Patent ID: 8165298

Claim:
A quantum cryptography communication apparatus adapted to perform a communication process based on quantum cryptography, the quantum cryptography communication apparatus comprising: a communication terminal on a receiving side; a communication terminal on a sending side; and a communication channel connecting the communication terminal on the receiving side and the communication terminal on the sending side, the communication terminal on the receiving side including: (a) a light source adapted to generate a light pulse, (b) a light beam splitter adapted to split the light pulse into a signal light and a reference light, (c) a first optical path, (d) a second optical path, (e) a delay hardware unit disposed in the first optical path or the second optical path, (f) a first light transmitting hardware unit adapted to transmit the signal light and the reference light over the communication channel, the signal light having been output from the light beam splitter and having been passed via the first path, the reference light having been output from the light beam splitter and having been passed via the second optical path, (g) a light hardware separator adapted to: (i) receive the signal light and the reference light transmitted from the communication terminal on the sending side via the communication channel; and (ii) separate the received signal light and reference light from each other, (h) a first phase hardware modulator adapted to perform random phase modulation, on a pulse-by-pulse basis, on the reference light output from the light hardware separator and passing via the first optical path or the signal light output from the light hardware separator and passing via the second optical path, and (i) a communication information acquisition hardware unit adapted to acquire communication information based on: (i) the reference light output from the light hardware separator and passed via the first optical path; and (ii) the signal light output from the light hardware separator and passed via the second optical path, the communication terminal on the sending side including: (a) a second light transmitting hardware unit adapted to transmit the signal light and the reference light, received from the communication terminal on the receiving side via the communication channel, over the communication channel via a particular optical path, (b) a single acousto-optic device including: (i) a frequency hardware shifter adapted to shift frequencies of the signal light and the reference light passing via the particular optical path, and (ii) a light hardware attenuator adapted to attenuate an intensity level of the signal light passing via the particular optical path, and (c) a second phase hardware modulator adapted to perform phase modulation corresponding to the communication information, on a pulse-by-pulse basis, on the signal light passing via the particular optical path.