Figure 1

On-chip SPDC photon-pair source. (a) Schematic illustration of an on-chip photon-pair source based on a χ⁽²⁾ nonlinearity connected to SSPD on another chip. Higher-energy pump photons (visible wavelengths) are coupled to a microring resonator and the generated lower-energy photon pairs (IR wavelengths) are randomly split on the detector chip for coincidence measurements with integrated SSPDs. A fiber-coupled silicon filter (labeled as off-chip filter) is used to reject the remaining pump light reflected back from the fiber-to-chip interface. (b) Effective refractive indices of modes in microring. The phase-match condition is satisfied with waveguide width around 1.10 μm. Lower-left inset: the cross-section of the AlN waveguide. Insets on the right: The electric field profiles at the cross-section of microring of two phase-matched modes. (c–e) Device images of AlN down-conversion photon-pair source. The white dashed box shows the enlarged region. (c) Optical image of an array of microring photon-pair sources with on-chip WDMs. (d) Enlarged image of a single microring resonator with both IR (top) and visible (bottom) bus waveguides. (e) SEM picture showing the coupling region of visible light bus waveguide (narrow) with microring resonator (wide).