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Long Yaoqiang, Shan Xiao, Wu Wen, Liang Yan. Low-noise GHz InGaAs/InP single-photon detector (invited)[J]. Infrared and Laser Engineering, 2023, 52(3): 20220901. doi: 10.3788/IRLA20220901
Citation: Long Yaoqiang, Shan Xiao, Wu Wen, Liang Yan. Low-noise GHz InGaAs/InP single-photon detector (invited)[J]. Infrared and Laser Engineering, 2023, 52(3): 20220901. doi: 10.3788/IRLA20220901

Low-noise GHz InGaAs/InP single-photon detector (invited)

doi: 10.3788/IRLA20220901
Funds:  National Key Research and Development Program of China (2021YFB2801100); National Natural Science Foundation of China (62175152, 61927813)
  • Received Date: 2022-12-27
  • Rev Recd Date: 2023-02-24
  • Available Online: 2023-03-20
  • Publish Date: 2023-03-25
  •   Objective  With the development of quantum information science, laser radar and deep space detection, the traditional linear photoelectric detection technology has been unable to meet the needs of sensitive optical signal detection. The single-photon detection technology has gradually become an important research in the fields of weak light detection. InGaAs/InP avalanche photodiodes (APDs) are widely used in near-infrared single-photon detection due to the small size, low power consumption and fast response. The detection rate of most commercial InGaAs/InP detectors is at the level of 100 MHz, which cannot meet the application requirements for high counting rate. Meanwhile, low noise of the APD will bring smaller false counts to the system and further improve the performance. Therefore, a low-noise InGaAs/InP single-photon detector operating at the repetition frequency of GHz was demonstrated. Furthermore, the whole detector is evaluated with the quantum detector tomography technology, providing support for its application in quantum information technology such as quantum communication and quantum computation.   Methods  In order to determine the detection frequency of gating signals, the response bandwidth of the APD is analyzed in the linear mode, and the bandwidth range is calculated to be 1-2 GHz. The spectral distribution characteristics of APD avalanche and noise signals are analyzed in the Geiger mode. It could be figured out that the noise is mainly distributed in the gating frequency and its harmonic frequencies, while the avalanche signal is mainly distributed below 1 GHz. Therefore, a cascade scheme of sine wave gating combined with low-pass filtering is proposed (Fig.3). The detector comprises high-speed gate generation and delay regulation module, temperature feedback control module, etc. Sine wave gating could be precisely controlled from many parameters which include frequency, amplitude, delay in a wide range. Feedback is added in the temperature control module to improve the stability of the detector. In addition, quantum detector tomography (Fig.2) is introduced to calibrate the detector, which is regarded as a "dark box". The positive operator-value measuring matrix can fully characterize the detector, which is obtained from input states and output results. The Wigner function is employed to describe whether the detector has quantum properties at high input photons.   Results and Discussions   Sine wave gating combined with low-pass filtering is designed in the system, and signal-to-noise ratio is over 40 dB. The relationship between the detection efficiency and the afterpulse probability at the frequencies of 1-2 GHz is recorded. When the working rate is 1.5 GHz and the detection efficiency is set to be 20.0%, the afterpulse probability is 6.6% with the dark count rate of only 6.7×10−7 per gate (Fig.4). At constant detection efficiency of 20.0%, the DC bias voltage of the APD increases with temperature, showing a linear trend. While the afterpulse probability decreases, showing a contracting trend. The dark count rate degrades with the decrease of temperature and the trend is reversed at −30 ℃ (Fig.5), which might be related to high afterpulse or the intrinsic defection of APD. During the 12-hour test period, the detector performs perfectly stable and the variance of detection efficiency is 1% (Fig.8). Quantum detector tomography technology is employed to verify that high background noise does not affect the quantum properties (Fig.7).   Conclusions  A GHz low noise InGaAs/InP detector is designed, and its detection efficiency, false count, saturation count rate and stability are explored. Based on the analysis of the response bandwidth of APD, a cascade scheme of sine wave gating combined with low-pass filtering is determined, realizing a low noise single photon detection below 2 GHz. In addition, quantum detector tomography technology is employed to calibrate the detector and verify its quantum properties. The structure of the detection technology is simple and the detector can run stably in the long term, which provides strong support for the practical application of single photon detector in deep space communication, laser mapping, optical time domain reflection and other fields.
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Low-noise GHz InGaAs/InP single-photon detector (invited)

doi: 10.3788/IRLA20220901
  • School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
Fund Project:  National Key Research and Development Program of China (2021YFB2801100); National Natural Science Foundation of China (62175152, 61927813)

