Special issue-Advances in single-photon detection technology

Research progress of InGaAs single-photon avalanche focal plane (invited)
Cui Dajian, Ao Tianhong, Xi Shuiqing, Zhang Cheng, Gao Ruoyao, Yuan Junxiang, Lei Yong
2023, 52(3): 20230016. doi: 10.3788/IRLA20230016
[Abstract](823) [FullText HTML] (85) [PDF 2337KB](290)
  Significance   Single photon detector is a kind of highly sensitive device that can realize single-photon-level signal detection. Compared with photomultiplier tubes (PMT) with large dark counts rate and large device sizes and superconducting single photon detectors (SSPD) with large-volume refrigeration devices and difficult integration into arrays, the single-photon avalanche photodiode (SPAD) with small size and easy integration into arrays exhibit the advantages of high speed, high sensitivity and high quantum efficiency. InGaAs has the characteristics of direct band gap, large ionization coefficient ratio and lattice constant matching with InP, which is currently the infrared detector material with the best performance in the near-infrared band. And InGaAs/InP SPAD is an ideal detector for active laser detection at 1.06 μm and 1.55 μm. Through the integrated packaging of high-efficiency InGaAs SAPD array and counting CMOS readout integrated circuit (ROIC), the obtained InGaAs SAPD focal plane detector has the characteristics of high sensitivity, high accuracy, small size, and solid-state packaging. The device has been widely used in 3D LIDAR, deep-space laser communication, sparse photon detection and other fields and a research hotspot in the field of single-photon detection in recent years.   Progress   The research progress of InGaAs SAPD focal plane detector can be illustrated by the performance improvement of SPAD array chip and the application progress of ROIC. And the research progress of SPAD array chip includes the research progress of array scale and pixel center distance, crosstalk suppression, photo detection efficiency (PDE) and dark count rate (DCR). The array scale and pixel center spacing of the SPAD array chip determine the spatial resolution of the device. In the early stage, a single CMOS ROIC and a SPAD wafer were electrically connected by face-to-face bonding with epoxy resin, but the disadvantage was that it occupied a large area. Furthermore, by optimizing the device structure and using indium column interconnection, the pixel spacing of the device can be reduced to 50 μm (Fig. 5). In China, the 64×64 InGaAs SPAD focal plane detector developed by Chongqing Institute of Optoelectronic Technology is shown in Fig. 6, which has been successfully extended to 256×64, and the performance parameters are shown in Table1. For a SPAD large array device with high gain characteristics, a very small amount of photons or drift current generated by neighboring pixels is an important factor that generates crosstalk and affects imaging quality. Effective ways to reduce crosstalk include: using planar isolation trench method, setting spectral filter layer and spatial filter layer method (Fig. 7(c)), and pixel isolation technology combined with substrate removal. Among them, the pixel isolation technology can be applied to the manufacture of avalanche focal plane devices to ensure high detection efficiency and effectively suppress array pixel crosstalk. PDE and DCR are parameters that reflect the ability of a device to detect photons correctly. The PDE can be improved by optimizing the parameters of each material layer in the SPAD device structure through the established mathematical model. And DCR can be reduced by improving the quality of the epitaxial material. InGaAs SPAD focal plane detectors have different application directions such as 3D LIDAR, deep-space laser communication, sparse photon detection, thus there are also different solutions for CMOS ROIC. The Flash laser radar system that detects the laser echo by the SPAD array chip is suitable for the application that needs to accurately quantify the "photon time of flight". At present, the mainstream process node of the CMOS ROIC used for the SPAD array chip is 180 nm, which has the characteristics of low power consumption, high time resolution and high frame frequency. The lidar system using a large array of InGaAs SPAD focal plane detector can realize wide-area topographic mapping and fast imaging with an elevation difference of 1000-2500 m, with a resolution of ten-centimeters-level (Fig. 9). The high-sensitivity InGaAs SPAD focal plane detector with small size and integrated capture, tracking and communication can also be used as a receiver for ultra-long-distance laser communication links. Currently, asynchronous readout circuit architectures are available to meet the requirements of shorter readout times and larger data volumes than lidar in optical communication applications (Fig. 11). The InGaAs SPAD focal plane detector with asynchronous ROIC has realized the two-way laser communication link between the lunar orbit and the ground (Fig. 10), with a highest uplink transmission of hundred-Mbps-level. The avalanche focal plane with high PDE and low DCR can also be used to count the number of photons arriving at each pixel. In order to satisfy the counting function requirements, a readout circuit scheme with a counter is used, including counting overflow bit (Fig. 12), multi-statistical time data superposition, etc.   