Main Characteristics of Fiber Optics Communication System. - Light propagation in of Plastic Fibers. (Source: raudone.info). Identify the basic components of a fiber optic communication system. • Discuss light propagation in an optical fiber. • Identify the various types of optical fibers. PDF | Optical Fiber Communication-An Introduction | ResearchGate, the professional network for scientists.
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Fiber optic data transmission systems send information over fiber by turning electronic signals into light. ❑ Light refers to more than the portion of the. Element of an Optical Fiber Transmission link. Basic block diagram of optical fiber communication system consists of following important blocks. 1. Transmitter. 2. image, and the first application of optical fibers to imaging was conceived. development of optical fiber communications was primarily a materials one—it was.
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Optical Fibre Communications: Principles and Practice
Keiser, G. Bowers, J. Miller and I. Tsang, W.
CrossRef Google Scholar Kobayashi, K. Lightwave Technol. Mukai, T. Green, P. Personick, S. Forrest, S. Gimlett, J. Ogawa, K.
Quantum Electron. Tran, D. Henry, P. From the bust of the dot-com bubble through , however, the main trend in the industry has been consolidation of firms and offshoring of manufacturing to reduce costs. Modern fiber-optic communication systems generally include an optical transmitter to convert an electrical signal into an optical signal to send through the optical fiber, a cable containing bundles of multiple optical fibers that is routed through underground conduits and buildings, multiple kinds of amplifiers, and an optical receiver to recover the signal as an electrical signal.
The information transmitted is typically digital information generated by computers, telephone systems and cable television companies. The most commonly used optical transmitters are semiconductor devices such as light-emitting diodes LEDs and laser diodes. The difference between LEDs and laser diodes is that LEDs produce incoherent light , while laser diodes produce coherent light.
For use in optical communications, semiconductor optical transmitters must be designed to be compact, efficient and reliable, while operating in an optimal wavelength range and directly modulated at high frequencies. In its simplest form, an LED is a forward-biased p-n junction , emitting light through spontaneous emission , a phenomenon referred to as electroluminescence. However, due to their relatively simple design, LEDs are very useful for low-cost applications.
The large spectrum width of LEDs is subject to higher fiber dispersion, considerably limiting their bit rate-distance product a common measure of usefulness. LEDs have also been developed that use several quantum wells to emit light at different wavelengths over a broad spectrum and are currently in use for local-area WDM Wavelength-Division Multiplexing networks.
The narrow spectral width also allows for high bit rates since it reduces the effect of chromatic dispersion. Furthermore, semiconductor lasers can be modulated directly at high frequencies because of short recombination time. Laser diodes are often directly modulated , that is the light output is controlled by a current applied directly to the device.
For very high data rates or very long distance links , a laser source may be operated continuous wave , and the light modulated by an external device, an optical modulator , such as an electro-absorption modulator or Mach—Zehnder interferometer.
External modulation increases the achievable link distance by eliminating laser chirp , which broadens the linewidth of directly modulated lasers, increasing the chromatic dispersion in the fiber. A transceiver is a device combining a transmitter and a receiver in a single housing see picture on right.
Fiber optics have seen recent advances in technology. The main component of an optical receiver is a photodetector which converts light into electricity using the photoelectric effect. The primary photodetectors for telecommunications are made from Indium gallium arsenide The photodetector is typically a semiconductor-based photodiode.
Several types of photodiodes include p-n photodiodes, p-i-n photodiodes, and avalanche photodiodes. Metal-semiconductor-metal MSM photodetectors are also used due to their suitability for circuit integration in regenerators and wavelength-division multiplexers. Optical-electrical converters are typically coupled with a transimpedance amplifier and a limiting amplifier to produce a digital signal in the electrical domain from the incoming optical signal, which may be attenuated and distorted while passing through the channel.
