Theory of power coupling between multimode optical fibres

In this paper power coupling between two multimode optical fibres is investigated. A formalism (based on a geometrical approach) suitable for analysing any coupling configuration between fibres with any index profile and any radiance distribution is presented. The model is applied to obtain coupling losses both in uniformly excited parabolic- and step-index fibres, in the presence of all kinds of coupling errors. Numerical results of extensive utility are shown and useful asymptotic expressions of coupling efficiency, valid for small values of coupling error parameters, are derived together with some practical rules for error combination. Mention is also made of some experimental results we have obtained, which corroborate some previous assertions. The work can supply a useful tool in the design of joints and connectors between single fibres or optical cables.     

卡塞格林系统光学装调技术研究

介绍卡塞格林系统非球面主镜使用三坐标测量仪进行定心装调的方案。系统的主镜口径为300 mm,需要使用结构胶进行胶结固定,选用微应力粘接方法,将胶层粘接应力与热应力变形控制在极小的范围内。利用ZYGO干涉仪获得光学系统的波前信息,将测得的波相差转化为初级像差,根据光学系统失调量与像差的关系对卡塞格林系统进行计算机辅助装调。调试后,系统的RMS值达到0.10,分辨率达到1以内,检测结果表明:该系统的成像质量接近理论衍射分辨率,该方案可以实现快速定心,并且能够满足计算机辅助装调对定心精度的要求。     

Mode coupling in graded-index optical fibres due to microbending

The effects of microbending on mode coupling in graded-index optical fibres are investigated through a ray-optics approach and the standard Fokker-Planck theory. This model can be applied to any kind of index profile and statistics of the perturbation. In particular, for a parabolic index fibre and for a perturbation with microscopic correlation, a closed form expression of the optical power steady-state distribution is derived.     

激光雷达系统快速准直的方法和光学装置

研制了一种能够方便、快速调节激光雷达收发光路准直的光学装置,分析了装置楔角的选取要求、准直误差及其相应的矫正方法。该装置结构简单,主要由两个楔形光学平板组成,通过电机转动两个楔板可使出射光束方向在一定范围内任意改变,该调节范围由楔板的楔角和折射率决定。利用折射定律,严格推导了装置中两个楔形光学平板的旋转角度与出射光束方向之间的关系。提出了将该光学装置插入到激光雷达发射光路,采用螺旋式粗扫、圆形和径向细扫相结合的光束扫描方式实现对激光雷达准直的方法,并给出了系统准直调节过程中的判断准则和具体的准直步骤。     

用于折反式红外光学系统的辅助装调镜设计

针对大口径折反射红外光学系统设计过程中正主、次镜的像差为单独校正,无法实现高精度调试的问题,提出设计一套可见光波段辅助装调镜的方法,辅助镜用于补偿主次镜之间的像差,完成高精度装调。辅助透镜研制过程中,严格控制加工精度,减少对系统精度的影响。采用ZYGO干涉仪对系统进行了调试,波像差实际值为0.3,设计值0.14。最后,更换中继透镜组,光学系统成像质量达到红外搜索跟踪系统的要求。     

激光雷达系统快速准直的方法和光学装置

 研制了一种能够方便、快速调节激光雷达收发光路准直的光学装置,分析了装置楔角的选取要求、准直误差及其相应的矫正方法。该装置结构简单,主要由两个楔形光学平板组成,通过电机转动两个楔板可使出射光束方向在一定范围内任意改变,该调节范围由楔板的楔角和折射率决定。利用折射定律,严格推导了装置中两个楔形光学平板的旋转角度与出射光束方向之间的关系。提出了将该光学装置插入到激光雷达发射光路,采用螺旋式粗扫、圆形和径向细扫相结合的光束扫描方式实现对激光雷达准直的方法,并给出了系统准直调节过程中的判断准则和具体的准直步骤。     

图像处理在光路自动准直系统中的应用

光路自动准直系统应用于惯性约束聚变的高功率激光装置中的光束自动调整。图像处理是光路自动准直的关键技术之一。针对神光Ⅲ原型装置,结合阈值化、重心法、中值滤波和圆拟合等多种不同的图像处理方法设计了一套合理的准直方案,并且在模拟实验平台上进行了实验验证。实验结果表明,光路自动准直系统能够在15min之内顺利完成光路的自动调整,光束近场调整精度优于近场光斑的±0.5%,光束远场调整精度≤±0.3″,满足了原型装置的总体要求。     

Mode coupling in graded-index optical fibres due to perturbation of the index profile

Applied Physics A - Core diameter fluctuations in graded-index optical fibres entail a perturbation of the whole index profile whose effects on mode coupling are investigated. The model here...     

共轴三反光学系统卧式装调技术

共轴三反光学系统是空间光学遥感器常用的设计形式,以“高分一号”遥感卫星高分辨率相机装调为例,对共轴三反系统计算机辅助装调技术进行了研究。提出以主镜光轴为装调基准,通过调整三镜控制系统视场和调整次镜控制系统像差的装调方法,分析了次镜和三镜的失调量与Zernike系数变化关系,由光学设计软件求得系统灵敏度矩阵,用于指导系统装调工作,提高了装调精度,缩短了装调周期。测试结果表明:光学系统各视场Zernike系数优于0.05λ,系统波相差RMS值优于0.06λ,系统通过在轨成像测试,图像清晰,层次丰富。     

Fluoride fibres for optical transmission

Optical fibres made from heavy metal fluorides have been under development for much of the past decade. There have been significant advances in understanding the fundamental characteristics of these materials. Progress towards achieving low optical losses and in optimizing the design of fluoride fibres for use in long transmission systems is reviewed.     

