Superconducting nanowire single-photon detectors (SNSPDs) are an enabling technology for myriad quantum-optics experiments that require high-efficiency detection, large count rates, and precise timing resolution. The system detection efficiencies (SDEs) for fiber-coupled SNSPDs have fallen short of theoretical predictions of near unity by at least 7%, with the discrepancy being attributed to scattering, material absorption, and other SNSPD dynamics. We optimize the design and fabrication of an all-dielectric layered stack and fiber coupling package in order to achieve 98.0 ± 0.5 % SDE, measured for single-mode-fiber guided photons derived from a highly attenuated 1550 nm continuous-wave laser. This enforces a smaller bound on the scattering and absorption losses in such systems and opens the use of SNSPDs for scenarios that demand high-SDE for throughput and fidelity.
Superconducting nanowire single-photon detectors (SNSPDs) are an enabling technology for myriad quantum-optics experiments that require high-efficiency detection, large count rates, and precise timing resolution. The system detection efficiencies (SDEs) for fiber-coupled SNSPDs have fallen short of theoretical predictions of near unity by at least 7%, with the discrepancy being attributed to scattering, material absorption, and other SNSPD dynamics. We optimize the design and fabrication of an all-dielectric layered stack and fiber coupling package in order to achieve 98.0 ± 0.5 % SDE, measured for single-mode-fiber guided photons derived from a highly attenuated 1550 nm continuous-wave laser. This enforces a smaller bound on the scattering and absorption losses in such systems and opens the use of SNSPDs for scenarios that demand high-SDE for throughput and fidelity.
Ever since superconducting nanowire single-photon detectors (SNSPDs or SSPDs) were demonstrated, they have attracted a considerable attention due to the detectors’ promising performance that includes high detection efficiency (DE), low dark count rate (DCR), broadband sensitivity, and low timing jitter. The system detection efficiency (SDE) has been improved to be over 90% with a wavelength of 1550 nm in a fiber-coupled system by embedding the SNSPD in optical cavities. However, the implementation of optical cavity usually reduces the bandwidth of SNSPDs. As a result, there are some recent works on increasing the bandwidth of SNSPD. Furthermore, the size of the active area of meandered nanowires has to be compatible with the core size of an optical fiber such that good optical coupling can be achieved; this setup requires a long nanowire with a large kinetic inductance, thus resulting in a small counting rate and a large timing jitter, particularly for multi-mode fiber-coupled devices. Nevertheless, a particularly impressive waveguide-coupled SNSPD has been developed in recent years. By placing an SNSPD atop an optical waveguide that has been fabricated on various substrate materials, photons propagating in the waveguide have been found to be evanescently absorbed by nanowires that are only a few tens of microns long. The on-chip DE of this device has been estimated to be over 90%, thus indicating that it has both high absorptance and high intrinsic DE. If the waveguide and the nanowire are correctly dimensioned, the absorptance of this device can reach over 90% for a wavelength range of more than 700 nm. Furthermore, the length of the nanowire is shorter than that of the fiber-coupled SNSPD, thus leading to a higher count rate and lower timing jitter (~18 ps). However, unsatisfactory coupling losses between the optical fiber and the waveguide in such devices can decrease its SDE (~10%), thus limiting its applicability to quantum photonic integrated circuits (QPIC). Recently, we proposed a type of SNSPD that was coupled with microfibers (MFs), and simulations for this SNSPD indicated that its absorption would be as high as 90%. Microfibers and nanofibers, tapered adiabatically from standard fibers, with diameters close to or smaller than the wavelength of the guided light were demonstrated to have low transmittance losses by Tong et al. in 2003. MFs have been shown to have many interesting properties, such as strong evanescent fields, tight optical confinement, wideband abilities, and small masses; these properties are appealing for applications such as optical sensing and coupling. MFs also provide seamless connections with high transmittance from standard fibers; therefore, MF-coupled SNSPDs can achieve both high SDEs and wideband compatibility. We proposed and demonstrated the MF-coupled SNSPDs successfully. The simulation results indicate that with optimal device structure, the optical absorption with efficiency < 90% can be realized over a wavelength range of 350 nm to 2150 nm. The fabricated MF-coupled SNSPD, shows unparalleled broadband system detection efficiencies (SDEs) of more than 50% from 630 nm to 1500 nm. The SDEs reach 66% at 785 nm and 45% at 1550 nm. These results pave the way for ultra-broadband weak light detection with quantum-limit sensitivity.
Superconducting nanowire single-photon detector (SNSPD) with near-unity system efficiency is a key enabling, but still elusive, technology for numerous quantum fundamental theory verifications and quantum information applications. The key challenge is to have both a near-unity photon-response probability and absorption efficiency simultaneously for the meandered nanowire with a finite filling ratio, which is more crucial for NbN than other superconducting materials (e.g., WSi) with lower transition temperatures. Here, we overcome the above challenge and produce NbN SNSPDs with a record system efficiency by replacing a single-layer nanowire with twin-layer nanowires on a dielectric mirror. The detector at 0.8 K shows a maximal system detection efficiency (SDE) of 98% at 1590 nm and a system efficiency of over 95% in the wavelength range of 1530-1630 nm. Moreover, the detector at 2.1 K demonstrates a maximal SDE of 95% at 1550 nm using a compacted two-stage cryocooler. This type of detector also shows the robustness against various parameters, such as the geometrical size of the nanowire and the spectral bandwidth, enabling a high yield of 73% (36%) with an SDE of >80% (90%) at 2.1 K for 45 detectors fabricated in the same run. These SNSPDs made of twin-layer nanowires are of important practical significance for batch production.
Fast and efficient detection of single photons with high timing accuracy is a crucial requirement in most quantum optics experiments and enables novel sensing and imaging solutions. Superconducting nanowire single-photon detectors (SNSPD) achieve technology-leading performance in terms of detection efficiency, dark count rate, timing jitter, and detector dead times. However, conventional SNSPDs with high system detection efficiency typically rely on resonant enhancement of the absorption efficiency, thus only achieving attractive detector benchmarks over narrow spectral windows. Waveguide-integrated SNSPDs allow for leveraging the wideband material absorption in superconducting nanowires by absorbing light in a traveling-wave geometry but have been limited to low system detection efficiencies due to interface losses when coupling to optical fibers. Here, we show how high system detection efficiencies of 22%–73% are realized over a broad wavelength range from 532 nm to 1640 nm in a single waveguide-integrated SNSPD device. We accomplish efficient coupling between optical fibers and waveguide-integrated nanowire detectors by employing a 3D interface, produced in direct laser writing, that relies on total internal reflection for achieving a broad transmission bandwidth. We further find low timing jitter of 25.7 ps and detector decay times of 9.8 ns, allowing for single-photon counting with high repetition rates up to 100 MHz. Our work paves the way for an efficient single-photon detector solution that combines the spectral requirements of an extremely wide range of quantum optics experiments in a single device. The coupling approach and SNSPD-integration with nanophotonic circuits are further well-suited for realizing large-scale detector arrays.
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.
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.
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.