Lee Oesterling

To support the development of quantum cryptography technologies that utilize entangled photon pairs for operation, our research has focused on the development of sources and components that efficiently generate entangled photon pairs and couple them into optical fibers for routing. To generate entangled photon pairs, we have integrated optical waveguides into periodically poled lithium niobate (PPLN) chips and utilize spontaneous parametric down conversion. Currently, the coupling loss from the PPLN waveguide to the optical fiber is the dominant loss mechanism. To increase the probability that the entangled photon pairs are received in cryptographic systems, we have been exploring various optical designs to increase the coupling efficiency between waveguide and fiber. Similar approaches have been utilized in standard telecommunications applications to reduce optical coupling losses, but the impact of these configurations for entangled photon pair sources has not been studied previously. In order to benchmark coupling efficiency of entangled photon pairs, we constructed an experiment to measure both single photon counts and photon pair coincidence counts. The results of the entangled photon pair coincidence measurements as a function of optical coupling design will be presented, and the impact of these waveguide geometries on entanglement will be discussed.