FIBER OPTIC TECHNOLOGY FUNCTIONS History of Light Theory
FIBER OPTIC
History of Information Transmission with Light
The history of information communication goes back a long way. In ancient times, people used a fire to convey the information they wanted to convey. They transferred it from one hill to another. In this first communication using light, human beings are perhaps still the most He used the advanced light detector, that is, the eye. Fire is used as the source that produces light, and this light is visible to the human eye. is perceived and information is transferred from one point to another. The biggest difficulty in this primitive communication technique is communication distances were very limited and the amount of information transferred was small. developed later Communication technologies enable the transmission of information by using various media. Commonly used electrical These were technologies based on transferring the signal from one point to another through conductive cables. But the last fifty years In this period, the method used in ancient times was returned and light began to be used again in communication. in recent years It is correct to say that the basis of the leap in communication technologies is the developments in fiber optic technologies. It is possible.
History of Light Theory
To better understand why fiber optics affects people so much, perhaps we should first examine the theory of light. You need to look at its history. Of the dozens of theories about light developed in the last 3000 years, the six most important are as follows:
1) Touch
2) Radiation
3) Particle
4) Wave
5) Electromagnetic
6) Quantum
The history of information communication goes back a long way. In ancient times, people used a fire to convey the information they wanted to convey. They transferred it from one hill to another. In this first communication using light, human beings are perhaps still the most He used the advanced light detector, that is, the eye. Fire is used as the source that produces light, and this light is visible to the human eye. is perceived and information is transferred from one point to another. The biggest difficulty in this primitive communication technique is communication distances were very limited and the amount of information transferred was small. developed later Communication technologies enable the transmission of information by using various media. Commonly used electrical These were technologies based on transferring the signal from one point to another through conductive cables. But the last fifty years In this period, the method used in ancient times was returned and light began to be used again in communication. in recent years It is correct to say that the basis of the leap in communication technologies is the developments in fiber optic technologies.
he next two theories are Sir Isaac Newton's particle theories and Christian Huygens' wave theories. These, Theories that are completely opposite to each other. According to Newton, light travels in a straight line as a particle. Another one In other words, light is a system of particles and they travel in straight lines in all directions from their source. Newton's physics The law can explain the reflection of particles from objects. Huygens's wave theory does not accept Newton's theory. According to him, if light consisted of particles, The beams of light that encountered each other had to destroy themselves. To explain this, Huygens describes two water currents that meet. showed an example. Indeed, light does not show such a feature, and when light beams meet, they occur in the water sample. An event occurs as it happens. Huygens suggested that light was a wave. According to him, light and events related to it It had to be based entirely on wave theory. On the other hand, Newton said that if light was a wave, it would encounter He rejected the wave theory, claiming that it should also turn corners, but this did not happen. If today's science is It can show that light actually turns corners. However, due to the very small wavelength, this phenomenon It is not possible to see it with the naked eye. Wave theory was accepted in the 1800s. Particle theory dates back to the 1800s. It was completely abandoned in the end. In the late nineteenth century, James Clerk Maxwell combined electricity, magnetism, and light into a theory. This The theory was called electromagnetic theory. According to Maxwell, light is an electromagnetic wave and other electromagnetic waves. Shows the properties of waves. Maxwell calculated the speed of light by using electric and magnetic constants. Though The speed found is within the acceptable value; However, Maxwell's theory cannot explain the photoelectric effect.
