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Chinese Physics B

Superconducting nanowire single photon detector with efficiency over 90% at 2 μm wavelength

Zhen Wan, Jia Huang, Guangzhao Xu, Yu Ding, Xiaoyu Liu, Yiming Pan, Hongxin Xu, Hao Li, Lixing You

Published Nov 5, 2025• 0 citations
Publisher

Abstract

Abstract We here report a high system detection efficiency (SDE) superconducting single-photon detector (SSPD) at 2 μm wavelength. The device integrates a SiO 2 /Ta 2 O 5 distributed Bragg reflector (DBR) and a sandwich-structured double-layer NbN nanowire to enhance the optical absorption efficiency. A cold development technique is implemented to optimize the superconducting nanowires with sub-40-nm linewidths, thus enhancing the intrinsic detection efficiency (IDE). The fabricated SSPD shows an SDE exceeding 90% at 2 μm wavelength. Moreover, the detector allows an operational working temperature of 2.2 K provided by a compact GM cryo-cooler. This detector delivers excellent performance at the 2 μm wavelength, and its optimized structural design implies promising potential for extending detection toward longer infrared bands. It thus holds value for advancing high-sensitivity quantum technologies, mid-infrared optical communications, and dark matter detection research.

DOI
10.1088/1674-1056/ae1b79

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Abstract We here report a high system detection efficiency (SDE) superconducting single-photon detector (SSPD) at 2 μm wavelength. The device integrates a SiO 2 /Ta 2 O 5 distributed Bragg reflector (DBR) and a sandwich-structured double-layer NbN nanowire to enhance the optical absorption efficiency. A cold development technique is implemented to optimize the superconducting nanowires with sub-40-nm linewidths, thus enhancing the intrinsic detection efficiency (IDE). The fabricated SSPD shows an SDE exceeding 90% at 2 μm wavelength. Moreover, the detector allows an operational working temperature of 2.2 K provided by a compact GM cryo-cooler. This detector delivers excellent performance at the 2 μm wavelength, and its optimized structural design implies promising potential for extending detection toward longer infrared bands. It thus holds value for advancing high-sensitivity quantum technologies, mid-infrared optical communications, and dark matter detection research.
Single photon detection advanced rapidly in the last decade. The superconducting nanowire single-photon detector (SNSPD) is an emerging technology, which offers low dark count rates, broadband sensitivity from visible to mid-infrared wavelengths and very high quantum efficiency. All these features are appealing for future emerging applications in remote gas sensing, quantum key distribution and quantum information processing. By enclosing the detector in an optical cavity, tuned to the operating wavelength, the total system detection of the SNSPD is improved. Based on the cavity design, the detector absorption is boosted at the desired experimental wavelength. Devices have been fabricated and tested, in this thesis, with enhanced detection efficiency at near-infrared, infrared and mid-infrared wavelengths. NbTiN detectors fabricated on Ta2O5 / SiO2 distributed Bragg reflectors (DBR) for front-side coupling exhibit a system detection efficiency of ≈ 90% at λ = 940 nm for the best device measured. SNSPDs were also fabricated in NbTiN on metallic mirrors for back-side coupling for 1550 and 2333 nm experimental wavelengths. The first design exhibited a system detection efficiency of ≈ 84.5%, at λ = 1550 nm for the best device measured. The second exhibited low system detection efficiency since the device suffered from unexpectedly high dark count rate mainly due to blackbody radiation at 2.2 K. However, it was possible to measure the timing jitter of this device at 350 mK indicating a FWHM of 84 ps. Another technique to improve the total system detection efficiency of the SNSPD, is by fabricating a hairpin-shaped nanowire atop a single mode waveguide. In this design, photons travel through the waveguide and via evanescent coupling are absorbed in the nanowire. These SNSPD devices have been designed to thread along single mode Si ridge waveguides using a hairpin-shaped nanowire structure, which offers enhanced coupling and absorption efficiency via evanescent coupling. These ultra-thin superconducting MoSi detectors are precisely patterned on top of a single mode Si waveguide (600 nm) with alignment error less than 40 nm. Low temperature electrical and nano-optical characterization was carried out using a two-stage pulse tube (PT) coldhead, using an additional 4He / 3He sorption pump, low vibration characterization of SNSPD devices at 350 mK was carried out. Characterised devices exhibit low dark count rate <5 counts per second and timing jitter of ≈ 83 ps full width half maximum (FWHM) at wavelength (λ) = 1550 nm and at critical current ≈ 30 µA.
