Design and optimization of phase plates for shaping partially coherent beams by adaptive genetic algorithms

The adaptive genetic algorithms (AGAs) are applied to the design and optimization of phase plates for shaping partially coherent beams. The simulation procedure based on the AGAs is described. Numerical examples for shaping partially coherent Cosh-Gaussian (ChG) and Hermite-Gaussian (HG) beams demonstrate the advantage of the AGAs in applications to the partially coherent beam transformation and shaping.     

Limitation in the intrinsic method of EDFA gain optimization for 32 × 40 Gbit/s WDM systems

The gain flattening of the erbium doped fiber amplifier (EDFA) is one of the most important aspects in the EDFA which the gain is wavelength dependent. For the first time the limitation of EDFA gain optimizing for a 32-channel wavelength division multiplexing (WDM) systems is investigated and reported in this paper. In a 32-channel WDM system the most favorable flatness gain achieved was 23.16 ± 1.51 dB with an average noise figure of 5.70 dB. This outcome proposes that the method does not achieve a uniform spectral gain in a 32-channel WDM system that incorporates a bandwidth of around 25 nm. Based on the simulation results the intrinsic optimization of EDFA causes the poor SNR and peak signal power with great variation over a transmission distance of 480 km single mode fiber.     

Optical design and multi-objective optimization with fuzzy method for miniature zoom optics

In this paper a thinning L-type zoom lens design was proposed to exploit the reflecting and refracting surfaces connected by a prism. However, in the L-type designs, the modulation transfer function (MTF) value is comparatively low compared with that in its coaxial counterparts. If we increase the MTF, that would cause the relative illuminace (RI) degradation. We propose a combination of the Taguchi method and fuzzy approach to improve both the RI and MTF in L-type zoom systems. The resulting experimental values of orthogonal array L9 of the Taguchi method were used as inputs for fuzzy approach to obtain the MPCI value. The MPCI value was then analyzed by variance, revealing that the two most significant factors were (1) the surface 7 to image length and (2) the semi-aperture of the front element. In our proposed method, the appropriate weight of MTF and RI for the inputs of fuzzy controllers increased the MTF by 3.74%, but the RI only reduced by 0.13% in the systematic wide-angle end, respectively.     

Investigation of positioning algorithm and method for increasing the linear measurement range for four-quadrant detector

The paper studied the relationship between the light spot position and the output voltage in the case of laser spot which is in the four-quadrant (4Q) detector whose shape is circle or elliptic, energy distribution uniform or Gaussian. The study is based on add–subtract algorithm, diagonal algorithm and difference over sum (Δ/∑) algorithm. By using methods of polynomial fitting it can get a simple polynomial expression to enhance measuring speed and the simulation error is given. A method of using Binary Optics Elements (BOE) to shape the laser beam in the 4Q detector to square light spot with uniform intensity distribution is proposed to expand linear measurement range. The simulation result is verified for a circular spot with Gaussian energy distribution.     

Nonlinear filtering and beam shaping with χ nonlinear polarization interferometer

Novel χ⁽³⁾-based nonlinear polarization interferometer is theoretically and experimentally investigated. It enables efficient spatial and temporal filtering of femtosecond pulses via generation of cross-polarized wave. By changing the interferometer parameters different beam shapes can be obtained.     

Design and fabrication of diffractive elements for laser material processing applications

Diffractive optical elements have an important role to play in the provision of process adapted beam shaping for laser-materials processing applications. The design techniques and dominant methods of fabrication are described for intra-cavity and external beam shaping diffractive elements fabricated in a variety of dielectric and metallic materials for use with a wide range of laser sources. Theoretical and experimental examples are given in each section.     

实现散射场强整形的微散射体阵列逆向设计方法

本文提出一种基于全介电微散射体的散射阵列结构逆向设计方法,用以实现散射电场强度整形.该方法基于空域傅里叶变换与角谱变换,从给定目标区域处期望实现的散射场强分布出发,逆向求得所需的感应源,再利用电磁感应源理论,逆向设计微散射体阵列,且只需通过解析计算便能够快速地求取出微散射体阵列的电磁参数值分布.基于提出的逆向设计方法,文中提供了三维情况下的具体算例,实现了给定方形面目标区域的散射场强整形.理论计算结果与全波仿真结果符合良好,表明本文提出的逆向设计方法具有可行性与有效性.     

