Strain and Temperature Sensing Characteristics of Single-Mode–Multimode–Single-Mode Structures

We present a comprehensive study of the strain and temperature-sensing characteristics of single-mode–multimode–single-mode (SMS) structures based on the modal interference of guided modes of graded index multimode fiber (MMF) section spliced in between two single-mode fibers. A detailed theoretical study of the structures in terms of the refractive index distribution, effect of dopant and their concentrations, and the variation of core diameter has been carried out. Our study shows that for the SMS structure with a ${rm GeO}_{2}$-doped MMF there exists a critical wavelength on either side of which the spectrum shows opposite spectral shift with a change in temperature/strain, whereas for structures with a ${rm P}_{2}{rm O}_{5}$-doped MMF it shows monotonic red shift with increasing temperature/strain. It has been found that the critical wavelength shifts toward higher wavelengths with decreasing “ $q$” value/doping concentration. Using different MMFs, both the red and blue spectral shifts have been observed experimentally. It has also been found that the SMS structure has higher sensitivity toward this critical wavelength. The study should find application in designing strain-insensitive high-sensitive temperature sensors or vice versa.      

基于单模异芯光纤结构的液位传感器

提出了一种新颖的光纤液位传感器。在普通单模光纤(SMF)中间熔接一段细芯单模光纤(TCSMF),构成共轴光纤马赫曾德尔干涉仪(MZI)。液位的变化引起包层模与芯模的相位差发生改变,从而导致干涉仪的透射光谱发生改变。对传感器的工作原理和测量灵敏度及精度进行了理论分析,实验结果显示透射光谱中特征峰波长漂移量跟液位变化量呈较好的线性关系,且灵敏度随待测液体折射率的增大而增高,与理论分析结果相一致。测量得到纯水和饱和氯化钠溶液的测量灵敏度分别为0.160 nm/mm和0.228 nm/mm。该传感器采用全光纤结构,制备简单、测量精度高,可适用于折射率低于光纤包层折射率液体的高精度液位测量。     

单模无偏准直器的设计与制作

介绍了单模无偏准直器的原理与测试方法，并对一些制作工艺进行了讨论和比较。     

Single-Mode Fiber Connector Using Core-Centered Ferrules

Fiber connectors using single-mode fibers have been fabricated with an average connection loss of 0.32 dB without index matching. All dimensions of the connector parts, including those of the ferrules and fibers require only low precision. A special lathe is used, in a simple operation, to eliminate the errors of the ferrule-terminated fiber assembly.     

基于PLZT开关的全光纤单模调Q掺Yb3+光纤激光器

PLZT电光陶瓷具有良好的透明性、高电光系数等特性,用来实现全光纤调Q开关具有很大的优势.分析了PLZT全光纤调Q开关的原理,测量了调Q开关的时间波形,研究了基于PLZT开关的全光纤单模环形调Q掺Yb3 光纤激光器.抽运光功率为180 mW,莆复频率为1 kHz时,得到峰值功率25.6 W,脉冲宽度80 ns,光谱宽度1 nm,脉冲能量2.0 μJ的调Q脉冲.此外,分别研究了抽运功率和重复频率对脉冲峰值功率和脉冲宽度的影响,结果表明,同一重复频率情形下,随着抽运功率的升高,峰值功率增大,脉冲宽度降低;同一抽运功率水平下,随着重复频率的增大,脉冲的峰值功率减小,脉冲宽度增大.     

反射型单模光纤星形耦合器

本文介绍光纤局部区域网构网的一种关键器件——由2×2光纤耦合器和光纤环组成的反射型单模光纤星形耦合器的构造方法及特点。对光纤环的反射特性与耦合特性关系作理论分析。最后,报道了研制的反射型单模光纤8端口星形耦合器的实验结果。     

Single-Mode Fiber Design for Minimum Dispersion

The value of the radius of the core of a single-mode step-index optical fiber for minimum dispersion is calculated with the normalized frequency in the range 1.0/spl les/ V/spl les/2.5, using the approximation for the eigenvalue U proposed by Miyagi and Nishida [1]. This calculation is made by solving the total dispersion equation for the core radius when the wavelength assigned is assumed to be that necessary for minimum total dispersion. The computational procedure presented is simple enough to be accomplished on a programmable calculator or microcomputer. This work makes possible the characterization, with reasonable precision, of tbe ideal fiber that should be used with the available optical source.     

Buried Sol-gel/SiON Waveguide Structure for Passive Alignment to Single-Mode Fiber on Si Substrate

Buried sol-gel/SiON waveguide structure is proposed for efficient optical coupling to single-mode fiber (SMF) using passive alignment technique on silicon substrate. Difficulties of photolithographic patterning on highly nonplanar surfaces were resolved by fabricating the waveguide devices at a distance from the proximity of deep grooves and by using the sol-gel material for producing negative images of the cores in the buried waveguide structure. A good optical coupling between the waveguide and SMF is obtained by bringing the SMF in close contact to the waveguide facet after saw-cutting the SiON cladding away. The loss due to fiber displacement is about 0.6 dB per facet     

Polarization Characteristics of Single-Mode Fiber Couplers

The polarization characteristics of fiber couplers made of birefringent single-mode fibers are studied. The effect of anisotropic interfiber coupling, fiber birefringence, angular misalignment of fibers, and twisting on the coupler characteristics are identified. The polarization characteristics of the couplers are compared with that of isolated uncoupled fibers of the same birefringence and length. The equivalent lumped element representations for three classes of fiber couplers are also presented.     

