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1、1,第六章 光纤无源及有源器件,2,光器件：光通信网络的基础,3,光无源器件,定义：不需要外加能源驱动工作的光电子器件光纤连接器（固定、活动,FC/PC,FC/APC）光纤定向耦合器/分支器光分插复用器（OADM)光波分/密集波分复用器（WDM/DWDM)光衰减器（固定、连续）光滤波器（带通、带阻）光纤隔离器与环行器（偏振有关、无关）光偏振态控制器、光纤延迟线、光纤光栅,4,光有源器件,定义：需要外加能源驱动工作的光电子器件半导体光源(LD,LED,DFB,QW,SQW,VCSEL)半导体光探测器(PD,PIN,APD）光纤激光器（OFL:单波长、多波长）光放大器(SOA,EDFA)光波长转换
2、器(XGM,XPM,FWM)光调制器（EA）光开关/路由器,5,光器件与电器件的类比,6,光器件的应用,7,6.1 自聚焦透镜,8,球透镜与自聚焦透镜,1、均匀折射率分布材料2、依靠弯曲的光学界面 实现光学成像3、通过非球面来克服像差，提高成像质量,1、渐变折射率分布材料2、依靠光线轨迹的弯曲 实现光学成像3、通过优化折射率分布，提高成像质量,9,自聚焦透镜,应用：无源器件的耦合系统、复印机、传真机、计算机光盘系统、摄影物镜、显微物镜、医用内窥镜等方面。,10,自聚焦透镜的基本特征,平方率折射率分布光线轨迹为cos或sin曲线从一点发出的不同角度的光线将会聚于另一点，形成“自聚焦”具有独到特点
3、：体积小、平端面超短焦距组合透镜成像特性可以弯曲成像,11,直角坐标系中的射线方程,12,13,14,光线的传播轨迹,15,透镜传输矩阵,q,ds,dx,dy,dz,16,近轴子午光线近似,17,透镜传输矩阵,18,矩阵光学符号公约,(1)原点:顶点、主点或焦点(2)线段:以原点为基点,顺光线传播方向为正,反之为负;(3)角度:以光轴或端面法线为基轴,从基轴向光线转动,顺时针为负,逆时针为正;(4)标记:在成象图中出现的几何量(长度和角度)均取绝 对值,正量直接标注,负量冠以“-号之后标注。,19,透镜成像矩阵,20,总成像矩阵,利用透镜传输矩阵S进行简化:,21,GRIN透镜的成像（I）,2
4、2,GRIN透镜的成像（II）,23,GRIN透镜的成像（III）,24,GRIN透镜的成像（III）,25,GRIN透镜的成像（IV）,26,GRIN透镜的成像（V）,27,透镜成像性质,28,GRIN透镜的应用：准直-聚焦,29,0.25P lens:on axis,30,0.25P lens：off axis,双光纤准直器,波分复用器件,31,GRIN透镜的应用：光源耦合,32,0.23P lens：angle compress,33,0.29P lens：facula compress,34,自聚焦透镜的重要特性,重要性能参数：焦距：f=-1/n0A1/2sin(A1/2L)聚焦参数：
5、A=2D/a2数值孔径：NA=n0(2D)1/2节距：P=2p/A1/2成像特性：与透镜长度有关：1/4 节距透镜1/2 节距透镜0.23节距透镜0.29 节距透镜,35,GRIN透镜的应用：准直-聚焦,36,0.25P lens:on axis,单光纤准直器,光无源器件,37,0.25P lens：off axis,双光纤准直器,波分复用器件,38,GRIN透镜的应用：光源耦合,39,0.23P lens：angle compress,40,0.29P lens：facula compress,41,自聚焦透镜的重要特性,重要性能参数：焦距：f=-1/n0A1/2sin(A1/2L)聚焦参数
6、：A=2D/a2数值孔径：NA=n0(2D)1/2节距：P=2p/A1/2成像特性：与透镜长度有关：1/4 节距透镜1/2 节距透镜0.23节距透镜0.29 节距透镜,42,6.2 光纤定向耦合器,43,6.2.1 耦合器的基本知识,44,耦合器的分类,45,6.2.2 耦合器的工作原理,两光纤的纤芯很接近时，光场导致介质极化，模场互相渗透，发生耦合,46,平行光纤之间的耦合,耦合波方程组：dR/dz-jdR=-jKS;dS/dz+jdS=-jKRAm=R exp(-jdz);An=S exp(jdz)失谐系数：d=(bn-bm)/2 耦合系数:K,47,耦合波方程组的解,边界条件:R(0)=
7、1,S(0)=0,48,两参数相同光纤的耦合,d=0，R2(z)=cos2(Kz)S2(z)=sin2(Kz)耦合长度：Lc=p/2K耦合系数：,可以通过控制平行光纤的长度以及两光纤间距来控制耦合比,49,耦合长度,耦合长度定义为对于确定波长的光信号功率从一根光纤100%耦合进入另一根光纤的最小长度。光信号功率耦合的强弱以及耦合长度取决于两光纤纤芯的间距，间距越大耦合耦合长度就越长。耦合长度与传输的波长也紧密相关！不同波长的光具有不同的耦合长度。耦合长度的波长相关性,50,相同波长光信号耦合,R(0)=1,S(0)=0,d=0，R2(z)=cos2(Kz)S2(z)=sin2(Kz),耦合长度
8、:Lc=p/2K功率100%耦合,P1,P2,P3,P4,51,光互易定理,当耦合器的参数相同时(1)相同波长间的耦合总是会引入3dB(50%)损耗(2)不可能利用光纤耦合器将两个光纤的相同波长光信号功率耦合到同一根光纤之中！,52,不同波长光信号的耦合(分波),两个波长从输入端口P1输入,分别在输出端口P2,P3输出,P1,P2,P3,53,不同波长光信号的耦合(合波),两个波长从P1,P4端口输入,在同一个输出端口P2输出,P1,P2,P4,54,光纤耦合器WDM,(1)对EDFA注入光功率（泵浦光信号光）(2)对简单的 WDM系统作波长分离(3)对DWDM系统增加管理信道,55,1XN
9、耦合器,56,Tap 耦合器,从主干线传输光信号功率中分出一小部分光功率供监控等应用；典型分光比:99:1 或 1%tap耦合器。,57,星型耦合器,58,性能参数,5.回波损耗：沿输入光路返回的光功率与输入光功率之比,59,制备工艺,60,6.3 光隔离器与环行器,61,1.光隔离器,光隔离器是一种光的非互易传输器件，只允许光波沿着一个方向传输，而光的另一个方向的传输是禁止的。也就是说，光信号沿着指定正方向传输时损耗低，光路被接通；光信号沿着反方向传输时损耗大，光路被阻断。,62,法拉第效应,把磁光介质放到磁场中，使光线平行于磁场方向通过介质时，入射的平面偏振光的振动方向就会发生旋转，转移角
