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Enhancing spectral sensitivity and scalability of superconducting nanowire photon detectors: mid-infrared characterization and near-infrared integration

Adan Azem, D. Morozov, Daniel Kuznesof, Ciro Bruscino, Becky Lin, Shangxuan Yu, Robert H. Hadfield, Lukas Chrostowski, Jeff F. Young

Published May 30, 2025• 0 citations
Publisher

Abstract

We present enhancements in the spectral sensitivity and scalability of superconducting nanowire single-photon detectors based on U-shaped NbTiN nanowires. Designed on a silicon-on-insulator photonic platform, our detectors exhibit near-unity internal detection efficiency under flood illumination across wavelengths from 1550nm to 3502nm. Additionally, we demonstrate arrays of waveguide-integrated superconducting nanowire single-photon detectors optimized for operation at 1550nm. Cryogenic light coupling to the arrays is achieved through a photonic wire bonding technique, enabling low-loss coupling and high-density integration, thereby facilitating the scaling of detector counts per cryostat for near-infrared applications.

DOI
10.1117/12.3054783

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We present enhancements in the spectral sensitivity and scalability of superconducting nanowire single-photon detectors based on U-shaped NbTiN nanowires. Designed on a silicon-on-insulator photonic platform, our detectors exhibit near-unity internal detection efficiency under flood illumination across wavelengths from 1550nm to 3502nm. Additionally, we demonstrate arrays of waveguide-integrated superconducting nanowire single-photon detectors optimized for operation at 1550nm. Cryogenic light coupling to the arrays is achieved through a photonic wire bonding technique, enabling low-loss coupling and high-density integration, thereby facilitating the scaling of detector counts per cryostat for near-infrared applications.
Superconducting nanowire single-photon detectors are widely used for detecting individual photons across various wavelengths from ultraviolet to near-infrared range. Recently, there has been increasing interest in enhancing their sensitivity to single photons in the mid-infrared spectrum, driven by applications in quantum communication, spectroscopy, and astrophysics. Here, we present our efforts to expand the spectral detection capabilities of U-shaped NbTiN-based superconducting nanowire single-photon detectors, fabricated in a 2-wire configuration on a silicon-on-insulator substrate, into the mid-infrared range. We demonstrate saturated internal detection efficiency extending up to a wavelength of 3.5 μm for a 5 nm thick and 50 nm wide NbTiN nanowire with a dark count rate less than 10 counts per second at 0.9 K and a rapid recovery time of 4.3 ns. The detectors are engineered for integration on waveguides in a silicon-on-insulator platform for compact, multi-channel device applications.
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.
Mid-infrared (MIR) single-photon detection is emerging as an important technology for various applications. Superconducting nanowire single photon detectors (SNSPDs) fabricated with superconducting films with energy gaps of a few meV are natural broadband single-photon detectors. Recently, extending SNSPDs’ operation wavelengths into the MIR region is highly attractive. γ-Nb4N3 has a reduced N content and lower energy gap than the commonly used δ-NbN, making SNSPDs based on γ-Nb4N3 film more sensitive to low energy photons. We report on a Nb4N3-SNSPD based on 62-nm wide nanowire, with an optical absorption enhancement design and an optimized device package for efficient ZBLAN fiber coupling and dark count filtering. The developed device has a unity intrinsic detection efficiency (IDE) in the 1.5–4 µm wavelength region, and the device detection efficiency at 2.95 µm was measured to be 32.5%, with an uncertainty of 12.7%. Furthermore, we reduced the device geometry, and measured 3–10 µm photon response of a device based on 5-nm film and 42-nm nanowire, with an IDE of 95%, 81%, 40%, and 6% for 4.8, 6, 8, and 10 µm, respectively.
Broadband photon detectors are a key enabling technology for various applications such as spectrometers, light detection and ranging. In this work, we report on an ultra-broadband single-photon detector based on a microfiber (MF)-coupled superconducting nanowires structure operating in the spectral range from visible to near-infrared light. The MF-coupled superconducting nanowire single-photon detector (SNSPD) is formed by placing an MF on top of superconducting niobium nitride (NbN) nanowires, allowing ultra-broadband photon detection due to their nearly lossless transmission/absorption and nearly unity internal efficiency for ultra-broad waveband. The simulation results indicate that with optimal device structure, the optical absorption with efficiency > 90% can be realized over a wavelength range of 350 nm to 2150 nm. The fabricated MF-coupled SNSPD shows unparalleled broadband system detection efficiencies (SDEs) of more than 50% from 630 nm to 1500 nm. The SDEs reach 66% at 785 nm and 45% at 1550 nm. These results pave the way for ultra-broadband weak light detection with quantum-limit sensitivity.
Single photon technology is enabling for quantum communication and processing. Combining single photon sources, routing circuitry and highly efficient detectors in a high yield, low-loss and scalable fashion represent today a major challenge. Nanophotonic devices allow for the realization of on-chip small footprint architectures for generating, manipulating and detecting single photons. Waveguide-integrated superconducting nanowire single photon detectors are today state-of-the art devices capable of detecting single photons propagating in an integrated photonic circuit with high efficiency, speed and low timing uncertainty. Their excellent metrics in the near-infrared allows to directly interface on-chip devices with existing C-Band communication technology systems. To move towards high communication speed, efficient detectors able to sustain Gcps count rate are desirable. Here we present the design process and the experimental characterization of a new generation of fast detectors, consisting of µm-long NbN superconducting nanowires embedded in a SOI two-dimensional photonic crystal cavity. Almost 70% efficiency at telecommunication wavelengths has been achieved with negligible dark counts and sub-ns recovery time, which could enable Gcps count rates.