激光点火系统用高功率光纤光开关

 仿真和实验研究了一种控制Nd:YAG脉冲激光能量通断的光纤直接连接型光开关。建立光纤耦合模型,分析了光纤对准误差中对耦合效率的影响,其中横向偏移的影响最显著。采用微机电系统V型槽固定光纤,微小型凸轮作为制动器,步进电机驱动凸轮旋转,微小型凸轮与移动光纤相切,带动光纤移动,实现两光纤的错开和对准。制造了这种高功率直接连接型光纤光开关原理样机,并进行了主要性能测试。测试结果表明,这种光开关能够满足激光点火系统的大容量、高隔离度的要求。     

激光点火系统用高功率光纤光开关

仿真和实验研究了一种控制Nd:YAG脉冲激光能量通断的光纤直接连接型光开关。建立光纤耦合模型,分析了光纤对准误差中对耦合效率的影响,其中横向偏移的影响最显著。采用微机电系统V型槽固定光纤,微小型凸轮作为制动器,步进电机驱动凸轮旋转,微小型凸轮与移动光纤相切,带动光纤移动,实现两光纤的错开和对准。制造了这种高功率直接连接型光纤光开关原理样机,并进行了主要性能测试。测试结果表明,这种光开关能够满足激光点火系统的大容量、高隔离度的要求。     

Optical fiber modulator derivates from hollow optical fiber with suspended core

A fiber optic integrated modulation-depth-tunable modulator based on a type of hollow optical fiber with suspended core is proposed and investigated. We synthesized magnetic fluid containing superparamagnetic Fe(3)O(4) nanoparticles and encapsulated it in the hollow optical fiber as the cladding layer of the suspended core by fusing the hollow optical fiber with the multimode optical fibers. The light with a wavelength of 632.8 nm is coupled in and out of the modulating element by a tapering technique. Experimental results show that the light attenuation in the system can be greatly influenced by only 2.0×10(-2) μL of the magnetic fluid under different magnetic field strengths. The saturated modulation depth is 43% when the magnetic field strength is 489 Oe. The response time of the system is <120 ms. Significantly, this work presents information for the development of all-fiber modulators, including other integrated electro-optic devices, such as optical switch, optical fiber filter, and magnetic sensors utilizing the special structure of this hollow optical fiber with suspended core and superparamagnetic magnetic fluid.     

基于光纤的光学频率传递研究

随着光钟研究的发展, 光钟的稳定度和不确定度均达到10^-18量级. 通过光纤可以实现光钟频率信号的高精度传输, 有望用于未来“秒”定义的复现. 演示了百公里级实验室光纤上的光学频率传递. 对于在实验室70 km光纤盘上实现的光频传递, 光纤相位噪声抑制在1-250 Hz傅里叶频率范围内均接近于光纤延时极限, 对应传输稳定度(Allan偏差)为秒级稳定度1.2×10^-15, 10000 s稳定度为1.4×10^-18. 实验室100 km光纤的光频传递秒级稳定度也达到了5×10^-15. 提出了光纤噪声用户端补偿的方案, 可以简化星形传递网络中心站的复杂度. 在25 km光纤上演示了该传递方案, 实现的传输稳定度接近传统前置补偿传递方案.     

Laser-initiated ignition of hydrogen-air mixtures

The subject of investigation is the kinetic mechanisms intensifying chain reactions that proceed in a hydrogen-air mixture when O₂ molecules dissociate under the action of laser radiation with wavelength λ _I = 193.3 nm and are excited into the b ¹Σ _g ⁺ electron state by radiation with λ _I = 762.346 nm. The efficiencies of both methods to initiate ignition are compared. Numerical simulation shows that the ignition temperature for the laser-induced excitation of O₂ molecules into theb ¹Σ _g ⁺ state is lower than for the dissociation of O₂ molecules by UV laser radiation, with the energy supplied to the mixture being the same. However, both photochemical methods are much more efficient than mere heating of the mixture by laser radiation or another source of heat.     

Nonlinear transmission of a single-mode optical fiber with a sharp change of core diameter

Nonlinear transmission of a cylindrically symmetric weakly guiding single-mode optical fiber with a sharp change of core diameter is estimated in the approximation of weak nonlinearity of the fiber material and is calculated by direct numerical simulation of light propagation. It is shown that an increase or a decrease of nonlinear transmission in comparison with the linear value depends on the way in which the width of the radial mode distribution changes with changing diameter of the structure. Domains of fiber diameters corresponding to an increase of nonlinear transmission in comparison with the linear value are determined.     

