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optical fiber communication full report
Post: #1

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Optical Fiber Communications


1.0 Introduction of Optical Fiber Communications

Our current age of technology is the result of many brilliant inventions and discoveries, but it is our ability to transmit information, and the media we use to do it, that is perhaps most responsible for its evolution. Progressing from the copp cable, our increasing ability to transmit more information, more quickly and over longer distances has expanded the boundaries of our technological development in all areas. An optical fiber (or fiber that carries light along its length. overlap of applied science and engineering concerned with the design and application of optical fibers. Optical fibers are widely used in fiber optic communications, which permi longer distances and at higher bandwidths high frequency than any other form of radio signal than other forms of communications. Light is kept in the core of the optical fiber by total internal reflection. This causes the fiber to act as a waveguide. Fibers are used instead of metal wires because signals travel along them with less loss, and they are also immune to electromagnetic interference, which is caused by thunderstorm. Fibers are also used for illu wrapped in bundles so they can be used to carry images, thus allowing Fiber:- copper wire of a century ago to todayâ„¢s , fiber) is a glass or plastic fiber Fiber optics is the permits transmission over (data rates) because light has . Illumination, and are er fiber optic mination, viewing in tight spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers. 2.0 History of Fiber Optic Technology:- In 1870, John Tyndall, using a jet of water that flowed from one container to another and a beam of light, demonstrated that light used internal reflection to follow a specific path. As water poured out through the spout of the first container, Tyndall directed a beam of sunlight at the path of the water. The light, as seen by the audience, followed a zigzag path inside the curved path of the water
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Post: #2
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Fiber-Optic Communication Systems An

Introduction

Presented By
Xavier Fernando
Ryerson University



Why Optical Communications?

¢ Optical Fiber is the backbone of

modern communication networks
“ Voice (SONET/Telephony) - The

largest traffic
“ Video (TV) over Hybrid Fiber

Coaxial (HFC)
“ Fiber Twisted Pair for Digital

Subscriber Loops (DSL)
“ Multimedia (Voice, Data and Video)

over DSL or HFC

Why Optical Communications?

¢ Lowest attenuation à attenuation

in the optical fiber (at 1.3 µm and 1.55

µm bands) is much smaller than electrical

attenuation in any cable at useful

modulation frequencies
“ Much greater distances are

possible without repeaters
“ This attenuation is independent of

bit rate
¢ Highest Bandwidth (broadband) à

high-speed
“ Single Mode Fiber (SMF) offers the

lowest dispersion à highest bandwidth à

rich content
¢ Upgradability: Optical

communication system can be upgraded to

higher bandwidth, more wavelengths by

replacing only the transmitters and

receivers
¢ Low Cost for fiber

Why Opti-Comm for you?
¢ Most of you will eventually work

in Information and Communications

Technology (ICT) area
“ 138,000 ICT engineers hired in US

in 2006 compared to 14000 in biomedical
(http://bls.gov/oco/ocos027.htm)
¢ Canada produces 40% of the worlds

optoelectronic products (Nortel, JDS

Uniphase, Quebec Photonic Cluster¦)

Different Scenarios
¢ Digital fiber optic (SONET)

systems in the backbone“ Mostly deployed
¢ Dynamic multi-access Ethernet

systems “ LAN, GPON, EPON Access Networks

¢ Microwave (analog) fiber optic

(MFO) Systems “ CATV, Satellite base

stations
¢ Radio over fiber systems for

wireless communications (ROF)
¢ Infrared optical-wireless systems

(Free Space Optics, IrDA)

Synchronous Optical Networks

¢ SONET is the TDM optical network

standard for North America (called SDH in

the rest of the world)
¢ We focus on the physical layer
¢ STS-1, Synchronous Transport

Signal consists of 810 bytes over 125 us
¢ 27 bytes carry overhead

information
¢ Remaining 783 bytes: Synchronous

Payload Envelope
Post: #3

Reported by: Edward Yin
Student ID: 8920213

Fiber-Optic Communication System Introduction
First, the history of optical fiber communication
Modern "optical fiber communication" development began in the 1960s, while making the "optical" has become the main force of the present and future of communication is based upon our two events of excitation: first, in 1960 the U.S. physicist de Umenoto (Theodore Harold Maiman) succeeded in making the ruby oscillation have a "laser light." The second was de 1966, scientists Charles Kao (Charles Kao), and George A. Hockham, they predicted the production of "optical fiber" to let "waves" in which one kilometer transmission, there is still the original 1% of light energy, then the fiber optic cable will be able to like the general, as a transfer tool. Because at the time, even the best optical fiber, light waves in which the transmission had to make 20 meters to the original light energy to reduce energy by 1%.
That by the year 1970, the Bell Labs can be successfully produced at room temperature continuous oscillation of the semiconductor laser (Semi-Conductor-Laser), and the Corning glass works (Corning Glass Work) to produce bad per kilometer is less than 20 dB lower eradication loss of quality Quartz (Silica) fiber, the "fiber" technology by leaps and bounds.
Today, due to the development of optoelectronic technology, each less than 1 dB km decline eliminate, the transmission bandwidth is higher than 800MHZ optical cable already mass-produced, coupled with the "high-end digital multi-tasking" (High Order Digital Multiplex) technology development and high performance, "Optical Components" (Opto-Electronic Device) the development, per-second transmission speeds of up to 90 million "bit (bit)", and even per second, 400 million "bits" of the high-speed large-capacity optical communication systems, and currently has practical stage.
Second, the principle of optical fiber communication
When we use the radio transmission information, you must first into a series of telecommunications numbers, by the base stations has become a "radio signals (Radio Signal)", while the receiving station, after receiving these signals, and then convert it into a telecommunications number, after decoded into the information we need. Similarly, light can also blink through light source, such as the flash on or off signal arising from a series of graphics, which we call "light signal." Light greater than the electrical capacity of the transmission of information, meaning that light can be broken into shorter pulses, so at the same time can form a higher density and informative graphics. In this rate, through the merger of a graphic element into a "heap (Stack)", can be in the same fiber at the same time send a lot of different information. Just like cars from the interchange into the highway, it would not hit the other car. This is why the "optical fiber" can accommodate a lot of information in which the transfer reason.
Third, the advantages of optical fiber communication
(A) long-distance communications, reduce costs:
1. For example, 1.3 micron wavelength of the optical fiber for transmission, each kilometer of about 0.4 ~ 0.5dB loss;
The 1.5-micron fiber of about 0.2 ~ 0.25dB per km of the low transmission loss.
2. And the traditional copper cable transmission system comparison, the optical fiber communication so that the relay transmission distance increased to
Dozens of kilometers, and can significantly reduce the number of repeaters to reduce the cost of communications systems.
3. For example: If from Taipei to Keelung, the distance, but more than 20 kilometers; the use of a fiber optic connections,
Then the Keelung area will be no need for large rooms. As the low-loss optical fiber transmission, an increase of relay range
Transmission, reducing system cost and complexity, more suitable for long-distance transmission.
(B) optical quality of thin, light and rich could be around, easy assembly into a beam, so the assembly into a fiber optic cable laid, the
Channel space can be saved. Effectively improve the channel utilization, configuration space, economy, and suitable for
Aircraft, satellites and ships.
© The fiber has great communication bandwidth, bandwidth of up to 1 ~ 2GHz or more. An ordinary one coaxial cable
Cable's bandwidth is about 330MHz ~ 550MHz, contrast, optical fiber has a high capacity of the set hearing.
(D) the general Jie Wei quartz glass fiber material, which has a non-corrosive, fire-resistant, water resistant and long life of the special
, Coupled with optical fiber to have excellent flexibility and response, good protection of outside and tensile material,
So that optical transmission can save operating costs.
(E) Since optical media such as quartz glass, are a good insulator, will not be of electromagnetic waves, etc.
Interference, that are easily affected by lightning or high electric field area, can greatly enhance the communication fidelity.
(Vi) confidentiality is not a high optical signal radiation away from the fiber is suitable for the military, banking and electrical connections
Brain network.

As the optical fiber system has many advantages mentioned above, allowing all countries are optimistic about the prospects for optical fiber communications, and has devoted considerable financial and human resources to research and development. With the advent of the information age, large capacity, low loss, excellent communication network reliability is essential, while the optical fiber communication system is the best option. Therefore, can be expected in the near future, most of the copper cable will be replaced by optical fiber.

4, optical fiber communication system type
The whole range of fiber optic communication industry, including very wide, from the central office equipment, transmission equipment, transmission equipment in the components, and client network equipment ... and others have proprietary fiber-optic communications products, although the product rather complicated, but in order to is now available commercially mass-production products to the classification of its components can be broadly classified into three categories: made of fiber and optical fiber cable, optical active components, and optical passive components, etc..

The so-called optical fiber, quartz glass is still based on the fine fiber made from the most important product, has also recently appeared in plastic as the material of plastic optical fiber; the number of core plus the cladding material be merged into Fiber cable is referred to as fiber optic cable; while light active component will include the provision of the light source optical transmitter, receive the light source optical receivers, and optical amplifiers ... and so on; in the optical passive components in the product contained more numerous, for example, the most common fiber optic connectors, optical modulators, optical isolation devices, optical fiber coupler, optical attenuator ... and so on. (See Table 1)

Table 1: Optical Fiber Communication System type
Category Description
Fiber can be divided into three layers: core layer (core), cladding layer (clad), the protection layer (optical cable).

According to material can be roughly divided into: Glass fiber (SiO2) and the Plastic Optical Fiber (PC, PS, mCOC, PMMA, Sol-Gel).
Including the single-mode fiber optic cable (48%), multi-mode fiber optic cable (9%), submarine optical cable (43%).
According to material can be roughly divided into: Indoor (PE), outdoor (PVC).
Between the optical active component related to photovoltaic energy conversion, including: optical transmitter, optical receivers, optical transceivers, optical amplifiers, surface-emitting laser (VCSEL), optical switches, tunable lasers, L Band Amplifier.
Optical Passive Components Optical connectors (the largest share), optocouplers, optical attenuator, optical signal modulation, optical polarizer, optical isolation, filters, light source Splitter, waves Splitter.
Other DWDM systems
Optical Communication Materials
Optical local area network equipment
Telecommunications optical transmission equipment
CATV optical transmission equipment
Fiber-optic communications equipment, measurement

The following will be more important to explain the several parts:
Fiber:
1. Fiber glass SiO2, snag material made of plastic optical transmission medium, as light waves can be transmitted through optical fibers to transfer data and other information, with a transmission frequency band, communication volume, low-loss, immune to electromagnetic interference, light weight characteristics of .
2. Fiber structure, the inner layer contains a very fine glass column, called the axis core (core), outer circle known as the coating layer longer (cladding) surrounding the glass, due to the refractive index coating layer of glass over shaft Core glass column is small, axial core in the conduction of light to the coating layer, if refraction, total reflection will be the way turn back the core axis, the light waves also increased the efficiency of transmission of many. Therefore, the optical fiber from the inside out is divided into three parts: 1, shaft core part (Core): namely, fiber optical signal transmission part. 2, coating layer part (Cladding): coating the shaft core periphery, in order to send light to the core. 3, protective layer (Jacket): coating layer of shell, to prevent external damage to the coating layer and the fiber core axis.
3. Fiber practical application, it can set multi-beam optical fiber, and then to protect the layer of ways to enhance protective shell, it becomes the so-called fiber optic cable. As the fiber bandwidth can be used greatly at this stage to use an area of approximately 565 Mbps up and down in the future, cutting through the bandwidth and the WDM mode, the transmission bandwidth is expected to further expand the
4. Fiber type areas: can be summarized into a single film, more film and special optical fiber, in which single-mode fiber transmission due to only one mode, suitable for large-capacity long-distance optical fiber communication, optical fiber backbone built when the demand for cloth the largest share of output value over the years the proportion is about Bacheng, multi-fiber core diameter larger membrane, which can transmit a variety of modes of transmission performance while poor natural result of the application at the regional optical networks is the use of, the future growth rate is better than single-mode fiber . Will include a special plastic optical fiber and other optical fiber, the market volume is relatively small.

