Linearly Polarized Polarization-Maintaining Er^(3+)-Doped Fluoride Fiber Laser in the Mid-Infrared

We demonstrated the~2.8-μm and~3.5-μm linearly polarized continuous wave(CW)laser outputs from a polarization-maintaining(PM)Er^(3+)-doped fluoride fiber laser.By introducing a film polarizer into the cavity to select the laser polarization orientation,the~2.8-μm linearly polarized CW laser with a high polarization extinction ratio(PER)of~23 dB and maximum output power of 2.37 W was achieved under double-end pumping at 976 nm.By adding another 1981-nm pump source simultaneously,the~3.5-μm linearly polarized CW laser was also obtained,giving higher PER of~27 dB and maximum output power of 307 mW which is only limited by the available power of 1981-nm pump.To the best of our knowledge,this is the first report on a mid-infrared linearly polarized CW PM fiber laser in the>2.5-μm mid-infrared region.This work not only opens up opportunities for some new mid-infrared applications,but also provides a promising platform for developing high-stability and versatile mid-infrared laser sources.

Low-noise compact fiber laser based on nonlinear polarization evolution in an all-polarization-maintaining figure-8 cavity

We demonstrate an all-polarization-maintaining(APM)fiber mode-locked laser based on nonlinear polarization evolution(NPE).A well-designed Sagnac fiber loop is employed to establish the nonlinear polarization evolution process in a polarization beam splitter(PBS)figure-8 fiber laser.Nonlinear loss curves are calculated to verify the saturable absorption characteristic of this NPE-based APM oscillator.Then,we simulate the pulse propagation process in the cavity to demonstrate the pulse mode-locked formation.Finally,we also design a realizable compact scheme to further reduce noise disturbances,achieving a 101-fs mode-locked pulse train with a 0.3-mrad integrated phase noise and a 0.006%integrated relative intensity noise(RIN).This figure-8 fiber laser provides a new scheme for compacting low-noise compact APM fiber lasers based on the NPE mode-locked mechanism.

Electromagnetism and Absorptivity of the Modified Micro-coiled Chiral Carbon Fibers

Micro-coiled chiral carbon fibers are modified by nano-Ni. X-ray diffraction （XRD） and scanning electron microscopy （SEM） are used to compare the composition and morphology of the unmodified and the modified fibers. The results show that electromagnetism parameters of the modified are different from those of the unmodified. After modification by nano-Ni, the micro-coiled chiral carbon fibers have decreased permittivity and electrical loss. The permeability and magnetic loss of the modified carbon fibers become larger than those of the unmodified ones. Moreover, the modification of unmodified chiral carbon fibers into the modified is much like changing hollow electric windings into those with magnetic cores inside. The modifier intensifies the cross polarization of the chiral carbon fibers and makes the permittivity and the permeability get closer to each other which improves the matching performance and enhances absorbability of coatings. In the range of 6-18 GHz, the reflectivity of the coating is 6-8dB and the bandwidth is 12 GHz. The area density of the coating is below 3 kg/m^2.

A kind of multiwavelength erbium-doped fiber laser based on Lyot filter

A multiwavelength tunable ring-cavity erbium-doped fiber laser(EDFL)based on a Lyot filter was presented.For the proposed Lyot filter,a comb filter consisting of an EDF-polarization-maintaining fiber(EDF-PMF),a polarization controller(PC),and a circulator with four ports was used to suppress the mode competition.The light transmission direction was guaranteed by the circulator.For the proposed fiber laser,tunable single,dual,triple,quadruple,quintuple,sextuple,and septuple wavelengths were realized.A single-wavelength laser output with an optical signal-to-noise ratio(SNR)of up to30.56 dB was realized,and a tuning range of 1590.54 nm to 1599.54 nm was achieved by tuning the PC.The stability of the single,dual,triple,and quadruple-wavelength center power fluctuations was less than 0.05 dB,0.98 dB,5.07 dB,and7.71 dB respectively.When the laser was operated in the multiwavelength condition,the SNR was more than 20.97 dB.The proposed erbium-doped fiber laser is suitable for fiber-sensing system applications.

