WDM networks make a very effective utilization of the fiber bandwidth
and offer flexible interconnections based on wavelength routing, In hi
gh capacity, dynamic WDM networks, blocking due to wavelength contenti
on can be reduced by wavelength conversion, Wavelength conversion addr
esses a number of key issues in WDM networks including transparency, i
nteroperability, and network capacity, Strictly transparent networks o
ffer seamless interconnections with full reconfigurability and interop
erability. Wavelength conversion may be the first obstacle in realizin
g a transparent WDM network, Among numerous wavelength conversion tech
niques reported to date, only a few techniques offer strict transparen
cy, Optoelectronic conversion (O/E-E/O) techniques achieve limited tra
nsparency, yet their mature technologies allow deployment in the near
future, The majority of all-optical wavelength conversion techniques a
lso offer limited transparency but they have a potential advantage ove
r the optoelectronic counterpart in realizing lower packaging costs an
d crosstalk when multiple wavelength array configurations are consider
ed, Wavelength conversion by difference-frequency generation offers a
full range of transparency while adding no excess noise to the signal,
Recent experiments showed promising results including a spectral inve
rsion and a 90 nm conversion bandwidth, This paper reviews various wav
elength conversion techniques, discusses the advantages and shortcomin
gs of each technique, and addresses their implications for transparent
networks.