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A new erbium-doped optical fiber boosts the efficiency of signal amplifiers for L band (1.58 microns) long distance, large capacity multiplexed optical communications systems.
Improved erbium-doped optical fiber for L band use
Erbium doped optical fiber sections for use in optical fiber boosters allow amplification of the optical signals directly using external light sources. They eliminate the need for converting the optical signals into electrical signals and then back into optical signals, thereby greatly simplifying the boosters, improving reliability, and reducing cost. Erbium doped optical fiber is currently used for the current generation of C band (1.55 microns) optical communications systems. Sumitomo Electric has long been a leader in the deveopment of erbium-doped optical fiber. In 1992 it unveiled a sol-gel technique to produce erbium doped quartz optical fibers for use in signal boosting modules for long distance optical communications systems. This process made possible a more than 30-fold increase in the quantity of erbium that can be incorporated into the fiber as compared with conventional doping techniques. This allowed shortening of the length of the fiber used in the boosters, thereby reduce booster size. 0.1 percent is the maximum concentration of erbium in the fiber produced using the conventional VAD method because of the difficulty with this process for obtaining uniformity of density. This small concentration of erbium has made it necessary to use fiber lengths of 500 meters for each booster. This technique made it possible to increase the erbium concentration of 5.6 percent. It uses tetraethoxysilane (TEOS), water, chloric acid, and erbium chloride. The result was a ten-fold increase in the level of optical amplification to be obtained. There has been much interest in supplementing the C band systems with L band systems. The L band fiber cables would use erbium doped fiber for signal amplification sections just as the C band cable does Amplifiers developed for the L band until now have had a low efficiency as compared with those for the C band. This has required the use of lengths of erbium-doped optical fiber about ten times the length of those for the C band. Sumitomo Electric has overcome this problem by improving the structure to attain a higher effective density of the erbium ions. This results in both a high amplification efficiency and low noise. it also makes possible a large reduction in space consumption of the coil section of the optical amplifier. Company officials expect that it will contribute to the development and installation of wave multiplexing communications systems which use the L band. They project that sales will reach three million dollars annually in about three years. Sumitomo Electric is Japan's largest manufacturer of quartz optical fiber as well as copper wire and cable. It is a core company in Japan's Sumitomo industrial group, which also includes NEC, Japan's largest producer of telecommunications equipment.
W. Ford, VCS Data Technologies, Copyright (C) 1999. All Rights Reserved. |
