A new optical method for the detection of in-plane motion of ultrasound propagating in metals

This paper describes a laser optical technique for the detection of in-plane (IP) motion of ultrasonic waves propagating in solids. This interference-based laser optical technique includes a tiny square indentation with a width of about 30 microm on the sample surface and a relatively simple optical arrangement. The current technique is applied for the detection of in-plane motions of Lamb waves propagating in a thin brass plate. Measurement of S(0) mode dominated by in-plane motion in the low fd (frequency times thickness) regime is successfully demonstrated with the current technique. The newly proposed non-contact technique provides an alternative other than the heterodyne and Fabry-Perot techniques for the detection of IP motions with a relatively simple optical arrangement. This technique is not readily applicable to general NDE applications, where a position scan or an arbitrary selection of inspection location is needed. However, this technique can be useful in the areas such as fixed-position ultrasound monitoring or laboratory research activities involving optical detection of IP motion.     

大气激光通信非对称限幅光正交频分复用技术

将一种新的正交频分复用调制技术运用到大气激光通信系统中,分析了采用这种非对称限幅光正交频分复用调制技术的大气激光通信系统在大气湍流信道下的性能.在此基础上,把非对称限幅光正交频分复用调制方案与传统的开关键控及直流偏置光正交频分复用调制方案进行了比较,并在大气湍流信道中进行了仿真.仿真结果表明:非对称限幅光正交频分复用调...     

光外差-磁旋转-浓度调制光谱技术

介绍了一种针对瞬态分子光谱测量的新技术:光外差磁旋转浓度调制光谱技术,这种光谱技术具有很高的灵敏度,综合了光外差探测技术、磁旋转光谱技术和浓度调制光谱技术的特点,利用浓度调制光谱技术针对寿命很短的瞬态分子和激发态分子的光谱进行测量,利用光外差探测技术可以消除来自光源的幅度涨落噪声,实现散粒噪声的测量极限,利用磁旋转光谱技术可以对顺磁性分子进行选择性的测量,并且进一步提高探测灵敏度。详细讨论了这种光谱技术的工作原理,并用这种技术对O2分子的b1Σg+-X3Σg-三重禁戒跃迁光谱进行测量,获得了很好的测量信噪比。并对该技术的灵敏度作了详细的分析,估计最小相对吸收度可达1.9×10-9以及O2分子三重禁戒跃迁的吸收截面为σ=2.4×10-24cm2。     

非球面复制成型技术的研究

光学非球面复制成型技术是一种通过面形转移的方法成型光学非球面的技术,即将高精度非球面光学元件(母模)的表面利用脱模膜和胶粘剂转移到球面光学元件(基体)的表面上,并保持原非球面光学元件的光学品质,使球面变成非球面。介绍了该技术的基本原理以及所进行的工艺实验(镀膜、脱模、胶合等),给出了母模和复制件的面形图,证明了该技术用于中小口径非球面光学元件的制造具有较高的精度。     

Ring-based PON supporting multiple optical private networks using OCDMA technique

This work is a novel attempt to provide local communications for multiple optical private networks (PNs) within ring-based passive optical network (PON). In order to improve network throughput performance, PNs traffic is decentralized from PON traffic let no extra traffic management into optical line terminal (OLT). To achieve multiple secure optical private networking over ring-based PON layout, optical code division multiple access (OCDMA) technique is applied. This technique leads to interconnect optical network units (ONUs) in the same PN sharing the same codeword while other PNs benefiting from different codewords. This scheme can be used in access networks to establish discrete communications between different sites in an enterprise or a university campus or even a residential accommodation. The proposed network architecture is then set up and its bit error rate performance is experimentally demonstrated. Finally, the network scalability and throughput performance of the proposed scheme are analyzed.     

近场记录光盘的写入能量的研究

近场记录光盘是一种新的光盘记录技术,它有二个特点：（１）极高的记录密度;（２）很高的寻道速度。本文介绍了近场光盘技术的特性;提出了近场光盘记录技术中动态条件下读写中的写入能量地头盘间的能量传输问题进行了仿真计算。     

Measurement of wedge angle of a transparent parallel plate using quasi-monochromatic light source and phase shifting interferometry

A new technique (to our knowledge), for the measurement of residual wedge angle (RWA) of high optical quality transparent nearly parallel plate (PP), using a quasi-monochromatic light source, is presented. Advantages and drawbacks of the technique and the results obtained for a PP, using a filtered white light source, is discussed. A slightly modified optical setup for accurate determination of RWA, using phase shifting interferometry (PSI), has been described. Results obtained, applying PSI, for a validation experiment and for the determination of RWA of a quasi-PP is presented. The PSI based technique does not suffer from any measurement ambiguities due to limitation in effective beam aperture. Hence the technique is suitable for high accuracy measurement of RWA of PP. In both the optical setups, presented in this paper, the respective interfering beams travel the same optical circuit and are thus subject to same perturbation in optical path, due to external mechanical vibration, which finally cancels out. Thus the measurements are much less affected by external vibrations. Since the respective interfering beams undergo identical reflections and transmissions, the visibility or contrast of the interference fringes is very good.     

