Study of all optical metropolitan area networks

Abstract

In this work we show how new optical devices can improve network performance. The multiplexing technique mainly taken into consideration is TDM. We have considered two different network topologies: the first is a TDMA network where signal information is simultaneously broadcast to all users; the second is a multihop network. The first is useful mainly for circuit switching, while the second is useful for packet switching. To overcome bit rate limitation due to the fibre chromatic dispersion, soliton propagation is considered. In both the networks the multiplexing process is obtained by means of optical delay lines and couplers, while the demultiplexing process is obtained by means of optical logic AND gates, implemented by means of the process of the second harmonic generation in a KTP crystal. For the multihop network, the routing process is obtained at an optical level by means of soliton dragging gates. In the TDMA network all the user signals are multiplexed in an optical central star, therefore each user receives signals from all the other users. The switching operation is directly obtained by optical demultiplexing. This network presents a total throughput of 130 Gbit/s corresponding to 200 users working at 625 Mbit/s. In the proposed multihop network, we consider nodes with two inputs and two outputs communicating at a bit rate equal to 50 Gbit/s. Furthermore, supposing that all the users work with pulses at the same optical frequency, using communication on different fibres, the total throughput, for 64 users, can reach the value of 1 Tbit/s.