Cable
1. Malpractices fiber optic cable assembly, add water, coating as well as supporting media in order to achieve the maintenance of the existing optical fiber transmission characteristics, ease of construction and protection of fiber optic capabilities. The structure in general can be divided into optical fiber cable buffer layer, and anti-tension cable heart body, coating, and waterproof layer and some other. But according to their structural differences, may be slightly divided into (1), loose belt-type cable (2), groove-type cable (3), groove-type ribbon cable (4), four types of ribbon fiber optic cable (5), optical / electrical hybrid cable (6), indoor fiber optic cable (7), communications cable and other broad categories
2. China now truly home-made fiber manufacturers are not many, mostly by foreign buying optical fiber, coupled with a sealed tube into a fiber optic cable manufacturing. Foreign firms to Corning optical fiber, Lucent, Alcatel, Sumitomo, etc. for the industry leader. (See appendix 1, appendix II)

optical active components:
The entire fiber-optic communications system architecture which, fiber optic active components can be described as playing a "continuity," an important role as the main function of optical active components are carried out optical (or electro-optical) conversion, and optical signal amplification and so on.

Through the electro-optical conversion, the original use of electrical signals can be the process of dissemination of information, freedom to switch to optical signals for the, soon after arrival to photoelectric conversion, the optical signals into electrical signals back to the original, and then from other electronic equipment application , it makes the optical fiber communication can be achieved. In addition, the process of transmission, the signal inevitably be subject to the environment and the impact of communication media, the growth of decay as the propagation distance, in order to to maintain the accuracy of information, so in the dissemination process, you must use the amplifier will have a signal attenuation of the enhanced continue to send. Precisely because of optical active components, and so has the conversion and amplification functions, the dissemination of information to make more efficient use of fiber-optic whom, it does have a fiber optic active components, "continuity" function.

A, optical transceiver modules:
i. Department of integrating optical transceiver module optical transmitter (transmitter) and the optical receiver (receiver) two functions, while the formation of a single optical signal transceiver module. Therefore, it can be divided into communication with the light source (transmitter) and review the majority of optical device 2, in which communication with the light source some of the major use of two kinds of LED and LD light sources, LED unit though relatively inexpensive, but the LD light source in nature due to better coupled with newly developed surface-emitting laser (VCSEL) light source superior performance, with the proportion of LD of the optical transceiver modules there is a rising trend.
ii. while the inspection part of the optical device is particularly optical transceiver module of the most important key components need to have high sensitivity, high bandwidth, high reliability and low cost, easy manufacturing requirements. The current inspection devices used in optical components, mainly divided into PIN diodes, and APD diodes into two categories, Among them, the PIN diodes with lower production costs, accounting for a larger proportion.
iii. the future of optical networking will continue to enhance the transmission rate request, light source and review the performance requirements of optical devices will become the key to the development of optical networks.

B, optical amplifiers:
i. In the past, before the invention of optical amplifiers have not yet, you must first restore the optical signal back to electronic signals, the use of electronic signal amplifiers amplified and then converted to optical signal transmission. Such a process is not only complicated, but the application of electronic signal amplifier transfer rate and bandwidth is fixed, if the transmission speed optical fiber communication systems, you must upgrade all of the next update, and so makes the equipment costs have increased, but the optical amplifier does not have this trouble. Recent high-density WDM (Dense Wavelength Division Multiplexing, DWDM) system, introduction, making data transfer rates of surge, but was able to spread, it is thanks to optical amplifier to remove the barriers of traditional photoelectric conversion thanks. In addition to being in the relay transmission, the optical amplifier can be added to the transmitter to increase the output power, or for the receiver as a preamp to increase the sensitivity.
ii. optical amplifier is a photoelectric conversion without conditions, direct the optical signal to be amplified optical active components, due to long-distance fiber-optic communications will face serious light signal attenuation issue, so fiber optic network at appropriate distance from the namely, the need for repeaters or optical amplifier to amplify signals. Because of the optical amplifier without having photoelectric conversion, the network upgrade or adjust the format, then we do not like a repeater in general be replaced.
iii. optical amplifier can be divided into three categories: (1), optical fiber amplifier (OFA); (2), semiconductor optical amplifier (SOA); and (3), Raman amplifier (RA) three categories. Fiber amplifier is the use of rare-earth ions doped glass gain characteristics of the fiber directly to the signal amplification; semiconductor optical amplifier principle is similar with the laser diodes can be in the DC bias will be incident on the active layer of the optical amplification; la Man is the use of optical amplifiers and fiber non-linear interaction between atoms to produce the Stoke line up amplification. Current technology more mature optical amplifiers are erbium-doped fiber amplifier (EDFA), praseodymium-doped fiber amplifier (PDFA), three kinds of semiconductor optical amplifier.

optical passive components:
The main function of optical passive components is the optical signal for continuation and differences, filtering, attenuation or isolation, so that such components, including connectors, couplers, wavelength division multiplexer (Wavelength-Division Multiplexer), optical switches, filters, isolators and attenuation, etc.. Optical fiber communication systems throughout the building fabric, the overall communication network links all depends on fiber optic passive components to achieve, while the passive components are closely related to the quality of virtue or vice and communications. For example, a good passive components can make a link insertion loss (insertion loss) as low as possible, allowing a clearer signal, and ensure the stability of the link line will not drop it or loose a result of bad communication, so it can be said passive components is a fiber optic communications infrastructure.

A, optical connectors:
i. Fiber Optic Connector is a device at the fiber end mechanical devices can be used as a fiber optic connection time path of successive parts. Different types according to their follow-fiber, fiber optic connectors can be broadly divided into single-mode fiber optic connector and multimode fiber connectors, while the Ruozai according to semi-permanent and permanent continuation of the use of a different fiber, they can still be divided into light in the mechanical bonding, as well as two follow-mode welding machine.
ii. general measure of how good or bad performance of fiber optic connectors, optical signals pass through the two connected in the connector, its depletion of energy derived from the insertion loss and reflection from the connector end surface reflection loss calculated data will be the main two criterion. In the future in line with line construction and ease of end-use fiber-optic connectors, fiber-optic network rollout in the high labor cost factors, will be the main growth products. "Table 2"

Table II: a variety of environmental requirements for the connector loss
The degree of damage use of the environment
0.2dB below the long-range communication system to connect with the
02.-0.75dB system connection within the building or facility with the
1-3dB at cost as a priority consideration, applications used to connect

B, fiber couplers:
i. Fiber Optic Coupler Splitter in general may be called, the main light signal used to carve up from an optical fiber section, due to optical signal transmission is not like the copper wire inside Telecom's general ease of differences, thus wishing to light signals scattered to a different pipeline, that is required to spectrophotometric optical fiber coupler.
ii. Therefore, the optical fiber coupler is widely used in the user loop system, LAN, cable TV network systems. Configuration in general can be divided into pairs of branches, tree / star and the three types of WDM; while according to the different manufacturing methods can also be divided into welding optical fiber sintering, micro-optics and planar waveguide-type three types of optical fiber coupler.
iii. which is a graded refractive micro-optical lens, optical fiber rods will be oriented parallel to the light, after the expansion, and then semi-transparent mirror to light into two parts, respectively, after focusing rod lens coupling into the fiber. Malpractices two optical fiber sintering and melt together, stretched, so that the nuclear core due to synergies and integration to achieve light coupling, the current lowest cost, highest reliability and the highest rate of the domestic industry producing the coupler products. Planar waveguide approach is the use of flame hydrolysis deposition and optical lithography, the waveguide structure fabricated on silicon on in order to achieve spectral coupling, foreign operators to use the technology to produce a higher proportion of couplers.

C, sub-wave multiplexer:
i. WDM errant simultaneously with an optical fiber transmission of several different wavelengths of light signals to double the capacity of optical fiber transmission technology developed by the division of labor, due to WDM EDFA can be combined such as optical signal amplification technology, give full play to optical transmission The high-bandwidth features, will be hundreds of different wavelengths of light signals transmitted in the same fiber at the same time, while the principles developed in accordance with its sub-wave multiplexer (WDM: Wavelength Division Multiplexing) has become associated in recent years, the most popular fiber-optic passive components .
ii. a two-way wavelength division multiplexer of passive components, its performance can be multi-wavelength optical signals of different combinations of an optical fiber, and its solution may be a multi-tasking performance fiber optic transmission of signals of different wavelengths of light separated.

Ding, fiber grating:
Fiber Bragg Grating is a new technology, its fairly wide range of applications, therefore not only be used for optical fiber communication, so in the future market, the application will be quite optimistic about the market; fiber Bragg grating from the fiber core principle of its work Bragg grating in the reflection mechanism, as of now the most extensive and most economical of the system into the phase mask method, production method is to strip fiber coating, the place some time after the high-pressure hydrogen tank removed, and then placed in the phase mask ( Phase Mask), the longer excimer laser (Excimer Laser) exposure of about ten minutes can become a reflection of a certain wavelength of the reflector, while the reflected wavelength determined in accordance with the phase mask; while major equipment required for the KrF quasi - molecular laser, phase mask and the associated optical apparatus; The following diagram is an icon system to do.

Figure 1: the production of optical fiber grating icon


Fiber Bragg Grating fairly wide range of applications that can be used
¢ Tunable Wavelength Laser (Tunable Laser)
¢ EDFA filter (gain modified components)
¢ Smart Structure (Smart Structure)
¢ Wavelength selector
¢ WDM filter module manufacturing
¢ band suppression filter
¢ fiber optic coupler and fiber with spin-wave devices can be done to take Wong Zao multiplexer (OADM)
¢ chirped phase mask (Chirped Phase Mask) produced chirped grating (Chirped Fiber Grating) as a dispersion compensator (Dispersion Compensator)
Therefore, optical communication fiber Bragg grating is a very important research and development firms focused
E, light switches:
Optical switch for all-optical network, optical fiber signal cross-linked the main components, its role will be primarily to establish or interrupt a light path in order to determine the direction of optical signal transmission.