Accurate measurement of scattering and absorption loss in microphotonic devices

We present a simple measurement and analysis technique to determine the fraction of optical loss due to both radiation (scattering) and linear absorption in microphotonic components. The method is generally applicable to optical materials in which both nonlinear and linear absorption are present and requires only limited knowledge of absolute optical power levels, material parameters, and the structure geometry. The technique is applied to high-quality-factor (Q=1x10(6) to Q=5x10(6)) silicon-on-insulator (SOI) microdisk resonators. It is determined that linear absorption can account for more than half of the total optical loss in the high-Q regime of these devices.     

Measurement of birefringence in integrated optical waveguides by use of a microwave-modulated optical wave

We present a technique for measuring birefringence (B) in integrated optical waveguides by use of a microwave-modulated optical wave. It is shown that the technique is able to yield an accurate measurement of birefringence. In addition, an approximate estimate of birefringence dispersion (dB/dlambda) can be achieved by means of tuning the wavelength of the light source and measuring the dependence of the birefringence on the wavelength. As an example of the use of the technique, we show how to evaluate an innovative Ti:LiNbO (3) waveguide. The results show that such a Ti:LiNbO (3) waveguide has a birefringence of 0.0783+/-0.0001 and a birefringence dispersion of 0.05+/-0.01mum (-1) when the optical wavelength is approximately 1.560mum .     

Multi-angle observation scheme for bubbles and droplets

Abstract  

The split-screen imaging technique, in which the field of view of a single video/still camera is divided into two (or more) regions, is one of the techniques for observing, using a single camera, liquid droplets, bubbles or particles translating in another fluid from two (or more) different directions. A drawback of the split-screen imaging technique is that it generally requires a longer optical path than the ordinary multi-camera technique that allots each view axis to each of two (or more) synchronized cameras. This study presents an optical arrangement that minimizes the optical path for the two-directional split-screen imaging so as to allow the use of a camera lens with a short working distance. Its modification configured for the three-directional split-screen imaging of translating bubbles or drops is also presented.     

A novel technique for measuring 3D deformation of adhesively bonded single lap joint

An easy-to-implement yet practical single-camera microscopic stereo-digital image correlation(stereo-DIC) technique is proposed for surface three-dimensional(3D) deformation measurement of singe lap joint(SLJ) samples subjected to mechanical loads. The basic principles, optical configurations and implementation procedures of the proposed technique are described in detail. Compared with existing single-camera 2D-DIC technique, which has been regularly used for in-plane deformation measurement of a SLJ specimen, the proposed technique offers the special merit of simultaneously determining all the three displacement components by simply adding two additional optical elements to existing single-camera 2D-DIC systems. The accuracy and effectiveness of the proposed technique is demonstrated by measuring the 3D deformation of a SLJ specimen subjected to quasi-static tensile loads.     

Enhancement of Transfer Efficiency of Cold Atoms Using an Optical Guiding Laser Beam

We transfer cold ^87 Rb atoms from a vapour cell chamber to a spatially separated UHV magneto-optical trap （MOT） with the assistance of a red-detuned optical guiding beam and a normal push beam. Efficient optical guiding of the cold atoms is observed within a small detuning window. A pulsed optical guiding beam enhances the transfer efficiency and hence allows us to collect more atoms in UHV MOT in a shorter time, which is favourable for our experiment of achieving Bose-Einstein condensates （BEC）. Besides the easy operation, another advantage of this optical guiding technique is also demonstrated such that slower atomic beams may be efficiently transferred along horizontal direction. This study is a direct application of the optical guiding technique as a powerful tool.     

