球形光纤端面效应及其应用

本文介绍了球形光纤端面的制作方法,采用射线理论和等效透镜法分析了圆球形端面多模光纤的端面效应,并给出了两个不同端面多模光纤之间耦合的实验结果。结果表明：圆球形端面光纤具有聚光特性,与平端面相比,使用圆球形端面光纤不仅可以提高光器件之间的耦合效率,而且增大了它们之间的耦合距离,利于光路调试;可广泛应用于光源与光纤、光纤与光纤、光纤与探测器之间的耦合。     

光纤探测方式下全积分球与半积分球性能对比研究

为比对全积分球和半积分球在光路传输、输出信号上的差异,根据积分球基本原理分别建立了全积分球和半积分球的光学传输模型,推导了两种积分球在光纤探测方式下的输出信号强度表达式,并从理论和实验上对这两种积分球的探测性能进行了比对。结果表明,全积分球与半积分球的输出信号和探测灵敏度均与积分球涂层反射率、积分球半径、光纤数值孔径角有关;半积分球性能是否优于全积分球取决于漫反射涂层以及平面反射镜反射率的选取。当理想情况下平面反射镜的反射率等于1时,半积分球的信号强度是全积分球的2倍。     

Theoretical comparison of optical traps created by standing wave and single beam

We used generalised Lorenz–Mie scattering theory (GLMT) to compare submicron-sized particle optical trapping in a single focused beam and a standing wave. We focus especially on the study of maximal axial trapping force, minimal laser power necessary for confinement, axial trap position, and axial trap stiffness in dependency on trapped sphere radius, refractive index, and Gaussian beam waist size. In the single beam trap (SBT), the range of refractive indices which enable stable trapping depends strongly on the beam waist size (it grows with decreasing waist). On the contrary to the SBT, there are certain sphere sizes (non-trapping radii) that disable sphere confinement in standing wave trap (SWT) for arbitrary value of refractive index. For other sphere radii we show that the SWT enables confinement of high refractive index particle in wider laser beams and provides axial trap stiffness and maximal axial trapping force at least by two orders and one order bigger than in SBT, respectively.     

镜面偏心测量光学系统设计及其杂光分析

为了解决现有镜面偏心测量设备存在的问题,本文研究了一种采用切换镜头和调焦相结合的方法来设计的镜面偏心测量光学系统,使用这个光学系统,既能使被测镜面的曲率半径扩展到-∞~+∞范围,又能保证测量精度。通过Lighttools软件对这个光学系统进行光线追迹,分析其杂光分布,结果表明:准直镜头内部多次反射产生的杂光强度很低,可以忽略。而当被测镜头中存在相邻球心像距的镜面时,产生的杂光强度比较大,在后续的图像处理过程中,必须增强目标图像的对比度。利用研制的镜面偏心测量设备进行测量实验,结果进一步验证了杂光分析的正确性。     

微磨削斜面光纤透镜平面度试验研究

为了研究微磨削参数对斜面光纤透镜平面度的影响,减小微磨削方法加工斜面光纤透镜的平面度误差,采用正交试验法对直径Ф125 μm单模光纤的30°斜面光纤透镜的微磨削进行了试验。结合微磨削的磨削力模型和材料力学弹性梁变形理论, 分析微磨削过程中随着磨削用量的变化所导致的光纤透镜被磨削斜面的平面度的变化规律。理论分析和实验结果表明:光纤悬伸长度对斜面光纤透镜平面度的影响最大,增大光纤悬伸长度将导致较大的斜面光纤透镜平面度的轮廓误差,恰当的磨削用量组合能够获得较小的平面轮廓误差。通过试验磨削出了平面度误差为3 μm的30°斜面光纤透镜。     

Chromatic dispersion behavior of Si-NC-Er doped optical fiber

The chromatic dispersion for conventional and Er-doped fibers using the refractive index approximation is examined. A first, analytical method for investigation of dispersion in step index triple clad optical fiber is used. To design of zero-dispersion shifted fiber for optical communication purpose manipulation of the refractive index and radius of the core are considered. We show that in presence of the Si-NC-Er ions, zero-dispersion wavelength is displaced and the dispersion quantity is increased. In this work, we try to optimize system parameters to obtain minimum dispersion and dispersion shifted fiber with control of the doping levels of Er ions and Si-NC as well as doping profiles. For especial case, we assumed the Gaussian inhomogeneous core refractive index for zero-dispersion wavelength and dispersion managements.     

