All fiber tunable- or dual-wavelength Yb-doped fiber laser covering from dissipative soliton to dissipative soliton resonance

In this Letter, a simple and passively mode-locking Yb-doped all fiber laser using a nonlinear polarization ro- tation technique operating under dissipative soliton （DS） or dissipative soliton resonance （DSR） conditions is proposed. Furthermore, using a combination of a bandpass filter and a Loyt filter, tunable single-wavelength or dual-wavelength operation under two different conditions is realized, respectively. The tunable single- wavelength DS laser has a 5 nm tuning range from 1029 to 1034 nm with a pulse width of 110 ps. The tunable single-wavelength DSR operation laser has a range of 4 nm. In-depth research on the mechanism of the con- version between DS and DSR is carried out. Particularly, under dual-wavelength DSR operation, the obtained step-like pulses consist of two rectangular pulses with different energies. This work could help give a deeper insight into normal dispersion pulses.

All-fiber linearly polarized laser oscillator by fiber coiling loss control

In this paper,we demonstrate an all-fiber linearly polarized fiber laser oscillator.The single polarization of the oscillator is achieved through the careful designing of the active fiber coiling.The relationship between fiber coiling diameter and polarization extinction ratio and optical efficiency is studied,whose results lead to an optimized system.The thermal management of the oscillator is also refined,which allows the oscillator to reach a maximum output power of44.1 W with an optical-to-optical efficiency of 57.9%.A high average polarization extinction ratio of 21.6 d B is achieved during a 2-hour stability test.The oscillator also owns a narrow 3-d B bandwidth of 0.1 nm,as well as near-diffraction-limit beam quality of M^2～ 1.14.

High-energy pulse generation using Yb-doped Q-switched fiber laser based on single-walled carbon nanotubes

An all-fiber laser using a single-walled carbon nanotube（SWCNT） as the saturable absorber（SA） for Q-switched operation in the 1031 nm region is demonstrated in this work. A lasing threshold as low as 17 mW was realized for continuous wave operation. By further increasing the pump power, stable Q-switched pulse trains are obtained when the pump power ranges from 38 mW to 125 mW, corresponding to repetition rate varying from 40.84 kHz to 66.24 kHz, the pulse width from 2.0 μs to 1.0 μs,and the highest single pulse energy of 40.6 nJ respectively.

Effect of Modulation Error on All Optical Fiber Current Transformers

For actively modulated In-line Sagnac interferential all optic fiber current transformers (AOFCTs), the accuracies are directly affected by the amplitude of the modulation signal. In order to deeply undertand the function of the modulator, a theoretical model of modulation effect to AOFCTs is built up in this paper. The effect of the amplitude of the modulation signal to the output intensity of AOFCTs is theoretically formulated and numerical calculated. The results show that the modulation voltage variation could affect the output accuracies significantly. This might be some references on the investigation for practical applications of AOFCTs.

Design and applicability analysis of independent double acquisition circuit of all-fiber optical current transformer

The advantages of the all-fiber optical current transformer include but are not limited to being small in size,having no magnetic saturation,exhibiting high measurement accuracy,and boasting strong electromagnetic interference resistance.However,the high cost of the all-fiber optical transformer limits its promotion and application in engineering.This paper proposes a design scheme of an independent double acquisition loop for the all-fiber optical current transformer based on the single optical path.Firstly,based on the closed-loop control mode and open-loop control mode,the twochannel sampling signal demand for relay protection,and the independent dual-acquisition loop design scheme of the all-fiber optical current transformer are proposed.Secondly,the reliability and economic feasibility of the scheme are demonstrated by an analysis of system failure and cost.The results show that the scheme can actualize the acquisition function of two independent all-fiber optical current transformer products on a single all-fiber current transformer in an integrated manner,which greatly reduces the cost of the all-fiber optical current transformer in engineering applications.

A 168-W high-power single-frequency amplifier in an all-fiber configuration

We present a high-power, single-frequency, narrow linewidth fiber amplifier based on master oscillator power amplification chains in an all-fiber configuration. The effect of the delivery fiber on the maximum output power is studied. A home-made 1064-nm seed laser with a 20-kHz linewidth is boosted to 129 W, and limited by stimulated Brillouin scattering （SBS） when the delivery fiber is 1.2 m long By shortening the delivery fiber length to 0.7 m, the SBS threshold is increased efficiently and the maximum output power rises to 168 W with an 82.9% power conversion efficiency. The experimental results indicate that the output power can be further raised by shortening the delivery fiber length and increasing the pump power.

