Generation of a uniform line source using a binary filter

A uniform or nearly uniform 10 mm long line source has been generated from a gaussian laser beam using a binary filter. This is done by processing the binary filter throughout a well corrected optical system, so that the equivalent of a continuous inverse gaussian filter is obtained at the final image plane. This equivalent continuous filter generates a uniform line source with maximum conversion efficiency of 50%.     

Adaptive feedforward control of a rectangular panel using a wave filter constructed with point sensors

This paper presents the wave filtering method for a rectangular panel, which is necessary for a feedforward wave control system, and clarifies its validity in the control system. Firstly, a wave solution of a rectangular panel is derived to describe the wave dynamics of the structure. This is followed by the derivation of the wave filtering equations that indicates the structure of the filter. It is found that the proposed wave filter consists of a modal filter, a rearrangement filter and a wave decomposition filter. Then, from the viewpoint of numerical simulations, the characteristics of the wave propagation in a rectangular panel as well as the accuracy of the wave fitter are verified. For the evaluation of the filter accuracy, the condition number is used as a performance index. Finally, an experiment on the adaptive feedforward control system using the wave filter is carried out, demonstrating that the reflected wave absorbing control enables the inactivation of vibration modes.     

Design of a widely tunable laser with a chirped ladder filter

We theoretically investigated a digitally tunable laser with a chirped ladder filter and a ring resonator to obtain a wide wavelength tuning range covering the whole C- or L- band. The clear relation between the tuning range and laser structure, especially the ladder filter, is described analytically. The introduction of a chirped structure into a ladder filter is effective in achieving both wide tunability and a stable lasing mode. A numerical simulation based on multimode rate equations shows that a tuning range of over 40 nm and a mode suppression ratio over 40 dB can be achieved by introducing a chirped ladder filter.     

Analysis of a second-order polarization-independent filter made of a single ring resonator and a Sagnac interferometer

A novel second-order polarization-independent filter made of a single ring resonator and a Sagnac interferometer (SRRSI) is proposed, and its filtering characteristics are investigated. By using birefringence in waveguide, a single ring resonator can be used to synthesize a filter with second-order response. Analytical formulas are derived for characteristics of the SRRSI varied with waveguide parameters, such as the coupling coefficient; and the critical condition of a second-order Butterworth filter is given. The influence of loss in the ring resonator is also analyzed.     

Design of a Composite Wavelet Matched Filter Using Breeder Genetic Algorithm

We outline a method to design a composite wavelet matched filter using the breeder genetic algorithm. The composite filter consists of a linear combination of wavelet and matched filters. Breeder genetic algorithm has been used to find the optimal weighting coefficients for the wavelet and the matched filters that constitute the composite filter. For the breeder genetic algorithm, the geometric mean has been used as the crossover operator and the creep has been used as the mutation operator. The performance of the filter is tested in the presence of additive white Gaussian noise. The performance of the composite wavelet matched filter has also been compared with that of the phase only filter and the classical matched filter. The designed filter can be used in an optical correlator to separate two classes of input images for fingerprint-based user identification in security systems.     

Tunable all-optical microwave notch filter with a negative tap based on a semiconductor optical amplifier and a dispersive medium

A tunable all-optical microwave notch filter with a negative tap based on a semiconductor optical amplifier and a dispersive medium is demonstrated. A negative tap is realized through the cross gain modulation in the semiconductor optical amplifier. The free spectrum range of the notch filter can be tuned by tuning the wavelength of one of the two laser sources. The influence of the amplitude mismatch of the two lasers on the performance of the filter is analyzed. The present notch filter is easy to implement and cost-effective.     

Simulation and design of a bandpass filter on metasubstrates

This work presents an analysis of the microstrip bandpass filter on metamaterial substrates. The filter is composed of two ring resonators with quarter-wavelength side-coupled sections. The filter input is provided, as well as the output port, using a quarter-wavelength side-coupled microstrip line section. Simulations by finite element method have been carried out to verify the effect of the metamaterial substrate properties on the filter performance, and to compare these results to those obtained considering isotropic substrate.     

