Bell Labs charts new territory in optical-transmission rates
The tremendous growth in the areas of Internet access and high-speed data transfer is increasing the demands for fiber-optic capacity at a phenomenal rate, not to mention much sooner than most service providers expected. Deploying additional fiber into the network is not only an expensive solution but offers limited flexibility for future growth. Technological advances in optical equipment, however, are providing solutions aimed at squeezing more and more bandwidth from a single strand of fiber--and scientists continue to set new milestones for fiber-optic technology.
Two such milestones were recently announced by Bell Labs, the research and development arm of Lucent Technologies (Murray Hill, NJ). Scientists there demonstrated the transmission of information at the rate of 160 Gbits/sec over an optical fiber using a single wavelength. As if that wasn't enough to provide the extra capacity service providers seek, a second achievement was recorded by transmitting data over 1022 wavelengths through a single optical fiber with each wavelength carrying a distinct stream of information.
Combining the two accomplishments would produce 160 Gbits/sec across 1022 separate wavelengths--a total capacity of more than 163 Tbits/sec. While such a combination is impossible today, the confluence of such work appears to be where optical networks are headed in the future.
Bell Labs plans to expand the 160-Gbit/sec system by using dense wavelength-division multiplexing (DWDM). The experiment used the same semiconductor-based transmitter and demultiplexer found in commercial systems today. The 160-Gbit/sec transmission was done over 200 km of Lucent's TrueWave RS (reduced-slope) fiber. According to Lucent, today's high-speed single-wavelength commercial transmission systems are only beginning to approach 40 Gbits/sec.
In its second experiment, Bell Labs used a single ultra-high-speed laser to generate signals over the 1022 wavelengths, rather than using a separate laser for each wavelength, which is common practice in conventional multiwavelength systems. DWDM signals in such conventional systems currently use a minimum of 50-GHz frequency spacing. The 1022-channel system operates at a density of 10-GHz spacing, each channel occupying only 10 GHz of frequency bandwidth.
The 1022-channel transmitter carries information at the rate of 37 Mbits/sec for a total capacity of more than 37 Gbits/sec. Bell Labs scientists believe the system can be scaled up to OC-48 (2.4-Gbit/sec) rates, providing several terabits of capacity.
With more than 25,000 patents, over 2000 in optical technology alone, Bell Labs plans to continue breaking new ground in the optical-networking domain. The company says commercial products using the new transmitter and DWDM breakthroughs are most definitely in the foreseeable future of fiber-optic telecommunications.