1、Fiber-Optic Communication Technology,Chapter 2 Optical Fibers,2018/9/22,OE, HUST,2,Total internal reflection 全内反射Step-index fiber 阶跃折射率光纤Graded-index fiber 渐变折射率光纤Core-cladding interface 芯层和包层界面Modal dispersion 模式色散Numerical aperture 数值孔径Impulse 冲激Meridional rays 子午光线Parabolic-index fiber 抛物线折射率分布光纤
2、Refractive index 折射率Absorption coefficient 吸收系数Chromatic dispersion 色度色散Optical mode 光模式Mode index 模式折射率Effective index 有效折射率Cutoff condition 截止条件Normalized frequency 归一化频率Single-mode condition 单模条件Eigenvalue equation 本征值方程Birefringence双折射,PMD 偏振模色散Confinement factor 限制因子Field radius 模场半径Attenuation
3、 coefficient 衰减系数Impurity 杂质Intrinsic absorption 本征吸收Rayleigh scattering 瑞丽散射Mie scattering 米氏散射Waveguide imperfection 波导不完善Macrobending 宏弯Microbending 微弯GVD: 群速度色散Intramodal dispersion: 模内色散Intermodal dispersion： 模间色散Dispersion parameter：色散参数Material dispersion：材料色散Waveguide dispersion：波导色散Sellmeie
4、r equation：塞米尔方程Zero-dispersion wavelength：零色散波长Dispersion-shifted fiber：色散位移光纤,2018/9/22,OE, HUST,3,Dispersion-flatten fiber：色散平坦光纤Dispersion decreasing fiber：色散渐减光纤Dispersion compensation fiber：色散补偿光纤Dispersion slope：色散斜率Differential-dispersion parameter：微分色散参数Polarization mode dispersion：偏振模色散Pul
5、se broadening 脉冲展宽Chirped Gaussian pulse 啁啾高斯脉冲FWHM: 半高全宽Raman scattering 喇曼散射Brillouin scattering 布里渊散射SRS 受激喇曼散射SBS 受激布里渊散射Electrostriction 电致伸缩效应Brillouin shift 布里渊频移Acoustic phonon 声学声子Inhomogeneous非均匀的Germania 锗Isotropic 各向同性Self-phase modulation 自相位调制,Cross-phase modulation 交叉相位调制Large effecti
6、ve-area fiber 大有效面积发光Phase-matching condition 相位匹配条件Optical phase conjugation 光相位共轭Elastic scattering 弹性散射Inelastic scattering 非弹性散射Fiber Manufacturing：光纤制作 Doubly clad：双包层Depressed-cladding fiber: 凹陷包层光纤Cylindrical preform：预制棒MCVD：改进的化学汽相沉积OVD：轴外汽相沉积VAD：轴向沉积PCVD：等离子体化学汽相沉积Flame hydrolysis 火焰裂解Sinte
7、ring ：烧结Light-duty cable 轻型光缆Heavy-duty cable 重型光缆Connector 连接头Furnace 熔炉,2018/9/22,OE, HUST,4,Chapter 2. Optical Fibers,Geometrical Optics & Wave Optics in FiberLossDispersionNonlinearity,2018/9/22,OE, HUST,5,2.1 Geometrical Optics & Wave Optics in Fiber,2.1.1 Geometrical Optics suited for a Multim
8、ode Step-Index Optical Fiber,weak-waveguided fiber,2018/9/22,OE, HUST,6,2018/9/22,OE, HUST,7,2018/9/22,OE, HUST,8,Multimode Graded-Index Optical Fiber,2018/9/22,OE, HUST,9,collimator,0.25 pitch：on axis,2018/9/22,OE, HUST,10,2018/9/22,OE, HUST,11,2.1.2 Wave Optics,suited for a ,2018/9/22,OE, HUST,12,
9、2. Basic ConceptsNormalize FrequencyMode Index,n2,n1,n2,n1,n2,2018/9/22,OE, HUST,13,2018/9/22,OE, HUST,14,Birefringence 双折射 HE11 two orthogonally polarized fiber modes x, y,Uniform:,Nonuniform:,linear elliptical linear,modal birefringence,beat length,y,x,2018/9/22,OE, HUST,15,2018/9/22,OE, HUST,16,P
10、MF: Polarization-Maintaining Fiber,Spot Size,w: field radius,1.2V7m): vibrational resonances,ultraviolet ( 0.4m): electronic resonances,0.81.6 m : 0.1dB/km,400nm,Transitional metal (Fe, Cu, Co, Ni):,2018/9/22,OE, HUST,20,2. Scattering (方向偏折， 能量不转换),Rayleigh Scattering Intrinsic, on a scale smaller t
11、han ,Mie scattering Waveguide Imperfection, on a scale larger than ,3. Bending (模式泄漏，能量不转换),MacrobendingInstalling,MicrobendingCabling,2018/9/22,OE, HUST,21,Chapter 2. Optical Fibers,Geometrical Optics & Wave Optics in FiberLossDispersionNonlinearity,2018/9/22,OE, HUST,22,Inter-symbol interference !
