Patent ID: 8477939

Claim:
An apparatus for receiving a quantum cryptographic key, comprising: a polarization-insensitive optical phase modulator for receiving optical signal photons, and modulating and outputting a phase of the optical signal photons without being affected by a polarization state of the optical signal photons; an asymmetric Mach-Zehnder interferometer for causing interference in and outputting the optical signal photons received from the polarization-insensitive optical phase modulator; and photon detectors for detecting the optical signal photons received from the asymmetric Mach-Zehnder interferometer, wherein the polarization-insensitive optical phase modulator is formed by separating an optical phase modulator from the asymmetric Mach-Zehnder interferometer, and wherein the polarization-insensitive optical phase modulator comprises: an optical circulator for outputting the input optical signal photons in only one direction according to the position of input ports; a polarization beam splitter connected to the optical circulator, and reflecting the input optical signal photons along a first optical path or transmitting it along a second optical path according to the polarization state of the optical signal photons; an optical phase modulator disposed between the polarization beam splitter and a 90-degree polarization controller, and modulating and outputting the phase of the optical signal photons, and wherein the 90-degree polarization controller is disposed between the polarization beam splitter and the optical phase modulator, and rotates the polarization state of the input optical signal photons by 90 degrees.