Today Superconducting Nanowire Single-Photon Detectors (SNSPDs) are commonly used in different photon-starved applications, including testing and diagnostics of VLSI circuits. Detecting very faint signals in the near-infrared wavelength range requires not only good detection efficiency, but also very low Dark Count Rate (DCR) and jitter. For example, low noise is crucial to enable ultra-low voltage optical testing of integrated circuits. The effect of detector temperature and background thermal radiation on the noise of superconducting single-photon detectors made of NbN meanders is studied in this paper. It is shown that two different regimes can be identified in the DCR vs. bias current characteristics. At high bias, the dark count rate is dominated by the intrinsic noise of the detector, while at low bias current it is dominated by the detection of stray photons that get onto the SNSPD. Changing the detector temperature changes its switching current and only affects the high bias branch of the characteristics: a reduction of the DCR can be achieved by lowering the SNSPD base temperature. On the other hand, changing the temperature of the single-photon light source (e.g. the VLSI circuit under test) only affects the low bias regime: a lower target temperature leads to a smaller DCR.
Today Superconducting Nanowire Single-Photon Detectors (SNSPDs) are commonly used in different photon-starved applications, including testing and diagnostics of VLSI circuits. Detecting very faint signals in the near-infrared wavelength range requires not only good detection efficiency, but also very low Dark Count Rate (DCR) and jitter. For example, low noise is crucial to enable ultra-low voltage optical testing of integrated circuits. The effect of detector temperature and background thermal radiation on the noise of superconducting single-photon detectors made of NbN meanders is studied in this paper. It is shown that two different regimes can be identified in the DCR vs. bias current characteristics. At high bias, the dark count rate is dominated by the intrinsic noise of the detector, while at low bias current it is dominated by the detection of stray photons that get onto the SNSPD. Changing the detector temperature changes its switching current and only affects the high bias branch of the characteristics: a reduction of the DCR can be achieved by lowering the SNSPD base temperature. On the other hand, changing the temperature of the single-photon light source (e.g. the VLSI circuit under test) only affects the low bias regime: a lower target temperature leads to a smaller DCR.
We present the performances of a superconducting nanowire single-photon detector (SNSPD) in an ultralow-temperature region from 16 mK to 4 K. The system detection efficiency of the SNSPD showed saturation in the bias-current and temperature dependences, and reached the considerably high value of 15% for 100 Hz dark count rate below 1.4 K at a wavelength of 1550 nm even without an optical cavity structure. We found that the dark count exists even at 16 mK and black body radiation becomes its dominant origin in the low temperatures for fiber-coupled devices.
Superconducting nanowire single photon detector (SNSPD) has been widely used in many fields such as quantum computing, quantum key distribution and laser radar, due to its high detection efficiency, low dark count rate, high counting rate, and low timing jitter. In most cases, the SNSPD works under the DC-bias mode that can detect single photons arrived at any time. In some cases such as satellite laser ranging and single-photon laser radar where the light pulses arrive regularly, the AC-bias mode enables the SNSPD to work with higher counting rates and lower background dark counts, which however requires complicated readout due to the low signal-to-noise ratio of the photon response. In this work, we report on an AC-biased SNSPD system with a self-differential readout circuit. The system includes a 2-pixel SNSPD consisting of two parallel nanowires, which are biased with 100 MHz sinusoidal current. The output signals of these two nanowires are amplified and combined for the differential readout of the photon response. The resulting response pulse possesses a signal-to-noise ratio ten times higher than that extracted before self-differential readout. In addition, the dark counts are reduced by a factor of 4, and the count rates are increased by a factor of 1.5, in comparison with those under the DC-bias mode. This work provides a specific method to read out the AC-biased SNSPD.
