《光电系统噪声分析》AnalysisofNoiseinOptoelectrical

1、光电系统噪声分析AnalysisofNoiseinOptoelectrical光电系统噪声分析AnalysisofNoiseinOptoelectrical绪 论 Introduction一、意义 Importance：1、光电信号检测在任何一个光电子系统中都是必不可少的部 分。PD is a necessary part for any photo-electric system.2、光电信号检测水平高低对于光电子系统整体特性有十分重要的影响。=光电信号检测理论与技术是光电子技术的重要组成部分。The level of PD has deciding influence to the pro

2、pert. of the system, = the theory & techn. are an important part of photo-electronics techniques.二、特点 Features： 光电信号多数比较微弱，需采用微弱信号检测手段。Most of the PD signals are feeble, = the techn. for feeble signal detec. should be used.光电系统噪声分析AnalysisofNoiseinOptoelectrical三、设课目的 The Aim of Offering This Course

3、 ：1、系统地认识与理解光电信号检测理论； To understand systematically the theory of PE signals detection. 2、掌握光电信号检测的基本方法；为后续课程及将来工作 奠定基础。 To master the fundamental methods of PES; to be prepared for thecontinued courses and the job in the future. 四、主要内容 The Main Contents ： 光探测器工作原理与性能、光辐射的检测方法、光电信号处理的一般方法等。 The princ

4、iples & features of PD, the detection methods of optical radiation, the general approaches of PE signalprocessing, etc.光电系统噪声分析AnalysisofNoiseinOptoelectrical第一章 光探测器 Chapter 1 Light Detectors引言 Introduction：一、光辐射探测器是实现光电转换的关键元件，其性能如何直接关系到整个系统性能好坏。 The PDs are the key components, whose characteristi

5、cs will determine the performance of the systems.二、分类 Classification：光子探测器 Photodetectors 热探测器 Thermodetectors1 、光子探测器 Photodetectors ： 原理：光子与物质相互作用引起的光电效应 The Photoelectric Effect describing the interaction between photon & material is the working principle of photodetectors.光电系统噪声分析AnalysisofNoise

6、inOptoelectrical 分类 Classification：（1）光电子发射探测器 Photon Detecting Diode: 真空/充气光电二极管 vacuum/gas filled photoelectric diode 光电倍增管 photomultiplier (tube): PMT （2）半导体光电探测器Semiconductor PD: 光导探测器 Photoconductive(PC)、光生伏特探测器 Photovoltaic(PV) 特点 Features：（1）灵敏度高 high sensitivity （2）响应速度快 quick response（3）波长选

7、择性敏感 sensitive to working wavelength（4）半导体光导探测器通常工作于低温 work at low temperature光电系统噪声分析AnalysisofNoiseinOptoelectrical2、热探测器 Thermodetectors： 原理：光辐射产生的热效应 Thermal Effect produced by O.R. 分类：Classification（1）测辐射热电偶/热电堆 TE Couple（温差电效应）Thermoelectric effect （2）测辐射热敏电阻 Thermistor（体电阻温度敏感性）Temperature se

8、nsitivity （3）热释电探测器 TEED（热电晶体的热释电效应）Thermal Electron Emitting Effc. （4）高莱管 Golay Tube（气体受热辐射后力学参量改变）Dynamic Param. Change 特点 Features：（1）灵敏度比光子探测器低1-2量级 Low sensitivity for 1-2 order（2）响应速度较慢 Slow response speed（3）无波长选择性 No wavelength selectivity（4）工作于室温 Working at room temperature 光电系统噪声分析Analysiso

9、fNoiseinOptoelectrical第一节、探测器的性能参数及测量Section 1 Parameters of PDs & their measurement1.1 性能参数：测量和使用条件参数 Meas. & Appl. Conds. Params. 性能指标参数 Performance Target Params.一、几何参数 Geometric Params.1、探测器的面积 Area of PD 标称面积 nominal ：制造厂家提供的探测器的响应面积选用面积 used ：实际使用（起作用）的面积有效面积 effective ：探测器整体响应度与最大响应度比值The rat

10、io of total responsibility over the maximum of the responsibility: （）光电系统噪声分析AnalysisofNoiseinOptoelectrical2、探测器的视场角和立体角 Apparent angle & Solid angle（1）视场角：致冷型探测器响应元的中心对冷光阑的张角 Apparent angle: the angle of the center of response element to diaphragm（2）权重立体角 ：若来自（ ）方向的光辐射照射到探测的选用面积S上某点（x, y）处引起的响应度为

