Tunable optical narrowband filter using a gain-coupled phase-shift-controlled distributed feedback laser

In this paper, we have proposed and analyzed a new tunable optical narrowband filter using gain-coupled phase-shift-controlled distributed feedback (GC-PSC-DFB) laser diode. Coupled-mode equations are solved by using the transfer matrix method (TMM). The GC-PSC-DFB filters offer a stable single-mode bandpass output, similar to that obtained with phase-shifted index-coupled structures. However, GC structures do not suffer from the severe longitudinal spatial hole burning (SHB) that occurs in high-coupling quarter-wave-shifted DFB filters. This SHB can cause multimoded behavior for high-input signal power. Various filter parameters such as wavelength tuning range, side-mode suppression ratio (SMSR), and channel gain deviation have been investigated and discussed. Our results show that the GC DFB structures offer a wider tuning range of 23.3 /spl Aring/ compared with the similar index-coupled DFB structures with nearly steady bandwidth of 12 GHz, while maintaining 41.8-dB constant gain.     

Chromatic dispersion measurements of long optical fibers by meansof optical ranging system using a frequency-shifted feedback laser

We describe the experimental results on the chromatic dispersion measurement of long optical fibers by means of optical ranging system using a wavelength-tunable frequency-shifted feedback (FSF) laser. The optical ranging system using an FSF laser has high spatial resolution of several centimeter over 10-km measurement range, and then the dependence of the group delay time of the lightwave in the optical fibers on the wavelength can be directly measured. The chromatic dispersion and the zero-dispersion wavelength of an 80-km-long dispersion shifted fiber was estimated, which is in good agreement with the result obtained by the phase method     

An adaptive control scheme using multiple reference models

This paper develops an extended model reference adaptive control scheme to expand the capacity of state feedback state tracking adaptive control to handle the plant‐model matching uncertainties for single‐input LTI systems. The extended scheme is developed, using multiple reference model systems (only one of which is required to be able to match the controlled plant), and multiple controllers (which are updated from adaptive laws generated from multiple reference model systems based estimation errors), as two key features of such design to relax a plant‐model matching condition. A switching mechanism is constructed using those multiple estimation errors, capable of selecting the suitable control input from the multiple control signals, to achieve the desired system performance. An aircraft flight control example is presented to show the capacity of such design in relaxing a practical design condition. Copyright © 2013 John Wiley & Sons, Ltd.     

An improved analysis of semiconductor laser dynamics under strong optical feedback

We present an improved theoretical model to analyze dynamics and operation of semiconductor lasers under optical feedback (OFB). The model is applicable for arbitrary strength of OFB ranging from weak to very strong. The model has been applied to investigate the dynamics and operation of lasers over wide ranges of OFB and injection current. An improved set of modified rate equations of lasers operating under OFB were proposed. We introduced a theoretical model to determine the power emitted from both the laser back facet and external reflector. The results showed that the operation of semiconductor lasers is classified into continuous wave, chaotic, and pulsing operations, depending on the operating conditions. The light versus current characteristics were examined in the operating regions of the classified operations. Under strong OFB, we predicted for the first time pulsing operation of lasers at injection currents well above the threshold. We observed the pulsing operation in experiments in good correspondence with the simulated results.     

基于确定系数的失灵保护优化技术方案

失灵保护方案的优化对维持电网的安全稳定运行至关重要。详细地分析了电流互感器电流拖尾对失灵保护整定时间的影响,提出了利用最小二乘拟合算法识别电流互感器二次电流特征的方案,进而构建了基于确定系数的新失灵保护启动逻辑。最后分析了拟合数据的选取以及CT选型对新方案的影响。新的启动逻辑既能缩短失灵保护整定时间,又能确保失灵保护不误动。基于PSCAD算例分析验证了新方法的有效性。     

Generation of strong optical field in soft X-ray region by using high-order harmonics

For further development of a variety of applications, one of the most important issues is the improvement of output harmonic energy and conversion efficiency. We review our work on the energy scaling of high-order harmonic generation based on phase-matching using a loosely focused beam. Our harmonic energy scaling method can be universally applied to harmonic generation in the neutral rare gas target. In addition, we demonstrate a new concept for spatial separation between the high-energy pump and harmonic beam to increase the available soft X-ray energy for the applications. This method is very simple and highly useful for not only high-order harmonic generation but also longitudinally pumped X-ray lasers. By combining the high-energy high harmonic source and new spatial separation method, we successfully demonstrate focusing of the soft X-ray beam with a peak intensity of 1/spl times/10/sup 14/ W/cm/sup 2/, which is to our knowledge the highest ever reported in the soft X-ray region.     

