User talk:Santoshverma05/sandbox

LED structure and Point to Point links in optical fiber communication
LED Structure :


 * To be useful in fiber transmission applications an LED must have a high radiance output, a fast emission response time, and a high quantum efficiency.Its radiance (or brightness) is a measure, in watts, of the optical power radiated into a unit solid angle per unit area of the emitting surface.


 * High radiance are necessary to couple sufficiently high optical power levels into a fiber.


 * The emission response time is the time delay between the application of a current pulse and the onset of optical emission.


 * This time delay is the factor limiting the bandwidth with which the source can be modulated directly by varying the injected current.The quantum efficiency is related to the fraction of injected electron-hole pairs that recombine radiatively.


 * To achieve a high radiance and a high quantum efficiency, the LED structure must provide a means of confining the charge carriers and the stimulated optical emission to the active region of pn junction where radiative recombination takes place . Carrier confinement is used to achieve a high level of radiative recombination in the active region of the device , which yields a high quantum efficiency . Optical confinement is of importance for preventing absorption of the emitted radiation by the material surrounding the pn junction.


 * To achieve carrier and optical confinement, LED configurations such as homojunctions and single and double hetrojunctions have been widely investigated. Two LED configurations are being used for fiber optics are surface emitters and edge emitters.

Point to Point links in optical fiber communication :


 * The design of an optical link involves many interrelated variables among the fiber, source, and photo detector operating characteristics , so that the actual link design and analysis may require several interactions before they are completed satisfactorily.


 * Since performance and cost constraints are very important factors in fiber optic communication links, the designer must carefully chose the components to ensure that the desired performance level can be maintained over the expected system lifetime without over specifying the component characteristics.


 * Following key system key requirements are needed in analyzing a link.

* The desired transmission distance. * The data rate or channel bandwidth. * The bit error rate (BER)


 * A point-to-point fiber optic data link consists of an optical transmitter, optical fiber, and an optical receiver. Point to Point links are part of optical fiber communication system which provides data connection between two points as shown below.

Information Source -->Optical Transmitter Fiber->Optical Receiver ---> User


 * All fiber optic systems are simply sets of point-to-point fiber optic links. Different system topologies arise from the different ways that point-to-point fiber optic links can be connected between equipment. The term topology, as used here, refers to the configuration of various equipment and the fiber optic components interconnecting them. This equipment may be computers, workstations, consoles, or other equipments. Point-to-point links are connected to produce systems with linear bus, ring, star, or tree topologies. Point-to-point fiber optic links are the basic building block of all fiber optic systems.

References :


 * 1) Optical Fiber Communcations - Fourth Edition by Gerd Keiser
 * 2) http://www.tpub.com/neets/tm/112.htm

By Santosh Kumar Verma, BITS ID : 2014HZ97005