26-12-2012, 06:24 PM
SEMINAR ON OPTICAL FIBER
OPTICAL FIBER.pptx (Size: 242.41 KB / Downloads: 24)
INTRODUCTION
An optical fiber is essentially a waveguide for light
It consists of a core and cladding that surrounds the core
The index of refraction of the cladding is less than that of the core, causing rays of light leaving the core to be refracted back into the core
Advantages of optical fiber include:
Greater bandwidth than copper
Lower loss
Immunity to crosstalk
No electrical hazard
Fiber-Optic Cables
There are two basic types of fiber-optic cable
The difference is whether the fiber is free to move inside a tube with a diameter much larger than the fiber or is inside a relatively tight-fitting jacket
They are referred to as loose-tube and tight-buffer cables
Both methods of construction have advantages
Loose-tube cables—all the stress of cable pulling is taken up by the cable’s strength members and the fiber is free to expand and contract with temperature
Tight-buffer cables are cheaper and generally easier to use
HISTORY OF FIBER OPTIC
Daniel Celadon first described this “light fountain” or “light pipe” in an 1842 article entitled On the reflections of a ray of light inside a parabolic liquid stream. This particular illustration comes from a later article by Celadon, in 1884
FIBER OPTIC CABLE
Optical fiber is made from thin strands of either glass or plastic
It has little mechanical strength, so it must be enclosed in a protective jacket
Often, two or more fibers are enclosed in the same cable for increased bandwidth and redundancy in case one of the fibers breaks
It is also easier to build a full-duplex system using two fibers, one for transmission in each direction
Principle of operation
An optical fiber is a cylindrical dielectric waveguide (non conducting 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.
Coatings
The light is "guided" down the core of the fiber by an optical "cladding" with a lower refractive index that traps light in the core through "total internal reflection."
The cladding is coated by a "buffer" that protects it from moisture and physical damage. The buffer is what gets stripped off the fiber for termination or splicing. These coatings are UV-cured urethane acryl ate 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
APPLICATIONS OF FIBER OPTIC
Optical fiber can be used as a medium for telecommunication and computer networking because it is flexible and can be bundled as cables.
It is especially advantageous for long-distance communications, because light propagates through the fiber with little attenuation compared to electrical cables. This allows long distances to be spanned with few repeaters.
Additionally, the per-channel light signals propagating in the fiber have been modulated at rates as high as 111 gigabits per second by NTT,[23][24] although 10 or 40 Gbit/s is typical in deployed systems