Equiangular-spiral bent lightpipes with arbitrary bent angle

A recent study proposed the concept of a leakage-free bent lightpipe with an equiangular-spiral shape [S.-C. Chu, J.-L. Chern, Opt. Lett. 30 (2005) 3006]. This paper extends the design of a leakage-free equiangular-spiral bent lightpipe with arbitrary-bend-angle and addresses in detail the mathematical formalism required to build such an equiangular-spiral bent lightpipe. Furthermore, a comparison of the proposed equiangular-spiral bent lightpipe and a conventional circular bent lightpipe is provided. Numerical verifications are discussed, and experimental explorations with different bent shapes and angles are carried out for comparison. Results show that equiangular-spiral bent lightpipes with different bent angles exhibit a theoretical 100% transmission with more than 76% efficiency when practically propagating, which is much better than conventional circular bent lightpipes. The output irradiance distributions of bent lightpipes with different bent shapes are also investigated.     

弯曲光纤针尖及其法向力压电探测技术

本文介绍一种弯曲光纤针尖及其法向力压电探测的新技术.与目前普遍采用的方法不同,弯曲针尖的制作是先利用电阻丝加热,将光纤弯曲成所需的角度,然后再在缓冲氢氟酸中腐蚀成针尖,得到曲率半径为300μm,弯曲角度为120°,长度为500μm的弯曲针尖.同激光或电弧熔拉、弯曲的方法相比,这种方法工艺简单,成本低廉.由弯曲针尖与蜂鸣器压电片组成的悬臂,利用压电片的正、逆压电效应实现弯曲针尖法向力的非光学法探测.实验表明,这种弯尖法向力的探测较直尖切变力具有更高灵敏度,探测距离提高了一倍以上,给实际应用带来很大的便利.     

弯曲波导之间的耦合分析

采用极坐标下的光束传播法分析了两条平行变曲波导的中心间距、曲率半径等因素对模式耦合的影响,得到了耦合长度、耦合强度随中心间距、曲率半径的变化规律,并将直波导作为变曲波导的一种特殊情况进行了分析.     

Characteristics of vertical bent coupling between straight and curved rectangular optical waveguides

In terms of the coupled mode theory (CMT) and the transfer matrix method, we present a technique and relative formulas including the bent coupling coefficient, amplitude coupling ratio, amplitude transmission ratio and propagation power for analyzing the vertical bent coupling between a curved rectangular waveguide and a straight one. Investigations show that the bent coupling appears in an effective coupling region by both sides of the central coupling point. Beyond this effective coupling region, however, the bent coupling is very weak, and the propagation power in the waveguide is closer to a constant. As the bent radius increases, or the thickness of the coupling layer between these two waveguides decreases, this effective coupling region becomes wider, in which the coupling behavior becomes stronger.     

弯曲波导研究进展及其应用

本文主要分析了弯曲波导损耗机理,包括传输损耗、辐射损耗、模式转换损耗。重点综述了设计低损耗弯曲波导的方法,包括波导材料、弯曲波导的曲线形状、波导种类、脊型波导的宽度、脊高、弯曲半径、模场分布、弯曲波导曲线形状和其他新型波导结构等。简要概括了近年来设计和制备低损耗弯曲波导的代表性工作。介绍了弯曲波导在集成光学中的应用。通过对弯曲波导的损耗及耦合机制理论的不断完善,实现光在较小弯曲半径的低损耗传输,从而提高集成光学的集成度是弯曲波导今后的发展趋势。     

Bent crystal channeling of 255 MeV electrons

Charged particles channeled in a bent crystal plane are known to be deflected along the bent plane. Such studies have mainly been performed for high-energy positively-charged particles such as protons, and recently for electrons with energies from 855 MeV to 20.35 GeV. In this work, we present experimental results on the bent crystal channeling of electrons for a lower energy region (255 MeV), where the multiple scattering effect in a crystal is expected to be more dominant. Angular distributions of electrons transmitted through a bent Si crystal have been measured, which are in good agreement with the simulation results.     

