WO2021253931A1 - 一种基于双线结构消减snspd暗计数的设计 - Google Patents

一种基于双线结构消减snspd暗计数的设计 Download PDF

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WO2021253931A1
WO2021253931A1 PCT/CN2021/085775 CN2021085775W WO2021253931A1 WO 2021253931 A1 WO2021253931 A1 WO 2021253931A1 CN 2021085775 W CN2021085775 W CN 2021085775W WO 2021253931 A1 WO2021253931 A1 WO 2021253931A1
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nanowire
snspd
nanowires
dark count
wire structure
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French (fr)
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张蜡宝
印睿
张彪
陈奇
吕嘉煜
葛睿
康琳
吴培亨
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南京大学
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/44—Electric circuits
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J11/00—Measuring the characteristics of individual optical pulses or of optical pulse trains
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/80—Constructional details
    • H10N60/83—Element shape
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/44—Electric circuits
    • G01J2001/4413—Type
    • G01J2001/442—Single-photon detection or photon counting
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/44—Electric circuits
    • G01J2001/444—Compensating; Calibrating, e.g. dark current, temperature drift, noise reduction or baseline correction; Adjusting
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/44—Electric circuits
    • G01J2001/4446—Type of detector
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/44—Electric circuits
    • G01J2001/4446—Type of detector
    • G01J2001/446—Photodiode
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
    • G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
    • G01J5/20—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
    • G01J2005/208—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices superconductive
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/80—Constructional details
    • H10N60/84—Switching means for devices switchable between superconducting and normal states

Definitions

  • the invention belongs to the technical field of superconducting single-photon detection, and specifically relates to a dark count subtraction technology.
  • the superconducting nanowire single photon detector (SNSPD) is a new type of photodetector that can detect single photons efficiently, quickly and accurately.
  • the photosensitive part is a winding nanowire structure made of superconducting thin film materials.
  • the detector When the detector is working, it is biased at a position slightly lower than its superconducting critical current. When the nanowire absorbs photons, the superconducting state in the absorption region is destroyed and a heat island is generated. The heat island area grows with the assistance of the current Joule heat. To a certain extent, the heat island disappears after the nanowire itself and the substrate are cooled, and the nanowire returns to its original state.
  • the process by which the detector absorbs photons appears on the circuit as an electric pulse that rises quickly and then decays exponentially. By amplifying this pulse signal, the detector can identify the arrival of a single photon.
  • DCR Dark Count Rate
  • the present invention proposes a dual-wire structure SNSPD device, which prepares two intertwined but non-intersecting nanowires.
  • the unique performance of the device is combined with the external circuit.
  • the processing can effectively suppress the influence of the intrinsic dark count of the SNSPD system.
  • the present invention adopts the following technical solutions.
  • Two niobium nitride nanowires are wound without crossing each other to form a superconducting nanowire single-photon detector SNSPD with a double-wire structure.
  • One nanowire is used to control the behavior of the other nanowire, and the bias current is adjusted close to the superconductivity.
  • Critical current use optical fiber to introduce optical signal into the photosensitive area of the detector, and output two signals through two nanowires respectively, so that the dark counts between the two nanowires are mutually excited, and the dark counts are subtracted through the voltage comparator and the exclusive OR gate Signal, keep the photon response signal.
  • winding two niobium nitride nanowires without crossing each other includes: arranging the two nanowires side by side, the length from left to right is 10 to 20 ⁇ m, the width is 50 to 80 nm, and the thickness is designed to be 5 to 8 nm , The minimum spacing of two nanowires is 50-120nm, the maximum spacing is 300-400nm, and the winding cycle is 9-20 times.
  • the outer nanowire at the corner of the nanowire surrounds the inner nanowire.
  • the inner radius of the corner is 200-250nm, and the outer radius is 300-400nm.
  • the width of a single line is 80nm, and the two nanowires are respectively led out by 4 electrodes, and the winding cycle is 9 times. .
  • the side length of the nanowire chip is 5mm, the center area is a nanowire structure, and 11 wide to narrow gradient electrodes are distributed around it.
  • the widest part is 0.7mm to connect to the external circuit, and the narrowest part is 0.01mm to connect to the nanowire.