Conclusions and Prospects   SPAD is a photodetection device with high sensitivity and high temporal resolution. Develop infrared high-speed, low-noise focal plane devices based on the integration of InGaAs APD arrays and CMOS timing/counting ROIC, which can be widely used in single-photon-level signal detection for 1.06 μm and 1.55 μm optical fiber communications. The core of SPAD array chip development is to improve its performance, which requires larger array scale, smaller pixel center spacing, high spatial resolution, high PDE, low DCR, time jitter, and low crosstalk to obtain clearer target information. And CMOS ROIC are developing towards large arrays, small pixels, and multi-functions. At the same time, problems such as dynamic power consumption, bias voltage of deep submicron processes, and total output bandwidth need to be solved. Due to its excellent performance, the InGaAs SPAD focal plane detector is widely used in laser three-dimensional imaging, long-distance laser communication, sparse photon detection and other fields, and will continue to expand its application range in the future.
Linear-mode HgCdTe avalanche photodiode detectors for photon-counting applications (invited)
Guo Huijun, Chen Lu, Yang Liao, Shen Chuan, Xie Hao, Lin Chun, Ding Ruijun, He Li
2023, 52(3): 20230036. doi: 10.3788/IRLA20230036
[Abstract](305) [FullText HTML] (69) [PDF 3567KB](157)
  Significance   Single-photon counting has great application prospects in weak signal detection and time ranging. Since the first photon counting system in the visible spectrum was developed in the 1970s, in order to fully amplify the photon signal and reduce the readout noise of electronic equipments, many groups in the research field are constantly developing and improving the photon counting techniques. Electron multiplying charge coupled devices (EMCCDs) can replace the traditional visible light photon counting system and have higher quantum efficiency. While due to large avalanche noise, accurate acquisition of incident photon number under multiplication is difficult. The excess noise factor of mercury cadmium telluride avalanche photodiode (HgCdTe APD) is close to 1, there is almost no excess noise. Compared with the Geiger mode avalanche photodiodes, the linear mode HgCdTe APD has no dead time and after pulse, does not need to quench the circuit, has ultra-high dynamic range and adjustable spectrum with wide response range. Its detection efficiency and false count rate can be independently optimized. It opens up a new infrared photon band counting imaging application. It is of great value in astronomical exploration, laser radar, free space communication and other applications.   Progress   Raytheon and DRS Technologies in the United States, CEA/LETI Laboratory and Lynred in France, and Leonardo in the United Kingdom have successively realized single photon counting of linear HgCdTe APD detectors. This paper summarizes the technical routes and research status of linear mode photon counting HgCdTe APD detectors in Europe and America. The performance of HgCdTe APDs, photon counting ability and the advantages and disadvantages of detector preparation with three structures, namely, separation of absorption and amplification (SAM), planar PIN type and high density vertically integrated photodiode (HDVIP), are analyzed. Raytheon Company has prepared SAM short-wave HgCdTe APD detectors with hole multiplication mechanism by molecular beam epitaxy (MBE), with gain of 350, photon detection efficiency of more than 95% and operating temperature of more than 180 K. DRS Technologies has prepared an electron-multiplication HDVIP medium wave HgCdTe APD detector using liquid phase epitaxy (LPE) material. The detector can respond in the visible to mid-infrared band from 0.4 μm to 4.3 μm, with the highest gain up to 6100 and the photon detection efficiency greater than 70%. It can realize free space communication of 110 Mbps data transfer. CEA/LETI Laboratory and Lynred Company have prepared PIN-type short-wave and medium-wave HgCdTe APD detectors with electron multiplication mechanism by molecular beam epitaxy or liquid phase epitaxy. The gain of short-wave detector is up to 2 000, the maximum gain of medium-wave is up to 13000, the internal photon detection efficiency is up to 90%, the free space communication of 80 Mbps data transfer is realized, and bandwidth up to 10 GHz is