Abstract:   Objective  With the development of quantum information science, laser radar and deep space detection, the traditional linear photoelectric detection technology has been unable to meet the needs of sensitive optical signal detection. The single-photon detection technology has gradually become an important research in the fields of weak light detection. InGaAs/InP avalanche photodiodes (APDs) are widely used in near-infrared single-photon detection due to the small size, low power consumption and fast response. The detection rate of most commercial InGaAs/InP detectors is at the level of 100 MHz, which cannot meet the application requirements for high counting rate. Meanwhile, low noise of the APD will bring smaller false counts to the system and further improve the performance. Therefore, a low-noise InGaAs/InP single-photon detector operating at the repetition frequency of GHz was demonstrated. Furthermore, the whole detector is evaluated with the quantum detector tomography technology, providing support for its application in quantum information technology such as quantum communication and quantum computation.   Methods  In order to determine the detection frequency of gating signals, the response bandwidth of the APD is analyzed in the linear mode, and the bandwidth range is calculated to be 1-2 GHz. The spectral distribution characteristics of APD avalanche and noise signals are analyzed in the Geiger mode. It could be figured out that the noise is mainly distributed in the gating frequency and its harmonic frequencies, while the avalanche signal is mainly distributed below 1 GHz. Therefore, a cascade scheme of sine wave gating combined with low-pass filtering is proposed (Fig.3). The detector comprises high-speed gate generation and delay regulation module, temperature feedback control module, etc. Sine wave gating could be precisely controlled from many parameters which include frequency, amplitude, delay in a wide range. Feedback is added in the temperature control module to improve the stability of the detector. In addition, quantum detector tomography (Fig.2) is introduced to calibrate the detector, which is regarded as a "dark box". The positive operator-value measuring matrix can fully characterize the detector, which is obtained from input states and output results. The Wigner function is employed to describe whether the detector has quantum properties at high input photons.   Results and Discussions   Sine wave gating combined with low-pass filtering is designed in the system, and signal-to-noise ratio is over 40 dB. The relationship between the detection efficiency and the afterpulse probability at the frequencies of 1-2 GHz is recorded. When the working rate is 1.5 GHz and the detection efficiency is set to be 20.0%, the afterpulse probability is 6.6% with the dark count rate of only 6.7×10−7 per gate (Fig.4). At constant detection efficiency of 20.0%, the DC bias voltage of the APD increases with temperature, showing a linear trend. While the afterpulse probability decreases, showing a contracting trend. The dark count rate degrades with the decrease of temperature and the trend is reversed at −30 ℃ (Fig.5), which might be related to high afterpulse or the intrinsic defection of APD. During the 12-hour test period, the detector performs perfectly stable and the variance of detection efficiency is 1% (Fig.8). Quantum detector tomography technology is employed to verify that high background noise does not affect the quantum properties (Fig.7).   Conclusions  A GHz low noise InGaAs/InP detector is designed, and its detection efficiency, false count, saturation count rate and stability are explored. Based on the analysis of the response bandwidth of APD, a cascade scheme of sine wave gating combined with low-pass filtering is determined, realizing a low noise single photon detection below 2 GHz. In addition, quantum detector tomography technology is employed to calibrate the detector and verify its quantum properties. The structure of the detection technology is simple and the detector can run stably in the long term, which provides strong support for the practical application of single photon detector in deep space communication, laser mapping, optical time domain reflection and other fields.

    • 随着量子信息科学[1]、激光雷达[2-4]、深空探测[5]等技术的快速发展,传统的线性光电探测技术已经无法满足灵敏光信号检测的需求。新型的单光子探测技术逐渐成为国内外研究弱光探测领域的重要研究内容。常见的单光子探测器有InGaAs/InP雪崩光电二极管 (APD)、光电倍增管(PMT)、超导纳米线单光子探测器(SNSPD)[6]等。然而PMT驱动电压高,SNSPD制冷条件比较苛刻。文中主要研究InGaAs/InP APD实现近红外单光子探测。

