function is to connect the light source to the cable.

The Fiber Optic consists of a fiberglass or plastic core, a cover, and a protective layer. The coupling device of the fiber-to-light detector is also a mechanical coupler.

The light detector is usually a PIN diode or an APD (avalanche photodiode). Both convert light energy into the current. Consequently, a current to voltage converter is required that transforms changes in the detector current to changes in voltage in the output signal.

Fiber Optic Pros

• A band of extensive passage, which allows very high flows (of the order of the GHz).
• Small size, therefore occupies little space.
• Excellent flexibility, the radius of curvature can be less than 1 cm, which greatly facilitates installation.
• Very light, the weight is of the order of a few grams per kilometer, which is about nine times less than that of a conventional cable.
• Total immunity to electromagnetic disturbances, which implies an outstanding transmission quality, since the signal is immune to storms, sizzling.
• Excellent security: the intrusion into an Fiber Optic is easily detectable by the weakening of the light energy in reception,also, it radiates nothing, which is particularly interesting for applications that require a high level of confidentiality.
• It does not produce interference.
• Insensitivity to parasites, which is a property mainly used in profoundly disturbed industrial environments (for example, in subway tunnels). This property also allows coexistence by the same non-metallic optical cable conduits with the electric power cables.
• Minimum attenuation independent of the frequency, which allows saving significant distances without intermediate active elements.
• High mechanical resistance (tensile strength, which facilitates installation).
• Resistance to heat, cold, corrosion.
• Easy to locate the cuts thanks to a process based on telemetry, which allows to quickly detect the location and subsequent repair of the fault, simplifying maintenance work.

FIber Optic Cons

Despite the advantages listed above, the Fiber Optic has severalproblems compared to other transmission media, the most relevant being the following:

• Large brittleness of the fibers.
• Need to use more expensive transmitters and receivers.
• Splices between fibers are difficult to perform, especially in the field, which makes repairs difficult in case of cable breakage.
• You can not transmit electricity to intermediate power repeaters.
• The need to carry out, in many cases are electrical-optical conversion processes.
• Conventional fiber optic cannot transmit high powers.
• There are no optical memories.

Likewise, the cost of the fiber is only justified when its large bandwidth capacity and low attenuation are required. For low bandwidth, it can be a much more expensive solution than the copper conductor.

The Fiber Optic does not transmit electrical energy, and this limits its application where the receiving terminal must be energized from an electrical line. Power must be provided by separate conductors.

Hydrogen molecules can diffuse into silicon fibers and cause changes in attenuation. Water erodes the surface of the glass and turns out to be the most critical mechanism for fiber optic aging — incipient international regulations on some aspects related to the parameters of the components, transmission quality, and tests.

Applications

Its use is very varied: from digital communications, through sensors and reaching decorative methods, such as Christmas trees, candles, and other similar elements. Single-mode fiber applications: submarine cables, intercity cables, etc.

Fiber optic communications

Internet

The fiber-optic Internet connection service breaks down the most significant limitation of cyberspace: its exasperating slowness. The purpose of the following article is to describe the mechanism of action, the advantages, and its disadvantages.

To navigate the worldwide network of networks, the Internet, not only a computer, a modem and some programs are needed, but also a hefty dose of patience. The cyberspace is a slow world to despair. A user can spend several minutes waiting for a page to load or several hours trying to download a program from the Network to their PC.

It is because the telephone lines, the means used by the majority of the 50 million users to connect to the Internet, were not created to transport videos, graphics, texts and all other elements that travel from one place to another in the Net.

But telephone lines are not the only way to cyberspace. Recently a service allows you to connect to the Internet through fiber optics. The Fiber Optic makes it possible to surf the Internet at a speed of two million bps, unthinkable in the conventional system, in which the majority of users connect at 28,000 or 33,600 bps.

Nets

Fiber Optic is increasingly used in communication because light waves have a high frequency, and the ability of a signal to carry information increases with frequency.

In the communications networks, laser systems with Fiber Optic are used. Many fiber networks for long-distance communication work today, providing transcontinental and transoceanic connections. An advantage of fiber optic systems is the great distance that a signal can travel before needing a repeater to recover its intensity.

Currently, fiber optic repeaters are separated from each other about 100 km, compared to approximately 1.5 km in electrical systems. Recently developed fiber optic amplifiers can further increase this distance. Another increasingly widespread application of fiber optics is local area networks. Unlike long-distance communications, these systems connect a series of local subscribers with centralized equipment such as computers (computers) or printers. This system increases the performance of the material and allows the incorporation of new users into the network efficiently.

