Optical Fiber Technology
Optical fiber is a flexible, transparent fiber cable prepared by drawing glass (silica) or plastic to a little thicker diameter than, that of a human hair. Optical fibers are used most often for the transmission of light between two ends of fiber optic cable and have large usage in fiber-optic communications systems. The optical fiber cable transmits “signal” by light to a receiving end, where the light signal is decoded as data. Therefore, fiber optics is actually a transmission medium used to carry signals over long distances at very high speeds.
It is a reliable medium to transmit light signals over long distances and at higher bandwidths (data transfer rates) as compared to electrical cables. Fibers are used in their place of metal wires because signals travel along them with low loss; in addition, fibers are immune to electromagnetic interferences or noise. Optical Fibers are also used for illumination and imaging and are often enfolded in bundles so that, they may be used to carry light into, or images out of confined spaces. Specially designed fibers are also used for a variety of applications, some of them being fiber optic sensors and fiber lasers.
Construction and working
Optical fiber typically has a core material surrounded by transparent cladding material. The cladding refracting index is lower than the refractive index of the core material. The light signal travels in the core by the phenomenon of total internal reflection. So, fiber optics transmit data in the form of light particles known as photons that pulse through a fiber optic cable. The glass fiber core and the cladding each have a different refractive index that helps to bend of incoming light at a certain angle. When light signals are sent through the fiber optic cable, they reflect off the core and cladding in a series of zig-zag motion, obeying total internal reflection.
Fig. Fiber optic cable structure
Types: Fibers are classified based on the propagation modes they support.
Single-mode fibers: That supports a single mode of propagation. Generally used for longer distances communication due to the smaller diameter of the glass fiber core, which minimizes the possibility of attenuation. The smaller opening isolates the light into a single beam, which offers a more direct path and allows the signal to travel a longer distance. Single-mode fibers also have higher bandwidth than multimode fiber. The light source used for single-mode fiber is normally a laser.
Multi-mode fibers:That supports many propagation paths or transverse modes. Multi-mode fiber has a wider core diameter and is used for short-distance communication links and for applications where high power must be transmitted. The larger diameter of fiber permits multiple light pulses to be sent through the cable at one time, which results in more data transmission rates. This also means that there is more possibility for signal loss, attenuation or interference, however. Multimode fiber optics typically uses an LED as a light source.
Advantages and disadvantage of fiber optic cable
Higher Bandwidth: No other cable-based data transmission medium offers the bandwidth that fiber optic cable does. The volume of data that fiber optic cables transmit per unit time is far greater compared to copper cables.
Larger Distance: Optical cables are capable of providing low power loss, which enables signals to be transmitted over longer distances than copper cables.
Resistance to Electromagnetic Interference: Practical fiber has a very low bit error rate of (10 EXP-13), as a result, fiber being so resistant to electromagnetic interference. Fiber optic transmission is practically noise-free.
Low Security Risk: There is no way to detect the data being transmitted by “listening in” to the electromagnetic energy “leaking” through the cable, which ensures the total security of information.
Small Size and lightweight
Disadvantages: Over many advantages there exist some disadvantages too.
Fragility: Optical fiber cables are made of glass, which makes it more fragile than electrical wires. In addition to it, glass can be affected by various chemicals including hydrogen gas making them need more care when deployed underground.
Hard to Install: Splicing fiber optic cable is not easy, and if they are bending too much, they will break. The fiber cable is highly susceptible to cut or damaged during installation or construction activities. All these things make it difficult to install.
Attenuation & Dispersion: As transmission distance becomes longer, the light will be attenuated and dispersed, which requires extra optical components like EDFA.
Cost Is Higher Than Copper Cable