Measuring Optical Length and Analyzing Accuracy Error Based on All-Fiber Optic Interferometer

An optical length measuring system base on all-fiber optic interferometer is proposed. The theoretical analysis indicates that, when the two branches of the interferometer are equal, the output have the maximum coherent intensity. Therefore, the optical length can be obtained by measuring the distance of collimator movement. Through the experiment and simulation, the impact of the signal-to-noise ratio and fluctuation of the coupling efficiency on null error has been obtained.

High-energy femtosecond Yb-doped all-fiber monolithic chirped-pulse amplifier at repetition rate of 1 MHz

A high-energy femtosecond all ytterbium fiber amplifier based on a chirped-pulse amplification（CPA） technique at a repetition rate of 1 MHz seeded by a dispersion-management mode-locked picosecond broadband oscillator is studied.We find that the compressed pulse duration is dependent on the amplified energy,the pulse duration of 804 fs corresponds to the maximum amplified energy of 10.5 μJ,while the shortest pulse duration of 424 fs corresponds to the amplified energy of 6.75 μJ.The measured energy fluctuation is approximately 0.46% root mean square（RMS） over 2 h.The low-cost femtosecond fiber laser source with super-stability will be widely used in industrial micromachines,medical therapy,and scientific studies.

Six-bit all-optical quantization using photonic crystal fiber with soliton self-frequency shift and pre-chirp spectral compression techniques

In this paper, we propose an optical quantization scheme for all-optical analog-to-digital conversion that facilitates photonics integration. A segment of 10-m photonic crystal fiber with a high nonlinear coefficient of 62.8 W-1/kin is utilized to realize large scale soliton self-frequency shift relevant to the power of the sampled optical signal. Furthermore, a 100-m dispersion-increasing fiber is used as the spectral compression module for further resolution enhancement. Simulation results show that 317-nm maximum wavelength shift is realized with 1550-nm initial wavelength and 6-bit quantization resolution is obtained with a subsequent spectral compression process.

A theoretical and experimental study on all-normal-dispersion Yb-doped mode-locked fiber lasers

We report on a theoretical and experimental study of an all-normal-dispersion （ANDi） Yb-doped mode-locked fiber laser, in which nonlinear polarization rotation （NPR） is used to realize mode-locking without any dispersion compensation. Based on the coupled nonlinear Schr6dinger （CNLS） equation, a model simulating the mode-locked process of an all-normal-dispersion ring fiber laser is developed, which shows that the achievement of stable mode-locking depends on the alignment of the polarization controller （PC） along the fast-polarization axis of the fiber, the birefringence intensity, and the net cavity dispersion. According to the theoretical analysis, stable mode-locked pulses with pulse duration 300 ps and average output power 33.9 mW at repetition rate 36 MHz are obtained.

基于QEPAS技术的痕量气体高灵敏度检测系统研究

搭建了一种用于乙炔痕量气体高灵敏度探测的全光式石英音叉增强型光声光谱系统。为了提高系统探测灵敏度,采用光功率放大技术提高激励光源功率,采用直角棱镜使激光束穿过两个共振管,采用光纤珐珀传感技术测量音叉叉股面外单向振动代替面内对称振动;同时利用自稳定技术提高系统的稳定性。采用有限元分析方法对传统商用石英音叉的振动进行了模拟和分析。在对激光调制深度、微共振管结构尺寸和激光输出功率等参数优化基础上,得到了2.9 ppb的系统检测极限,归一化等效噪声系数为2.4×10^(-9)cm^(-1)·W·Hz^(-1/2);二次谐波信号幅值与C_(2)H_(2)浓度呈现良好的线性关系,其线性相关系数达到0.999。最后经过1小时的连续实验验证了通过自稳定技术可以有效提高系统的稳定性。

