Dynamics of radiation in optical fibers with a dispersive effective cross-section area of the mode

By using a graded-index optical fiber with a parabolic distribution of the refractive index as an example, it is shown that shock waves of envelopes can arise in optical fibers with a significantly dispersive (frequency-dependent) effective cross-section area of the mode. In principle, the shock wave caused by this dispersion can appear at the leading edge of the wave packet. The possibility of forming soliton pulses in media with a dispersive area of the mode is considered.     

非线性延时修正光纤孤子方程的稳态解问题Ⅰ.静态扭结孤波解

严格求解含非线性延时修正光纤孤立子方程,得到一类完全不同于光纤中已知的亮孤子和暗孤子的新型光学孤波解,并讨论了其物理含义及在光纤实验中观察这种扭结孤波的可能性。     

Nano-manipulation performance with enhanced evanescent field close to near-field optical probes

Recently, interest in nano-manipulation using the evanescent wave generated by nano-objects has been growing, but the analyses of manipulation flexibility and performance haven't been solved. In this paper the near-field optical trap utilizing a tapered metalized probe used in NSOM is described in detail. By employing a generalization of the conservation law for momentum using three-dimensional FDTD method, rigorous calculations of field distributions and trapping forces in near-field region are conducted. Calculations show that the particle with radius larger than the aperture is pushed away from the metal-coated fiber probe, while it tends to be trapped in larger effective region as its radius becoming smaller. The particle that is placed very near the aperture and around two field peaks intends to be dragged to the aperture edge, while the particle placed at other position tends to be attracted to the center surface of the probe tip. Furthermore, a preferable method using the combination of the near-field optical fiber probe and the AFM metallic probe is proposed, for more efficient non-contact manipulation and better observation of one single nano-particle. The analyses of trapping potential along the probe axis and the near-field distribution show the possibility of particle trapping.     

氙气中辐射激波的发光特性

本文模拟研究了氙气中X射线加热产生辐射激波的发光特性.辐射激波采用Zinn模型计算,并在模型中输入氙气的辐射不透明度和状态方程参数.研究发现,辐射激波伴随着丰富的光学演化过程,激波对外辐射强度表现出两个明显的亮度峰值和一个亮度极小值,辐射光谱也经常偏离黑体辐射光谱.对氙气不同位置光学特性的分析可知,激波和内部高温区的辐射吸收系数的动态演化导致了辐射激波的发光位置和辐射强度的变化.     

Generation of a sequence of frequency-modulated pulses in longitudinally inhomogeneous optical waveguides

The conditions for the generation and efficient amplification of frequency-modulated soliton-like wave packets in longitudinally inhomogeneous active optical waveguides have been studied. The possibility of forming a sequence of pico- and subpicosecond pulses from quasi-continuous radiation in active and passive optical waveguides with the group-velocity dispersion (GVD) changing over the waveguide length is considered. The behavior of a wave packet in the well-developed phase of modulation instability with a change in the waveguide inhomogeneity parameters has been investigated based on the numerical analysis.     

超跨声涡轮叶栅尾缘激波系流动研究

本文通过分析超跨声涡轮尾缘波系的流动机理给出了详细的尾缘激波系流动图画,强调了尾缘分离激波的重要作用.经过分析,认为基底区压力是通过影响基底区宽度来影响涡轮叶栅尾缘激波强度的.最后将上述机理应用到某叶栅S1计算程序的改进工作中,数值计算和叶栅试验结果表明,改进工作有效提高了该程序对超跨声涡轮叶栅尾缘激波流动的模拟能力.     

Shock waves in periodically inhomogeneous active fibers

The dynamics of the pulse-envelope shock wave is studied in amplifying fibers whose gain, groupvelocity dispersion, and nonlinearity are nonuniform with respect to the fiber length. It is demonstrated that, in inhomogeneous fibers, picosecond pulses can exhibit a substantial steepening of the leading edge at lengths of less than 10 cm.     

锗在吸收边附近的压力—折射率系数

目前半导体锗在吸收边附近(1550 nm)的压力-折射率系数在实验和理论上并未研究清楚.本文通过测量在不同压力下镀在光纤端面的高结晶度锗薄膜的反射率,来计算得到锗在吸收边附近的压力-折射率系数.本文的实验结果显示,锗在吸收边附近出现反常色散现象,即折射率随能量变化呈正相关,并且其压力-折射率系数出现反常,为正值,这是由于多晶结构中的激子吸收所引起.通过引入描述激子色散的临界点模型,得到锗在吸收边附近的反常色散范围和压力-折射率系数呈正值的范围.本文的结果将有助于基于锗薄膜的通信C波段光学器件的研究.     

