Determining the effective cutoff wavelength of single-mode fibers: An interlaboratory comparison

The National Bureau of Standards (NBS), in cooperation with the Electronic Industries Association, conducted an interlaboratory measurement comparison among six fiber manufacturers to determine the effective cutoff wavelength of single-mode fibers. Measurement techniques based on transmitted power were used to determine cutoff wavelength on four fibers designed for single-mode operation at 1300 nm. NBS also contributed results using a spectral near-field technique. One standard deviation measurement spreads for the various techniques range from 6 to 12 nm. With the appropriate data analysis, single bend attenuation and power step methods give the same results. Both techniques are easily implemented as extensions to the usual spectral attenuation measurement.     

Control of fiber manufacturing processes

A review of applications of lasers to measurement and control of optical fiber fabrication processes is given. The unique laser properties of high intensity and good coherence permit accurate measurement and control functions to be performed. Both preform and fiber drawing processes are discussed with the major emphasis being in the drawing operation where the applications are more mature.     

基于单向传输的光纤时延波动测量

为了与现有光纤通信网络兼容,研究了一种基于单纤单向传输的光纤时延波动测量方法。基于色散温变效应和Sellmeier等式,建立了利用温度的准确测量和双波长光信号传输时延差波动反推单向时延波动的比例模型。令模型中的比例系数是单波长时延波动和双波长时延差波动的比,仿真研究了温度和波长差对比例系数的影响。搭建了75 km光纤单向时延波动测量实验平台,实验结果表明:实测比例系数?258.4接近于理论比例系数?277.3,对应单向传输时延波动误差为660 ps,实验结果验证了模型的正确性和基于单向传输的光纤时延波动测量的可能性。     

激光告警系统中的光纤时间延迟测向技术研究

理论分析了光纤时间延迟技术基本原理,并对其在激光测向告警系统中的应用进行了 实验研究。实验中采用高速数字滤波器滤除干扰信号,再通过测量光强重心的光纤延迟时间来解算激光辐射的入射角,从而降低了激光告警系统的虚警率,大幅度提高了延迟测向的准确性与稳定性。     

Optical Fiber Cable Measurements in the Field

The optical fiber cable measurement instruments developed by NTF for field use in the 1.3 μm wavelength are discussed. The properties of a stabilized optical light source for single-mode fiber attenuation measurement, optical time-domain reflectometer using a Q-switched Nd:YAG laser as a light source, and chromatic dispersion measurement instrument are described. From the measurement results, these instruments are revealed to be suitable in constructing and maintaining singlemode fiber optical transmission lines.     

Measuring the individual attenuation distribution of passive branched optical networks

We propose a new method for measuring the individual attenuation distribution of passive branched optical networks and describe our experimental results. This test method employs two techniques. One is a passive optical distribution technique, whereby communication light is uniformly distributed to all branched fibers, and test lights are distributed to each branched fiber according to their wavelength. The other is an attenuation distribution measurement technique using an optical time domain reflectometer (OTDR) which can control the test light wavelength.     

Measurement of dispersion using short lengths of an optical fiber and picosecond pulses from semiconductor film lasers

Group velocity dispersion spectra have been determined for 7.8-m lengths of a single-mode optical fiber. The dispersion spectra are derived from measurement of the transit delay time of picosecond pulses (4-10 ps) from optically pumped ultrashort cavity semiconductor film lasers. The delay time spectra have been measured to 1 ps precision over the range from 1.11 to 1.53 μm for single-mode step-index and quadruple-clad fibers. This is the highest temporal resolution achieved for any pulse delay measurement in optical fibers. The resulting dispersion spectra are in good agreement with measurements made for the same fibers by other techniques.     

基于安捷伦VNA网络分析仪实现长延时器件的测量

无论在光纤通信系统还是在国防应用系统中,都存在着很多长延时器件,譬如声表面波滤波器和长距离的光纤.对于几十公里的光纤,就可能有几百微秒的延时.基于安捷伦矢量网络分析仪(VNA),很多工程师不能准确地测量出长延时器件的衰减和群时延(GroupDelay).针对这一问题,本篇文章探讨如何使用VNA来测试长延时器件.     

