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Laser & Photonics Review

Speckle‐Insensitive Fractal Superconducting Nanowire Single‐Photon Detector Coupled with Multimode Optical Fiber (Laser Photonics Rev. 18(10)/2024)

Kai Zou, Yun Meng, Zifan Hao, Song Li, Adrian Iovan, Thomas Descamps, Val Zwiller, Xiaolong Hu

Published Oct 1, 2024• 0 citations
Publisher

Abstract

Efficiently Detecting Single Photons from Multiple Spatial Modes Speckles may reduce detection efficiency and induce modal noise in photodetection. Xiaolong Hu and co-workers (article number 2400342) show that a superconducting nanowire single-photon detector (SNSPD) patterned into the fractal geometry can be insensitive to the speckles and they demonstrate an efficient fractal SNSPD coupled with multimode fiber.

DOI
10.1002/lpor.202470062

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Efficiently Detecting Single Photons from Multiple Spatial Modes Speckles may reduce detection efficiency and induce modal noise in photodetection. Xiaolong Hu and co-workers (article number 2400342) show that a superconducting nanowire single-photon detector (SNSPD) patterned into the fractal geometry can be insensitive to the speckles and they demonstrate an efficient fractal SNSPD coupled with multimode fiber.
Abstract Speckles are ubiquitous phenomena associated with multi‐spatial‐mode optics, which may reduce detection efficiency and induce modal noise if the photoresponse of the detector is polarization‐dependent. Thus far, they limit the performance of superconducting nanowire single‐photon detectors (SNSPDs) coupled with multimode optical fibers (MMF). To solve this problem, here, it is shown that SNSPDs patterned into the fractal geometry is insensitive to speckles and generates minimal modal noise that would otherwise be induced by the polarization‐dependent local device efficiency of the meander and spiral SNSPDs. Using this advantageous property of the fractal SNSPDs, system detection efficiency at the wavelength of 1530 nm and 42‐ps timing jitter is demonstrated when we couple a fractal SNSPD with 50‐micrometer‐core, step‐index MMF. This work not only demonstrates a scheme to achieving high system detection efficiency for MMF‐coupled SNSPDs that can be used in many applications, but also provides insight on how engineered nanostructures of photodetectors can reduce modal noise when detecting light from multiple spatial modes.
We demonstrate superconducting nanowire single-photon detectors (SNSPDs) based on a fractal design of the nanowires to reduce the polarization sensitivity of detection efficiency. We patterned niobium titanium nitride thin films into Peano curves with a linewidth of 100 nm and integrated the nanowires with optical microcavities to enhance their optical absorption. At a base temperature of 2.6 K, the fractal SNSPD exhibited a polarization-maximum device efficiency of 67% and a polarization-minimum device efficiency of 61% at a wavelength of 1550 nm. Therefore, the polarization sensitivity, defined as their ratio, was 1.1, lower than the polarization sensitivity of the SNSPDs in the meander design. The reduced polarization sensitivity of the detector could be maintained for higher-order spatial modes in multimode optical fibers and could tolerate misalignment between the optical mode and the detector. This fractal design is applicable to both amorphous and polycrystalline materials that are commonly used for making SNSPDs.
Single-photon detectors with high detection rates are the foundation for the high-speed remote laser communication. Although a total detection rate of gigahertz has been achieved with multiple superconducting nanowires, the coupled single-mode fibers are incompatible with most large-aperture optical telescopes, and the uneven response distribution between nanowires also limits the system performance in practice. Here, we report a multimode fiber coupled superconducting nanowire single-photon detector (SNSPD) with a gigahertz detection rate through 16 intertwined niobium nitride nanowires operated at 2.4 K. The SNSPD is coupled with a 62.5 μm multimode fiber through beam compression. Overcoming the interference of speckles in multimode fibers, all nanowires perform highly uniform with narrow distributions of detection efficiencies (5.48% ± 0.136%), achieving a total detection efficiency of 87.6% and a total system detection efficiency of 52.3%, a maximum detection rate of 1.3 Gcps when the efficiency drops by 3 dB, and a highest detection rate of 3.1 Gcps before latching occurs. The significance of the uniform performance of pixels in terms of system speed is verified by modeling the combined detection rate vs the detection efficiency distribution, which is crucial in high-speed laser communication.