Abstract: The invention provides an apparatus and method for generating quantum-correlated and/or polarization-entangled photon pairs with unequal wavelengths. The photon pairs generated collinearly with respect to the pump light via a nonlinear process in a nonlinear optical medium are collected into a single mode fiber and split using a dichroic device. The wavelengths of photons constituting a pair are selected such that, first, their efficient propagation in the same single mode optical fiber, and second, their efficient splitting with high switching ratio, is possible. A detected rate ˜105-106 pairs/s and >98% quantum interference visibility of polarization entanglement is observed. This source, given its performance, robustness and minimum alignment requirements is ideal for quantum communication schemes, in particular for entanglement-based quantum cryptography.