On the possibility of laboratory shock wave studies of the equation of state of a material at gigabar pressures with beams of laser-accelerated particles

The possibility of laboratory shock wave studies of the equation of state of a material with beams of laser-accelerated charged particles at pressures an order of magnitude higher than those reached in current experiments has been discussed. The possibility of the generation of a plane quasistationary shock wave with a pressure of several gigabars behind its front at the irradiation of a target by a laser beam with an energy of several kilojoules and an intensity of about 10¹⁷ W/cm², which is accompanied by the generation of fast electrons with an average energy of 20–50 keV, has been justified.     

Non-contact sound speed measurement by optical probing of beam deflection due to sound wave

We report a non-contact and non-invasive method of sound speed measurement by optical probing of deflected laser beam due to normally incident degenerated shock wave. In this study the shock wave from an exploding wire was degenerated to an ordinary sound wave at the distance exceeding 0.23 m. Temporal resolution of the deflected beam signal was improved by passing through an adequate electronic high-pass filter, as a result we obtained a better temporal resolution than that of the acoustic pressure detection by PZT transducer in terms of rising time. The spatial resolution was improved by passing the refracted beam signal into the edge of focusing lens to make a larger deflection angle. Sound speed was calculated by monitoring the time of flight of transient deflected signal at the predetermined position. Sound speed has been measured in air, distilled water and acryl, agreed well with the published values. The sound speed measured in the solution of glycerin, magnesium sulfate (MgSO4), and dimethylformamide with various mole fractions also agrees within 3% of relative error with those measured in the present work by ultrasonic pulse echo method. The results suggest that the method proposed is to be reliable and reproducible.     

Water wave frequency detection by optical fiber sensor

An optical fiber sensor has been developed and applied to measure frequency of water waves based on wave induced polarization change of the light. The fiber sensor can accurately detect water wave frequency for regular and irregular waves. The optimum sag of sensing fiber to the sensor output’s linearity has been studied. The agreement of the fiber sensor and wave gauge in frequency and time domain suggests that the fiber sensor has great potential for passive acoustic sensing and wave monitoring.     

Technique for determining the channel expansion rate at the stage of electrical breakdown using a grounded intercepting ring

A method is described that allows one to study the conductivity dynamics of a channel produced by explosion of a wire at the stage of electrical breakdown. Experimental data have been presented for the expansion rate of the conductivity channel in extended (up to 1.9 m long) arbitrarily shaped gapes that were produced by an exploding copper wire 90 µm in diameter. The initial stored energy and applied voltage were, respectively, 2.7–3.7 kJ and 8–10 kV. It has been shown that the expansion rate of the conductivity channel coincides with the propagation rate of a shock wave and is inversely proportional to the square root of its radius and propagation time. The radius of the shock wave is a linear function of the square root of its propagation rate. Experimental data are in satisfactory agreement with the calculated results obtained by Lin [18] in terms of the model of an intense shock wave. It has been shown that the diameter of the conductivity channel depends on the position of the trailing edge of the shock wave.     

布里渊动态光栅原理及其在光纤传感中的应用

自从2007年布里渊动态光栅被首次提出用于实现光存储以来,该技术得到了国际上的广泛关注和研究.布里渊动态光栅本质上是由相干声波场激发的折射率光栅,一般情况下两束抽运光(频率差等于光纤的布里渊频移)以相同的偏振态从光纤两端注入到光纤中,通过受激布里渊散射效应激发出相干声波场,即形成布里渊动态光栅.光纤布里渊动态光栅因具有全光产生、参数灵活可控的优点,已被广泛研究应用于光纤传感、光纤特性表征、光存储、全光信号处理、微波光子学和高精度光谱分析等.本文分析布里渊动态光栅产生和探测原理,重点探讨在高性能分布式光纤传感上的应用,这些应用包括高灵敏度温度和应变分布式传感、温度和应变同时解调、分布式横向压力传感、分布式静压力(气压或液压)传感、高空间分辨率分布式传感和高精度光谱分析.     

单模光纤中四波混频的自诱导相位匹配

报道了无双折射单模光纤中四波混频的一种新型相位匹配方式,这种相位匹配仅由抽运光产生的自相位调制和互相位调制的共同作用即可提供,文中报道了实验结果,并从理论上成功地解释了该四波混频相位匹配的机理,与实验符合得很好。     

Design of multiplexed fiber optic chemical sensing system using clad-removable optical fibers

