The Path to Increasing the Coincidence Efficiency of Integrated Photon Sources

摘要

Silicon ring resonators are used as photon pair sources by taking advantageof silicon's large third order nonlinearity with a process known as spontaneousfour wave mixing. These sources are capable of producing pairs ofindistinguishable photons but typically suffer from an effective $50\%$ loss.By slightly decoupling the input waveguide from the ring, the drop portcoincidence ratio can be significantly increased with the trade-off being thatthe pump is less efficiently coupled into the ring. Ring resonators with thisdesign have been demonstrated having coincidence ratios of $\sim 96\%$ butrequiring a factor of $\sim 10$ increase in the pump power. Through themodification of the coupling design that relies on additional spectraldependence, it is possible to achieve similar coincidence ratios without theincreased pumping requirement. This can be achieved by coupling the inputwaveguide to the ring multiple times, thus creating a Mach-Zehnderinterferometer. This coupler design can be used on both sides of the ringresonator so that resonances supported by one of the couplers are suppressed bythe other. This is the ideal configuration for a photon-pair source as it canonly support the pump photons at the input side while only allowing thegenerated photons to leave through the output side. Recently, this device hasbeen realized with preliminary results exhibiting the desired spectraldependence and with a coincidence ratio as high as $\sim 97\%$ while allowingthe pump to be nearly critically coupled to the ring. The demonstrated nearunity coincidence ratio infers a near maximal heralding efficiency from thefabricated device. This device has the potential to greatly improve thescalability and performance of quantum computing and communication systems.