Free-space daylight single-photon communications over 1.6 km

Summary form only given. The QKD transmitter, Alice, consists of three diode lasers (a timing laser and two data lasers: one data laser transmits vertical polarized photons, while the other transmits 45 degree polarized photons, two matching interference filters (IF), two optical attenuators, two linear polarizers, two non-polarizing beamsplitters, a 27/spl times/ beam expander, and a single-photon detector (SPD). The two data-laser (dimpulse) wavelengths are temperature controlled and constrained by the IF to 773/spl plusmn/0.5 nm, while the timing-laser (bright-pulse) transmitted wavelength is temperature controlled to /spl sim/768 nm. The data-lasers are configured to emit dim-light pulses of /spl sim/1 ns duration, and the SPD measures the average photon number per transmitted dim-pulse. This system uses the B92 QKD protocol, but could be easily adapted to the BB84 QKD protocol. The transmitter incorporates no active polarization switching.