Patent ID: 8265280

Claim:
Apparatus for producing entangled photon pairs, said apparatus comprising: a source of a plurality of photons; the source connected to a polarization maintaining optical circulator followed by a polarization differential group delay element, wherein one of polarization maintaining connections between the source and the delay element being oriented at a 45 degree angle in the way that the source photons are split evenly into photons of both polarization axes of the delay element, the photons in each of the two polarization axes being delayed relative to each other before being coupled into a nonlinear optical fiber generating signal and idler photons via a four-wave mixing process; an output of the nonlinear optical fiber being coupled to a non-reciprocal reflector and upon retro-reflection from the reflector back through the nonlinear fiber and the polarization differential group delay element the signal and idler photons in each of the two polarization axes are recombined into an output light with unpolarized entangled photon state that is collected by the polarization maintaining circulator, further comprising: an external laser source emitting external laser photons at the signal and idler wavelengths being injected into the polarization differential group delay element for the purposes of creating a polarized alignment signal to be used to align polarization apparatuses to a specified axis with respect to both polarized components of the output light.