Been, optical attenuator:
i. optical attenuator can be used to absorb or reflect light signal margin, or for system loss evaluation and testing. As the optical signals through the various components of the transmission, both will lead to the light source frequency drift and the line noise, therefore, through the optical attenuator to absorb the associated noise will be to ensure the quality of an important high-speed optical communication components.
ii. optical attenuator is now widely used in optical communications market, with its output after the connector, coupler, the market demand is still steadily growing.

G, optical isolator:
Optical isolator is a two-port optical passive components, the main function is to enable the optical signal attenuation in the transmission direction is very small, but in the opposite direction of the light will not be reflected. Mainly used in optical transmitter modules, optical amplifiers, as well as in high-transmission system, to reduce the noise impact.

Sim, high-density wavelength division multiplexer
High-density wavelength division multiplexer (Dense Wavelength-Division Multiplexer) for the recent communication was a major invention, its working principle and the same wavelength division multiplexer, but its work on the same wavelength bands, and the interval between the different wavelengths less than 1nm, is because of its very short wavelength interval, so used to be very narrow bandwidth light source, such as DFB lasers, because of its narrow bandwidth of up to 0.2nm, it is quite suitable for use. In addition, due to multi-tasking part of the solution used in the filter must also be very high precision in order to ensure the purity of the output signals. DWDM light source mainly used 1550nm wavelength range, different wavelength interval is only about 0.8nm, and therefore use more of its light source and narrow bandwidth DFB laser, while the filter characteristics to the decision to DWDM good or bad. "See Appendix III"
5, optical fiber communication applications
In the optical transmission less than 30 years of history, the early stage of development are mainly based telecommunications transmission, but due to the technological sophistication and the different needs of the increase in the past 10 years has gradually amplified optical fiber application development to the optical local area network and cable television optical transport market, because the transmission of optical communication must be very precise, it has also led to associated to the measurement of optical communications market's rise.
The application of optical fiber communication systems at present can be divided into three broad categories: telecommunications optical transmission, fiber-optic local area network connection, cable connection, the bottom of the 11 to be explored.

1. Telecommunication optical transmission in
Telecommunications optical transmission equipment for the optical communications industry, the largest application of those
In the most early stage telecommunications structure is determined by a central switch (Centralized Switch, also known as the clearing house) and all users (End User) a direct connection, known as the central switching network (see Figure 2), which only serves a single line end-users, but in which the distance between the various users of varying lengths, in order to avoid long lines confined to only be occupied by a user, resulting in communications equipment due to inefficient use of waste formed, so class network (Hierarchical Network) also made derivatives. Class network architecture (see Figure 3), in principle, at the local clearing house by the and user switching network composed of a central responsibility of the central switching network and then to a larger bandwidth trunk (Carrier Trunks ) mutual connection, and use multi (Multiplexing) approach to increase the transmission capacity of trunk, and now the use of more multi-tasking technology is TDM (Time Division Multiplexing, TDM)-based; in class, under Network , due to regional communications by various regions of the central switching network processing, while the long-distance communications will be via the multi-tasking machine to transmit through the trunk, so a regional communication and long-distance communications, the use of resources can be more efficient allocation of and have access to a larger transmission capacity.
Figure 2: The Central Exchange network infrastructure (Centralized Switching)


Figure 3: class network infrastructure (Hierarchical Network)



Optical fiber transmission bandwidth and speed far superior to copper cable

Telecommunications infrastructure in the past, due to a single voice transmission channel (voice channel) can only 64Kbps of bandwidth, so in all regions of the trunk between the majority of the clearing-house use only accommodate a higher throughput of copper cable as the connection media, such as DS3 (also known as T3, 44.736Mbps) and E3 (34.368Mbps) ... and so on, but with the increase in the amount of telecommunications transmission, copper lines in the past has gradually been insufficient bandwidth to use, so have a higher transmission capacity The cable also begun to use the trunk, and even has begun to replace copper cables; in the traditional fiber-optic systems, optical fiber transmission speed is several times more than copper cables, such as Synchronous Optical Network Systems / synchronous digital hierarchy (SONET / SDH), the lower optical fiber transmission rate up to OC-3 rates were 155Mbps, the speed of nearly 5 times the copper E3, if a high optical transmission rate OC-192 (10Gbps), its speed E3 is almost 300 times (see Table III).

Table III Comparison of copper and fiber optic transmission speed

With the increasing application of fiber-optic technology, SONET / SDH optical transmission protocol standard also been worked out, SONET (Synchronous Optical Network, Synchronous Optical Network) and SDH (Synchronous Digital Hierarchy, SDH) are based on the basic structure synchronous transfer mode as a basis, but by the United States to set SONET fiber-optic transmission standard (U.S. regulation), SDH is the ITU (International Telecommunication Union) is modeled according to SONET, followed by the set adapted for the world outside the United States simultaneous transmission standard, this In addition to the standard applied to optical fiber network, but also applicable to other synchronous transfer be based on a standard transmission. At present many countries around the world long-distance backbone network are commonly used by SONET / SDH fiber-optic network, most of them in order to provide 2.5Gbps, 5Gbps, or a 10Gbps system mainly on the relay route is the OC-3 and OC - 12 for most.

ATM fiber optic network enables a more flexible and scalable

But because the SONET / SDH synchronous transmission technology such as a part of the inherent limitations and data information transfer increases, ATM network transmission will be the future of another major backbone transmission infrastructure, next generation backbone network will be designed for a number of ATM architecture . ATM (Asynchronous Transfer Mode, ATM), as its known as a non-synchronous transfer mode, the most important special place that is to use a number of fixed-length frame (Fixed-length Cells) (53 bytes) for information transmission, This shipping method provides a chronological nature of information (such as voice and video) for high-speed (2.5Gbps and above) transmission, and can achieve the quality of service (Quality of Service, QoS) guarantees. As the ATM network construction with a flexible, future equipment, scalability, and speed ... and other features, so the rise of ATM will also be useful in the development and prevalence of optical networking, optical fiber transmission can play an even greater effectiveness. WDM and DWDM multiplexing techniques such as the emergence of optical fiber transmission can be more efficient, greatly enhance the scope of application of optical fiber communication.
Although the SONET / SDH fiber-optic transmission for the present a more accessible means of transmission, but due to fiber-optic SONET architecture information is only a single frequency (ie, monochromatic) is transmitted in the current era of bandwidth demand to that seems to be more inconsistent with the benefits, it also has a different wavelength as a multi-tasking WDM (Wavelength Division Multiplexing, WDM) technology, WDM is to use the simple principle of a fiber optic transmission of two or more different wavelengths (colors ) of optical signals in order to achieve additional capacity or bandwidth of the multi-effects; In recent years, fiber-optic multiplexing technique to further high-density reached WDM (Dense Wavelength Division Multiplexing, DWDM), the so-called DWDM and WDM principle is similar, except to be as high-density DWDM way for eight or more different wavelengths of light through an optical fiber transmission of information at the same time, to today's technology can be a maximum of about 80 multi-pen data packet transmitted on a single optical fiber in order to fully to achieve the effect of broadband and optical fiber communication greatly reduces the transmission costs; If DWDM technology combined with erbium-doped fiber amplifier (EDFA) the use of, and now has become a wired communications to increase transmission capacity of the best solution.
2. Fiber optic local area network connection

People for the bandwidth demand-led the development of fiber-optic local area network

As mentioned earlier, due to high prices and demand, so is limited to the early development of long-distance fiber optic communications lines on the use of, but in recent years a rapid increase in traffic volumes and the explosive growth of the Internet, the optical networking applications long-distance transportation from the past (Long Haul Transport) of the backbone network extended to the city transport (Metro Transport) of the district lines, the next one or two years because of Datacom traffic will increase, technological advances, and the cost of optical communication down, leaving the application of optical communication access once again to the end of transmission (Edge Transport) of the relay route (such as Fiber to the Building ... and so on) development.
While the rapid decline in the price of fiber optic products, fiber optic product prices due to the average consumer should be reduced to an acceptable range and the actual project erection difficulties, so in the near future fiber-to-table (Fiber to the Desk, FTTD) should remain a non - more common, but in the fiber optic local area network is the backbone of the coming year can be seen. Optical local area network currently in the mainstream of Fast Ethernet (100Mbps and above) and Gigabit Ethernet (1Gbps or above), due to optical local area network on the cost considerations are more important than the telecommunications backbone network, so most of its light source using low-cost LED and the newly developed VCSEL (Vertical Cavity Surface Emitting Laser, Vertical Cavity Surface Emitting Laser), will increase the popularity of optical fiber local area network.
The popularity of the current regional fiber optic network backbone on a limited, but based on the evaluation of this market is not inferior to the telecommunications backbone network of the market, if the future due to decline in the price of fiber optic products can be achieved FTTD, then the relevant active and passive components market, a huge would be beyond words.

3. CATV optical transmission

CATV HFC bi-directional transmission led to the rise, has also increased the demand for optical fiber cable

Early cable television transmission medium is used coaxial cable (Coaxial Cable) transmission by use of the coaxial cable from the band is only 50MHz to 550MHz, running approximately 100 channels, the other remaining bands formed because of not using a waste, after Because HFC (Hybrid Fiber Coaxial, fiber coaxial cable) architecture and the emergence of two-way transmission, so cable systems can also be used in data transmission. HFC is mainly used to signal from the ground-side optical fiber (Head-end) sent to the user in the vicinity of the light cast Placement (Optical Network Unit, ONU), then after the concatenation way coaxial cable to high-quality RF signals sent to the 500 ~ 1000 users at.
HFC with the 50 ~ 550MHz frequency band to download TV shows, and the other using the band 550 ~ 750MHz modulation approach to data, images, or phone ... such as a digital download service, in addition to re-use 5 ~ 35MHz frequency band as the uplink signal using the .
Because these two years the use of coaxial cable for bi-directional transmission market is a multiple of the growth of the old type of traditional architecture have to be re-laying cable HFC, so cable TV transmission market will also be a fiber optic transmission equipment and components, the other fast-growing a driving force.
6 Conclusion
Sum up the above, in the future bandwidth requirements have continued to grow, the trend of optical communication is already taking shape, the Taiwanese firms naturally can not give up enormous opportunities in this one. On the whole, the communications equipment market is still dominated by major players in Europe and the United States, in the master specification formulation and existing market base, the scope of domestic manufacturers can not dwell, therefore the main opportunities for Taiwan businessmen are still in optical communication Zero Group parts manufacturing.
In the optical communications components, our firms more time engaged in passive components, development of a more mature and the current degree of automation of production is not high, are more dependent on manpower, so carry European and American firms outsourcing orders more easily. Be relatively low especially in the future of communications components, including various types of connectors, couplers and filters and other passive components and low-power active components, this part of the product requirements is not as harsh long-distance transmission, focusing on the costs are low, and the demand is huge, this part just right for Taiwanese manufacturers to develop, therefore, Taiwanese firms should be aware that this block of the current market.
Because Taiwan is only a few manufacturers to produce optical fibers, so output is still small, but the cable industry is quite developed, most of the optical fiber is imported from abroad, and then processed into mainland China in its cable, cable operators are beginning to meet Taiwan The domestic demand, but as capacity development and the input of many industry, at present the cable companies are active in the international market
In short, fiber-optic communications to flourish in today's occasion, domestic manufacturers can play an active investment products and manufacturing technology R & D, coupled with an appropriate strategic alliance, the future business opportunities will be very large, while the fiber optic industry will become a future star in the Taiwan stock market industry.
Post: #4
[attachment=2580]

OPTIC FIBRE COMMUNICATION SYSTEM
ABSTRACT
The circuit for OPTIC FIBRE COMMUNICATION SYSTEM is designed to demonstrate the transmission and reception of a digital data through an optic fibre cable. The optic signals generated by the transmitter circuit are received by the optical receiver circuit after transmission through an optic fibre cable.This communication is much more effective than ordinary communication. It provides bandwidth in the GHz range.lt provides minimum transmission loss. It finds many applications in communication systems, measuring systems, industrial, medical and military applications.

