Guiding Properties of a Tapered Photonic Crystal Fiber Compared with Those of a Tapered Single-Mode Fiber

We have fabricated tapered photonic crystal fibers using a fusion splicer and experimentally observed the near-field mode distribution and the beam divergence of it. We have also compared characteristics of the tapered photonic crystal fiber with those of a tapered standard single-mode fiber. Unlike a tapered standard single-mode fiber, the mode field profile of a tapered photonic crystal fiber shows a good confinement of its field within the core region. The numerical apertures of tapered photonic crystal fibers are increased as the diameter of the fiber is decreased.     

Guiding Properties of a Tapered Photonic Crystal Fiber Compared with Those of a Tapered Single-Mode Fiber

We have fabricated tapered photonic crystal fibers using a fusion splicer and experimentally observed the near-field mode distribution and the beam divergence of it. We have also compared characteristics of the tapered photonic crystal fiber with those of a tapered standard single-mode fiber. Unlike a tapered standard single-mode fiber, the mode field profile of a tapered photonic crystal fiber shows a good confinement of its field within the core region. The numerical apertures of tapered photonic crystal fibers are increased as the diameter of the fiber is decreased.     

锥台光纤的功率转换效率研究

 锥台光纤在激光束到单模光纤以及多模光纤到单模光纤的耦合中,在一些需要质量很高光束的同时有较高功率要求的场合有广泛应用。在这些应用中,锥台光纤的功率转换效率是很重要的一个参数。介绍了锥台光纤的熔拉研磨制作方法,分析了锥台光纤的传输特性。建立了高斯近似模型,采用模场耦合理论,计算了锥台光纤的功率转换效率。在以下参数条件下对细端半径分别为（4±1）μm,(5±1)μm,(6±1)μm,(7±1)μm和(8±1)μm的锥台光纤的功率转换效率进行了实验测定,激光器输出光波长532 nm;多模光纤NA＝0.11,纤芯半径a=12.5 μm;得到了与理论计算吻合的结果。     

锥形光纤间耦合特性的分析与检测

将通信光纤的末端拉制成锥形，利用光信号在光纤锥形区特有的传输和耦合特性，实现了光纤的耦合、连接和分束。用耦合模理论分析了锥形光纤间的传输和耦合性质，给出了光信号两锥形光纤间的耦合与两锥形光纤的距离和锥形区重叠长度等实验结果。     

Influence of resonance tube geometry shape on performance of thermoacoustic engine

Based on the linear thermoacoustics, a symmetrical standing-wave thermoacoustic engine is simulated with a cylindrical tube and a tapered one as the resonance tube, respectively. The experiments with both cylindrical and tapered tubes are carried out. The suppression of nonlinear effects due to tapered tube as the resonance tube is discussed. Both simulation and experimental results show that the performance of the tapered tube is better than cylindrical one as the resonance tube.     

锥形光纤间的耦合特性

将通信光纤的末端拉制成锥形,利用光信号在光纤锥形区特有的传输和耦合特性,实现了光纤的耦合、连接和分束.用耦合模理论分析了锥形光纤间的传输和耦合性质,给出了光信号两锥形光纤间的耦合与两锥形光纤的距离和锥形区重叠长度等实验结果.     

锥形脊结构半导体光放大器的有限元分析

为提高半导体光放大器与单模光纤耦合效率，建立了半导体放大器的锥形脊结构模型。在该模型下利用有限元数值模拟方法分析，计算了波导区折射率、锥尖宽度、条形波导尺寸、渐变折射率波导层对锥形脊结构模式扩展的影响。通过完善锥形脊结构参量的设计，获得了锥形脊结构半导体光放大器与单模光纤95％的耦合效率。     

契形结构光纤表面等离子体共振传感器研究

提出了一种契形端面结构的光纤表面等离子体共振(SPR)传感器激励模型. 采用时域有限差分法对契形SPR波导的共振模型进行数值模拟, 通过在光纤出射端抛磨契形角度并进行敏感膜修饰, 制出具有契形端面结构的类Kretschmann微棱镜式光纤SPR传感器, 实现激发SPR的光波调制.结果表明, 在1.3330–1.4215折射率范围内, 制备的契形光纤SPR传感器相对于常规光纤SPR传感器, 其平均灵敏度提高了近1–6倍, 1倍和6倍分别出现在小角度结构(15° 契形) 传感器和大角度结构(60°契形) 传感器, 且仍保持 10^-5 等级的分辨率. 该类型结构的传感器具有契形端面激励模式, 设计灵活性高、制备工艺简单、可微量检测样本等优点, 能够很好地适应于不同环境和测量条件的实际生化检测、环境监测需求. 关键词： 光纤传感器 表面等离子体共振 契形端面结构 折射率灵敏度     

