Silicon-Based Optical-Pump Rejection Filter for Quantum Circuits

Silicon photonics appears to be the most promising technology to address the quantum photonics developments, because it is suitable to implement all stages of a quantum photonic system, such as sources, manipulation devices and receivers. In this paper, we analyse and design a pump filter with large extinction ratio (ER), narrow bandwidth (BW) and small insertion loss (IL), to achieve an efficient single-photon detection, as required by photon-pair systems. Most promising on-chip silicon-based solutions, mainly based on ring resonators and Mach-Zehnder interferometers (MZIs) are reviewed. The main drawbacks of these technologies have been critically investigated, with reference to the ER-BW conflict. To overcome this bottleneck, an additional research effort needs to investigate new high-performance devices in terms of ER, IL and BW combined with small footprint.