11、则探测器的有效权重立体角为 （） 式中 是 的极大值。 Weighted solid angle: If the responsibility at a certain point on the used areaS induced by the optical radiation from direction of ( ) is光电系统噪声分析AnalysisofNoiseinOptoelectricalThen the Effective Weighted Solid Angle is given aswhere the is the maximum of the . 该公式的物理含义见下

12、图图1.1 权重立体角的物理含义 Fig.1 the physical meaning of the EWSA光电系统噪声分析AnalysisofNoiseinOptoelectrical 解释: The explanations（1） 为探测器接受面积S上坐标为（x, y）的面元对来自（ ）方向的光辐射的响应度 The is the responsibility of the area element with coordinatesof (x, y) on the receiving area S of a detector induced by the optical radiation

13、coming from the direction of ( ). （2） 为立体角元。 The is the solid angle element. （3） 乘 为（ ）方向的光辐射在法线N方向的投影，因为响应度定义中要求以法线方向入射光电系统噪声分析AnalysisofNoiseinOptoelectrical (4) 分子的物理含义：来自所有可能入射方向的光辐射换算到法线入射后探测器的响应 The meaning of the numerator: The response of the detector after converting the optical radiation f

14、rom all incident directions into that along the normal line direction. (5) 分母的物理含义：全面积上的最大响应 The meaning of the denominator: The maximum responsibility on the area. (6) 分子除以分母后，仅余下立体角在法线方向的投影，故称为权重立体角 Only the projection of the solid angle along the direction of normal line is left after dividing th

15、e numerator by the denominator. 光电系统噪声分析AnalysisofNoiseinOptoelectrical二、电参数 The Electric Parameters1、阻抗 Impedance（1）定义：探测器两端电压对瞬时电流的导数 其复表达式为 其中: 为直流电阻、 为工作频率、 为探测器电容量、分式为容抗 。 Def.: The derivative of the voltage between the two ends of a detector with respect to the instantaneous current: , the com

16、plex expression of which is , where is DC resistance, is working frequency, is capacity, the fraction is capacitive reactanceof the detector. 光电系统噪声分析AnalysisofNoiseinOptoelectrical（2）依阻抗对探测器分类：Classification according to impedance1低阻探测器： ，需用变压器等阻抗变换元件与放大器连接 Detectors with low impedance, impedance t

17、ransformation element such as transformer is needed when it is connected with an amplifier. 2中阻探测器： ，可直接与放大器耦合 Detectors with mid-impedance, can be coupled directly with an amplifier.3高阻探测器： ，需与高输入阻抗放大器连用，热噪声与时间常数均较大。 Detectors with high impedance have higher thermal noise and time constant, should

18、be used with an amplifier with high input impedance.光电系统噪声分析AnalysisofNoiseinOptoelectrical 2、偏置条件 Bias conditions （1）光伏探测器：反偏，以便与前放匹配 inverse biasing （2）光电导或光敏电阻探测器：正偏 forward biasing 三、其它参数 Other Parameters （1）波长范围 wavelength range （2）工作频率范围（调制频率范围）modulation freq. range （3）放大器噪声带宽 noise bandwidth

19、 of amplifier （4）探测器工作温度 working temperature of amplifier 四、性能指标 Performance Target Parameters 1、量子效率 Quantum effect下一页上一页光电系统噪声分析AnalysisofNoiseinOptoelectrical（1）探测器工作的物理过程 The working physical procedure of photodetectors 探测器吸收辐射于其上的光子而产生光电子，光电子在探测器内及外加电路中形成光电流。光电流强度 与入射光功率 成正比。 Detector produces

20、photo-electrons after absorbing the photons impinged on its light sensitive area. The photo-electrons forms optical current inside thedetector and in the outside circuit. The current intensity is directly proportionalto the incident optical power: （） （2 ）光电转换因子 : The photon-electron transforming fac

21、tor 光电系统噪声分析AnalysisofNoiseinOptoelectrical 上式中 称为光电转换因子 The in Form. (1.1.3) is called the photon-electron transforming factor. 的微观含义 The microscopic meaning of : 由(1.1.3)可得 ,可知其微观含义为: 单位时间内,一个具有能量 的光子在探测器中产生的光电子电量（每个光电子电量为e），或: 一个具有能量 的光子在探测器中产生的电流强度。From obtained from Eq.(1.1.3), one can see that

