Modal characteristics and bistability in twin microdisk photonic molecule lasers

We demonstrate coupled-mode characteristics and bistability in photonic molecule lasers composed of evanescent-coupled GaInAsP twin microdisks. First, we show room-temperature continuous-wave operation by photopumping and discuss the unique behavior of coupled modes, i.e., the anticrossing and splitting characteristics of bonding and antibonding modes. Next, we present the clear bistability, which is observed for the antibonding mode by nonuniform pumping with an effective power of nearly 40 /spl mu/W. It is explained by rate equation analysis, which assumes saturable absorption. The analysis also predicts mode switching by the carrier-induced refractive index change. A micron-sized device with a very low power consumption will allow large scale integration of optical memories, optical flip-flops, and so forth.     

Photonic Crystal-Based MOEMS Devices

In this paper, a new class of microoptoelectromechanical system (MOEMS) devices combining photonic crystals (PCs) formed in in-plane waveguiding membranes (in-plane 1-D or 2-D large contrast modulation of the optical index) and a multilayer stack (1-D "vertical" modulation of the optical index) according to the so-called 2.5-D micronanophotonics approach is reported. The operation of the devices is based on the resonant coupling between radiated optical modes and slow Bloch modes waveguided in the particular membranes of the stack, which are laterally patterned to form a PC. Use of high-index contrast PC gratings result in enhanced lateral compactness of the devices. The MOEMS functionality is achieved via micromechanical subwavelength vertical displacement of some of the suspended membranes. Recent demonstrations of devices (including tunable filters and surface-emitting microsources) operating along these principles are presented     

Optical coupling of whispering-gallery modes of two identical microdisks and its effect on photonic molecule lasing

The lasing characteristics of a photonic molecule in the form of two optically coupled semiconductor microdisks are investigated. Electromagnetic analysis of the lasing spectra and linear thresholds of the coupled whispering-gallery (WG) modes of four different symmetry classes is presented. Here, Maxwell's equations and accurate boundary and radiation conditions are considered as a specific "cold-cavity-with-gain" eigenvalue problem. Each eigenvalue is a pair of real-valued parameters -frequency and threshold material gain. In the two-dimensional (2-D) approximation, based on the introduction of an effective refractive index, this problem is reduced to a determinant equation with favorable features. A secant-type method is further used to calculate thresholds and lasing frequencies numerically. Results obtained show that optical coupling may lead to a further reduction of the ultralow thresholds of the WG modes, although the opposite, i.e., threshold spoiling, is more common.     

Experimental investigation of a new method for advanced fast reactor shutdown cooling

We consider a new method for fast reactor shutdown cooling using a decay heat removal system (DHRS) with a check valve. In this method, a coolant from the decay heat exchanger (DHX) immersed into the reactor upper plenum is supplied to the high-pressure plenum and, then, inside the fuel subassemblies (SAs). A check valve installed at the DHX outlet opens by the force of gravity after primary pumps (PP-1) are shut down. Experimental studies of the new and alternative methods of shutdown cooling were performed at the TISEY test facility at OKBM. The velocity fields in the upper plenum of the reactor model were obtained using the optical particle image velocimetry developed at the Institute of Applied Physics (Russian Academy of Sciences). The study considers the process of development of natural circulation in the reactor and the DHRS models and the corresponding evolution of the temperature and velocity fields. A considerable influence of the valve position in the displacer of the primary pump on the natural circulation of water in the reactor through the DHX was discovered (in some modes, circulation reversal through the DHX was obtained). Alternative DHRS designs without a shell at the DHX outlet with open and closed check valve are also studied. For an open check valve, in spite of the absence of a shell, part of the flow is supplied through the DHX pipeline and then inside the SA simulators. When simulating power modes of the reactor operation, temperature stratification of the liquid was observed, which increased in the cooling mode via the DHRS. These data qualitatively agree with the results of tests at BN-600 and BN-800 reactors.     

Improvement of LiNbO 3 Surface Roughness by Using a Multi-Step Process: Relationship Between Optical and AFM Analysis

In this study, we present the results on the growth of lithium niobate (LiNbO 3 ) films on sapphire with good crystalline quality and morphology. Various transfer function were defined for the epitaxial deposition of LiNbO 3 . In order to overcome the difficulty of producing thick and smooth films of LiNbO 3 , we have developed a multi-step process based on the successive growth of LN layers: no degradation of the surface roughness was observed with the film thickness. A complete optical characterization based on prism coupling technique was proposed to carefully establish a relationship between the surface morphology and the optical informations, i.e. guided modes excited inside the layer. The evolution of the surface roughness (r ms ) as a function of the LiNbO 3 film thickness was comparable to that of the full width at half maximum ( j θ) of TE 0 guided-modes. We found a close relationship between j θ and the surface roughness r ms : j θ of 0.1 is associated to r ms of 2nm.     