High-power laser beam shaping by inseparable two-dimensional binary-phase gratings for surface modification of stamping dies

For surface modification of stamping dies, an inseparable two-dimensional binary-phase gratings is introduced to implement the wavefront transformation of high-power laser beams. The design and fabrication of the gratings are described in detail. Two-dimensional even sampling encoding scheme is adopted to overcome the limitations of conventional Dammann grating in the design of two-dimensional output patterns. High diffractive efficiency (>70%) can be achieved through the transformation of the Gaussian laser beam into several kinds of two-dimensional arrays in focal plan. The application of the binary-phase gratings in the laser surface modification of ductile iron is investigated, and the results show that the hardness and the wear resistance of the sample surface were improved significantly by using the binary-phase gratings.     

Vector fuzzy control iterative algorithm for the design of sub-wavelength diffractive optical elements for beam shaping

The vector fuzzy control iterative algorithm (VFCIA) is proposed for the design of phase-only sub-wavelength diffractive optical elements (SWDOEs) for beam shaping. The vector diffraction model put forward by Mansuripur is applied to relate the field distributions between the SWDOE plane and the output plane. Fuzzy control theory is used to decide the constraint method for each iterative process of the algorithm. We have designed a SWDOE that transforms a circular flat-top beam to a square irradiance pattern. Computer design results show that the SWDOE designed by the VFCIA can produce better results than the vector iterative algorithm (VIA). And the finite difference time-domain method (FDTD), a rigorous electromagnetic analysis technique, is used to analyze the designed SWDOE for further confirming the validity of the proposed method.     

用于光束整形的衍射光学元件设计的混合算法

提出了一种用于衍射光学元件优化设计的混合遗传迭代爬山算法,该算法将迭代量化傅里叶变换算法融入到遗传算法中,然后在整体遗传算法结束后,对找到的当前最优解再用爬山法进行局部寻优,从而得到最优的衍射光学元件表面相位分布.用该混合方法设计了衍射光学元件,可以将入射的高斯光束整形成方形的均匀光斑.模拟结果表明:该混合算法具有收敛速度快、设计准确度高等优点.相比于其它设计方法,本文提出的方法能较好地改善整形效果,特别适用于光束整形的衍射元件设计.     

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ITER实验包层模块(TBM)的中子学问题与系统的氚增殖、热工水力、安全等问题密切相关,因此TBM的中子学优化设计极为重要。在CHHCSBTBM设计描述报告的一维中子学计算模型的基础上,利用一维中子输运计算程序ONEDANT和配套的数据库,以功率密度和氚增殖比等参数为优化目标进行中子学优化设计,得到了更为合理的中子学设计方案。     

Minimization of sound radiation from baffled beams through optimization of partial constrained layer damping treatment

An optimization study is presented with aim to minimize the sound power radiated by a simply supported, baffled beam with constrained layer damping (CLD) treatment. The governing equation of motion for the calculation of time-harmonic response of a partially CLD covered beam is derived first on the basis of energy approach. Assumed-modes method is used to solve the equation with obtained frequency response functions at different beam locations, which are further used for the calculation of its radiated sound power into half free-space by using Rayleigh’s integral. The optimization problem is then formulated to minimize the sound power radiated by the beam over a frequency range of interest covering multiple resonant modes. A genetic algorithm-based penalty function method is employed to search for the optimum of location/length of the CLD patch and the shear modulus of viscoelastic layer. Optimal results show that for a simply supported beam with a transverse force applied at its central location, it is not necessary to fully cover the structure using CLD patch in order to achieve the largest reduction in the sound power radiated by the beam over a frequency range. With inclusion of the amount of damping material to be minimized, the optimal CLD coverage length is only one-fourth of the base beam’s. Moreover, the optima of three design variables, the CLD coverage length, location on the beam and the shear modulus of viscoelastic layer, are highly relevant to each other.     