A liquid lens-based broadband variable fiber optical attenuator

To the best of our knowledge, proposed is the first variable fiber optical attenuator (VFOA) using an electronically controlled variable focus liquid lens. The approach uses the changes in the radius of curvature of the liquid lens edge to enable an electronically controlled optical wedge that produces a varying beam tilt angle. In effect, changing beam tilt within a single mode fiber (SMF) lens free space coupling assembly leads to a polarization independent broadband VFOA design. The demonstrated VFOA experiment shows broadband operation over the 1530-1560 nm C-Band with a 40 dB dynamic range, <0.5 dB resolution, 0.3 dB polarization dependant loss, 4.3 dB fiber-to-fiber optical loss, 3 dB optical bandwidth from 1510 nm to 1700 nm, and switching time of <100 ms. Applications for this VFOA include use in hand held test and measurement equipment.     

Design of an optical fiber sensor for linear thermal expansion measurement

Design and operation of an optical fiber device for temperature sensing and thermal expansion measurement are reported. The modulated intensity has been measured by using a pair of 450 μm core fiber, one acting as the source and the other one as receiving fiber. In this design, the light intensity modulation is based on the relative motion of the optical fibers and a reflective coated lens. By using displacement calibration data for this sensor, the linear thermal expansion of the aluminum rod is determined. This sensor shows an average sensitivity of about 11.3 mV/°C for temperature detection and 7 μm/°C for thermal expansion detection. Device resolution for a linear expansion measurement is about 3 μm for a dynamic range of 600 μm corresponding to a temperature change of 100°C. The measured linear expansion results are checked against the expected theoretical ones and an agreement within ±2 μm is noticed. The operation of this sensor was also compared with other types and some advantages are observed, which verify the capability of this design for such precise measurements.     

Exploring fabrication tolerances of optical systems by solving inequalities

A scheme to study fabrication tolerances of optical components and systems is presented. By solving a set of non-linear inequalities an optimal set of lens parameters is found. Then, by selecting another, but strict, set of boundaries to the non-linear inequalities system, a new set of lens parameters is found. The fabrication tolerances are determined by the intersection domain of each lens parameters obtained by solving the set of non-linear equations, with a condition that one solution should come from a strict set on boundaries of the non-linear equation system. This scheme is applied to a classical triplet lens system, used as starting point, and is compacted in effective and back focuses lengths, showing the versatility to study the fabrication tolerances.     

新型矿灯二次配光系统的仿真研究

将光纤照明技术运用到矿灯领域中,需要根据光纤照明的特点设计相应的二次配光系统,以满足实际配光的需求。利用光学仿真软件TracePro开展了对新型光纤LED矿灯系统的二次配光问题的仿真研究。配光器件主要采用单个反光腔、透镜及其组合。从反光腔形状、深度和口径、透镜类型和尺寸等方面入手,探讨了各个因素对配光效率、光斑大小、光照均匀度的影响。通过对仿真结果的比较和分析发现,反光腔主要影响配光效率,而透镜主要影响光照均匀度和光斑大小。得到了合适的新型光纤-矿灯的二次配光系统,即锥形腔配合菲涅尔透镜。结果表明,该组合具有配光效率高、光照度均匀、光斑大小适中、实际尺寸小、方便井下作业等优点。     

Designing a coupler for the intersatellite optical communication system

Coupling a single-mode laser diode with 200 mW to a single-mode fiber (SMF) through an orthonormal aspherical cylindrical lens and a GRIN lens for the intersatellite optical communication system is proposed and demonstrated. We experimentally studied how the coupling efficiency changes with the SMF's position displacement and axial angle variation, and obtained 80 mW output power at the end of the SMF, which shows that the coupling units have satisfied the designed request.     

光纤式微液滴光学检测与计数单元仿真分析

为实现微流控芯片上微液滴的检测与计数，设计了光纤式检测与计数单元，使用TracePro软件进行建模仿真以便为检测信号处理提供依据。根据液滴通过检测区域时引起的光强变化来实现计数，分析了照明光束准直性、液滴尺寸、液滴相对溶液折射率以及接收光纤相距芯片距离对光强变化的影响。仿真实验结果表明，照明光束准直性越差，液滴半径越大，相对溶液折射率越低，接收光纤距离越近，相对光强变化越明显，并且液滴大小决定着光强变化曲线中是否会出现双波谷现象，液滴半径小于13 μm时，液滴检测信号为明显的单波谷，半径大于17 μm时，液滴信号为明显双波谷。根据仿真结果提出了检测信号的处理方法，表明该单元可以实现微流控芯片上微液滴的检测与计数功能。     

Impact of polarization mode dispersion on the performance of optical CDMA transmission system

The impact of fiber polarization mode dispersion (PMD) on the bit error rate (BER) performance of a direct sequence optical code-division multiple-access system is analyzed by the split-step Fourier method based on the coupled nonlinear Schrödinger equation, the three-dimensional Poincare sphere theory and the Jones matrix method. When the incident pulse's width is bigness than the chip duration, which causes spreading and overlapping of chips and degrades system performance due to increased interchip interference and reduced received optical power conduce cannot decoding or error decoding. When the incident pulse's width is less than the chip duration, good encoding/decoding performance can be achieved.     