10、度的大小与磁光介质的性质、光程和磁场强度等因素有关。磁光效应的非互易性:光波的偏振方向总是沿与磁场（H）方向构成右手螺旋方向旋转，而与光波的传播方向无关。当光正、反方向两次通过法拉第旋光片时，偏振方向旋转角度将迭加而不抵消。磁光效应的基本材料:钇铁石榴石（YIG：Yttrium-Iron-Garnet）、康宁（Corning）8363号玻璃等,63,偏振相关光隔离器,自然偏振光入射功率损耗50!与起偏方向垂直的偏振光入射损耗100！.随机偏振光入射带来严重的偏振噪声!,64,偏振无关光隔离器,将入射的任意偏振光分解为两束相互正交的线偏振光；分别处理这两束线偏光；再将经过处理的两束线偏振光合束输
11、出。,65,同轴结构光隔离器,1、3：偏振分束镜：YVO4双折射晶体（“Walk-off”）2：非互易的法拉第旋光片与光互易的玻片,1 2 3,66,应用,高速光通信系统中的DFB激光器的光隔离光放大器中的光隔离光纤环行腔中的单向器。,67,2.光环形器,光环形器总是使得光沿着规定的路径进行传输，即从器件的1端口输入，2端口输出；由2端口输入，就由3端口输出，由3端口输入，就由4端口输出，由4端口输入，就由1端口输出。,68,顺序传输,对于从1端口向2端口传输的光，由端口1输入的光，被第一双折射镜(block A)分成偏振方向互相正交的两束光，这两束光经45法拉第旋光片与互易旋光片后，偏振方向
12、均发生90的旋转，在第二双折射镜(block B)处，两光束再次折射并合成，由2端口输出。,69,逆序传输,由2端口向1端口传输的光，首先由block B进行分光，两束互相正交的偏振光经45法拉第旋光片与互易旋光片后，两束光的偏振态维持不变，由block B输出后，两光束通过反射棱镜和偏振分光镜作合并，最终由3端口输出。,70,应用,应用光环形器组成光反射镜,应用光环形器构成单纤双向传输,71,课堂习题（8）,自聚焦透镜与球透镜成象的异同点?常用的自聚焦透镜有哪几种?如图1所示的光纤耦合器,L为1/2耦合长度,计算input 1=100mw,input 2=0mw求 output 1,outp
13、ut 2各为多少?input1=50mw,input2=50mw,且波长相同,求output1 为多少?,图1,72,6.4 光纤光栅,73,衍射光栅,74,光纤光栅,掺锗光纤,紫外吸收,折射率周期变化,光纤光栅,75,分类,布拉格光栅（Fiber Bragg Grating）:前向传输的模式和后向传输模式的耦合,反射带通滤波光栅，对特定的波长反射并后向传输；长周期光栅（Long Period Grating）:导模和包层模耦合,带阻透射滤波，从透射光中滤除某些特定波长光；闪耀光栅(Blaze FBG)：对特定的波长反射并滤除掉。相移光栅(Phase-Shift FBG)：FP型透射滤波光纤光
14、栅。,76,An in-fibre Bragg grating is constructed by varying the refractive index of the core lengthwise along the fibre.Light of the specified wavelength traveling along the fibre is reflected from the grating back in the direction from which it came.Wavelengths which are not selected are passed throu
15、gh with little or no attenuation.,光纤布拉格光栅,77,工作原理,resonant wavelengths are reflected back toward the source non-resonant wavelengths are transmitted through the device without loss.The centre wavelength is given by:,78,Principle of Operation,The grating forms an electromagnetic resonant circuit.Powe
16、r from the forward direction is coupled into the resonant circuit and then reflected back.Non-resonant wavelengths are not affected very much.,79,结构参数,The grating period is the distance between modulations of the refractive index in the grating.The grating length.The“modulation depth”,determined by
17、the RI contrast within the grating.The RI contrast profile.,80,性能参数,Centre Wavelength This is the wavelength at the centre of the gratings reflection band.Bandwidth This is the width of the reflection band and specifies the range of wavelengths reflected.Reflectance Peak This is a measure of the pro
18、portion of incident light reflected at the centre wavelength.,81,分析理论,模式耦合理论 前向模式与后向模式之间的耦合薄膜光学理论高低折射率相间的1/4光学厚度膜层结构滤光片。,82,Dielectric Fabry-Perot Filters,flat passband；polarization independent；low insertion loss；good temperatutre performance(0.001nm/oC)。,0/2,0/2,0,0,1，2，3，n,0,1，3，n,0/4,0,Mirror Cav
19、ity MirrorStack Stack,83,反射谱,(a)typical reflection spectrum of a 1 cm long FBG with relatively low RI contrast.The height of the peak is 100%reflection and the width of the reflection band is.2 nm;(b)same grating with a stronger contrast.The reflection band has been broadened;(c)same grating as part
