In this article, we demonstrate a superconducting nanowire single photon detector (SNSPD) at a wavelength of 2000 nm. We use numerical simulations to optimize the parameters of the device structure. Guided by the obtained numerical results, we fabricated and measured the device that operates at 2000 nm at 2.3K. The results indicate that our device responses well in 2000nm with a dark count rate of 100Hz. The recovering time is 100ns.
In this article, we demonstrate a superconducting nanowire single photon detector (SNSPD) at a wavelength of 2000 nm. We use numerical simulations to optimize the parameters of the device structure. Guided by the obtained numerical results, we fabricated and measured the device that operates at 2000 nm at 2.3K. The results indicate that our device responses well in 2000nm with a dark count rate of 100Hz. The recovering time is 100ns.
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.
In this paper,the fabrication details and optimization of micro-fabrication process are presented for developing superconducting nanowire single-photon detectors (SNSPD). Besides,the device failure analysis is also introduced. With those methods,we successfully fabricated high-quality SNSPDs whose maximum system efficiencies were up to 30% for 660 nm wavelength and 4.2% for 1550 nm wavelength according to the single-photon detection experiment. At the dark count rate of 10 c/s,the detection efficiencies were 20% (660 nm) and 3% (1550 nm) with the SNSPD fabricated with above mentioned methods.
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.
For photon-counting applications at ultraviolet wavelengths, there are currently no detectors that combine high efficiency (> 50%), sub-nanosecond timing resolution, and sub-Hz dark count rates. Superconducting nanowire single-photon detectors (SNSPDs) have seen success over the past decade for photon-counting applications in the near-infrared, but little work has been done to optimize SNSPDs for wavelengths below 400 nm. Here, we describe the design, fabrication, and characterization of UV SNSPDs operating at wavelengths between 250 and 370 nm. The detectors have active areas up to 56 μm in diameter, 70 - 80% efficiency at temperatures up to 4.2 K, timing resolution down to 60 ps FWHM, blindness to visible and infrared photons, and dark count rates of ∼ 0.25 counts/hr for a 56 μm diameter pixel. These performance metrics make UV SNSPDs ideal for applications in trapped-ion quantum information processing, lidar studies of the upper atmosphere, UV fluorescent-lifetime imaging microscopy, and photon-starved UV astronomy.
Implementations of quantum information require single-photon detectors (SPDs) with high detection efficiency (DE) at a wavelength of 940 nm, which is a challenge for the available semiconducting SPDs. Superconducting nanowire SPDs (SNSPDs) are capable of detecting visible and near-infrared single photons with high DE. However, these detection capabilities place stringent design requirements on the cavity and nanowire geometry structures. We design, fabricate, and measure SNSPDs with high DE optimized for the 940-nm wavelength. The NbN SNSPDs were fabricated on 1-D photonic crystals for high optical absorptance. By tuning the filling factor of the nanowire through numerical simulations and experiments, we were able to obtain an SNSPD (7 nm thick, 125 nm width, and 0.57 filling factor, as well as active area of18∗18μm) with a saturated system DE of 83.6$\pm3.7\pm$0.02. To our best knowledge, this is the highest value reported for NbN SNSPDs at 940-nm wavelength. The availability of an SNSPD with high system DE at 940 nm may have a profound impact in the field of photonic quantum technologies, such as multiphoton entanglement.
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.