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 [1] or quantum key distribution (QKD) [2]. Especially in the field of QKD a popular wavelength combination is 810 & 1550nm, generated by spontaneous parametric down conversion (SPDC) [3]. Previous schemes facilitated two nonlinear crystals behind each other [4], hence limiting the propagation length to a few millimeters. In this work we 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.