      InGaAs/InP APD通常工作在盖革模式下来响应单个光子。单个载流子触发产生的自持雪崩无法自然停止,为了再次响应光子信号,需要快速将APD加载的偏压降低至雪崩以下,对其抑制后恢复到探测模式。雪崩过程中,倍增层部分载流子被其中的缺陷及杂质捕获,随后在不可预期的时间点由热激发释放出来触发雪崩,即后脉冲[7]。GHz门控信号加载到APD时能够快速实现雪崩和淬灭的效果,提升了探测速率,同时有利于降低载流子数量,从而降低后脉冲。对于需要高计数率的应用来说,提高探测器的门控频率非常重要。然而,随着工作速率的提升,一方面门控信号在APD上产生的容性噪声增大,APD雪崩持续时间变短导致有效光生信号变小,探测器信噪比变低;另一方面,APD冷却时间变短,光生载流子无法得到充分释放,探测器误计数增大。因此高速门控的关键技术就是从较大的容性响应微分信号中提取微弱的雪崩信号[8]。目前发展较为成熟的方案主要有自差分自平衡、正弦门控方案等。2007年,Z. L. Yuan等提出自差分平衡方案,在探测频率为1.25 GHz,探测效率10.8%,后脉冲概率为6.16% [9]。2009年,华东师范大学曾和平课题组采用自差分法设计了重复频率200 MHz的InGaAs/InP APD单光子探测器[10]。自差分平衡方案是将信号分成两路,将其中一路延时一个时钟周期与另一路差分从而抵消尖峰噪声。该方案缺点是难以精确保证两路信号的幅度和延时,雪崩信号进行差分后幅度减小等。2006年,日本大学N. Namekata等提出正弦门控方案,采用带阻滤波器除去APD输出的容性噪声,门控频率为800 MHz,在探测效率为8.5%时,后脉冲概率为6.0%[11]。随后N. Namekata等在 2020 年报道了过偏压超过12 V,高探测效率的正弦门控 InGaAs/InP SPAD,在1.27 GHz门控频率下,55.9%探测效率时,后脉冲概率仅为4.8%[12]。然而正弦门控带阻方案面临着雪崩信号完整性破坏,时间抖动变大等问题[13]。2016年,重庆理工大学高家利设计了1~1.3 GHz门控的探测器,探测效率为18%时,暗计数为5.6×10−6/gate[14]。中国科学技术大学课题组在2017年报道了采用混合封装的雪崩提取单片读出电路技术,将级联的低通滤波器与低噪声放大器封装为集成电路芯片,实现了门控探测频率1.25 GHz,探测效率为27.5%,暗计数率为1.2 kHz的InGaAs/InP单光子探测[15]。随后该课题组在2020年报道了室温下使用1.25 GHz正弦门控,探测效率高达 60%的InGaAs/InP单光子探测器[16]。2022年,云南大学报道了室温SPAD,门控频率为1 MHz,探测效率为23.26%,暗计数率为1.2 kHz,后脉冲概率为0.42%。近年来,韩国的Wooriro公司、美国Princetion公司、欧洲Toshiba Research公司开发出了商用InGaAs/InP 单光子探测器[17]。不过这些商用产品的工作频率一般在百兆赫兹级。2019年,笔者课题组报道了100 MHz~1.25 GHz探测器,分析了InGaAs/InP APD雪崩和噪声信号的频谱分布特征,发现尖峰噪声分布在门控频率及其谐波位置,雪崩信号则主要分布在门控信号基频以下位置[18]

      在此基础上提出低通滤波技术,采用截止频率低于门控信号基频的低通滤波器,滤除高频尖峰噪声信号的同时尽可能多地保留有用的低频雪崩信号。为了保障探测器的信噪比,采用了低通滤波级联方案。APD的响应带宽约为2.3 GHz,实验中设计了1.0~2.0 GHz门控系统方案。对门控信号做了精密的调控,包括重复频率、幅度、延时等,在温度控制模块加入反馈来提高稳定性。对于各个模块,采用板级集成来缩小尺寸,并用上位机来实现对APD的性能表征,可以快速记录GHz探测频率、APD输出计数、温度等参数指标。当工作速率为1.5 GHz、探测效率设置为20.0%时,后脉冲概率为6.6%,暗计数率仅为6.7×10−7/gate,并且能够12小时稳定运行。为了完整描述探测器的量子特性,引入量子探测器层析技术进行标定。

