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.
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.
Superconducting nanowire single photon detectors with an optical resonant cavity structure are fabricated directly on the single crystal substrate. In order to enhance the photons absorption of incident light and improve system detection efficiency (SDE) efficiently, the structure of SNSPD was designed and optimized using the finite-difference time-domain analysis for different kinds of substrates. The NbN-SNSPDs fabricated on different substrates are measured and compared. The SDE of NbN-SNSPD on MgO substrate reaches 66 % at the wavelength of 940nm at a dark count rate of 100 cps by illuminating from the back of the device through single mode optical fiber.
Superconducting nanowire single photon detectors (SNSPDs) have demonstrated advantages over traditional detectors in many fields [1]. Most fiber-coupled SNSPDs are coupled to single mode fibers, limiting their usability for applications where large surface area detectors are needed, for example fluorescence detection and satellite-based quantum communication [2][3]. Other important requirements for many applications are broadband detection efficiency, and low timing jitter [4]. So far, the increased meander length of multimode detectors, and the therefore increased kinetic inductance and number of imperfections due to film inhomogeneities have limited the timing jitter [5]. Moreover, combining low timing jitter with high detection efficiency and low dark count rate in one device is challenging due to the tradeoffs between different properties of SNSPDs [6]. In this paper, we achieved high efficiency and strong saturation over a broad wavelength range with a low timing jitter of 16.99 ps while maintaining a low dark count rate of < 0.2 Hz for an SNSPD coupled to a 50 µm core multimode fiber. To enhance the broadband absorption from 405 nm to 830 nm, detectors were fabricated on an optimized SiO2 cavity and Aluminum mirror. The geometry of the nanowire was also tuned to reach a good internal saturation of efficiency over the visible/NIR range but also to carry high current to get a large signal. Furthermore, a cryogenic readout amplifier was optimized to improve the signal to noise ratio and thus lead to high time resolution. Our devices can be readily used to enable higher resolution and faster quantum optics, bio-imaging, laser ranging and other optical experiments.
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.
Generally, a superconducting nanowire single-photon detector (SNSPD) is composed of wires with a typical width of ∼ 100 nm . Recent studies have found that superconducting strips with a micrometer-scale width can also detect single photons. Compared with the SNSPD covering the same area, the superconducting microstrip single-photon detector (SMSPD) has smaller kinetic inductance, higher working current, and lower requirements in fabrication accuracy, providing potential applications in the development of ultralarge active area detectors. However, the study of SMSPD is still in its infancy, and the realization of its high-performance and practical use remains an open question. This study demonstrates a NbN SMSPD with a nearly saturated system detection efficiency (SDE) of ∼ 92.2 % at a dark count rate of ∼ 200 cps , a polarization sensitivity of ∼ 1.03 , and a minimum timing jitter of ∼ 48 ps at the telecom wavelength of 1550 nm when coupled with a single-mode fiber and operated at 0.84 K. Furthermore, the detector’s SDE is over 70% when operated at a 2.1 K closed-cycle cryocooler.
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.
Superconducting nanowire single-photon detectors (SNSPDs) play a pivotal role in infrared single-photon-detection applications owing to their free-running mode, near-unity detection efficiency, and excellent time resolution. However, conventional niobium nitride- (NbN) SNSPDs often have a trade-off between optimal detection efficiency and time resolution. We herein demonstrate NbN SNSPDs in the combination of high efficiency and time resolution by using the helium-ion-irradiated film of 10 nm and a homemade cryogenic amplifier to improve the signal-to-noise ratio. The proposed 18-μm-diameter device operated at 850 mK shows a saturated system detection efficiency of ∼90.5% at 1550 nm wavelength with a dark count rate below 50 counts per second (cps), and minimum system timing jitter of ∼14.7 ps. Meanwhile, the recovery time is 21.2 ns owing to its lower kinetic inductance. The time-of-flight light detection and ranging with this device was further carried out indoors, which demonstrates a submillimeter (<0.5 mm) depth resolution, as well as good depth and intensity reconstruction of a low-signature object even under the dwell time of 0.5 ms. It indicates that our device has a great advantage and potential in high-time-resolution and weak-signal-detection applications, such as real-time imaging, fluorescence lifetime detection, and remote laser sensing.