Integrated spatially multiplexed single-photon sources in a bidirectionally pumped spiral waveguide

Silicon-based integrated spiral waveguides are extensively used as on-chip single-photon sources. However, inherent uncertainties and limitations in single-photon fidelity pose significant theoretical performance bottlenecks. These challenges often necessitate the multiplexing of multiple sources. In this paper, we propose a novel scheme for spatial multiplexing using bidirectional spirals. By pumping a spiral waveguide bidirectionally, photon pairs are generated in both clockwise (cw) and counterclockwise (ccw) directions, each producing signal-idler photon pairs in a two-mode squeezed state. Consequently, a single spiral waveguide can function as two spatially multiplexed sources. Using CMOS fabrication technology, we constructed a bidirectional spiral waveguide structure. We measured the coincidence count rates, heralded second-order correlation function, and coincidence to accidental ratio (CAR) as functions of pump power, both before and after multiplexing. Our experimental results demonstrated a 1.67-fold increase in performance post-multiplexing. This finding underscores the potential of bidirectional spirals as spatially multiplexed sources, paving the way for the largescale integration of future photonic quantum chips.