    • InGaAs/InP APD (GD5522-SM-FC/UPC,重庆光电技术研究所)为单模光纤耦合入射光子。在线性模式下分析测试了InGaAs/InP APD的响应带宽。在光脉冲宽度50 ps的情况下,使用带宽4 GHz的DSA 70404 C系列示波器在APD线性模式测得结果如图1所示。上升时间$ \tau $约为151.4 ps,由$ BW=0.35/\tau $计算可知APD的响应带宽约为2.3 GHz。考虑到盖革模式比线性模式增益高得多,根据增益与带宽的关系,盖革模式下的带宽有所下降。最终将门控频率设置在1.0~2.0 GHz。

      Figure 1.  APD test chart in linear mode

    • 量子探测器层析(Quantum Detector Tomography, QDT)[19]省去了传统“自下而上”的标定方法。将量子探测器视为“暗箱”,由已知的输入态和测量得到的输出结果来获得正定算子取值测度(Positive Operator-valued Measure, POVM)矩阵[20],可全面表征探测器。

      由波恩定则[21],探测器输出结果为${{s}}$的概率由以下公式表示:

      式中:入射场密度为$\; \widehat{\rho } $$ {P}_{\rho ,s} $探测输出结果为${s} $的概率;${\widehat{\textit{Π }}_{s}}$ 为POVM矩阵。

      QDT实验装置图如图2所示,用脉冲激光器调节数字衰减器使得每脉冲光子数直至探测器输出饱和计数,根据输入平均光子数$\; \mu $,探测器探测到光子输出计数$ {t}_{\mu } $,计算探测器输出概率:

      式中:T为激光器参考频率。

      Figure 2.  Diagram of the QDT experimental setup

      为了进一步研究探测器的量子性能,引入Wigner函数[22],Wigner函数是动量与位置联合的准概率分布,原点函数值负值表示探测器具有量子特性[23]

      对应于探测器POVM矩阵$ {\mathrm{\Pi }}_{z} $的Wigner函数可以表示为:

      式中:$M$为截止光子数; $ {\theta }_{z,n} $为当n个光子入射时探测器探测到z个光子的条件概率;$ {W}_{n}\left(x,p\right) $为每个光子数态对应的Wigner函数;$ {L}_{n} $为拉盖尔多项式。

    • 该方案的工作原理如图3(a)所示。图中,HVC-直流偏置电压电路; FSC-频率合成器电路;VA-数字控制衰减器;AMP1-高功率放大器;HPF表示高通滤波器;LPF表示低通滤波器;AMP2-射频放大器;PSC-脉冲整形电路;PID-温控调节电路;DCC-延时电路; LD-激光器及驱动;Atten-数字光学衰减器;CM-通信电路; PC-电脑; FPGA-现场可编程门阵列。FPGA驱动锁相环频率合成器产生与参考频率相位锁定的可调GHz正弦信号,可调的范围是35 MHz~4.4 GHz,能满足门控1.0~2.0 GHz设计需求。由于放大器和频率合成器对不同频率下的增益不同,增加数字衰减器(范围0~7 dB,步进1 dB)可以灵活调节门控幅度,从而使雪崩信号质量达到最佳。有些低频信号可能会在放大器的作用下影响APD雪崩信号,使用900 MHz的高通滤波器在放大器后面来滤除GHz以下的低频噪声。将得到纯净的高频门控信号和直流偏置电压一起作用在APD阴极,使APD工作在盖革模式。由于APD的容性特征使其在雪崩时会产生图3(b)所示的尖峰噪声信号,将雪崩信号湮没。通过频谱仪分析,尖峰噪声信号主要集中分布在GHz信号基频以及谐振频率上,因此选用截止频率700 MHz的低通滤波器来滤除噪声信号。将提取出来的雪崩信号经过低噪声射频放大器放大后再滤除一次,目的是为了提高信号的信噪比。图3(b)信号幅度的电压峰峰值Vs约为601.2 mV,图3(c)中噪声峰峰值Vn约为5.92 mV,根据SNR=20 lg(Vs/Vn)=40.1 dB。此处噪声信号经过了增益为40 dB的放大器放大,故实际上噪声抑制比远大于40 dB。如图3(c)所示,尖峰噪声信号经过低通滤波后信噪比十分明显,将得到干净的雪崩信号送入脉冲整形电路整形。死时间的延长则可以屏蔽雪崩计数,降低后脉冲概率,实验设置的逻辑死时间为18 ns。将整型的脉冲信号再经过电平转换最终得到FPGA识别的数字信号,从而实现雪崩信号计数的功能。