Single-Mode Fiber OTDR: Experiment and Theory

An OTDR measurement technique with an end detection dynamic range of 63 dB is described for use with single-mode fibers. A theoretical analysis of single-mode fiber backscattering is presented which predicts loss penalties in single-mode OTDR'S compared with multimode fibers. The prediction of the critical power levels of about 3 - 4 W for the onset of nonlinear effects in fibers is shown to be in good agreement with experiment. Fusion welded splices do not demonstrate significant backscattered power.     

Broadband Single-Polarization Single-Mode Photonic Crystal Fiber Coupler

In this letter, a novel design for a photonic crystal fiber coupler with single-polarization single-mode (SPSM) functionality is proposed and investigated using a vector plane-wave expansion method and a vector finite-element method. We study the changes in the coupling lengths between the two orthogonal polarizations and the width of the SPSM coupling region with respect to the air-hole parameters. We demonstrate that the SPSM coupling range can be more than 200 nm wide for a variety of air-hole parameters and show that the position and width of the SPSM coupling region can be tailored via the diameters of the large inner air holes and the small cladding air holes.     

声扭波在单模光纤中的应用

光纤中的基模LP01有两种偏振态,通过在油光纤方面加入声扭波可以引起两个偏振模发生耦合,本文主要介绍了声扭波和振幅和色散关系,同时也发现,采用高阶声扭波可以提高耦合系数的值。     

Single-Mode Fiber Refractive Index Sensor Based on Core-Offset Attenuators

Mach-Zehnder and Michelson interferometers using core-offset attenuators were demonstrated. As the relative offset direction of the two attenuators in the Mach-Zehnder interferometer can significantly affect the extinction ratio of the interference pattern, single core-offset attenuator-based sensors appear more robust and repeatable. A novel fiber Michelson interferometer refractive index (RI) sensor was subsequently realized by a single core-offset attenuator and a layer of ~ 500-nm gold coating. The device had a minimum insertion loss of 0.01 dB and maximum extinction ratio over 9 dB. The sensitivity (0.333 nm) of the new sensor to its surrounding RI change (0.01) was found to be comparable to that (0.252 nm) of an identical long period gratings pair Mach-Zehnder interferometric sensor, and its ease of fabrication makes it a low-cost alternative to existing sensing applications.     

光纤脉冲压缩技术及其进展

本文系统地综述了基于单模光纤的脉冲压缩方法、原理及其进展，介绍了我们最近的研究结果，讨论了实现高效率脉冲压缩的途径。     

基于单模光纤选模机制的单模输出6芯光纤激光器

为了实现多芯光纤激光器的单模输出,提出一种新的选模机制,即利用单模光纤进行选模。采用单模光纤和全反镜相结合作为选模器件,可以使6芯光纤激光器中同相位超模的耦合效率远远大于其他高阶超模,从而使高阶超模得到有效的抑制,实现高亮度的同相位超模单模输出。为了提高同相位超模的耦合效率,可以进一步优化单模光纤纤芯尺寸,同时调节单模光纤和6芯光纤之间的间隙距离。将同相位超模的耦合效率代入速率方程进行理论模拟,证明输出功率和耦合效率之间的必然联系,结果显示同相位超模输出功率随着耦合效率的增大而增大,得到单模输出的最大光-光转换效率为63.7%。     

Statistics of Rayleigh Backscatter From a Single-Mode Fiber

This paper contains a detailed analysis of the statistical properties of the Rayleigh backscatter signal from a single-mode optical fiber. Derivations of the first- and second-order statistics, autocorrelation function, and power spectral density of the backscatter wave are given. The probability density functions of the amplitude and intensity of the backscatter signal are also calculated.     

半导体激光器到单模光纤的高效耦合技术

本文在阐述了半导体激光器到单模光纤的耦合损耗来源之后，对几种典型的耦合技术作了较为详细的分析和比较，明确了增大数值孔径、减小系统球差和椭圆度校正三个主要因素对进一步提高耦合效率的意义。最后，探讨了耦合技术的发展前景。     

High Extinction-Ratio Polarizing Endlessly Single-Mode Photonic Crystal Fiber

We present the fabrication of a polarizing, endlessly single-mode microstructured fiber with high polarization-dependent loss. The fiber was fabricated by the stack-and-draw method. The resulting structure consists of a pure silica core surrounded by a regular lattice of air holes, in which four air holes in the inner ring have been enlarged. An extinction ratio of 16 dB/m with a transmission loss of 0.9 dB/m was achieved at a wavelength of 1550 nm     

Design of Wideband Single-Polarization Single-Mode Photonic Crystal Fiber

The present paper proposes a novel design for achieving single-polarization single-mode (SPSM) operation in photonic crystal fiber (PCF), using a rectangular-lattice PCF with two lines of three central air holes enlarged. The proposed PCF that is composed entirely of silica material is modeled by a full-vector finite element method with anisotropic perfectly matched layers. The position of the region of single polarization can be tuned freely by adjusting the size of the central enlarged air holes. Using this structure, an SPSM PCF with confinement loss less than 0.1 dB/km within the wavelength range from 1.20 to 1.66 mum and effective mode area about 5.9 mum² at 1.55 mum has been successfully designed. The proposed fiber is a nonlinear SPSM, which may be useful for nonlinear optical applications or applications with a wide SPSM operating bandwidth requirement