光学玻璃均匀性的全息法检验

光学玻璃的均匀性是衡量其性能的重要指标之一,因此,在实际应用中对它的精密检测有着重要意义。全息干涉技术是一种高精度的无损检测技术,较为详细地论述了二次曝光全息技术在玻璃均匀性测量方面的应用,做了一些理论上的推导和实验方法上的探索与尝试,并对其可行性进行了理论分析和实验验证,该结果与理论符合较好。而且把这种方法运用于普通玻璃材料,也能够定性地分析其均匀性。这种检测方法是非接触性的无损检测,可以方便用白光光源再现,而且检测精度较高。     

Tailoring electron vortex beams with customizable intensity patterns by electron diffraction holography

An electron vortex beam(EVB) carrying orbital angular momentum(OAM) plays a key role in a series of fundamental scientific researches, such as chiral energy-loss spectroscopy and magnetic dichroism spectroscopy. So far, almost all the experimentally created EVBs manifest isotropic doughnut intensity patterns. Here, based on the correlation between local divergence angle of electron beam and phase gradient along azimuthal direction, we show that free electrons can be tailored to EVBs with customi...     

显微全息的一种光路设计

一、引言 显微全息术是显微和全息相结合的技术,其特点是将微小物体通过显微技术进行放大,通过全息技术进行三维信息贮存,这两种技术的先后次序是可以互换的,因此显微全息术分两种类型,一种是用显微术将标本图像放大再记录其全息图称预放大;另一种是先拍摄标本的全息图再用显微镜进行观察称后放大。显微全息术最突出的优点是可以拍摄生物活标本的瞬态全息图,便于进行三维观察或“冻结”它的某个瞬态进行长期保存。这种情况通常需使用脉冲激光器或高功率连续激光器,这些光源价格昂贵,而且由于照射在活标本上的激光束功率密度高,往往会影响甚至破坏它的正常生长。本文介绍的一种显微全息光路,它无需庞大的防震     

Low-noise optical receiver for high-speed optical transmission

This paper describes the design of a low-noise optical receiver using Si bipolar transistors for high-speed optical transmission. The conventional common emitter-common collector circuit (CE-CC pair) and Darlingtou circuit (transimpedance amplifiers with parallel feedback) are studied. Optimal CE-CC pair collector-biasing current for attaining minimum noise current with a 400-MHz bandwidth is 2.7 mA, and less than 1.2 mA for the Darlington circuit. It is confirmed that the Darlington circuit is better than the CE-CC pair in signal-to-noise ratio by about 1.5 dB. The low-noise Darlington optical receiver with a Ge-avalanche photodiode has achieved an optical sensitivity of -41 dBm for a 400 Mbit/s RZ pulse with a bit error rate of 10^-10. This is a 2.5-dB improvement in optical sensitivity over that of the conventional CE-CC receiver.     

Low-noise optical receiver for high-speed optical transmission

This paper describes the design of a low-noise optical receiver using Si bipolar transistors for high-speed optical transmission. The conventional common emitter-common collector circuit (CE-CC pair) and Darlington circuit (transimpedance amplifiers with parallel feedback) are studied. Optimal CE-CC pair collector-biasing current for attaining minimum noise current with a 400-MHz bandwidth is 2.7 mA, and less than 1.2 mA for the Darlington circuit. It is confirmed that the Darlington circuit is better than the CE-CC pair in signal-to-noise ratio by about 1.5 dB. The low-noise Darlington optical receiver with a Ge-avalanche photodiode has achieved an optical sensitiyity of -41 dBm for a 400 Mbit/s RZ pulse with a bit error rate of 10^-10. This is a 2.5-dB improvement in optical sensitivity over that of the conventional CE-CC receiver.     

菲涅耳波带板在光学扫描全息术中的作用

本文研究了非运动卷积中的投影式卷积装置，并讨论了二函数在该装置中的卷积与解卷积过程，为了验证在光学扫描全息术中菲涅耳波板与物体波函数之间卷积的作用，本文利用投影式卷积装置实现了菲涅耳波带板与物体波函数之间的卷积与解卷积过程，文中给出了实验装置及实验结果。     

光纤全息技术研究与发展

本文介绍了光纤全息技术的原理和到目前为止国内外出现的各种技术方案.同时对光纤全息技术的应用前景作了简要阐述.     

Formation of self-trapped filaments by self focusing

It is shown that under suitable conditions the self-focusing of a Gaussian beam can lead to the self-trapped solution of Chiao et al. [2]. The properties of the focused region are described in detail.     

