CSIS 160
Josh Ancel
Final Project
 
 
 
Fiber Optics
 
"A relatively new technology with vast potential importance, fiber optics is the channeled transmission of light through hair-thin glass fibers."
 
·        Fiber is less expensive than copper cables
·        Fibers raw materials is silica sand
·        Fiber is less expensive to maintain If damaged, restoration time is faster (although more users are affected)
·         Fiber is a backbone to the Telecommunications Industry 
 
     Information (data and voice) is transmitted through the fiber digitally by the use of high speed LASERs (Light Amplification through the Simulated Emission of Radiation) or LEDs (Light Emitting Diodes).  Each of these methods create a highly focused beam of light that is cycled on and off at very high speeds. Computers at the transmitting end convert data or voice into "bits" of information.  The information is then sent through the fiber by the presence, or lack, of light.  Computers on the receiving end convert the light back into data or voice, so it can be used.
       
   All of this seems to be a very "modern" concept, and the technology we use is. The concept though, was the idea of Alexander Graham Bell in the late 1800's. He just didn't have a dependable light source... some days the sun doesn't
shine!  He thought of the idea that our voices could be transmitted by pulses of light.  The people who thought that audio, video, and other forms of data could
be transmitted by light through cables, were present day scientists.  Most of the things that are possible today, Alexander Graham Bell could never even have dreamed of.
 
     Although the possibility of light waves communications occurred to Alexander Graham Bell (who invented the telephone), his ideas couldn't be used until the LASER or LED had been invented. Most of these advances occurred in the 1970s, and by 1977 glass-purifying and other fiber-optic manufacturing techniques had also reached the stage where interoffice light wave communications were possible. Sprint was the first to start this implementing these new technologies, and many intercity routes were in operation by 1985, and most transoceanic routes were being completed by 1999.  Now communication is virtually instantaneous to any location, from any location.
 
     The light is prevented from escaping the fiber by total internal reflection, a process that takes place when a light ray travels through a medium with an Index of Refraction higher than that of the medium surrounding it. Here the fiber core has a higher refractive index than the material around the core, and light hitting that material is reflected back into the core, where it continues to travel down the fiber.
 
      The glass fibers used in present-day fiber-optic systems are based on ultra-pure fused silica (sand). Fiber made from ordinary glass is so dirty that impurities reduce signal intensity by a factor of one million in only about 16ft of fiber. These impurities must be removed before useful long-haul fibers can be made. But even perfectly pure glass is not completely transparent.  It weakens
light in two ways. One, occurring at shorter wavelengths, is a scattering caused by unavoidable density changes within the fiber.  In other words, when the light
changes mediums, the change in density causes interference. The other is a longer wavelength absorption by atomic vibrations. For silica, the maximum transparency, occurs in wavelengths in the near infrared, at about 1.5 micron (micrometers).
                    
      Fiber-optic technology has been applied in many areas, although its greatest impact has come in the field of telecommunications, where optical fiber offers the ability to transmit audio, video, and data information as coded light pulses.  Fiber optics are also used in the field of medicine, all of the wire-cameras and lights are forms of fiber optic cable.   In fact, fiber optics have
quickly become the preferred mode of transmitting communications of all kinds. Even in your household stereo. Its advantages over older methods of transmitting data are many, and include greatly increased carrying capacity (due to the very high frequency of light), lower transmission losses, lower cost of basic materials, much smaller cable size, and almost complete immunity to any interference. Other applications include the simple transmission of light for illumination in awkward places, image guiding for remote viewing, and sensing. 
   
      This copper cable contains 3000 individual wires.
It takes two wires to handle one two-way conversation.
That means 1500 calls can be transmitted simultaneously on each cable. Each fiber optic cable contains twelve fiber wires. Two fibers will carry the same number of simultaneous conversations as one whole copper cable. Therefore, this fiber cables replace six of the larger ones. And 90,000 calls can be transmitted simultaneously on one fiber optic cable.
 
      AT&T's Northeast Corridor Network, which runs from Virginia to Massachusetts, uses fiber cables carrying more than 50 fiber pairs. Using a semiconductor LASER or a light-emitting diode (LED) as the light source, a transmitter codes the audio  or visual input into a series of light pulses, called bits. These travel along a fiber at a bit-rate of 90 million bits per second (or 90 thousand kbps). Pulses need boosting, about every 6.2 miles, and
finally reach a receiver, containing a semiconductor photodiode detector (light sensor), which amplifies, decodes, and regenerates the original audio or visual
information. Silicon integrated circuits control and adjust both transmitter and receiver operations. 
 