An efficient MAI cancellation technique in Optical CDMA

Optical code division multiple access (OCDMA) is a promising operational system for future backhaul optical networks especially for switching and optical signal multiplexing. However, OCDMA operation is restricted by multiple access interference (MAI) due to the asynchronous nature of transmission. In this study, we discuss an efficient MAI technique for OCDMA systems that depends not only on using hybrid frequency shift keying (FSK) modulation but also on employing the double padded modified prime code (DPMPC) as a signature sequence. MAI cancellation is performed by subtracting a reference signal from the received signal of the desired user. The simulation results show that the performance of the FSK-OCDMA technique is superior to the performance of the PPM-OCDMA technique. Furthermore, the obtained results illustrate that the FSK-OCDMA technique is able to accommodate a large number of simultaneous active users with low error-rate.     

Design of an off-axis HOE light concentrator to focus light from multiple directions in a plane

The attractive and multifunctional properties of holographic optical elements (HOEs) offer an opportunity to create compact optical systems for a wide range of applications. In this paper, we propose a novel method of focusing light onto a small region of space by an off-axis HOE that is illuminated from multiple directions in a plane. An off-axis spherical wave generated from a microscopic objective (0.65 NA) is combined with sequentially illuminated five reference waves at the recording plane. A multi-exposure technique is adopted for recording. A comparison between single-exposure and multi-exposure technique is also presented. The design parameters, performance and possible applications of these optical devices are described.     

New applications of the method of caustics

The method of caustics is a very powerful technique for measuring the value of the stress-intensity factor. This method, however, cannot be applied to the three-dimensional stress analysis technique of stress-freezing, and it is rather difficult to apply to materials which exhibit small deformations such as ceramics.

In this paper, several new application techniques for caustics are shown. These new applications are: (i) the analysis of the individual values of the optical constants using a simple method based on the theory of caustics, (ii) the analysis of the reason why the caustic pattern cannot be obtained in the frozen-stress model in the immersion liquid by the conventional caustics technique using those optical constants, and the proposition of a new technique to apply the caustic method on such a frozen-stress model, (iii) the caustic coating technique, (iv) the multiplication technique of the caustic, and (v) some examples of the application of caustics to ceramics.     

Schlieren成像和声场可视化

Schlieren技术是利用声场引起透明媒质光折射率的变化而实现声场可视化的光学成像技术。它具有对声场无干扰、快速、瞬态成像的特点。本文利用二维光学Fourier变换分析了Schlieren技术的成像原理,在采用连续激光和高速ICCD的Schlieren成像系统中,实验研究了平面波声场和线聚焦声场中换能器光学校准方法和声压的定量检测技术。发展声场瞬态和动态成像技术,观测了声波的聚焦过程和固-液界面的声场分布和变化。这些结果表明Schlieren技术是一种有效的声场可视化和定量检测的光学成像技术。     

掺Er3+玻璃的光限幅特性研究

利用波长为532 nm的皮秒脉冲激光,研究了掺Er3 玻璃的光限幅特性和反饱和吸收.当入射功率不断增加且超过一定阈值时,透射功率不再随着入射功率快速增大,而是逐渐趋向于较稳定状态,从而实现了对强激光的光限幅效应.进一步利用布居速率方程讨论了其机制并给出了激发态的吸收截面,结果表明激发态吸收是其主要的光限幅机理.     

三阶非线性光学材料及其表征技术研究进展

介绍三阶非线性光学材料及其表征技术的研究进展。分析几种典型的三阶非线性光学材料及今后的发展趋势，指出介质物理材料的非线性光学特性将成为今后的研究热点。随着表征技术研究的进一步拓展，准波导技术将可能作为一种新的表征技术应用于非线性光学材料研究中。     

二元光学元件和新型超分辨光盘读写头的设计研究

本文采用杨-顾相位恢复算法数值模拟设计了一个用于光盘读写头的二元光学元件,并构思了一种新型超分辨光盘读写头,在现有光盘读写头的激光波长处和数值孔径基础上,利用该二元光学元件实现光学超分辨,从而提高光盘存储容量.     

Optical sectioning in differential interference contrast microscopy

While developing a three-dimensional (3-D) measurement technique for the retardation-modulated differential interference contrast (RM-DIC) microscope, we encountered a problem. The problem was that the measurement range was restricted in λ because it applies weak phase approximation.To overcome this drawback, we propose a 3-D reconstruction method with z-axis scanning. This technique needs high optical sectioning, like confocal microscopy.We investigated the characteristic of optical sectioning in a DIC microscope, then we confirmed experimentally that a DIC microscope has high optical sectioning. We also confirmed that a RM-DIC microscope has higher optical sectioning.By combining the optical sectioning of a RM-DIC microscope and z-scanning, we developed a new 3-D reconstruction method. This novel technique overcomes the observed problem as the measurement range is increased to micron order.