22、 the microscopic meaning of is the electric quantity of photo-electrons (e per photo-electron) produced in unit time interval by a photon with energy of .Or: The current intensity produced by a photon with energy inside the detector. 光电系统噪声分析AnalysisofNoiseinOptoelectrical 的宏观含义: The macroscopic mea

23、ning of 将(1.1.3)改写为 ,可知其宏观含义为: 单位入射光功率可产生的光电流强度。 Rewriting Eq.(1.1.3) as , one can obtain the macroscopicmeaning of : The optical current intensity produced by unit incident optical power. 量子效率 : The quantum effect 由(1.1.3)移项得量子效率的定义式: Transposing Eq.(1.1.3), we have (1.1.4)光电系统噪声分析AnalysisofNoisein

24、Optoelectrical 分子：单位时间内由吸收的光子激励产生的光电子数 The numerator is the number of photo-electrons produced by the photonsabsorbed in unit time interval. 分母：单位时间内入射到探测器表面的光子数 The denominator is the number of the photons impinged on the surface of the detector in unit time interval. 量子效率 ：单位时间内入射到探测器上的每个光子能产生的光电子

25、数量。 Quantum effect : The number of photo-electrons produced by eachphoton impinged on the surface of the detector in unit time interval.理想情形： for ideal cases、实际情形： for practical ones。光电系统噪声分析AnalysisofNoiseinOptoelectrical2、响应度R : Responsibility R(1) 定义：Definition 一般定义：探测器输出电压或电流与入射到探测器上的辐射功率之比 The

26、general definition: The ratio of the output voltage or current of detector over the incident optical power is defined as the responsibility of PD. 确切定义：在入射辐射垂直投射到探测器响应平面的条件下，探测器输出的基频信号开路电压的方均根值或基频信号短路电流的方均根值与入射辐射功率中基频功率的方均根值之比。 (1.1.5-1) 光电系统噪声分析AnalysisofNoiseinOptoelectrical或 (1.1.5-2)The exact de

27、finition: The ratio of the rms value of the open circuit output voltage or the short circuit output current of the basic frequency signal overthe rms value of the basic frequency component of the incident optical power. （2）影响R的因素: The Factors affecting R 入射光波长 The wavelength of incident light、调制频率 T

28、he modulation frequency、探测偏置条件 The bias conditions of detector、工作温度 The working temperature及测量R所用的放大器的噪声带宽and the noise bandwidth of the amplifier used to measure R of detectors.（3）电子带宽与噪声等效带宽： Electronic bandwidth & Noise bandwidth光电系统噪声分析AnalysisofNoiseinOptoelectrical 电子带宽 ：Electronic bandwidth 放

29、大器的电压增益或电流增益下降到其峰值增益的一半 (-3dB)时的频率间隔。The freq. Interval corresponding to the points where the gain of the V or I declines to the half of the peak value. 噪声等效带宽 ：Noise equivalent bandwidtha. 一般情形：General cases 将实际功率增益对频率变化曲线下的面积化为等面积的矩形功率增益曲线时的频率间隔。The freq. Interval corresponding to thepoints where

30、the area of the rectangle equals to that under the practical pf curve. 光电系统噪声分析AnalysisofNoiseinOptoelectricalb. 白噪声情形： White noise cases where is the gain of the amplifier, is the peak gain of the amplifierworking at the peak frequency , is the peak frequency at which the amplifier has the maximum

31、gain. 3 、 噪声等效光功率NEP（最小可探测光功率） N. Equivalent P. (Minimum value of the detectable optical power) （1）探测器的探测能力由响应度和自身噪声电平决定The detectionability is determined by the responsibility & the noise level of the detector.光电系统噪声分析AnalysisofNoiseinOptoelectrical（2）NEP的物理含义： 考虑到探测器自身噪声电平后探测器的最小可探测光功率。 Phys. Mean

32、ing: The minimum value of detectable optical power after considering the noise level of detectors themselves.（3）定义 ：使输出方均根电压或电流与无入射时探测器的方均根 噪声电压或电流等值的入射光功率称为噪声等效光功率。 Definition: The incident optical power of PD, which makes the output rms V (or I) equal to the noise rms V (or I) without incident opt

33、ical power, is called the Noise Equivalent Power.（4）定义的数学表达式： The mathematical expression of the definition:光电系统噪声分析AnalysisofNoiseinOptoelectrical 依定义，将公式（）中分子与分母分别用噪声 电压与噪声等效光功率代替有: Substituting the numerator and denominator by noise voltage and NEP, we have 将上式移项得: Transposing it one can obtain:

