High-speed drawing of optical fibers with pressurized coating

To make progress in high-speed drawing of optical fibers, a pressurized coating method was developed on the basis of viscous flow behavior of the coating resin. In a pressurized die, when the shear rate at the fiber surface is minimized, the pressure which is affected by the resin viscosity reaches on optimum condition, resulting in the coating diameter being dependent only on fiber and die diameters. Coating tension is given as a function of pressure so that it is closely related to the optimum pressure through the viscosity. Based on these fundamentals, a 1200-m/min drawing speed was achieved, indicating a smooth and uniform coating with good concentricity. It is clarified that fiber transmission loss does not fundamentally change in relation to the speed.     

Spontaneous and stimulated Brillouin scattering gain spectra in optical fibers

We study the Brillouin scattering behavior in several single-mode fibers with different waveguide characteristics in terms of their longitudinal mode structures in the gain spectrum, linewidth narrowing, and stimulated Brillouin scattering (SBS) threshold levels. Evolution from spontaneous to SBS is investigated by monitoring the Brillouin line-shape and the behavior of the longitudinal acoustooptic resonance modes that exist in the core. We compare our results with the current theory of Brillouin scattering generated from noise in the undepleted pump approximation. We also present experimentally Brillouin gain spectra in the highly depleted pump regime, where there is no analytical solution, by showing the evolution of the gain spectrum as a function of the injected laser intensity.     

Fusion mass-splices for optical fibers using high-frequency discharge

This report describes a high-frequency discharge massheating technique and a fiber aligning mechanism for fusion mass-splicing of silica fibers, and a reinforcement technique for the spliced fibers. Splice loss, operation time, and loss stability of reinforced mass-splices were evaluated by using fiber ribbon units comprising five graded-index fibers with 50-μm core and 125-μm outer diameters. They proved the excellence of the method.     

三五阶非线性光纤中光脉冲的啁啾和频谱

为了探讨光纤的五阶非线性对光脉冲传输的影响,利用同时考虑三阶和五阶非线性效应的非线性薛定谔方程,在忽略光纤色散的情况下,解析并计算研究了超高斯光脉冲的非线性相移、频率啁啾。数值模拟了光脉冲传输的功率频谱。结果表明,与只有三阶非线性折射率的情形相比,正五阶非线性折射率的存在使光脉冲在光纤中传输的非线性相移和最大频率啁啾增大,使无啁啾光脉冲的频谱宽度变宽,谱峰数目增多,高斯脉冲初始啁啾对频谱的影响与三阶非线性折射率的情形类似;负五阶非线性折射率则使光脉冲传输的非线性相移和频率啁啾呈现新的特点,并使无啁啾光脉冲的频谱宽度变窄,谱峰数目减少。     

Optical loss property of silica-based single-mode fibers

The optical loss property of silica fibers has been investigated theoretically and experimentally based on their Rayleigh scattering and absorption losses. The Rayleigh scattering loss for fibers has been estimated using Rayleigh scattering coefficients and power distribution in the fiber. The Rayleigh scattering coefficients are measured for preforms prepared for fiber fabrication and are discussed for GeO₂ -doped and F-doped glasses. The relationship between the optical loss and fiber parameters is clarified. Moreover, the loss increase due to residual stress which occurs during the drawing process is simulated. The optical loss limitations for GeO₂-doped and pure silica core fibers are shown     

Rare-earth doped optical fibers for temperature sensing

The feasibility of using a variety of rare-earth doped optical fibers for measuring spatially averaged temperatures from ~0 to ~100°C over distances of 10 to 20 m is discussed. Such distributed temperature sensors would be particularly well-suited for building climate control systems and industrial processing applications. The temperature-dependent absorption spectra of 6 MCVD processed fibers containing different concentrations of Nd³⁺, Pr³⁺, and Yb³⁺ rare-earth ions were characterized and used to determine thermally active dopant species, optimal dopant concentrations, and most sensitive operating wavelengths for use as dual wavelength distributed temperature sensors     

半导体纳米材料光学吸收谱的温度效应

观测了半导体纳米薄膜材料,在室温下的紫外-可见吸收光谱及随测量温度变化至液氦温区的光谱变化,考察光吸收边随温度降低发生蓝移的情况,进而分析温度效应对晶格参数及电子-声子相互作用的影响,造成其能带漂移.     

