A compact source of polarization-entangled photons includes a laser source, producing a laser beam, a pair of nonlinear crystals, in optical contact with each other, with one of the pair of nonlinear crystals having an input face, with the laser beam incident on the input face, and another of the pair of nonlinear crystals rotated 90°, along an axis perpendicular to the input face, with respect to each other and a fiber coupling point, configured to receive a pair of single-mode fibers. Pairs of polarization-entangled photons are produced through spontaneous parametric down conversion of the laser beam and provided to the fiber coupling point.