achieved at 300 K and gain of 1. British Leonardo Company has prepared SAM type HgCdTe APD detector with electron multiplication mechanism by metal organic vapor deposition (MOVPE). The detectors were named Selex Avalanche Photodiode HgCdTe Infrared Array (SAPHIRA), the device gain can reach 66@14.5 V, single photon detection efficiency is more than 90%. A 24 μm pitch 320×256 array SAPHIRA detectors were supplied to First Light Imaging Company in France to develop a C-RED ONE camera. The C-RED ONE camera was successfully applied to the Michigan Infrared Combiner (MIRC) for astronomical exploration in the United States, which reduced the system noise of MIRC by 10 to 30 times and greatly improved the signal-to-noise ratio of fringe detection. The research on HgCdTe APD detectors started relatively late in China. The main research institutions include Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Kunming Institute of Physics and North China Research Institute of Electro-Optics. Limited by chip preparation technology and circuit technology of HgCdTe APDs, the ability of photon counting has not been realized at present, but some progress has been made in the development of focal plane at home. The single element, 128×128 array and 320×256 array medium wave HgCdTe APD detectors with PIN structure are developed by Shanghai Institute of Technical Physics, Chinsese Academy of Sciences. The gain of the detectors can reach more than 1000, the gain normalized dark current density is less than 1×10−7 A/cm2 within the gain of 100, and the excess noise factor is less than 1.5 within the gain of 400. At the gain of 133, the noise equivalent photon number is 12, and the short integration time fast imaging is demonstrated. Bandwidth of single element detector is up to 300-600 MHz. The single element and 256×256 array medium wave HgCdTe APD device with PIN structure are developed in Kunming Institute of Physics. The gain of the single element detector can reach more than 1 000. When the bias voltage is less than 8.5 V, the average gain normalized dark current of focal plane is 9.0×10−14-1.6×10−13 A, and the excess noise factor F is between 1.0 and 1.5.  Conclusions and Prospects   In China, HgCdTe APD devices with planar PIN structure are mainly developed, and the technical path is basically the same as that of France. Therefore, our country can learn from the successful experience of CEA/LETI Laboratory and the business model of Lynred Company, and continue to promote research on HgCdTe APD detectors in order to reach the international advanced level as soon as possible, and realize single-photon detection and photon counting application.
Advancement of shortwave infrared single-photon detectors (invited)
Shi Yanli, Li Yunxue, Bai Rong, Liu Chen, Ye Haifeng, Huang Runyu, Hou Zepeng, Ma Xu, Zhao Weilin, Zhang Jiaxin, Wang Wei, Fu Quan
2023, 52(3): 20220908. doi: 10.3788/IRLA20220908
[Abstract](427) [FullText HTML] (36) [PDF 3486KB](251)
  Signifacance   InP/InGaAs shortwave infrared single-photon avalanche diodes (SPADs) have proved to be the most practical tool for the detection of near-infrared single-photon because of their small volume, near-room-temperature operation, and ease of integration and fabrication of a focal plane array based on the conventional semiconductor manufacturing process. They have achieved wide application including quantum secure communication, spectrum analysis, weak signal detection, Light Detection and Ranging (LiDAR), as well as self-driving vehicles considering the eye-safe laser requirement. etc. The further mass application depends on the performance and price of the SPADs, so the issues about the avalanche diode design and processing, as well as the solution are very important for accelerating the practical application. The review and analyses about the advancement of the shortwave infrared SPDs is very essential for both the academic research and application.  Progress   The separate absorption, grading, charge, and multiplication (SAGCM) structure has been used for InP/InGaAs SPADs since it was designed. This ensures the low electrical field in InGaAs absorption layer and high field in multiplication layer, then tunnelling current arising from high electrical field in absorption layer is remarkably suppressed, so the dark counts. Except for the essential material structure design, the electrical field uniformity in the multiplication layer also influences the performance such as the dark counts of the SPADs. The afterpulsing problem is another issue limiting the maximum count rate of the SPD in the current period. Focusing these issues of InP/InGaAs SPADs, solutions for them are concluded from the long-term study of InP/InGaAs SPADs.The high detection efficiency SPADs, room-temperature SPADs, and high count rate SPADs reported in the past decade by various institutions at home and abroad are summarized in