光纤折射率剖面的折射近场法测量的研究

本文叙述了折射近场法(简称RNF)测量光纤折射率剖面的基本原理及实验方法.提供了对单模光纤和多模光纤的测量结果,并与反射法、近场法进行了比较.实验中获得空间分辨率优于0.8μm,折射率灵敏度优于2×10~(-4).     

基于光导微探针的近场/远场可扫描太赫兹光谱技术

太赫兹技术已经成为涉及公共安全、军事国防和国民经济等国家核心利益的前沿研究领域.以往太赫兹测量技术中通常以远场测量为主,如常用的太赫兹时域光谱仪.近年来太赫兹近场技术得到了迅猛的发展,特别是基于光导天线的探针技术的发展,为可扫描的太赫兹近场测量提供了可能.本文详细报道了我们近期在可扫描太赫兹近场光谱仪研究中的进展.采用光纤耦合的光导微探针实现了方便灵活的太赫兹近场/远场三维扫描,并同时获得振幅和相位信息.该系统将有可能广泛应用于人工微结构、石墨烯、表面等离子激元、波导传输、近场成像、生物样品检测、芯片检测等研究领域.     

纤维光学 其他

TN25 2006043342光纤阵列自动测量系统的研制=Development of auto-measuring systemfor fiber array[刊,中]/廖强华(深圳职业技术学院机电学院.广东,深圳(518055)) ,钟江生∥激光与红外.—2006 ,36(4) .—285-287介绍一种光纤阵列自动测量系统,该系统依靠计算机图像处理和识别技术,应用高精度的运动平台,结合光栅尺的反馈数据,识别并测量出光纤阵列各个纤芯的位置,从而计算出纤芯与纤芯间的相对距离,实现自动测量,其测量精度可达0 .1μm。将自动分析和输出测量结果供生产监控,极大地提高了测量精度与生产效率,实现了光纤阵列检测的自动化…     

光纤探针型近场光镊光阱力特性研究

基于动量守恒原理,结合麦克斯韦应力张量和三维时域有限差分方法,建立了近场空间内激光光镊对纳米微粒的光阱力计算模型.分析了光纤探针型近场光镊的近场分布以及操作纳米微粒时各轴向光阱力的分布情况,并探讨了光纤探针尖端的捕获尺寸、捕获位置和操作稳定性.结果表明:微粒应处于光纤探针针尖的近场空间内才可实现稳定可靠的纳米操作,不同...     

多边形光纤远近场扰模特性

天文探测中类地行星的探测需要进一步提高视向速度的测量精度。但圆形光纤扰模效果不佳所引起的入射信息变化时的谱线漂移,成为限制测量精度提高的一个主要因素。采用多边形光纤改善光纤传输系统的扰模特性。利用搭建的测试光纤远场和近场光斑质量的光学系统,通过对光纤出射场光斑质量进行评价,研究了圆形、长方形、正方形和八边形光纤在不同入射条件下的远场和近场分布及远场光斑的光强变化和近场光斑的质心偏移,得出了不同光纤的扰模增益系数。实验表明,在相同入射条件下,多边形光纤具有较好的扰模特性,其中八边形光纤的远场光强变化最小,近场光斑质心偏移最少,扰模特性最好。以八边形光纤代替圆形光纤,可有效减小入射偏差引起的谱线漂移,提高视向速度的测量精度。     

单模及多模光纤折射率分布测量方法研究

通过对几种单模及多模光纤折射率分布测量方法的分析研究，得到单模光纤与多模光纤折射率分布测量方法的根本区别。由于单模光纤芯径比较小，因而只能用波动理论分析其传输机理，其中的远场法和近场法测量都是基于标量亥姆霍兹波动方程，即以单模光纤的基本传输理论进行测量；而多模光纤由于其芯径比较大，故而用射线理论分析其传输原理较为合理。多模光纤的折射近场法和近场扫描法均是以纤芯半径处数值孔径不同，对应的折射模和传导模不同为依据来进行测量的。     

光纤探针型近场光镊光阱力特性研究

基于动量守恒原理,结合麦克斯韦应力张量和三维时域有限差分方法,建立了近场空间内激光光镊对纳米微粒的光阱力计算模型.分析了光纤探针型近场光镊的近场分布以及操作纳米微粒时各轴向光阱力的分布情况,并探讨了光纤探针尖端的捕获尺寸、捕获位置和操作稳定性.结果表明:微粒应处于光纤探针针尖的近场空间内才可实现稳定可靠的纳米操作,不同尺寸的微粒具有不同的捕获效果,且随初始位置的不同微粒的捕获位置亦不同.计算结果为激光近场光镊纳米操作装置的设计和制造提供了理论基础.     