DONE BY: GUIDED BY:
ANJUS ANU ANAND ASHA JOHN
Ms.SumoI.N.C Mr. Asini.H

INTRODUCTION
This project done on communication using optic fibres can be used for data transmission over small distances in computer networks, closed circuit T.V s etc. The information carrying capacity is directly proportional to the frequency or bandwidth of the carrier wave. This system uses light as a carrier wave in the frequency range 10A13 Hz to 10A16 Hz. Hence information transmission capacity increases by several order of magnitude.Thus it overcome almost all the drawbacks of communication systems involving electrical signals.
BLOCK DIAGRAM EXPLANATION
The block diagram given in the figure shows a basic optic fibre communication system.lt mainly consists of three elements
1) Optical transmitter
2) The optic fibre cable
3) The optical receiver
This general description is appropriate for analog as well as digital communication systems.Fibre optic technology and communication technology are involved in this system.
1) The optical transmitter
It consists of electronic components which convert the electrical signals into corresponding optical signals. The data in the form of electrical signal is provided to drive the circuit. This is achieved by using an astable multivibrator which generate a series of digital data in the form of ones and zeroes. This signal is used to turn ON and OFF an LED.This is done by means of a transistor switching circuit.The electrical signals are converted into light signals by an optical source consisting of an LED. These light signals are then transmitted through the optic fibre cable. The LED provides light of constant wavelength and low transmission loss. The light injected into the OFC is a faithful representation of the information.
2) The optic fibre cable
It consists of glass fibres which act as wave guide for optical signal. For long distance transmission^ or more fibres are joined together. The optic fibre is made of three layers namely core, cladding and protective covering.Optic fibre works on the principle of total internal reflection.
3) The optical receiver
It consists of a photo detector, amplifier and a signal indicator. The photodetector converts optical signal into corresponding electrical signal. Here an LDR is used to detect the incoming light signals. The amplifier amplifies the signal. An LED is used to indicate the reception of the data.
TRANSMITTER
CIRCUIT DIAGRAM
RECEIVER
CIRCUIT DIAGRAM EXPLANATION
OPTICAL TRANSMITTER
The circuit for a basic optic fibre communication system for transmitting a series of digital data is shown in the figure. For the purpose of generating the digital signals, an astable multivibrator is designed.
When the circuit is connected as shown in the above figure(pin 2 and 6) connected it triggers itself and free runs as a multivibrator.The external capacitor charges through Rl and R2 and discharges through R2 only. Thus the duty cycle may be precisely set by the ratio of these two resistors. In the astable mode of operational charges and discharges between 1/3 Vcc and 2/3 Vcc. As in the triggered mode ,the charge and discharge times are therefore frequency are independent of the supply voltage.
The charge time(output high) is given by: tl=.693(Rl+R2)Cl And the discharge time (output low) by : t2=0.693(R2)Cl Thus the total period t is given by : T=tl+t2= 0.693(R1+2R2)C1 The frequency of oscillation is then : f=l/T=1.44/(Rl+2R2)Cl The duty cycle is given by Big Grin=R2/R1+2R2
The output signals thus produced by the astable multivibrator is fed to a
transistor switching circuit.For this a BF 194 transistor is used. Switching circuit
An LED is connected to the collector of the transistor which will be turned ON and OFF according to the input digital data. As the input to the base of the transistor goes high ,the transistor switches to saturation. Current passes through the transistor and therefore LED glows. As the input to the transistor goes low ,the transistor switches to cut off and therefore LED doesn't glow. Superluminiscent LEDs are used here. For proper operation of astable multivibrator ,a +10 V supply and for the switching circuit a +5V supply is used. The LED thus produces the optical signals which are to be transmitted. The LED is coupled to the OFC by means of suitable coupler without any loss of data.Thus the signal is effectively transmitted through the OFC. OPTIC FIBRE CABLE
Here multimode type OFC is used. The OFC is made from silica glass. A plastic coating is also provided. They have larger numerical aperture to facilitate efficient coupling to inherent light sources such as light emitting diodes. They provide bandwidth in the GHz range.
Optic fibre works on the principle of total internal reflection of light. When a ray of light passes from a dielectric medium of refractive
index nl (denser) to other of refractive index n2(rarer) ,and when the angle of incidence is critical angle e, then the refracted ray in the fibre just grazes the surfaces separating the two medium.ie the angle of refraction becomes 90°.When the angle of incidence becomes greater than critical angle, the light ray gets totaly internally reflected into the same medium. This phenomenon is called total internal reflection. Any light ray incident on the fibre edge at an angle greater than 0a meets the core cladding interface at an angle less than critical angle and will not be totally internally reflected and transmitted. Only the light rays that enter the fibre edge within the angle Oa will be accepted by the fibre for total internal reflection. Thus this angle of incidence 0a is called the acceptance angle. The numerical aperture of a fibre deopends on the acceptance angle 0a by the relation Sin Oa=NA.
Optic fibres are very light and easy to handle. Using these the hazards due to short circuit can be avoided. It is also ideal for secret communication because it is very difficult to tap. Optic fibres are unaffected by outdoor atmospheric conditions like lightning. Besides there is no possibility of spark from broken fibre. It will not corrode and is unaffected by most chemicals. They are also immune to electromagnetic interference and avoid crosstalk.Also transmission losses are very low.
OPTICAL RECEIVER
The light transmitted through the OFC has to be properly received. For this optical signal has to be converted into corresponding electrical form . To perform this optical detectors are used. Here an LDR is used for this purpose. The OFC is effectively coupled to the LDR without lossage of incoming data. The LDR is placed in the biasing circuit of the transistor BF547.As the incoming signal goes high, the resistance of the LDR goes low. Current flows and proper biasing is achieved. The transistor then switches to saturation. An LED is connected at the collector of the transistor as an indicator of the incoming signal. As the transistor switches to saturation, current flows and LED glows. When the incoming signal goes low ,the resistance of the LDR becomes high. Current doesn't flow. Transistor switches to cut off and therefore the LED turns OFF. Thus the data has been effectively transmitted from the transmitter circuit to the receiver.
This circuit forms the basis of all optic fibre systems.
POWER SUPPLY
A regulated power supply is an electronic circuit that is designed to provide a constant dc voltage of predetermined value across load
terminals irrespective of ac mains fluctuations or load variations. It mainly consists of an ordinary power supply and a voltage regulating device
The system requires a regulated +5 v supply for the switching circuit and a +10V supply for the astable multivibrator. A +5V supply is also needed for the receiver circuit. These can be delivered from the 230V domestic supply. Before applying this to the system we must step down this high voltage to an appropriate value. After that it should be rectified. This will provide a unidirectional current. To achieve a +5V DC we should regulate this. All these are done in power supply circuitry, which is explained below.
A 12-0-12 V step down transformer is connected to provide the necessary low voltage. The transformer also works as an isolator between the hot and cold end. The hot end refers to the 230 V supply, which is a hazardous one, and the cold one refers to the safe, low voltage. Now the hot portion appears only at the primary of the transformer.The secondary of the transformer deliver 12 V ac pulses along with a ground. This ac supply goes to a center tap rectifier, which converts the ac into a unidirectional voltage.The ripples in the resulting supply is filtered and smoothed by a 2200 microfarad /25V capacitor. The 0.1 microfarad capacitor bypasses any
high frequency noises.The resulting supply has the magnitude above 17 V. This voltage is fed to the regulator IC 7805 and 7810.This IC 7805 provides a regulated 5V positive supply at its 3rdpin.The required input for this is more than 7.5 V. The IC 7810 provides a regulated 10V positive supply at its 3 rd pin
Device Output Maximum Minimum
type voltage in input input
volts voltage in voltage in
volts volts
7805 +5 35 7.3
7810 +10 35 12.5
PCB DESIGNING AND FABRICATION
DESIGN AND PCB FABRICATION
The PCB consists of an insulating base material on which copper conductors are etched by photolithography or screen printing. The insulating materials provides electrical isolation and mechanical rigidity for the printed conductors as such it should possess the essential electrical and mechanical properties and good flexural strength, reasonable high temperature with standing capability, low moisture absorption warpage, good merchantability, good electrical resistance, high dielectric strength, low dielectric constant, low dissipation factor etc.
PHOTOGRAPHIC METHOD OF PCB FABRICATION
Photographic method is another commonly used PCB fabrication method. It is more expensive and widely used for massive production.
SCREEN PRINTING
In this method, a mesh is prepared and is placed over the copper sheets. Screen printing material is pasted over the areas where the circuit is to be land. All other areas are kept open. The different steps used in PCB fabrication are listed below :-
Cutting copper clad lamination
The copper clad laminates are manufactured in 4 inch*3 inch size. From this sheet pieces are cut off to the required size using a shearing machine. For the purpose of handling the PCB during fabrication, borderline of PCB. Hence atleast cutting PCB provides 10 mm of additional space from the actual required PCB size.
Cleaning
The copper oxides may build up on the copper surface. Inorder to remove this following procedure is required :-
a) Wipe with cotton wool socked in trichloro ethylene
b) Dipping in 10% HC1 for 1 minute at room temperature.
c) Scrub with pumice powder.
PCB LAYOUT
TRANSMITTER
PCB SCHEMATIC
CONCLUSION
This circuit can be considered as the basis for all systems utilizing the optic fibre technology. The project explains the transmission of data through an optic fibre cable. Optic fibre sensors like smoke or pollution detector,LDV,crack sensors etc has wide usage today. Besides optic fibres finds many applications in telecommunication, LAN networks, industrial applications like horoscope and remote sensing, medical applications, military applications like antitank missile system, secret communication links etc. It is expected that Photonics ,the light based systems rather than electronics, the electron flow devices will dominate in the coming years.
NE555 SA555 - SE555
GENERAL PURPOSE SINGLE BIPOLAR TIMERS
LOW TURN OFF TIME
MAXIMUM OPERATING FREQUENCY
GREATER THAN 500kHz
TIMING FROM MICROSECONDS TO HOURS
OPERATES IN BOTH ASTABLE AND
MONOSTABLE MODES
HIGH OUTPUT CURRENT CAN SOURCE OR
SINK 200mA
ADJUSTABLE DUTY CYCLE TTL COMPATIBLE
TEMPERATURE STABILITY OF 0.005% PER°C
DESCRIPTION
The NE555 monolithic timing circuit is a highly stable controller capable of producing accurate time delays or oscillation. In the time delay mode of operation, the time is precisely controlled by one external re¬sistor and capacitor. For a stable operation as an os¬cillator, the free running frequency and the duty cy¬cle are both accurately controlled with two external resistors and one capacitor. The circuit may be trig¬gered and reset on falling waveforms, and the out¬put structure can source or sink up to 200mA. The NE555 is available in plastic and ceramic minidip package and in a 8-lead micropackage and in metal can package version.
D S08
(Plastic Micropackage)
PIN CONNECTIONS (top view)
c 1 J
8 J 1 - GND
2 - Trigger
L~ 2 7 J 3 - Output
4 - Reset
5 - Control voltage
L~ 3 6 1 6 - Threshold
7 - Discharge
8-Vcc
C 4 5 J
BLOCK DIAGRAM
R1 4.7k
R2 R3 830 4.7k
R12 6.8k
Q5^|-*-£Q6 Q7^| ¢ JoB Q9^
019*1 f
IQ2C
J Q2
i
1
THRESHOLD o
[,Q1 Q^J
[011 Q12 J 5k
R14
220 >
TRIGGER o
RESET O
DISCHARGE O
roi5
[QIC
¢ _ . Q16J ¢
ro,7
R15
7k
"1 i
014
R5 10k
R6 n 1 r7 n 1
100k 100k I
GND °
TRIGGER COMPARATOR
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
Vcc Supply Voltage 18 V
::=- Operating Free Air Temperature Range for NE555
for SA555 for SE555 0to70 -40 to 105 -55 to 125 °c
Tj Junction Temperature 150 °c
Storage Temperature Range -65 to 150 °c
OPERATING CONDITIONS
Symbol Parameter SE555 NE555 - SA555 Unit
Vcc Supply Voltage 4.5 to 18 4.5 to 18 V
Vthi Vttjg, VC|, Vreset Maximum Input Voltage Vcc Vcc V
ELECTRICAL CHARACTERISTICS
Tamb = +25°C, Vcc = +5V to +15V (unless otherwise specified)
Symbol Parameter SE555 NE555 - SA555 Unit