An improved laser ablation method using a shadow mask (eclipse method)

To eliminate droplet formation during the laser ablation thin film growth process, we proposed a new laser ablation technique, the “eclipse method,” which facilitated removing this droplet problem completely. In particular, YBa₂Cu₃O_y films obtained by this method had T_c ˜93 K and droplet‐free surfaces. To achieve growth rate enhancement in the low‐pressure condition and to introduce the activated species on the substrate in the eclipse method, we further proposed a new composite shadow mask method, the “eclipse angle method.” Furthermore, we found the Ar addition effect to improve the film qualities of Bi‐layered crystals. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 88–94, 2000     

An ATM-based intelligent optical backplane using CMOS-SEED smartpixel arrays and free-space optical interconnect modules

The architecture, smart pixel array chip design, and optical design of an intelligent free-space digital optical backplane for ATM switching are presented. The smart pixel chip uses reflective SEED (self-electrooptic effect device) optical modulators and detectors flip-chip bonded to CMOS circuitry. This chip is one of the most complex designs ever reported in this technology, and it operates at a simulated backplane clock rate of 125 MHz. The low-loss optical system employs f/4 diffractive minilenses and microlenses to interconnect clusters of smart pixels, and it is shown to allow 2060 connections per chip if 1-cm² -sized smart pixel chips are used. This gives a predicted bisection bandwidth of around 1 Tb/s across a 10-in circuit board edge for a full-sized system     

Determination of XUV optical constants by reflectometry using ahigh-repetition rate 46.9-nm laser

We report the measurement of the optical constants of Si, GaP, InP, GaAs, GaAsP, and Ir at a wavelength of 46.9 nm (26.5 eV). The optical constants were obtained from the measurement of the variation of the reflectivity as a function of angle utilizing, as an illumination source, a discharge pumped 46.9-nm table-top laser operated at a repetition rate of 1 Hz. These measurements constitute the first application of an ultrashort wavelength laser to materials research     

Measurement and analysis of field-induced crystallographic texture using curved position-sensitive diffraction detectors

This paper outlines measurement and analysis methodologies created for determining the structural responses of electroceramics to an electric field. A sample stage is developed to apply electric fields to ceramic materials at elevated temperatures during neutron diffraction experiments. The tested voltages and temperatures range from ?20 kV to +20 kV and room temperature to 200 °C, respectively. The use of the sample environment for measuring the response of ferroelectric ceramics to an electrical stimulus is demonstrated on the instrument Wombat, a monochromatic neutron diffractometer employing a curved positive sensitive detector. Methodologies are proposed to account for the geometrical effects when vector fields are applied to textured materials with angularly dispersive detector geometries. Representative results are presented for the ferroelectric (Bi_1/2Na_1/2)TiO₃-6%BaTiO₃ (BNT-6BT) which show both phase transformation and ferroelectric domain texturing under the application of an electric field. This experimental and analysis approach is well suited for time-resolved measurements such as stroboscopic and in situ studies on a variety of electro-active materials.     

Demonstration of a fully spatial coherent X-ray laser at 13.9 nm

We have recently reported the successful development of a fully coherent X-ray laser (XRL) at 13.9 nm by an oscillator-amplifier configuration with two targets. In the experiment, a seed XRL beam from the first target is injected into a plasma amplifier at the second target. The observed XRL beam has full spatial coherence and 0.2 mrad of nearly diffraction-limited divergence. In order to improve the output fluence, the amplification properties of the XRL beam have been investigated using various plasma lengths of the second amplifier target. The output energy has been improved by a factor of ten, increasing the length of the gain region to 10 mm, resulting in about 0.2 /spl mu/J of output energy.     

EHV transmission line protection using a morphological lifting scheme

This paper presents a novel algorithm for ultra-high-speed (UHS) protection relays of extra high voltage (EHV) transmission lines, using a morphological lifting scheme (MLS). The MLS focuses on identifying the gradient of the wavefront of a traveling wave contaminated by noise. The proposed algorithm can be used for either transient positional or directional protection. It is evaluated through a variety of simulation studies which are carried out on a typical 400 kV EHV transmission system model using the power simulation program PSCAD/EMTDC. The simulation results show that, with the MLS used, the algorithm is capable of providing accurate responses under various fault conditions in comparison with previous algorithms, such as wavelet transform (WT).     