保偏光子晶体光纤模场测量与放电调整技术

给出了保偏光子晶体光纤(PM-PCF)模场的计算模型,搭建了基于近场光斑成像法的PM-PCF非圆模场在线测量装置,采用红外成像系统实现了模场参数的绝对测量。在此基础上,研究了放电对PM-PCF模场的微调作用,结合仿真计算,获得模场参数变化规律。建立了PM-PCF与传统保偏光纤的耦合损耗计算模型,确定了低损耗耦合条件,并进行了熔接实验验证,实现了PM-PCF与传统保偏光纤的低损耗熔接。     

光纤及双光纤扰模器远/近场扰模性能的模拟分析

在高精度视向速度测量系统中,圆形光纤逐渐被多边形光纤替代,结合多边形光纤、透镜和圆形光纤的扰模方案也被陆续提出。通过光线追迹的方法,对圆形、八边形截面的两种光纤以及基于这两种光纤的双光纤扰模器的扰模性能进行了模拟分析。模拟结果表明:虽然圆形光纤有较好的远、近场角向扰模,但是径向扰模效果不佳;八边形光纤的近场径向和角向扰模性能均较优,但远场扰模与圆形光纤没有明显差异;双光纤扰模器能有效提高光纤扰模性能,而使用了八边形光纤的双光纤扰模器的远、近场扰模性能均较优。     

基于半导体纳米线/锥形微光纤探针的被动式近场光学扫描成像

本文结合近场扫描结构和纳米线-微光纤耦合技术,提出了一种基于硫化镉纳米线/锥形微光纤探针结构的被动近场光学扫描成像系统.该系统采用被动式纳米探针,保留了纳米探针对样品表面反射光的强约束优势.其理论收集效率为4.65‰,相比于传统的金属镀膜近场探针收集效率提高了一个数量级,可有效地提高扫描探针对样品形貌信息的检测能力;而后通过硫化镉纳米线与微光纤之间高效的倏逝场耦合,将检测的光强信号传输到远场进行光电探测,最终实现对目标样品形貌的分析成像,其样品宽度测量误差在7.28%以内.该系统不需要外部激发光路,利用显微镜自身光源进行远场照明,被动扫描探针仅作为样品表面反射光的被动收集系统.本文基于半导体纳米线/锥形微光纤探针的被动式近场光学扫描成像方案,可有效地降低探针的制备难度和目标光场的检测难度,简化扫描成像的结构,为近场光学扫描显微系统之后的发展提供新的思路.     

Design and application of a laser beam alignment system based on the imaging properties of a multi-pass amplifier

Image relaying is presented as a technique for aligning beams onto mm-sized target of high power laser. On the basis of summarizing the preceeding work on the near-field image relaying of multiple spatial filters,the far-filed image relaying is suggested firstly. The near-field and far-field image relaying properties of multiple spatial filters in laser beams automatic alignment system are analyzed. A geometrical optics approach and an ABCD ray matrix theory are used throughout. The reasonable and optimum scheme for automatically aligning multi-pass beam paths is presented and demonstrated on the multi-pass amplifier system of the SG-Ⅲ prototype.     

以LCD为目标的自动定焦判据选择

在光学综合自动测量中 ,使用液晶显示屏作为分划板可以大大简化结构 ,提高效率 ,真正地实现自动测量。由于液晶显示具有对比度低、噪声大等特点 ,所以根据液晶的这些特点以及图像处理和CCD信号接收的特点选择两种适用的判据进行了分析和试验比较 ,并给出了结果。结果表明 ,这两种判别函数都适用于以液晶显示屏为目标和用图像处理方法进行光学参数测量的系统 ,其中锐度判别函数更优于信息熵判别函数 ,前者具有更好的抗干扰性和稳定性 ,而且其判定结果更接近目视清晰度判别     

非接触光电窥测仪瞄准及定位方法研究

在非接触光电窥测仪的设计中需要解决两个基本问题：一是如何通过特殊的光学手段把在内孔狭小空间中的被测信息提取出来;二是如何进行测头定位来解决测量基准问题。本文报导了我们设计的非接触光电窥测装置的工作原理。通过方案比较,提出了以图像位置偏移作为瞄准判据及５ 步定位方法,分析了它们的精度及灵敏度     

FABRICATION AND APPLICATION OF NEAR-FIELD OPTICAL FIBRE PROBE

In this paper, the fabrication of a large cone angle near-field optical fibre probe, using the two-step chemical etching method and bent probe, is introduced, and the controlling parameters of the coated Cr－Al film at the probe tip are presented. The scanning electron microscopy images display that the tip diameter of the uncoated large cone angle fibre probe obtained is less than 50nm, the cone angle over 90°, and the diameter of light aperture at the coated probe tip is less than 100nm. The measured results of the optical transmission efficiency for various probe tips show that the uncoated straight optical fibre probe, film-coated straight probe and film-coated bent probe are 3×10^-1, 2×10^-3, and 1×10^-4 times that of the flat fibre probe, respectively. In addition, the force images and near-field optical images of a standard sample are acquired using a large cone angle and film-coated bent probe.     