detail. The typical performance parameter detection efficiency is improved by increasing the quantum efficiency via integrated absorption enhancement structure, the reported maximum value for 1 550 nm is 60%. The room temperature operation SPADs was carried out by both decreasing dark counts and sine-wave gated-quenching technology. About 20% detection efficiency and kHz dark counts at 293 K are acceptable for the practical application. Besides, the especial promising result for the room temperature SPDs is the reduced afterpulsing owing to the shortened carrier lifetime under the high temperature. The GHz SPDs benefit from the high and narrow sine-wave gate, as well as the simple harmonic wave noise out of the sine-wave gated-quenching technology. The typical performance parameter of high detection efficiency, room-temperature and high count rate InP/InGaAs SPDs are shown (Tab.1-Tab.3).Moreover, the InP/InGaAs SPAD focal plane arrays (FPAs) and the performance are concluded (Tab.4). The issues for the SPAD FPAs are mainly optical and electrical crosstalk between the adjacent pixels, solution such as mesa separation, microlens and optical filter, etc. are applied for decreasing the crosstalk. The clear three-dimensional image coded distance information was presented (Fig.13). The three-dimensional imaging with high sensitivity and long-distance detection ability attracts the enormous application requirement in both military and civil field. Finally, this paper introduces the novel SPDs technology including addition ionization engineering to the SPADs multiplication layer or using InAlAsSb digital alloys materials to further improve the performance. In0.52Al0.48As with smaller noise factor, wider band gap and matching the InGaAs lattice of the absorbing layer is used as the multiplication layer for electron ionization. Multiple layer ionization is applied to SPADs for increasing the ionization rate and detection efficiency.  Conclusions and Prospects   During the last decade the InP-based shortwave infrared single-photon detectors (SPDs) has gained the dramatic progress, the typical detection efficiency of the InP/InGaAs SPADs has been increased from 20% to 30%, and the dark count rate has been reduced to less than kHz. The high temperature SPADs up to room temperature operation, high speed SPADs up to GHz has appeared owing to the improvement of both avalanche diode and quench circuit. The single-photon focal plane arrays of 256×64 have also presented the clear three-dimensional image.The foreign countries including the United States, Switzerland, Italy, South Korea and Japan, etc. have performed long-term research on InP/InGaAs SPADs, and developed commercial self-products. Domestic research groups have successively prepared InP/InGaAs SPAD chips, and the performance is comparable to foreign reports. Furthermore, single-photon detector arrays have made certain progress, but the device format and performance need to be improved. Novel SPDs technology such as low noise factor material and ionization engineering are expected to further improve the performance. The high performance and low cost shortwave SPDs will further facilitate the quantity application including weak signal detection, LiDAR and digital imaging etc.
Key technologies and development trends of SPAD array readout circuit (invited)
Zheng Lixia, Wu Jin, Sun Weifeng, Wan Chenggong, Liu Gaolong, Wang Jiaqi, Gu Bingqing
2023, 52(3): 20220903. doi: 10.3788/IRLA20220903
[Abstract](296) [FullText HTML] (115) [PDF 1253KB](182)
  Significance   In recent years, the Single Photon Avalanche Diode（SPAD） with single-photon detection capability has been widely used in weak light detection fields such as laser radar, quantum communication, fluorescence spectrum analysis and so on because of its advantages of high sensitivity, fast response, strong anti-interference ability and small size. As a new nonlinear device, SPAD detector has complex manufacturing process. In addition, various applications of SPAD array need readout integrated circuits (ROIC) for detecting sensing signals to be matched with them to achieve the extraction and processing of SPAD detector avalanche signals. Various applications have increasingly high requirements for array size, detector signal extraction and processing capabilities. At the same time, the parasitic effect, power consumption, area and other problems caused by large-scale array are becoming more and more prominent, which seriously affects the imaging quality. The design of array-type SPAD readout circuit is facing great challenges.   