Spatial and spectral filtering of tapered lasers by using tapered distributed Bragg reflector grating

A 1040 nm tapered laser with tapered distributed Bragg reflector (DBR) grating is designed and fabricated. By designing the grating with tapered layout, the tapered DBR grating exhibits the scattering effect on side backward-traveling waves, thus achieving additional suppression of parasitic oscillation. Under the suppression of parasitic oscillation, the spatial and spectral characteristics of the tapered laser are improved. The experimental results show that a near-Gaussian far-field distribution and a kink-free P-I characteristics are achieved, and a single peak emission with a wavelength of 1046.84 nm and a linewidth of 56 pm is obtained.     

Packaging and Characteristics of a Tapered Fiber Sensor for Refractive-Index Measurements

In this study, we demonstrate the design and fabrication of a tapered fiber sensor with a sensing application based on a new (high-sensitivity) package. We study the effect of various geometric parameters such as the uniform segment diameter, the uniform segment length, and the incident angle of the optical wave on the tapered fiber sensor sensitivity for evanescent sensing. Our study shows that high sensitivity of the tapered fiber can be realized by optimizing its parameters. In addition, we design a novel packaging of a tapered-fiber sensor, which can efficiently ensure a uniform stress and reduce the cross sensitivity caused by stress in liquid detection using a tapered fiber sensor. We report the experimental results obtained using this tapered fiber sensor for refractive-index measurements. As the refractive index of liquids varies from 1.417 to 1.423, the measurement results show that the refractive-index sensitivity of the tapered fiber sensor is as high as 4860 nm/RIU.     

一种多模干涉耦合器的性能模拟

为减小多模干涉（Multimode Interference ,MMI）耦合器件的尺寸,提出一种多模波导宽度为指数型变化的Taper结构.理论分析了多模波导长度与该Taper结构的参量之间的关系.与已被用于减小MMI器件尺寸的抛物线型Taper结构相比,该结构可进一步减小器件的尺寸.就几种波导结构参量下的MMI耦合器,利用宽角光束传播法进行了数值模拟.结果表明,指数型MMI耦合器的性能与抛物线型MMI耦合器的性能类似.指数型Taper结构可以用于MMI器件以减小该类器件的尺寸.     

超连续谱光纤合束器的数值模拟

设计了一种用于超连续谱合束的光纤合束器,这种合束器通过将多路光子晶体光纤拉锥后对接到一路多模光纤制成。借助有限差分波束传输法对该合束器进行了数值模拟,结果表明拉锥过渡长度和拉锥比例对耦合损耗具有较大影响,当拉锥过渡长度小于拉锥衍射长度时合束器有较大传输损耗,而过渡长度足够大以及拉锥比例较小时,合束器具有较低的耦合损耗以及优良的宽光谱耦合特性。所得出的数值结果为光子晶体光纤拉锥和超连续谱光纤合束器研制提供了一定的参考依据。     

High power single transverse mode operation of a tapered large-mode-area fiber laser

To get high output power with good beam quality, a tapered section is introduced to large-mode-area (LMA) Yb-doped fiber laser. Output characteristics of the fiber laser without tapered section and with tapered section are compared experimentally. When the launched pump power is 119.1 W, 77.9 W with M² 3.08 and 56.4 W with M² 1.14 can be obtained, respectively. The corresponding slope efficiencies are 71.8% and 54.1%, respectively. Although output power of the tapered fiber laser has 30.6% penalty, brightness of it is as much as 5.28 times of the fiber laser without tapered section. Moreover, spectra of them are measured. It is found that tapered section makes lasing wavelength of the fiber laser shorter.     

