electronics Article Design and Implementation of a Compact Single-Photon Counting Module Ming Chen 1,2 , Chenghao Li 2, Alan P. Morrison 3, Shijie Deng 1,*, Chuanxin Teng 1, Houquan Liu 1, Hongchang Deng 1, Xianming Xiong 1,* and Libo Yuan 1 1 Guangxi Key Laboratory of Optoelectronic Information Processing, School of Electronic Engineering and Automation, Guilin University of Electronics Technology, Guilin 541004, China; [email protected] (M.C.); [email protected] (C.T.); [email protected] (H.L.); [email protected] (H.D.); [email protected] (L.Y.) 2 School of Information and Communication, Guilin University of Electronics Technology, Guilin 541004, China; [email protected] 3 Department of Electrical and Electronic Engineering, University College Cork, Cork T12 K8AF, Ireland; [email protected] * Correspondence: [email protected] (S.D.); [email protected] (X.X.) Received: 2 June 2020; Accepted: 9 July 2020; Published: 11 July 2020 Abstract: A compact single-photon counting module that can accurately control the bias voltage and hold-off time is developed in this work. The module is a microcontroller-based system which mainly consists of a microcontroller, a programmable negative voltage generator, a silicon-based single-photon avalanche diode, and an integrated active quench and reset circuit. The module is 3.8 cm 3.6 cm 2 cm in size and can communicate with the end user and be powered through a × × USB cable (5 V). In this module, the bias voltage of the single-photon avalanche diode (SPAD) is precisely controllable from 14 V ~ 38 V and the hold-off time (consequently the dead time) of the − − SPAD can be adjusted from a few nanoseconds to around 1.6 µs with a setting resolution of 6.5 ∼ ns. Experimental results show that the module achieves a minimum dead time of around 28.5 ns, giving a saturation counting rate of around 35 Mcounts/s. Results also show that at a controlled reverse bias voltage of 26.8 V, the dark count rate measured is about 300 counts/s and the timing jitter measured is about 158 ps. Photodetection probability measurements show that the module is suited for detection of visible light from 450 nm to 800 nm with a 40% peak photon detection efficiency achieved at around 600 nm. Keywords: single-photon counting; compact module; bias voltage control; hold-off time setting 1. Introduction Single-photon counting techniques have been used in low-light sensing applications such as LIDAR [1,2], quantum key distribution [3], medical imaging technology [4], and 3D imaging technology [5,6]. Photomultiplier tubes have been the traditional solution for photon counting applications, but in recent years single-photon avalanche diode (SPAD) has become an alternative candidate due to its lower cost, lower operating voltage, higher sensitivity, and smaller size. The dead time in a SPAD is the off time when the SPAD is quenched after every avalanche event to dissipate trapped charge, thereby minimizing the “afterpulsing” phenomenon. As a result, a trade-off exists between the maximum photon counting rate and an acceptable level of noise. An accurate adjustment of the dead time is important to achieve an optimal dead time (and consequently optimal maximum photon counting rate) in a single-photon counting system. The bias voltage has a major effect on the SPAD’s important performance parameters such as dark count rate (DCR) and photon detection Electronics 2020, 9, 1131; doi:10.3390/electronics9071131 www.mdpi.com/journal/electronics Electronics 2020, 9, 1131 2 of 11 Electronics 2020, 9, x FOR PEER REVIEW 2 of 11 edetectionfficiency (PDE).efficiency A higher(PDE). biasA higher voltage bias will voltage lead towill better lead PDE to better due toPDE the due increase to the in increase the avalanche in the triggeravalanche probability. trigger probability. However, theHowever, potential the drawbacks potential includedrawbacks higher include DCR higher and the DCR considerable and the afterpulsingconsiderable e afterpulsingffect. Therefore, effect. the Therefore, bias voltage the shouldbias voltage be adjustable should be and adjustable optimized and to optimized achieve best to overallachieve performance. best overall Severalperformance. SPAD-based Several single-photon SPAD-based countingsingle-photon modules counting have been modules developed have [been7–17 ] butdeveloped these modules [7–17] but are these limited modules in that are the limited dead in time that and thebias dead voltage time and of bias the detectorvoltage of are the di detectorfficult to change.are difficult This limitsto change. their This usefulness limits their in varying usefulne environmentsss in varying and environments for the case whereand for the the detector case where needs tothe be detector changed needs for di fftoerent be changed measurement for different purposes. measurement In addition, purposes. existing