In 1887, Heinrich Hertz discovered that light of a certain nature sent onto a metal caused electrons to move away from the metal surface. He found what he broke. In 1900, Max Planck developed another theory about light. Accordingly, light is energy that contains energy. It is transmitted in a small packet and absorbed by the substance. He called this small package "quanta". in Quanta Energy is directly proportional to the frequency of light. Albert Einstein fully accepted Planck's theory and explained that light is quanta He proposed that light, in addition to being transmitted and absorbed by matter, travels as quanta. Einstein, He accepted the photon as the quanta unit. In 1905, Einstein explained the photoelectric effect using quantum theory. Quantum theory consists of two basic theories, It was the unification of particle and wave theories. This combination was necessary; Light is sometimes a particle and sometimes a wave. shows the feature. Light is a form of energy. Photons exist only if this photon is in motion they become. The speed of light in vacuum is 3x108 meters per second. The closest relationship between fiber optics and light is reflection. Newton's laws can explain how light is reflected. Newton According to the theory, the angle of reflection does not change with the angle of incidence of light on a surface. A very important property of light is refraction. Refraction occurs when light travels in different environments. From an environment with a certain feature to an environment with another feature Light is refracted as it passes. The speed of light sometimes increases and sometimes decreases depending on the medium in which it moves. For example, light is in the air It goes faster than glass. From one environment to another. The change in the speed of light as it passes through the object causes it to break. Fiber optic technology is a result of the theory of light that has been developed over the last few centuries. We saw that in ancient times, fire was a signal. was used as a tool. As science developed, the signaling used in communication changed and this process became much more complex. It became confusing. Although the studies of scientists about light date back to ancient times, the developments in fiber technologies The development is quite new
Communication with Fiber Cables
As seen in the figure above, any information (sound, data or image) is first converted into an electrical signal. is converted. These signals are converted into light signals in the light source. An important point here is that fibers are both digital and It can also carry analog signals. Many people may think that fibers only carry digital signals (the light source by opening and closing). Once the signal is converted into a light signal, it travels through the fiber until it reaches the detector. Here the light signal is converted back into an electrical signal. Finally, the electrical signal is decoded to provide information. (audio, data or image) is converted. Fiber cables used in communication have three basic parts. The inner part of the fiber is the core, then the wall and the fiber core. In the outer part, there is the coating section of the cable (Figure 3). The figure below shows the cross section of a typical fiber cable. is showing. The vein is the part through which the light signal travels, in other words, the part where information is transmitted. Telecommunication Fiber cables with sizes ranging from 8.3 micrometers to 62.5 micrometers are generally used in the industry. Core diameter of standard telecommunication fiber is 8.3 micrometers (single mode), 50 micrometers (multimode), It is located around 62.5 micrometers (multimode). The radius of the wall surrounding the vascular area is 125 micrometers, and the radius of the entire fiber cable is 250 micrometers. It varies between 900 and 900 micrometers. We can compare these sizes with the diameter of a human hair, which is 70 micrometers. After light enters the fiber optic cable, it travels in a balanced manner and this is called mode. Depending on the type of fiber cable Hundreds of different modes can be created depending on the mode. Each mode carries a portion of the input light signal. A more general In other words, the number of modes in the fiber depends on the diameter of the fiber core, the wavelength of the light and the size called numerical aperture. It depends. There are two basic types of fiber optic cables in use today: single mode and multimode fibers. Exclude these It is not possible to distinguish them by their appearance. Both types are used as communication media. But different They are used in different ways in applications. Single Mode Fibers: They allow light to travel in a single mode or on a single path (Figure 4). Vessel diameters It is 8.3 micrometers. Single mode fibers have low signal losses and require high data communication speed. They are used in situations. Multimode Fibers: These are fibers that transmit more than one mode of light. Typical vessel diameters are 50 micrometers to 62.5 micrometers. varies between micrometers. Multimode fibers are used in short distance applications.
Basic Principles of Fiber Optics
It progresses by reflecting from the walls. Achieving full reflection depends on the angle of entry of the light beam into the fiber cable. Refractive index is a concept that shows the propagation speed of light in its environment. Light travels at a speed of 300 000 km per hour in a vacuum. progresses rapidly. The refractive index is obtained by dividing the speed of light in vacuum by its speed in any medium: Index of Refraction=(Speed of Light in Vacuum)!(Speed of Light in Medium) The refractive index in the gap is 1 in this case. The table below shows the refractive index for some typical media
Application Principles
We call the region of the electromagnetic spectrum that the human eye can perceive the visible region. in the visible region The wavelength of light can be expressed in light colors. Rainbow colors are red, orange, yellow, green, blue and purple They are located in the visible region as shown in the figure below. Electromagnetic devices used in fiber optic communication The wavelength of the waves lies above the visible region. Typical optical communication wavelengths, 850 nanometers (nm), 1310 nm, and 1550 nm. Both lasers and LEDs produce light signals over fiber optic cables. available. Laser sources are 1310 or 1550 nanometers and are suitable for single mode applications. LEDs are 850 or used in multimode applications at wavelengths of 1300 nanometers.