To prevent possible threats to public safety and economic loss from chemical leakage accidents, novel chemical sensing techniques for regular monitoring and leakage detection have been developed for various fields. We propose a fiber optic liquid chemical sensor (FOCS) system using specialty optical fibers and an optical time domain reflectometer (OTDR), and is based on the leaky wave mode sensing principle. OTDR enables simple multiplexing where individual sensor nodes along the fiber length could be interrogated by a common OTDR. The sensor node in the optical fiber is prepared by removing the desired length of a protective layer using mechanical stripping and chemical etching techniques. A novel laser stripping technique with superior capability to fabricate quasi-distributed dense sensor nodes is devised as well. The FOCS system is further analyzed to characterize the sensor response behavior in relation to the sensor node length and possible environmental and chemical temperature effect. Under the condition satisfying the leaky wave mode principle and within the minimum acceptable refractive index (RI) range by the system, this FOCS system could monitor numerous liquid chemicals with variable refractive indices and has been tested with positive results. In addition, the system shows the possibility for multi-point detection and is further expanded into a hybrid technique capable of estimating the refractive index range of the detected chemical.     

Terahertz-wave generation in a conventional optical fiber

We theoretically propose surface-emitted and collinear phase-matched terahertz (THz)-wave generation in a conventional optical fiber. The third-order nonlinear effect, four-wave mixing (FWM), is used to generate THz waves in an optical fiber. Surface-emitted THz-wave generation via FWM is realized using a single-mode fiber. Perfect phase matching is obtained at ~800 nm and 1.5 microm pumping, and it follows that third-order polarization in an optical fiber has the same phase at any point. In this situation, the optical fiber acts like a phased array antenna of the THz wave. Collinear phase-matching THz waves are obtained under the same conditions as for surface-emitted THz waves, and the THz wave is propagated in the silica cladding of the optical fiber. This is a promising method for realizing a reasonable THz-wave source.     

冲击压缩性的高精度测量技术

 详细介绍了在冲击压缩性测量中为提高冲击波速度测量精度，在减小样品尺寸测量的相对误差以及保证安装过程不破坏其原有加工精度的技术措施。还介绍了利用多路时间间隔测量仪记录冲击波传播时间时，如何减小传输误差以及利用探针的合理布局对冲击波阵面的倾斜和弯曲畸变进行修正的方法。此外，介绍了利用光纤技术同时获得冲击波速度和冲击温度信息的技术。采用上述技术措施后使弹丸速度的测量误差约为0.2%~0.4%，冲击波速度的测量误差约为~1%。     

掺氧化钙及相变对高压下立方氧化锆电子结构和光吸收的影响

研究表明,立方氧化锆可作为冲击波实验中的窗口材料.为了使得该材料在常态下保持结构稳定,需添加稳定剂——氧化钙.然而,掺杂会导致其在29 GPa的冲击压力下从立方转变为斜方Ⅱ结构相.因此,该材料在冲击压缩下的电子结构和光学吸收性质以及作为光学窗口的适用压力范围是值得研究的重要问题.本文运用第一性原理的方法,分别计算了在100 GPa范围内两种结构氧化锆的电子结构和光学吸收性质.结果表明:(1)在立方结构相区,冲击压力将导致其吸收边蓝移,而在斜方Ⅱ结构相区,却使得其吸收边红移;(2)在立方结构相区,掺杂将引起能隙变窄(吸收边红移),但对于斜方II相区,却导致能隙变宽(吸收边蓝移);(3)冲击结构相变使得能隙变窄,吸收边红移.本文数据建议,掺氧化钙的立方氧化锆在95GPa的冲击压力范围内可作为光学窗口材料.     

Formation of nonclassical states of vortex solitons in optical fibers with quantum dots

The problem of control for the quantum statistics of dissipative vortex optical solitons when using the Raman scheme of spin-flip transitions in an optical fiber doped with narrow-bandgap semiconductor quantum dots is considered. The possibility of forming individual bounded nonclassical quadrature squeezed light regions appearing within the spatial profile of a formed vortex soliton is demonstrated.     

Design theory and experiment of acousto-optical tunable filter by use of flexural waves applied to thin optical fiber

Spectral response of acoustically induced microbending through thin optical fiber is discussed from mode-coupling of core and cladding modes. The thin fiber is analyzed in three-layered structure (core-cladding-air) to gain insights into acousto-optic modulation. We explained the dependence of core and/or cladding diameters on acoustic source parameters from numerical calculations. According to the calculations, we successfully fabricated all-optical tunable filter using this thin fiber that yields an efficient mode-coupling at flexural wave frequencies less than 1MHz. To increase the acousto-optic effect, we used a specially designed thin optical fiber (80 μm of cladding diameter) in the section where flexural wave is produced, and spliced both ends of the thin fiber to the tapered 125 μm fibers. The frequency and voltage tuning of fabricated filter is also confirmed by changing the driven frequency and applied voltage of the PZT, respectively. This result suggests a possibility of fiber-optic device application as all-optical tunable filter at 1.55 μm.