【作者】 寇松峰；

【导师】 陈钱；

【作者基本信息】 南京理工大学 ， 光学工程， 2010， 博士

【摘要】 工作在盖革模式下的雪崩型光电二极管(APD)和二极管阵列(APD array)具备单光子探测能力,在天文观测、生物波导探测、通信、粒子物理学等领域具有广泛的应用前景,是各发达国家光电子学重点研究的课题之一。本文从光子统计特性和APD的瞬态响应特性入手,对APD器件光电响应原理及其固有缺陷产生机理进行了理论分析和实验研究,提出了一种新的基于盖革模式APD器件的微弱光成像方法。本文研究的内容既涉及到基本的物理问题,也涉及到未来的应用。在微弱光成像中,微弱的光信号更多地呈现出粒子特征,并伴随着随机的通量涨落,这种粒子性和随机性给成像系统带来的是与图像信息相关的离散信号,很难使用经典的图像噪声理论和方法进行处理。为了减小微弱光的粒子性对成像质量的影响,通常采用延长积分时间的方法对较宽时间范围内的微弱光信号进行能量积分,以抵消光子通量涨落和“群聚效应”造成的影响,这种能量平均的方法一方面需要对成像器件进行特殊处理以减小器件自身的暗电流和热噪声,另一方面则降低了成像频率。采用光子计数得到入射光的光子计数值,通过已知概率分布的反演方法快速准确地得到入射光的统计特性,成为克服微弱光探测难题的一个研究热点和难点。光子计数反演方法能否准确反映目标光场的强度分布则成为光子计数成像的一个核心科学问题。本文从半经典统计光学出发,建立了粗糙表面的单光子反射模型,采用蒙特卡罗仿真与物理实验相结合的方法对粗糙表面单光子反射特性进行了深入研究,得到了微弱光子信号经粗糙表面反射后的统计分布,证明了基于APD的光子计数反演方法能够准确反映目标光场的强度分布,为光子计数反演方法在APD光子计数成像中的应用奠定了理论基础。在单光子计数系统中,APD的时间响应特性和频率响应特性是很重要的。现有的APD响应模型多以载流子稳态平衡方程为基础,对单光子量级的瞬态入射信号响应精度较差。为了更加准确地描述单光子量级的瞬态信号入射状态下APD的响应特性,本文立足于单个载流子在耗尽层漂移和倍增区碰撞电离过程,将倍增区划分为厚度Δx→0的倍增区域,针对单个倍增区域建立时间-载流子浓度方程,通过时域积分方法建立了四层拉通型APD的时间响应模型,并对时间响应特性方程进行傅立叶变换得到APD的频率响应特性。数值仿真与实验结果的比较显示：在盖革模式下,APD的增益快速提高,光电流持续时间增加,导致APD的响应频率降低。采用门控技术和主动抑制技术可以在雪崩电流产生瞬间将APD的偏置电压降低到雪崩电压以下,抑制雪崩的继续,从而达到缩短光电流的持续时间、提高器件的响应频率的目的,满足微弱光照条件下光子计数成像的需要。采用APD进行光子计数成像时,受到器件恢复时间的限制,只能以门控工作方式对入射光子进行采样,这样就把有效时间分成了一组离散的时间间隔。显然,这样测量得到的信息要比光子本身出现时刻所载的信息量少,需要对接收到的光子事件进行统计特性的恢复和修正。为了尽量准确地对入射光场进行反演,我们建立了基于泊松点过程的光子事件模型和APD光子计数反演模型,通过蒙特卡罗仿真得到了所给标准图像的光子计数反演结果,对不同参数条件下的光子计数成像结果进行了比较,深入分析了非均匀性、暗计数等器件固有缺陷对成像质量的影响,给出了现有器件技术水平下APD光子计数成像的极限条件。构建了以硅APD单光子计数器为探测核心的实验平台,完成了相关的硬件和软件开发,实现了单元扫描方式的APD光子计数成像。在实验平台上进行了大量的实验测试,分析了成像模型仿真结果与实验结果之间的共同点以及两者产生差异的原因,对建立的光子计数成像模型进行了分析和评估,提出了进一步的改进措施。进行了APD光子计数成像与EMCCD微光成像的对比实验,对两者在不同光照度条件下的灰度响应、竖条纹分辨能力进行了比较,并对两者的灰度图像进行了质量评价。实验数据的统计分析和数学模型的仿真评估结果都表明,与现有的光电成像技术相比较,基于APD的光子计数成像技术在探测灵敏度上具有一定的优势。文章最后结合本文研究的不足之处,给出了今后研究的方向和APD光子计数成像技术研究展望。更多还原

