Today the manipulation of the light is controlled within a cable, with special terminations and special plates that make the transmission possible .
By looking in detail at how optical fiber is made up, we will understand its advantages and disadvantages, and we will also have a global vision of this medium. This example is about a cable composed of many parts, we must understand that there are many types of cables that adapt to different occasions (interior, exterior, etc.) but I took this as a reference because you can see in detail what elements may contain a cable. This will serve them because commonly in the catalogs of fiber optic cables, they specify that they are composed, therefore, knowing the components and so that they work, we will be able to choose the best cable for what we are assembling.
The advantages of fiber optic cables
-First, fiber optics offers much higher throughput than most current communications technologies.
-In addition, the fiber connection avoids the problems of packet loss, which makes it possible to reduce or even eliminate the screens that remain frozen for television broadcasting, for example. It offers a great comfort because at home, you can send your photos and videos, download content on the internet almost instantly, watch TV with excellent quality, phone, all at the same time. In addition to being very high, the bit rates are also symmetrical ie the bit rate is the same whether you download data or upload.
-Fiber optics also offers an advantage over signal attenuation, which remains very low, allowing transmission of more than one kilometer with multimode fibers, and more than ten kilometers with single-mode fibers. This loss of signal over a large distance is therefore much lower than during an electrical transmission in a metal conductor. It is therefore possible to cover a more remote area without loss of performance.
-Great security. The intrusion in an optical fiber is easily detectable, due to the weakening of the light energy in reception, besides it does not radiate anything, which is particularly interesting for applications that require a high degree of confidentiality.
– Resistance to heat, cold and corrosion.
-Unlimited and continuous access 24 hours a day, without congestion.
-Fiber optic makes it possible to surf the Internet, at a speed of 2 million bps, unthinkable in the conventional system, in which most users connect to 10mbps, 100mbps or 1000mbps.
– Video and sound in real time.
– The raw material to make it is abundant in nature.
The disadvantages of fiber optic cables
Fiber optics does not only have advantages. Indeed, like any system, nothing is perfect so we can notice various problems.
Although it is efficient and fast, there is always a loss of information since the totality of the light energy is not the same input or output. These attenuations are the result of some problems.
We thus find problems related to the impurity of the fiber, all the materials that make up the fiber are not totally pure.
The dispersion In general what is called dispersion is the spread of the light signal when it propagates in the optical fiber. If the dispersion is too large, errors in the receiver occur. In the case where different light radiation is used within the same fiber, there may be chromatic dispersion. This chromatic dispersion therefore occurs during Wavelength Division Multiplexing ( WDM) multiplexing , where several different wavelengths will be passed on the same fiber in order to increase the bandwidth of a fiber. The result will therefore sometimes lead to chromatic dispersion due to the difference in the propagation speed of the different wavelength signals.
Curvatures The bends may change the inclination at which the light beam will strike the wall of the sheath and thereby fail to satisfy the total reflection condition. There will be a simple refraction and loss of light in the sheath.
They are sources of many losses and have different names:
separation Radial or angular misalignment
Excentricity of cores
Ellipticity of cores
These problems are the main cause of the attenuation because the connection must be very precise. This means that there must be perfect alignment, which is not easy. For example, a monomode type fiber has a core of only 10 microns in diameter, so having a perfect alignment is very complicated.
Different materials according to their attenuation
Depending on the materials that make up the fiber optic as well as the type of fiber itself (that is to say, index jump, index gradient or monomode), the attenuation varies. Indeed, the material used which has the strongest attenuation is the plastic with 200 dB / km. There is also fluorinated glass with 1 dB / km, but despite its low attenuation it is dif fi cult to manufacture and therefore little used. Thus, the most used material in the optical fiber is silicon with a germanium doped core.
For this material, the attenuation depends on the type of the fiber:
For an optical fiber with a jump of index, the attenuation is from 2 to 5 dB / km.
For an optical fiber with an index gradient, it is 0.9 to 3 dB / km.
For a single-mode optical fiber, it is 0.5 to 1.3 dB / km.
This attenuation can nevertheless be measured using a reflectometer. This apparatus sends an optical pulse into the fiber. A screen allows to see the signal of the signal and thus to measure the losses during each connection. But the reflectometer does not give the total loss of the optical fiber, it only allows to visualize where it is.
In this diagram which shows the attenuation of the light signal according to the wavelength , it is noted that, according to the wavelength of the source, the weakening of the light in the fiber can vary. Thus, thanks to this drawing we see that the attenuation is greater in the red (850 nanometers) than in the infrared (1300-1550 nanometers). In order to maximize the performance of the optical fiber, it is imperative to know which are the wavelengths for which the attenuation will be minimal .
The installation of optical fiber cables is one of the main economic constraints since it generates costs equivalent to those of landfills and also requires qualified personnel to properly install these networks. In addition, transmitters and receivers placed at the ends are very expensive, which is why only large companies can afford the financing of such installations.
The cost is high in the fiber optic connection, the companies do not charge for the time of use, but for the quantity of information transferred to the computer, or any other equipment or household appliance connected to the internet, the information is measured bytes.
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