大型Schmidt望远镜光学系统调整方法

安装于紫金山天文台盱眙观测站用以观测近地天体的大型Schmidt望远镜,采用了平场Schmidt光学系统,改正镜通光口径为1m,球面反射镜口径为1.2m,焦距为1.8m,接收器用了4K×4K的高灵敏度CCD。本文叙述了该仪器光轴调整的方法及调整后观测获得的初步结果。叙述了望远镜光轴校正方法、校正结果、CCD靶面的调整及望远镜极轴高度、方位的调整及相应的照片。经实际观测的结果是:露光1s可拍到18等星;露光4s可拍到19.3等星;露光20s可拍摄到21.2等星。     

A new approach to investigating mode coupling phenomena in graded-index optical fibres

To study mode coupling in optical fibres a new technique is developed, based on mode selective excitation and output near-field analysis. Experimental results support decoupling of the problem into two phenomena which are effective on different scales of propagation length: azimuthal and longitudinal mode mixing. A statistical model providing a simulation of the experimental near-field patterns is developed. Comparison with measurements shows that azimuthal mixing is complete before 1 km propagation, while effects of uncomplete axial coupling are accounted for. This approach also suggests a method for measuring the steady-state distribution length, with useful system implications.     

Mode coupling effects in optical fibres: perturbative solution of the time-dependent power flow equation

Some new aspects of the perturbative solution of the time-dependent power flow equation are investigated. The roles of the amplitude in the fibre perturbation, of the intrinsic attenuation coefficient and of the launching condition are stressed. The reaching of the steady state is studied with particular attention in order to give predictions on attenuation and bandwidth of real optical links.     

Design and performance of a video-based laser beam automatic alignment system

A laser alignment system is applied to a high power laser facility for inertial confinement fusion.A designof the automated,close-loop laser beam alignment system is described.Its function is to sense beamalignment errors in a laser beam transport system and automatically steer mirrors preceding the sensorlocation as required to maintain beam alignment.The laser beam is sampled by a sensor package,whichuses video cameras to sense pointing and centering errors.The camera outputs are fed to a personalcomputer,which includes video digitizers and uses image storage and software to sense the centroid of theimage.Signals are sent through the computer to a stepper motor controller,which drives stepper motorson mirror mounts preceding the beam sampling location to return the beam alignment to the prescribedcondition.Its optical principles and key techniques are given.The pointing and centering sensitivities ofthe beam aligmnent sensor package are analyzed.The system has been verified on the multi-pass amplifier experimental system.     

用于光具座自动测量焦距的变焦光学系统设计

为了提高光具座自动测焦距时的测量精度,设计一套连续变焦光学系统。该系统包括自准直组件和变焦组件两部分,可以调节CCD靶面上接收到的图像大小,得到最佳测量结果。根据设计指标要求,在控制系统总长的基础上进行初始结构选择和像质优化。设计完成后的自准直组件焦距200 mm,变焦组件焦距200 mm~20 mm,对接后的变焦系统可实现图像大小1~10连续调节。模拟实验表明:变焦系统像质良好,MTF曲线接近衍射极限,弥散斑小于CCD像元大小,可以满足实际检测需求。     

无焦压缩光路系统的计算机辅助装调方法

为了解决随机成分多、调节灵敏度高的离轴反射式系统的精确装调问题,介绍了干涉测量与计算机优化技术相结合的方法,建立了各元件失调量与初级像差之间的关系,以及元件间的像差相互补偿关系,通过干涉测量采集系统全视场的波前差,反向优化得到各元件的失调量,在波长为632.8 nm时,无焦压缩光路系统全视场平均出射波前优于RMS0.055 ,压缩比误差小于5,实现了无焦压缩光路系统高精度、高效率的装调。     

光通信系统中分光系统光学调整的误差分析

在平行光路中,光学系统的光学元件的误差或微量运动可抽象为绕定点的微量转动,其成像关系可归结为在微量转动下物像共轭关系的依次迭代,利用光学系统这种动态成像关系的思想,建立一个统一的光学调整及误差分析的数学模型。利用此模型分析光通信系统中分光系统的机械安装误差对系统的影响,建立每个反射镜的机械调整坐标,从理论上指导分光系统中每个反射镜的机械调整,最终使通信激光发射系统和精信标激光接收系统的光轴平行度达到5。     

光学标校技术在舰炮武器系统中的应用研究

为了解决舰炮武器系统瞄星标校受天气影响较大的问题,针对雷达（光电）与舰炮一体化的武器系统,提出了一种不需要参照物的光学标校方法。该方法用激光束将炮管轴线引出,通过不失调光学组件进行平行移动并进入雷达（光电）接收窗口,从而获得雷达（光电系统）轴线与炮管轴线的角度差并进行标校。测试与试验结果表明,该方法具有操作简便、效率高、适时性强、标校误差不大于0.5 mrad等特点,与描星方法标校相比,受天气、环境因素影响较小,对充分发挥舰炮武器系统的作战效能具有显著作用。     

高精度自动贴片机视觉对准系统及其图像处理

阐述了高精度自动贴片机视觉对准系统的构成和原理。介绍了利用模式识别理论和图像的不变矩实现定位标志存在性判断的原理及算法和定位标志对准的原理及相关的图像处理算法,以及其中的点模式匹配算法。试验结果表明,定位标志存在性判断算法可以有效地区分不同的定位标志和判断定位标志是否在视场之内;定位标志对准算法在输入图像旋转、平移、定位标志被部分遮挡时,能精确地得到定位标志的位置偏差。