Tunable ultrabright source of entangled photons

Summary form only given. We present a novel arrangement, employing two adjacent, relatively thin, nonlinear crystals, which are operated with type-I phase matching. The identically cut crystals (ideally from a single larger crystal) are oriented with their optic axes (OA) aligned in perpendicular planes, e.g., the first (second) crystal's OA and the pump beam define the vertical (horizontal) plane.