Progress   The readout circuit of SPAD array is mainly composed of interface circuit and signal processing circuit. The interface circuit realizes the quenching and extraction of avalanche signal, and the switching between the cut-off and the state to be measured of SPAD. It is a dynamic bias circuit. With the expansion of the array scale, it is required to add SPAD anti-bias voltage adjustable circuit in the interface circuit, realize pixel-by-pixel or regionally adjustable bias of SPAD, and SPAD high-voltage breakdown protection circuit. At present, such technology is only used in small-scale, linear array and some applications, but still cannot be realized in the application of large area array. The main difficulty is that complex circuits cannot be used due to the limitation of pixel area. According to the application of SPAD, the signal processing circuit is divided into photon timing circuit and photon counting circuit. The photon timing circuit is used to measure the flight time of photons. In the circuit, the array-type time-to-digital conversion circuit (TDC) is used. Because the arrival time of each pixel is different, each pixel needs an independent TDC, and the circuit power consumption is very high. This is also one of the reasons that limit the scale expansion of SPAD array. A related research team has proposed a TDC sharing structure, such as the Lausanne Institute of Technology in Switzerland, which proposed a TDC sharing structure (Fig.3). At the same time, because the pixel area is not limited by sharing, multi-segment TDC can be used, and the time resolution of the circuit is less than 100 ps. Compared with the photon timing circuit, the structure of the photon counting circuit is relatively simple. It only needs to record the number of photons detected in a frame. The difficulty of this kind of circuit is to effectively adjust the dead time of the SPAD detector to achieve the best compromise between the detection rate and the dark count.   Conclusions and Prospects   With the demand for SPAD large arrays and the development of readout circuits, the following development trends have emerged in relevant readout circuits in recent years: on-chip data storage, multiple echo detection of returned photon events, and free detection mode. With the further development of the application requirements of SPAD array, the readout circuit will integrate more functions, further develop towards the integration of sensing, memory and computing, and finally truly realize single-chip imaging.
Evaluation and application of HgCdTe linear avalanche focal plane devices (invited)
Zhang Yingxu, Chen Xiao, Li Lihua, Zhao Peng, Zhao Jun, Ban Xuefeng, Li Hongfu, Gong Xiaodan, Kong Jincheng, Guo Jianhua, Li Xiongjun
2023, 52(3): 20220698. doi: 10.3788/IRLA20220698
[Abstract](259) [FullText HTML] (29) [PDF 2696KB](117)
  Significance   The HgCdTe linear avalanche focal plane detector has the characteristics of high gain, high bandwidth and low excess noise, and has shown great application potential in the field of aerospace, astronomical observation, military equipment and geological exploration. Based on their own HgCdTe infrared FPA detector technology, Leonardo, Raytheon, DRS and Sofradir have developed HgCdTe APD focal plane devices. The demonstration of active gating imaging, active/passive dual-mode imaging and 3D imaging have been completed, showing attractive application prospect of HgCdTe APD. However, the research on HgCdTe APD detector technology is still at the initial stage in China, and its application is still in the exploration stage due to the lack of evaluation method.   Progress   The parameters of the HgCdTe infrared focal plane array cannot completely cover the characterization of HgCdTe APD. According to the characteristics and application requirements of HgCdTe APD, in order to accurately characterize the performance of HgCdTe APD focal plane devices, it is necessary to introduce parameters such as gain, excess noise factor, noise equivalent photon number and time resolution. The gain of the APD is used to measure the amplification ability to the input, which is defined as the ratio of the response of the device with gain to the response without gain. The test method of the gain is given and the gain for an APD FPA prepared by Kunming Institute of Physics is shown (Fig.1, Fig.2). The average gain of the APD FPA has an exponential relationship with the bias. When the bias is −8 V, the gain of the FPA is 166 and the gain nonuniformity does not exceed 3.4%. The randomness of the carrier multiplication of the APD introduces excess noise, which makes the SNR of the output deteriorate when the input is amplified. Usually, excess noise factor is used to describe the deterioration of SNR, which can be calculated by the ratio of the device output SNR without gain to the device output SNR with gain. It's worth noting that the conditions need to be consistent during the test, otherwise, the change of the bandwidth will cause the test data not to reflect the true excess noise factor level of the device. The result is shown (Fig.1, Fig.3). Similar to noise equivalent temperature difference, noise equivalent photon number (NEPh) is used