      Figure 3.  (a) Diagram of sinusoidal gating experimental device based on low pass filtering; (b) APD output signal waveform at 1500 MHz gate frequency; (c) Avalanche signal after low-pass filter and amplification

      APD的工作温度对其探测性能至关重要,设计了PID温控调节电路,温控精度高于0.1 ℃。相对于PT100,选择灵敏度更高的PT1000作为温敏探头,通过控制16位数模转换芯片调节半导体制冷片工作电流,来达到高精度控制和长时间稳定的效果。

      1550 nm半导体激光器选择工作在脉冲模式下,脉冲宽度为50 ps,衰减后的相干光作为准单光子源。当门控信号重复频率设置在2 GHz时,测试的有效门宽为165 ps。相对于脉宽 50 ps 的脉冲光,使用高精度(步进为10 ps)的延时芯片。激光器经参考信号同步触发后,改变激光器脉冲信号与门控信号的相位位置,使其计数率最大。

      最后,通过LabVIEW上位机建立SAPD实时通信,快速分析其偏置偏压、门控频率和计数稳定性的关系。

    • InGaAs/InP APD的误计数主要包括暗计数和后脉冲。暗计数是指暗计数是 APD 在没有外界光子入射时,APD 由于自身及外界噪声影响引起的误计数。后脉冲概率$ {P}_{ap} $定义为一段时间内由前一个光子探测而后产生的后脉冲计数的概率[24]

      式中:$ {P}_{ap} $为后脉冲概率;$ {I}_{PH} $为激光器打开时,光子照射的门脉冲中的计数;$ {I}_{NI} $为没有光子入射的门脉冲中的计数;$ {I}_{D} $为激光器关闭时,每个门脉冲中的计数;R为门脉冲重复频率与光脉冲重复频率的比值。

      采用时间相关光子计数器(Time Correlated Single-photon Counter, TCSPC)对单光子探测器的后脉冲进行测量。激光脉冲的同步信号(25 MHz) 送入“Start”端口开始计数,单光子探测器的输入信号送入其 “Stop”端口。根据公式(5)计算即可获得后脉冲概率。

      在制冷温度设定−30.0 ℃,光脉冲重复频率为25.0 MHz,光在耦合APD之前衰减至0.1光子每脉冲。调节APD两端直流偏置电压至 10.0%的探测效率,测试了不同重复频率下,APD的误计数和后脉冲。如图4(a)所示,可以看到随着探测频率的提升,暗计数率和后脉冲率都在升高。后脉冲在超过1.50 GHz探测频率后变化明显。暗计数在1.50 GHz探测频率下分别为2.04、2.05、2.08×10−7/gate,暗计数变化很小维持在同一水平。暗计数超过1.50 GHz后最大只有2.5×10−7/gate, 没有数量级的改变,仍然处于很小的范围。低暗计数将给系统带来很小的噪声从而提升探测器性能。

      Figure 4.  (a) Dark counting and afterpulse probability at 10.0% detection efficiency; (b) Test chart of different detection frequencies at 20% detection efficiency

      鉴于1.00~1.5 GHz探测频率下,暗计数和后脉冲都比较小,随后又在此条件的基础上,提高探测效率,测试了不同探测频率下后脉冲的情况。如图4(b)所示,整体来看,随着探测效率的提升,不同探测频率下的后脉冲都在增加,探测效率越高增加的越明显。图中的虚线是在20.0%探测效率时,1.00、1.25、1.50 GHz探测频率的后脉冲分别为4.46%、6.62%、6.63%。在20.0%以内,后脉冲变化很小,探测效率超过20.0%后,分开的很明显。在10%探测效率这条虚线上,1.75 GHz和2.00 GHz后脉冲分别为10.4%和36.6%。高探测频率后脉冲很高的原因:是因为探测频率已经接近APD响应的极限带宽,无法快速响应信号。

    • InGaAs/InP APD是半导体器件,工作温度对其性能的影响非常大。通过上位机向FPGA发送制冷指令,分别设置了制冷温度为−50.0、−40.0、−30.0、−20.0、−10.0、0.0、10.0 ℃和室温25.0 ℃这几个比较有代表性的温度点。下面测试了1.50 GHz探测频率在20.0%探测效率时不同工作温度下直流偏置电压、后脉冲率、暗计数率的变化。