     These signals are sent through system called SONET (Synchronous Optical Network) which is a standard for optical telecommunications transport. It was formulated by the Exchange Carriers Standards Association (ECSA) for the American National Standards Institute (ANSI), which sets industry standards in the U.S. for telecommunications and other industries. The comprehensive SONET/SDH standard is expected to provide the transport infrastructure for worldwide telecommunications for at least the next two or three decades. The increased configuration flexibility and bandwidth availability of SONET provides significant advantages over the older telecommunications system. These advantages include:

 

SONET defines optical carrier (OC) levels and electrically equivalent. SONET defines a technology for carrying many signals of different capacities through a synchronous, flexible, optical hierarchy.  This is accomplished by means of a byte-interleaved multiplexing scheme. Byte-interleaving simplifies multiplexing, and offers end-to-end network management. The first step in the SONET multiplexing process involves the generation of the lowest level or base signal. In SONET, this base signal is referred to as Synchronous Transport Signal level-1, or simply STS-1, which operates at 51.84 Mb/s.

 Higher-level signals are integer multiples of STS-1, creating the family of STS-N signals in Table 1. An STS-N signal is composed of N byte-interleaved STS-1 signals. This table also includes the optical counterpart for each STS-N signal, designated

Optical Level

Electrical Level

Line Rate (Mbps)

Payload Rate (Mbps)

Overhead Rate (Mbps)

SDH Equivalent

OC-1

STS-1

51.840

50.112

1.728

-

OC-3

STS-3

155.520

150.336

5.184

STM-1

OC-9

STS-9

466.560

451.008

15.552

STM-3

OC-12

STS-12

622.080

601.344

20.736

STM-4

OC-18

STS-18

933.120

902.016

31.104

STM-6

OC-24

STS-24

1244.160

1202.688

41.472

STM-8

OC-36

STS-36

1866.240

1804.032

62.208

STM-13

OC-48

STS-48

2488.320

2405.376

82.944

STM-16

OC-96

STS-96

4976.640

4810.752

165.888

STM-32

OC-192

STS-192

9953.280

9621.504

331.776

STM-64

 
OC-N (Optical Carrier level-N).
Table: 1
      
      Light injected into a fiber can adopt any of several zigzag paths, or modes. When a large number of modes are present they may overlap, for each mode has a different velocity along the fiber. Mode numbers decrease with decreasing fiber diameter and with a decreasing difference in refractive index between the fiber core and the surrounding area.  Individual fiber production is quite practical, and today most high-capacity systems use single fibers. The present pace of technological advance remains impressive, with the fiber capacity of new systems doubling every 18 to 24 months. The newest systems operate at more than two billion bits per second per fiber pair. During the 1990s optical fiber technology extended to include both residential telephone and cable television service.
 
      
 
 
 
 
 
 
 
 
 
 
 
 
 
 
BIBLIOGRAPHY
 
1.   1995 Grolier Multimedia Encyclopedia, Grolier Electronic Publishing, Inc.
 
2.   1994 Compton's Interactive Encyclopedia, Compton's NewMedia.
 
3.   Fiber Optics abd Lightwave Communications Standard Dictionary, Martin H.
     Weik, D.Sc., Van Nostrand Reinhold Company, New York, New York, 1981.
 
4.   Fiber Optics and Laser Handbook, 2nd Edition, Edward L. Stafford, Jr. and
     John A. McCann, Tab Books, Inc., Blue Ridge Summit, Pennsylvania, 1988.
 
5.   Fiber Optics and Optoelectronics, Second Edition, Peter K. Cheo, Prentice
     Hall, Englewood Cliffs, New Jersey, 1990.
 

6. A Short History Of Telecommunications

http://www.sff.net/people/Jeff.Hecht/history.html

7. AT&T History Fiber Optic http://www.att.com/technology/history/chronolog/77fiber.html

 

8. About Fiber Optics

http://www.aboutfiberoptics.com/

 

9. The Birth Of Fiber Optics

http://inventors.about.com/library/weekly/aa980407.htm

 

10. Anatomy of Telecommunications

By. Tom Smith

 Abc TeleTraining, Inc., Geneva, IL 60134 C. 1998

 

11. The SONET Home Page

http://www.sonet.com/

 

12. Tektronix Optical Communications

http://www.tektronix.com/Measurement/cgi-bin/framed.pl?Document=/Measurement/App_Notes/SONET/&FrameSet=optical

 

13. How Stuff Works (subcategory Fiber Optics)

http://www.howstuffworks.com/fiber-optic.htm