Photon-pair source at 2090 nm for long-distance quantum communication

We report the generation of entangled photon pairs at 2090 nm, as a basis for free-space quantum communication in an atmospheric window with low solar background. The source is based on spontaneous parametric down-conversion in periodically poled lithium niobate crystal delivering high coincidence-to-accidental ratio. We demonstrate the two-photon Hong-Ou-Mandel quantum interference and polarization entanglement.