Further signal processing such as clock recovery from data CDR performed by a phase-locked loop may also be applied before the data is passed on. An optical communication system transmitter consists of a digital-to-analog converter DAC , a driver amplifier and a Mach—Zehnder-Modulator. Digital predistortion counteracts the degrading effects and enables Baud rates up to 56 GBaud and modulation formats like 64 QAM and QAM with the commercially available components.
The transmitter digital signal processor performs digital predistortion on the input signals using the inverse transmitter model before uploading the samples to the DAC. Older digital predistortion methods only addressed linear effects.
Recent publications also compensated for non-linear distortions. Berenguer et al models the Mach—Zehnder modulator as an independent Wiener system and the DAC and the driver amplifier are modelled by a truncated, time-invariant Volterra series.
Duthel et al records for each branch of the Mach-Zehnder modulator several signals at different polarity and phases. The signals are used to calculate the optical field. Cross-correlating in-phase and quadrature fields identifies the timing skew.
The frequency response and the non-linear effects are determined by the indirect-learning architecture. An optical fiber cable consists of a core, cladding , and a buffer a protective outer coating , in which the cladding guides the light along the core by using the method of total internal reflection. The core and the cladding which has a lower- refractive-index are usually made of high-quality silica glass, although they can both be made of plastic as well.
Connecting two optical fibers is done by fusion splicing or mechanical splicing and requires special skills and interconnection technology due to the microscopic precision required to align the fiber cores. Two main types of optical fiber used in optic communications include multi-mode optical fibers and single-mode optical fibers.
However, a multi-mode fiber introduces multimode distortion , which often limits the bandwidth and length of the link. Furthermore, because of its higher dopant content, multi-mode fibers are usually expensive and exhibit higher attenuation. Both single- and multi-mode fiber is offered in different grades. In order to package fiber into a commercially viable product, it typically is protectively coated by using ultraviolet UV , light-cured acrylate polymers , then terminated with optical fiber connectors , and finally assembled into a cable.
After that, it can be laid in the ground and then run through the walls of a building and deployed aerially in a manner similar to copper cables. These fibers require less maintenance than common twisted pair wires once they are deployed.
Specialized cables are used for long distance subsea data transmission, e. New — cables operated by commercial enterprises Emerald Atlantis , Hibernia Atlantic typically have four strands of fiber and cross the Atlantic NYC-London in 60—70ms.
The Chronicle Herald. Another common practice is to bundle many fiber optic strands within long-distance power transmission cable. This exploits power transmission rights of way effectively, ensures a power company can own and control the fiber required to monitor its own devices and lines, is effectively immune to tampering, and simplifies the deployment of smart grid technology.
The transmission distance of a fiber-optic communication system has traditionally been limited by fiber attenuation and by fiber distortion. By using opto-electronic repeaters, these problems have been eliminated. These repeaters convert the signal into an electrical signal, and then use a transmitter to send the signal again at a higher intensity than was received, thus counteracting the loss incurred in the previous segment.
An alternative approach is to use optical amplifiers which amplify the optical signal directly without having to convert the signal to the electrical domain. Optical amplifiers have several significant advantages over electrical repeaters. First, an optical amplifier can amplify a very wide band at once which can include hundreds of individual channels, eliminating the need to demultiplex DWDM signals at each amplifier. Second, optical amplifiers operate independently of the data rate and modulation format, enabling multiple data rates and modulation formats to co-exist and enabling upgrading of the data rate of a system without having to replace all of the repeaters.
Third, optical amplifiers are much simpler than a repeater with the same capabilities and are therefore significantly more reliable.
Optical amplifiers have largely replaced repeaters in new installations, although electronic repeaters are still widely used as transponders for wavelength conversion. Wavelength-division multiplexing WDM is the practice of multiplying the available capacity of optical fibers through use of parallel channels, each channel on a dedicated wavelength of light.
This requires a wavelength division multiplexer in the transmitting equipment and a demultiplexer essentially a spectrometer in the receiving equipment. Arrayed waveguide gratings are commonly used for multiplexing and demultiplexing in WDM.
