Confinement of THz surface waves on the subwavelength size metal waveguide

We investigate surface plasmon waves propagating on planar Goubau lines, so-called Goubau modes, using a guided-wave terahertz spectroscopy system based on a freely positionable electrooptic probe. We show the radial nature of the Goubau mode and its confinement around the Goubau line over a few tenths of microns (??/10).     

Optical-frequency balanced mixer

Optical signal processing devices based on quasi-phase-matched three-wave mixing and cascaded three-wave mixing in guided-wave geometries have been demonstrated to operate efficiently at practical pump-power levels. We describe operation of such devices in a balanced mode that allows mixing without wavelength offset and separation of mixed output from pump and signal input without wavelength-selective filters. We present a design for an optical-frequency balanced mixer using quasi-phase-matched, cascaded second-order nonlinear processes. Using this design, we fabricated a balanced mixer in periodically poled lithium niobate waveguides that has the expected linear and nonlinear optical performance.     

基于稀疏子空间的类星体光谱异常特征并行提取与分析

类星体是人类所观测到的最遥远天体,对于了解早期宇宙的演化具有重要科学意义。由于类星体距离地球较远,其红移一般较大,导致在光学观测窗口中只有很少的特征（发射线）,且难以识别。类星体光谱的异常特征提取与分析可对未知类星体的识别,提供有效的判别依据。离群检测作为数据挖掘领域的一个主要研究内容,旨在发现那些稀有、特殊数据对象及异常特征,可作为从海量类星体光谱数据中,发现特殊、未知类星体的一种有效途径和手段。Spark作为新一代大数据分布式处理框架,可为海量天体光谱的有效分析和处理,提供一个高效且可靠的并行编程平台。本文充分利用集群系统和Spark编程模型的强大数据处理能力,提出一种基于稀疏子空间的类星体光谱异常特征并行提取与分析方法,其工作由三个模块组成,即类星体光谱特征约减、类星体光谱的稀疏子空间构造和搜索、类星体光谱异常特征提取并行算法设计与分析。类星体光谱特征约减模块,通过属性相关性分析来识别呈现聚类结构的类星体光谱特征线,这些特征线通常会聚集在稠密区域且对类星体光谱异常特征检测毫无意义。光谱特征约减旨在运行异常特征检测算法之前剪枝类星体光谱的冗余特征线,缩小光谱数据检测范围。类星体光谱的稀疏子空间构造和搜索模块,通过设定的稀疏系数阈值来测量类星体光谱的子空间密度,并采用粒子群优化方法作为稀疏子空间的搜索策略,从而快速、高效地获取类星体的异常特征。在第三个模块中,提出了一种MapReduce框架下的类星体光谱异常数据并行检测算法,该算法由并行化数据约减策略、稀疏子空间并行搜索技术两个MapReduce构成,达到适应海量光谱数据的处理目标。最后对检测出的部分类星体异常特征进行了理论分析、测量及人眼证认,充分说明稀疏子空间可为识别特殊、未知类星体候选源,提供有效支持和有力证据。     

Highly efficient single-photon detection at communication wavelengths by use of upconversion in reverse-proton-exchanged periodically poled LiNbO3 waveguides

Conventional single-photon detectors at communication wavelengths suffer from low quantum efficiencies and large dark counts. We present a single-photon detection system, operating at communication wavelengths, based on guided-wave frequency upconversion in a nonlinear crystal with an overall system detection efficiency (upconversion + detection) exceeding 46% at 1.56 microm. This system consists of a fiber-pigtailed reverse-proton-exchanged periodically poled LiNbO3 waveguide device in conjunction with a silicon-based single-photon counting module.     

OFDM水声通信实时处理系统的多处理器并行

OFDM(正交频分复用)充分利用频带,具有较高的数据传输速率;ADSP-TS101是具有高速并行处理能力的高性能数学信号处理芯片。针对OFDM水声通信的实时处理要求,本文设计并研制了具有实时处理能力的水声通信系统。该系统包括由多片ADSP-TS101构成的松/紧联合耦合的并行处理结构作为处理核心、无相位偏差的多通道同步采样模块和FPGA(现场可编程门阵列)逻辑控制模块。湖上实验结果表明该系统具有良好的稳定性和实时处理能力,满足工程设计要求。     

Ring microresonator as a photonic structure with complex eigenfrequency

For the analysis of light propagation in photonic guided-wave ring microresonators, leaky-mode solvers for bent channel waveguides are often used. In the analytical approach, the leaky mode field is expressed in terms of cylindrical functions of complex arguments and a complex order which plays a role of the (azimuthal) propagation constant. In this contribution we present a modified approach which takes into account the circular symmetry of the structure. We calculate the eigenmodes of a lossy microresonator as modes with complex eigenfrequencies. In this approach, the eigenmodes are described by cylindrical functions of an integer order and a complex argument. Similarities and differences of both approaches are demonstrated using simple examples of 2D (planar) structures.     

