Single photon detectors are essential part of most optical quantum information applications. Among all candidates, superconducting nanowire single photon detectors (SNSPD) have the advantages of low jitter, low dark count rates and high maximum count rate. Commercial systems based on these detector elements currently cost on order $50-100K. In this project a circular meander design of a free-space SNSPD is fabricated and tested in house. Although the absolute absorption efficiency of the detector is low, because it was fabricated on a substrate optimized for other applications, the measured and modelled values for both incident polarizations agree within the uncertainties. The bias current dependence is almost constant from 50% to 100% of the breakdown threshold value, which should allow operation at intrinsic dark count rates extrapolated to be < 1 Hz at 2.05 K.
Single photon detectors are essential part of most optical quantum information applications. Among all candidates, superconducting nanowire single photon detectors (SNSPD) have the advantages of low jitter, low dark count rates and high maximum count rate. Commercial systems based on these detector elements currently cost on order $50-100K. In this project a circular meander design of a free-space SNSPD is fabricated and tested in house. Although the absolute absorption efficiency of the detector is low, because it was fabricated on a substrate optimized for other applications, the measured and modelled values for both incident polarizations agree within the uncertainties. The bias current dependence is almost constant from 50% to 100% of the breakdown threshold value, which should allow operation at intrinsic dark count rates extrapolated to be < 1 Hz at 2.05 K.
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) have emerged as a highly promising infrared single-photon detector technology. Next-generation devices are being developed with enhanced detection efficiency (DE) at key technological wavelengths via the use of optical cavities. Furthermore, new materials and substrates are being explored for improved fabrication versatility, higher DE, and lower dark counts. We report on the practical performance of packaged NbTiN SNSPDs fabricated on oxidized silicon substrates in the wavelength range from 830 to 1700 nm. We exploit constructive interference from the SiO2/Si interface in order to achieve enhanced front-side fiber-coupled DE of 23.2 % at 1310 nm, at 1 kHz dark count rate, with 60 ps full width half maximum timing jitter.
Photon detectors connect optical and electrical systems by converting light to electrical signals. Single photon detectors detect single photons which measure ultra-weak light. Traditional semiconductor single-photon detectors suffer from high dark count rates, low infrared detection efficiency, and poor temporal resolution. Superconducting-nanowire single-photon detectors (SNSPDs) overcome these limitations using the hotspot effect. SNSPDs have created a solid foundation for optical technologies and become key in quantum information, LiDARs and Deep-Space Communications. This paper reviews working principles and performance metrics: system detection efficiency, dark count rate, recovery time, and timing jitter. The study summarizes applications in quantum information (quantum key distribution, optical quantum computing), single-photon LiDAR, and deep-space optical communication, replacing most single-photon avalanche diodes (SPADs). Recent experiments show that SNSPD-based systems can achieve meter-scale detection of sea fog, interplanetary laser communication over billions of kilometers, and boson sampling with 20 photons. Ongoing research is expected to improve performance in maximum count rate, system integration, and cryogenic operation, as well as to find applications in emerging fields such as environmental monitoring.
We fabricated superconducting nanowire single-photon detectors (SNSPDs) made of NbTiN and NbN thin films in the same fabrication batch. Various parameters, such as critical temperature, resistivity, switching current, and kinetic inductance, were compared between the two types of SNSPDs. These data indicate that NbTiN SNSPD surpasses NbN SNSPD in many aspects, including a shorter recovery time due to smaller kinetic inductance, a lower timing jitter due to higher switching current, and better uniformity. Based on the measurement of 28 out of 121 NbTiN SNSPDs on a 2-in Si wafer, 71% of detectors show a system detection efficiency of over 50% at a dark count rate of 100 Hz, with the maximum efficiency being 77.5%.
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.
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.