Position of Semiconductor Optical Amplifiers in Wavelength Division Multiplexing Based Star and Tree Topology Networks

Abstract

Abstract

This thesis is mainly concerned with the use of semiconductor optical amplifiers (SOAs) in wavelength division multiplexing (WDM) broadcast topologies (star and tree). The aim of investigations is to determine the increase in the number of users when SOAs are placed in the above topologies as case study for fiber optic network in Sudanese Armed Forces. Various placements options have been considered in the above topologies.

A detailed study on the use of SOAs in WDM star topology is also carried out. Two schemes have been considered viz. SOAs as postamplifiers and preamplifiers. In the postamplifier scheme, SOAs are placed after the transmitter and in the preamplifier scheme before the receiver. In the postamplifier scheme, three cases have been investigated. First case corresponds to unsaturated SOAs, second to gain saturated SOAs and in third case effect of reflection noise is studied. Similarly, in the preamplifier case unsaturated SOAs, average gain saturated SOAs and average gain saturated SOAs with gain fluctuations with and without reflection noise have been considered. It is observed that for typical values of system parameters, SOAs as preamplifiers perform better than the postamplifiers.

The study on placement of SOAs has been extended to WDM tree-net topology. The tree-net consists of star as main topology and folded bus as auxiliary topology. Star portion consists of a star coupler. A tree-net with b branch uses b×b star coupler. The SOAs can be placed in the star portion of the tree-net to increase the supportable number of users. However, the number of SOAs can be smaller than b to support the same number of users as in star.

On comparison between tree-net with star, it is observed that a tree-net can support more users than a star for a given number of SOAs.

It is concluded that SOAs as preamplifiers perform better in star topology.

When SOAs are used in tree topology, number of users supported can be more than in star. Further, the required number of SOAs would be lesser in tree than in star for a given number of users.