飞秒激光加工铌酸锂晶体：原理与应用

由于具有超短的脉冲宽度和极高的峰值强度,飞秒激光微加工是一种有效的材料加工方法, 已广泛应用于光子集成器件的加工。铌酸锂晶体具有优异的电光、非线性光学和压电特性,是集成 光学和导波光学中常见的材料。本文综述了飞秒激光对铌酸锂晶体的处理,重点介绍了飞秒激光加 工的物理原理及其制备的铌酸锂基光子器件的最新进展。飞秒激光技术使铌酸锂晶体在微纳光子学 领域具有广阔的应用前景。     

基于DSP+FPGA的新型弹载计算机设计与实现

以某型号导弹飞行试验为研制背景,设计出一款精度高、通用性强的新型弹载计算机。该弹载计算机以高性能DSP和FPGA为系统框架,通过其丰富的外围接口和强大的处理能力,结合AD5764转换模块、MAX3490通信模块、ADUM1401四通道数字隔离器和ULN2801达林顿管驱动器组成的离散量输出等模块,解决了弹载计算机与弹上飞控部件之间复杂的并行数据处理以及多种控制算法实时解算问题,具有体积小、重量轻、精度高、实时性好等特点。经过多次飞行试验表明,该弹载计算机具有较高的可靠性和稳定性,应用前景非常广泛。     

Effect of detector noise in incoherent hybrid imaging systems

Hybrid imaging systems involve the joint design of an optical image-gathering module and digital processing algorithms to obtain a required final image. They have the potential to achieve imaging performance hitherto unobtainable by conventional imaging techniques. A reduction in the signal-to-noise ratio of the final image is one of their main disadvantages when one is considering linear signal processing. We analyze the effect of additive white noise at the detector on the performance of hybrid imaging systems under quasi-monochromatic incoherent illumination. We also show numerical results and computer-simulated images for an extended depth-of-field hybrid system.     

Femtosecond pulse shaping with space-to-time conversion based on planar optics

We propose a novel structure of planar optical configuration for implementation of the space-to-time conversion for femtosecond pulse shaping. The previous apparatuses of femtosecond pulse shaping are 4f Fourier-transforming type system that is usually large, expensive, difficult to align. The planar integration of free-space optical systems on solid substrates is an optical module with the attractive advantages of compact, reliable and robust. This apparatus is analyzed in details and the design of the particular lens for femtosecond pulse shaping based on planar optics is presented.     

Compact broadband 5-bit photonic true-time-delay module for phased-array antennas

Photonic true-time-delay (TTD) lines offer many advantages over their electronic counterparts and are attracting more and more research effort. We demonstrate a device with 32 TTD lines (5-bit) based on substrate guided-wave propagation combined with slanted photopolymer volume phase gratings on a quartz substrate. System design, device fabrication, optimization of fan-out intensity uniformity, and device performance evaluation are addressed as well. The device has a measured bandwidth of up to 2.4 THz and a measured fan-out delay step of 50 ps. The fan-out beam intensity uniformity is within +/-10% . The packing density is 2.5 delay lines/cm(2), which is to our knowledge the highest demonstrated thus far.     

A planar active sound control system using two-dimensional spatial harmonics

An active sound control system based on the extraction of orthogonal spatial harmonics is considered. The system comprises two parallel planar rectangular receiving arrays consisting of small monopole receivers and two planar rectangular transmitting arrays (installed parallel to the receiving arrays) consisting of small monopole transmitters. The field received by the receiving arrays is approximated by a finite number of propagating plane waves with the help of the Fourier transform. The transmitting arrays excite the same set of plane waves outside the system, their amplitudes being chosen so as to cancel the incident external field in a certain region near the system behind the transmitting arrays. The performance of the system is considered for both continuous and discrete distributions of transmitters and receivers. Allowance is made for random errors in the transmitters and receivers, individual to each device.     

基于单片FPGA的多通道磁共振成像接收模块

提出了一种基于FPGA的多通道磁共振成像接收模块,能对多个独立通道的磁共振信号进行直接采样、数字下变频,以及数据流控制,并对其进行了成像实验. 设计中采用Xilinx公司的系统级DSP开发工具--System Generator对FPGA内部所有功能进行建模、仿真并生成相应的硬件描述语言. 模块的采样速率为80MSPS,能灵活实现1 kHz~1 MHz范围的可变接收带宽,适用于1 T以下的磁共振成像系统;在单片FPGA内完成1~4个通道采样信号的数字正交解调,抽取滤波和数据流的处理,并可扩展至8通道. 实验证明模块具有体积小,集成度高,可重构性强和成本低等特点,为磁共振成像谱仪的多通道接收系统提供了一种高性能的数字化解决方案.     

On the modelling of non-linear guided-wave optics for all-optical signal processing

The application of a reduced variational formalism, to model guided-wave optical signal processing devices is reviewed. The focus is mainly on second-order non-linearities. First, approximate analytical solutions (solitary waves) are derived for propagation in second-order non-linear media. Next, these analytical results are validated through numerical simulation of the governing equations. To show the potential of this formalism by means of a practical example, the analytical results are applied to a soliton-based LiNbO3 non-linear directional coupler exploiting second-order non-linear effects. This revised version was published online in November 2006 with corrections to the Cover Date.     