Experimental investigations of harmonic synchronization conditionsand mechanisms of mode-locked laser diodes induced by optical-pulseinjection

We investigated the detailed characteristics of synchronization of mode-locked laser diodes (MLLD's) by subharmonic optical pulse injection. It was shown that optical harmonic injection mode-locking was not very sensitive to injection pulse shapes. In the time domain, subharmonic injection pulses were multiplexed inside the MLLD and these multiplexed pulses effectively modulated the absorbance of the saturable absorber at the MLLD's repetition frequency. It was also found in the spectral domain that injection pulse trains should have optical spectrum components broader than the MLLD's intermode spacing, and injection spectral components should couple to at least two modes of the MLLD     

An optical fiber sensor for biofilm measurement using intensitymodulation and image analysis

The development of an online sensor to determine the fouling properties of aqueous process fluids is described. A plastic optical fiber with its cladding removed over a sensitized length measures the growth of biofilms in a closed loop water process system by evanescent field attenuation and intensity modulation. The sensor detects material build-up at the core-cladding interface by means of refractive index modulation. A theoretical model is developed showing that an increase in cladding refractive index reduces the intensity of light propagating in the fiber and attenuates the high order modes. The modulation mechanism of the sensor is demonstrated using a CCD camera and frame grabber to record the far field modal distribution of the fiber, when the outer modes are excited. The intensity distribution changes spatially in response to the biofilm deposit on the sensor, indicating evanescent field attenuation     

钢管杆内部积水原因分析及防范措施

钢管杆内部积水直接造成地脚螺栓,特别是底部法兰与基础顶面间地脚螺栓及钢管内壁锈蚀,严重威胁到钢管杆的安全运行。通过分析钢管杆内部积水原因,提出了相应的处理措施。     

Comprehensive modeling of diffused quantum-well vertical-cavitysurface-emitting lasers

A numerical model for investigating the thermal, electrical, and optical characteristics of vertical-cavity surface-emitting: lasers (VCSELs) with a diffused quantum-well (QW) structure is presented. In the model, the quasi-three-dimensional (quasi-3-D) distribution of temperature, voltage and optical fields as well as the quasi-two-dimensional (quasi-2-D) diffusion and recombination of carrier concentration inside the QW active layer are calculated in a self-consistent manner. In addition, the quasi-3-D distribution of implanted ions before and after thermal annealing are computed. The variation of electrical conductivity and absorption loss as well as the influence of impurity induced compositional disordering on the optical gain and refractive index of the QW active layer are also taken into consideration. Using this model, the steady-state characteristics of diffused QW VCSELs are studied theoretically. It is shown that significant improvement of stable single-mode operation can be obtained using diffused QW structure     

Measuring the Modal Content of Large-Mode-Area Fibers

Spatially and spectrally resolved imaging of mode content in fibers, or more simply, S $^2$ imaging, is a new measurement technique for analyzing the mode content of large-mode-area (LMA) fibers. It works by spatially resolving the spectral interference that occurs when light in a few-mode fibers scatters into different modes that then propagate with different group delays. A scanning spatial filter in the form of a single-mode fiber probe coupled to an optical spectrum analyzer is utilized to provide both spatial and spectral resolution, and the data are analyzed via the Fourier transform of the optical spectrum. The wealth of data allows for imaging multiple modes simultaneously propagating in the fiber under test as well as quantifying their relative power levels. In addition, the ability to analyze mode images as a function of modal group delay allows distinguishing between discrete scattering at fiber surfaces and distributed scattering that occurs along the length of the LMA fiber. The all-fiber nature of the setup makes the measurement sufficiently stable to measure phase images of the higher order modes (HOMs). Because the method is interferometrically based, even very weak HOMs can be detected.      

利用光纤通道传输保护信号的相关分析

提出了继电保护对通信通道的要求;对光纤保护通道方式进行了比较;对涉及光纤保护通道的各类参数进行了分析,提出了指标要求和计算公式,并以实例加以分析;在总结目前重庆电网高压线路上应用的3类保护通道方案的基础上,结合重庆电网实际,提出了光纤保护通道的建设方案。     

光学振动监测系统在发电机在线监测方面的应用与实践

发电机定子绕组端部在线振动监测是保证发电机安全运行的重要措施，具有很高的技术难度。本文介绍了光学振动测量系统在发电机定子绕组端部振动在线监测方面的发展现状，以及在一台国产200MW汽轮发电机上的实践应用结果。     

Enhanced Second Harmonic Generation From Noncentrosymmetric Nanohole Arrays in a Gold Film

A subwavelength aperture array in a gold film is fabricated for the purpose of second harmonic generation (SHG). The sunglass aperture shape is chosen to have an apex to increase the local field; however, unlike past research on double-hole structures, the inversion symmetry of the structure is intentionally broken to enhance the SHG. A systematic study of the influence of array periodicity and aperture shape is provided. The conditions for maximum SHG are discussed in terms of local field enhancement, excitation of the localized surface plasmon resonances, and the influence of array periodicity. Fully vectorial finite-difference electromagnetic calculations provide the effective index of the aperture modes, as well as the surface electric field to quantify the discussion. Both the sunglass and double-hole structures are promising for future implementation with less-expensive optical lithography since it is mainly composed of two holes; yet they produce sharp apexes for enhanced local field and thereby enhanced nonlinear light–matter interaction.      