      图5(a)所示,加载在APD的直流偏置电压在−40.0~25.0 ℃呈现线性趋势,在−50.0 ℃有所下降。后脉冲整体随着温度提升而呈现下降趋势,后脉冲在−50.0 ℃到室温这个范围基本维持在6.6%。原因是APD 工作在低温时,雪崩的过程中倍增层载流子容易被陷阱能级捕获,而引发较高后脉冲。随着温度提升,倍增层的场强增大,载流子离化率大[25],被捕获的概率降低,从而后脉冲率也降低。

      Figure 5.  Performance test chart at different temperatures with 20.0% detection efficiency

      温度升高时APD 暗计数因热噪声激发的暗电流增大,误计数增大,而光生载流子会被暗电流湮没,这使得在常温下对单光子的探测极为困难。整体暗计数理论是随温度升高而升高的。但是暗计数在−50.0~−30.0 ℃中出现了反转情况。温度在−30.0 ℃时,暗计数为6.7×10−7/gate,但在此温度前后步进出现了数量级变化,而且出现了反转情况。推测其可能的原因,一是后脉冲在−30 ℃相对于热噪声占据了主导地位,从而引起反转;二是在确定的短死时间下,载流子被某一能级俘获后,在温度较高时才开始释放引发,温度较低时未释放。

    • 饱和计数率标定的方法为光子标定法,激光器发出的连续光经过衰减器衰减送入单光子探测器[24-26]。在调节偏置电压使其工作在20.0%探测效率时,通过调节数字光学衰减器(EXFO-LTB-1)增加平均入射光子数,如图6所示,探测器的饱和计数率约为56.2 MHz。饱和计数率反映了探测器探测光子通量的能力,通常为死时间的倒数。提升饱和计数率死时间相应会减少,这样也会导致后脉冲概率升高。

      Figure 6.  Counting without incident light intensity

      采集到不同平均光子数对应的输出概率后,用最大似然估计算法对公式(1)线性反演重建POVM矩阵。

      为了简化计算只考虑了探测效率和暗计数率,建立对应的POVM理论模型:

      式中:$ \eta $为探测效率;$ \nu $为暗计数/gate。

      图7(a)中发现实验数据点与QDT拟合的概率分布几乎重合,可以表明重新构建的POVM与实际量子探测器的量子特征有很好的一致性。QDT拟合和基于理论POVM拟合的概率分布也很接近,表明建立的理论模型是符合的。在光子数为0~5时,吻合度很高,三组数据具有相同的趋势。5~20光子实际与理论的曲线有所偏离。由于理论模型忽略了后脉冲概率,随着入射光子数的增加到一定数量,未被及时淬灭的光生载流子也随之增加到一定程度,导致后脉冲概率对探测器输出概率产生影响,而使理论模拟计算得到探测到光的概率相对偏高。

      Figure 7.  (a) QDT chromatography, fitting and theoretical diagram; (b) Wigner function diagram

      然后将基于QDT重建的POVM矩阵带入Wigner函数,如图7(b)所示,Wigner函数在原点处为负值验证了在高输入平均光子数时候并未破坏探测器的量子相干特性,表明探测器具备量子探测能力。

    • 对探测器的稳定性比较关心的一是探测效率的稳定性,二是探测器的工作温度稳定性。这些都是探测器实用化的必要条件。前者是整个探测器的计数稳定程度,后者主要是指APD工作温度的稳定性。计数的跳动太大或者温度变化太大都会降低探测器的实用性。这里,采用方差来评估这一参数。

      在探测频率为1.50 GHz时,探测效率设置在20.0%,12 h稳定性测试如图8所示。探测效率整条曲线的最低与最高探测效率之差为0.6%。探测效率的方差为1.0%。温度曲线上下浮动基本维持在±0.1 ℃,曲线整体集中分布,性能十分稳定。

      Figure 8.  12 hour stability test chart under 20.0% detection efficiency

    • 文中设计了一种GHz低噪声的InGaAs/InP探测器,并研究了其探测效率、误计数、饱和计数率及稳定性等特征。分析了APD的响应带宽,采用了正弦门控结合低通滤波级联方案,实现了2 GHz以下低噪声单光子探测。此外,还引入量子层析技术对探测器进行了标定,验证了其量子特性。该探测技术结构简单,能够长期稳定运行,为单光子探测器在深空通信、激光测绘、光时域反射等领域的实用化提供有力支撑。

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