Bent crystal application to formation and diagnostics of proton beam

The analysis of the deflection efficiency of high-energy proton beam with a bent crystal has been made and the optimum length of the bent crystal estimated. A bent Si crystal was used in the experiments at Serpukhov circular accelerator with 70 GeV proton beam. The results of the formation of a narrow proton beam and measurements of the beam phase volume are discussed.     

用极坐标下的广角光束传播法计算分析弯曲波导

采用了极坐标下的广角BPM(Beam Propagation Method)对弯曲波导进行了计算模拟,并与极坐标下近轴BPM方法进行了比较,取得很好的结果.     

Oblique detonation waves stabilized in rectangular-cross-section bent tubes

Oblique detonation waves, which are generated by a fundamental detonation phenomenon occurring in bent tubes, may be applied to fuel combustion in high-efficiency engines such as a pulse detonation engine (PDE) and a rotating detonation engine (RDE). The present study has experimentally demonstrated that steady-state oblique detonation waves propagated stably through rectangular-cross-section bent tubes by visualizing these waves using a high-speed camera and the shadowgraph method. The oblique detonation waves were stabilized under the conditions of high initial pressure and a large curvature radius of the inside wall of the rectangular-cross-section bent tube. The geometrical shapes of the stabilized oblique detonation waves were calculated, and the results of the calculation were in good agreement with those of our experiment. Moreover, it was experimentally shown that the critical condition under which steady-state oblique detonation waves can stably propagate through the rectangular-cross-section bent tubes was the curvature radius of the inside wall of the rectangular-cross-section bent tube equivalent to 14–40 times the cell width.     

Focusing of X-rays by bent crystals

The coefficient of X-ray reflection from a bent Bragg mirror is obtained on the basis of the principle of locality. The focusing of X-ray quanta by bent crystals is considered. The caustics for the X-rays reflected from the bent Bragg mirror are determined.     

用于X射线时空分辨测量的弯晶谱仪

为了测量激光聚变产生的0.2～0.37 nm范围内的等离子体X射线, 设计了一种基于空间和时间分辨的聚焦型弯晶谱仪. 将在700℃时弯曲后的LiF(2d＝0.403 nm)晶体作为色散元件, 布喇格衍射角的变化范围为30～67.5°, 弯晶粘贴在离心率和焦距分别为0.9586和1350 mm的椭圆形不锈钢基底上. 利用弯晶谱仪配X光CCD相机在星光Ⅱ激光(0.35 μm, 60～80J, 700 ps)装置上摄取了钛平面靶发射的X射线光谱, 实验结果表明它的光谱分辨率能达到0.001 nm.     

基于超环面晶体的X射线成像诊断

设计了可用于X射线成像用的聚焦型超环面晶体谱仪,讨论了基于布拉格几何结构的超环面及球面弯曲晶体聚焦特性,给出了基于超环面晶体X射线2维单能成像的光源、晶体及探测器的最佳位置,在中国工程物理研究院激光聚变研究中心进行了X射线背光成像实验.利用超环面弯曲晶体作为成像器件,其弧矢及子午平面的曲率半径分别为290 mm及190...     

Transmission Characteristics of 90° Bent Photonic Crystal Waveguides

There are several key factors that affect the transmission characteristics of the 90° (L-shaped) bent photonic crystal waveguides. The first factor is the direct coupling efficiency from the incident lights into the waveguides. The second one is the bandgap deviations of the photonic crystals. And the third factor is the optical reflections in the bent corners. In this article, we compare three types of L-shaped bent photonic crystal waveguides. One is the original type, which has an abrupt right-angle bend. Another is an improved 90° bend with a 45°-mirror. The other is an L-shaped bent photonic crystal waveguide with a 45°-transitional section. We investigate their respective frequency responses and observe the improvements in the total transmission efficiencies provided by the latter types.     