扭转角度对Shupe误差的影响及绕环工艺的优化

针对同一批次光纤环圈Shupe误差差异较大的问题,分析了扭转角度对Shupe误差的影响,并提出了绕环工艺优化方法。通过引入扭转角度重新推导了光纤环圈热致Shupe误差的理论公式并结合光纤环圈精细化有限元模型,建立了考虑扭转角度的光纤环圈Shupe误差模型。通过仿真对比不同扭转角度对Shupe误差的影响可知,扭转角度是造成同一批次光纤环圈Shupe误差可补偿性差的主要原因。通过优化绕环工艺方法,在分纤步骤即进行光纤退扭,可保证后续绕环环节张力控制的有效性和扭转角度的一致性。实验结果表明,采用退扭工艺后,光纤陀螺温度补偿后的零偏误差由0.01(°)/h降至约0.005(°)/h。

保偏光纤内外涂层应力对光纤双折射的影响分析

通过研究熊猫型保偏光纤的应力区结构和材料的热膨胀系数、杨氏模量、泊松比,得出了提升保偏光纤双折射的方法。根据内外涂层材料低温特性不同,得出了减小光纤涂层直径能增强光纤双折射的结论。利用COMSOL有限元分析软件建立了光纤环内部受力模型,并分析了光纤涂层材料和不同厚度比例对绕制张力的抑制效果。仿真结果表明,当光纤包层直径和外涂层直径一定时,存在内外涂层最佳厚度比例,较原光纤厚度比例抑制绕制张力效果提升约10%,内外涂层的杨氏模量、泊松比的改变也能有效地减小绕制张力的作用。

基于测井技术的连续油管应用现状与发展方向

随着非常规油气的深入开发,连续油管在测井领域的应用逐渐增加,但仍面临部分测井作业项目与井下作业重叠、应用方向不明确、技术特色不突出、应用规模小等挑战。该文深入剖析了连续油管在测井领域的应用现状,系统梳理了制约其发展的关键因素,结合当前非常规油气规模开发背景,探讨了连续油管测井在关键技术突破、测井工艺完善、应用场景拓展、光纤测井系统优化、数字化队伍建设以及光纤测井解释模型构建的等主要方面的解决策略。强调了发展连续油管光纤测井技术的重要性,提出该项技术在提高作业效率、促进地质工程一体化方面具有潜在价值。指出满足非常规油气资源开发的需求,建立与测井作业模式相匹配且具有测井特色的连续油管技术是未来该技术发展的方向,该技术将为油气田的高效、安全开发提供坚实的技术支持。

低折射率温度系数保偏光纤的变温性能验证

全温度环境下的工作精度水平是当前制约光纤陀螺在更多领域应用的主要瓶颈,主要体现在变温零偏稳定性指标,前人围绕着热设计、工艺实现和算法补偿等方法开展研究,大幅改善了光纤陀螺的变温性能。光纤环是光纤陀螺的敏感器件,保偏光纤是构成光纤环的主要材料,其性能与光纤环变温性能密切相关,而对保偏光纤与变温精度的相关机理分析和实验研究较少。因此,基于光纤环在变温环境下热致Shupe零位误差产生机理的分析,发现保偏光纤折射率温度系数是主要影响因素。通过有限元仿真分析并结合保偏光纤布拉格光栅(PMF FBG)测试折射率温度系数的试验方案,发现猫型保偏光纤(CAT PMF)相较于传统熊猫型保偏光纤(PANDA PMF)具有更低的折射率温度系数。最后,通过将两型保偏光纤绕制成光纤环进行测试,结果表明,相对于熊猫型保偏光纤,猫型保偏光纤绕制成光纤环的变温零偏极差压缩21.1%,变温零偏稳定性提升22.9%,进一步证实猫型保偏光纤具有提升光纤环变温性能的应用前景。

检偏器对轴角度误差对光纤环偏振耦合测量的影响研究

为了分析检偏器偏振轴与光纤偏振主轴间的对轴角度误差对光纤环偏振耦合强度测量结果的影响,从理论上分析了采用光相干域偏振检测(OCDP)技术测试光纤环偏振耦合强度的基本原理,建立了光纤环中偏振耦合点耦合强度与检偏器对轴角度间的关系模型。根据模型仿真分析了耦合点偏振耦合强度测量值随检偏器对轴角度的变化规律。仿真结果表明:当检偏器偏振轴与光纤环偏振轴夹角为45°时测量误差最小,夹角偏离45°越大,产生的强度测量误差越大。当检偏器偏振轴与光纤环偏振轴的对轴误差为0.6°时,对轴误差引起的偏振耦合强度测量误差为0.18 dB。将对轴误差控制在3°以内,可使得偏振轴对轴误差引起的偏振耦合强度测量误差<1 dB。