Using WDM technology now commercially available, the bandwidth of a fiber can be divided into as many as channels  to support a combined bit rate in the range of 1.
This value is a product of bandwidth and distance because there is a trade-off between the bandwidth of the signal and the distance over which it can be carried. Engineers are always looking at current limitations in order to improve fiber-optic communication, and several of these restrictions are currently being researched.
Each fiber can carry many independent channels, each using a different wavelength of light wavelength-division multiplexing.
Optical Fiber Communication Technology and System Overview
The net data rate data rate without overhead bytes per fiber is the per-channel data rate reduced by the FEC overhead, multiplied by the number of channels usually up to eighty in commercial dense WDM systems as of [update]. The following summarizes the current state-of-the-art research using standard telecoms-grade single-mode, single-solid-core fibre cables.
The following summaries the current state-of-the-art research using specialised cables that allow spatial multiplexing to occur, use specialised tri-mode fibre cables or similar specialised fibre optic cables. The NICT result is notable for breaking the record for throughput using a single core cable, that is, not using spatial multiplexing.
Research conducted by the RMIT University, Melbourne, Australia, have developed a nanophotonic device that has achieved a fold increase in current attainable fiber optic speeds by using a twisted-light technique.
The nanophotonic device uses ultra thin topological nanosheets to measure a fraction of a millimeter of twisted light, the nano-electronic device is embedded within a connector smaller then the size of a USB connector, it fits easily at the end of a optical fiber cable.
The device can also be used to receive quantum information sent via twisted light, it is likely to be used in a new range of quantum communication and quantum computing research. For modern glass optical fiber, the maximum transmission distance is limited not by direct material absorption but by several types of dispersion , or spreading of optical pulses as they travel along the fiber.
Dispersion in optical fibers is caused by a variety of factors.
Intermodal dispersion , caused by the different axial speeds of different transverse modes, limits the performance of multi-mode fiber. Because single-mode fiber supports only one transverse mode, intermodal dispersion is eliminated. In single-mode fiber performance is primarily limited by chromatic dispersion also called group velocity dispersion , which occurs because the index of the glass varies slightly depending on the wavelength of the light, and light from real optical transmitters necessarily has nonzero spectral width due to modulation.
Polarization mode dispersion , another source of limitation, occurs because although the single-mode fiber can sustain only one transverse mode, it can carry this mode with two different polarizations, and slight imperfections or distortions in a fiber can alter the propagation velocities for the two polarizations.
This phenomenon is called fiber birefringence and can be counteracted by polarization-maintaining optical fiber.
Dispersion limits the bandwidth of the fiber because the spreading optical pulse limits the rate that pulses can follow one another on the fiber and still be distinguishable at the receiver. Some dispersion, notably chromatic dispersion, can be removed by a 'dispersion compensator'.
This works by using a specially prepared length of fiber that has the opposite dispersion to that induced by the transmission fiber, and this sharpens the pulse so that it can be correctly decoded by the electronics.
Fiber attenuation , which necessitates the use of amplification systems, is caused by a combination of material absorption , Rayleigh scattering , Mie scattering , and connection losses. Although material absorption for pure silica is only around 0. Other forms of attenuation are caused by physical stresses to the fiber, microscopic fluctuations in density, and imperfect splicing techniques. Each effect that contributes to attenuation and dispersion depends on the optical wavelength.
There are wavelength bands or windows where these effects are weakest, and these are the most favorable for transmission. These windows have been standardized, and the currently defined bands are the following: Note that this table shows that current technology has managed to bridge the second and third windows that were originally disjoint. This region has zero dispersion. This region has the lowest attenuation losses and achieves the longest range. It does have some dispersion, so dispersion compensator devices are used to remove this.
When a communications link must span a larger distance than existing fiber-optic technology is capable of, the signal must be regenerated at intermediate points in the link by optical communications repeaters.
