We report the fabrication and characterization of a niobium titanium nitride (NbTiN)-based superconducting nanowire single-photon detector (SSPD or SNSPD) on the Si waveguide toward the realization of waveguide-coupled SSPD. The device consists of a silicon optical waveguide fabricated using a silicon-on-insulator (SOI) substrate and a 100-nm-wide NbTiN nanowire constructed on the waveguide, with an inductor to prevent latch operation. For the fabricated device, the observed superconducting critical temperature and critical current were 7.85 K and 34.4 μA at 0.3 K, respectively. We investigated the optical response of the fabricated device and found that the device exhibited a single-photon response by measuring of the input power dependence of the output count rate. Furthermore, the fabricated device showed a clear bias current dependence of the output counts similar to conventional SSPDs, and the pulse-generation probability is estimated to be 90.1% based on two assumptions: a sigmoidal model to the detection efficiency and the device has a 100% pulse-generation probability at the saturated region.
We report the fabrication and characterization of a niobium titanium nitride (NbTiN)-based superconducting nanowire single-photon detector (SSPD or SNSPD) on the Si waveguide toward the realization of waveguide-coupled SSPD. The device consists of a silicon optical waveguide fabricated using a silicon-on-insulator (SOI) substrate and a 100-nm-wide NbTiN nanowire constructed on the waveguide, with an inductor to prevent latch operation. For the fabricated device, the observed superconducting critical temperature and critical current were 7.85 K and 34.4 μA at 0.3 K, respectively. We investigated the optical response of the fabricated device and found that the device exhibited a single-photon response by measuring of the input power dependence of the output count rate. Furthermore, the fabricated device showed a clear bias current dependence of the output counts similar to conventional SSPDs, and the pulse-generation probability is estimated to be 90.1% based on two assumptions: a sigmoidal model to the detection efficiency and the device has a 100% pulse-generation probability at the saturated region.
We have fabricated and characterized a niobium titanium nitride (NbTiN)-based superconducting nanowire single- photon detector (SSPD or SNSPD) on the silicon (Si) waveguide toward the realization of waveguide-coupled SSPD. The superconducting critical temperature and critical current were 7.85 K and 34.4 μA at 0.3 K, respectively. We investigated the optical response of the fabricated device and found that the device exhibited a single-photon response. Furthermore, the fabricated device showed a clear bias current dependence of the output counts similar to conventional SSPDs.
We present high performance fiber-coupled niobium titanium nitride superconducting nanowire single photon detectors fabricated on thermally oxidized silicon substrates. By applying a double sided cavity structure, simulated absorptance in the nanowire meander reached 97% at 1550 nm wavelength. The fabricated device showed a system detection efficiency (DE) of 74% at 1550 nm, dark count rate of 100 c/s, and a full width at half maximum timing jitter of 68 ps under a bias current of 18.0 μA with a practical Gifford-McMahon cryocooler system.
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.
The Superconducting Nanowire single-photon detector (SNSPD) made with niobium-titanium nitride (NbTiN) thin films fabricated on oxidized silicon substrates are highly promising nanodevices. The SNSPD is an immensely capable infrared single photon detector. When cooled down with liquid helium the device exhibits high detection efficiency, low dark-counts in spite of fast response times, and low timing jitter. For good single-photon sensitivity at telecom wavelengths, picosecod timing resolutions (<100 ps), and high counting frequencies, the SNSPD is first choice compared to the alternatives like indium gallium arsenide avalanche diode detectors, silicon single photon avalanche diode detectors, and other superconducting single photon technology like, transition edge detectors. These SNSPD characteristics make it ideal for long distance quantum key distribution (QKD). \nAlthough the exploitation of the constructive interference that occurs at the SiO2/Si interface can boost detector efficiency, efficient packaging and fiber coupling is often a limiting factor in the overall system quantum efficiency (SQE). In an attempt to maximize SQE, we use a controlled expansion alloy for optimal performance at cryogenic temperatures. This nickel-iron alloy has a high relative permeability and, therefore, attenuates electromagnetic interference. Our report focuses on the theoretical and experimental methods used in the characterization of an un-patterned NbTiN superconducting nanowire. We use simulations based on the gathered experimental data to design an optimal SNSPD meander and calculate its expected SQE. We also use simulations to analyze the speed and value added to secure key rates in long distance QKD schemes up to 400 km with down-conversion sources with positively spectrally correlated and decorrelated photon pairs at 1550 nm wavelength.
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.
Superconducting nanowire single-photon detectors (SNSPDs or SSPD) are highly promising devices in the growing field of quantum information and communications technology. We have developed a practical SSPD system with our superconducting thin films and devices fabrication, optical coupling packaging, and cryogenic technology. The SSPD system consists of six-channel SSPD devices and a compact Gifford-McMahon (GM) cryocooler, and can operate continuously on 100 V ac power without the need for any cryogens. The SSPD devices were fabricated from high-quality niobium nitride (NbN) ultrathin films that were epitaxially grown on single-crystal MgO substrates. The packaged SSPD devices were temperature stabilized to 2.96 K ± 10 mK. The system detection efficiency for an SSPD device with an area of 20 × 20 ¿m2was found to be 2.6% and 4.5% at wavelengths of 1550 and 1310 nm, respectively, at a dark count rate of 100 Hz, and a jitter of 100 ps full-width at half maximum. We also performed ultrafast BB84 quantum key distribution (QKD) field testing and entanglement-based QKD experiments using these SSPD devices.