Alcatel (Paris: CGEP.PA, NYSE:ALA), a provider of intelligent optical networking, claims it has achieved a record in optical submarine transmission by transporting 1.6 terabits (Tbit/s) capacity over 321 kilometers (km) unrepeatered distance. This breakthrough was achieved using cascaded Raman amplification, which allows operators to reduce installation costs compared with current architectures for unrepeatered systems. With this demonstration, Alcatel also achieved a record sending 160 wavelengths over this unrepeatered distance. The previous record, held by Alcatel, reached 1.28Tbit/s over 250km, using 32 wavelengths.
Alcatel's use of cascaded Raman amplification utilizes only one high-power and two low-power sources, therefore improving the transmission quality while significantly reducing equipment costs. Raman pumps have been positioned in a cascaded configuration and arranged in the opposite direction of the signal. This ground-breaking method of installing the pumps is made possible using "second order pumping" -- in addition to the two pump sources at the standard wavelength of 100 nanometers (nm) below the signal, another pump at 90nm below the pump wavelengths was used. This configuration allows a high-power source to boost two low-power sources, pursuant to the first order pumping principle. The two low-power sources then amplify the transmission signals. This proves considerably less expensive than current systems, which require the use of two high-power pumps.
In this experiment, 160 wavelengths were transmitted over the unrepeatered distance of 321km, as a result of a reduction in channel spacing from 50 gigahertz (GHz) to 25GHz (or 0.2nm). These wavelengths were transmitted only on the C band where the attenuation is the lowest, paving the way for further developments to increase the bandwidth.
Finally, this achievement demonstrates Alcatel's ability to manage the combination of various types of fibers to optimize Raman gain and the signal-to-noise ratio (SNR). The SNR is the ratio, between the power of the signal and the noise generated by the transmission. In this experiment, the Pure Silica Core Fiber (PCSF) was combined with Enhanced PSCF (EPSCF) in order to enhance the quality of the transmitted signal.
Raman amplification, used by Alcatel for several years in submarine networks, relies on a natural phenomenon that occurs in all optical silica fiber. When power (pump wave) is sent down an optical fiber, the original optical signal is reinforced and subsequently, its higher power allows the signal to go further. This is due to the molecular vibrations (or phonons) in the glass material. This phenomenon is known as stimulated Raman scattering. Thus, in practical terms, Raman pumps are implemented into transmission systems to increase the length and/or the capacity of the link.
Alcatel provides both terrestrial and marine services for the installation and maintenance of global, seamless optical networks. For more information, visit www.alcatel.com.