V形高双折射光子晶体光纤特性研究

本文基于全矢量有限元法,设计了一种V形结构高双折射光子晶体光纤,数值分析结果表明:当光纤的包层孔间距Λ为1.0 μm,包层大空气孔D和小空气孔d分别为0.95 μm,0.7 μm时,在波长为1.55 μm处,该光纤的双折射度B达到1.225×10^-2,比传统光纤高约两个数量级. 另外,分别在可见光和近红外波段出现了两个零色散波长,使钛宝石飞秒激光器工作波段(700—980 nm) 处于光纤的反常色散区,为新颖的光子晶体 关键词： 光子晶体光纤 高双折射 有限元法 V形结构     

回音壁模式光纤激光器的阈值特性研究

研究了一种新型光纤激光器——消逝波激励的回音壁模式光纤激光器的阈值特性.将不同直径的石英光纤分别浸入低折射率的罗丹明6G乙醇和乙二醇混合溶液中,采用沿光纤轴向光抽运消逝波激励染料增益的方式,发现回音壁模式光纤激光辐射的阈值能量和混合溶液的折射率存在不同的依赖关系.随折射率的增加,对小直径光纤,阈值能量随之增加;对大直径光纤,阈值能量单调缓慢递减;对直径适中的光纤,阈值能量先减后增,存在一个和最小阈值能量对应的最佳折射率.用消逝波激励的回音壁模式激光理论,导出了回音壁模式光纤激光的阈值能量公式.理论计算曲线 关键词： 光纤激光器 回音壁模式 激光阈值 消逝波     

Optical tapping element for multimode fibers

We report on an optical tapping structure for multimode fibers. Its characteristic features are: 1. simple fabrication; 2. good reproducibility; 3. simple technology; 4. high coupling efficiency. The principle of the tap is based on a lateral displacement of waveguides which are butt joined. The displacement defines the fraction of power to be tapped off. With a lateral displacement of 15μm and a fiber with 100 μm outer diameter and 90 μm core diameter (acceptance angle ±30°) we measured a total coupling efficiency of 74% (73% remains in the main trunk line, ? 1% was tapped off) even though this fiber according to its high acceptance angle was not suited for the geometry of our structure. A diagram is given which shows the coupling efficiencies as a function of the lateral displacement of the fibers.     

单偏振光子晶体光纤

提出了一种能够在较宽波长范围内保持单偏振的光子晶体光纤,并利用频域有限差分法对其偏振特性进行了数值分析。在孔间距Λ取2.3μm,第一层较大空气孔直径dl取2.4μm,较小空气孔直径ds取1.4μm,包层中其它空气孔的直径d取0.6μm的条件下,这种单偏振光子晶体光纤在1.02-2.0μm波长范围内,保持较高的模式双折射。当较大空气孔直径dl取2.8μm,较小空气孔直径ds取1.4μm时,在1.35-2.0μm波长范围内,仅有一个偏振模能够存在,且波长1.31μm处的模式双折射度达到3.5×10-3。     

包层空气孔渐变的准光子晶体光纤的色散特性研究

设计了一种准光子晶体光纤,其包层由呈准周期分布的空气孔构成,其中靠近芯区的空气孔的直径是渐变的.采用带有良匹配层(APML)吸收边界的全矢量频域有限差分(FDFD)方法对其色散特性进行了数值分析,计算了孔间距取1.5μm～2.2μm,最小空气孔直径分别取0.4μm～0.6μm,从第一层到第三层直径线性递增量分别为0.1μm和0.2μm的条件下,这种光纤基模的色散曲线.结果表明:通过调节包层中三种不同尺寸的空气孔的大小以及孔间距这四个参数,可以得到不同平坦水平的色散曲线,甚至于超低超平坦的色散曲线.例如,当孔间距取1.7μm,空气孔直径分别取0.5μm、0.7μm、0.9μm,在1.4μm～1.7～m波段内,这种光纤的色散值可以控制在6.0±3.0 ps/km.nm范围内.     

LD泵浦的Nd:GdVO4/KTP腔内倍频激光器

基于对Nd:GdVO4晶体热焦距的测量及其1.06 μm激光基本性能,用三镜折叠腔研究了半导体激光器(LD)泵浦的Nd:GdVO4/KTP晶体的内腔倍频性质.当用从直径为200 μm的单光纤输出的低功率的半导体激光泵浦时,绿光的阈值是26 mW,光光转换效率为17.3%.当用从直径为1.55 mm的光纤束输出的高功率的半导体激光泵浦时,绿光的阈值是200 mW,光光转换效率为19.35%.     