  • magnetron sputtering is used to deposit NbN film
  • electron beam exposure is used to prepare nano lines
  • reactive ion etching transfers nano lines
  • ultraviolet lithography is used to prepare gold electrodes
  • plasma enhanced chemical meteorological deposition is used to prepare upper reflective cavity
  • magnetron sputtering to grow upper layers
  • the process of gold reflective layer to prepare nanowires use scanning electron microscope to observe the surface morphology of nanowires. If the edges of the nanowires are clear and the line roughness is small, it meets the design requirements.
  • the two low-level signal outputs are low-level, and the high-level and low-level signals caused by the photon response are output as high-level.
  • the present invention can effectively inhibit the generation of the dark count of the detector.
  • the later process is improved to further improve the coupling efficiency of the dark count of the SNSPD, and it is expected to completely suppress the dark count of the SNSPD system and greatly improve the detector.
  • the signal-to-noise ratio is improved to improve the coupling efficiency of the dark count of the SNSPD, and it is expected to completely suppress the dark count of the SNSPD system and greatly improve the detector.
  • Figure 1 is the structural difference between the dual-wire structure SNSPD and the traditional SNSPD.
  • Figure 2 is the corner design of the nanowire.
  • Figure 3 is the nanowire chip structure of the dual-wire structure.
  • Figure 4 is the bias IV characteristic curve of the nanowire. It is the circuit design of double-wire structure to reduce the dark count.
  • Figure 6 is the growth curve of dark count
  • Figure 7 is the coupling waveform of dark count
  • Figure 8 is the growth curve of light response
  • Figure 9 is the preparation process of nanowires
  • Figure 10 is The detector outputs pulses.
  • Figure 11 is the reflection of the two dark counts on the device
  • Figure 12 is the surface morphology of the nanowire.
  • the dual-wire structure SNSPD is a device composed of two niobium nitride (NbN) nanowires that are intertwined without crossing each other.
  • NbN niobium nitride
  • the difference between the dual-wire structure SNSPD and the traditional nanowire structure is that the traditional nanowire is a single nanowire. Wire winding.
  • the detector is biased at a position slightly lower than its superconducting critical current when it is working.
  • the nanowire absorbs photons, the superconducting state of the absorption region is destroyed and a heat island is generated.
  • the heat island area grows to a certain extent with the assistance of the current Joule heat.
  • the photon absorption process of the detector appears as a rapid rise in the circuit, followed by an exponentially decayed electrical pulse. This pulse signal Amplify, the detector can distinguish the arrival of a single photon, and the output pulse of the detector is shown in Figure 10.
  • Two nanowires are arranged side by side, the length from left to right is designed to be 10-20 ⁇ m, the line width of the nanowires is designed to be 50-80nm, the shortest spacing of the nanowires is designed to be 50-120nm, and the longest spacing is designed to be 300-400nm.
  • the thickness is designed to be 5-8nm, and the winding cycle is designed to be 9-20 times.
  • the corner design of the nanowire is shown in Figure 2.
  • the outer nanowire surrounds the inner nanowire.
  • the inner radius of the corner is designed to be 200-250nm, and the outer radius is designed to be 300-400nm.
  • the width of a single line is 80nm, and two nanowires are used.
  • the 4 electrodes are led out separately, and the winding cycle is designed to be 9 times to avoid the crowding effect of superconducting current.
  • the structure of the dual-wire nanowire chip is shown in Figure 3.
  • the chip side length is 5mm
  • the center area is a nanowire structure
  • the electrode is designed as a gradual structure from wide to narrow.
  • the widest part is 0.7mm, which is connected to the external circuit, and the narrowest part is 0.01mm, which is connected to the nanowire.
  • the nanowire preparation process is shown in Figure 9. Magnetron sputtering deposition of NbN film, electron beam exposure to prepare nanowires, reactive ion etching to transfer nanowires, ultraviolet lithography to prepare gold electrodes, and plasma-enhanced chemical weather deposition (PECVD) to prepare the upper layer The reflective cavity and magnetron sputtering to grow the upper gold reflective layer. After the nanowires are prepared, use a scanning electron microscope to observe the surface morphology of the nanowires. Require.
  • PECVD plasma-enhanced chemical weather deposition
  • the IV characteristic curve of the nanowire is characterized. As shown in Figure 4, one nanowire does not work, and the volt-ampere characteristic of the other nanowire is measured. At a temperature of 200mK, the superconducting critical current of the two nanowires It is 11.7uA, and the hysteresis current is 2.0uA.
