Compact sagnac-type source for entangled photon pairs

Sources of entangled photon pairs serve as basis for many quantum information experiments, such as quantum computing or quantum key distribution (QKD). Especially in the field of QKD a popular wavelength combination is 810 and 1550nm, generated by spontaneous parametric down conversion (SPDC). Previous schemes facilitated two nonlinear crystals behind each other, hence limiting the propagation length to a few millimeters. In this work, the authors present a novel implementation of a Sagnac-type photon source designed for operation at three wavelengths, obviating the need for any active stabilization loops. Due to the compact design and excellent stability properties it is a versatile tool for quantum experiments.