提高光纤环绕环质量和固化效率的优化设计

光纤环作为光纤陀螺的核心敏感元件,其质量直接影响光纤陀螺的整体性能。通过优化光纤环的绕制骨架和固化工艺,可提高光纤环绕环质量和固化效率。首先设计了一种高精度可微调槽宽的光纤环骨架装置,以实现调整光纤环绕制的最优宽高比,实验表明光纤环宽高比接近1时,光纤陀螺的全温零偏最稳定;其次设计了一种同时旋转固化多个光纤环的固化装置,采用该装置同时固化4只光纤环,对比未经旋转固化的光纤环,在-45℃~75℃的温度范围下测试光纤陀螺全温零偏稳定性至少提升0.026°/h,并且其全温零偏稳定性均优于0.024°/h。

玻璃纤维增强聚醚醚酮线圈骨架内径收缩控制

分析某控制棒驱动机构(简称CRDM)样机研制中,国产玻璃纤维增强聚醚醚酮线圈骨架内径收缩问题,通过试验查找问题原因,结合CRDM线圈制造工艺,提出线圈骨架原材料制造和线圈绕制中控制内径收缩改进措施,经过实践证明有效。

Electro-Optical Effect Measurement of Thin-Film Material Using PM Fiber Mach-Zehnder Interferometer

A polarization-maintaining （PM） fiber Mach-Zehnder （MZ） interferometer has been established to measure the EO effect of very thin film materials with optical anisotropy. Unlike a common MZ interferometer, all the components are connected via polarization-maintaining fibers. At the same time, a polarized DFB laser with a maximum power output of 10mW is adopted as the light source to induce a large extinction ratio. Here,we take it to determine the electro-optical coefficients of a very thin superlattice structure with GaAs, KTP, and GaN as comparative samples. The measured EO coefficients show good comparability with the others.

Generation of cavity-birefringence-dependent multi-wavelength bright-dark pulse pair in a figure-eight thulium-doped fiber laser

We experimentally demonstrated a stable multi-wavelength bright-dark pulse pair in a mode-locked thulium-doped fiber laser(TDFL).The nonlinear polarization rotation(NPR)and nonlinear optical loop mirror(NOLM)were employed in a figure-eight cavity to allow for multi-wavelength mode-locking operation.By incorporating different lengths of high birefringence polarization-maintaining fiber(PMF),the fiber laser could operate stably in a multi-wavelength emission state.Compared with the absence of the PMF,the birefringence effect caused by PMF resulted in rich multi-wavelength optical spectra and better intensity symmetry and stability of the bright-dark pulse pair.

Self-starting all-fiber PM Er:laser mode locked by a biased nonlinear amplifying loop mirror

A compact all-fiber polarization-maintaining Er:laser using a nonlinear amplifying loop mirror is reported. Fundamental single-pulse mode-locking operation can always self start, with a cavity round-trip decreased from ~ 4.7 m to~ 1.7 m. When the pulse repetition rate is 121.0328 MHz, output pulse is measured to have a center wavelength/3-d B spectral bandwidth/radio frequency signal to noise ratio(SNR)/pulse width of 1571.65 nm/18.70 nm/80 d B/477 fs, respectively. Besides, three states including the exponential growth, damping state, and steady state are investigated through the build-up process both experimentally and numerically. Excellent stability of this compact Er:laser is further evaluated,demonstrating that it can be an easy-fabrication maintenance-free ultrafast candidate for the scientific area of this kind.

Effect of Coiling Temperature on Ti(C,N) Precipitation and Properties of Batch Annealed DC06EK Enamel Steel

The effects of hot-strip coiling temperature on Ti（C,N） precipitation, texture and hydrogen permeation behavior in DC06 EK enamel steel were investigated by TEM, EBSD test and electrochemical hydrogen permeation experiment. It was found that the Ti（C,N） particles in hot-strip coarsened with increasing coiling temperature, whereas after cold-rolling and annealing, the size difference of Ti（C,N） particles was lessened. The hot-strip coiling temperature has a significant impact on the recrystallized texture in the subsequent cold-rolled and annealed sheet. Hot-strip using high temperature（700 ℃） coiling leads to strong {111} recrystallized texture in annealed sheet, with peak intensity 9.2. On the contrary, in annealed sheets using hot-strip coiling at 650 ℃, their {111} recrystallized textures were weaker, which was also reflected in their rmvalues. Even though the hydrogen diffusion coefficient is slightly lower（7.76×10^（-5） mm^2/s） in annealed sheet using low temperature coiling（600 ℃）, appropriately higher coiling temperature is more suitable for DC06 EK enamel steel combining both good drawability and fish-scale resistance.