All-optical demultiplexing of 4-ASK optical signals with four-wave mixing optical gates

A new all-optical technique to demultiplex quaternary-amplitude-shift keying (4-ASK) signals into two on-off keying (OOK) signals is proposed. We show that such quaternary-to-binary conversion may be performed with two types of optical gates (OGs); a first one that implements an S-shaped optical power transfer function (TF), which is also the characteristic TF of optical pulse reshaping devices, and a second type that implements a U-shaped TF. Furthermore, we describe a heuristic approach to design such OGs by using the fiber four-wave mixing effect in highly non-linear dispersion-shifted fibers. The performance of the technique is evaluated by simulating the demultiplexing of 4-ASK signals with these OGs. Results indicate that the proposed devices are able to provide binary signals with acceptable BERs even after the 4-ASK signals are propagated through a cascade of eight fiber links of 50 km followed by optical amplifiers with a 4.5-dB noise figure.     

Simple and high efficient optical trapping using a cylindrical lens and a single plane wave of incidence

We suggest a simple and high efficient method for trapping particles in the evanescent field. In this method, a single plane wave is normally incident on the cylindrical surface of a cylindrical lens and then incident on the plane surface of the lens at an angle larger than the critical angle. Multiple reflections of light within the cylindrical lens create two evanescent waves with different directions in the transmitted field. Interference of two evanescent waves comes into being a standing wave which can stably trap particles close to the top of the cylindrical lens. Based on the Rayleigh approximation, we obtain analytical expressions of optical force acting on a Rayleigh particle placed in the vicinity of the lens. We find that the trap stiffness and trap depth is dependent on the radius of the cylindrical lens, wavelength and polarization of light, and incident angle at the lens–liquid interface.     

基于白光干涉的光学球面半径测量研究

光学球面曲率半径是决定光学球面光学特性的重要参量,通过测量光学球面的曲率半径，可以审核光学元件设计制造质量。在基于白光干涉理论基础上，将莫尔光栅位移测量系统及CCD数字图像采集处理系统集成到迈克尔逊干涉仪上，利用CCD数字图像处理技术，构建了光学球面曲率半径自动测量系统。该测量系统对于大曲率半径的光学球面测量精度较高；对于半径R＝71.2037mm的光学球面,其测量标准误差σR＝0.4723mm。实验结果表明：设计的光学球面自动测量系统可以对大曲率半径光学球面实现高精度测量。     

Controllable optical bistability and multistability in a rare-earth-ion-doped optical fiber

We investigated the optical bistability and multistability in an Er³⁺-doped ZrF₄–BaF₂–LaF₃–AlF₃–NaF optical fiber inside an optical ring cavity. It is found that the optical bistability and multistability can be easily controlled via adjusting properly the parameters of the corresponding system. Our scheme may provide some new possibilities for technological applications in optoelectronics and optical-fiber communication.     

Optimized amplification of femtosecond optical pulses by dispersion management for octave-spanning optical frequency comb generation

We report a method for optimizing the amplification of femtosecond optical pulses by using dispersion management. The amount of dispersion provided to the seed optical pulse of an erbium-doped fiber (EBF) has an optimal region that enhances the output power of an amplifier. The power enhancement is accompanied by spectral broadening, which originates from adiabatic narrowing in the erbium-doped fiber. The amplified optical pulses can be used to generate an octave-spanning optical frequency comb (OFC) by employing a highly nonlinear fiber (HNLF).     

Optically controllable variable fiber optical attenuator integrated in conventional optical fiber

New type of optically controllable variable fiber optical attenuator based on thermo-optical effect in liquid cladding of optical fiber is described. The thermo-optical effect in liquid cladding optical fiber causes refractive index contrast changes in core–cladding interface, what enables to change the propagating optical signal power with temperature. The temperature change is achieved by fiber based heating element using laser radiation. Attenuation up to −12 dB was achieved in static dependence and dynamic response confirmed rise time up to 24 ms.     

Multi-focus optical fiber lens based on all-dielectric metasurface

A multi-focus optical fiber lens is numerically demonstrated based on an all-dielectric metasurface structure. The metasurface consists of an array of rectangular silicon resonators with varying widths in order to obtain the required phase distribution. The core diameter of the multimode fiber is large enough to contain sufficient resonance units. The spatial distribution of the dielectric resonators is dictated by spatial multiplexing, including interleaving meta-atoms and lens aperture division, to achieve multi-focus properties. The proposed optical fiber metalens can produce two or three focal points along the longitudinal direction with high focusing efficiency. The size of every focal point is close to the diffraction limit, and the relative intensity on each focus can be controlled by adjusting the number of the respective resonators. The proposed optical fiber lens will have a great potential in the fields of integrated optics and multifunctional micro/nano devices.