20、(a)but after apodisation.Note the reflection peak is now not quite 100%.,84,切趾光栅（变迹光栅）,Apodisation is a process of tapering the strength of the grating at either end so that the apparent RI change is gradual rather than abrupt.The reflection band of an apodised grating is shown in part(c)of the figu
21、re.,85,多波长光纤光栅,you can write many different FBGs into the same section of fibre-one on top of the other.Each grating will then respond quite separately and independently to light of its own resonant wavelength.,86,啁啾光栅,A“chirp”is where you get a variation in the period of the grating(and hence a var
22、iation in its response to different wavelengths)along the length of the grating:vary the period of the grating orvary the average RI of the grating.,87,啁啾切趾光栅,a good 100%reflection over the whole reflected band.,88,Caused by expansion and contraction of the fibre with temperature and consequent chan
23、ge in the spacing of the RI variations in the core;or a variation in the RI of the fibre itself with temperature.The unpackaged grating:a total variation of about 1 nm over a temperature range of 80C!,Temperature Stability of In-Fibre Bragg Gratings,89,FBG Packaging for Passive Thermal Compensation,
24、90,闪耀光栅,A blazed grating is constructed when the grating is written at an oblique angle to the centre axis of the core.The selected wavelength is reflected out of the fibre.Another usage is to equalise power across a range of wavelengths for example to“flatten”the response of an EDFA.,91,长周期光栅,Most
25、FBGs are constructed as first order gratings.That is the grating period is the same as the centre wavelength of the reflection band.A long-period grating is one where the grating period is many hundreds or thousands of times the resonant wavelength.,92,Principle,In LPG it couples forward guideing mo
26、de into a cladding mode.Thus after a while the coupled light leaves the system and is lost.A long-period grating then gives much the same effect as a blazed grating-resonant wavelengths are removed from the system.,93,Phase-Shifted FBGs,A“transmission fringe”is created in the centre of the reflectio
27、n band where light is transmitted through the filter rather than being reflected.,94,Writing the Grating光纤光栅的制作,(1)增敏掺锗(Ge),氢载(2)写光栅(准分子激光器 244nm)干涉法,衍射法,95,(1)Make the fibre core more sensitive,to increase the level of germanium dopant.this too far before mechanical effects in the fibre stop you.Co
28、-doping with boron and/or aluminium helps make the core more photosensitive.“Loading”the fibre with hydrogen,96,(2)Writing the Grating,The grating is written by exposing the fibre to UV light.UV light(244 nm)is able to make permanent modifications in the refractive index of the core.The change in th