  • the No. 1 nanowire couples its own intrinsic dark count to the No. 2 nanowire.
  • the dark count coupling efficiency is about 0.5, that is, about half of the intrinsic dark count of the No. 1 nanowire can excite the No. 2 nanowire to produce the corresponding DCR.
  • the oscilloscope captures the mutually coupled waveform of the dark counts.
  • the dark counts between the two nanowires appear in the oscilloscope at the same time.
  • the dark counts of the two nanowires appear almost simultaneously with a time difference of 1ns. the following.
  • the light response of the No. 1 nanowire basically cannot increase the light response count rate of the No. 2 nanowire.
  • the No. 2 nanowire is biased with the No. 1 nanowire.
  • the light response of the current changes, the light intensity used is 13pW, the light wavelength is 1064nm, the temperature of the device is 2.5K, the light response of No. 2 has no obvious growth trend with the increase of the light response of No. 1, between the two nanowires There is basically no coupling phenomenon in the light response.
  • the design circuit is shown in Figure 5, using optical fibers to introduce optical signals into the photosensitive area of the detector , Make the detector work in a temperature environment of 2.5K.
  • Two nanowires are used to output two signals respectively, represented by pulses No. 1 and No. 2.
  • the signals include photon response signals and dark count signals; the two signals are input into a voltage comparator to form a TTL signal, with No. 4 and No. 5 pulse represents the dark count signal output by SNSPD, and No. 3 and No. 6 pulses represent the photon response signal.
  • Two signals are input to the exclusive OR gate.
  • the photon response will not affect each other. It is output randomly in time sequence.
  • the two signals are high level at the same time.
