| In recent years,superconducting nanowire single-photon detector(SNSPD)have been developing rapidly.Compared with other types of single-photon detectors,SNSPD have superior performance,such as high efficiency,high speed,low dark count and low time jitter,and have become indispensable detectors in many advanced fields.However,due to the structural limitations of SNSPD,it is often difficult to combine all these excellent performance,and as the applications become more advanced,higher demands are placed on the overall performance of SNSPD.Improved device structure can be used to improve the overall performance of SNSPD,but this method is greatly affected by the preparation process,resulting in poor consistency,low yield,and requires complex readout circuitry.In this paper,we use a high-efficiency,low-dark-count SNSPD and optimize the count rate and time jitter by improving the readout circuit,without affecting the detection efficiency and dark counting of the device,to improve the overall performance of the SNSPD and expand its application.The details of the work are as follows:Firstly,the system construction for improving the counting rate of SNSPD at room temperature.The current system for improving the counting rate of SNSPD involves the low temperature integration,but the manufacturer generally does not provide the parameters of electronic components at deep low temperature,which requires several times of dismantling and tuning before it can be perfectly adapted to SNSPD,which will cause the system to be down for a long time and other problems.Therefore,this paper builds a distributed circuit model of the SNSPD system based on LTSPICE,and the simulation locates the key factor for the transmission integrity of the SNSPD signal across temperature zones as the transmission line length.The signal integrity problem is solved by reducing the transmission line length by about 2/3 through the introduction of a low-temperature band line with very low heat leakage,thus increasing the maximum count rate of the device from 1.3 MHz to 6.9 MHz at room temperature,an improvement of 5.3 times.Secondly,circuit optimization for improving the count rate of the SNSPD at room temperature.To address the problem that the SNSPD cannot respond to higher light intensities,we propose two improvements:(1)introducing parallel resistors in series to improve the thermoelectric feedback problem,increasing the maximum count rate of the device to 58.7MHz,a 45-fold improvement,while ensuring a linear relationship between light intensity and count rate.(2)The capacitive coupling effect is improved by adding a low-pass filter in parallel to the circuit,which further increases the maximum count rate to 75.7 MHz,an improvement of 58.2 times,while maintaining a good signal-to-noise ratio.Thirdly,to address the problem that circuit noise introduced by the amplifier reduces the SNSPD response signal-to-noise ratio,a low-temperature amplifier is designed,which uses a combination of emitter negative feedback and parallel resistive negative feedback to optimize the amplifier.Cryogenic test results show that the amplifier achieves 20 d B of gain,less than-10 d B of input and output return loss,and 19.8 m W of power loss over the frequency range of100 k Hz to 1 GHz when the supply voltage is 2.2 V.Interconnection with the SNSPD reduces the time jitter of the system by 9%. |
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