  We report on the generation of photon pairs in the 1550-nm band suitable for
long-distance fiber-optic quantum key distribution. The photon pairs were
generated in a periodically poled lithium niobate waveguide with a high
conversion-efficiency. Using a pulsed semiconductor laser with a pulse rate of
800 kHz and a maximum average pump power of 50 muW, we obtained a coincidence
rate of 600 s^-1. Our measurements are in agreement with a Poissonian
photon-pair distribution, as is expected from a comparison of the coherence
time of the pump and of the detected photons. An average of 0.9 photon pairs
per pulse was obtained.
