Alleviating Metro Meltdown - Technology Information

Telecommunications, April, 2001 by J. Scott Bagnall

Hybrid Silica/MEMS push DWDM into the billion-dollar metro market.

Few would argue that DWDM is the accepted technology to generate bandwidth for long-haul communications. Bits and bytes crisscross the world efficiently and cost effectively, encoded on a beam of light. But as those bits and bytes near their destinations, they enter the much narrower, less efficient metro-network gateways to the copper last mile and begin to hit traffic jams.

The ongoing fiber buildout of the metro network offers tremendous opportunities for equipment vendors. Service providers in this market segment already spend billions of dollars annually on technologies such as digital cross-connects, ATM switches, IP routers, SONET and SDH ADMs (add/drop multiplexers)--none of which offer the bandwidth potential or revenue-generation opportunities of DWDM. Despite the limitations of copper-wire electronic communication, it is in some ways more suitable for delivering consumer services than fiber light-waves because the existing infrastructure is in place and can be used efficiently for the demands of traditional voice and analog modem traffic. But even with xDSL, the limitations of copper are already breached in many of the new entertainment services such as interactive video-on-demand.

LEGs claim that DWDM systems are designed almost exclusively for long haul. Offering data rates higher than necessary for current bandwidth demands, these systems are cost-prohibitive for providing home or office services. But DWDM in metro networks is not about more bandwidth: It's about more wavelengths for delivering diverse services.

By rethinking the technology behind the components inside DWDM systems and focusing on satisfying the needs of local service providers, manufacturers can create equipment that will enable them to compete in the billion-dollar metro communications market.

Hybrid optical silica/MEMS (micro-electro mechanical systems) will be the driving force behind metro DWDM networks. Silica planar waveguides combined with MEMS can provide the technological and economical benefits necessary to implement true end-to-end AONs (all-optical networks) by offering a practical way to improve existing product lines while creating a logical migration path for future communication services and applications.

Metro DWDM

Only AONs can satisfy today's demand for more bandwidth. AONs are not just for broadband transport, but for access to the home or business. Once fiber optic cable reaches a neighborhood, all other forms of wired communications will be rendered obsolete. These fat, unencumbered optical pipelines can deliver more information faster and more reliably than anyone ever dared imagine. Furthermore, optical networks will open new revenue-generating opportunities for service providers.

Speed is just one of many reasons today's DWDM technology is suitable for regional metro networks. Speed is expensive. One way to lower cost is to select components that offer slower throughput with broader bandwidth. While that approach can reduce capital expenditure up front, it may limit tomorrow's migration path.

Applying long-haul DWDM technology to metro networks will not work because the applications are different. A MAN provides wavelengths for service delivery instead of long-range signal transport. In a MAN, the signal travels a much shorter distance and requires no signal regeneration or repeater amplification. Meanwhile, the multiple wavelengths must be able to deliver a wide variety of services such as broadcast TV, video-on-demand, telephony and 100 Mbps Ethernet.

Long-haul systems use the multiple wavelengths of DWDM to expand capacity, and they require amplification for distance travel. Furthermore, the discrete optical components used in long-haul systems equipment are too large, bulky, costly, power-hungry and expensive for metro applications. For metro applications, a different set of technology characteristics is required: low cost, high performance and functionality, small size and minimal power consumption.

Caught in a paradox of cost vs. performance, metro DWDM is not possible now because today's long-haul technology cannot meet the necessary performance criteria within a reasonable economic framework.

The Breakthrough

To make metro DWDM a reality, optical component vendors must meet new demands for appropriate functionality with a competitive price tag. It will take a new manufacturing approach to make that happen.

Hybrid silica/MEMS technology promises to be a cost-effective, practical solution to this dilemma. Optical MEMS technology development has been primarily focused on large array switching because all-optical cross-connect switching is in demand and has been necessary to break the network bottleneck of OEO (optical-electrical-optical) conversion that is required to route traffic. Hybrid silica/MEMS technology extends that solution to the network edge. By combining materials suited to perform specific optical functions needed for DWDM systems and fabricating them with standard chip manufacturing techniques used for ordinary integrated silicon circuits, custom-designed metro DWDM systems can be created quickly and cost effectively.