Theoretical investigation of a notch filter using a long-period grating based on the sampling theorem

A notch filter using a different grating scheme is investigated theoretically. The grating is the thermo-optic index change induced by individually controllable heaters that are periodically arranged on the filter surface. If the index change pattern induced by the heaters is in the form of sampling a periodic index change, the transmission spectrum of the filter has the same resonance band as that generated by the periodic index change. Simulation results show that the attenuation, bandwidth, and center wavelength of a resonance band are independently adjustable. In addition, it is shown that the transmission spectrum may be tailored to arbitrary predictable shapes. Finally, the realization of the filter is discussed.     

Dynamics of a filtered-feedback laser: influence of the filter width

The behavior of a semiconductor laser subject to filtered optical feedback is studied in dependence on the width of the filter. Of special interest are pure frequency oscillations where the laser intensity is practically constant. We show that frequency oscillations are stable in a large region of intermediate values of the filter width, where the dispersion of the filter is able to compensate for the well-known phase-amplitude coupling of the semiconductor laser. Our stability diagram covers the entire range from a very narrow filter, when the system behaves like a laser with monochromatic optical injection, to a very broad filter, when the laser effectively receives conventional (i.e., unfiltered) optical feedback.     

基于consensus滤波器的新型电压监测仪的设计

在进行深入分析consensus滤波器原理的基础上,提出了一种新的电压监测仪设计方法。首先将数模转换器在各个时刻测量的电压有效值看做一个小世界网络模型G中的一个节点。由于测量的电压信号容易被电网中的随机噪声所污染,通过consensus滤波器算法进行滤波,使得数模转换器测量的信号最终趋近于一个稳定的数值。仿真结果表明,该方法可以有效的还原被噪声污染的电压信号,而且即使在某一个时刻数模转换器出现故障失灵,所测量的数据也不受影响,仿真结果和实践应用表明了本文所提出方法的有效性和可行性。     

Design of a Label Recognition Filter for Crosstalk Suppression in a Label Recognition Unit using Optical Correlation Assuming the Assistance of Optical Time-Gating

To suppress crosstalk caused by matched filtering in label recognition based on optical correlation, we propose the novel design method of a label recognition filter to improve the discrimination performance. Assuming the assistance of optical time-gating, the label recognition filter is designed by a technique of a multiple-object discriminant filter (MODF) so that the crosstalk can be suppressed only at the center of correlation signals. This method can reduce the requirement for the performance of an optical thresholder. Simulation results show that the designed label recognition filter can successfully suppress the crosstalk.     

A new shunt DC active filter of power supply in a steady high magnetic field facility

A DC active power filter is an indispensable part in a high power and high stability power supply system, especially in the power supply system of the Steady High Magnetic Field Facility, which requires that the current ripple should be limited to 50 parts per million. In view of the disadvantages of the series DC active power filter and shunt Pulse Width Modulation DC active filter, this paper puts forward a novel DC active filter by combining the advantages of the transistor regulator and the shunt type. The structure and principle of the new shunt linear active filter are introduced. Meanwhile, the design of several key components that construct the new shunt linear active filter is also analyzed. The simulation model and an experimental prototype of the shunt linear active filter are developed, and the results verify that the parameter design is reasonable and the shunt active filter has a good filter effect.     