29、e refractive index is very small indeed.An index change of.0001 is sufficient to make an effective grating.,97,Interference Pattern Technique,98,Phase Mask Technique,99,Summary for FBGs,Consists of a periodic stack of regions of high and low refractive index along an optical fiber.Made by exposing t
30、he fiber to an interference pattern of ultraviolet(UV)light.Narrow band,almost square wavelength response.Low temperature sensitivity with athermal packaging(as low as 0.4pm/oc,For unpackaged grating it is about 0.01nm/oc)Need to use fiber Mach-Zehnder configuration or circulator to construct a demu
31、ltiplexer,100,Applications of FBGs,Wavelength Stable Lasers Dispersion Compensation Wavelength Selection in WDM Systems,101,Using in Dispersion Compensation,102,Using in OADM,103,In-Fibre Bragg Grating Filters,104,Using in OADM,105,Fiber grating sensors,是应变,是温度变化量,106,6.5 光纤放大器与光纤激光器,107,6.5-1 掺铒光纤放
32、大器,108,光-电-光中继放大,109,全光放大,光放大器是一种勿需光电转换即可对光信号进行直接放大的器件,110,How to make an OA,Amplifiers can be built in semiconductor:Semiconductor Optical Amplifiers(SOAs).Almost any semiconductor laser can be made into an amplifier with a few modifications-Amplifiers can be built in fibres:Fibre AmplifiersEDFA:Er
33、bium Doped Fibre Amplifiers(1530nm1610nm)PDFA:Praseodymium Doped Fibre Amplifiers(12601360)TDFA：Thulium Doped Fibre Amplifiers(14501490nm)SRFA:Stimulated Raman Fibre AmplifiersPFA:Plastic Fibre Amplifier,111,112,1550,EDFA,增益窗口,30nm 60nm,光,放,大,器,增,益,光,纤,衰,减,除去,OH,峰外,300nm,低损耗窗口,波长,nm,850,1310,PDFA,SO
34、A,SRA,Development of OA,EDFA,增益窗口,30nm 60nm,PDFA,SOA,SRA,113,工作原理,泵浦光实现掺铒光纤的粒子数反转，外界的信号光对反转粒子数形成受激辐射，从而实现信号光的放大,114,有源光纤,由掺有稀土杂质的增益介质所制成的光纤称为有源光纤。稀土元素(也称镧系元素),包括元素周期表中倒数第二行中从镧(La.原子序数为57)到镥(Lu.原子序数为71)的15个元素。目前较成熟的有源光纤中掺入的稀土离子有：铒(Er+3,发射中心波长为1.53m)钕(Nd+3,发射中心波长为0.92m、1.06m、1.4m)镨(Pr+3,发射中心波长为1.3m)。,
35、115,能级图,980nm波长泵浦：铒离子相当于三能级系统，粒子数完全反转，噪声特性好，但量子效率不高；1480nm波长泵浦：铒离子相当于二能级系统粒子数反转不彻底，尽管量子效率较高，但噪声特性变差,116,EDFAs,117,典型泵浦结构,118,重要计算公式,速率方程放大器增益噪声指数：当泵浦充分，且 时，噪声系数达到极限3dB,119,Technical Characteristics of EDFAs,Efficient pumpingMinimal polarisation sensitivityLow insertion lossHigh output power(this is
36、not gain but raw amount of possible output power)Low noiseVery high sensitivityLow distortion and minimal interchannel crosstalk,120,Definitions,Gain(amplifier):the ratio in decibels of input power to output power.Gain Coefficient:the small signal gain divided by the pump power.Bandwidth:the range o
37、f wavelengths over which the amplifier will operate.,121,Definitions,Gain Saturation:the point where an increase in input power ceases to result in an increase in output power.Polarisation Sensitivity:the difference in gain of an input signal in one polarisation to the gain in the orthogonal polaris
