Patent ID: 8116636

Claim:
A quantum cryptography transmitter comprising: a wavelength converter converting an optical pulse signal having a first wavelength into an optical pulse signal having a second wavelength; an optical attenuator attenuating an intensity of the optical pulse signal having the second wavelength; an optical phase modulator modulating a phase of the optical pulse signal having the attenuated intensity; a Faraday mirror rotating the polarization of the optical pulse signal having the modulated phase and reflecting polarized light of the optical pulse signal having the modulated phase as a reflected optical pulse signal; an optical coupler splitting an intensity of the optical pulse signal having the first wavelength into split optical pulse signals; an optical detector detecting an optical pulse signal from one of the split optical pulse signals; a controller receiving an output of the optical detector and transmitting a synchronized phase modulation signal to the optical phase modulator; a first optical circulator positioned before the wavelength converter, passing one of the split optical pulse signals from the optical coupler to the wavelength converter, and feeding the optical pulse signal having the second wavelength reflected from the Faraday mirror back to the optical coupler; and a second optical circulator positioned after the wavelength converter, passing the optical pulse signal having the second wavelength to the optical attenuator, and feeding the optical pulse signal having the second wavelength reflected from the Faraday minor back to the first optical circulator.