A distributed temperature sensor based on liquid-core optical fibers

The principles of operation, the design, and performance of a fiber-optic temperature-distribution sensor are discussed. The sensor uses optical time-domain reflectometry (OTDR) to detect temperature-induced changes of backscatter power at many separate locations in the fiber. In liquid-core fibers, a sensitivity of2.3 times 10^{-2}dB/°C (0.54 percent° C^-1) was observed. A measurement accuracy of 1°C with a spatial resoltuion of 1 m is attainable over a fiber length of 100 m.     

Increase in photosensitivity in silica-based optical waveguides on silicon

An increase in the photoinduced refractive-index change Delta n in GeO/sub 2/-doped silica optical waveguides on silicon is described. The increase is attained by the consolidation of a core film in a reducing atmosphere. A maximum Delta n of 3.9*10/sup -4/ is obtained for the TE mode by UV laser irradiation at 248 nm. This is four times larger than that in conventional waveguides.<>     

Simultaneous distributed measurement of strain and temperature fromnoise-initiated Brillouin scattering in optical fibers

The simultaneous determination of strain and temperature distributions from the measurement of noise-initiated Brillouin scattering (NIBS) power and frequency shift in optical fibers is discussed. Equations governing the growth of the NIBS signal are derived and from these, we calculate the dependence of the Brillouin power on temperature and strain. We study the potential problem given by the need to normalize the nonlinear Brillouin signal and present a new technique that solves this problem by mathematically combining the values of the Stokes and anti-Stokes powers to produce a linear effective power. Experimental results are presented that support this theory and allow the verification of the coefficients governing the dependence of the Brillouin power and frequency shift on temperature and strain. The signal-to-noise ratio of the sensor is discussed, and it is found that the noise associated with the field statistics plays a limiting role in the sensor performance and that an optimum value for the Brillouin gain factor can be determined. A simultaneous distributed temperature and strain sensor is demonstrated; preliminary results show a strain resolution of 100-μm strain, a temperature resolution of 4°C, and a spatial resolution of 40 m, over a sensing length of 1200 m     

High reliability optical splitters composed of silica-based planarlightwave circuits

The environmental and mechanical reliability of a planar lightwave circuit (PLC)-type optical splitter modules is investigated with reference to the Bellcore requirements. The module is composed of Y-branching silica-based waveguides on Si connected to optical fiber with UV-curable adhesives and is packaged in a metal case which is filled with humidity-resistant resin. High optical performance such as low loss, low reflection, and thermal stability are obtained through the use of this fiber connection technique. Ten reliability tests including long-term environmental and mechanical tests were carried out for more than ten PLC splitter modules. Under one of the most severe sets of conditions (75°C and 90% RH), all the 19 samples we tested were stable for more than 5000 hours. Other tests confirmed that the PLC splitters offer long-term stability and that their optical characteristics have sufficient mechanical strength. These results indicate that the PLC splitters can be used for practical applications     

Polarization in optical fibers

Recent research on fibers with very small or very large birefringence for polarization-dependent applications is reviewed. The nature of random coupling between normal modes of polarization is analyzed and discussed in connection with various applications.     

High-speed optical pulse transmission at 1.29-µm wavelength using low-loss single-mode fibers

Optical-fiber transmission experiments in the 1.3-μm wavelength region are reported. GaInAsP/InP double-heterostructure semiconductor laser emitting at 1.293 μm is modulated directly in nonreturn-to-zero (NRZ) codes at digit rates tanging from 100 Mbit/s to 1.2 Gbit/s. Its output is transmitted through low-loss GeO2-doped single-mode silica fibers in 11-km lengths. Transmitted optical signals are detected by a high-speed Ge avalanche photodiode. Overall loss of the 11-km optical fibers, including 11 splices, is 15.5 dB at 1.3 μm. Average received optical power levels necessary for 10^-9error rate are -39.9 dBm at 100 Mbit/s and -29.1 dBm at 1.2 Gbit/s. In the present system configuration, the repeater spacing is limited by loss rather than dispersion. It seems feasible that a more than 30 km repeater spacing at 100 Mbit/s and a more than 20 km even at 1.2 Gbit/s can be realized with low-loss silica fiber cables, whose loss is less than 1 dB/km. Distinctive features and problems associated with this experimental system and constituent devices are discussed.     