12、,2.3 Dispersion in SMF,SMF,2018/9/22,OE, HUST,23,Chromatic Dispersion (CD)Group Velocity Dispersion (GVD)Intra-modal DispersionHigh-order Dispersion (Dispersion Slope)Polarization Mode Dispersion (PMD),2018/9/22,OE, HUST,24,2.3.1 Group Velocity Dispersion,1. Dispersion parameter,L,T= L /Vg,2018/9/22
13、,OE, HUST,25,D: Dispersion Parameter, ps/(nmkm),对于工作波长为1.31m的单模光纤，D值一般为1ps/(nmkm)。即使光源采用多纵模半导体激光器（取24nm），此时系统通信容量（BL积）亦可达100Gb/skm。显然比多模光纤提高了几个数量级！,2018/9/22,OE, HUST,26,2. D ,2018/9/22,OE, HUST,27,n2g: the group index of the cladding material,2018/9/22,OE, HUST,28,2.3.2 Material Dispersion,Sellmeie
14、r equation:,2018/9/22,OE, HUST,29,2018/9/22,OE, HUST,30,2.3.3 Waveguide Dispersion,2018/9/22,OE, HUST,31,2018/9/22,OE, HUST,32,Realized by redesign the waveguide structure of fiber to enlarge,2.3.4 Dispersion Shift and Compensation,2018/9/22,OE, HUST,33,2018/9/22,OE, HUST,34,2018/9/22,OE, HUST,35,20
15、18/9/22,OE, HUST,36,D=-100ps/(nm km)L2=?,2018/9/22,OE, HUST,37,Dispersion Compensation by Using Chirped Bragg Grating,2018/9/22,OE, HUST,38,2.3.5 HighOrder Dispersion,Really?,Dispersion Slope (High-Order Dispersion),2018/9/22,OE, HUST,39,nx,ny,Ex,Ey,Pulse as it enters the fiber,Spreaded pulse as it
16、leaves the fiber,2.3.6 Polarization Mode Dispersion,2018/9/22,OE, HUST,40,2018/9/22,OE, HUST,41,A limiting factor for high bitrate lightwave systems,2018/9/22,OE, HUST,42,2.4 DispersionIntroduced Limitations,Optical pulse:,T0: half-width at 1/e intensity point,C: frequency chirp,2018/9/22,OE, HUST,4
17、3,When the source spectrum is Gaussian with the RMS spectral width,L: fiber length,0: RMS width of the input Gaussian pulse,: dispersion-introduced broadening of Gaussian input pulses,2018/9/22,OE, HUST,44,1. Optical Sources with a Large Spectral Width, ex. LED,non-zero-dispersion wavelength,2018/9/
18、22,OE, HUST,45,zero-dispersion wavelength,2. Optical Sources with a Small Spectral Width , ex. LD,non-zero-dispersion wavelength,2018/9/22,OE, HUST,46,zero-dispersion wavelength,2018/9/22,OE, HUST,47,2.5 Nonlinearities in Optical Fiber,2.5.1 Stimulated light scattering,Rayleigh Scattering : not to g
19、enerate new frequency,Raman Scattering : photon stokes photon + optical phonon,Brillouin Scattering: photon stokes photon + acoustic phonon,both directions, frequency shift is large,backward direction, frequency shift is small,Elastic scattering,Inelastic scattering,2018/9/22,OE, HUST,48,Inter-chann
20、el interference in time domain,Tilt in frequency domain,2018/9/22,OE, HUST,49,1. SRS,For common use, Pin10mW, SRS can be neglected,2018/9/22,OE, HUST,50,Figure 2.18: (a) Raman gain spectrum of fused silica at p = 1m and (b) energy levels participating in the SRS process.,Can optical amplifier or fib