Single-end polarization mode dispersion measurement usingbackreflected spectra through a linear polarizer

Routine characterization of polarization mode dispersion of single-mode fibers in installed cables requires simple and fast techniques. All standardized techniques use both fiber ends, one connected to the optical source and the other one for signal detection. Clearly, this causes several drawbacks in field tests because the two fiber ends are usually far from each other. Among standardized techniques, the fixed-polarizer method (also called wavelength scanning method) is one of the simplest to implement. In this work we present a new single-end measurement scheme based on the fixed polarizer method applied to the signal backreflected by the fiber far-end. We report analytical equations and numerical solutions that permit to calculate the mean value of the differential group delay measuring the crossings and/or extreme densities of the spectrum transmitted through a linear polarizer. We also show that the mean value of the differential group delay can be calculated using the Fourier transform of the detected signal. Finally, experimental results on cascades of single-mode step-index fibers confirm the robustness and easiness of our proposal for polarization mode dispersion measurements     

Explanation of launch condition choice for GRIN multimode fiberattenuation and bandwidth measurements

In order to predict the attenuation and bandwidth of a graded index (GRIN) multimode fiber system accurately, the fiber composing the system is best characterized by a restricted launch attenuation measurement and an over-filled-launch (OFL) bandwidth measurement of the fibers. The rationale for these launches is provided in terms of the power evolution in the fiber and its impact on system performance, and the basic physics of GRIN multimode fiber. Experimental results are shown that demonstrate the results     

Measurement of the beat length in high-birefringent optical fiberby way of magnetooptic modulation

One of the most important parameters about high-birefringent optical fiber is the beat length. Because of its shortness and periodicity, the measurement of the beat length Is very critical. Here, a highly accurate measurement method that relies on magnetooptic modulation techniques is proposed, and the theoretical analysis and discussion about the measurement theories and the instrument construction are given in detail. Finally, the construction of the beat length measurement instrument based on this novel method is described and several kinds of high-birefringent optical fiber samples are measured. The beat-length resolution of this instrument is better than 0.01 mm, and the final measuring results are not influenced by the external interference on the fiber or the status of the placement of the optical fiber     

Reflectometric measurements of PMD properties in long single-mode fibers

Polarization sensitive reflectometric measurements are effective tools for the characterization of polarization properties of optical-fiber link. The field of application of these techniques depends on whether they use a continuous wave source or a pulsed source to generate the probe signal. In the first case, reflectometric techniques may be successfully applied to perform single-end measurement of differential group delay and polarization dependent loss. In the second case—that is the case of polarization sensitive optical time domain reflectometry—the local birefringence of a single mode fiber can be measured and characterized. In this paper the theory and the applications of polarization sensitive reflectometric techniques are reviewed.     

The Er3+-fiber gain coefficient derived from a dynamicgain tilt technique

We describe a new method to determine the Er³⁺-fiber gain coefficient using a dynamic gain tilt technique. The method is based on attenuation measurement, gain measurements and crossover optimization of dynamic gain tilt. Results demonstrate that this method is very simple, highly accurate and especially useful for extended band erbium doped fiber amplifiers (EDFAs) design     

Phase Shift Technique for the Measurement of Chromatic Dispersion in Optical Fibers Using LED's

A sinusoidal technique is reported, which allows simple and accurate measurements of chromatic dispersion in optical fibers. It is based on the phase shift which a sinusoidally modulated light beam undergoes while traveling along a fiber when its wavelength is changed. The choice of a multiple LED's source permits the continuous spectral covering from 750 to 1600 nm; easily available instrumentation and devices are needed for the measurement setup. The technique is reported in detail by showing results obtained in multimode fibers; statistical evaluation of its accuracy and a comparison with conventional methods are carried out. An accuracy of a few picosecond in relative delay and of /spl I.chemc/1 ps/nm /spl dot/ km in chromatic dispersion are demonstrated, that compare very favorably with the existing techniques.     