Min. Typ. Max. Min. Typ. Max.
Ice Supply Current (RL °°) (- note 1) Low State VCc = +5V
Vcc = +15V High State VCc = 5V 3 10 2 5 12 3 10 2 6 15 mA
Timing Error (monostable) (RA= 2k to 100kfl, C = 0.1 uF) Initial Accuracy - (note 2) Drift with Temperature Drift with Supply Voltage 0.5 30 0.05 2
100 0.2 1
50 0.1 3
0.5 %
ppm/°C %N
Timing Error (astable)
(RA, RB = ika to lookn, c = o.iuF,
Vcc = +15V) Initial Accuracy - (note 2) Drift with Temperature Drift with Supply Voltage 1.5 90 0.15 2.25 150 0.3 %
ppm/°C %/V
VCL Control Voltage level
Vcc = +15V Vcc = +5V 9.6
2.9 10
3.33 10.4 3.8 9
2.6 10 3.33 11 4 V
Vth Threshold Voltage
VCC = +15V Vcc = +5V 9.4 2.7 10 3.33 10.6 4 8.8 2.4 10 3.33 11.2 4.2 V
Ith Threshold Current - (note 3) 0.1 0.25 0.1 0.25 uA
vtrig Trigger Voltage
Vcc = +15V Vcc = +5V 4.8 1.45 5 1.67 5.2 1.9 4.5 1.1 5 1.67 5.6 2.2 V
¦trig Trigger Current (Virig = 0V) 0.5 0.9 0.5 2.0 HA
Vreset Reset Voltage - (note 4) 0.4 0.7 1 0.4 0.7 1 V
I reset Reset Current
Vreset = +0.4V Vreset = 0V 0.1 0.4 0.4 1 0.1 0.4 0.4 1.5 mA
VOL Low Level Output Voltage Vcc = +15V, l0(sink)= 10mA lo(sink) = 50mA lo(sink) = 100mA lo(sink) = 200mA Vcc = +5V, lo(sink) = 8mA lO(sink) = 5mA 0.1 0.4 2
2.5 0.1 0.05 0.15 0.5 2.2
0.25 0.2 0.1 0.4 2
2.5 0.3 0.25 0.25 0.75 2.5
0.4
0.35 V
VOH High Level Output Voltage
Vcc = +15V, lo(source) = 200mA lo(source) = 100mA Vcc = +5V, lo(source) = 100mA 13 3 12.5 13.3 3.3 12.75 2.75 12.5 13.3 3.3 V
Notes: 1. Supply current when output is high is typically 1mA less.
2. Tested at Vcc = +5V and Vcc = +15V.
3. This will determine the maximum value of RA + RB for +15V operation the max total is R = 20M£2 and for 5V operation the max total R = 3.5M12.
3/10
ELECTRICAL CHARACTERISTICS (continued)
Figure 4 : Low Output Voltage versus Output Sink Current
0.01
Figure 5 : Low Output Voltage versus Output Sink Current
Figure 6 : Low Output Voltage versus Output Sink Current
vs= 10V
2S*C
ZS'C





55'C -













2 5 10 20 'SINK1"1*1
Figure 7 : High Output Voltage Drop versus Output
Figure 8 : Delay Time versus Supply Voltage
APPLICATION INFORMATION
MONOSTABLE OPERATION In the monostable mode, the timer functions as a one-shot. Referring to figure 10 the external capaci¬tor is initially held discharged by a transistor inside the timer.
Figure 11
The circuit triggers on a negative-going input signal when the level reaches 1/3 Vcc. Once triggered, the circuit remains in this state until the set time has elapsed, even if it is triggered again during this in-terval. The duration of the output HIGH state is given by t = 1.1 R1C1 and is easily determined by figure 12.
Notice that since the charge rate and the threshold level of the comparator are both directly proportional to supply voltage, the timing interval is independent of supply. Applying a negative pulse simultaneously to the reset terminal (pin 4) and the trigger terminal (pin 2) during the timing cycle discharges the exter¬nal capacitor and causes the cycle to start over. The timing cycle now starts on the positive edge of the reset pulse. During the time the reset pulse in ap¬plied, the output is driven to its LOW state. When a negative trigger pulse is applied to pin 2, the flip-flop is set, releasing the short circuit across the external capacitor and driving the output HIGH. The voltage across the capacitor increases exponen¬tially with the time constant x = R1C1. When the volt¬age across the capacitor equals 2/3 Vcc, the compa¬rator resets the flip-flop which then discharge the ca¬pacitor rapidly and drivers the output to its LOW state.
Figure 11 shows the actual waveforms generated in this mode of operation.
When Reset is not used, it should be tied high to avoid any possibly or false triggering.
10 100 1.0 10 100 10 (td) us us ms ms ms s
ASTABLE OPERATION
When the circuit is connected as shown in figure 13 (pin 2 and 6 connected) it triggers itself and free runs as a multivibrator. The external capacitor charges through Ri and R2 and discharges through R2only. Thus the duty cycle may be precisely set by the ratio of these two resistors.
In the astable mode of operation, C1 charges and discharges between 1/3 Vcc and 2/3 Vcc. As in the triggered mode, the charge and discharge times and therefore frequency are independent of the supply voltage.
Figure 13
Figure 15 : Free Running Frequency versus Ri, R2 and Ci
PULSE WIDTH MODULATOR When the timer is connected in the monostable mode and triggered with a continuous pulse train, the output pulse width can be modulated by a signal applied to pin 5. Figure 16 shows the circuit.
Figure 16 : Pulse Width Modulator.
D =
Ri + 2R2
-O Vcc*
Figure 14
Output O
LINEAR RAMP
When the pullup resistor, RA, in the monostable cir-cuit is replaced by a constant current source, a linear ramp is generated. Figure 17 shows a circuit con¬figuration that will perform this function.
¦O Vcc'
Output o
Figure 17.
Figure 18 shows waveforms generator by the linear ramp.
T =
VBE = 0.6V
The time interval is given by :
(2/3 Vcc RE (RI+ R2) C Ri Vcc - VBE (RI+ R2>
Figure 18 : Linear Ramp.
50% DUTY CYCLE OSCILLATOR
For a 50% duty cycle the resistors RA and RE may
be connected as in figure 19. The time preriod forthe
output high is the same as previous,
ti = 0.693 RA C.
For the output low it is t.2 =
[(RARB)/(RA + RB)] CLn1
-i
2RB - RA
Thus the frequency of oscillation is f ,
ti + t2
Note that this circuit will not oscillate if RB is greater Figure 19 : 50% Duty Cycle Oscillator.
than 1/2 RA because the junction of RA and RB can-not bring pin 2 down to 113 Vcc and trigger the lower comparator.
ADDITIONAL INFORMATION Adequate power supply bypassing is necessary to protect associated circuitry. Minimum recom¬mended is 0.1 u.F in parallel with 1uP electrolytic.
Vcc = 5V Top trace : input 3V/DIV
Time = 20us/DIV Middle trace : output 5V/DIV
Ri = 47kfl Bottom trace : output 5V/DIV
R2 = 100kfl Bottom trace : capacitor voltage
Re = 2.7k£2 1V/DIV
C = 0.01N.F
D
n i i n tn
[8 5 I 1 4 u_
Dimensions Millimeters Inches
Min. Typ. Max. Min. Typ. Max.
A 3.32 0.131
a1 0.51 0.020
B 1.15 1.65 0.045 0.065
b 0.356 0.55 0.014 0.022
b1 0.204 0.304 0.008 0.012
D 10.92 0.430
E 7.95 9.75 0.313 0.384
e 2.54 0.100
e3 7.62 0.300
e4 7.62 0.300
F 6.6 0260
i 5.08 0.200
L 3.18 3.81 0.125 0.150
Z 1.52 0.060
e3
ti
u u u u
Dimensions Millimeters Inches
Min. Typ. Max. Min. Typ. Max.
A 1.75 0.069
a1 0.1 0.25 0.004 0.010
a2 1.65 0.065
a3 0.65 0.85 0.026 0.033
b 0.35 0.48 0.014 0.019
b1 0.19 0.25 0.007 0.010
C 0.25 0.5 0.010 0.020
d 45° (typ.)
D 4.8 5.0 0.189 0.197
E 5.8 6.2 0.228 0.244
e 1.27 0.050
e3 3.81 0.150
F 3.8 4.0 0.150 0.157
L 0.4 1.27 0.016 0.050
M 0.6 0.024
S 8° (max.)
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifi-cations mentioned in this publication are subject to change without notice. This publication supersedes and replaces all infor-mation previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.
© The ST logo is a trademark of STMicroelectronics
© 1998 STMicroelectronics - Printed in Italy - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - France - Germany - Italy - Japan - Korea - Malaysia - Malta - Mexico ¦ Morocco The Netherlands - Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A.
Post: #5
[attachment=2758]