to evaluate the sensitivity of APD device in active imaging mode, which is mainly determined by the device gain, dark current level, background flux and readout circuit noise. Generally, NEPh refers to the limiting performance of the device, which is generally tested under the non-background limit (the optical current caused by the background flux should be less than the dark current). In the same conditions, the NEPh of APD device in high gain state decreases with the decrease of integration time (Fig.4). Coupling the APD device with the ROIC with timing function, the distance information can be obtained, which can be evaluated by time resolution. The time resolution reflects the minimum time interval of the pulse laser reaching the focal plane which can be distinguished by the APD, representing the minimum distance that can be distinguished. Finally, combined with the application of HgCdTe linear avalanche device and its characteristics, its application in active/passive infrared imaging and fast infrared imaging is discussed in detail, which can be used as a reference for the application of the HgCdTe APD FPA.   Conclusions and Prospects   Firstly, the key parameters that characterize the performance of HgCdTe APD focal plane chip are analyzed. Secondly, based on the characteristics of HgCdTe linear avalanche focal plane devices, the applications of HgCdTe avalanche focal plane devices in active/passive imaging, fast imaging and 3D imaging are discussed. Finally, the future development of HgCdTe avalanche focal plane devices is prospected. With the development of HgCdTe material growth, fabrication of devices, readout circuit design and processing and testing technology, there will be HgCdTe APD focal plane products with better performance, larger area, smaller pixel center distance and higher frame rate, which meet the demands of high-performance detectors in various applications such as 3D imaging, active/passive dual-mode imaging and single-photon detection.
Low-noise GHz InGaAs/InP single-photon detector (invited)
Long Yaoqiang, Shan Xiao, Wu Wen, Liang Yan
2023, 52(3): 20220901. doi: 10.3788/IRLA20220901
[Abstract](286) [FullText HTML] (51) [PDF 1844KB](141)
  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.
Miniaturized free-running InGaAs/InP single-photon detector (invited)
Jiang Lianjun, Fang Yuqiang, Yu Chao, Xu Qi, Wang Xuefeng, Ma Rui, Du Xianchang, Liu Ming, Wei Ta, Huang Chuancheng, Zhao Yukang, Liang Junsheng, Shang Xiang, Shentu Guoliang, Yu Lin, Tang Shibiao, Zhang Jun
2023, 52(3): 20230017. doi: 10.3788/IRLA20230017
[Abstract](312) [FullText HTML] (49) [PDF 4957KB](134)
  Objective  Single-photon detectors have the highest sensitivity of light detection. The utilization of single-photon detectors in LiDAR system can greatly improve the comprehensive performance of the system. Laser in the second near-infrared region (1.0-1.7 μm) has the advantages of high atmospheric transmittance, weak scattering and weak solar background radiation, which is the ideal working band of aerosol remote sensing and three-dimensional imaging LiDAR system. Therefore, a high-performance miniaturized free-running single-photon detector is designed in this paper.   Methods  The single-photon detector is based on InGaAs/InP negative feedback avalanche photodiode (NFAD), allowing it to operate in the free-running mode (Fig.1). A precise bias circuit and a precise temperature control circuit provide the bias voltage and cooling for the NFAD, respectively (Fig.2, Fig.3). In order to meet the needs of photon time-of-flight measurement for LiDAR system, the time-to-digital converter (TDC) function is realized by FPGA based on carry delay chain (Fig.4). Through the built-in micro controller unit (MCU) with integrated counting rate and afterpulse correction algorithm, it can make real-time correction of TDC data and output via USB interface.   Results and Discussions   The detector has dimensions of 116 mm×107.5 mm×80 mm (Fig.5). The maximum detection efficiency is more than 35% at 1.5 μm (Fig.6), and the time jitter (full width at half maxima, FWHM) is as low as 80 ps (Fig.7). The time measurement accuracy of internal TDC can reach 100 ps. The miniaturized LiDAR product using this single-photon detector can detect up to 15 km with a range resolution of less than 30 m (Fig.8).   Conclusions  The QCD600 series miniature free-running InGaAs/InP single-photon detector provides a compact and real-time data post-processing single-photon detection solution for LiDAR systems in the near infrared band with high efficiency, low noise, low time jitter. In the future, free-running single-photon detector will be developed in the direction of miniaturization using integrated refrigeration technology and ultra-low noise using deep refrigeration technology, which will provide more powerful technical support for LiDAR, QKD and other applications.
