Understanding Optical Fiber Communication Systems

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What is Communication ?? Exchange of information

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 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 OUT Electric signal In LIGHT Signal OPTICAL TRANSMITTER OPTICAL RECEIVER OPTICAL FIBER

http://www.dki.dk/images/Transceiver.gif Transmitter The transmitter is like the sailor on the deck of the sending ship. It receives and directs the optical device to turn the light "on" and "off" in the correct sequence, thereby generating a light signal. http://www.usswisconsin.org/Pictures/1940%20Pic/097%20Signal%20light%2024inc..JPG Produces and encodes the light signals. 9

Optical Regenerator Signal loss occurs when the light is transmitted through the fiber, especially over long distances Optical Regeneratorsis spliced along the cable to boost the degraded light signals. Consists ofoptical fibers with a special coating (doping). Regeneratoris a laser amplifier for the incoming signal. 10

Optical Receiver http://www.dki.dk/images/Transceiver.gif Optical receiver is like the sailor on the deck of the receiving ship. Takes the incoming digital light signals, decodes them and sends the electrical signal to the other user's computer, TV or telephone (receiving ship's captain). The receiver uses a photocell or photodiode to detect the light.

How Are Optical Fibers Made? Optical fibers are made of extremely pure optical glass. Making a preform glass cylinder Drawing the fibers from the preform Testing the fibers http://www.fiberdyne.com/products/images/lc.jpg 12

How Does an Optical Fiber Transmit Light? Shine a flashlight beam down a long, straight hallway Total internal reflection. Light signal degrades within the fiber Signal degrades depends on the purity of the glass and the wavelength of the transmitted light 850 nm = 60 to 75 percent/km 1,300 nm = 50 to 60 percent/km 1,550 nm is greater than 50 percent/km 13

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

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