A multi-parameter sensor system using concentric core optical fiber

We, for the first time, report an experimental demonstration of multi-parameter fiber sensor system using the concentric core optical fiber, which can simultaneously determine the stress, the position of stress and the cracks. A high bending-sensitive concentric core optical fiber has been used in a mesh type structure to form the multi-function sensor.     

Guiding mode in elliptical core microstructured polymer optical fiber

A kind of microstructured polymer optical fiber with elliptical core has been fabricated by adopting insitu chemical polymerization technology and the secondary sleeving draw-stretching technique. Microscope photography demonstrates the clear hole-structure retained in the fiber. Though the holes distortion is visible, initial laser experiment indicates that light can be strongly confined in the elliptical core region,and the mode field is split obviously and presents the multi-mode characteristic. Numerical modeling is carried out for the real fiber with the measured parameters, including the external diameter of 150μm, the average holes diameter of 3.3μm, and the averageole spacing of .3μm by using full-vector plane wave method. The guided mode fields of the numerical simulation are consistent with the experiment result.This fiber shows the strong multi-mode and weak birefringence in the visible and near-infrared band, and has possibility for achieving the fiber mode convertors, mode selective couplers and so on.     

Laser spark ignition of a jet diffusion flame

In this work we report preliminary results on the laser ignition of a jet diffusion flame with jet flow rates ranging from 35 (Re=1086) to 103 cm³/s (Re=3197). The laser spark energy of about 4 mJ was used for all the tests. The relative amounts of fuel and air concentrations at the laser focus have been estimated using a variant of laser-induced breakdown spectroscopy. The ignition and the flame blow out times were measured using the time-resolved OH emission. Ignition times in the range from 3 to about 10 ms were observed depending on the experimental conditions and they increased towards the rich as well as the lean sides. The early time and late-time OH emissions indicate that chemical reactions during the initial stage of the blast wave expansion are not immediately responsible for the ignition. The ultimate fate of an ignition depends on the reactions at later times which determines whether the gas could undergo a transition from hot plasma to a propagating flame.     

A theoretical investigation of soliton induced supercontinuum generation in liquid core photonic crystal fiber and dual core optical fiber

The supercontinuum generation (SCG) in liquid core photonic crystal fiber (LCPCF) with versatile nonlinear response and the spectral broadening in dual core optical fiber is presented. The analysis is presented in two phase, phase I deals with the SCG in LCPCF with the effect of saturable nonlinearity and re-orientational nonlinearity. We identify and discuss the generic nature of the saturable nonlinearity and reorientational nonlinearity in the SCG, using suitable model. For the physical explanation, modulational instability and soliton fission techniques is implemented to investigate the impact of saturable nonlinear response and slow nonlinear response, respectively. It is observed that the saturable nonlinearity inevitably suppresses the MI and the subsequent SCG. On the other hand, the re-orientational nonlinearity contributes to the slow nonlinear response in addition to the conventional fast response due to the electronic contribution. The phase II features the exclusive investigation of the spectral broadening in the dual core optical fiber.     

Modeling of a step index segmented core single mode optical fiber as a dispersion compensator

A segmented core central step index dispersion compensating fiber (DCF) has been modeled by using spot size optimization technique. We have designed and optimized the DCF by suitably adjusting different fiber parameters, i.e. inner core radius (a), central relative refractive index difference (Δ), normalized outer core position (p), width (b) and height (h) at different values of given Petermann-II spot sizes . The studies on the propagation behavior as well as bendloss and other losses of the DCF have been presented here. The proposed design of the DCF can possess improved bend performances over single core DCFs. At the same time higher negative dispersion coefficient in the single mode region as well as considerably high value of figure of merit (FOM) for optimized fiber parameters can be achieved for smaller spot sizes of the DCF. Further, inclusion of length independent splice loss modified this conventional FOM to a slightly lesser value of modified FOM.     

Laser ignition of low-rank coal

The measured thresholds (H _cr) and kinetic characteristics of the ignition of the volatile substances and the coke residue of low-rank coal under the action of the pulses of a neodymium laser (1064 nm, 120 μs) are reported here. The ignition of volatile substances was observed in microsecond (H _cr = 0.3 J/cm²) and millisecond time intervals (H _cr = 1.2 J/cm²). The combustion of the coke residue occurred in a time interval of 30–100 ms (H _cr = 2.6 J/cm²).     

