Current commercial OTM offerings can now scale
to well over 100 wavelengths per fiber with 10 Gbps wavelength speeds, yielding unmatched
terabit capacity.
The generic OTM design is shown in Figure 8.3 and consists of client interfaces,
wavelength transponders, amplifiers, and multiplexing/demultiplexing filters. The
transponders perform optical modulation for client signals, and new compact pluggable
interfaces are widely available for most protocol interfaces, e.g., Fast Ethernet, Gigabit
Ethernet, 10 Gigabit Ethernet, Fibre Channel, SONET/SDH OC-n/STM-n, and so on.
These interfaces can be bypassed if the client gear directly supports ITU-T-compliant
DWDM optics on their interface cards; for instance, many SONET/SDH and Ethernet/
IP platforms are equipped with 1550 nm lasers for direct interconnection purposes.
Moreover commercial DWDM systems??”particularly metro/regional??”also offer staged
filter designs to reduce up-front costs and facilitate ???pay-as-you-grow??? expansion, as
shown in the parallel and serial designs depicted in Figure 8.4. In general, the latter
can give low first cost but are more expensive to scale and tend to yield higher losses
(2??“3 dB per stage), see [3].
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