Effect of single point defect on the confinement losses of air-guiding photonic bandgap fibers

The confinement losses in air-guiding photonic bandgap fibers (PBGFs) with air hole missing are studied with full-vector finite-element method. It is confirmed that there are two loss peaks (1.555 and 1.598 μm), if there is a hole missing in the cladding far from the core. The closer to the core the hole missing is, the larger the confinement losses are, even no mode could propagate in the core. The main power of the fundamental mode leaks from the core to the cladding defect. The quality of PBGFs can be improved through controlling the number and position of defects.     

Effect of single point defects on the confinement losses of air-guiding photonic bandgap fibers

The confinement losses in air-guiding photonic bandgap fibers (PBGFs) with air hole missing are studied with the full-vector finite-element method. It is confirmed that there are two loss peaks (1.555 and 1.598 μm) if there is a hole missing in the cladding far from the core. The closer to the core the hole missing is, the larger the confinement losses are, and even no mode could propagate in the core. The main power of the fundamental mode leaks from the core to the cladding defect. The quality of PBGFs can be improved through controlling the number and position of defects.     

Lasing in thulium-doped polarizing photonic crystal fiber

We describe lasing of a thulium-doped polarizing photonic crystal fiber. A 4 m long fiber with 50 μm diameter core, 250 μm diameter cladding, and d/Λ ratio of 0.18 was pumped with a 793 nm diode and produced a polarized output with a polarization extinction ratio (PER) of 15 dB and an M(2) of <1.15. An intracavity polarizer and half-wave plate minimally increased the PER to 16 dB. The output power had 35% slope efficiency relative to the absorbed pump power. The maximum cw output power was limited to 4 W due to the quantum defect heating of the fiber.     

低损耗宽带近零色散高非线性光子晶体光纤设计

提出了一种兼具低损耗、宽带近零色散和高非线性的光子晶体光纤结构,该结构光纤包层空气孔直径从纤芯向外层方向渐进增加;应用多极法,通过改变包层空气孔间距Λ、各层空气孔直径和空气孔层数N_r,对光子晶体光纤色散、损耗和非线性特性进行分析,获得了各特性随包层结构参数变化的规律,并最终设计出最佳结构参数。计算结果表明,该结构光纤存在3个零色散点,在1.25～1.55 μm较宽的波长范围内,色散值波动小于0.27 ps·nm⁻¹·km⁻¹,色散斜率小于0.008 ps·km⁻¹·nm⁻²,1.55 μm波长处损耗为0.021 dB/km,在常用的飞秒激光泵浦波长0.8,1.06,1.55 μm处非线性系数分别达到78.6,60.4,38.2 W⁻¹·km⁻¹。     

利用位相共轭激光器加工微孔

报道了利用带ＳＦ６气体池受激布里渊散射位相共轭Ｎｄ：ＹＡＧ激光器对０．１ｍｍ厚的刀片进行了微孔加工试验，初步实验结果表明，利用该激光器小的光束发散角这一优点，可加工出出口孔径为２０μｍ微孔。     

Mode field diameter preserving fiber tapers

An approach for preserving the mode field diameter (MFD) in fiber tapers is demonstrated. The approach utilizes concentric dual-core fibers, which couple light from an inner core to an outer core through a taper. Fibers with a 6 μm MFD feedthrough and a 15 μm polarization maintaining feedthrough are demonstrated experimentally. Simulations of the MFD in the tapered dual-core fibers are also presented.     

Characteristics of WDM Couplers Based on 80 μμ m Cladding Fiber

We have fabricated 1310/1550 and 1480/1550nm WDM couplers using a fiber of 80 μm cladding diameter,whose tapering length is shortened by 4～8mm for the identical coupling strength compared to those of 125μm cladding fibers. We also report their splicing loss to conventional single mode fibers.     