  • the XOR gate output is low, it corresponds to the dark counting situation; when only one of the two signals is high, the XOR gate output is high, corresponding to the photon response; both signals are low At the level, the XOR gate output is low, which corresponds to the situation where there is no photon response and no dark count.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Measurement Of Radiation (AREA)
  • Superconductor Devices And Manufacturing Methods Thereof (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)

Abstract

本发明公开了一种基于双线结构消减SNSPD暗计数的设计，将2根氮化铌纳米线不交叉的相互缠绕，构成双线结构的超导纳米线单光子探测器SNSPD，用一根纳米线调控另一根纳米线的行为，调节偏置电流接近超导临界电流；采用光纤将光信号引入探测器光敏区，通过2根纳米线分别输出2路信号，使两根纳米线之间的暗计数相互激发，经电压比较器和异或门，消减暗计数信号，保留光子响应信号；通过使用双线结构SNSPD独特性能，能有效抑制探测器暗计数的产生，后期通过工艺提升，进一步提高SNSPD暗计数的耦合效率，有望实现完全抑制SNSPD系统的暗计数，极大提升探测器的信噪比。

Description

一种基于双线结构消减SNSPD暗计数的设计 技术领域
本发明属于超导单光子探测技术领域，具体涉及一种暗计数消减技术。
背景技术
超导纳米线单光子探测器(SNSPD)是一种高效、快速、准确的探测单光子的新型光探测器，感光部分为使用超导薄膜材料制成的纳米线蜿蜒结构。
探测器工作时，被偏置在稍低于其超导临界电流的位置，当纳米线吸收光子后，吸收区域的超导态被破坏，产生热岛，热岛区域在电流焦耳热的协助下，增长到一定范围，经纳米线自身和衬底的冷却，热岛消失，纳米线恢复到初始状态。
探测器吸收光子的过程，在电路上表现为快速上升、随后指数衰减的电脉冲，通过将此脉冲信号放大，探测器就可以鉴别单光子的到达。
暗计数(Dark Count Rate，DCR)是指，在没有光子入射时，SNSPD输出的响应脉冲，标志着SNSPD器件的本底噪声，一般将SNSPD的暗计数分为背景辐射暗计数和本征暗计数，背景辐射暗计数主要是光纤的背景热辐射和外界干扰造成的，本征暗计数的成因目前还没有得到明确的实验证实，理论物理学家们围绕这个问题，给出了不同的解释。
目前大家比较能接受的暗计数的形成，有基于磁通-反磁通破对和基于纳米线边界磁通穿越两种，背景辐射暗计数一般在低偏置电流时起作用，计数率相对较低，一般为几到几十Hz，本征暗计数在偏置电流接近超导临界电流时起作用，计数率相对较高，而且随着电流增加，本征暗计数剧烈增加。
暗计数会降低系统的信噪比，降低SNSPD输出信号的可靠性，当SNSPD应用于通信系统中，DCR会大大增加系统的误码率，因此，降低SNSPD暗计数一直是研究的热门方向。
对于背景辐射暗计数，目前常用的方法主要是，在低温下采用光纤滤波器的方式，消除背景辐射，而对于本征暗计数，目前为止还没有比较好的通用方法。
发明内容
本发明为了解决现有技术存在的问题，提出了一种双线结构SNSPD器件，制备2根相互缠绕而又不相交叉的纳米线，为了实现上述目的，通过器件的独特性能，结合外部电路的处理，能够有效的抑制SNSPD系统本征暗计数的影响，本发明采用了以下技术方案。
将2根氮化铌纳米线不交叉的相互缠绕，构成双线结构的超导纳米线单光子探测器SNSPD，用一根纳米线调控另一根纳米线的行为，调节偏置电流接近超导临界电流；采用光纤将光信号引入探测器光敏区，通过2根纳米线分别输出2路信号，使两根纳米线之间的暗计数相互激发，经电压比较器和异或门，消减暗计数信号，保留光子响应信号。
进一步的，将两根氮化铌纳米线不交叉的相互缠绕，包括：将2根纳米线并排排列，从左到右的长度为10至20μm，宽度为50～80nm，厚度设计为5～8nm，2根纳米线的最小间距为50～120nm,最大间距为300～400nm，缠绕周期为9～20次。
纳米线转角处的外部纳米线包围内部纳米线，转角内部半径为200～250nm，外部半径为300～400nm.单根线条宽度80nm，2根纳米线使用4根电极分别引出，缠绕周期为9次。
纳米线芯片边长5mm，中心区域为纳米线结构，周围分布11根由宽到窄的渐变电极，最宽处0.7mm，连接外部电路，最窄处0.01mm，连接纳米线。