An abnormal increase in the SDE was observed for superconducting nanowire single-photon detectors (SNSPDs) when the bias current (I(b)) was close to the switching current (I(sw)). By introducing the time-correlated single-photon counting technique, we investigated the temporal histogram of the detection counts of an SNSPD under illumination. The temporal information helps us to distinguish photon counts from dark counts in the time domain. In this manner, the dark count rate (DCR) under illumination and the accurate SDE can be determined. The DCR under moderate illumination may be significantly larger than the conventional DCR measured without illumination under a high I(b), which causes the abnormal increase in the SDE. The increased DCR may be explained by the suppression of I(sw) under illumination.
Superconducting nanowire single photon detectors (SNSPD) have unique characteristics of ultra low dark counts and wide spectrum sensitivity. These natures are indispensable for the evaluation of ultra-broadband parametric fluorescence, which are used for the quantum optical coherence tomography and novel optical non-linear experiments. Here we report the spectral dependence of the detection efficiency of a meander type SNSPD device, having reduced strip width of 50 nm, over a wide spectrum range up to near infra-red wavelength. The fiber coupled, meander type device was fabricated using 6 nm thick Niobium nitride (NbN) nanowires of reduced strip width, 50 nm, patterned over a MgO substrate with active area of 10 x 10 μm2. A maximum efficiency of 32% at 500 nm, 30% at 600 nm, 16% at 800 nm, 10% at 1000 nm, and 1% at 1550 nm with the normalized bias current of 0.95 (bias 37 μA ) was observed at 4.2 K. The salient feature of the device is, it exhibits a very low dark count rate (DCR) of only 2 Hz at the standard operating bias of 37 μA and ultra low DCR of 0.01Hz at 34 μA. Moreover, at this reduced bias with 0.01Hz DCR, the detection efficiency is not appreciably decreased in the visible region (32% at 500 nm and 30% at 600 nm) and an order decrease is observed (0.1%) at 1550 nm. The noise equivalent power (NEP) is of the order 10-19 WHz-1/2 in the visible region and 10-17 WHz- 1/2 in the near IR region. Ultra-broad band parametric fluorescence of band width from 791 nm to 1610 nm generated by a quasi-phase matched (QPM) device was successfully detected with this SSPD.
We experimentally demonstrate an improved optical biasing scheme for superconducting nanowire single-photon detectors (SNSPDs), which employs a cryogenic InGaAs-InP photodiode (PD) as a local bias source. It is found that, under illumination from a stable external light source, this PD generates a stable photocurrent in a cryogenic environment (~2.3 K), with fluctuations in the photocurrent primarily attributed to fluctuations in the incident optical power. Furthermore, by screening and effectively blocking stray photons leaking from the PD, which give rise to background dark counts, we have achieved an SNSPD exhibiting an ultra-low intrinsic dark count rate of 1e-4 cps. Utilizing this improved optical biasing technique, our SNSPD achieved performance comparable to that obtained under conventional electrical biasing: a system detection efficiency of 80.7%, a background dark count rate of 32.6 cps, and a minimum timing jitter of 57.5 ps. These results indicate that cryogenic-PD-based optical biasing serves as a viable, low-noise, and low-jitter alternative to traditional electrical biasing. Moreover, this work offers useful design guidance for the future development of PD-based low-noise bias sources and for the construction of all-photonic SNSPD systems tailored for high-precision quantum photonics applications.
Suppressing the dark count rate (DCR) is one of the main issues in the development of the superconducting nanowire single-photon detector. Here, we study the effect of suppressing DCR using the various optical bandpass filters cooled at 3 K. The DCR, which is dominated by the background blackbody radiation at room temperature through an optical fiber, can be strongly suppressed by introducing the cold filter. Using the bulk commercial filter with the bandwidth of 10 nm and the high transmission above 85%, the DCR is improved about 29 dB with 2.4 dB of decrease in the system detection efficiency (η). The noise equivalent power reaches 1.5 × 10-18and the figure of merit reaches 1.8 × 109. These values are compared to the results using other type of filters.