Excess delay estimation from time-varying mobile radio channelimpulse response measurements

This letter proposes a method for estimating the instantaneous excess delay in time-varying mobile radio channel impulse response measurement data using image processing techniques. The method is shown by example to produce more accurate mean power delay profiles than those produced assuming either constant or linearly varying excess delay     

单频激光宽频段频率和强度噪声测量技术

报道了一种mHz至MHz宽频段激光噪声的规范测量技术。通过研制基于迈克耳孙光纤干涉仪的相关延时自外差频率噪声测量装置和具有定标功能的光外差拍频测量装置,结合频谱分析仪和快速傅里叶变换分析仪等标准仪器,规范地测量出了单频激光在mHz至MHz宽频段内的频率和强度噪声特性,并验证了测量结果的准确性。该测量技术有望应用于引力波探测和精密测量等应用中的激光噪声评估。     

一种基于高衰减光纤的光纤光栅热线式流量计

为了发展全光学流量测量技术,提出了一种基于掺钴高衰减光纤的光纤光栅热线式流量计。通过解调光纤布拉格光栅(Fiber Bragg Grating, FBG)中心波长进行流量测量,具体包括传感器制作、温度传感特性测定和流量测量实验。结果表明,基于衰减系数为8.9 dB/cm、工作波长约为1480 nm的掺钴光纤的FBG具有10.3 pm/℃的温度灵敏度;流量计在400～3700 L/h液体流量范围内可高重复性地实现测量;流量--FBG中心波长遵循特定非线性函数计算模型;流量计的平均灵敏度约为0.15 pm/(L·h^-1),低流速下灵敏度最高可达到1 pm/(L·h^-1)。所提出的流量计丰富了光纤光栅用于液体流量测量的研究。设计中采用了掺钴高衰减光纤自发热和单端毛细管封装,为流量传感器的全光学化、微型化和高灵敏度发展提供了新思路。     

Distributed polarization-mode dispersion compensation using polarizers

We numerically evaluate the performance of two kinds of distributed polarization-mode dispersion compensation techniques using either linear or elliptic variable polarizers. Each in-line compensator is characterized by only one or two degrees of freedom and the average power is used as a monitor signal, which simplifies the control algorithm. The use of polarizers causes inevitable attenuation of the optical signal, which induces additional noise in amplified systems. Nevertheless, the noise enhancement due to the distributed polarizer-induced loss is shown to be limited in systems operated with erbium-doped fiber amplifiers in gain saturation and the tolerable differential group delay can be improved if the frequency of insertions is increased.     

Attenuation and ratio—National standards

In national standards laboratories, the popular attenuation measurement techniques are: RF, IF, vector IF, and AF substitution; power ratio, voltage ratio, time-interval ratio, and six-port methods; and a procedure that employs a Josephson junction in a superconducting ring. These nine techniques are briefly described, the dynamic ranges and accuracies achieved with them are reported, and their relative merits are discussed. The later sections are devoted to: attenuation measurement techniques used in industry and elsewhere, voltage doubling circuits, attenuation traveling standards, errors and uncertainties associated with attenuation measurements, and international attenuation comparisons. An analysis of the results obtained in four recent international comparisons is included.     

Measurement and frequency extrapolation of microwave attenuation statistics on the earth-space path at 13, 19, and 30 GHz

The program to use the Crawford Hill sun tracker for measurement of attenuation on the earth-space path at 13, 19, and 30 GHz is described. Cumulative attenuation statistics for a year of data are presented, along with a discussion of likely sources of error. The results of the data analysis can be briefly summarized. 1) The extrapolation procedure proposed by Hogg, wherein attenuation measurements at two frequencies are used to predict attenuation at a third, yields results in good agreement with observation except at very high attenuation levels. 2) Because of limits on the measuring range of the sun tracker, more accurate estimates of fading statistics for fades >30 dB at 30 GHz can probably be made by extrapolation than by direct measurement.