不同钢纤维掺量全轻混凝土梁落锤冲击试验研究

由于全轻混凝土结构抗剪承载力较低,因此有必要探究钢纤维的加入对全轻混凝土梁动力性能的影响。设计钢纤维体积掺量为0%、1%、2%共3根适筋梁,对其跨中区域进行落锤冲击试验,并利用LS-dyna有限元软件进行数值模拟,对比分析各试件破坏形态、冲击力时程曲线、跨中位移时程曲线。试验结果表明:在相同冲击荷载作用下随着钢纤维体积掺量的增加抑制裂缝产生和发展的现象越显著,并且裂缝相对更加集中于梁跨中区域,支座处裂缝相对减少。钢纤维的加入不影响试件冲击力最大值,但随着钢纤维体积掺量的增加,各试件冲击力第二峰值与最大值之比增加14%和26%,跨中位移最大值与残余位移分别降低3、8mm与3、7mm。经研究得出钢纤维的加入显著提高全轻混凝土梁抗冲击性能。

全光纤结构的2.8μm增益开关激光器

波长为2.8μm的中红外脉冲激光器在科研及生物医疗领域具有重要应用.自主研制基于增益开关的976 nm高功率脉冲激光器,并以此为泵浦源,两端刻有光纤光栅的Er^(3+):ZBLAN(ZrF_(4)-BaF_(2)-LaF_(3)-AlF_(3)-NaF)光纤线型腔作为振荡器,通过级联增益开关的方式,实现了全光纤结构的2.8μm增益开关激光器.输出脉冲的重复频率为50 kHz,脉宽为1.27μs,最大输出功率为175.2 mW,相应的脉冲能量为3.54μJ.由于采用增益开关和光放大方案制备的976 nm泵浦源输出稳定性较高,与采用传统电调制泵浦源方案相比,利用本研究泵浦源方案实现的2.8μm增益开关激光器具有更高的输出脉冲稳定性.该工作从提升输出特性方面拓展了2.8μm全光纤增益开关激光器的研究,并为其他波段增益开关激光器在提高输出脉冲稳定性方面提供了有益借鉴方案.

全光纤微震监测技术在底板突水监测中的应用研究

目前国内的光纤微震监测系统多是基于光学光栅传感技术,而光纤光栅波长解调限制了系统检测频率与灵敏度,且长时间、连续不间断的微震监测成功案例较少。针对上述问题,提出了一种新型全光纤微震监测系统。以潘二煤矿11023工作面回采过程中底板突水监测为工程背景,使用全光纤微震监测系统与ESG微震监测系统进行对比,得出全光纤微震监测系统具有以下优势:记录的波形频谱特征更清晰,表现出高信噪比优势;对扰动深度的监测范围更大,远距离监测效果更好;震源定位结果分布更加合理,更符合工作面实际开采情况。在监测工作面回采全周期内,分析了11023工作面断层异常区底板破坏与微震活动性关系:在断层和煤层变薄异常区附近,微震事件的数量增多、强度增大;工作面初采期间应力集中释放,受采动影响,底板破坏较深;相对大能量事件主要分布在断层异常区的底板,底板破坏深度约为27 m,微震事件在3煤底板60 m以下没有成线或成面聚集的情况,说明裂隙并未扩展,未形成导水通道,工作面安全回采。

具有偏振互易结构的温度不敏感型全光纤振动传感技术

文中提出一种具有温度自抑制功能的全光纤、微型化振动传感器,实现电力设备振动信号精确捕获。通过在保偏光纤上制作微型悬臂梁,将外部振动转为两个正交偏振态之间的相位变化,实现对外部振动的测量。为有效抑制环境温度对光纤传感器的干扰,在传感器中形成了偏振互易式光路结构,有效消除温度双折射而引入的相位误差。测试结果表明所提出传感器在100 Hz~6 kHz范围内具有平坦的响应频带,振动测量灵敏度达到87.76 mV/(m·s^(2)),且在25℃至60℃的温度范围内显示出优异的稳定性。为验证所提出传感器对电力设备振动的监测有效性,在实验室开展了变压器油中燃弧过程中设备外壳的振动冲击检测试验,试验结果表明传感器有效捕获燃弧过程设备外壳的振动波形,燃弧过程振动持续时间约为20 ms,振动主频率为800 Hz,最大振幅达4.2 m/s^(2)。

基于GPON的校园全光网建设与实践

目前,广州大学(以下简称“我校”)的新建楼宇正式投入使用。为构造智慧校园建设所需的网络环境,文章以全光网络技术在该大楼率先落地试点,讨论了现今高校传统三层校园网架构存在的弊端及全光校园网的实际落地过程,旨在以千兆无源光网络(Gigabit-capable Passive Optical Networks,GPON)技术为基础实现校园全光网建设。

