APPLICATIONS IN FIBER-OPTIC NETWORKS
Optical Channel Monitors are increasingly needed as telecom carriers and multi-service operators migrate to reconfigurable and self-managed fiber-optic networks. Network operators benefit with OpEx savings provided by higher network reliability and more efficient operation, administration and provisioning. There are three key applications for optical channel monitors:
Channel Monitoring for ROADMs: Every ROADM requires an Optical Channel Monitor. In today's ROADM system, it is incumbent upon the DWDM channel monitor to provide an inventory of the incoming wavelengths to avoid “wavelength collision” with added channels, as well as an inventory of the outgoing channels when the ROADM is used for multi-degree ring-to-ring switching applications. The DWDM channel monitor is also relied on to provide channel-power information to the VOA control electronics so that the added channels can be equalized with the pass-through channels.
Multi-Haul Fiber-Optic Transmission: Designers rely on dynamic components for automatic span configuration at setup and self-adjustment over time to compensate for changing environmental conditions, thus enabling the designers to maintain ever tighter system margins. But many of these new dynamic components will not function effectively without a feedback control loop of some sort. To implement this critical function, new multihaul system designs now routinely call for DWDM channel monitors, which effectively build more intelligence in the optical node. The resulting design is a self-managed optical node that can adjust for changing environmental and input conditions, which makes it much easier to test and regression-test in network configurations. This will naturally lead to network architectures with increasingly distributed intelligence that will drive more embedded DWDM channel monitoring, not only in every optical node, but eventually in every optical submodule as well.
"Alien Wavelength" Management: As the number of wavelengths increase, so does the regenerator cost as a percentage of the total DWDM system cost. It is therefore no surprise that carriers are now requiring equipment vendors to devise ways to reduce the number of regenerators. A simple solution is to eliminate regenerators on DWDM systems and require the client line cards (for example on routers) to source long-reach DWDM channels instead of short-reach 1310-nm ones. Yet removing regenerators on DWDM systems also removes the SONET/SDH monitoring capability at that network node. The alternative is the implementation of DWDM channel monitors simply because they offer DWDM channel visibility regarless of the native modulation format for each DWDM wavelength.
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Tunable filters are also ideal for next generation Telecom PON and Cable HFC access networks where “broadcast and select” is the core architecture. These networks will evolve to overlay multiple wavelengths downstream. Such networks are specifically designed with high optical power launch that maximizes the number of signal splits downstream. At each split location, tunable filters can be used to dynamically tune to the desired wavelength on demand. Aegis is using its tunable thin film filter technology to develop products to meet these needs of future access networks.