designsIn addition, are usually existing bulky designs and cumbersome,are usually bulky which and limits cumbersome, their usefulness which limits in applications their usefulness that require in applications compact that solutions. require compact solutions.In this work, a compact multi-parameter adjustable single-photon counting module is developed. The moduleIn this is work, a microcontroller-based a compact multi-parameter system mainly adjustable consisting single-photon of a programmable counting negative module voltage is generator,developed. a The silicon-based module is SPAD,a microcontroller-based an active quenching system and mainly reset integrated consisting circuit of a programmable (AQR-IC) and I/negativeO components. voltage generator, In this module, a silicon-based a custom SPAD, designed an active SPAD quenching was fabricated and reset and usedintegrated with circuit its bias voltage(AQR-IC) precisely and I/O controllable components. from In this14 Vmodule, ~ 38 Va usingcustom a programmabledesigned SPAD negative was fabricated voltage and generator. used − − Withwith theits bias AQR-IC, voltage the precisely hold-off controllabletime (consequently from −14 theV ~ − dead38 V time)using ina programmable the SPAD can negative be adjusted voltage from agenerator. few nanoseconds With the to AQR-IC, around the 1.6 µhold-offs with atime setting (consequently resolution the of dead6.5 ns. time) A microcontroller in the SPAD can of be the adjusted from a few nanoseconds to around 1.6 μs with a setting∼ resolution of ∼6.5 ns. A module is used to drive and control the SPAD’s bias voltage and hold-off time which can also be microcontroller of the module is used to drive and control the SPAD’s bias voltage and hold-off time connected to a PC through USB for the graphical user interface. With the control of the bias voltage and which can also be connected to a PC through USB for the graphical user interface. With the control high-resolution setting of the dead time, intelligent control can be added to the module for detection of the bias voltage and high-resolution setting of the dead time, intelligent control can be added to optimizations under varying environments that greatly improve the SPAD-based photon counting the module for detection optimizations under varying environments that greatly improve the SPAD- system’s robustness. In addition, the module developed is about 3.8 cm 3.6 cm 2 cm in volume, based photon counting system’s robustness. In addition, the module developed× is about× 3.8 cm × 3.6 allowing it to be used in compact photon counting systems. Experimental results show that the module cm × 2 cm in volume, allowing it to be used in compact photon counting systems. Experimental achieves a minimum dead time of around 28.5 ns which demonstrates a saturation counting rate results show that the module achieves a minimum dead time of around 28.5 ns which demonstrates of around 35 Mcounts/s. At a controlled reverse bias voltage of 26.8 V, the DCR measured is about a saturation counting rate of around 35 Mcounts /s. At a controlled reverse bias voltage of 26.8 V, the 300 counts/s and the timing jitter measured is about 158 ps. Photodetection probability measurements DCR measured is about 300 counts/s and the timing jitter measured is about 158 ps. Photodetection show that the module is suited for detection of visible light from 450 nm to 800 nm with a 40% peak probability measurements show that the module is suited for detection of visible light from 450 nm PDE at around 600 nm. to 800 nm with a 40% peak PDE at around 600 nm. 2. System Description 2. System Description Figure1 shows the block diagram of the single-photon counting module consisting of the following Figure 1 shows the block diagram of the single-photon counting module consisting of the parts: (1) A Microcontroller (STC89C52RC) circuitry which is used to communicate with the user following parts: (1) A Microcontroller (STC89C52RC) circuitry which is used to communicate with end (PC) via an USB to TTL chip and also used for the control of bias voltage and the hold-off time; the user end (PC) via an USB to TTL chip and also used for the control of bias voltage and the hold- (2) A programmable negative voltage generator which is used to generate a stable and controllable off time; (2) A programmable negative voltage generator which is used to generate a stable and negative high voltage for the SPAD; (3) An active quenching and reset integrated circuit (AQR-IC) for controllable negative high voltage for the SPAD; (3) An active quenching and reset integrated circuit the hold-off time setting in the SPAD and (4) A custom designed SPAD. (AQR-IC) for the hold-off time setting in the SPAD and (4) A custom designed SPAD. FigureFigure 1.1. Block diagram of the single-photo single-photonn counting counting module module developed.