高功率毫米波圆波导TM01—TE11模式变换分析

 在数值研究高功率毫米波TM₀₁—TE₁₁光滑弯曲圆波导模式变换的基础上，对弯曲波导的几何结构进行了优化分析。在模式耦合理论的基础上，优化出了比较好的几何结构，并发现了圆波导半径、弯曲圆波导曲率和频率以及频带宽度之间的变化规律。以此数据设计的模式变换器的转换效率可达99%，带宽超过29.8%。     

Circuit-oriented modelling of ring-resonators

In this work we propose a circuit-based analysis of both a ring phase shifter and a single ring filter, taking into account the effects of imperfections in the directional couplers and polarization conversion in bent waveguides. New models for the directional coupler and for the bent waveguide are proposed and used to find an analytical expression of the transfer functions of ring based devices. The numerical results obtained with the new models show that defects in directional couplers and polarization conversion in bent waveguides are responsible of spectral impairments often observed experimentally, confirming the validity of the model.     

Ultralow-bending-loss surface-plasmon-polariton waveguides

We report the transmission, reflection and loss properties of 90-degree and 135-degree bent silicon waveguide and 90-degree and 135-degree bent surface-plasmon polariton (SPP) waveguides composed of metal thin film and silicon. Finite difference time domain simulation analysis shows that the maximum bending transmittances of 90-degree bent and 135-degree bent silicon waveguides are 51% and smaller than 10%, respectively, and the maximum bending transmittances of 90-degree bent and 135-degree bent SPP waveguides are 80% or so, and they are higher 30% and 70% than that of identically-bent silicon waveguides, respectively. Moreover, the SPP waveguide bend with metal thin film as inner layer of the bend and silicon as outer layer of the bend has much higher transmission than ones with silicon as the inner layer and metal thin film as the outer layer. The waveguide bend with metal as the inner layer and dielectric as the outer layer will be potential for integrated photonic devices and subsystem.     

球面晶体分析器在X射线成像诊断中的研究

 为诊断激光等离子体X射线,研制了基于Bragg衍射原理的球面弯曲晶体。球面晶体可提高空间分辨、光谱分辨及立体角收集辐射能力。实验采用球面弯曲石英晶体作为分析器,X射线成像板作为成像器件,利用X射线衍射仪铬靶 Kα单色谱成像,验证了0.2 mm间隔双丝的单能像,球面弯晶具有较高的光谱分辨力和信噪比,谱分辨力可达1 000,聚光效率在同样距离条件下比平晶分析器高一个数量级以上。     

Characterization and on‐line adjustment of the sagittal‐bent Laue crystal profile

The sagittal‐bent Laue monochromator can provide an ideal way to focus high‐energy X‐ray beams. However, the anticlastic curvature induced by sagittal bending has a great influence on the crystal performance. Thus, characterizing the bent‐crystal shape is very important for predicting the performance of the bent‐crystal monochromator. In this paper the crystal profile is measured by off‐line optical metrology and on‐line X‐ray experiments. The off‐line results showed that the bent‐crystal surface could be well fitted to a saddle surface apart from a redundant cubic term which was related to the different couples applied on the crystal. On‐line characterization of the meridional and the sagittal radius of the bent crystal includes double‐crystal topography and ray‐tracing measurement. In addition, the double‐crystal topography experiment could be used as a quick diagnostic method for the bending condition adjustment. The sagittal radius of the bent crystal was characterized through a ray‐tracing experiment by using a particularly designed tungsten mask. Moreover, rocking curves under different bending conditions were measured as well. The results were highly consistent with analytical results derived from the elastic theory. Furthermore, radii along different vertical positions under various bending conditions were measured and showed a quadratic relationship between the vertical positions and the meridional radii.     

Analytical solution of crystal diffraction intensity

Plasma density and temperature can be diagnosed by x-ray line emission measurement with crystal, and bent crystals such as von Hamos and Hall structures are proposed to improve the diffraction brightness. In this study, a straightforward solution for the focusing schemes of flat and bent crystals is provided. Simulations with XOP code are performed to validate the analytical model, and good agreements are achieved. The von Hamos or multi-cone crystal can lead to several hundred times intensity enhancements for a 200μm plasma source. This model benefits the applications of the focusing bent crystals.     

变曲率弯晶的粒子退道行为

利用正弦平方势和变曲率的抛物线近似描写了弯曲硅单晶的粒子退道效应,进一步证实利用弯晶来偏转(或控制)带电粒子运动方向的可能性。导出弯晶的退道系数并讨论了它的可能应用。 关键词：