The transverse momentum correlation of photon pairs generated by noncollinear spontaneous parametric down-conversion with type-I phase matching is transformed into polarization entanglement. A robust wavefront-splitting interferometer scheme is used, due to which the phase of the entangled state does not require active stabilization. Frequency-degenerate signal and idler photons are separated and coupled into single-mode optical fibers. The concept is demonstrated in a compact and modular setup. A straightforward alignment process for producing any of the Bell states is presented. The entangled source has an output photon flux of $8.33\pm 1.27$ kcps/mW normalized to pump power (150 mW), and $17\pm 3\%$ heralding ratio. The measured state fidelity with respect to the negative anticorrelated Bell state is $0.951\pm 0.004$.

• Received 23 May 2022
• Accepted 25 November 2022

DOI:https://doi.org/10.1103/PhysRevA.106.063710