38、ation.(typical.01.1 dB).Noise Figure:the ratio of the SNR at the input to the SNR at the output(in decibels).,122,Gain Saturation,123,高性能（低噪声）掺铒光纤放大器,利用980nm和1480nm两不同泵浦波长的掺铒光纤放大器级联,在高增益下实现近量子噪声极限,124,Gain Characteristics of EDFAs,125,Response of Cascaded EDFAs,126,Flattening the Gain Curve,Operatin
39、g the device at 77oK.Introducing other dopant materials(such as aluminium or ytterbium)along with the erbium into the fibre core.Amplifier length is another factor influencing the flatness of the gain curve.Controlling the pump power(through a feedback loop)is routine to reduce ASE.,127,Flattening t
40、he Gain Curve,Adding an extra WDM channel locally at the amplifier.This is called“gain clamping”.Manipulating the shape of the fibre waveguide within the amplifier.Fibres with dual cores have recently been shown to produce much superior gain flatness characteristics.,128,Flattening the Gain Curve,Us
41、ing“blazed”fibre Bragg gratings as filters to reduce the peaks in the response curve.In other words,reduce the response at all wavelengths to that of the worst wavelength.This approach has been reported to work well in field trials.Using channel preemphasis on the signals as they are transmitted.Tha
42、t is,transmit different WDM channels at different power levels to compensate for later amplifier gain characteristics.,129,LPG for Flattening the Gain,130,增益钳制EDFA,131,增益的自动控制,132,Cladding Pumps,Output powers of up to 10 watts!,133,MultiStage EDFAs,1)To increase the power output whilst retaining low
43、 noise2)To flatten the total amplifier gain response3)To reduce ASE noise,134,Remote Pumping,Two fibres are used in the connection-one for the signal and one for the pump.to pump at 1480 nm In a typical undersea system to extend the distance from around 100 km to 150 or even 200 km.,135,EDFA System
44、Resilience,Signal passes through the failed amplifier relatively unchanged!,136,Using OTDRs in Amplified Links,To diagnose link condition right through the amplifier.,137,EDFA的应用,Preamplifiers Power Amplifiers Line Amplifiers,138,6.5-2 掺铒光纤激光器,139,光纤激光器的构成,激光增益介质：有源光纤激光谐振腔：直腔、环行腔泵浦源：光泵,140,光纤激光器的谐振腔
45、,谐振腔的基本要求：透射泵浦光、反射激光谐振腔的基本形式：法布里-珀洛(FP)平行平面镜谐振腔光纤光栅对谐振腔光纤环行腔,141,法布里-珀洛(FP)平行平面镜谐振腔,PumpingLight(980nm),LasingLight(1550nm),EDF,M1,M2,142,光纤光栅对谐振腔,PumpingLight(980nm),LasingLight(1550nm),EDF,FBG1,FBG2,143,光纤环行腔,PumpingLight(980nm),LasingLight(1550nm),EDF,Coupler,Isolator,144,环形腔光纤激光器谐振腔,145,光纤激光器的泵浦
46、技术,端面泵浦技术侧面泵浦技术分布式泵浦技术双向泵浦技术泵浦合束技术,PumpingLD(980nm),LasingLight(1550nm),EDF,FBG1,FBG2,PumpingLD(980nm),PumpingLD(980nm),146,输出特性,147,重要的计算公式,输出光功率：阈值泵浦功率：斜率效率：最佳掺铒光纤长度,148,光纤激光器的性能,高的内量子效率：在有源光纤中产生的光子被限制在由纤芯波导内,使其只能沿光纤轴向传播。高的泵浦效率：可用波长与稀土离子吸收带相匹配的体积很小的高功率半导体激光器来直接泵浦。良好的散热特性：由于光纤具有很高的表面积与体积比,因而能在不加强制冷却的情况下连续工作。有源光纤可以方便地与光纤系统高效率地联接。光纤的固有柔性还给光纤激光器在光纤通信与医学上的应用带来很大方便。不足之处：高功率半导体激光器成本昂贵；光谱线宽较宽(510nm),不适合于相干性要求高的场合应用。,149,重要应用,窄线宽单纵模光源；超短脉冲激光光源,多波长激光光源,
