  The near-unity detection efficiency and excellent timing resolution of
superconducting nanowire single-photon detectors (SNSPDs), combined with their
other merits, have enabled many classical and quantum photonic applications.
However, the prevalent design based on meandering nanowires makes the detection
efficiency dependent on the polarization states of the incident photons; for
unpolarized light, the major merit of high detection efficiency would get
compromised, which could be detrimental for photon-starved applications. In
quantum-key distribution systems, the polarization dependence of detection
efficiency of the SNSPDs could also be a vulnerable security loophole. Here, we
create SNSPDs with an arced fractal topology that almost completely eliminates
this polarization dependence of the detection efficiency while preserving other
major merits of the SNSPDs. We experimentally demonstrated 91$\pm$2% system
detection efficiency at the wavelength of 1590 nm for photons in any
polarization state and 19 ps timing jitter. The detector was fiber-coupled and
fully packaged in a 0.1-W close-cycled Gifford-McMahon cryocooler. This
demonstration provides a novel, practical device structure of SNSPDs, allowing
for operation in the visible, near- and mid-infrared spectral ranges, and paves
the way for polarization-insensitive single-photon detection with high
detection efficiency and high timing resolution.
