In this paper, we report results of our study with respect to the number of
wavelength division multiplexer/demultiplexers that should be provided in
optical cross-connect switches (optical XCs) installed in the nodes of opti
cal wavelength multiplexed transmission networks. Optical XCs perform the s
witching and add/drop operations of optical signal routes in the nodes, as
well as establish lightwave paths between two arbitrary nodes. In many case
s, the optical XCs proposed in the past had wavelength division multiplexer
/demultiplexers connected to all input/output optical fibers that, after se
parating all lightwave paths transmitting wavelength multiplexed signals, p
erformed switch and add/drop operations. However, when all lightwave paths
input in an optical XC from an optical fiber are relayed to only one differ
ent output optical fiber, there is no need to perform wavelength demultiple
xing between the input and output optical fibers. If a light wave path pass
es through a node without separation of optical signals as they were multip
lexed in the optical fiber (cut-through), the number of wavelength division
multiplexer/demultiplexers can be reduced. The authors considered two algo
rithms for lightwave path allocations whose purpose is to minimize the numb
er of wavelength division multiplexer/demultiplexers and evaluated them on
an example of an m x n mesh network. The results of evaluation suggest that
it is possible to reduce the number of wavelength division, multiplexer/de
multiplexers that must be installed by 10% to several dozen percent compare
d to the case when the dividers are installed on all input fibers. (C) 2000
Scripta Technica, Electron Comm Jpn Pt 2, 83(10): 44-59, 2000.