Patent ID: 8149501

Claim:
A quantum entangled photon pair generating device comprising: a polarization maintaining loop path; a loop input unit for receiving excitation light from a first optical path, separating the excitation light into a first excitation light component and a second excitation light component, the first excitation light component and the second excitation light component having mutually orthogonal polarization, feeding the first excitation light component into the polarization maintaining loop path in a clockwise direction, and feeding the second excitation light component into the polarization maintaining loop path in a counterclockwise direction; a second-order nonlinear optical medium disposed in the polarization maintaining loop path and producing a second-order nonlinear optical effect, for generating first up-converted light from the first excitation light component by second harmonic generation, generating first down-converted light from the first up-converted light by spontaneous parametric down-conversion, generating second up-converted light from the second excitation light component by second harmonic generation, and generating second down-converted light from the second up-converted light by spontaneous parametric down-conversion, the first up-converted light and the first down-converted light propagating on the polarization maintaining loop path in the clockwise direction, the second up-converted light and the second down-converted light propagating on the polarization maintaining loop path in the counterclockwise direction; a loop output unit for receiving the first down-converted light and the second down-converted light from the polarization maintaining loop path, combining the first down-converted light and the second down-converted light to obtain combined light, and outputting the combined light on a second optical path; and a polarization manipulation unit for manipulating a polarization direction of at least one of the first excitation light component, the second excitation light component, the first down-converted light, and the second down-converted light, thereby causing the loop output unit to output the combined light as polarization entangled light.