The range of quantum cryptography systems using optical fibers is limi
ted to roughly 30 km because amplifiers cannot be used. A fully operat
ional system for quantum cryptography based on the transmission of sin
gle photons in free space under daylight conditions has been demonstra
ted. The feasibility of a global system for quantum cryptography based
on a network of ground stations and satellites is discussed. (C) 1996
Optical Society of America