Study of the Performance of an All-Optical Half-Adder Based on Three-Core Non-Linear Directional Fiber Coupler Under Delayed and Instantaneous Non-Linear Kerr Responses

Abstract

Recently, much attention has been given to the influence of the relaxation process of the non-linear response, because the usual assumption of instantaneous non-linear response fails for ultra-short pulses, and additional contributions coming from non-linear dispersion and delayed non-linearity have to be taken into account. This article presents a numerical analysis of the symmetric planar and asymmetric planar three-core non-linear directional fiber couplers operating with a soliton pulse, where effects of both delayed and instantaneous non-linear Kerr responses are analyzed for implementation of an all-optical half-adder. To implement this all-optical half-adder, eight configurations were analyzed for the non-linear directional fiber coupler, with two symmetric and six asymmetric configurations. The half-adder is the key building block for many digital processing functions, such as shift register, binary counter, and serial parallel data converters. The optical coupler is an important component for applications in optical-fiber telecommunication systems and all integrated optical circuit because of its very high switching speeds. In this numerical simulation, the symmetric/asymmetric planar presents a structure with three cores in a parallel equidistant arrangement, three logical inputs, and two output energy. To prove the effectiveness of the theoretical model for generation of the all-optical half-adder, the best phase to be applied to the control pulse was sought, and a study was done of the extinction ratio level as a function of the Δ > parameter, the normalized time duration, and the Sum and Carry outputs of the (symmetric planar/asymmetric planar) non-linear directional fiber coupler. In this article, the interest is in transmission characteristics, extinction ratio level, normalized time duration, and pulse evolution along the non-linear directional fiber coupler. To compare the performance of the all-optical half-adders, the figure of merit of the logic gates was used. All results were obtained numerically, considering a simple model for generation of an all-optical half-adder.     

Blackfin DSP并行外围接口在红外视频处理通用模块中的应用研究

介绍了Blackfin系列DSP的并行外围接口,提出了一种红外视频处理通用模块的构架,省略了数据缓冲硬件环节,缩短了数据等待时间,提高了DSP的运算效率。     

Image stack alignment in full‐field X‐ray absorption spectroscopy using SIFT_PyOCL

Full‐field X‐ray absorption spectroscopy experiments allow the acquisition of millions of spectra within minutes. However, the construction of the hyperspectral image requires an image alignment procedure with sub‐pixel precision. While the image correlation algorithm has originally been used for image re‐alignment using translations, the Scale Invariant Feature Transform (SIFT) algorithm (which is by design robust versus rotation, illumination change, translation and scaling) presents an additional advantage: the alignment can be limited to a region of interest of any arbitrary shape. In this context, a Python module, named SIFT_PyOCL, has been developed. It implements a parallel version of the SIFT algorithm in OpenCL, providing high‐speed image registration and alignment both on processors and graphics cards. The performance of the algorithm allows online processing of large datasets.     

The design of the apodizing functions for guided-wave EOTF

A design method of the apodizing functions for guided-wave four-port electrooptic tunable filter (EOTF) is proposed. As an example, the specific form of Gaussian apodizing function is designed by analyzing the crosstalk performance of EOTF. Crosstalk is calculated based on the transient response of the filter to an input optical pulse. It is concluded that crosstalk level below -30 dB for 20-Gb/s data rates and 100-GHz channel spacing is achievable with presently available substrate dimensions.     

基于JASMIN三维势场快速多极子算法的并行实现

在JASMIN上,基于进程/线程两级并行实现策略,研制三维Laplace核函数FMM(fast multipole method)的解法器模块"JASMIN-3DLapFMM".该解法器已成功应用于三维静电场远场势的并行计算.固定单机问题规模,在上万个处理器核上运行百亿粒子的大规模问题,获得进程级几乎线性的并行可扩展性.固定总的问题规模和1024个进程,4个线程时,获得大约3倍的加速.     

Sensitivity improvement of aluminum-based far-ultraviolet nearly guided-wave surface plasmon resonance sensor

An aluminum (Al) based nearly guided-wave surface plasmon resonance (NGWSPR) sensor is investigated in the far-ultraviolet (FUV) region. By simultaneously optimizing the thickness of Al and dielectric films, the sensitivity of the optimized Al-based FUV-NGWSPR sensor increases from 183°/RIU to 309°/RIU, and its figure of merit rises from 26.47 RIU^-1 to 32.59 RIU^-1 when the refractive index of dielectric increases from 2 to 5. Compared with a traditional FUV-SPR sensor without dielectric, the optimized FUV-NGWSPR sensor can realize simultaneous improvement of sensitivity and figure of merit. In addition, the FUV-NGWSPR sensor with realistic materials (diamond, Ta₂O₅, and GaN) is also investigated, and 137.84%, 52.70%, and 41.89% sensitivity improvements are achieved respectively. This work proposes a method for performance improvement of FUV-SPR sensors by exciting nearly guided-wave, and could be helpful for the high-performance SPR sensor in the short-wavelength region.