Scalability of Optical Multi-Wavelength Switching Networks: Power Budget Analysis

Scalability with bit rate, number of wavelengths, number of input/output fibres per node is analysed, giving networks with very high data capacity (2000 Tb/s.km). Limits are optical noise accumulation, gain saturation, Raman scattering, dispersion. length division multiplexed (WDM) optical nodes in the transport network is one alternative to increase the capacity and flexibility of today’s netwotks[l]. Fig. (1) shows Splitters Fib= Amp 3 Introduction: The introduction of rearrangeable, wavethe multi-wavelength transport network (MWTN) optical node architecture of Ref. [l], which is the starting point Tunable Transmitter Unit. for the analysis in this paper. The purpose of this paper is to analyse the power budget of the MWTN for different node sizes, which will exemplify the scalability of optical multi-wavelength switching networks. The node has three input and three output fibres Carbandwidth of 30 nm, which would fit within the erbium rying four WDM channels each and four monolithic Indoped fibre amplifier (EDFA) gain bandwidth. When N j GaASP/InP 4x4 gate Switch matrices[21 with about 0 dB is increased, N j x N j switches are designed from already insertion 1thanks to integrated semiconductor optical demonstrated 4 ; ~ 4 gate switch matrices, and fibre-optic amplifiers (SOA’s). The node needs Nx number of Nf XN-f power splitters[5]. For large space division switch stages, Space switches, where Nf = 4 is the number of input Or it can be advantageous to include a preamplifier stage Output connections (including transmitters/receivers) to immediately before the space switch stage. the node and N x = Model: The computer model is based on Ref. [6], which per fibre. The channel selection is accomplished with tuntakes into accou,lt amplified spontaneous emission (ASE) able optical filters. The equalisers (variable attenuators) accumulation and static gain saturation in the EDFA’S are used both for power equalisation between the WDM and SOA’s. Me;uurements show that dynamic gain satchannels and for power regulation from node to nodeuration effects in the SOA’s can be avoided if the input Here, the measure of the total data capacity of a network power to the integrated 4x4 switch is below 0 dBm[7]. The is defined as C = ( N j l)Nx(Nn ~ ) I B R , where Nn is measured gain-flattened EDFA’s have unsaturated gain of the number of nodes that can be passed with bit error Go = 35 dB with -3 dB gain saturation output power rate 5 = 50 km is the of +10 dBm. The power budget is also limited by fifibre length between two nodes, and BR is the bit rate per bre non-linearities, mainly stimulated Raman scattering channel. To expand the data capacity, BR, Nx, or N j can (SRS), modelled like in Ref. [SI. Crosstalk and polarisabe increased, giving different node sizes. tion mode dispersion are not included in the analysis. Means of increase in data capacity: For high BR, Results: In Fig. (2), scaling with the number of WDM we assume dispersion compensating fibres (DCF’s)[3] at channels per fibre, Nx, is illustrated. The solid and dashed every node input with a broadband DCF figure of merit lines show the ASE and gain saturation calculation. There of 120 ps/(nm.dB). When Nx is increased, the channel sepis a significant decrease in N, due to gain saturation for aration can be performed through additional power splitincreasing Nx when power splitters and combiners and ting and filtering at the node input with the corresponding tunable filters are used. Wavelength /de/multiplexers imcombining function at the node output. It is better to use prove the performance. However, with increasing number wavelength selective /de/multiplexers[4], whose insertion of WDM channels, the threat from SRS increases (dashloss are assumed to be independent of the number of chandotted lines). In this case, the gain in the EDFA’s could nels. 16 channels with spacing 2 nm would give a total be reduced to increase the SRS power limit. For Nx = 16, 16 Figure 1: Optical node architecture for the MWTN[l]. is the number Of WDM (node 1 is transmitting),