Modeling high-speed optical transmission systems

Computer simulation of a 2.5-Gb/s intensity-modulated/direct-detected optical system with high path dispersion is described. This simulation, based on single-mode laser diode rate equations, includes transmit and receiver circuit filtering, receiver circuit noise, avalanche photodiode noise, fiber dispersion, and laser chirp. The rate equations are sufficiently general to model mode-offset distributed feedback laser diodes. The system power penalty, due to laser chirp and fiber dispersion, is calculated using Gaussian quadrature numerical integration. By simulating a population of some 12800 laser diodes and correlating the performance of each laser in a transmission system with its spectral characteristics, it is possible to deduce laser specifications that will assure satisfactory operation in long-span links. These results are used to study a laser diode specification under consideration by CCITT, and, by studying the simulated laser line shapes, some modifications to the CCITT specification are considered     

1550-nm volume holography for optical communication devices

The two-lambda method can provide a strategic approach to implement all-optical devices for communication wavelength division multiplexing (WDM) signal processing based on volume holography. By writing holograms at 488 nm in LiNbO/sub 3/:Fe and reading them in the third window of optical communication systems (1550 nm), the feasibility of WDM demultiplexers and holographic memories for digital bytes is here demonstrated.     

高速光纤通信系统中PMD补偿算法的研究

第一次引入CPSO算法作为二阶PMD反馈补偿算法,克服T原有PSO算法容易陷入局部最优值的缺点.叙述了算法流程,比较了两种算法的特点,分析了CPSO算法在收敛过程中的优越性.最后在4×40Gb/s的仿真系统中对CPSO反馈控制算法进行了验证.     

A high-speed GaAs MESFET optical controller

Optical interconnects are being considered for control signal distribution in phased array antennas. A packaged hybrid GaAs optical controller with a 1:16 demultiplexed output that is suitable for this application is described. The controller, which was fabricated using enhancement/depletion mode MESFET technology, operates at demultiplexer-limited input data rates up to 305 Mb/s and requires less than 200 μW optical input power     

Recent progress on high-speed optical transmission

The recently reported high spectral efficiency (SE) and high-baud-rate signal transmission are all based on digital coherent optical communications and digital signal processing (DSP). DSP simplifies the reception of advanced modulation formats and also enables the major electrical and optical impairments to be processed and compensated in the digital domain, at the transmitter or receiver side. In this paper, we summarize the research progress on high-speed signal generation and detection and also show the progress on DSP for high-speed signal detection. We also report the latest progress on multi-core and multi-mode multiplexing.     

Subcarrier multiplexing for high-speed optical transmission

The performance of high-speed digital fiber-optic transmission using subcarrier multiplexing (SCM) is investigated both analytically and numerically. In order to reduce the impact of fiber chromatic dispersion and increase bandwidth efficiency, optical single-sideband (OSSB) modulation was used. Because frequency spacing between adjacent subcarriers can be much narrower than in a conventional DWDM system, nonlinear crosstalk must be considered. Although chromatic dispersion is not a limiting factor in SCM systems because the data rate at each subcarrier is low, polarization mode dispersion (PMD) has a big impact on the system performance if radiofrequency (RE) phase detection is used in the receiver. In order to optimize the system performance, tradeoffs must be made between data rate per subcarrier, levels of modulation, channel spacing between subcarriers, optical power, and modulation indexes. A 10-Gb/s SCM test bed has been set up in which 4 × 2.5 Gb/s data streams are combined into one wavelength that occupies a 20-GHz optical bandwidth. OSSB modulation is used in the experiment. The measured results agree well with the analytical prediction     

A proposed new high-speed optical detector

The small-signal optical detection properties of the barrier injection transit-time (BARITT) diode structure are presented. At low frequencies, the device behaves as a punch-through phototransistor while at frequencies near the transit-time frequency the device is capable of additional gain due to negative-resistance reflection-type amplification.     

高速光交换机竞争调度策略

在光交换网络中,当同一波长两个或多个光分组同时离开光交换机的同一个输出端口时将会发生对输出端资源的竞争,竞争失败的光分组将受阻,如何有效地调度将使光交换系统性能受到很大影响,文章综述了目前解决光交换网分组冲突的几种方案,阐述了各种解决方法的原理、实现方式及特点,展望了今后可能采用的最佳竞争调度方案.     

计算机与光学方法相结合的彩色彩虹全息术

提出了计算机制全息与光学全息相结合制作彩色全息图的彩色彩虹伞息术.通过计算机对彩色图像进行自动分色,制作红、绿、蓝3幅丰计算全息图H1,以H1的再现像为对象,用激光制作彩色彩虹全息图H2,用白光再现获得彩色再现像.该方法把汁算机制全息与传统的光学全息相结合,发挥了计算全息与光学全息的优势.在全息图的计算中采用了快速傅里叶变换,加快了计算速度.给出了理论分析和实验结果.     

改善光学扫描全息聚焦层图像效果的实验研究

为了改善光学扫描全息系统聚焦层重建图像的效果,采用随机相位光瞳替代传统针孔光瞳的方法,进行了理论的分析和实验验证,分别得到了传统光学扫描全息和基于随机相位编码的光学扫描全息系统下重建图像和原图像之间的信噪比、相关系数以及频谱分布比较结果。结果表明,在实验条件相同的情况下,基于随机相位编码的光学扫描全息系统重建的图像具有更高的信噪比和相关系数,且其图像频谱和原图像频谱曲线的变化趋势更相似,因而更接近于原图像。