Fiber Optics Technology
Optical Fibers are glass fibers usually about 120 micrometers in diameter that are used to deliver wave signals in the form of pulses of light over distances up to 50 km without the using repeaters. These wave signals may be coded voice communications or computer data.
How Fiber Works
The working of an optical fiber is dependent on the principle of total internal reflection. Light reflects or refracts based on the angle at which it strikes a surface. This principle is at the center of how optical fiber works. Restricting the angle at which the light waves are delivered makes it possible to control how efficiently they reach their destination. Light waves are covered with the core of the optical fiber in much the same way that radio frequency signals are covered with coaxial cable. The light waves are directed to the other end of the fiber by being reflected within the core.
The creation of the cladding glass relative to the core glass decides the fiber's capability to reflect light. That reflection is usually occurred by creating a higher refractive index in the core of the glass than in the surrounding cladding glass creating a "waveguide". The refractive index of the core is improved by slightly changing the composition of the core glass generally by adding small amounts of a dopant. Alternatively the waveguide can be composed by decreasing the refractive index of the cladding using different dopants.
Design of Fiber
Core, Cladding, and Coating
An optical fiber is made up of two different types of highly pure, solid glass composed to form the core and cladding. A protective coating surrounded with the cladding. In most cases the protective coating is a double layer composition.
In the manufacturing process, a protective coating is applied to the glass fiber as the final step. This coating protects the glass from scratches and dust that can affect fiber strength. This protective coating can be composed with two layers: a soft inner layer that act as cushions to the fiber and permits the coating to be uncovered from the glass mechanically and a harder outer layer that protects the fiber during handling particularly the cabling, installation, and termination processes.
Types of Fiber
There are two types of optical fiber: single-mode and multimode.
Single-Mode and Multimode Fibers
Multimode fiber was type to be used for commercial purpose. It is provided with larger core than single-mode fiber permitting hundreds of modes of light to propagate through the fiber simultaneously. Additionally the larger core diameter of multimode fiber makes possible the use of lower-cost optical transmitters or vertical cavity surface emitting lasers and connectors.
Single-mode fiber is provided with smaller core that permits only one mode of light at a time to propagate through the core. Single mode fibers are developed to maintain spatial and spectral integrity of each optical signal over longer distances permitting more information to be delivered. Its vast information-carrying capacity and low intrinsic loss have made single mode fiber the ideal transmission medium for a multitude of applications. For longer-distance and higher-bandwidth applications single mode fiber is used. In systems with short transmission distances such as premises communications, private data networks, and parallel optic applications, multimode fiber is used.
Optical Fiber Sizes
The standard used for outer cladding diameter of most single-mode optical fibers is 125 microns (µm) for the glass and 245 µm for the coating. This standard is vital because it provide guaranteed compatibility among connectors, splices and tools used throughout the industry.
Standard single-mode fibers are developed with a small core size approximately 8 to 10 µm in diameter. Multimode fibers use core sizes of 50 to 62.5 µm in diameter.
Outside Vapor Deposition (OVD) Process
Basic OVD optical fiber designing consists of three steps: Laydown, consolidation, and draw.
1) Laydown
A soot preform is made from ultra pure vapors in the laydown step as they travel through a traversing burner and react in the flame to form fine soot particles of silica and germanium.
The OVD process is separated by the method of depositing the soot. These particles are placed on the surface of a rotating target rod. The core material is placed first followed by the pure silica cladding. As both core and cladding raw materials are vapor-placed the entire preform becomes totally synthetic and extremely pure.
2) Consolidation
The lure rod is removed from the center of the porous preform when deposition is complete and the preform is placed into a consolidation furnace. The water vapor is removed from the preform during the consolidation process. This high-temperature consolidation step converts the preform into a solid, dense, and transparent glass.
3) Draw
The completed glass preform is then placed on a draw tower and drawn into one continuous strand of glass fiber.
Fiber from these spools is tested and then measured for performance of relevant optical and geometrical parameters. Each fiber has a unique identification number that can be traced to all relevant developing the data. Each fiber spool is then placed into protective shipping containers and prepared for shipment to customers worldwide.
Advantages
1) Capacity:
Optical fibers transfer signals with much less energy loss than copper cable and with a much higher bandwidth. This means that fibers can transfer more channels of information over longer distances and with fewer repeaters needed.
2) Size and Weight:
Optical fiber cables used are much lighter and thinner than copper cables with the same bandwidth. This means that much less space is needed in underground cabling ducts.
3) Security:
Optical fibers provide more security than any other cables. They are protected to Electromagnetic interference from radio signals, car ignition systems, lightning etc. They can be delivered safely through explosive or flammable atmospheres.
Areas of Application
1) Telecommunication's:
Optical fibers are now the used as link between telephone substations.
2) Local Area Networks (LAN's):
Multimode fiber is commonly used as the "backbone" to deliver signals between the hubs of LAN's from where copper coaxial cable takes the data to the desktop.
3) Cable TV:
Cable TV networks make use of optical fiber because of its low power utilization.
4) CCTV
Closed circuit television security systems make use of optical fiber because of its inbuilt security as well as the other benefits.
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