Dynamic thermometry of a solid via optical diffraction method at pulsed irradiation

A method for the fast measurement of the temperature of solids under the action of a high-power light pulse is proposed and demonstrated. This method is based on the application of the Fraunhofer diffraction and is implemented for silicon samples heated to melting temperatures T _melt = 1412°C by a high-power light pulse. The current silicon temperature was determined by measuring the varying diffraction angle of the probing laser beam. The diffraction angle was varied over time because the period of the diffraction grating increased as a result of the dynamic thermal expansion of the crystal. An initial grating was formed on the surface of the silicon plate with a period of d = 4 μm. The radiation beam of a He-Ne laser with λ = 0.6328 μm was used as the probing beam; the measured signal was recorded in the pair of symmetric fifth-order diffraction maxima.     

Thermal expanded core ultraviolet fiber for optical cavity mode matching

We have demonstrated a mode matching method between two different fibers by a hybrid thermal expanded core technique, which can be applied to match the modes of fiber-based Fabry–Pérot cavities. Experimentally, this method has achieved an expansion of the ultraviolet fiber core by 3.5 times while keeping fundamental mode propagation. With the experiment parameters, the fundamental mode coupling efficiency between the fiber and micro-cavity can reach 95% for a plano-concave cavity with a length of 400 μm. This method can not only have potential in quantum photonics research but also can be applied in classical optical fields.     

Supercontinuum generation in highly Ge-doped core Y-shaped microstructured optical fiber

We report experimental results on supercontinuum generation in a highly Ge-doped core Y-shaped microstructured optical fiber using pump pulses of 9 ns duration at 1064 nm. The fiber is easy to fabricate due to its simple structure and shows good compatibility with standard fiber. The generation of nonlinear effects takes advantage of the large nonlinear refractive index and Raman gain of the Ge-doped core, as well as the air hole structure that surrounds the core. Although the fiber was pumped in normal dispersion and relatively far from the zero dispersion wavelength, flat and smooth supercontinuum in the fundamental mode from 550 nm to beyond 1750 nm was generated with a rather moderate value of fiber length and pump peak power product of 13 kW?m.     

Spatial optical solitons in inhomogeneous elliptic core saturating nonlinear fiber

We have investigated the propagation characteristics of spatial optical solitons in saturating nonlinear waveguide employing JWKB and paraxial ray approximation. We have obtained two second-order coupled nonlinear differential equations for transverse soliton widths of solitons. Threshold power for stable propagation of the beam has been calculated from these coupled equations. We have undertaken stability analysis, which predicts robustness of these solitons. Both guiding as well as antiguiding cases have been considered and shown that stable spatial soliton propagation is possible in both cases.     

New plastic optical fiber using polycarbonate core and fluorescence-doped fiber for high temperature use

This article describes the development of a plastic optical fiber composed of a polycarbonate core with a glass transition temperature of 150°C, and a cladding of newly developed poly-4-methyl penten-1, which softens at 173°C. This cladding is suitable for use at temperatures up to 130°C. The minimum optical attenuation is 0.8 dB/m at 765 nm in the near-infrared region. The cause of the attenuation of the PC-core fiber was analyzed and the intrinsic loss limit was estimated to be 0.4 dB/m at 765 nm. The fiber has excellent characteristics, including thermal stability up to 125°C, high flexibility, high strength, and self-extinguishing properties.

The polycarbonate core fiber, doped organic fluorescing materials, has also been developed for automotive uses such as light guide and illuminator. Light can be transmitted through this fiber with incident optical beam perpendicular to the fiber as well as the beam parallel to the fiber.     

New plastic optical fiber using polycarbonate core and fluorescence-doped fiber for high temperature use

This article describes the development of a plastic optical fiber composed of a polycarbonate core with a glass transition temperature of 150°C, and a cladding of newly developed poly-4-methyl penten-1, which softens at 173°C. This cladding is suitable for use at temperatures up to 130°C. The minimum optical attenuation is 0.8 dB/m at 765 nm in the near-infrared region. The cause of the attenuation of the PC-core fiber was analyzed and the intrinsic loss limit was estimated to be 0.4 dB/m at 765 nm. The fiber has excellent characteristics, including thermal stability up to 125°C, high flexibility, high strength, and self-extinguishing properties.

The polycarbonate core fiber, doped organic fluorescing materials, has also been developed for automotive uses such as light guide and illuminator. Light can be transmitted through this fiber with incident optical beam perpendicular to the fiber as well as the beam parallel to the fiber.