FREQUENCY
There are certain wavelength range windows where fiber works best. These can be called working windows. Each The window forms around the typical wavelength (Figure 7). The table below gives these windows
Window Wavelength
800 - 900 nm 850 nm
1250-1350nm 1310nm
1500—l600nm 1550nm
The reason why these windows were chosen is because they are the areas where fiber optics work best, in other words, the available light The best match of communication features with the source. The frequency of the system is understood as follows: The modulation frequency of the digital or analog signal, or in other words The number of signals sent by the light source per second. Frequency is measured in hertz. 1 hertz every second corresponds to pulse (pulse). The practical unit used in communication is the megahertz (MHz), which has one million pulses per second. corresponds.
Losses in Fiber Optic Cables
The energy and therefore the shape of the light signal traveling through the fiber cable is lost for various reasons (Figure 8). This The loss is measured in decibels (dB/km). The fiber used over a certain distance must be low loss. Therefore Low loss fiber optic systems are preferred. For example, loss of 50% of the initial output power results in a loss of 3.0 dB. corresponds. When fiber cables are combined or mounted within the system, some losses are encountered (Figure 9). If two fiber cables are joined end to end, the typical loss is 0.2 dB. Although the causes of loss are many, they are internal and external. Losses can be divided into two classes. If the light signal reaches any irregular region within the fiber cable, it is scattered and the scattered signal is It may be absorbed by the region and prevent its progression. Rayleigh scattering is the most important type of scattering (generally 96%). The light inside the fiber interacts with the glass atoms that make up the fiber. Light waves collide elastically with atoms and the light wave is scattered. If, after scattering, the light strikes the wall at an angle greater than the angle that provides complete refraction, If it hits, the fiber leaves the cable and runs away. The second type of internal loss is the absorption of the light signal by the fiber. Such losses constitute 3-5% of overall losses. The reason why the light signal is absorbed by the fiber is the impurities in the glass that forms the fiber. These are vibrations or cause other types of energy losses (Figure 10). The other type of loss is external losses. For example, if the fiber optic cable is bent, the tension in this region increases and the increase in tension changes the refractive index. In this case, full reflection of the light signal does not occur and the vascular causes the area to be abandoned. This type of bending is called macro bending. If these bends occur inside the cable at a micro level, the signal is lost by leaving the core area of the fiber. why does it happen The light pulse propagates as it travels through the fiber cable. In this case, the throw expands to the previous or next one. coincides with the next throw; that is, the transmitted light signal becomes inseparable. As a result, the information transmitted its characteristic feature is lost. In other words, information is lost. As described previously, propagation causes the light signal to disperse. This dispersion causes the light pulses to combine with each other. The pulse sent at a certain distance and at a certain frequency cannot be read by the receiver. becomes. Apart from this, overlapping and mixing of signals, which generally appear in multi-mode fibers, can also lead to loss of information. causes. The bandwidth of systems is measured in megahertz (MHz) per kilometer. For example, if a system's bandwidth If the range is 200 MHz-km, 200 million pulses per second reach the sensor without interfering with each other in a kilometer fiber.
Results and Trends
Looking at the development of the industry, it would not be wrong to say that the information age started in 1985 and its pace slowed down after 1995. We are now rapidly moving into a new age, the age of communication. The most important character of this age, accessing and distributing information through new communication tools. People's start to use the Internet and the rapid increase in demand in this regard has caused the national communication infrastructure to be reviewed and renewed. Chromatic distribution depends on the wavelength range used in the light source. produced by laser or LEDs The wavelength of light is within a certain range. Waves of different wavelengths traveling through the fiber have different speeds. has. Therefore, they cover equal distances in different times; This causes the signal to spread. of the signal Excessive dissemination distorts its character and causes information to be lost. Such losses are single mode It is very important in fiber optic applications. Band Gap: Band gap refers to the features that the detector at the other end can distinguish after the light signal is sent. We can define it as the amount of information it carries. The most important criterion for keeping up with this era on a national basis is the size of the communication traffic in the country. Naturally, the way to increase communication and keep up with the times depends on the infrastructure being good enough. Therefore fiber The intensive use of technologies in our country is a necessity of vital importance. In the information age, people were looking for a way to access information in a more