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Fluoro-aluminate amplifier for second telecom window

Exploitable results

The majority of terrestrial optical fibre networks utilize the second transmission window of silica which lies at the wavelengths of 1280-1340 nm. World-wide, 55 million km of second window silica fibres have been installed. Currently 80% of UK telephone traffic is being carried by optical fibres operating in the second window. At these wavelengths no efficient and marketable optical amplifier is at present available, necessitating the use of electronic repeaters. Compared with optical amplifiers, electronic repeaters are more expensive, slower and less flexible in operation. Therefore in order to take full advantage of the potential capacities of optical fibre communications, it is necessary to upgrade the networks to all optical systems. The project concerns the realization of a neodymium-doped optical fibre amplifier for the second telecommunications window and the demonstration of a fully characterized industrial prototype for future network trials of these components. At the present state of the project, glass compositions have been carefully optimized with significantly reduced absorption compared with other commercially available glasses. Moreover new methods have been developed for host glass design allowing the blue-shifting of the emission spectrum and the achievement of a flat gain curve on the long wavelength side, thus making possible wavelength division multiplexing (WDM) applications. Gain curves at 1.3 um of three neodymium-doped fluoro-aluminate glasses were recently developed. Two highly important facts are immediately apparent. First, the peak of the gain curve in the new glasses is blue-shifted by about 5 nm compared with the old glass. Second, the effect of absorption is greatly reduced in the new glasses. Fibre drawing is a core activity of the project; after having improved the preform fabrication process a fibre with significantly reduced losses has been obtained. Further technology refinement will allow achievement of low loss single mode doped fibre suitable for an amplifier device.