Observation of nanometer-scale optical property discrimination by use of a near-field scanning apertureless microscope

We examine fundamental issues related to discriminating structural and optical features in near-field scanning apertureless microscopy. We report a series of controlled experiments with nanosphere-sized standard spheres in which we observed significant differences in resolution and structure between an atomic-force microscope image and a simultaneously acquired near-field optical (NFO) image. Further, in experiments that employed a mix of dyed and undyed nanospheres we found that we can observe differences in the same NFO image for adjacent nanospheres. Therefore we conclude that near-field scanning apertureless microscopy not only meets the criteria for a NFO image but also is capable of measuring optical properties below the diffraction limit. The two-point resolution was at least 200 nm when we were detecting optical phase and 50 nm when we were detecting optical intensity. The edge response was typically 15 nm, and the minimum observable features were of the order of 3 nm.     

A virtual optical probe based on evanescent wave interference

A virtual probe is a novel immaterial tip based on the near-field evanescent wave interference and small aperture diffraction, which can be used in near-field high-density optical data storage, nano-lithography, near-field optical imaging and spectral detection, near-field optical manipulation of nano-scale specimen, etc. In this paper, the formation mechanism of the virtual probe is analysed, the evanescent wave interference discussed theoretically, and the sidelobe suppression by small aperture is simulated by the three-dimensional finite-difference time-domain method. The simulation results of the optical distribution of the near-field virtual probe reveal that the transmission efficiency of the virtual probe is 10²－10⁴ times higher than that of the nano-aperture metal-coated fibre probe widely used in near-field optical systems. The full width at half maximum of the peak, in other words, the size of virtual probe, is constant whatever the distance in a certain range so that the critical nano-separation control in the near-field system can be relaxed. We give an example of the application of the virtual probe in ultrahigh-density optical data storage.     

SETUP AND APPLICATION OF SCANNING NEAR-FIELD OPTICAL MICROSCOPY

The research on the setup and application of scanning near-field optical microscopy (SNOM) performed in our laboratory is reviewed in this report. We have constructed a versatile low temperature scanning near-field optical microscope with the capability of near-field imaging and spectroscopy, operating at liquid nitrogen temperature. A special designed coaxial double lens was used to introduce the illumination beam through a 200μm fiber; the detected optical signal was transmitted via a fiber tip to an avalanche photon detector. The performance test shows the stability of the new design. The shear force image and optical image of a standard sample are shown. A system of SNOM working at room temperature and atmosphere was used to characterize semiconductors and bio-molecular samples. It revealed the unique features of semiconductor microdisks in the near-field that is significantly different from that of far-field. The effects of different geographic microstructures on the near-field light distribution of InGaP, GaN, and InGaN multi-quantum-well microdisk were observed.     

The preparation of optical fibre nanoprobe and its application in spectral detection

As an important component of scanning near-field optical microscope (SNOM), optical fibre nanoprobe has been applied to many fields extensively. A melt-stretched etching method is proposed to produce optical fibre nanoprobe with low cost. Firstly, optical fibre tip with micrometer-sized diameter is created by the melt-stretched measure. Next, it is dipped into hydrofluoric acid (HF), and a fine optical fibre nanoprobe will be made after a short-time etching. Owing to the taper structure of tip, it can be etched again in acid if a nanoprobe is not constructed when the first etching is completed. In addition, optical fibre nanoprobe is applied to spectral investigation, and the fluorescence spectroscopy of rhodamine B (Rh B) solution is collected by an optical investigation system with a bifurcated fibre.     

Fully automatic system for the coupling alignment of optical fibres

To realize the low-loss connection of two optical fibres intended as a transmission medium for optical signals, very tight tolerances have to be observed on account of the small geometrical dimensions involved. The present work describes a fully automatic system for the alignment of optical fibres in thex-y planes relative to a light source, which has only a single intensity peak, so that maximum optical power is launched into the fibre. The light source can be, for instance, the radiating end of a fibre, a semi-conductor laser or a light-emitting diode. The optical power coupled into the fibre serves as the control signal. Three precision displacement stages driven by stepping motors serve to align the fibres. Various sequential control algorithms for optimal coupling are investigated with reference to theory. Two algorithms are tested with the aid of a computer with reference to the alignment accuracy and speed requirements which have to be met and the one shown by theoretical simulation to be the more favourable is selected for technical realization. The resulting system was used for numerous alignment operations for the coupling of two graded-index fibres. The alignment time is below 1 s and the coupling efficiency compared with manual coupling alignment efficiency (= 100%) is above 99%, corresponding to an additional loss of <0.05 dB.     

动态化学腐蚀法制备大锥角近场光纤探针

基于液压传递原理,设计出一种用动态化学腐蚀法制备大锥角近场光纤探针的装置.实验结果表明,在传统的化学腐蚀法制备光纤探针的过程中,通过控制腐蚀液液面的上升速度,可以有效地控制探针针尖的形状以及锥角的大小.在此基础上,还论述了分步控制光纤与腐蚀液液面的相对位移的方法在大锥角光纤探针的制备中所具有的独特优越性.利用所制备的大锥角近场光纤探针在扫描近场光学显微镜上对直径为200nm的小球进行探测,其力学像证实该探针具有较高的形貌分辨率(约为50nm). 关键词： 动态化学腐蚀法 大锥角 近场光纤探针