进一步的，采用磁控溅射沉积NbN薄膜、电子束曝光制备纳米线条、反应离子刻蚀转移纳米线条、紫外光刻制备金电极、等离子增强化学气象沉积制备上层反射腔、磁控溅射生长上层金反射层的工艺制备纳米线，使用扫描电子显微镜观察纳米线表面形貌，若纳米线边缘清晰、线条粗糙度小，则符合设计要求。
进一步的，断开一根纳米线不工作，测量另一根纳米线的伏安特性，在200mK温度下，使两根纳米线的超导临界电流为11.7uA，回滞电流为2.0uA。
保持2根纳米线之间的光响应不耦合，使一根纳米线将自身的本征暗计数耦合到另一根纳米线，在时序上同时输出。
将2路包含光子响应信号和暗计数信号的脉冲信号输入电压比较器，整形成TTL信号输入异或门，将暗计数导致的两路高电平信号输出为低电平，将没有光子响应导致的两路低电平信号输出为低电平，将光子响应导致的一路高电平、一路低电平的信号输出为高电平。
本发明通过使用双线结构SNSPD独特性能，能有效抑制探测器暗计数的产生，后期通过工艺提升，进一步提高SNSPD暗计数的耦合效率，有望实现完全抑制SNSPD系统的暗计数，极大提升探测器的信噪比。
附图说明
图1是双线结构SNSPD和传统SNSPD在结构上的区别，图2是纳米线的转角设计，图3是双线结构纳米线芯片结构，图4是纳米线的偏置IV特性曲线，图5是双线结构消减暗计数的电路设计，图6是暗计数的增长曲线，图7是暗计数的耦合波形，图8是光响应的增长曲线，图9是纳米线的制备流程，图10是探测器输出脉冲，图11是两种暗计数在器件上的反映，图12是纳米线表面形貌。
具体实施方式
以下结合附图对本发明的技术方案做具体的说明。
双线结构SNSPD是由两根相互缠绕而又不交叉的氮化铌(NbN)纳米线构成的器件，双线结构SNSPD与传统的纳米线结构不同之处在于，传统的纳米线为单根纳米线缠绕。
探测器工作时被偏置在稍低于其超导临界电流的位置，当纳米线吸收光子后，吸收区域的超导态被破坏，产生热岛，热岛区域在电流焦耳热的协助下增长到一定范围，随后经过纳米线自身和衬底的冷却，热岛区域消失，纳米线恢复到初始状态，探测器吸收光子的过程在电路上表现为快速上升，随后指数衰减的电脉冲，通过将此脉冲信号放大，探测器就可以鉴别单光子的到达，探测器输出脉冲如图10所示。
背景辐射暗计数一般在低偏置电流时起作用，计数率相对比较低，一般为几到几十Hz，本征暗计数在偏置电流接近超导临界电流的时候起作用，计数率相对较高，而且随着电流增加，本征暗计数剧烈增加，两种暗计数在器件上的具体反映如图11所示。
双线结构SNSPD和传统SNSPD的区别如图1所示，为了叙述方便，将两根纳米线的编号分别定义为1号和2号。
两根纳米线并排排列，从左到右的长度设计为10～20μm，纳米线的线宽设计为50～80nm，纳米线的最短间距设计为50～120nm,最长间距设计为300～400nm，厚度设计为5～8nm，缠绕周期设计为9～20次。
纳米线的转角处设计如图2所示，外部的纳米线包围内部的纳米线，转角内部半径设计为200～250nm，外部半径设计为300～400nm.单根线条宽度80nm，两根纳米线使用4根电极分别引出，缠绕周期设计为9次，避免超导电流的拥挤效应。
双线结构纳米线芯片结构如图3所示，芯片边长5mm，中心区域为纳米线结构，周围为11根金电极，实际使用的只有1、3、9、11四根电极，其他电极备用，电极由宽到窄，设计为渐变结构，最宽处0.7mm，连接外部电路，最窄处0.01mm，连接纳米线。
纳米线制备流程如图9所示，磁控溅射沉积NbN薄膜、电子束曝光制备纳米线条、反应离子刻蚀转移纳米线条、紫外光刻制备金电极、等离子增强化学气象沉积(PECVD)制备上层反射腔、磁控溅射生长上层金反射层，纳米线制备完成后，使用扫描电子显微镜观察纳米线表面形貌，如图12所示，若纳米线边缘清晰、线条粗糙度小，则符合设计要求。
器件制备完毕，表征纳米线的IV特性曲线，如图4所示，一根纳米线不工作，测量另一根纳米线的伏安特性，在200mK温度下，两根纳米线的超导临界电流为11.7uA，回滞电流为2.0uA。
使用双线结构SNSPD中的一根纳米线来调控另一根纳米线的行为，如暗计数、IV特性、光响应等特征，调节偏置电流接近超导临界电流，保持光响应不耦合，使1号纳米线将自身的本征暗计数耦合到2号纳米线。
如图6所示，在50mK温度时，当1号纳米线的偏置电流从11.5uA变化到12uA时，产生的基本都是本征暗计数，纳米线2的暗计数增加量分别以不同的增长速率以S型曲线增 长。
在纳米线2的偏置电流接近临界电流时，DCR增量接近饱和，将1号纳米线的暗计数一定时，2号纳米线暗计数增加量与1号纳米线暗计数的比值，定义暗计数耦合效率η 12。
暗计数耦合效率约为0.5，也就是说，约有一半的1号纳米线的本征暗计数能激发2号纳米线产生相应的DCR。
如图7所示，示波器捕捉到暗计数相互耦合的波形，两根纳米线之间的暗计数同时出现在示波器中，在时域上，两根纳米线的暗计数几乎同时出现，时间差在1ns以下。
