A CW pumped Raman preamplifier in a 45 km long fiber transmission system operating at 1.5micron and 1 Gbit/s.
11 July 2007
A signal propagating in an optical fiber can be amplified by the presence of a a shorter wavelength pump beam via the stimulated Raman mechanism. Such amplification provides the basis for an in-fiber preamplifier in a lightwave transmission system. This paper describes the characteristics of a 45 km long single mode fiber system where light from a distributed feedback laser, operating at 1.57micron and modulated a 1 Gbit/s, is amplified by a CW beam at 1.47micron from a color center laser. A linear gain of 5.3 dB at 150 microwatt pump power is measured. The increase in receiver sensitivity is measured from the Bit Error Rate. The sensitivity increase is within 1 dB of the measured gain and the excess penalty can be accounted for by pump intensity jitter and background scatter. Since these penalties can be eliminated we conclude that Raman amplification is feasible in transmission systems.