Research On Superconducting Nanowire Single Photon Detector In Quantum Communication

The continuous development of quantum information technology is expected to bring new breakthroughs to traditional information science.Quantum information technology mainly includes three fields:quantum computing,quantum communication and quantum measurement.Practical quantum communication network is the current research hotspot,and one of the key devices in quantum communication system,superconducting nanowire single photon detector(SNSPD),has attracted the attention of scientific researchers because of its outstanding performance,such as high detection efficiency,high count rate,broadband response,low dark count and low time jitter.SNSPD is the single photon detection technology with the best comprehensive performance in the near-infrared band.It has been widely used in many fields,including quantum key distribution,satellite communication,single photon imaging and biological detection.However,complex applications will demand greater performance from SNSPD in many aspects.In this paper,the simultaneous optimization of multiple performance parameters of SNSPD is studied.By constructing the device structure to meet the requirements,and using simulation calculation to optimize the structural parameters,three SNSPDs with simultaneous optimization of multiple parameters are finally designed:high-efficiency,high-speed and high polarization sensitive SNSPD,high-efficiency,high-speed multispectral SNSPD and multilayer superconducting nanowire SNSPD.The specific research results are as follows:1.In order to solve the problem of mutual restriction between absorption efficiency and detection speed caused by SNSPD using large-area winding superconducting nanowires,this paper innovatively uses the resonant cavity composed of silicon(Si)grating and silver(Ag)reflector to improve the absorption efficiency of relatively sparse superconducting nanowires,so as to optimize the absorption efficiency and detection speed at the same time.The results show that when the incident light is TM wave,the SNSPD shows a high absorption efficiency of 84.4%when the nanowire filling factor is 16.5%;for TE wave,the SNSPD shows a high absorption efficiency of 67.0%when the nanowire filling factor is 11.7%.We then focus on another problem arising from the meandering nanowires,namely the different responses of SNSPDs to incident light of different polarization states.Through electromagnetic simulation,we find that the polarization sensitivity of the designed SNSPD is further strengthened.When the incident light is TM wave,the polarization extinction ratio(PER)of the SNSPD is as high as 562.9,while for TE wave,the PER is 7.4,both of which are much higher than the performance of traditional SNSPD.The SNSPD can achieve high absorption efficiency,high counting rate and high polarization sensitivity at the same time,and has a very wide application prospect.2.To design a multispectral SNSPD,we placed niobium nitride(NbN)superconducting nanowires at the center of the Si grating,coupled with an Ag reflective layer,so that the superconducting nanowires can achieve higher absorption efficiency when the incident light wavelength is 1064 nm or 1550 nm.The simulation results show that the absorption efficiency of the designed SNSPD can achieve more than 80%,no matter the incident wavelength is 1064 nm or 1550 nm.At the same time,the filling factor of the superconducting nanowires used is only 12%,which is 24%of that of the traditional SNSPD(the filling factor is generally 50%),and its recovery time can be roughly estimated to be 24%of that of the traditional SNSPD,which greatly improves the detection speed.So this paper designs a multispectral SNSPD that can work efficiently and at high speed in two bands at the same time,which can significantly reduce the complexity of quantum key distribution(QKD)system using wavelength division multiplexing(WDM).3.In order to expand the absorption spectrum of SNSPD,a SNSPD with multilayer superconducting nanowire structure is designed in this paper.The nanowires are separated by dielectric isolation layer,and Si strips with a certain thickness are filled on both sides of each layer of nanowires.With such an innovative structure,the SNSPD can have high absorption efficiency and short recovery time at three communication wavelengths(1550nm,1310nm and 1064nm),so as to expand the response bandwidth of SNSPD.At the same time,the position of target wavelength can be adjusted by changing the thickness of isolation layer,which improves the application flexibility of SNSPD.The calculation results show that the absorption efficiency of the SNSPD at three target wavelengths(1550nm、1310nm 和 1064nm)can exceed 85%when the nanowire filling factor is 20%.At the same time,its recovery time is about 40%of that of traditional SNSPD,which greatly improves the detection speed.This SNSPD can improve the reusability of ssingle-photon detectors and reduce the economic cost of the detection system,which has a wide application prospect.