S波段锥形磁绝缘线振荡器粒子模拟和实验研究

 提出了一种由弱变锥形主工作区和强变锥形提取区组成的锥形磁绝缘线振荡器结构。该结构主工作区采用弱变结构,在保持频率基本不变的情况下,可有效增加群速度,利于微波提取。模拟结果表明：该结构可以在二极管电压500 kV、电流32 kA的条件下稳定输出平均功率2.5 GW、频率为2.65 GHz的微波;实验上也获得了GW级、频率为2.69 GHz的微波输出。     

高功率离子束在漂移管中的中性化传输

介绍了“闪光二号”加速器产生的高功率离子束在漂移管中的传输实验。对比了采用中性化措施前后的传输情况，分析了中性化措施对离子束束斑半径、束流均匀性的影响。根据实测的二极管电压模拟得到了传输一定距离后的束流波形，与实测结果符合较好。采取适当的中性化措施后，高功率离子束可以有效传输80 cm以上，束流发散得到抑制，束流均匀性得到改善。     

Visible supercontinuum generation in tapered photonic crystal fiber pumped by picosecond pulse at 1064 nm

Short photonic crystal fibers (PCFs) with different tapered waist diameter are made to extend the continuum spectrum in the visible range. The diversification of output continuum spectrum with the diameter of the tapered waist is experimentally observed. An all fiber visible supercontinuum source with 1.88 W output is demonstrated in our experiments. To the best of our knowledge, it is the highest all fiber visible supercontinuum generation in tapered PCF, pumping by picosecond pulse at 1064 nm. The suitably designed short tapered PCF can extend the visible spectrum, while, how to preserve the tapered waist is crucial for the all fiber visible supercontinuum source in the practical applications.     

渐变掩蔽图形超低压选择区域生长法制备高质量InGaAsP多量子阱材料

采用超低压(22 mbar)选择区域生长(Selective Area Growth, SAG)金属有机化学汽相沉积(Metal-organic Chemical Vapor Deposition, MOCVD)技术成功制备了高质量InGaAsP/InGaAsP多量子阱(Multiple Quantum Well, MQW)材料. 在较小的掩蔽宽度变化范围内(15—30μm)，得到了46nm的光荧光(Photoluminescence, PL)波长偏移量，PL半高宽(Full-Width-at-Half- 关键词： 超低压 选择区域生长 渐变掩蔽图形     

锥形光纤激发盘腔光学模式互易性研究

光学谐振腔由于其高Q值特性,作为谐振式陀螺的核心元件,有望实现谐振式陀螺的小型化、集成化,但是非互易性噪声成为制约其精度提高的不利因素. 介绍了采用传统半导体工艺制备的盘型腔与熔融法拉制的锥形光纤组成的耦合系统. 当盘型腔在光纤锥区的不同位置进行耦合谐振时,将输入输出正/反对调,观察到输出透射谱发生偏差,谐振频率、耦合效率以及Q值均发生变化,即存在非互易性现象. 用Rsoft软件对锥形光纤倏逝场分布特性进行仿真,理论分析了非互易性产生的原因. 以此可抑制谐振式光学陀螺应用中由锥形光纤与谐振腔组成的耦合系统产生的非互易性噪声. 关键词： 光学谐振腔 锥形光纤 非互易性 谐振式陀螺     

Tapered microstructured fibers for efficient coupling to optical waveguides: a numerical study

We report the possibility of using tapered microstructured fibers to improve the coupling efficiency from a standard single-mode fiber to a photonic crystal waveguide. The tapered microstructured fiber allows for the reduction of the mode mismatch between the output of the standard fiber and the input of the waveguide while maintaining single-mode guidance, which results in an enhanced coupling efficiency. Numerical simulations are conducted in order to optimize the cross section of the microstructured fiber as well as the taper profile. An improvement of more than 4 dB is obtained compared to non-tapered fibers. For further improvement, an elliptical-core tapered microstructured fiber is analyzed. The effect of misalignment between the tapered microstructured fiber and the waveguide is also studied.     

95 GHz TE03模回旋管内置渐变波导设计

在耦合波理论的基础上,结合波导渐变曲线给出了普适高阶渐变波导设计方法,研究了95 GHz回旋管内置 TE03模式改进Dolph-Chebychev渐变波导。采用编制的数值计算程序进行优化,得到了可靠的最优几何参量,设计出了紧凑的95 GHz渐变波导。经全电磁场仿真验证,该内置渐变输出结构对杂模的抑制达30 dB,满足设计要求。回旋管的热测实验中测出的模式样图表明,所设计的内置渐变波导有效地实现了回旋管内径变化。该方法可以高效地指导高阶过模圆波导渐变结构的设计。