BEPCII横向束流反馈系统的梳状滤波器

 BEPCII是一个多束团、大流强的装置, 由于高频腔的高次模和电阻壁阻抗等因素，不可避免地会出现束流不稳定性。BEPCII中采用束流反馈系统来抑制束流不稳定性。横向束流反馈系统主要包括前端电子学、信号处理电子学、反馈器件和放大器等几个部分。梳状滤波器是信号处理电子学的重要部件，利用两根长短不同的电缆以及一个功分器和合成器构成了一种简单有效的梳状滤波器，其梳状深度达到-41 dB，使用这种梳状滤波器的横向反馈系统成功地抑制了束流中出现的不稳定性。     

Modifying NL-means to a universal filter

Despite a state-of-the-art filter for removing Gaussian noise, non-local means filter (NLM), like its local counterpart (the mean filter), is no longer so effective in removing salt-pepper noise which is common in real world as well. By contrast, adaptive median filter (AMF) is concise and can remove this type of noise effectively. Inspired by the AMF filtering strategies, in this paper, we modify NLM to a novel non-local universal filter (UNLM) which can remove not only either of Gaussian noise and salt-pepper noise but also their mixture. Experiments on artificial and benchmark images validate its feasibility and effectiveness.     

Calculation of a laser with a self-clearing optical shutter

The filter operates with a two-level system and affects the emission kinetics of the laser; allowance is made for the effects of pumping in the laser and of relaxation in the laser and filter. It is found that oscillation with several peaks is possible. The requirements for single-peak operation are formulated. Examples are given of emission calculations, with analytic estimates of the output power, energy, and pulse length.     

Frequency-locking of a CW dye laser to some absorption lines of a neon discharge by a Faraday filter

Single-mode oscillations of a CW dye laser at the center of five absorption lines from the 1s states to the 2p states of neon were obtained by means of a neon discharge Faraday filter, without any other frequency-selective elements. The most striking thing observed is that saturated absorption takes place at the center of several absorption lines in a Faraday filter, in addition to optical rotation.     

Engineering implementation of a hybrid optical correlator using SLMs

Optical correlators have been widely used for such applications as automatic target identification, invariant pattern recognition and machine vision. In hybrid optical correlators, Spatial light modulators (SLMs) are used to dynamically update the input and the filter. However, implementation is difficult because of the interference of “ghost” images; rigorous requirements for filter registration, accurate and effective filter sizing and complex valued filtering functions. This paper proposes some practical approaches to handle these issues and provides engineering details of how to build a hybrid optical correlator, where a SLM serves as an updateable intensity filter for real-time pattern recognition.     

Photonic generation of a microwave signal by incorporating a delay interferometer and a saturable absorber

A novel approach to generate microwave signals is presented by employing a dual-wavelength erbium-doped fiber ring laser. By using a delay interferometer as a comb filter cascaded with a tunable bandpass filter and a saturable absorber formed by an unpumped polarization-maintaining erbium-doped fiber, a stable wavelength-tunable dual-wavelength single longitudinal-mode laser is achieved. A microwave signal at 20.07 GHz with a linewidth of <25 kHz is demonstrated by beating the two wavelengths at a photodetector.     

一种基于单负Metamaterials成对结构的带通滤波器的设计

提出了一种基于单负Metamaterials对的带通滤波器的设计原理,给出了这种带通滤波器的谐振频率的表达式,对其谐振频率及带宽与其决定因素之间的关系进行了计算,对计算结果进行了讨论,为设计单负Metamaterial对带通滤波器的理论与方法提供了依据。研究结果表明：利用单负Metamaterials对的确可以实现带通滤波器;ENG板的磁导率μ1、MNG板的介电常数ε2、电等离子体频率ωep、磁等离子体频率ωmp、两个层的厚度比值a这五个因素决定了这种滤波器的中心频率;两个层的厚度及二者之间的比值决定这种滤波器的带宽。     

密集波分复用薄膜滤光片的群延迟补偿设计

设计了一种基于薄膜干涉理论的反射式相位补偿器件，用以补偿密集型波分复用窄带滤光片所产生的群延迟，使50GHz薄膜滤光片的群延迟特性适应于40Gb／s系统的要求，在0．2nm带宽下群延迟波动从10ps左右下降到0．76ps以下。