Patent ID: 7266304

Claim:
An optical transmission system for transmitting a binary code, comprising: a sender; a receiver; and a transmission line disposed between said sender and said receiver, the sender comprising: phase-shifter means for imposing a phase-shift on a first amplitude modulation signal, said imposed phase-shift being a function of the binary code to be transmitted; means for generating a light beam, amplitude modulated by the first phase-shifted amplitude modulation signal, which produces a central mode and first and second lateral modes; and means for attenuating an intensity of the modulated light beam so that there is at most only one photon total in the lateral modes; and the receiver comprising: phase-shifter means for imposing a phase-shift on a second modulation signal synchronized with the first amplitude modulation signal, said imposed phase-shift being randomly chosen from two values; means for modulating the received light signal by the second phase-shifted modulation signal; means for detecting a presence of a photon in the lateral modes after modulation of the received light signal; wherein the phase-shifter means of the sender impose a randomly chosen phase-shift to one of 0 and Π/2 for a first bit value or equal to one of Π and 3Π/2 for a second bit value of the binary code; wherein the phase-shifter means of the receiver impose a randomly chosen phase-shift equal to one of 0 and Π/2; and wherein the detector means of the receiver include means for detecting the presence of the photon in the first lateral mode and means for detecting the presence of the photon in the second lateral mode, the first bit value of the binary code being detected if the presence of the photon is detected in the first lateral mode and the second bit value being detected if the presence of the photon is detected in the second lateral mode.