OTDR原理(中文)

nullOTDR 原理和应用OTDR 原理和应用OTDR 功能OTDR 功能距离 / 长度测量 米, 千米, 英尺 光纤损耗测量 dB/km, dB 连接器 / 接续损耗测量 dB 损耗 回波损耗 工作原理工作原理折射率 折射率 IOR = c/v (IOR：折射率) c = 真空中的光速 = 3 x 108 米/秒 v = 给定媒介中的光速 计算故障或事件点在光纤上的位置: L = vT/2 或 L = cT/(2  IOR) L = 到故障或事件点的距离 T = 反射脉冲在双路由上的总时延 OTDR 方块图OTDR 方块图典型的踪迹典型的踪迹Distance光纤损耗光纤损耗2PA = 两点近似法 LSA = 最小均方根近似法连接器损耗连接器损耗接续损耗接续损耗回波损耗回波损耗背向散射 背向散射 脉冲宽度脉冲宽度更大的脉冲宽度: 更大的功率, 即更大的动态范围 更小的脉冲宽度: 更好的分辨率, 但动态范围减小, 需要更多的平均。采用折衷办法脉冲宽度和分辨率脉冲宽度和分辨率2PTR=两点分辨率 PW=脉冲宽度 BW=检波器带宽 c=光速 n=光纤折射率分辨率分辨率读数分辨率 水平方向 垂直方向 空间分辨率 反射性 非反射性(接续点) 抽样分辨率 5,001 点, 可达50厘米(MW9070B) 50,000 点, 可达5厘米(MW9076 series)精度精度长度 时钟精度 偏移误差标记位置 IOR（折射率）误差 损耗 线性度 dB/dB 激光波长盲区 – 菲涅耳反射盲区 – 菲涅耳反射依赖于: 脉冲宽度/ 开关 / 接收器带宽 发射连接器回损/ 清洁度 噪声和平均噪声和平均平滑平滑BeforeAfter接续点增益和双向测量接续点增益和双向测量实际损耗 = (0.5-0.1)/2 = 0.2dB接收器饱和接收器饱和衰减器衰减器自动, 手动“完整踪迹”“完整踪迹”衰减器自动减小直至在一个屏幕上显示整个动态范围的波形鬼影 (1/3)鬼影 (1/3)鬼影 (2/3)鬼影 (2/3)鬼影 (3/3)鬼影 (3/3)LSA/2PA (1/7)LSA/2PA (1/7)2PA – 在两个标记数据点之间简单地画一条线LSA/2PA (2/7)LSA/2PA (2/7)LSA- 最接近于标记之间的数据点LSA/2PA (3/7)LSA/2PA (3/7)端到端损耗， 2PALSA/2PA (4/7)LSA/2PA (4/7)端到端损耗，LSA 接续或菲涅耳反射会产生误差LSA/2PA (5/7)LSA/2PA (5/7)接续损耗, 2个标记LSA/2PA (6/7)LSA/2PA (6/7)接续损耗 , 2PA 标记位置决定结果LSA/2PA (7/7)LSA/2PA (7/7)接续损耗, LSA – 正确的方法Chromatic DispersionChromatic DispersionWhat is Chromatic Dispersion?Chromatic DispersionChromatic DispersionChromatic dispersion is due to Fiber materials dispersion Reflective index of the fiber material Waveguide dispersion When different wavelength is input to the fiber, the different signal strength distributed to the core and cladding causes different transmission speed. Different wavelength components of the signal Due to modulation and wide spectrum light sourcenullBasic Of DispersionMaterial Dispersion The refractive index of the fiber materials (quartz glass) varies according to the wavelength of the input light, and differences in transmission speed create dispersion.Waveguide Dispersion When an optical signal with different wavelengths is input, the different strength distribution in the core and cladding cause different transmission speeds, creating dispersion.Chromatic Dispersion UnitsGenerally, chromatic dispersion is expressed as ps/km/nm. This means that the pulse width is widened by 1 ps when an optical pulse of 1-nm width is transmitted over 1 km.Chromatic DispersionSingle Mode Fiber DispersionSingle Mode Fiber Dispersion1.31 1.5518Material dispersionWaveguide dispersionChromatic dispersionWavelength (um)Dispersion (ps/km/nm)Fiber Dispersion Characteristics & Transmission DistanceFiber Dispersion Characteristics & Transmission DistanceRecent progress in photonic devices for DWDM systems by Akira Himeno and Tetsuo MiyaFiber amplifier rangeSMF zero-dispersion fiberNon zero-dispersion fiber (+)DSFNDSF(-)Wavelength (nm)Dispersion (ps/nm/km)Chromatic Dispersion Measurement PrinciplesChromatic Dispersion Measurement PrinciplesOTDR MethodStep 1: Find group delay time (t) using arrival time difference of Fresnel reflection at each wavelength of OTDR (1.31/1.41/1.55/1.625 µm).Measured Fresnel ValueChromatic Dispersion Measurement PrinciplesChromatic Dispersion Measurement PrinciplesStep 2: Perform fitting using the following approximation method for the actual values measured in step 1. Approximation method: A2 + B  + C (polynomial expression) … DSF A  2 + B + C  -2 (Cellmeyer) … SMFGroup Delay Time Fitted CurveChromatic Dispersion Measurement PrinciplesChromatic Dispersion Measurement PrinciplesStep3: Find the chromatic dispersion by differentiating the approximated curve found in 2 by the wavelength. And obtain the dispersion slope waveform by differentiating the dispersion by the wavelength.Chromatic dispersion CurveChromatic Dispersion Measurement PrinciplesChromatic Dispersion Measurement PrinciplesPulse MethodPulse GeneratorChromatic Dispersion Measurement PrinciplesChromatic Dispersion Measurement PrinciplesPhase Method1. Measure the modulation signal from the measured fiber with the network analyzer and find the phase difference () between each waveform.2. Find the group delay time (t) from the phase difference. 3. As in the OTDR Method above, find the group delay characteristics for the obtained waveform using polynomial approximation. Then find the chromatic dispersion by differentiating with the wavelength.t = 2 f x L/ Wavelength (nm)Dispersion (ps/km/nm)Wavelength (nm)Dispersion (ps/km/nm)1Features of Each Measurement MethodFeatures of Each Measurement MethodHP, PK, EG&GAnritsuBoth-ends measurement High costBoth-ends measurement Reduced accuracy with short fibersReduced accuracy with short fibersDe-meritsHigh accuracySingle-end measurement Low cost and portable Measure fiber connectionsMeritsPhase Method (EIA/TIA-455-169A)Pulse Method (EIA/TIA-455-168A) OTDR MethodMaker