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Optical fiber
- 1. OPTICAL FIBERS الرحمن ا بسم الرحيم
- 2. Agenda: • Introduction • History • Why optical fiber • Physics of optical fiber • Working • Types • Applications • Advantages • Disadvantages • Interesting points • References
- 3. Introduction: • Optical fibers are long, thin strands of very pure glass or plastic, usually 120 µm in diameter. They are arranged in bundles called optical cables and used to transmit light signals over long distances.
- 4. HISTORY • In 1854, John Tyndall • In 1880, Alexander Graham Bell • In 1970, Corning Glass researchers Robert Maurer, Donald Keck and Peter Schultz .
- 5. HISTORY • First installed in Chicago, USA in 1976 • By the early 1980s, fiber networks connected the major cities on each coast in USA.
- 6. • the amount of bandwidth required increased . • Initially communication. • Then came the telephone and telegraph. Why Optical Fibers ?
- 7. • 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. Why Optical Fibers ?
- 8. Parts of Optical Fiber • Core • Cladding • Buffer Coating
- 9. Transmission of Light Through Optical Fibers • The optical fiber cables are constructed being based on the principle of Total Internal Reflection
- 11. Total internal reflection occurs when: • a ray of light is incident upon a boundary with an optically rarer medium (one that makes it speed up) and • the angle of incidence is greater than the critical angle.
- 12. How Does an Optical Fiber Transmit Light?
- 13. Total Internal Reflection in optical fiber: • The angle of the light is always greater than the critical angle. • Cladding does not absorb any light from the core. • The extent that the signal degrades depends upon the purity of the glass and the wavelength of the transmitted light.
- 14. Total Internal Reflection in optical fiber: • The refractive index of the core is always greater than the index of the cladding. By this way Light is guided through the core, and the fiber acts as an optical waveguide. * Refractive index of the medium = [Speed of light in a vacuum / Speed of light in the medium]
- 15. How optical fiber works • 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.
- 16. Block diagram of fiber-optic communication system
- 17. Types of Optical Fibers Optical fibers come in two types: • Single-mode fibers • Multi-mode fibers
- 18. Single-mode fibers • Single-mode fibers are used to transmit one signal per fiber (used in telephone and cable TV). • light can travel through it only in a single path. • So narrow, they have small core (9 microns in diameter) • This type of cable is extremely expensive.
- 19. Multi-mode fibers • Multi-mode fibers are used to transmit many signals per fiber (used in computer networks). • They have larger cores (62.5 microns in diameter) • gives light beams the freedom to travel several paths.
- 20. Types of Optical Fibers
- 21. Wavelength Division Multiplexing • Signals with different wavelengths are combined, transmitted together, and separated again.
- 22. Time Division Multiplexing • Several optical signals are combined, transmitted together, and separated again based on different arrival times.
- 23. Bandwidth • Fiber bandwidth is given in MHz-km. • A product of frequency and distance, bandwidth scales with distance • For a 100-meter run (as allowed for twisted pair cable), the bandwidth for 62.5/125-micrometer fiber is 1600 MHz at 850 nm and 5000 MHz at 1300 nm.
- 24. Applications • Carry plain old telephone service (POTS) • For transmission of data • Transmitting broadband signals • In the biomedical industry • Non-Communication Applications (sensors etc…) • Military application
- 25. Advantages • Low cost as compared to copper (as glass is made from sand..the raw material used to make OF is free...) • High information Carrying Capacity • Less Signal Degradation • No cross talk and disturbances • small in diameter and size • light weight • is dilectric in nature so can be laid in electrically sensitive surroundings • difficult to tap fibers, so secure
- 26. Disadvantages • Fiber optics are that the cables are expensive to install. • The termination of a fiber optic cable is complex and requires special tools. • They are more fragile than coaxial cable. • Connectors tend to come loose after a period of time.
- 27. Interesting points: • 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.!!! • zero resale value (so theft is less)
- 28. The laser light used with single-mode has a longer wavelength than can be seen. The laser can seriously damage eyes. Do not look at the near end of a fiber that is connected to a device at the far end.
- 29. References 1. http://www.authorstream.com/ 2. http://www.howstuffworks.com/ 3. http://www.osun.com/ 4. http://www.visualphotos.com 5. http://www.wikipedia.com/ 6. http://www.rkm.com.au 7. http://computer.howstuffworks.com/fi ber-optic2.htm
- 30. ANY QUESTION ?
Editor's Notes
- In 1854, John Tyndall demonstrated to the Royal Society that light could be conducted through a curved stream of water, proving that a light signal could be bent. In 1880, Alexander Graham Bell invented his 'Photophone', which transmitted a voice signal on a beam of light. Bell focused sunlight with a mirror and then talked into a mechanism that vibrated the mirror. At the receiving end, a detector picked up the vibrating beam and decoded it back into a voice the same way a phone did with electrical signals. Many things -- a cloudy day for instance -- could interfere with the Photophone, causing Bell to stop any further research with this invention.
- As mans need and hunger for communication increased, the amount of 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.
- Hundreds or thousands of these optical fibers are arranged in bundles in optical cables. The bundles are protected by the cable's outer covering, called a jacket.
- This picture shows a much larger example of an optical fiber. The green laser beam enters the waveguide and is trapped by total internal reflection and travels down the the waveguide without any of the light escaping. These fibers are used to send light very long distance with very little loss of light. This allows for fast and efficient optical communications. To know more about on which bases the optical fiber works, first I would like to explain the phenomena of toatal internal reflection.
- Suppose you want to shine a flashlight beam down a long, straight hallway. Just point the beam straight down the hallway -- light travels in straight lines, so it is no problem. What if the hallway has a bend in it? You could place a mirror at the bend to reflect the light beam around the corner. What if the hallway is very winding with multiple bends? You might line the walls with mirrors and angle the beam so that it bounces from side-to-side all along the hallway. This is exactly what happens in an optical fiber. The light in a fiber-optic cable travels through the core (hallway) by constantly bouncing from the cladding (mirror-lined walls), a principle called total internal reflection. Because the cladding does not absorb any light from the core, the light wave can travel great distances
- 1- An encoder or modulator converts the data from electronic to an optical signal. 2- A transmitter lunches the signal in the fiber. 3- To compensate for gradual loss of signal strength (known as attenuation), repeaters are used to periodically amplify the signal during its passage through the optical cable. 4- When the signal arrives at its detination, a detector converts it back into an electrical signal. 5- A demodulator decodes the structure of the original signal and sends it on to various devices.
- difficult to tap fibers, so secure means = optical fiber not trnasfering signal, son