Agile Photonic Technologies for Next-Generation High-Capacity Dynamic Optical Networks

John E. Bowers and Volkan Kaman
Calient Networks, 25 Castilian Drive, Goleta, CA 93117, USA

With the rapid deployment of commercial broadband services (FTTH, VoD, VoIP, etc.) and high-bandwidth applications (grid-computing, e-science, etc.), next-generation metro and backbone core optical networks are forecasted to require aggregate capacities of hundreds of terabits per second. The increase in traffic capacity naturally necessitates in parallel a continuous reduction in cost, size and power consumption per bit, which is achieved by gradually driving the non-scaling electronics out of the high-capacity core network to the lower bandwidth edge user interfaces. The transition to higher efficiency all-optical communication is most evident with the deployment of the EDFA (and consequent elimination of expensive OEO repeaters) in the early 1990’s, which revolutionized communication system capacity by widespread implementation of data rate transparent point-to-point DWDM. Currently, capacity increase is envisioned through spectrally efficient high-speed data rates of 40 Gb/s SONET and 100 Gigabit Ethernet using advanced modulation formats, transparent photonic devices such as optical amplifiers, optical switches, and tunable dispersion compensators will also require colorless operation over a wider DWDM spectrum.

Along with an increase in bandwidth capacity, the concept of an ‘agile bit’ is also envisioned through dynamic bandwidth allocation in next-generation all-optical networks. Carriers have already implemented all-optical bypass of express traffic by removing costly inline OEO transponders at switching nodes while the next generation of remotely reconfigurable multi-degree ROADM’s are currently under development for interconnecting rings and mesh architectures. Since the cost of edge add-drop transponders, regenerators and wavelength converters dominate the overall network cost, the switching node needs to provide the highest degree of add-drop access agility. This means directionless, colorless, and contentionless access of each transponder to the network for any-to-any dynamic reconfiguration. Hence, the key enabling technologies for realizing the concept of the agile bit are fully efficient multi-degree ROADM’s together with fully tunable tranponders. An accompanying technology that will be of great value for extending the reach of high-speed DWDM signals in optical networks is the all-optical multi-wavelength regenerator. Furthermore, all-optical edge grooming techniques such as optical packet and burst switching are also expected to increase the agility of future high capacity networks.