Presented By:
VINEESH V
D3 :EE
OPTICAL FIBER COMMUNICATION

CONTENT
Introduction
History
Principles of operation
How optical fiber works
Index of refraction
Total internal reflection
Multi mode fiber $ single mode fiber
Special purpose fiber
Mechanism of attenuation
Light scattering
Manufacturing
Process
Applications
Advantages
Disadvantages
Conclusion
Reference
INTRODUCTION

An optical fiber is a glass or plastic fiber that carries light along its length. Fiber optics is the overlap of applied science and engineering concerned with the design and application of optical fibers. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communications. Fibers are used instead of metal wires because signals travel along them with less loss, and they are also immune to electromagnetic interference. Fibers are also used for illumination, and are wrapped in bundles so they can be used to carry images, thus allowing viewing in tight spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers.
HISTORY


The use of optic fibers for communication purposes were first carried out in Western Europe in the late 19th and early 20th century, such as they were used to diagnose a patient's stomach by a doctor, and those communications within short ranges. Especially, the transfer of images by optical fibers was largely popularized at the beginning of 21st century, due to the growing medical and television demands In 1991, the emerging field of photonic crystals led to the development of photonic-crystal fiber[12] which guides light by means of diffraction from a periodic structure, rather than total internal reflection. The first photonic crystal fibers became commercially available in 2000
PRINCIPLES OF OPERATION

Snellâ„¢s Law
In 1621, a Dutch physicist named Willebrord Snell derived the relationship between the different angles of light as it passes from one transparent medium to another. When light passes from one transparent material to another, it bends according to Snell's law which is defined as:
n1sin(1) = n2sin(2)
where:
n1 is the refractive index of the medium the light is leaving
1 is the incident angle between the light beam and the normal (normal is 90° to the interface between two materials)
n2 is the refractive index of the material the light is entering
2 is the refractive angle between the light ray and the normal
HOW OPTICAL FIBER WORKS

An optical fiber is a cylindrical dielectric waveguide (nonconducting waveguide) that transmits light along its axis, by the process of total internal reflection. The fiber consists of a core surrounded by a cladding layer, both of which are made of dielectric materials. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The boundary between the core and cladding may either be abrupt, in step-index fiber, or gradual, in graded-index fiber.
FIBER


Optical fiber is a long, thin strand of very pure glass about the diameter of a human hair. Optical fibers are arranged in bundles called optical cables and used to transmit light signals over long distances.
Optical fibers are based entirely on the principle of total internal reflection. This is explained in the following picture.
TECHNOLOGY

Transmitter

Modern fiber optic communication systems generally include an optical transmitter to convert an electrical signal into an optical signal to send into 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 cables television companies. The most commonly used optical transmitters are semi conductor devices such as Light emitting diodes [LED] and laser diodes
RECEIVER
The main component of an optical receiver is a photodetector , which converts light into electricity using the photoelectric effect. The photodetector is typically a semiconductor based photodiode. Several types of photidiode include p-n photodiodes , and avalanchae photodiodes. Metal-semiconductor-metal[MSM]photodetectors are also used due to there suitability for circuit integration in regenerators and wavelengh-division multipexers
REFRACTION OF LIGHT

As a light ray passes from one transparent medium to another, it changes direction; this phenomenon is called refraction of light. How much that light ray changes its direction depends on the refractive index of the mediums.
REFRACTIVE INDEX

Refractive index is the speed of light in a vacuum (abbreviated c, c=299,792.458km/second) divided by the speed of light in a material (abbreviated v). Refractive index measures how much a material refracts light. Refractive index of a material, abbreviated as n, is defined as
n=c/v
TOTAL INTERNAL REFLECTION

When a light ray crosses an interface into a medium with a higher refractive index, it bends towards the normal. Conversely, light traveling cross an interface from a higher refractive index medium to a lower refractive index medium will bend away from the normal.
If the light hits the interface at any angle larger than this critical angle, it will not pass through to the second medium at all. Instead, all of it will be reflected back into the first medium, a process known as total internal reflection.
STRUCTURE OF OPTICAL FIBER

For the most common optical glass fiber types,
which includes 1550nm single mode fibers and
850nm or 1300nm multimode fibers, the core
diameter ranges from 8 ~ 62.5 µm. The most
common cladding diameter is 125 µm.
The material of buffer coating usually is
soft or hard plastic such as acrylic, nylon and with diameter ranges from 250 µm to 900 µm. Buffer coating provides mechanical protection and bending flexibility for the fiber.
Typical optical fibers are composed of core, cladding and buffer coating.
The core is the inner part of the fiber, which guides light. The cladding surrounds the core completely. The refractive index of the core is higher than that of the cladding, so light in the core that strikes the boundary with the cladding at an angle shallower than critical angle will be reflected back into the core by total internal reflection.
OPTICAL FIBER MODE

An optical fiber guides light waves in distinct patterns called modes. Mode describes the distribution of light energy across the fiber. The precise patterns depend on the wavelength of light transmitted and on the variation in refractive index that shapes the core. In essence, the variations in refractive index create boundary conditions that shape how light waves travel through the fiber, like the walls of a tunnel affect how sounds echo inside.


We can take a look at large-core step-index fibers. Light rays enter the fiber at a range of angles, and rays at different angles can all stably travel down the length of the fiber as long as they hit the core-cladding interface at an angle larger than critical angle. These rays are different modes.
Fibers that carry more than one mode at a specific light wavelength are called multimode fibers. Some fibers have very small diameter core that they can carry only one mode which travels as a straight line at the center of the core. These fibers are single mode fibers. This is illustrated in the following picture.
OPTICAL FIBER INDEX PROFILE

Index profile is the refractive index distribution across the core and the cladding of a fiber. Some optical fiber has a step index profile, in which the core has one uniformly distributed index and the cladding has a lower uniformly distributed index. Other optical fiber has a graded index profile, in which refractive index varies gradually as a function of radial distance from the fiber center. Graded-index profiles include power-law index profiles and parabolic index profiles. The following figure shows some common types of index profiles for single mode and multimode fibers.
MECHANISM OF ATTENUATION

Attenuation in fiber optics, also known as transmission loss, is the reduction in intensity of the light beam (or signal) with respect to distance traveled through a transmission medium. Attenuation coefficients in fiber optics usually use units of dB/km through the medium due to the relatively high quality of transparency of modern optical transmission media. The medium is typically usually a fiber of silica glass that confines the incident light beam to the inside. Attenuation is an important factor limiting the transmission of a digital signal across large distances. Thus, much research has gone into both limiting the attenuation and maximizing the amplification of the optical signal. Empirical research has shown that attenuation in optical fiber is caused primarily by both scattering and absorption.
MANUFACTURING MATERIALS


Glass optical fibers are almost always made from silica, but some other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses, are used for longer-wavelength infrared applications. Like other glasses, these glasses have a refractive index of about 1.5. Typically the difference between core and cladding is less than one percent.
Plastic optical fibers (POF) are commonly step-index multi-mode fibers with a core diameter of 0.5 millimeters or larger. POF typically have higher attenuation coefficients than glass fibers, 1 dB/m or higher, and this high attenuation limits the range of POF-based systems.
SILICA
The amorphous structure of glassy silica (SiO2). No long-range order is present, however there is local ordering with respect to the tetrahedral arrangement of oxygen (O) atoms around the silicon (Si) atoms.
Silica exhibits fairly good optical transmission over a wide range of wavelengths. In the near-infrared (near IR) portion of the spectrum, particularly around 1.5 µm, silica can have extremely low absorption and scattering losses of the order of 0.2dB/km. A high transparency in the 1.4-µm region is achieved by maintaining a low concentration of hydroxyl groups (OH). Alternatively, a high OH concentration is better for transmission in the ultraviolet (UV) region.
FLUORIDE
Fluoride glass is a class of non-oxide optical quality glasses composed of fluorides of various metals. Because of their low viscosity, it is very difficult to completely avoid crystallization while processing it through the glass transition (or drawing the fiber from the melt). Thus, although heavy metal fluoride glasses (HMFG) exhibit very low optical attenuation, they are not only difficult to manufacture, but are quite fragile, and have poor resistance to moisture and other environmental attacks. Their best attribute is that they lack the absorption band associated with the hydroxyl (OH) group (3200“3600 cm-1), which is present in nearly all oxide-based glasses.
PHOSPHATES
Phosphate glass constitutes a class of optical glasses composed of metaphosphates of various metals. Instead of the SiO4 tetrahedra observed in silicate glasses, the building block for this glass former is Phosphorus pentoxide (P2O5), which crystallizes in at least four different forms. The most familiar polymorph (see figure) comprises molecules of P4O10.
Phosphate glasses can be advantageous over silica glasses for optical fibers with a high concentration of doping rare earth ions. A mix of fluoride glass and phosphate glass is fluorophosphate glass.[35][36]
CHALCOGENIDES
The chalcogens”the elements in group 16 of the periodic table”particularly sulfur (S), selenium (Se) and tellurium (Te)”react with more electropositive elements, such as silver, to form chalcogenides. These are extremely versatile compounds, in that they can be crystalline or amorphous, metallic or semiconducting, and conductors of ions or electrons.
COATING
Fiber optic coatings are UV-cured urethane acrylate composite materials applied to the outside of the fiber during the drawing process. The coatings protect the very delicate strands of glass fiber”about the size of a human hair”and allow it to survive the rigors of manufacturing, proof testing, cabling and installation.
Todayâ„¢s glass optical fiber draw processes employ a dual-layer coating approach. An inner primary coating is designed to act as a shock absorber to minimize attenuation caused by microbending. An outer secondary coating protects the primary coating against mechanical damage and acts as a barrier to lateral forces.
TERMINATION AND SPLICING
Optical fibers are connected to terminal
equipment by optical fiber connectors.
These connectors are usually of a standard type such as FC, SC, ST, LC, or MTRJ.
Optical fibers may be connected to each other by connectors or by splicing, that is, joining two fibers together to form a continuous optical waveguide. The generally accepted splicing method is arc fusion splicing, which melts the fiber ends together with an electric arc. For quicker fastening jobs, a "mechanical splice" is used.
FREE SPACE COUPLING
It is often necessary to align an optical fiber with another optical fiber, or with an optoelectronic device such as a light-emitting diode, a laser diode, or a modulator. This can involve either carefully aligning the fiber and placing it in contact with the device, or can use a lens to allow coupling over an air gap. In some cases the end of the fiber is polished into a curved form that is designed to allow it to act as a lens.
In a laboratory environment, a bare fiber end is coupled using a fiber launch system, which uses a microscope objective lens to focus the light down to a fine point. A precision translation stage (micro-positioning table) is used to move the lens, fiber, or device to allow the coupling efficiency to be optimized. Fibers with a connector on the end make this process much simpler: the connector is simply plugged into a pre-aligned fiberoptic collimator, which contains a lens that is either accurately positioned with respect to the fiber, or is adjustable. To achieve the best injection efficiency into single-mode fiber, the direction, position, size and divergence of the beam must all be optimized. With good beams, 70 to 90% coupling efficiency can be achieved.
FIBER FUSE
At high optical intensities, above 2 megawatts per square centimeter, when a fiber is subjected to a shock or is otherwise suddenly damaged, a fiber fuse can occur. The reflection from the damage vaporizes the fiber immediately before the break, and this new defect remains reflective so that the damage propagates back toward the transmitter at 1“3 meters per second (4-11 km/h, 2“8 mph).[44][45] The open fiber control system, which ensures laser eye safety in the event of a broken fiber, can also effectively halt propagation of the fiber fuse.[46] In situations, such as undersea cables, where high power levels might be used without the need for open fiber control, a "fiber fuse" protection device at the transmitter can break the circuit to prevent any damage
APPLICATIONS

