Alcatel (Paris: CGEP.PA and NYSE: ALA), a provider of intelligent optical networking, achieved what the company claims to be a breakthrough in optical long-haul transmission by carrying 32 DWDM (dense wavelength division multiplexing) wavelengths at 40 Gbit/s over 2,400 km. This laboratory experiment was made possible by the use of distributed Raman amplification.
This technology represents an alternative solution to traditional repeatered (or erbium doped fiber amplifiers, EDFAs) long-haul transmission by ensuring high-quality transmission and enlarging the amplification bandwidth over long distances.
The record was set using Alcatel's 40 Gbit/s systems, advanced non-zero dispersion shifted TeraLight fiber and full Raman amplification. Alcatel mastered Raman amplification in the unrepeatered undersea cable domain and extended it to higher bit rates, such as 40 Gbit/s.
The distributed or in-line Raman amplification scheme has two potential advantages over traditional EDFA:
(1) Improved signal to noise ratio or SNR (ratio between the power of the signal and the noise generated by the transmission required to reach a certain level of signal quality): Raman amplification creates less noise than EDFAs, which is a key advantage for very high bit rates such as 40 Gbit/s. Thus, longer distances can be reached with the required quality of transmission.
(2) Increase of accessible amplification bandwidth: the Raman effect allows for a significantly larger amplification bandwidth than conventional EDFAs, by adding appropriate pumped wavelengths. This further increases system capacity.
The other key contributor to the success of this experiment is the fiber arrangement combining Alcatel's TeraLight optical fiber with a prototype "reverse fiber." This reverse fiber has a negative dispersion and a negative slope that exactly compensate the chromatic dispersion of the TeraLight fiber over a wide spectral range. Together, the fibers complement each other optically to optimize high-speed transmission over extremely long distances while avoiding the need for additional dispersion compensating devices. This optimal fiber combination ensures high transmission quality of 40 Gbit/s optical signals with a high 0.4bit/s/Hz spectral efficiency achieved over long distances.
Alcatel builds next generation networks, delivering integrated end-to-end voice and data networking solutions to established and new carriers, as well as enterprises and consumers. For more information, visit www.alcatel.com.