Delivering 40 Gbps on ROADM Networks

The Metro/Regional DWDM market is currently undergoing a dramatic expansion driven by operator deployment of advanced broadband and IPTV services worldwide. These deployments are being necessitated by the mass adoption of Web 2.0 and peer to peer video services. These operators are now aggressively deploying Reconfigurable Add/Drop Multiplexers (ROADMs). While these new ROADM based DWDM networks are initially being deployed at 10 Gbps, traffic growth will necessitate that new 40 Gbps wavelengths be added beginning in 2008.

The use of Reconfigurable Optical Add/Drop Multiplexers (ROADMs) creates the availability of all wavelengths at all locations in the network. CapEx savings occur due to less equipment and more efficient wavelength grooming. OpEx savings occur due to the elimination of truck rolls at mid-points, decreasing provisioning time and time to revenue. In order to take full advantage of the flexibility provided by ROADMs, DWDM solutions need to be engineered to accommodate the presence of multiple ROADMs in a link. Filter concatenation can be a significant source of penalty in ROADM networks, even with 100GHz channel spacing, as operators want the flexibility to express through 16 or more ROADMs in a link without regenerating the signal. This poses additional challenges at 40Gbps due to the inherently wider optical spectrum.

Due to its spectral efficiency and resilience to narrowband optical filtering, Phase Shaped Binary Transmission (PSBT) is ideally suited for 40Gbps DWDM transmission through multiple cascaded ROADMs. In fact, the performance of PSBT actually improves slightly due to the narrowband optical filtering. By using 40Gbps PSBT transponders with tunable lasers and broadband receivers, the advantages of using ROADMs are maintained. 40Gbps wavelengths can be added to the existing 10Gbps DWDM infrastructure without replacing ROADMs or severely constraining the link engineering rules.

At StrataLight, we have developed 40 Gbps line cards with modulation schemes that are performance and cost optimized for Metro through to ULH applications. The figure below illustrates the target applications for the two complementary modulation schemes implemented by StrataLight.

More information can be found under the technical paper and white paper sections of the public web site.