ADVANTAGES
Lower material cost , where large quantities are not required
Lower cost of transmitters and receivers
Much smaller cable size
Not electromagnetically radiating
No sparks-important in flammable or explosive gas environments
Lighter weight
DISADVANTAGES
Optical fibers are more difficult and expensive to splice
At higher optical powers , optical fibers are susceptible to fiber fuse wherein a bit too much light meeting with an imperfection can destroy several meters per second
Its life period is short
CONCLUSION
Fiber Optics is a significant technology used in many different areas of communications. With the explosion of the internet, fiber optics can readily provide the capacity of data that is transmitted with its gigabit speeds. As more breakthroughs in technology occur, it will spread to every aspect of the industry. Telephones, Fax Machines, Radios, Television Broadcasting, and even satellites use this highly reliable light wave technology. The telecommunications industry receives the most benefits from fiber optics. It allows for the transmission of audio, video, and data information in high quality.

REFERANCE
^ a b Bates, Regis J (2001). Optical Switching and Networking Handbook. New York: McGraw-Hill. p. 10. ISBN 007137356X.
^ Tyndall, John (1870). "Total Reflexion". Notes about Light. http://archivedetails/notesofcourseofn00tyndrich.
^ Tyndall, John (1873). "Six Lectures on Light". http://archivedetails/sixlecturesonlig00tynduoft.
^ The Birth of Fiber Optics
^ Nishizawa, Jun-ichi; Suto, Ken (2004). "Terahertz wave generation and light amplification using Raman effect". in Bhat, K. N.; DasGupta, Amitava. Physics of semiconductor devices. New Delhi, India: Narosa Publishing House. p. 27. ISBN 8173195676. http://books.googlebooksid=2NTpSnfhResC&pg=PA27&lpg=PA27&dq=Jun-ichi+Nishizawa+proposal+on+use+of+optical+fiber&source=bl&ots=iufv_Gmp98&sig=eqBUDA5OOfotJGSajaExFFf1cvA&hl=en&ei=aznYSf_DB4OoM9mO6PQO&sa=X&oi=book_result&ct=result&resnum=1#PPA27,M1
Post: #6
[attachment=10604]
Introduction to Optical Fibers.
 Used to carry signals in the form of light over distances up to 50 km.
Fibers of glass
 Usually 120 micrometers in diameter
 No repeaters needed.
 Core – thin glass center of the fiber where light travels.
 Cladding – outer optical material surrounding the core
 Buffer Coating – plastic coating that protects the fiber.
Advantages of Optical Fibre
 Thinner
 Less Expensive
 Higher Carrying Capacity
 Less Signal Degradation& Digital Signals
 Light Signals
 Non-Flammable
 Light Weight
Type of Fibers
Optical fibers come in two types:

• Single-mode fibers – used to transmit one signal per fiber (used in telephone and cable TV). They have small cores(9 microns in diameter) and transmit infra-red light from laser.
• Multi-mode fibers – used to transmit many signals per fiber (used in computer networks). They have larger cores(62.5 microns in diameter) and transmit infra-red light from LED.
How Does Optical Fibre Transmit Light??
 Total Internal Reflection.
 When light travelling in a dense medium hits a boundary at a steep angle (larger than the "critical angle" for the boundary), the light will be completely reflected.
How are Optical Fibre’s made??
 Three Steps are Involved
-Making a Preform Glass Cylinder
-Drawing the Fibre’s from the preform
-Testing the Fibre
Testing of Optical Fiber
 TENSILE STRENGTH TEST
 Abrasion Test
 CRUNCH TEST (COMPRESSION TEST)
 Impact test
 REPEATED BENDING TEST
 TORSION TEST
 WATER PENETRATION TEST
Areas of Application
 Telecommunications
 Local Area Networks
 Cable TV
 CCTV
 Optical Fiber Sensors
Post: #7
[attachment=10899]
ABSTRACT
Communication is an important part of our daily life. The communication process involves information generation, transmission, reception and interpretation. As needs for various types of communication such as voice, images, video and data communications increase demands for large transmission capacity also increase. This need for large capacity has driven the rapid development light wave technology; a worldwide industry has developed. An optical or light wave communication system is a system that uses light waves as the carrier for transmission. An optical communication system mainly involves three parts. Transmitter, receiver and channel. In optical communication transmitters are light sources, receivers are light detectors and the channels are optical fibers. In optical communication the channel i.e, optical fibers plays an important role because it carries the data from transmitter to the receiver. Hence, here we shall discuss mainly about optical fibers.
Optical Fibers in Communications
1. Introduction

Optical fibers are arguably one of the world’s most influential scientific developments from the latter half of the 20th century. Normally we are unaware that we are using them, although many of us do frequently. The majority of telephone calls and internet traffic at some stage in their journey will be transmitted along an optical fiber. More indirectly, many of the systems that we either rely on or enjoy in everyday life such as banks, television and newspapers as (to name only a very limited selection) are themselves dependent on communication systems that are dependent on optical fibers.
There are various other uses of optical fibers which are irrelevant to this essay, although it is interesting developed to detect chemicals along pipelines (by using unprotected chemically sensitive fiber), detect plutonium smuggling, monitor strain in yacht masts, allow communication with CAT scan patients, construct gyroscopes with no moving parts, transmit images from telescopes, and possibly guide atoms (although this is very early in the stages of development).
In this essay I shall attempt to cover the many areas of importance in optical fiber design. Only some crucial areas such as fiber design will be covered in detail; others such as signal sources and detectors will be discussed more briefly.
I shall also give some indication of the systems currently in use commercially and some of the systems currently being developed.
2. Why Optical Fiber?
Why has the development of fibers been given so much attention by the scientific community when we have alternatives? The main reason is bandwidth – fibers can carry an extremely large amount of information. I shall discuss the advantages and disadvantages of fiber compared to the four other commonly used media.
Twisted Pair Cable is used for, and is still suitable for, simple telephone links (known as the local loop) from the consumer to the nearest telephone exchange. The bandwidth is low, but is adequate for carrying low quality analogue voice signals. Attenuation of the signal is not significant over the short distances such signals are carried. The main advantage of twisted pair cable is the very low cost.
Coaxial Cable can carry a much larger amount of data – especially by multiplexing (the process of transmitting several signals of different wavelengths along the same cable) analogue signals. Multiplexing however is also possible with fiber, and fiber provides significantly higher bandwidth. Digital signals can be transmitted, but the bandwidth is limited if signal quality is to be maintained. Again, fiber is more expensive for many applications where coaxial cable is still used.
3. Fundamentals Of Fibers
The fundamental principle that makes optical fibers possible is total internal reflection. This is described using the ray model of light
From Snell’s Law we find that refraction (as shown by the dashed line) can only occur when the angle theta1 (between the incident ray and the material boundary) is large enough. This implies that as the angle is reduced, there must be a point when the light ray is reflected, where theta1 = theta2 (note that this is only true when the refractive index of the initial medium is greater than that of the adjacent medium, as shown by the value of n on the diagram). The angle where this happens is known as the critical angle and is:
Cladding. The core is (according to the ray model) where the light rays travel and the cladding is a similar material of slightly lower refractive index to cause total internal reflection. Usually both sections are fabricated from silica (glass). The light within the fiber is then continuously totally internally reflected along the waveguide.
When light enters the fiber we must also consider refraction at the interface of the air and the fiber core. The difference in refractive index causes refraction of the ray as it enters the fiber, allowing rays to enter the fiber at an angle greater than the angle allowed within the fiber
This acceptance angle, theta, is a crucial parameter for fiber and system designers. More widely recognized is the parameter NA (Numerical Aperture) that is given by the following equation:
Also crucial to understanding fibers is the principle of modes. A more in-depth analysis of the propagation of light along an optical fiber requires the light to be treated as an electromagnetic wave (rather that as a ray). Unfortunately there is not room for such a mathematical treatment in this essay, but we should note that it leads to a quantisation of the ‘angles’ at which ‘rays’ can travel through the fiber.
Figure 3 – Modes
The solid line is the lowest order mode shown on figure 3. It is clear that according to the ray model the lowest order mode will travel down a given length of fiber quicker than the others. The electromagnetic field model predicts the opposite – that the highest order mode will travel quicker. However, the overall effect is still the same – if a signal is sent down the fiber as several modes then as it travels along the fibre the pulse will spread out (this process is known as modal dispersion); this can lead to the pulses merging and becoming indistinguishable.
One further classification of rays can be made; meridional rays pass through the fiber axis; skew rays (hybrid rays) constantly rotate without passing through the fiber axis.
One other significant point should be noted from the electromagnetic field model – the evanescent field. The model predicts that the EM field does not suddenly drop to zero at the core-cladding boundary – it instead decays as a negative exponential within the cladding (see figure 4). This is crucial for various technologies relating to fibers.
This method of signal transmission has benefits in terms of security – for the signal to be ‘tapped’ the fiber must be broken (since effectively no energy escapes from the fiber) and this can easily be detected (when no signal reaches the other end of the fiber!). This is one of the many advantages of the medium.
4.The Development of Fiber
I shall consider the development of fiber in several sections rather than giving a general discussion of fiber properties. Two types of material are used to manufacture fibers – glass and plastic. There are several properties of a material that dictate how useful it is as a fiber:
• Purity
• Refractive Index (wavelength-dependent)
• Attenuation (wavelength-dependent)
We must remember that there are many different types of fiber and applications for fiber. The different properties of fibers can be combined to provide a suitable fiber for a particular job – not all fibers will be applicable for every situation.
The purity of the fiber will be reflected in both its attenuation properties (consider the scattering effect of an impurity particle) and its refractive index. The original breakthrough in reducing fiber attenuation was achieved by purifying the glass used to make the fibers. There are other intrinsic and extrinsic factors which contribute to the attenuation, such as absorption by OH- ions, absorption of infra-red radiation leading to molecular vibrations, leakage from the core (can be caused by Rayleigh Scattering and fiber curvature) and leaky modes. Curvature is important in fiber specification; again a more detailed analysis of the propagation of light through fibers is required to fully explain this, but essentially a small amount of the light is radiated as the fiber bends. Leaky modes are modes slightly below the cut-off, but can be propagated for a short distance along the fiber; they can be initially avoided at the light source by restricting the angle at which light enters the fiber, but can be introduced along the fiber by microbending. Microbends are minute bends in the fiber which can be introduced during manufacture or cabling (see later for more detail on cabling); they can cause power to be transferred between modes, possibly to leaky modes and hence can result in power loss.
Post: #8
[attachment=11477]
Optical Fiber & OF Cables
HISTORY REPEATS ITSELF
WHAT ARE OPTICAL FIBERS ?