Analyzing dynamic performance of power systems over parameter spaceusing normal forms of vector fields-part II: comparison of the systemstructure

This is part II of a two-part paper dealing with dynamic performance of power systems over the parameter space. The companion paper (part I) proposes an approach to identify unfavorable operating regions by searching for resonance and near-resonance. The results show that near-resonance among critical inertial modes and control modes may contribute to the unsatisfactory behavior of the system. In this paper, the effect of strong nonlinear modal interactions on machine states is quantified. A new index is derived to measure the relative severity of the near-resonance. The linear and nonlinear characteristics of the system are separated and correlated to the transient stability of the system     

Performance of traveling-wave electroabsorption modulators depending on microwave properties of waveguides calculated using the FDTD method

We present a method to analyze electrical and optical characteristics of traveling-wave electroabsorption modulators (TW-EAMs) using the finite-difference time-domain method. We consider the interaction between electromagnetic fields and optical powers in waveguides in time domain to model electrical and optical behaviors of TW-EAMs. The effects of microwave properties of waveguides on modulation response and output optical power of TW-EAMs are analyzed by the proposed method. The characteristic impedance of TW-EAMs is more important than microwave index to obtain large modulation bandwidth of TW-EAMs when impedance matching techniques are not used. However, effective refractive index match between microwave and lightwave becomes important as the waveguide length increases. The microwave property closely related to the extinction ratio of output optical powers is the microwave loss. When impedance match is achieved by low-impedance termination, the velocity matching between microwave and lightwave becomes important.     

工频电场对ADSS光缆特性的影响

通过实验观测输出光功率与不同电场强度等级及时间的关系，在假设的基础上分析了工频电场引起光纤晶体的晶轴角度的偏转，详细说明了工频电场对光纤折射率及光传输模式的影响及其改善方法。     

基于超高频法GIS局部放电监测技术的研究

对于GIS局部放电的测量,超高频法是一种较为有效的方法。将频谱仪设置为零扫描模式,采用高频窄带的方法,通过安装在GIS内的超高频传感器获得的局放信号可以通过相位解析的方法表征其局放的点波波形。笔者给出了GIS中几种不同绝缘缺陷的点波波形及其指纹图。通过点波波形及指纹图,可以识别GIS中不同的绝缘缺陷类型。     

Novel multimode fiber for narrow-band Bragg gratings

We propose a novel multimode fiber structure with modal propagation characteristics tailored to facilitate the creation of narrow-band high-reflectivity fiber Bragg gratings. The fiber structure proposed consists of concentric cylindrical shells of higher and lower refractive index material. A full vector second-order finite-element method is used to analyze the proposed multimode fiber structure. Simulations of the modal profiles show that high-order modes are localized to particular high-refractive index shells. We present the theoretical characterization of the modal propagation constant as a function of inner shell radius, shell separation, and harmonic-mode parameter. It is shown that a fiber with a minimum inner shell radius of at least 25λ (where λ is the vacuum wavelength), and a minimum shell separation of at least 10λ provides a reasonable tradeoff between fiber size and grating performance. A simulation of the multimode fiber grating shows that a grating with a full-width at half-maximum bandwidth on the order of 10^-4λ is theoretically possible, if optical power is launched strictly into modes with angular harmonic parameter p=1     

基于复合模式的电力系统超低频振荡产生机理

从电力系统内部非线性结构特性出发,运用正则形理论这一有效的非线性分析方法,通过对复合模式在stressed系统中作用的深入研究,提出复合模式成为主导模式可以构成电力系统超低频振荡的振荡模式这一全新看法.从正则形理论复合模式的角度对超低频振荡的产生机理加以阐述,通过时域仿真,并运用Prony方法对其进行检验,表明所提出的这一新见解和新方法的正确性.     

Wave propagation through a photonic crystal in a negative phase refractive-index region

The wave propagation through a photonic crystal with a triangular lattice of air holes realized in the InP-InGaAsP heterostructure are studied theoretically for the transverse magnetic modes. The photonic crystal possesses a negative refractive index, and the self-focus of the beam is successfully observed. The weak side beams are observed due to high-order Bloch waves in the photonic crystal. The coupling efficiency for the outgoing waves to a waveguide is also studied.