one-way, non-interactive way. In new condition, In other words, conditions are changing rapidly in the age of communication. In the new situation, people have double needs in accessing information and communicating with others. They use versatile and interactive tools. Fiber optic cables are now rapidly replacing copper cables and other means of communication in all countries. Fiber optic The most important difference between cables and other communication media is the high speed of voice, data and image communication. fiber cable The ends will soon extend into our living room. At the other extreme, millions of information sources and interactive communication Considering that there are people we can provide, it is undoubtedly easier to understand what globalization is and its importance. it will be easy. COLOR SEQUENCE OF 60-96-144 FIBER CABLE 
The working principle of fiber is based on basic optical rules. A beam of light travels from a less dense medium to a more dense medium. While passing into the medium, depending on the angle of incidence, it is either reflected (full reflection) or refracted and goes out of the medium (this It is based on the logic of "undesirable situation". The cable consists of 3 parts. INDEX: The difficulty coefficient of a light ray moving through matter. INDEX OF REFRACTION: The ratio of the speed of light in a vacuum to the speed of light in a substance is called the index of refraction. CORE: It is the part in the center of the cable through which the light travels. It is made of very pure glass and is flexible. Well It can be bent within certain limits, depending on its type, its diameter is between 8 micrometers and 100 micrometers, depending on whether it is single-mode or multi-mode. varies between micrometers (note: a human hair is around 100 micrometers). SHEATH: It covers the core, typically 125 micrometers in diameter, and prevents the light injected into the fiber from exiting the core. It is the blocking part. It is made of glass just like the core, but it is approximately 1% less in terms of index difference. Due to the index difference, the light ray does not pass into the sheath after being injected into the core (unless there is excessive folding or crushing). The ray returns to the core from the sheath core boundary and proceeds within the core as a series of reflections. COATING: The coating, which does not have any optical properties, may be polymer or plastic and may have one or more layers. It has no optical properties, it only protects the fiber from impacts and shocks.
Some of the Fiber Optic cable types
Injecting the Beam into the Fiber
The beam or signal to be sent is injected into the core of the fiber. However, a certain angle must be created within the fiber to prevent it from passing into the sheath. This angle is called the critical angle. Calculation is as follows.
Gradual Index Fiber Multimode graded index fiber is one of the simplest fiber types. It has a core diameter between 100 – 970µm. A larger core diameter is beneficial in terms of carrying more modes. However, modal diffusion is mostly of this type. It happens in fiber. The propagation is 15-30 nanoseconds per km. The number may seem like 15 to 30 billionths of a second, but It is at a level that will cause errors in all coding systems. The acceptable amount of spread is 1 ns per km.
Wavelengths and Spectral Width of Light Every ray has a wavelength. This wavelength is where the light is visible or invisible or where it is on the electromagnetic spectrum. and determines what properties it has. For example, infrared rays are beyond the limit that the human eye can perceive. is below.
The speed at which a beam of light travels through the core depends on its wavelength. For example, purple light, that is, violet light, has waves. its length is 455 nm, the wavelength of red light is 620 nm. This means that these two rays do not travel at the same speed through the fiber. red ray It progresses faster (in each cycle) as the wavelength difference between them increases. This feature of light returns to us as a disadvantage. returns(as modal propagation). mode Mode can generally be defined as each ray injected into a fiber and partly reflects the information-carrying capacity of the fiber. expresses. The number of modes that each fiber can carry depends on the diameter and structure of the core. Number of modes the fiber can transmit First, the normalized numerical aperture frequency (V) is found. Then the number of modes (N) that can be transmitted is found.
Modal Diffusion The rays injected into the fiber at the same time reach the end of the fiber at different times, this is called modal propagation and only Occurs in multimode fibers. There are 3 ways to reduce modal spread. · choosing the fiber to be used to allow fewer modes, thus enduring narrower bandwidth · Using graded index fiber: When graded index fiber is used, all rays are transmitted regardless of wavelength. They will follow the same path due to the structure of the core. This is the most effective method. There are also restrictions in terms of bandwidth does not bring · Using single-mode fiber, there is no delay since there is only one mode in this type of fiber.
https://tekniksatgroup.com.tr/uploads/docs/fiber-optik-hakkinda-bilgiler-icin.pdf
https://www.bulbapp.io/p/41268caa-3104-49aa-931b-5b3a99528599/fiber-teknoloji-uluslar-arasi-geliim-part-1
https://www.bulbapp.io/p/216f0488-4b12-49a3-b968-29dd71c320e4/fiber-teknoloji-uluslar-arasi-geliim-eu-germany-france-holland-part-2