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

Local area network or LAN, a set of computers that can share data, applications, and resources (for example, printers).

Computers in a local area network (LAN) are separated by distances of up to a few kilometers and are often used in university offices or campuses. A LAN allows the fast and efficient transfer of information within a group of users and reduces operating costs. Other connected computer resources are extensive area networks (WAN) or particular switchboards (PBX).

WANs are similar to LANs, but they connect computers that are separated by greater distances, located in different places in one country or different countries; They employ specialized and expensive physical equipment and lease communications services. PBXs provide continuous computer connections for the transfer of specialized data such as telephone transmissions but are not suitable for issuing and receiving short-lived data peaks used by most computer applications.

Public Communication Networks

Public communication networks are divided into different levels; according to the operation, the transmission capacity, as well as the scope they define. For example, if you are approaching from the outside to the inside of a large city, you have first the interurban network and the provisional network, then the long lines providing lower capacity traffic from remote areas (agricultural system), towards the center the urban system and finally the subscriber lines.

The parameters dictated by the practice are the transmission section that can be covered and the specific bit rate as well as the appropriate type of Fiber Optic, that is, cables with single-mode or multimode fibers.

Telephony

On the occasion of the standardization of existing interfaces, fiber optic transmission systems are available for public telecommunications network levels in a comprehensive application, contrary to subscriber network systems (subscriber line), there are first and foremost A series of considerations.

For the connection of a telephone, it is entirely sufficient with the existing copper conductors. Precisely with the implementation of broadband services such as videoconferencing, video telephony, etc., the Fiber Optic will become essential for the subscriber.

With the BIGFON (an integrated urban network of broadband fiber optic telecommunications), extensive experiences in this aspect have been collected. According to the strategy developed, broadband services will subsequently be expanded with radio and television distribution services in a broadband integrated telecommunications network ( IBFN ).

Fiber optic sensors

Fiber Optics can be used as sensors to measure tension, temperature, pressure, and other parameters. The small size and the fact that no electric current circulates through them gives certain advantages over the electronic sensor.

Fiber Optics are used as hydrophones for earthquakes or sonar applications. Hydroponic systems with more than 100 sensors have been developed using fiber optics. Hydrophones are used by the oil industry as well as the navies of some countries. The German company Sennheiser developed a microphone that worked with a laser and Fiber Optics.

Fiber optic sensors for temperature and pressure have been developed for oil wells. These sensors can work at higher temperatures than semiconductor sensors. Another use of fiber optic as a sensor is the optical gyroscope used by the Boeing 767 and the application in hydrogen microsensors.

illumination

Another form we can give to the Fiber Optic is to illuminate any space. Due to the advantages that this type of lighting represents in recent years, it has begun to be widely used.

Among the advantages of fiber lighting, we can mention:

• Absence of electricity and heat: This is because the fiber only can transmit the light beams in addition to the lamp that illuminates the texture is not in direct contact with it.
• You can change the lighting color without turning the lamp: This is because the fiber can transport the light beam of any color regardless of the color of the thread.
• With a lamp you can make a full illumination utilizing fiber: This is because with a light you can illuminate several threads and place them in different places.
• More fiber-optic applications
• It can be used as a waveguide in medical or industrial applications where it is necessary to guide a beam of light to a target that is not in the line of sight.
• The Fiber Optic can be used as a sensor to measure tensions, temperature, pressure as well as other parameters.
• It is possible to use fiber hoses together with lenses to make long and thin viewing instruments called endoscopes. Endoscopes are used in medicine to visualize objects through a small hole. Industrial endoscopes are used for similar purposes, such as to inspect the interior of turbines.
• Fiber Optics have also been used for decorative uses including lighting, Christmas trees.
• Subscriber lines
• Fiber Optics are widely used in the field of lighting. For buildings where the light can be collected on the roof and taken by a fiber optic to any part of the building.
• It is also used to trick the sensory system of taxis causing the meter (some call it counters) does not mark the actual cost of the trip.
• It is used as a component in the manufacture of translucent concrete, an invention created by the Hungarian architect Ron Losonczi, which consists of a mixture of concrete and fiber optics forming a new material that offers the strength of the concrete but additionally, presents the particularity of letting the light fully.

Conclusion

The implementation of Fiber Optic is heir to centuries of research and experimentation on light and its properties, since ancient times when the Greeks communicated through the reflection of sunlight in small mirrors, the optical experiments of the Scientific Revolution, until the invention of visual telegraphy in 1792 by Claude Chappe, and the subsequent work of French physicists Jean-Daniel Colladon and Jacques Babinet, and the Irishman John Tyndall, all at the end of the 19th century.