Structures, parameters, and transmission properties of optical fibers

Signal-transmission characteristics of optical-fiber waveguides are determined largely by their structural geometries, physical parameters, and materials properties. This paper reviews these factors and discusses the roles they play in determining loss and bandwidth in both single-mode and multimode fibers. Effects of polarization and of waveguide perturbations are included, and recent work on tailoring the bandwidth spectrum of single-mode fibers is presented.     

Design and fabrication of broad-band silica-based optical waveguidecouplers with asymmetric structure

Waveguide-type directional couplers with different guide widths in the interactive region are designed and fabricated with silica-based waveguides on silicon substrates. It is demonstrated that these asymmetric couplers have broadband coupling-ratios of, for example, 50%±5%, 25%±3%, or 5%±2% over a wide wavelength range from 1.3 to 1.55 μm, which are in good agreement with the results calculated using the beam propagation method (BPM). The excess loss of these couplers is as low as 0.7 dB, including input and output single-mode fiber coupling losses     

Intensity effects on the stimulated four photon spectra generated by picosecond pulses in optical fibers

The intensity dependence of stimulated four photon mixing (SFPM) spectra generated in 15 m of a 4-mode optical fiber by 25- ps pulses has been investigated. Despite the shortness of pulses, the SFPM conversion was highly efficient due to the intrinsic phase matching condition. In addition to usual features of SFPM spectra generated by nanosecond pump pulses, picosecond SFPM spectra were broadened by self phase modulation (SPM) and cross phase modulation (XPM). At the highest pump powers, intensity saturated frequency continua, arising from the combined effects of SFPM, stimulated Raman scattering (SRS), SPM, and XPM were generated all over the visible spectrum.     

BOTDR的已敷设传感光纤温度和应变区分测量方法

为了解决已敷设传感光纤中布里渊谱峰功率初值难以获取,基于频移和功率双参量的温度和应变区分测量误差大等问题,提出了解决方法。通过标定实验确定布里渊频移和相对谱峰功率的温度和应变系数、频移初始值;根据布里渊散射功率特性方程,通过试探法,利用已敷设光路中温度和应变已知的参考光纤确定方程系数,建立了谱峰功率初始值;利用归一化方法克服了传感系统中乘性噪声导致的测量误差;利用谱宽变化消除了温度和应变突变点处的谱峰功率异常峰值;最后,根据光纤复合海底电缆的现场情况建立了模拟光路,并进行了温度和应变测量实验。结果表明,在5.6 km处可实现4.3℃和110 的测量精度,可实现已敷设传感光纤整条光路上的温度和应变区分测量,为工程应用提供了理论和实验依据。     

Dispersion and bandwidth spectra in single-mode fibers

Bandwidth spectra of single-mode fibers are calculated from experimentally obtained chromatic-dispersion-versus-wavelength curves. Results include second-order effects on bandwidth which depend on the curvature of the dispersion curves. Examples illustrate how bandwidth spectra change as a function of source power spectra. They also show how small changes in fiber dimensions and refractive-index differences can cause significant bandwidth changes at 1.3 μm wavelength.     

High-speed photodetectors in optical communication system

This paper presents a review and discussion for high-speed photodetectors and their applications on optical communications and microwave photonics.A detailed and comprehensive demonstration of high-speed photodetectors from development history,research hotspots to packaging technologies is provided to the best of our knowledge.A few typical applications based on photodetectors are also illustrated,such as free-space optical communications,radio over fiber and millimeter terahertz signal generation systems.     

High-speed, burst-mode, packet-capable optical receiver andinstantaneous clock recovery for optical bus operation

This paper describes an enhanced performance version of a high-speed burst-mode compatible optical receiver and its application to 622-Mb/s optical bus operation in conjunction with an instantaneous clock recovery scheme. The receiver is fabricated in a 12 GHz f_t silicon bipolar technology and consists of a differential transimpedance amplifier with an auto-threshold level controller and a high-speed quantizer. Using an InGaAs avalanche photodiode, the typical burst mode sensitivity is around -34 dBm (10^-9 BER) at bit rates up to 1.5 Gb/s with a dynamic range of 26 db for both pseudorandom and burst signals. The results using a laser beam modulated by a high-speed external modulator indicate that the receiver can be operated at bit rates higher than 2 Gb/s. With a worst-case self-resetting time <50 ns for the threshold control circuit, the receiver is usable for optical packet communication where data signals with varying optical power are employed. This receiver was demonstrated in a 622-Mb/s optical bus application where the clock signal was recovered from the packet data signal using a novel high-speed CMOS instantaneous clock recovery IC