Repeaters add substantial cost to a communication system, and so system designers attempt to minimize their use. Recent advances in fiber and optical communications technology have reduced signal degradation so far that regeneration of the optical signal is only needed over distances of hundreds of kilometers. This has greatly reduced the cost of optical networking, particularly over undersea spans where the cost and reliability of repeaters is one of the key factors determining the performance of the whole cable system.
The main advances contributing to these performance improvements are dispersion management, which seeks to balance the effects of dispersion against non-linearity; and solitons , which use nonlinear effects in the fiber to enable dispersion-free propagation over long distances. Although fiber-optic systems excel in high-bandwidth applications, optical fiber has been slow to achieve its goal of fiber to the premises or to solve the last mile problem.
However, as bandwidth demand increases, more and more progress towards this goal can be observed. All of the major access networks use fiber for the bulk of the distance from the service provider's network to the customer. The choice between optical fiber and electrical or copper transmission for a particular system is made based on a number of trade-offs. Optical fiber is generally chosen for systems requiring higher bandwidth or spanning longer distances than electrical cabling can accommodate.
Thousands of electrical links would be required to replace a single high bandwidth fiber cable. Another benefit of fibers is that even when run alongside each other for long distances, fiber cables experience effectively no crosstalk , in contrast to some types of electrical transmission lines.
Fiber can be installed in areas with high electromagnetic interference EMI , such as alongside utility lines, power lines, and railroad tracks. Nonmetallic all-dielectric cables are also ideal for areas of high lightning-strike incidence.
In short distance and relatively low bandwidth applications, electrical transmission is often preferred because of its. Optical fibers are more difficult and expensive to splice than electrical conductors.
And at higher powers, optical fibers are susceptible to fiber fuse , resulting in catastrophic destruction of the fiber core and damage to transmission components. Because of these benefits of electrical transmission, optical communication is not common in short box-to-box, backplane , or chip-to-chip applications; however, optical systems on those scales have been demonstrated in the laboratory.
In certain situations fiber may be used even for short distance or low bandwidth applications, due to other important features:. Optical fiber cables can be installed in buildings with the same equipment that is used to install copper and coaxial cables, with some modifications due to the small size and limited pull tension and bend radius of optical cables. Optical cables can typically be installed in duct systems in spans of meters or more depending on the duct's condition, layout of the duct system, and installation technique.
Longer cables can be coiled at an intermediate point and pulled farther into the duct system as necessary. In order for various manufacturers to be able to develop components that function compatibly in fiber optic communication systems, a number of standards have been developed. The International Telecommunications Union publishes several standards related to the characteristics and performance of fibers themselves, including.
Other standards specify performance criteria for fiber, transmitters, and receivers to be used together in conforming systems.
Some of these standards are:. TOSLINK is the most common format for digital audio cable using plastic optical fiber to connect digital sources to digital receivers. From Wikipedia, the free encyclopedia. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.
Find sources: Main article: Optical amplifier. Wavelength-division multiplexing. Last mile. July 2, Alcatel-Lucent Bell Labs announces new optical transmission record and breaks Petabit per second kilometer barrier". September 28, Archived from the original on October 18, The Fiber Optics Association.An optical communication system transmitter consists of a digital-to-analog converter DAC , a driver amplifier and a Mach—Zehnder-Modulator.
However, a multi-mode fiber introduces multimode distortion , which often limits the bandwidth and length of the link. Fiber optic cables are the most secure way for data transmission. Due to much lower attenuation and interference , optical fiber has large advantages over existing copper wire in long-distance, high-demand applications.
Green, P. Transmitters[ edit ] A GBIC module shown here with its cover removed , is an optical and electrical transceiver. Electronic nose E-textiles Flexible electronics Molecular electronics Nanoelectromechanical systems Memristor Spintronics Thermal copper pillar bump.
Laser relative-intensity-noise and nonlinearities are shown to limit the performance of analog systems. This return signal is digitally processed to detect disturbances and trip an alarm if an intrusion has occurred.
The power loss is very low and hence helpful in long-distance transmissions.
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