Optical Fibers are thins long (km) strands of ultra pure glass (silica) or plastic that can to transmit light from one end to another without much attenuation or loss.
The glass used to make Optical Fibers is so pure that if the Pacific Ocean was filled with this glass then we would be able to see the ocean bottom form the surface….!!!!
This is to be believed as repeater distances on long haul routes for optical fibers vary from 50 to 150 km
Q.) And how deep is the Pacifica ocean?
Ans) At the deepest point called the Marina Trench, The pacific ocean is all of just 13km deep…..!!!!!
Working of Optical fibers?
The light source (LAZER) at the transmitting (Tx) end is modulated by the electrical signal and this modulated light energy is fed into the Optical Fiber.
At the receiving end (Rx) this light energy is made incident on photo-sensors which convert this light signal back to electrical signal.
Why Optical Fibers ?
bandwidth required increased exponentially.
Initially we used smoke signals, then horse riders for communicating. But these ways were way to slow and had very little bandwidth or data caring capacity.
Then came the telephone and telegraph that used copper wires for communication. But soon demand out striped the capacity and capability of copper wires and data transport got added to voice communication. Then came Coaxial copper cables, VHF and UHF Radios, Satellite but demand still outstripped the supply.
It was not until Optical Fibers came on the scene that large amount of communication bandwidth became economically and easily available to everyone.
As an example 50,000 voice / data circuit copper cable is massive in size and very expensive, while a single Optical Fiber, the diameter of human hair, can carry 5,00,000 circuits of voice and data. This capacity is increasing day by day as supporting electronics is developing. In itself the capacity of Optical Fibers is limitless.
ADVANTAGES OF OPTICAL FIBERS
1. VERY HIGH INFORMATION CARRING CAPACITY.
2. LESS ATTENUATION (order of 0.2 db/km)
3. SMALL IN DIAMETER AND SIZE & LIGHT WEIGHT
4. LOW COST AS COMPARED TO COPPER (as glass is made from sand..the raw material used to make OF is free….)
5. GREATER SAFETY AND IMMUNE TO EMI & RFI, MOISTURE & COROSSION
6. FLEXIBLE AND EASY TO INSTALL IN TIGHT CONDUICTS
7. ZERO RESALE VALUE (so theft is less)
8. IS DILECTRIC IN NATURE SO CAN BE LAID IN ELECTICALLY SENSITIVE SURROUNDINGS
9. DIFFICULT TO TAP FIBERS, SO SECURE
10. NO CROSS TALK AND DISTURBANCES
DISADVANTAGES OF OPTICAL FIBERS
1. The terminating equipment is still costly as compared to copper equipment.
2. Of is delicate so has to be handled carefully.
3. Last mile is still not totally fiberised due to costly subscriber premises equipment.
4. Communication is not totally in optical domain, so repeated electric –optical – electrical conversion is needed.
5. Optical amplifiers, splitters, MUX-DEMUX are still in development stages.
6. Tapping is not possible. Specialized equipment is needed to tap a fiber.
7. Optical fiber splicing is a specialized technique and needs expertly trained manpower.
8. The splicing and testing equipments are very expensive as compared to copper equipments.
APPLICATIONS OF OPTICAL FIBERS…
1. LONG DISTANCE COMMUNICATION BACKBONES
2. INTER-EXCHANGE JUNCTIONS
3. VIDEO TRANSMISSION
4. BROADBAND SERVICES
5. COMPUTER DATA COMMUNICATION (LAN, WAN etc..)
6. HIGHT EMI AREAS
7. MILITARY APPLICATION
VARIOUS TYPES OF OPTICAL FIBER CABLES
1. OPGW Cable
2. ADSS type OF Cable
3. Self-Support AERIAL figure 8 type OF Cable
4. LASHED type OF Cable
5. UNDERGROUND / BURRIED type OF Cables
6. DUCT Type OF Cable
Post: #9
Submitted
Sana Rao
SIR TiSMAN PASHA

[attachment=11888]
HISTORY
 Alexander Graham Bell patented an optical telephone system called the photo phone in 1880 .
That same year, William Wheeler invented a system of light pipes.
WHAT ARE OPTICAL FIBERS ?
 Optical Fibers are thins long (km) strands of ultra pure glass (silica) or plastic that can to transmit light from one end to an other.
 Basic Information
What is Optical Fiber Cable?
Optical cables used to transmit light signals over long distances.
It has basic three parts:
Core:
Cladding
Coating:
 Working of Optical fibers?
 TX
 RX
Principle of operation
 Dielectric (nonconducting ) that transmits light along its axis
 Total internal reflection.
 Refractive index
 Step-index fiber
 Graded-index fiber.
Optical Fiber Classification
Can be classified in a number of ways
 On the basis of manufacturing
 On the basis of profile
Types of Optical Fiber
There are two basic types of fiber:
 Multi Mode Optical Fiber:
Used to transmit many signals per fiber (Multi Mode generally are used for in computer networks, LAN applications)
 Single Mode Optical Fiber:
Used to transmit one signal per fiber (Single Mode generally are used for in telephones and cable TV applications)
Types of fiber optic cable of structures
 Glass Optical Fiber:
Glass fiber-optic cable has a Glass core and cladding.
 Plastic Optical Fiber (POF):
Plastic fiber-optic cable has a plastic core and cladding.
 Plastic Coated Silica Cable:
(PCS). PCS fiber-optic cable has a Glass core and Plastic cladding.
APPLICATIONS OF OPTICAL FIBERS
 Telephone Systems
 Internet
 Video Feeds
 Medical Operations
 Home Theater Systems
 Optical fiber communication
 Optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables .
 Over short distances.
USES
 Medical
 Defense/Government
 Data Storage
 Telecommunications
Fiber is laid and used for transmitting and receiving purposes
 Networking
Used to connect users and servers.
 Industrial/Commercial
 Broadcast/CATV
ADVANTAGES OF OPTICAL FIBERS
 VERY HIGH INFORMATION CARRING CAPACITY.
 SMALL IN DIAMETER AND SIZE & LIGHT WEIGHT
 LOW COST AS COMPARED TO COPPER
 GREATER SAFETY
 ZERO RESALE VALUE
FIBER OPTIC CABLE ADVANTAGES OVER COPPER:
 • SPEED: Fiber optic networks operate at high speeds - up into the gigabits
 • BANDWIDTH: large carrying capacity
 • DISTANCE: Signals can be transmitted further without needing to be "refreshed" or strengthened.
 • RESISTANCE: Greater resistance to electromagnetic noise such as radios, motors or other nearby cables
 • MAINTENANCE: Fiber optic cables costs much less to maintain.
Disadvantages of Fiber Optic Cabling
 Adding additional nodes is difficult
 Cost of transmission equipment is Higher than copper
 Cost of installation is Higher than copper
 Difficult to Install
 Expensive over short distance (less 5 km)
 Requires highly skilled installers
Post: #10
PRESENTED BY:
ASHEESH KUMAR

INTRODUCTION
Modern fiber-optic communication systems generally include an optical transmitter to convert an electrical signal into an optical signal to send into 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 data transmitted is typically digital data 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. The main component of an optical receiver is a photodetector, which converts light into electricity using the photoelectric effect. The photodetector is typically a semiconductor-based photodiode. Several types of photodiodes include p-n photodiodes, a 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. An optical fiber 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.
APPLICATION
• Due to much lower attenuation and interference, optical fiber has large advantages over existing copper wire in long-distance and high-demand applications.
• Optical fiber is used by many telecommunications companies to transmit telephone signals, Internet communication, and cable television signals.
• Since 2000, the prices for fiber-optic communications have dropped considerably. The price for rolling out fiber to the home has currently become more cost-effective than that of rolling out a copper based network. Prices have dropped to $850 per subscriber in the US and lower in countries like The Netherlands, where digging costs are low.
Post: #11
hi please send me seminars report
:angel:
Post: #12
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OPTICAL FIBER COMMUNICATION
What is Communication ??
What is Optical Fiber ?

Optical fibers are thin, transparent strands almost the size of a human hair made from a dielectric cylinder surrounded by another transparent dielectric cylinder
Optic fiber is made up of 3 parts :
Core, Cladding and jacket
The inner most part is the core which contains one or more thin fibers that are made up of plastic or glass
Each of the fiber in the core is covered by a cladding which has different optical properties from the core
The outer most part of the optical fiber is made up of plastic or other materials ,which is called the jacket
How does it work ?
You hear about fiber-optic cables whenever people talk about the telephone system, the cable TV system or the Internet. Fiber-optic lines are strands of optically pure glass as thin as a human hair that carry digital information over long distances.
The light in a fiber-optic cable travels through the core by constantly bouncing from the mirror-lined walls, ……………total internal reflection.
The reflections inside the walls are possible because of high refractive index material of the inner cylinder.
OPTICAL FIBER
Optical communication system
Transmitter. Converts electrical signal into light signal.
Optical fiber. Conducts the light signal over the distance.
Optical regenerator. May be required to boost the light signal for longer distances.
Optical receiver. Converts light signals back to electrical signal.
Typical Optical communication system.
Electric signal In
Transmitter
Optical Regenerator
Optical Receiver
How Are Optical Fibers Made?
How Does an Optical Fiber Transmit Light?
Advantages of using optical fiber
Less expensive.
Less volume (thinner than copper wires).
Higher capacity.
Less signal degradation.
No interference between two signals.
Low power.
Lightweight.
Flexible.
Applications
Some applications use fiber optics for the communication
Communication
Medical
Industry
Sensors
Military Application
Post: #13
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