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.

Derivation of General Formula for Coupling Loss of Single-mode Fiber Collimators with Gradient-index Rod Lenses

Gradient-index rod lens (GRIN-lens) whose pitch is ordinary value with bevel ferrule coupling system is analyzed, an equivalent method which can be used to analyze this system is put forward, and a general formula for determining the coupling loss with axes mismatch, radial mismatch, and angular mismatch is derived by use of the Gaussian field approximation and mode-field coupling theory. The experimental results are in good agreement with the theory prediction. It indicates that these formulas are suitable to analyze the gradient-index rod lens coupling system with pigtail fiber.

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.

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.

Coherent beam combination of adaptive fiber laser array with tilt-tip and phase-locking control

We present an experimental study on tilt-tip（TT） and phase-locking（PL） control in a coherent beam combination（CBC） system of adaptive fiber laser array.The TT control is performed using the adaptive fiber-optics collimator（AFOC）,and the PL control is realized by the phase modulator（PM）.Cascaded and simultaneous controls of TT and PL using stochastic parallel gradient descent（SPGD） algorithm are investigated in this paper.Two-fiber-laser-,four-fiber-laser-,and six-fiber-laser-arrays are employed to study the TT and PL control.In the cascaded control system,only one high-speed CMOS camera is used to collect beam data and a computer is used as the controller.In a simultaneous control system one high-speed CMOS camera and one photonic detector（PD） are employed,and a computer and a control circuit based on field programmable gate array（FPGA） are used as the controllers.Experimental results reveal that both cascaded and simultaneous controls of TT using AFOC and PL using PM in fiber laser array are feasible and effective.Cascaded control is more effective in static control situation and simultaneous control can be applied to the dynamic control system directly.The control signals of simultaneous PL and TT disturb each other obviously and TT and PL control may compete with each other,so the control effect is limited.

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.

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.

模场直径可调的光纤微准直器

针对传统光纤准直器的输出模场直径单一问题,提出了一种模场直径可调的光纤微准直器,将单模光纤与不同的2段多模光纤组合,形成“三明治”结构;通过调整中间段光纤的长度,实现模场直径的任意可调,并构建了仿真实验模型,制备了多个尺寸不同的光纤微准直器样品。实验结果表明:该结构在1 550 nm波段下,能实现输出模场直径在20~40μm范围内的可调性。该光纤准直器制备方法简便、结构紧凑,并能根据需求灵活调整光场的模场直径,以适应不同的应用场景。

光纤旋转连接器的发展及其军事应用

光纤旋转连接器是一种广泛应用于军事国防、工业等领域的关键器件。光纤旋转连接器的功能为将光信号从旋转平台传输到静止平台。介绍了光纤旋转连接器的具体用途,描述了单通道光纤旋转连接器和多通道旋转连接器的工作原理和具体制作方法。介绍了国外光纤旋转连接器的发展动态和技术指标。制作了插入损耗小于2 dB的单模单通道光纤旋转连接器。进行了光纤旋转连接器的温度冲击对比实验,测试结果好于国外产品。分析了光纤旋转连接器的特点。重点介绍了光纤旋转连接器在军事国防的各个领域的用途。

基于mini-bar的光纤耦合实验研究

基于mini-bar的光纤耦合是一种进一步提高二极管激光器光纤耦合系统出光亮度的有效方法。本文对Osram公司的一款连续60W mini-bar的发光特性进行了实验研究,选用的mini-bar在工作电流60 A时输出功率60 W,电光转换效率最大为60%,中心波长973.7 nm,慢轴发散角为9.3°(1/e2)。分析了其慢轴准直的特性,了解慢轴准直透镜的选择原则。器件准直后的慢轴发散角为47.6 mrad。通过对光束参量积的计算了解到mini-bar的光束可以直接耦合进入600μm的光纤,并进行了单片mini-bar的耦合实验,得到准直系统与耦合透镜组的传输效率为83%～85%,光纤的耦合效率为86%～93%,整个系统的光光效率大于72%。

微光学元件阵列面阵LD光束整形及光纤耦合

采用微透镜阵列组成的快、慢轴准直器件进行高功率面阵半导体激光器阵列光束准直,从而减小其光参数积,进一步采用棱镜阵列对准直光束进行整形,实现两方向光束质量的平衡,使激光束的综合光参数积小于光纤的光参数积,提高光束质量,获得高耦合效率的光纤耦合模块。对5个吧条组成(每个吧条40W、总输出功率为200W)的面阵半导体激光器光束进行准直、整形聚焦并耦合到芯径800μm、数值孔径0.22的多模光纤,获得125.4W的激光输出。

大坝变形监测自动化系统进展

分析比较三种较新的大坝变形监测自动化系统的实际运行情况 .对于真空激光准直系统 ,提高其稳定性的关键是提高安装质量 ,保证其密封性 ,同时保证波带板起落 (翻转 )系统的灵活性和复位精度 ,此外还要选用高质量的激光管 ,并采用防潮和稳压措施 ;对于GPS系统为节约投资和提高精度采用双频双星卫星接收机和增加基准点数、优化基点布置的方法 ;对于光纤系统 ,其关键是解决光纤的保护和仪器系列化问题 .

C-lens准直特性分析

运用矩阵光学理论结合高斯光束的复参数传输规律对新型的微光学元件C-lens的准直特性进行定量分析,确定了光纤头与C-lens之间距离的最佳范围,并推导出了C-lens光纤准直器工作距离的解析表达式和特性曲线.研究结果对C-lens的设计与优化及提高C-lens光纤准直器的性能有实用价值.

基于半导体激光光纤组件的激光准直仪

介绍一种基于半导体激光光纤组件的激光准直仪 ,讨论了使用角锥棱镜作为活动靶镜的测量原理 ,给出了准直仪的软硬件设计方案。通过各种实验表明 ,本准直仪可直接应用于工业测量。

基于提高准直器插入损耗的研究

在几何光学和高斯光束传输理论的基础上,利用矩阵光学原理和高斯光束耦合理论对准直器的原理和损耗进行计算和分析,并提出一种能有效降低插入损耗的方法。

C-lens准直器回波损耗的理论计算与分析

用矩阵光学和几何光学的方法计算了C-lens准直器的回波损耗,分析了影响回波损耗的各主要因 素,并绘出了回波损耗对各影响因素的响应曲线,对C-lens光纤准直器的设计和优化具有一定指导意义.

自适应光纤光源准直器的结构设计

设计了一种可以快速高精度调节光纤准直激光束发射角度的自适应光纤光源准直器。该器件利用双压电驱动器控制光纤端面的位置,通过准直透镜实现出射激光束的准直。建立了自适应光纤光源准直器的物理模型,通过理论分析得出了光纤端面的偏移与器件结构参数的关系。研制了一个器件,并对其光纤端面偏移量、谐振频率等进行了测试。实验结果表明,理论分析与研制的自适应光纤光源准直器具有较好的一致性。该工作对自适应光纤光源准直器的结构设计具有指导意义。