21、er sensing utilize Raman scattering ?,Stokes photon,2018/9/22,OE, HUST,51,Simulation 1,2018/9/22,OE, HUST,52,2. SBS,Note: frequency shift 10GHz, channel spacing 100GHz ,not to generate crosstalk, but the loss of signal power,How does AM-VSB CATV increase the threshold of Brillouin scattering?,2018/9
22、/22,OE, HUST,53,Figure 2.17: Brillouin-gain spectra measured using a 1.525-m pump for three fibers with different germanium doping: (a) silica-core fiber; (b) depressed-cladding fiber; (c) dispersion-shifted fiber. Vertical scale is arbitrary.,2018/9/22,OE, HUST,54,2.5.2 Phase Modulation,Power depen
23、dence of refractive index!,1. SPM,nonlinear refraction,propagation constant,2018/9/22,OE, HUST,55,nonlinear phase shift,2018/9/22,OE, HUST,56,SPM特点,SPM导致频率啁啾，啁啾为负值(前沿红移，后沿蓝移)，频率啁啾将导致脉冲谱宽增加。SPM与光纤色散共同作用，在正常色散区，加剧脉冲展宽速度；在反常色散区，减低脉冲展宽速度(但SPM将导致脉冲畸变)。在一定条件下，可以使色散效应与SPM效应互相抵消，实现脉冲无畸变传输孤子。,2018/9/22,OE, H
24、UST,57,Simulation 2,2018/9/22,OE, HUST,58,2. XPM,assuming equal channel power,SPM distortion of optical pulse & spectral broadeningXPM intensity noise,2018/9/22,OE, HUST,59,2.5.3 Four-Wave Mixing,Also originates from the three-order nonlinear susceptibility,Easily to realize phase-matching at zero-d
25、ispersion wavelength !,large effective area non-zero dispersion-shifted fiber is available!,How to solve all the above problems in DWDM application?,2018/9/22,OE, HUST,60,Simulation 3,2018/9/22,OE, HUST,61,2.5.4 Fiber evolution,2018/9/22,OE, HUST,62,Loss Spectrum,900,1100,1300,1500,1700,0.5,1.0,1.5,
26、2.0,2.5,Attenuation (dB/km),Wavelength (nm),2,3,1,C-Band:15301565nm,O-Band:12601360nm,2018/9/22,OE, HUST,63,B*L!,Bitrate Distance Product,3M Technologies,2018/9/22,OE, HUST,64,Multi-level Modulation,Multi-mode,Multi-core,2018/9/22,OE, HUST,65,Multi-core Fiber,2018/9/22,OE, HUST,66,Multi-core EDFA,20
27、18/9/22,OE, HUST,67,FewMode Fiber & Mode MUX/DEMUX,2018/9/22,OE, HUST,68,Cable,陆地光缆,海底光缆,有源光缆,2018/9/22,OE, HUST,69,Connector & Adapter,2018/9/22,OE, HUST,70,Review,光纤基本参量计算：数值孔径，归一化频率，模场半径，相对折射率差光纤损耗，损耗系数单位的转换，损耗的机理，瑞利散射的特点，光纤通信的三个工作窗口光纤色散，色散单位的含义，群速度色散，色散位移光纤，色散补偿光纤，偏振模色散，高阶色散，色散补偿光纤实现色散补偿的原理色散致脉冲
28、展宽：谱宽较窄和谱宽较宽的情况，不同条件下的色散限制非线性：SRS、SBS、SPM、XPM的产生机理及功率预算，FWM的危害和克服方法各种光纤的特点：G.651、G.652、G.653、G.655、大有效面积光纤、DCF、全波光纤。,2018/9/22,OE, HUST,71,课堂作业,某光纤通信线路长90km，光纤色散系数D16ps/nmkm。请计算：当工作在1550nm时，使用线宽很窄的单纵模激光器，只考虑二阶群速度色散的影响，该线路最高工作速率为多少？某光纤通信线路长90km，使用的光纤芯层折射率为1.45，相对折射率差为0.3，截止波长为1m，光纤损耗只与瑞利散射有关，色散系数D16p
29、s/(nmkm)，非线性折射率系数是2.010-20m2/W。工作在1310nm时，输入功率为2mW，接收到功率为29.4dBm。请计算：该线路工作在1550nm时，在相同的输入条件下SPM引起的相移是多大？,2018/9/22,OE, HUST,72,课堂作业,某光纤通信线路长90km，使用的光纤芯层折射率为1.45，相对折射率差为0.3，截止波长为1m，光纤损耗只与瑞利散射有关，色散系数D16ps/(nmkm)，非线性折射率系数是2.010-20m2/W。工作在1310nm时，输入功率为2mW，接收到功率为29.4dBm。请计算：该线路工作在1550nm时，在相同的输入条件下SPM引起的相移是多大？,
