  Photon number resolving (PNR) capability is very important in many optical
applications, including quantum information processing, fluorescence detection,
and few-photon-level ranging and imaging. Superconducting nanowire
single-photon detectors (SNSPDs) with a multipixel interleaved architecture
give the array an excellent spatial PNR capability. However, the
signal-to-noise ratio (SNR) of the photon number resolution (SNRPNR) of the
array will be degraded with increasing the element number due to the electronic
noise in the readout circuit, which limits the PNR resolution as well as the
maximum PNR number. In this study, a 16-element interleaved SNSPD array was
fabricated, and the PNR capability of the array was investigated and analyzed.
By introducing a level comparator circuit (LCC), the SNRPNR of the detector
array was improved over a factor of four. In addition, we performed a
statistical analysis of the photon number on this SNSPD array with LCC, showing
that the LCC method effectively enhances the PNR resolution. Besides, the
system timing jitter of the detector was reduced from 90 ps to 72 ps due to the
improved electrical SNR.
