Abstract: A combining unit for combining a first optical input and a second optical input, the first optical input comprising a first polarisation maintaining fibre “PMF” having a fast optical axis and a slow optical axis, the second optical input comprising a second PMF having a fast optical axis and a slow optical axis, the combining unit being configured to combine the first optical input with the second optical input in free space such that the fast and slow optical axis of the first PMF and the second PMF are rotated with respect to one another by a non-zero angle to produce a combined signal.

Abstract: A method of, and module for, converting position or momentum correlation of correlated photon pairs to a polarization entangled photon pair, and a source for polarization entangled photon pairs. The method comprises a conversion step of separating the correlated photon pairs into first and second groups based on their generated position at the crystal (position correlation) or their direction about the propagation axis (momentum correlation) and rotating a polarization of the first correlated photon pair group such that the polarization of the first correlated pair group is at 90 degrees relative to the polarization of the second correlated photon pair group; and a combining step of combining the first and second correlated photon pairs such that at least respective portions of respective spatial distributions of the first and second photon pair groups overlap with negligible wavelength dependent phase difference.

Abstract: A method of, and module for, converting position or momentum correlation of correlated photon pairs to a polarization entangled photon pair, and a source for polarization entangled photon pairs. The method comprises a conversion step of separating the correlated photon pairs into first and second groups based on their generated position at the crystal (position correlation) or their direction about the propagation axis (momentum correlation) and rotating a polarization of the first correlated photon pair group such that the polarization of the first correlated pair group is at 90 degrees relative to the polarization of the second correlated photon pair group; and a combining step of combining the first and second correlated photon pairs such that at least respective portions of respective spatial distributions of the first and second photon pair groups overlap with negligible wavelength dependent phase difference.