与暗计数能相互耦合的情况所不同的是，1号纳米线的光响应基本不能增加2号纳米的光响应计数率，如图8所示，2号纳米线随着1号纳米线偏置电流变化的光响应变化，所用光强为13pW，光波长为1064nm，器件所处温度为2.5K，2号光响应随着1号光响应的增加没有明显的增长趋势，两根纳米线之间的光响应基本没有耦合现象。
利用双线结构SNSPD中，纳米线之间的暗计数存在耦合，耦合效率为50％，而光响应不存在耦合的现象，设计电路如图5所示，采用光纤将光信号引入探测器光敏区，使探测器工作在2.5K的温度环境。
通过2根纳米线分别输出2路信号，用1号和2号脉冲分别表示，信号中包含光子响应信号和暗计数信号；将2路信号输入电压比较器，整形成TTL信号，用4号和5号脉冲表示SNSPD输出的暗计数信号，3号和6号脉冲表示光子响应信号，将2路信号输入异或门。
由于两根纳米线之间的暗计数相互激发，在时序上同时输出，而光子响应不会相互影响，在时序上随机输出，利用异或门的逻辑运算，两路信号同时为高电平的时候，异或门输出为低电平，对应暗计数的情况；两路信号只有一路为高电平的时候，异或门输出为高电平，对应光子响应的情况；两路信号都为低电平的时候，异或门输出为低电平，对应没有光子响应，也没有暗计数的情况。
Figure PCTCN2021085775-appb-000001
通过这样的方式，在异或门输出端，有效抑制SNSPD的暗计数输出，最终输出只有3号和6号脉冲，也就是光子响应信号。
上述作为本发明的实施例，并不限制本发明，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均包含在本发明的保护范围之内。

Claims (8)

  1. 一种基于双线结构消减SNSPD暗计数的设计，其特征在于，包括：将2根氮化铌(NbN)纳米线不交叉的相互缠绕，构成双线结构的超导纳米线单光子探测器SNSPD，用一根纳米线调控另一根纳米线的行为，调节偏置电流接近超导临界电流；采用光纤将光信号引入探测器光敏区，通过2根纳米线分别输出2路信号，使两根纳米线之间的暗计数相互激发，经电压比较器和异或门，消减暗计数信号，保留光子响应信号。
  2. 根据权利要求1所述的基于双线结构消减SNSPD暗计数的设计，其特征在于，所述将两根氮化铌纳米线不交叉的相互缠绕，包括：将2根纳米线并排排列，从左到右的长度为10至20μm，宽度为50～80nm，厚度设计为5～8nm，2根纳米线的最小间距为50～120nm,最大间距为300～400nm，缠绕周期为9～20次。
  3. 根据权利要求1或2所述的基于双线结构消减SNSPD暗计数的设计，其特征在于，所述双线结构，包括：纳米线转角处的外部纳米线包围内部纳米线，转角内部半径为200～250nm，外部半径为300～400nm.单根线条宽度80nm，2根纳米线使用4根电极分别引出，缠绕周期为9次。
  4. 根据权利要求1所述的基于双线结构消减SNSPD暗计数的设计，其特征在于，所述超导纳米线单光子探测器SNSPD，包括：纳米线芯片边长5mm，中心区域为纳米线结构，周围分布11根由宽到窄的渐变电极，最宽处0.7mm，连接外部电路，最窄处0.01mm，连接纳米线。
  5. 根据权利要求1所述的基于双线结构消减SNSPD暗计数的设计，其特征在于，所述超导纳米线单光子探测器SNSPD，包括：采用磁控溅射沉积NbN薄膜、电子束曝光制备纳米线条、反应离子刻蚀转移纳米线条、紫外光刻制备金电极、等离子增强化学气象沉积制备上层反射腔、磁控溅射生长上层金反射层的工艺制备纳米线，使用扫描电子显微镜观察纳米线表面形貌，若纳米线边缘清晰、线条粗糙度小，则符合设计要求。
  6. 根据权利要求1所述的基于双线结构消减SNSPD暗计数的设计，其特征在于，所述调节偏置电流接近超导临界电流，包括：断开一根纳米线不工作，测量另一根纳米线的伏安特性，在200mK温度下，使两根纳米线的超导临界电流为11.7uA，回滞电流为2.0uA。
  7. 根据权利要求1所述的基于双线结构消减SNSPD暗计数的设计，其特征在于，所述使两根纳米线之间的暗计数相互激发，包括：保持2根纳米线之间的光响应不耦合，使一根纳米线将自身的暗计数耦合到另一根纳米线，在时序上同时输出。
  8. 根据权利要求7所述的基于双线结构消减SNSPD暗计数的设计，其特征在于，所述经电压比较器和异或门，包括：将2路包含光子响应信号和暗计数信号的脉冲信号输入电 压比较器，整形成TTL信号输入异或门，将暗计数导致的两路高电平信号输出为低电平，将没有光子响应导致的两路低电平信号输出为低电平，将光子响应导致的一路高电平、一路低电平的信号输出为高电平。
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