An energy optimized control scheme for a transformerless DVR

The dynamic voltage restorer (DVR) is considered as the most effective and economic solution for voltage disturbances. This paper presents an energy optimized control scheme for a transformerless DVR. The DVR structure is based on a cascaded H-bridge multilevel inverter topology to eliminate the need of insertion transformers. The proposed control algorithm maintains a balanced load-side voltage even during the compensation of unbalanced disturbances with a minimum active power injection. Moreover, the proposed scheme maximizes the ride-though capability of the DVR during voltage sags. This feature is verified by using capacitors instead of dc sources as energy storage elements for the DVR. Furthermore, the proposed minimum energy scheme prevents the rise in the dc-side voltage of the inverter when compensating voltage swells. The performance of the proposed DVR system is evaluated for compensating different types of voltage disturbances. The results validate the robustness and the accuracy of the proposed system.     

Improved parallelism measurement using a laser interferometer

The authors discuss an improved method for obtaining parallelism measurements of two straight bars in a plane, considering the specific problem of making two vertical surfaces parallel to each other to within 0.00005 of an inch over a 50 inch length. The authors compare the existing method of using dial indicators and a slider with that of using a laser interferometer, cable and pulley system, and a microcomputer. Possible errors this system may generate and solutions to help minimize them are presented. The procedure presented will help to minimize errors due to the operator such as `reading between the lines' on an indicator and hand applied pressure. These methods allow improved parallelism resolution over that obtainable with the indicator     

Development of a 2-kW XeCl laser with a surface coronapreionization scheme and a spiker-sustainer circuit

A maximum average power of 2.1 kW is demonstrated in a XeCl laser with an efficiency of 3.0% at a repetition rate of about 800 Hz. The 2-kW laser has a discharge region of 4 cm in gap length, 2.5 cm in discharge width, and an effective discharge length of 3 m with a resonator length of 5.2 m. A reverse voltage mode spiker-sustainer circuit makes it possible to apply a steep voltage rise of nearly 1000 kV/μs across the main discharge electrodes and to supply excitation energy effectively into the discharge region. The control of the preionization timing before the initiation of the spiker circuit is found to be indispensable in maintaining a homogeneous volume discharge under high repetition-rate operation. These techniques enable the laser to realize a long pulse excitation under the high repetition-rate operation conditions. The excitation process is analyzed by computer-model simulation. The application of a cascaded stable resonator has improved the average power by 6% compared with that of a conventional stable resonator     

Planar waveguide optical spectrum analyzer using a UV-inducedgrating

An optical spectrum analyzer is demonstrated using a UV-induced, chirped grating on a planar waveguide and a linear detector array. The grating provides both the dispersion with respect to wavelength and the imaging function. The spectral response has a full-width at half-maximum of 0.15 nm and a bandwidth of 7.8 nm. A chirp of -1.75 nm/cm and a 12-cm focal length were used. The design parameters are discussed in terms of the chirp, focal length and resolution. The wavelength dependence of the optimal chirp limits the resolution for small focal lengths. For longer focal lengths, the spotsize is diffraction limited and high resolution can be achieved with minimal fabrication complexity     

光纤保护通道配置

在超高压电力线路中配置双套纵联继电保护装置，是快速排除电力系统故障，使之安全、畅通的必要保障。论文着重对利用光纤通道传输纵联保护数据信号的两种主要传输方式和技术特点作了详细的论述和比较；并以沙芙超高压电缆线路中所选择的光纤保护及通道配置方案为例，分析了作者在参加此项工作所取得的经验及体会。     

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     

谐振式光学陀螺入谷信号的判断方案

谐振式光学陀螺是一种新型的惯性传感器件,通过控制扫描频率锁定在谐振谷中,检测频率变化引起的光强变化从而计算出转速信号。在谐振陀螺系统中,入谷电压的判断是谐振陀螺检测系统中的第一步。由于选用的光源不同,对于光源的调频方式不同,调频方式对于光源的影响也不相同,因此对于入谷电压的判断方法也不同。根据两种光源条件下对于光源入谷电压的判断进行了分析,并且对于光源功率随频率变化的情况进行了重点分析,提出了两种入谷电压的判断方案,通过比较两种方法的差别,最终选用了模拟方法,并且经过实验验证,取得了很好的效果。     

广东电网光纤保护通道配置方案

广东电网电力光纤网已初具规模，如何基于该网络来发展光纤保护是日前继电保护研究的课题。本文介绍了光纤保护通道接入方式，通过对日前各类光纤保护接口特点进行分析，以寻求今后广东电网光纤保护通道配置最佳方案。