Integrated low-noise near-infrared single-photon detector based on InGaAs NFAD (invited)
Dong Yakui, Liu Junliang, Sun Linshan, Li Yongfu, Fan Shuzhen, Gao Liang, Liu Zhaojun, Zhao Xian
2023, 52(3): 20220907. doi: 10.3788/IRLA20220907
[Abstract](203) [FullText HTML] (20) [PDF 1753KB](121)
  Objective  Single-photon detection technology has attracted attention of researchers increasingly in recent years. The development of negative feedback avalanche diode (NFAD) which integrates a quenching resistor for fast quenching has greatly lessened the afterpulsing effects in InGaAs/InP based near-infrared single-photon detectors. Moreover, the integration of the thermal-electric cooler (TEC) with the NFAD has made the detector small in size and low in power consumption. However, the integration of the quenching resistor with large resistance reduces the amplitude of the avalanche current output to tens of μA. Though it can be read out using a broadband pre-amplifier, the long bonding wire of the TEC-integrated NFAD makes it prone to electro-magnetic interference. In addition, the large parasitic inductance and capacitance of the long bonding wire, combined with the low amplitude of the avalanche signal, makes it hard to cancel the noise induced by the capacitive response of the recovery signal of the NFAD, and hence it is difficult to use active-quenching circuits for better performance. Therefore, it is required to design a sophisticated circuit to solve the problems above to facilitate the application of the NFAD-based single-photon detector.   Methods  An integrated free-running InGaAs near-infrared single-photon detector was developed based on negative feedback avalanche diode (NFAD). In order to tackle with the problem that the readout of the avalanche current is prone to interference when using an amplifier, a high-impedance differential circuit without pre-amplifier was proposed for avalanche signal extraction. By introducing a specially designed resistive-capacitive network and signaling, the active-quenching technique was successfully combined with NFAD and was able to work stably. In addition, shielding material was applied to the amplifier-free readout circuitry for further interference shielding. The design above enhanced the quenching performance and stability of the detector at the same time. Moreover, in order to lower the dark-count rate, the circuit and the heat-dissipation structure of the detector was optimized to maximize the thermal contact area, and hence the high heat from the integrated thermal-electric cooler of the NFAD and the high-speed quenching circuit can be quickly dissipated to achieve lower cooling temperature.   Results and Discussions   The performance of the quenching circuit, the thermal design, and the anti-interference were verified through experiments. Waveforms at the inputs of the comparator (in Fig. 3) showed that the performance of the detector without pre-amplifier was stable. The maximum detection efficiency for 1550 nm wavelength reached 33%, and the minimum dead time available was 120 ns at the detection efficiency of 10%, at −50 ℃, where the dark-count rate and afterpulse probability were as low as 890 Hz and 10.6%, respectively. The heat-dissipation performance was good enough to maintain the temperature of the NFAD at −58 ℃ with fan cooling when the ambient temperature was 20 ℃. At −30 ℃, the afterpulse probability was approximately 70% of the value at −58 ℃, at the cost of a higher dark count rate of 13.2 times of the value at −58 ℃.   Conclusions  The proposed amplifier-free avalanche extraction and active-quenching circuit was able to work with the NFAD stably with a threshold of 9 mV, showing an excellent anti-interference performance. The afterpulse probability was as low as 10.6% at 10% detection efficiency, 120 ns dead time, −50 ℃, indicating that the hybrid quenching performance of the active-quenching circuit with NFAD was sufficient for low-dead-time free-running operation of the detector. In addition, good heat-dissipation performance was achieved by the large-thermal-contact-area design, where the temperature of the NFAD reached −58 ℃ with fan cooling at an ambient temperature of 20 ℃. It is indicated that this highly integrated low-noise near-infrared single-photon detector for communication wavelengths is especially suitable for use in the applications where high performance and minimum space usage are required.

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