Fiber-Optic. Communication Systems. Third Edition. GOVIND E? AGRAWAL. The Institute of Optics. University of Rochester. Rochester: NY. Read "Fiber-Optic Communication Systems" by Govind P. Agrawal available from Rakuten Kobo. Sign up today and get $5 off your first download. This book. As of today we have 78,, eBooks for you to download for free. No annoying ads, no Fiber Optic Communications Fundamentals and Applications
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Fiber optics has become the backbone of all communications systems, including telecom – landline and wireless - the Internet, CATV, LANs, etc. Most books. Get this from a library! Fiber optics: communication and other applications. [ Henry Zanger; Cynthia Zanger]. Identify the basic components of a fiber optic communication system. • Discuss light propagation in an optical fiber. • Identify the various types of optical fibers.
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Institutional Subscription. Free Shipping Free global shipping No minimum order. This book will be of value to communications engineers, designers, and researchers. The receiver performs the OE transducer function. Figure Schematic of an Optical Receiver A receiver is generally designed with a transmitter. Both are modules within the same package. The light detection is carried out by a photodiode, which senses light and converts it into an electrical current.
However, the optical signal from the fiber-optic cable and the resulting electrical current will have a small amplitude. There might even be filters and equalizers to shape and improve the information-bearing electrical signal. The receiver schematic in Figure shows a photodiode, bias resistor circuit, and a low-noise pre-amp.
The output of the pre-amp is an electrical waveform version of the original information from the source. To the right of this pre-amp is an additional amplification, filters, and equalizers.
All of these components can be on a single integrated circuit, a hybrid, or discretely mounted on a printed circuit board. The receiver can incorporate a number of other functions, such as clock recovery for synchronous signaling, decoding circuitry, and error detection and recovery. The receiver must have high sensitivity so that it can detect low-level optical signals coming out of the fiber-optic cable.
The higher the sensitivity, the more attenuated signals it can detect. It must have high bandwidth or a fast rise time so that it can respond fast enough and demodulate high-speed digital data. It must have low noise so that it does not significantly impact the BER of the link and counter the interference resistance of the fiber-optic cable transmission medium.
In most premise applications, the PIN is the preferred element in the receiver. This is mainly due to fact that it can be operated from a standard power supply, typically between 5 and 15V.
APD devices have much better sensitivity. In fact, APD devices have 5 to 10 dB more sensitivity. They also have twice the bandwidth. They also require a stable power supply, which increases their cost.
APD devices are usually found in long-haul communication links and can increasingly be found in metro-regional networks because APDs have decreased in cost. The demodulation performance of the receiver is characterized by the BER that it delivers to the user. The sensitivity curve varies from receiver to receiver. The sensitivity curve considers within it the SNR parameter that generally drives all communications-link performance.
What cabling of the fiber is required-strength members, power conductor, size, weight? How easy is it t o make a splice under operating conditions? Does the connector have to keep out water or gases? Where should these devices be located to maximize the signal-to-noise ratio? What is best spacing? These and other questions must be answered to accomplish a successful design that meets the link objectives [I]. To the beginning worker in fiber optics technology the choices can be overwhelming.
It is the purpose of this text to allow the user of fiber optics technology to accomplish a first-order design of a link for an application, while appreciating the tradeoffs required to achieve the desired performance goal. Japan Europe 1. The traditional way of meeting this requirement has been t o increase the carrier frequency, as the information bandwidth is constrained t o be, at most, equal t o the carrier for baseband transmission or some fraction of the carrier.
Hence, t o meet the increased bandwidth demands, information carriers have transitioned from HF to VHF to UHF to microwaves t o millimeter waves and, finally, to light waves.
Fiber Optics Engineering
The bandwidth of a copper-based medium is tied t o the losses in that medium. In coaxial-line technology, the cable losses in decibels per length increase linearly with the carrier frequency. Reduction of the losses at any particular frequency can be achieved by increasing the diameter of the cable, but eventually the cable becomes too large and bulky.
Fiber-optic cables do not exhibit this linear increase in loss with frequency, and the losses can be made quite small by the proper fiber construction and the proper choice of operating wavelength. In considering dat a rates, some benchmark dat a rates might be useful.
The telephone industry has established standard data rates for various applications.
Fiber Optics Engineering
Table 1. Suppose that the signal extends from 0 Hz t o an upper frequency of BW Hz. For example, an audio signal extends from dc t o 20, Hz; a video signal in the United States extends from 0 to 5 MHz. Such a signal, before it is modulated onto a carrier wave, is called a baseband signal. Reasonable values of S range from 6 to The number of bits N per sample depends on the accuracy required.
Eight bits allows the data to be divided into 2' quantization levels. More accuracy requires more bits. Twelve bits allows the sample to be represented as one of levels; sixteen bits would give 65, levels. Currently eight bits usually represents the low end of acceptable accuracy and sixteen bits represents the high end except in cases calling for extreme accuracy.
So, we find that the data rate of the digitized signal in units of bits per second will be where S x BW is seen to be the number of samples per second and N is the number of bits per sample. We can estimate the bandwidth B of a channel that carries a data rate of DR as It is important to separate in your mind the bandwidth BW of the information signal from the bandwidth B of the carrier required for the digitized version of the signal.