基于不同泵浦方案的全光纤少模放大器放大特性对比研究

设计并构建全光纤型少模掺铒放大器,实验对比研究不同泵浦模式及方向对LP01、LP11a、LP11b这3个信号模式的增益特性影响.实验对泵浦功率、输入信号功率以及多波长情况下的放大器特性进行分析.结果表明,4种泵浦方案中,前向LP11泵浦情况下放大器有最佳性能,在整个C波段上信号增益超过20 dB、模式增益差低于0.9 dB,噪声系数小于9.6 dB;信号输入功率为-10 dBm/模式时,在1550 nm处,3个信号模式的增益均超过20.8 dB、DMG低至0.3 dB、LP01信号光的噪声系数低于6.2 dB以及LP11信号光的噪声系数低于9.6 dB.4种泵浦方案下对比不同泵浦方向可得:前向泵浦放大器的噪声系数最小,但3种信号模式的增益也较小,而采用后向泵浦时,高阶信号模式增益增加,但噪声系数也会变大.对比泵浦模式可发现,相比于LP01泵浦,LP11泵浦能大幅提高LP11信号光的增益,对LP01信号光增益影响较小,从而可降低DMG值.

光电复合缆载流量监测系统光电子器件可靠性分析

针对构成光电复合缆载流量监测系统的分布式光纤温度传感器(DTS)和全光纤电流互感器(FOCT)的运行可靠性问题,基于可靠性框图法,对其中的关键光电子器件及信号处理模块建立可靠度、失效率和平均寿命分析模型,仿真分析了使用环境、运行时间和管芯温度对系统可靠性的影响。结果表明,DTS和FOCT系统中关键光电子器件的失效率均随管芯温度的增加而增加,可靠度随管芯温度和使用时间的增加而降低,平均寿命随管芯温度的增加而降低,且使用环境越恶劣,整体可靠性越低,在光源管芯温度为50℃,运行时间为31500 h,使用环境良好的条件下,DTS和FOCT系统的失效率、平均寿命及可靠度估计值分别为9.84×10^(-5)1/h、10160.96 h、0.2342和1.026×10^(-5)1/h、97434.947 h、0.65316。

混杂纤维对全沙漠砂混凝土基本力学性能的影响

为研究混杂纤维对全沙漠砂混凝土力学性能的影响,将聚乙烯醇纤维(PVA)、聚丙烯纤维(PP)以不同比例混合后掺入全沙漠砂混凝土中进行了抗压、抗折等试验,同时建立了材料单轴压缩应力-应变本构模型,并采用ABAQUS软件进行数值模拟验证。研究结果表明:在混杂纤维总体积掺量为1.5%的条件下,试件抗压强度无显著变化,随着PVA纤维比例提高,试件抗折强度、拉伸强度及拉伸峰值应变明显提高;较于普通全沙漠砂混凝土,混杂纤维全沙漠砂混凝土峰值应力与弹性模量略微降低,变形能力提升显著;PP纤维和PVA纤维掺量分别为0.5%、1.0%时具有最优的混杂效应,与普通全沙漠砂混凝土相比,抗折强度、单轴拉伸强度和延性分别提高了77%、55%、16%;基于过镇海模型提出的轴压应力-应变本构模型与试验实测曲线拟合程度较好,并与ABAQUS软件的数值模拟验证结果相似。

AFOCT系统中敏感光纤器件的老化对系统测量准确性的影响

研究了全光纤电流互感器(AFOCT)系统中敏感光纤器件老化对系统测量准确性的影响。首先,基于法拉第磁光效应,采用琼斯矩阵建立AFOCT系统的传输模型;结合存在双折射的传感光纤的琼斯矩阵,给出系统的注入电流测量值的表达式。进一步,搭建了光学测试系统,实验表征传感光纤的双折射率;基于测试结果,对传感光纤的琼斯矩阵以及系统传输模型进行校准,以降低AFOCT系统注入电流的测量误差。最后,对传感光纤开展了相当于实际运行3个月的加速老化试验,并测试获得老化后传感光纤的双折射率。采用校准后的AFOCT系统传输模型,分析了老化后双折射率的变化对系统注入电流测量值的影响。实验结果表明,在传感光纤老化3个月之后,系统就已经产生了0.2955%的相对误差。