AT&T Co is to use a 1.5 micron wavelength semiconductor laser in the the SL 420 Cable System optical under-sea transmission system, currently under construction in Taiwan: Nippon Telegraph & Telephone is already using 1.5 micron semiconductor lasers in its optical transmission networks but most current systems use 1.3 micron lasers with relays every 30 miles and the switch to 1.5 microns means that repeaters can be 120 miles apart.
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