陀螺用超细径保偏光纤机械强度评估方法

针对陀螺应用场景下超细径保偏光纤机械强度评估需求,提出一种基于可拉伸骨架的超细径保偏光纤强度评估方法,超细径保偏光纤绕制于可拉伸骨架之上形成光纤环圈可模拟出成环应力过程,采用该光纤环圈构建光纤陀螺,环圈骨架内的压电堆栈可驱动骨架带动超细径保偏光纤周期性拉伸,对超细径保偏光纤起到应力激励施加效果可激发光纤疲劳以实现光纤强度快速评估与筛选,同时在超细径保偏光纤内形成相位调制功能以实现陀螺偏置调制,陀螺信号长期输出变化情况可表征超细径保偏光纤力学特性优劣。该方法能够体现出超细径保偏光纤成环应力施加的复杂性和陀螺应用光纤长期张紧、弯曲等条件下应力长期演变性,有助于陀螺用超细径保偏光纤强度评估与筛选。

双端输出全光纤振荡器突破8 kW高功率输出

双端输出光纤激光振荡器可以通过一个单谐振腔结构实现两路激光输出,能够减少高功率光纤激光系统的体积和成本,在工业领域有着很好的应用前景。基于双端泵浦谐振腔结构,采用稳波长981nm光纤耦合半导体激光器(LD)泵浦纤芯/包层直径为30/400μm的双包层掺镱光纤,首次实现了总功率大于8 kW的双端输出光纤激光振荡器。在总最高泵浦功率为10.951 kW时,A端输出功率为3769 W,B端输出功率为4400 W,总功率为8169 W,激光器光-光转换效率74.6%,A、B端激光光束质量M2因子分别约2.13和2.36。在最高输出功率时,两端输出激光中均未观察到动态模式不稳定效应(TMI)和受激拉曼散射(SRS),通过进一步增加泵浦功率,有望实现更高功率的激光输出。

基于改进YOLO算法的光纤环绕制缺陷检测

作为光纤陀螺仪的核心部件,光纤环的绕制质量对光纤陀螺的精度至关重要。为了保证光纤环绕制的准确率和效率,提出了一种基于改进YOLO算法的目标检测方法。该方法采用Shufflenetv2网络来替代YOLO主干网络中的卷积层和池化层,提升了网络的特征提取能力;加入Focus模块提升训练速度;采用K-means聚类算法对原始锚框进行聚类,得到适用于光纤绕制缺陷的预测框,提高缺陷检测的准确率;同时修改损失函数,使用CIOU来计算定位损失,使用Focal Loss作为置信度损失和分类损失函数,加快网络收敛;并进行了数据增强,增强了网络的泛化能力。实验结果表明,改进后的YOLO算法的平均准确率达到了99.63%,相比于原始的YOLOv3-tiny算法提升了2.06%,检测速度达到91 fps,这将保证了光纤环的绕制系统的实际应用。

Polarization-maintaining few mode fiber composed of a central circular-hole and an elliptical-ring core

We propose a novel waveguide design of polarization-maintaining few mode fiber(PM-FMF) supporting ≥10non-degenerate modes, utilizing a central circular air hole and a circumjacent elliptical-ring core. The structure endows a new degree of freedom to adjust the birefringence of all the guided modes, including the fundamental polarization mode. Numerical simulations demonstrate that, by optimizing the air hole and elliptical-ring core,a PM-FMF supporting 10 distinctive polarization modes has been achieved, and the effective index difference Δn_(eff) between the adjacent guided modes could be kept larger than 1.32 × 10^(-4) over the whole C +L band. The proposed fiber structure can flexibly tailored to support an even larger number of modes in PM-FMF(14-mode PM-FMF has been demonstrated as an example), which can be readily applicable to a scalable mode division multiplexing system.

Design of PANDA ring-core fiber with 10 polarization-maintaining modes

We present a polarization-maintaining PANDA ring-core fiber(PM-PRCF) characterized by the combination of a ring-core structure with two stress-applying rods. This special fiber design separates the adjacent modes and avoids the cutoff of the higher-order modes, which is a common problem in elliptical core polarization-maintaining few-mode fibers. Using a high-contrast index ring and stress-induced birefringence, the PM-PRCF features support for 10 vector modes, with effective refractive index separations from their adjacent modes >10^(-4).Broadband performance is investigated subsequently over a wide wavelength range from 1500 to 1630 nm.The proposed fiber is targeted at applications in space-division multiplexing while eliminating the complex multiple-input multiple-output signal processing.