We develop single-photon detectors comprising single-mode fiber-coupled superconducting nanowires, with high system detection efficiencies at a wavelength of 940 nm. The detector comprises a 6.5-nm-thick, 110-nm-wide NbN nanowire meander fabricated onto a Si substrate with a distributed Bragg reflector for enhancing the optical absorptance. We demonstrate that, via the design of a low filling factor (1/3) and active area (Φ = 10 μm), the system reaches a detection efficiency of ∼60% with a dark count rate of 10 Hz, a recovery time <12 ns, and a timing jitter of ∼50 ps.
Superconducting single photons detectors (SSPDs) have emerged in recent years as a promising alternative for fast and sensitive infrared detectors working in the photon counting mode. In particular, those detectors combine very low dark count rates (below 1 Hz), high speed (above 1 GHz), photon number resolution and reasonable quantum efficiency (10% at telecom wavelengths). They already found applications in quantum cryptography systems and integrated circuit failure analysis, but could also be used as ultimate sensors in matrix configurations. We show here the optimization of SSPD fabrication and their optical metrology at CEA. SSPD are fabricated by patterning a 80 nm wide nanowire in a very thin (4 nm) NbN film on sapphire, forming a pixel of several microns size. A cryogenic all-fibered optoelectronic system has been developed and allows precise metrology of the optical performances of SSPD. When biasing near the critical current of the nanowire, we demonstrate a detection quantum efficiency of 8% at 1.55 µm, which is also found to be strongly polarization dependent. This quantum efficiency being limited by optical absorption, we propose a prism coupling based absorption enhancing structure that allows reaching 100% quantum efficiency.
We demonstrate superconducting nanowire single photon detector (SNSPD) for the wavelength at around 2 μm. The linewidth of the NbN nanowire is squeezed to 56 nm to increase the intrinsic response efficiencies at longer wavelengths such as 2 μm. Serially connecting avalanche architecture is applied to increase the signal-to-noise ratio (SNR) of the response signal. Further, the optical cavity is optimized to improve the absorption of the device. A silica single-mode fiber is adopted to introduce photons to the SNSPD at a temperature of 2.25 K using a Gifford-McMahon cryocooler. The SNSPD exhibits detection efficiencies of 58%, 67%, and 63% at wavelengths of 1550, 1700, and 2000 nm, respectively, with dark count rate of ~12 kcps, which is reduced to 2 cps when the attached fiber pigtail is all placed inside the 40-K cryostat. The detection efficiency at 2000 nm is 2.5 times greater than that of the best previously developed detector with an efficiency of 25%. Our SNSPD is promising for practical applications in molecular science and earth meteorology.
Abstract This paper presents the development of a superconducting nanowire single-photon detector (SNSPD) integrated into a distributed Bragg reflector (DBR) with a design center wavelength of 830 nm and a bandwidth of 200 nm. This SNSPD is made of a superconducting niobium nitride (NbN) thin film that is produced using plasma-enhanced atomic layer deposition. The DBR is made of 15 alternating layers of silicon nitride and silicon oxide that are produced through plasma-enhanced chemical vapor deposition. The reflection efficiency of the mirror is 90% at a wavelength of 830 nm. For sufficient optical coupling, an optical micro-connector optimized for multimode or single-mode optical fibers with a diameter of 128 μm was formed using two-photon polymerization techniques. The niobium nitride film was deposited onto the DBR surface in-situ in two separate reactors connected by a vacuum transfer. The in-situ technique of deposition of a superconducting niobium nitride film and a DBR has allowed achieving a system detection efficiency of 90% at a wavelength of 830 nm and a dark count rate of 10 s−1 at a temperature of 2.5 K. Additionally, the detector jitter was 50 ps.
Nanowire superconducting single-photon detectors (SSPDs) consist of a superconducting wire of nanoscale cross-section [1], typically 4×100 nm2. A current close to the device critical current renders the nanowire sensitive to single photons. SSPDs are known for their high efficiency, low jitter, low dark count rate and fast reset time. An important challenge for future application of SSPDs is to extend the useful wavelength range towards the infrared without comprising detector speed or dark count rate. To this end, we explore optical designs with wider nanowires that utilize efficient detection of single photons at the edge of the nanowire. Silicon nanowires on top of a NbN nanowire increase both the calculated total absorption and the internal detection efficiency significantly compared to a standard meandering wire geometry.