【Abstract】 When biased above the breakdown voltage, which called Geiger mode, avalanche photodiodes (APDs) and avalanche photodiode arrays (APD arrays) have the ability of single-photon detecting, find applications in many areas like astronomy, biochemistry, waveguide photodetector, telecommunication, particle physics and general instrumentation. With APDs and APD arrays, many geometrical and device parameters can be adjusted to optimize their performance for a particular application. A new low-level-light imaging technology was proposed based on the statistical properties of photons and the photoelectric response of APDs. The topics which we have studied include both fundamental physics and future applications. The main achievements are as follow:In low-level-light imaging system, very low-level-light appears more particle characters than wave characters, going with luminous flux fluctuations randomly, which can’t be properly treated with classical image processing theories and techniques. Time domain integration is the common method to reduce the effects of corpuscular property and luminous flux fluctuations. To achieve longer integration time, the detector need some special handling to reduce dark current noise and thermal noise of detector itself, causing response frequency decreased. Photon counting technology is a useful method to solve this difficult problem. In this way, we can get low-level-light image quickly and accurately based on inversion techniques with photon counting result and the known probability distribution of incident light. It is very important to study on the probability distribution of reflect light in photon counting image technology. We derived the model of photon reflecting from rough surface based on semiclassical statistical optics, conducted the thorough research to photon reflection properties of rough surface with a combination of Monte Carlo method and physics experiment. In this work, statistical distributions of low-level-light based on APDs are derived, which will lay a foundation of further application of photon counting image technology.Time and frequency responses of APDs are very important in photon counting system, and there are many models for circuit simulation. But these studies generally based on the carrier rate equations of steady-state condition, disagree with the single-photon-indicate condition. In this work, the absorption region and the multiplication are proposed as many little regions of△χ→Othickness. Based on sub-domain carrier integration equations, a mathematical model describing the time and frequency response of four-layer reach-through APDs was derived, under some reasonable assumptions. The results presented here for the electrons clearly indicate that, under Geiger mode, gain of APDs increased rapidly, which lead to avalanche current duration expanded. The analysis assumes gated-mode and active quenching operation of the APDs and APD arrays can reduce dead time, increase response frequency greatly.As we know, Geiger mode APDs and APD arrays must work under gated-mode because of their quenching time. In this working mode, the continuous incident light signals are divided into discrete time interval. Obviously, the informations of photon counting results were decreased because of gated-mode sampling, recovery and correction must be done to the counting resulting. In this work, a photon counting image model based APD arrays’response characters and Poisson point process of photons was developed. To validate the model, an image correlated by pixels and photons number was used as standard image, which processed by the arithmetic of photon counting image model. And Monte Carlo simulation methods were used to investigate the relationship between the qualities of photon counting image and the inherent disadvantage of APDs such as nonuniformity and dark counting. As a result, illumination limit of APD counting image technology based on existing APDs is given.AS an important work, we developed an experimental platform based on silicon APD single-photon conter, achieved photon counting image through serial scanning mode of single APD. Focusing on models of photon counting image technology, a large amount of experimental were conducted, sameness and diference were compared with the simulation results. This work also studies on the applications of photon counting image technology in low-level-light image enhanced technology through contrast experiment on gray response and vertical fringe resolution between APD photon counting image and EMCCD. In conclusion, all experimental test, simulation comparison and application results indicate that photon counting image technology based on APDs has better sensitivity than traditional photoelectric imaging technology.Finally, research directions of future work are considered including possible photon counting image technology extensions.更多还原