Below is a 11/15 article on CWDM. Article mentions that CWDM is likely to provide a boost for SOA's. Wasn't
Optical Crossing working on SOA's?
Coarse WDM: More than an Interim Solution
Often touted as a make-do solution when budgets are tight, Coarse Wavelength Division Multiplexing (CWDM) might be a permanent solution for some access networks. What's more, these systems are likely to provide a boost for the Semiconductor Optical Amplifiers (SOAs) market.
November 15, 2002
By Mark Lutkowitz, CIR Vice President | Optical Networking Research CIR can confidently say that CWDM, with wavelength
channels typically 20 nanometers apart, is here to stay for a very long time. This is because there is really no such thing as an interim solution in the public telecommunications equipment market. Once a technology has firmly established itself as a tool, it tends to remain a tool indefinitely despite superior alternatives. The continuing viability of asynchronous M13 (DS-1 to DS-3) multiplexers, despite the SONET revolution, is one of the most impressive examples of devices holding onto a clear niche.
With the current industry downturn and capital under tight control, the emphasis in access systems has shifted from simply getting a relatively high number of channels to adding a few much cheaper channels. This can only be a boon for CWDM, where specifications are less demanding. As a result, CWDM will remain viable with simple, low-end, access-type applications where a small number of wavelengths are required, and distances are fairly short and mostly point-to-point.
There has been a widespread belief that Dense WDM (DWDM) will continue to be deployed in the long-haul networks and CWDM will make more headway closer to the end user, but CIR believes that there is now a chance that metro core DWDM applications, especially in ring configurations, may never take off in a big way. There have already been five-and-a-half years of hype with nothing close to realization in the networks and it will be at least another two or three years before DWDM metro rings become widespread.
Deploying DWDM has often been an extraordinarily painful and complex process given that adding another lambda frequently means that the carrier has to re-engineer the system and readjust all of the power levels. While there have been improvements in automating this process on newer metro gear, apprehension of these kinds of hassles continues to linger in the minds of network operators.
Significantly, the all-important Regional Bell Operating Companies (RBOCs) have only used DWDM when there was no other alternative, as in cases of fiber exhaust. This preference for lighting single-wavelength fibers has hardly been discouraged by the long-standing fear among RBOCs that the regulators will make them unbundle wavelengths to
other competitors.
Joining the legion of reasons to postpone deployment of metro DWDM, Microduct cable-laying techniques will allow even more fiber to be placed into metro conduit. And what's more, the need for sheer capacity can still be provided by SONET gear in the metro core, which has only just begun to embrace 10 Gbps capacity.
CWDM AND SOAS
Having established that there is a healthy niche for metro CWDM, the next question is whether there will be a need for CWDM amplifiers, and if so, which technology is best-suited to the task? Certain experts in the industry believe that amplifiers will not be needed in CWDM situations. Of course, the same expectation was widespread about metro DWDM and that also turned out to be false. Clearly, there are longer links in some potential CWDM cases such as in the
access loops of independent telcos in the U.S. And
applications for greater distances appear to be even more common in Asia, South America, and in the Caribbean.
Finding a feasible amplifier is a challenge for CWDM systems because one would need a smaller device at significantly lower cost but with comparable functionality to a metro DWDM amp. The only practical and cost-effective means to meet these requirements is to use an SOA that could handle as many as four of the channels simultaneously.
While many in the industry do not seem convinced that SOAs are ready for prime time, two system-house contacts are convinced that semiconductors have already reached a sufficient level of maturity-in particular, the type of device offered by California-based Genoa. One fullsystem vendor describes Genoa's device as having "beautiful
performance" with no failures and says that "turning
them on was as simple as flipping a switch."
Another potential customer points out that the SOAs, from a technological perspective, are quite similar to pump lasers or distributed feedback lasers, which are already mass-produced and so provide a familiar package and footprint. This interviewee also contends that the SOA offers a fairly cheap multiwavelength amp because it is similar to the cost of these standard semiconductor lasers, that the SOA does not need sophisticated control, and that early technical
hurdles with these products have been overcome.
There are viable alternatives to SOAs such as electronic regeneration that could be used instead, according to some CWDM experts. With a couple of regenerators, they say, an entire CWDM metro system would still cost less than a metro DWDM system. Other alternatives for stretching transmission include the use of avalanche photodiodes and forward error
correction.
CONCLUDING THOUGHTS
There will likely be long-term niche opportunities for CWDM in applications between single-wavelength and DWDM. There might not be more than 10 percent of CWDM network applications where a CWDM amp would be needed to get farther or to compensate for higher span losses, but the opportunities for SOAs could be there.
As metro DWDM costs come down, price points on CWDM will also be driven down. Since specifications for DWDM are much more exacting, differentials on cost between the two will be maintained indefinitely. If nothing else, CWDM can represent the first implementation of wavelengths when DWDM is simply not needed right away. Most significantly, the very healthy, long-term outlook for CWDM should be a guard
against obsession with bleeding-edge solutions and promote the use of cheap and simple technology in telecommunications networks.
This article is based on CIR research within the
Networking Systems and Services Advisory Program. For
more information regarding this and other services,
please contact John Jackson, Vice President of Sales,
via email john.jackson@cir-inc.com or by phone
714-777-2033. |
