Optimal tapers for efficient entangled photon pair generation in silica tapered optical fibers

Sources of entangled photon pairs are key components for quantum cryptography which is a perfectly secure way of communication based on the laws of physics. Benefiting from a versatile, fully fibered, and inexpensive source is a real challenge in this area. We present a design of an entangled photon pair source based on spontaneous parametric down-conversion using a silica nanofiber. This nanofiber is connected to the original standard telecom fiber by two tapers. The control of light propagation in these tapers until the nanofiber is essential for adiabatic power transfer to the nanofiber to maximize photon pair generation rate. The modest efficiency of this process is compensated by the very low insertion losses of the nanofiber in quantum networks using its two adiabatic tapers. An optimal design of these adiabatic tapers is investigated