Waveguide Integrated Superconducting Single Photon Detectors

Nanophotonic circuits employ waveguiding devices to route light across quasi-planar integrated optical chips in analogy to electrical wires in integrated electrical circuits. Using materials with high refractive index allows for confining light into sub-wavelength dimensions as efficient optical wires. Interaction with the environment is possible through near-field coupling to the evanescent tail of propagating optical modes, given that the measurable system is close to the waveguide surface. The interaction length can then be conveniently tailored by simply choosing a sufficiently long waveguide. This approach is particularly interesting for designing highly sensitive detectors which are able to register individual photons. Because nanophotonic circuits are well-suited for the study of single photon effects on chip, such detectors constitute a fundamental building block for emerging quantum photonic technologies. Here I introduce the concept of waveguide integrated single photon detectors, with a focus on superconducting nanowire single photon counters. The chapter covers the basics of single photon threshold detection, as well as advanced designs for multi-photon and coherent detection. The co-integration with nanophotonic circuits to realize hybrid systems enables advanced on-chip platforms for emerging applications in integrated quantum photonics.