34、(1.1.6-1) or (1.1.6-2)（5）相关因素：Relative factors 入射光波长 incident wavelength、探测器偏置条件 bias conditions of PD、工作温度 working temperature、探测器面积 area of PD、调制频率 modulation frequency、放大器噪声带宽 noise bandwidth of PD光电系统噪声分析AnalysisofNoiseinOptoelectrical（6）物理含义：Phys. meaning NEP越小探测能力越强，或灵敏度越高。 The less the NEP, t

35、he stronger the detection ability, or the higherthe sensitivity.4、探测度D Detectivity(1) 探测度D Detectivity 定义：噪声等效光功率的倒数称为探测度D (1.1.7) Def.: The reciprocal of NEP is defined as the detectivity.光电系统噪声分析AnalysisofNoiseinOptoelectrical 物理含义: 单位入射光功率时探测器的电压信噪比。 Phys. Meaning: The signal noise (voltages) rat

36、io (SNR) of the PD with unit incident optical power. 推论: 将(1.1.7)移项得 Inference: Transposing Eq. (1.1.7), we obtain (1.1.8)表明: 探测度一定时,输出电压信噪比与入射光功率成正比。which shows that the output SNR is directly proportional to the incidentoptical power when the detectivity of the PD has a certain value. (2) 归一化探测度 N

37、ormalized detectivity 为何引入 Why the normalized detectivity should be introduced?光电系统噪声分析AnalysisofNoiseinOptoelectrical 当探测器的噪声等效带宽不太大时,多数探测器的NEP与探测器的面积的平方根成正比，与噪声等效带宽的平方根成正比，为消除上述二因素的影响，需引入 。 When the noise equivalent bandwidth of is not too great, the NEP of most of PDs is directly proportional to

38、the square root of the area and thesquare root of the noise equivalent bandwidth of the PD. Therefore, the should be introduced to eliminate the Influences of these two factors. 定义式：Definition formula Since , define normalized NEP as ,Taking the reciprocals of both sides of the equality, we have (1.

39、1.9)光电系统噪声分析AnalysisofNoiseinOptoelectrical 用途：用于同类型不同面积探测器间性能比较 Applications: To compare the performances of the same kind PDs with different areas.（3） : Double asterisked D 致冷型探测器的探测度还与视场角有关，为消除视场角 的影响，还需引入 。 The detectivity of a cold-typed detector is relative to the apparent angle. To eliminate

40、this influence, the should be introduced. 定义 definition： (1.1.10)Where is the given apparent angle. 光电系统噪声分析AnalysisofNoiseinOptoelectrical 物理含义： 是给定视场角条件下的 , 是 时 的归一化探测度 。 Phys. Meaning: is the working at a given apparent angle, or say, is the normalized detectivity when . 5、光谱响应 Spectrum Response

41、(1) 定义： 当入射光功率、调制频率和偏置条件固定时，探测器的响 应度或归一化响应度对波长的依赖关系称为探测器的光谱响应。 Definition :The dependence of the normalized responsibility on the workingwavelength is called the Spectrum Response of a detector when the incident optical power, the modulation frequency & the bias conditions are fixed. 光电系统噪声分析Analysi

42、sofNoiseinOptoelectrical(2) 物理含义：对探测器针对不同波长入射光的响应能力的度量。 The measurement of the response ability of a detector to the incident light with different working wavelength, respectively.(3) 表示法：Expressions 绝对光谱响应曲线：纵轴为 或 Absolute spectrum response curve: The vertical axis represents or . 相对光谱响应曲线：纵轴为 Rela

43、tive spectrum response curve: The vertical axis represents .(4) 特征量：Characteristic values 热探测器：无波长选择性，其光谱响应为一直线。光电系统噪声分析AnalysisofNoiseinOptoelectrical Thermal Detectors: The spectrum response curve is a straight line,because they are not sensitive to the working wavelength. 光子探测器: 响应曲线的极大值称为峰值响应, 记为 。 The maximum of the response curve is called the Peak Response which is denoted as . 相应的波长称为峰值响应波长,记为 。 The corresponding wavelength is called the Peak Response wave-length, which is denoted as . 光谱响应降至峰值响应一半时对应的波长称为截止波长，它决定探测器的光谱响应范围。The corresponding wavelen