Hence, we see that the data rate will always be a multiple of the bandwidth of the information signal.
From this multiplier factor we understand that increased accuracy in the data requires a significant increase in the data rate-the perfect justification for fiber optics. Among the potential advantages offered by optical fiber communications are: Wide bandwidth. The bandwidth of a medium depends directly on the carrier frequency. Optical carriers are superior to rf and microwave carriers because of their higher frequen- cies. Optical fibers offer the possibility of several thousands of GHz i.
Light weight and small size. Due to their small volume and lower density, optical fiber cables enjoy considerable weight advantages over typical coaxial cables.
As a measure of the size of a reel of fiber-optic cable, a rule of thumb is that one can achieve "fifty miles per gallon," i. Immunity to Electromagnetic Interference. Since optical fibers are nonconducting, they will neither generate nor receive electromagnetic interference. This feature allows the use of fibers in regions of high electric fields, as with power electronics, radar feed horns and antennas, nuclear explosions, and other such sources of intense electromagnetic 1.
Indeed one of the thriving applications of fiber optics is sending control signals into power stations, where switching transients could obliterate them.
Telemetry links for bringing information out of a system exposed t o high electromagnetic signals, such as EMP electromagnetic pulse or lightning-strike testing of military aircraft and missiles, also use fiber optics.
Finally, optical fibers are used t o telemeter information out of underground atomic-bomb test caverns, where the EMP from the blast would contaminate the data from the experiment. One form of EM1 occurs when two con- ducting lines lie near enough t o each other to allow the signal from one t o leak into the other called crosstalk because of overlapping electromagnetic fields.
Traditional solutions have included further separation of the cables or increased shielding i. However, the optical fields extending from an optical fiber are negligible, eliminating optical pickup between adjacent cables.
For special purpose applications that require transmission of infor- mation through hazardous cargo areas e. For example, circuitous routes are followed in electrically transmitting information from an aircraft fuselage to the wing stations t o avoid the fuel tanks in the wings. Use of fiber optics allows the line to be routed by the most direct path. The physical dimensions of the fiber-optic sources, detectors, and connectors, as well as the fiber itself, are compatible with modern miniaturized electronics.
Most components are available in dual in-line packaging DIP packs , making mounting on a printed circuit board extremely easy. This compact size of components is of prime importance in making this new technology acceptable to today's electronic designer. Copper is a critical commodity on the world market; as such, it is subject t o rapid upward and downward fluctuations in price. The primary ingredient of silica- based glass fibers, on the other hand, is widely available and is not a critical commodity.
The price tradeoffs, comparing a fiber-optic link with alternative technology, are usually dependent on dat a rate since low data rates can use more economically coaxial cable. All economic analyses show that, at some value of data rate, a fiber link becomes cost effective. The exact location of the price crossing point is sensitive to many variables, but the trend is clear-fiber-optic technology is cost effective only for wideband signals with data rates typically in excess of tens of megabits per second.
Of course, if one is using another of the special properties of fiber optics e. This requirement for wideband signals to justify an economic advantage for fiber optics works t o a disadvantage in the American market, where regulation inhibits a telephone carrier from providing other services such as cable TV. While other nations combine their telephone, postal and broadcasting services and are investigating the use of a single-fiber drop t o provide broadband services, in the United States only cable television companies currently have the potential bandwidth demand t o justify fiber-optic home hookups unless new services, such as electronic-catalog shopping, are offered to telephone subscribers.
Since fiber optics is a nonradiating means of information transfer, no government licenses are required t o implement a link. This offers potential advantages t o companies that desire a point-to-point communication link between two locations for temporary use and that wish t o avoid the time-consuming licensing process.
Although rights-of-way must be negotiated for the fiber-cable route, this is frequently preferable to the licensing process. Along with the advantages, of course, come some potential disadvantages.
These include: 0 Lack of Bandwidth Demand. Although fiber-optic systems have been demonstrated with multigigabit data rates and even terabitls rates , few users have requirements for such data rates today. The total traffic in North America was estimated t o be about one-third of a terabit per second i. Since at lower data rates, fiber links cost more than conventional links, they are not yet suited for these applications.
Many installed fiber links have excess capacity beyond their present usage. Historic trends predict, however, that society will require high data rates as we become more information dependent.
Even at present, applications appear on the horizon that require the real-time transmission of high-resolution pictorial information, or the multiplexing of many channels into a dat a superhighway. In addition, lower-cost components are being devised for low-data-rate links. The cost of low-loss fibers, plastic connectors, long-wavelength light-emitting diode sources, and other economic components is steadily reducing the cost of the lower-performance links. Users of fiber optics find it advantageous, in some cases, t o anticipate future demands for bandwidth, since installation of a fiber optic link is typically a capital investment with an anticipated lifetime of over 20 years.Figure 1.
Figure Schematic of an Optical Receiver A receiver is generally designed with a transmitter. Light weight and small size. Turquet de Beauregard, R. Please select Ok if you would like to proceed with this request anyway.
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