In this paper, a superconducting nanowire single photon detector (SNSPD) is expressed as an equivalent circuit model. Combined with the theory of transmission line and impedance matching, the model is analyzed and a method is presented to design a SNSPD with high efficiency and dual broadband. Take the λ=1310 nm and λ=1550 nm as an example, geometry parameters of the device are calculated by this method and verified by the commercial software FDTD Solutions.
In this paper, a superconducting nanowire single photon detector (SNSPD) is expressed as an equivalent circuit model. Combined with the theory of transmission line and impedance matching, the model is analyzed and a method is presented to design a SNSPD with high efficiency and dual broadband. Take the λ=1310 nm and λ=1550 nm as an example, geometry parameters of the device are calculated by this method and verified by the commercial software FDTD Solutions.
In this paper, we propose a structure of a superconducting nanowire single-photon detector (SNSPD) with a composite cavity. Compared with the SNSPD in previous studies, our device exhibits a property of high efficiency and dual broadband. Based on the transmission line theory, the structure is abstractedly expressed as an equivalent circuit model and a design method is presented. Taking λ = 1310nm and λ = 1550nm as an example, the structural parameters are calculated and verified by commercial software FDTD Solutions. The simulation results show that peaks of the absorption curve appear at both wavelengths and peak values are all larger than 97.5%. The influence of the upper half cavity on the full width at half maximum (FWHM) of the absorption peak is discussed. Our works provide a reference for designing an SNSPD with different FWHM.
The efficiency is one of the most important parameter of single photon detector (SPD). The ideal SPD is expected to have 100% efficiency without false counts (always called dark counts). Improving the efficiency and reducing dark counts are interesting work for both scientific research and practical applications. Superconducting nanowire single photon detector (SNSPD) was intensively developed for its merit of low dark count, less than 1 count per second. However, its efficiency was limited by the optical absorption of superconductor nanowire. In this work, we analyzed the optical absorption of superconductor nanowire of SNSPD in theory. Then, we designed a SNSPD considering film growth and microfabrication process by optimizing the device structure, including the filling factor, films thickness, substrate index and cavity. With the SNSPD, a high absorption of 97% was calculated by FDTD method and a detector efficiency of 90% was achieved in experiments assisted by beam compressing settings.
High-efficiency superconducting nanowire single-photon detectors (SNSPDs), which have numerous applications in quantum information systems, function by using the optical cavity and the ultrasensitive photon response of their ultra-thin superconducting nanowires. However, the wideband response of superconducting nanowires is limited due to the resonance of the traditional optical cavity. Here, we report on a supercontinuum SNSPD that can efficiently detect single photons over an ultra-broad spectral range from visible to mid-infrared light. Our detection approach relies on using multiple cavities with well-separated absorbed resonances formed by fabricating multilayer superconducting nanowires on metallic mirrors with silica acting as spacer layers. Thus, we are able to extend the absorption spectral bandwidth while maintaining considerable efficiency, as opposed to a conventional single-layer SNSPD. Our calculations show that the proposed supercontinuum SNSPD exhibits an extended absorption bandwidth with increased nanowire layers. Its absorption efficiency is greater than 70% over the entire range from 400 to 2500 nm (or 400 to 3000 nm), when using two-layer (or three-layer) nanowires. As a proof of principle, the SNSPD with bilayer nanowires is fabricated based on the proposed detector architecture with simplified geometrical parameters. The detector achieves broadband detection efficiency over 60% from 950 to 1650 nm. This type of detector may replace multiple narrow band detectors in a system and find uses in the emerging and rapidly advancing field of atomic and molecular broadband spectroscopy.
This Superconducting nanowire single-photon detectors (SNSPDs) are efficient devices that absorb and convert incident photons to discriminable signals. However, the multi-spectral response of it is limited due to the resonance of the traditional optical cavity. In this work, we present a multi-spectral SNSPD that can detect single photon at multiple wavelengths with high efficiency simultaneously. The stack structure consists of nanowires embedded in the high refractive index dielectric strips, spacer layers and the reflection layer. The designed detector shows absorption efficiencies of over 85% at the three target wavelengths of 1550 nm, 1310 nm and 1064 nm while the filling factor of nanowire is only 20%. Meanwhile, the reset time is dramatically reduced by applying the low-filling-factor nanowire. Such ultrafast, high-performance single-photon detectors are promising for the rapidly advancing fields of multi-spectral imaging, satellite laser ranging and quantum communications.
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 detector (SNSPD) has been widely used in quantum communication, quantum computing and other fields because of its excellent timing jitter and response speed. However, due to the mutual restraint of the technical parameters of SNSPD nanowires, there are technical challenges to further improve the comprehensive performance of SNSPD, and thus limiting its application on a large scale. Combining high detection efficiency with high timing performance is still an outstanding challenge. In this work, we report the SNSPD with 12-μm small active area, which has high speed, high efficiency, low jitter and broadband absorption. Au/SiO2 membrane cavity, which is determined by finite element analysis simulation, is used to widen the optical response bandwidth. And it is easier to process and improve the alignment accuracy at the same time. The flat substrate is more conducive to the growth of superconducting thin films, so flattening process is introduced. Device package is also optimized to match smaller detector. Self-aligned packaging makes optical alignment more convenient and time-saving. Special optical fibers with small mode-field diameters can reduce the negative effect of the detector on optical coupling. The detector can achieve a maximum SDE of 82% at the central wavelength of 1310 nm and the temperature of 2.2 K, and the SDE of more than 65% in the wavelength range of 1200–1600 nm, with DCR of 70 cps. The detector also exhibits a count rate of 40 MHz@3 dB and a timing jitter of 38 ps, which is significantly improved compared with 23-μm active area detector. Furthermore, the minimum timing jitter of 22 ps can be obtained by using cryogenic amplifier readout. In this work, high comprehensive performance detector is developed, which provides an important technical reference for practical and product SNSPD.