AT&T Corp’s Bell Laboratories has announced an experimental 16-channel fibre optic transmission system that it says enables a single optical fibre to carry 40G-bits of information a second, representing 2.5m simultaneous phone calls. The system represents a vast improvement over the current maximum of 3.4G-bits per second, or 80,000 simultaneous calls using current lightwave and has set a new world record for lightwave transmission. It claims to have transmitted 2.5G-bits of information a second, error-free over each of 16 wavelengths through over 875 miles of optical fibre. The prototype wavelength division multiplexing system used Silica-based Erbium-doped fibre optical amplifiers from both Bell Labs and AT&T Microelectronics, spaced from 60 to 77 miles apart, to boost the signal. The outputs of eight distributed-feedback lasers and eight external-cavity lasers with 0.8-nanometer channel spacings were passively multiplexed, using directional couplers. The multiplexed channels passed through a polariser, a polarisation controller, and a Lithium-Niobate Mach-Zehnder modulator with a small-signal bandwidth of 4.5GHz. Bell Labs says the system is still very much in the research stage, and it currently has no timetable for the introduction of a commercial system but adds that it should have great potential, particularly for submarine cable systems and, theoretically, it could be used for optical networks with the capability of adding or dropping 2.5Gb channels along the transmission path. The findings of Bell Labs’ experimental work were presented at the fifth Optoelectronics Conference staged in Tokyo a week or two ago.
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