双芯复合格点光子晶体光纤的负色散特性

介绍了一种双芯复合格点负色散光子晶体光纤,其包层是由连续电介质纯硅背景上挖出的两种大小不同的空气孔构成,芯区是由掺锗的高折射率的材料构成。为了实现负色散,还移去了包层中的一圈空气孔。采用频域有限差分法对其负色散特性进行分析表明,通过调整空气孔间距和两种空气孔的尺寸,可以得到不同程度的宽带负色散。当内芯半径取0.95μm,孔间距取2.15μm,大空气孔直径取1.9μm,小空气孔直径取1.1μm时,可在1.55μm处实现宽带负色散,其半峰全宽超过了200 nm。这种光纤的包层中空气孔呈六边形分布,空气孔的尺寸均大于1μm,降低了制作的难度。这种光纤可以用于波分复用光纤通信系统中的宽带色散补偿。     

A Multi‐Thresholding Algorithm for Sizing out of Focus Particles

A methodology is presented that enables efficient acquisition of sufficient droplet information (e.g. diameter and aspect ratio) from images of in and out of focus droplets. The newly developed multi‐threshold algorithm is successfully implemented in the automatic particle/droplet image analysis (PDIA) system. Under the same optical hardware set‐up, and compared to the dual threshold methods [1], the multi‐threshold method increases the measurable/acceptable depth of field (DoF) of particles, especially for the small particles of diameters less than 50 μm (1098 pixels in this optical set‐up). When testing the 70 μm~110 μm and 100 μm~200 μm moving glass spheres, the dual threshold method can only detect 11%~29 % of the particles found by the multi‐threshold method. The multi‐threshold method is also capable of generating the aspect ratios of particles more accurately than dual threshold methods.     

高功率InGaAs量子阱垂直腔面发射激光器的研制

采用AlAs氧化物限制工艺实验制备了衬底出光的高功率大出光窗口（直径为300 μm）InGaAs/GaAs量子阱垂直腔面发射半导体激光器,实现了器件室温准连续工作（脉冲宽度为50 μs,重复频率为1000 Hz）,并对器件的伏安特性、光输出特性、发射光谱,以及器件的远场发射特性等进行了实验测试.器件阈值电流为460mA,器件的最大光输出功率为100mW,发射波长为978.6nm, 光谱半功率全宽度为1.0 nm,远场发散角小于10°,垂直方向的发散角θ_⊥为8°,水平方向的发散角θ_∥为9°,基本为圆形对称光束.     

Titanium-doped sputter-deposited AlN infrared whispering gallery mode microlaser on optical fibers

Optical fibers of 12 μm diameter were coated with a sputter-deposited layer (4 μm thick) of titanium (1 at. %)-doped amorphous aluminum nitride. When optically pumped by an Nd:YAG green laser at 532 nm, laser action was observed in whispering gallery modes around the fiber (in a ring shape) at 780.5 nm with a quality factor Q > 1500. Other modes were also observed between 775 and 800 nm. The primary and secondary modes give a mode separation of 4.6 nm. No waveguide modes were observed in the cavity.     

High average power large-pitch fiber amplifier with robust single-mode operation

Ytterbium-doped large-pitch fibers with very large mode areas are investigated in a high-power fiber amplifier configuration. An average output power of 294?W is demonstrated, while maintaining robust single-mode operation with a mode field diameter of 62?μm. Compared to previous active large-mode area designs, the threshold of mode instabilities is increased by a factor of about 3.     

Performance of data link modules as a function of multimode fiber size

Commercial data link modules from three manufacturers were measured for transmitter launch power and receiver sensitivity when used with the five common graded-index multimode fiber types: 50 μm core/NA_mk, = 0.20; 50 μm/NA_m = 0.23; 62.5/0.275; 85/0.26: and 100/0.29. Depending on the model, transmitters launched from 2.8 to 4.4 dB more power into the 100 pm fiber than the 62.5 μm fiber, whereas receiver sensitivities decreased by up to 3.5 dB. These variations in launch power and receiver sensitivity complicate the selection of an ideal fiber and emphasize the need for specifying data link performance with the particular fiber of interest. In general, the system gain of typical transmitter/receiver pairs is less favorable to large diameter fibers than previously believed.     

Selection of mandrel wrap mode filters for optical fiber loss measurements

A selection criterion for mode filters based on far-field patterns is developed. The criterion is used to select a mandrel wrap filter for 50 μm core diameter, 125 μm outside diameter fibers with δ=1.1%. When cut-back loss measurements were made using the mandrel wrap chosen in this way, loss scaled with length to within ± 0.05 dB/km in three 2-km fibers.