MODERN TRENDS IN OPTICAL COMMUNICATION
(FIBER OPTIC COMMUNICATION)
❖ Advantages of Fiber Optics
❖ Optical Transmitters
❖ The Optical Fiber
❖ Launching the Light
❖ Losses in Optical Fiber
❖ Optical Fiber Bandwidth
❖ Fiber Optic Cable Construction
❖ Other Types of Fibers
❖ Optical Receivers
Our current "age of technology" is the result of many brilliant inventions and discoveries, but it is our ability to transmit information, and the media we use to do it, that is perhaps most responsible for its evolution . Progressing from the copper wire of a century ago to today's fiber optic cable, our increasing ability to transmit more information, more quickly and over longer distances has expanded the boundaries of our technological development in all areas. Today's low-loss glass fiber optic cable offers almost unlimited bandwidth and unique advantages over all previously developed transmission media. The basic point-to-point fiber optic transmission system consists of three basic elements: the optical transmitter, the fiber optic cable and the optical receiver.
The Optical Transmitter:
The transmitter converts an electrical analog or digital signal into a corresponding optical signal. The source of the optical signal can be either a light emitting diode, or a solid state laser diode. The most popular wavelengths of operation for optical transmitters are 850, 1310, or 1550 nanometers. Most Fiberlink® transmission equipment manufactured by Communications Specialties operates at wavelengths of 850 or 1310nm. [pic]
|The Optical Fiber | |Launching the Light | |the transmitter has converted the electrical input signal into whatever form of modulated light is desired, the light must be "launched" into the optical fiber. | |As previously mentioned, there are two methods whereby light is coupled into a fiber. One is by pigtailing. The other is by placing the fiber's tip in very close proximity to | |an LED or LD. When the proximity type of coupling is employed, the amount of light that will enter the fiber is a function of one of four factors: the intensity of the LED or | |LD, the area of the light emitting surface, the acceptance angle of the fiber, and the losses due to reflections and scattering. Following is a short discussion on each: | |Intensity: The intensity of an LED or LD is a function of its design and is usually specified in terms of total power output at a particular drive current. Sometimes, this | |figure is given as actual power that is delivered into a particular type of fiber. All other factors being equal, more power provided by an LED or LD translates to more power | |"launched" into the fiber. | |Area: The amount of light "launched" into a fiber is a function of the area of the light emitting surface compared to the area of the light accepting core of the fiber. The | |smaller this ratio is, the more light that is "launched" into the fiber. | |Acceptance Angle: The acceptance angle of a fiber is expressed in terms of numeric aperture. The numerical aperture (NA) is defined as the sine of one half of the acceptance | |angle of the fiber. Typical NA values are 0.1 to 0.4 which correspond to acceptance angles of 11 degrees to 46 degrees. Optical fibers will only transmit light that enters at | |an angle that...
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