Simplified mesh techniques for design of beam-shaping diffractive optical elements

This paper describes a simplified mesh generation technique that is based on the finite element method of calculation of beam-shaping diffractive optical elements (DOEs). The mesh generation technique uses the inherent symmetry of the incident beam to generate a mesh. Using the meshes so generated, DOEs that convert a Gaussian intensity beam to one of a specified shape, are calculated. Simulations of the results of such beam-shaping elements will be presented. Such elements have uses in industrial and medical applications where both the shape as well as the intensity distribution on the material that is to be processed is very important. For example, in industrial applications the beam may be used to uniformly heat up a specific area in which case the intensity has to be uniform across the beam. The Gaussian intensity variation of a laser has to be converted to a flat-top beam in order to achieve this. To reiterate, beam shaping refers to changing both the intensity distribution and the shape of the beam. Experimental results of the fabricated gratings will also be presented. These results will include experimental data on the method of additive lithography which can be used to improve the efficiency of DOEs.     

低A声级贯流风机叶片周向角不等距优化设计

叶轮产生离散噪声的原因是叶片间周向夹角均匀布置,因此降低叶轮离散噪声的有效手段就是破坏叶片周向夹角的均匀布置,通过合理布置各叶片夹角降低叶轮离散噪声。本文提出了采用叶片周向角不等距布置降低叶轮总离散噪声A声级的一种优化设计模型,模型充分考虑了A计权函数与波动力对脉动流场响应参数Sc乘积有关的综合衰减曲线的高低频段衰减较大的特性和人可听域频率范围在20-2000Hz之间的特点,通过算例验证采用该模型可以降低总离散噪声A声级。     

用于光束整形的衍射光学元件设计的混合算法

提出了一种用于衍射光学元件优化设计的混合遗传迭代爬山算法,该算法将迭代量化傅里叶变换算法融入到遗传算法中,然后在整体遗传算法结束后,对找到的当前最优解再用爬山法进行局部寻优,从而得到最优的衍射光学元件表面相位分布.用该混合方法设计了衍射光学元件,可以将入射的高斯光束整形成方形的均匀光斑.模拟结果表明:该混合算法具有收敛速度快、设计准确度高等优点.相比于其它设计方法,本文提出的方法能较好地改善整形效果,特别适用于光束整形的衍射元件设计.     

Channel temporal correlation-based optimization method for imperfect underwater acoustic channel state information

The rapid time variations and large channel estimation errors in underwater acoustic (UWA) channels mean that transmitters for adaptive resource allocation quickly become outdated and provide inaccurate channel state information (CSI). This results in poor resource allocation efficiency. To address this issue, this paper proposes an optimization approach for imperfect CSI based on a Gauss–Markov model and the per-subcarrier channel temporal correlation (PSCTC) factor. The proposed scheme is applicable to downlink UWA orthogonal frequency division multiple access systems. The proposed PSCTC factors are measured, and their long-term stability is verified using data recorded in real-world sea tests. Simulation and experimental results show that the optimized CSI effectively mitigates the effects of the temporal variability of UWA channels. It demonstrates that the resource allocation scheme using optimized CSI achieves a higher effective throughput and a lower bit error rate than both imperfect CSI and the CSI predicted by the recursive least-squares (RLS) algorithm.     

YG算法设计分数傅里叶变换衍射光学光束整形器件

针对分数傅里叶变换衍射光学光束整形器件,比较了按离散点与按菲涅耳积分计算得到的变换矩阵间的差距,从中分析得出按离散点计算的变换矩阵引入的离散化误差与分数傅里叶变换系统参数的关系.模拟计算结果表明,该离散化误差不能忽略.为了在输出面上得到真实的光强分布,应采用菲涅耳积分计算其变换矩阵.鉴于该变换矩阵非幺正,本文利用YG算法进行了光束整形器件的设计.     

用于光束整形的多功能衍射相位板的设计

提出一种设计多功能衍射相位板的随机搜索和模拟退火混合设计方法利用这种方法,通过采用多个评价函数,可设计出在不同观察面上同时产生所需光强分布的衍射相位板设计用于高斯光束整形的多功能衍射相位板可以在焦面上产生高能量利用率、小旁瓣的光强分布,同时在离焦面上获得具有良好顶部均匀性的光强分布该方法提高了衍射器件的设计灵活性,对于设计同一块器件在光路的不同位置产生所需的光强分布提供了新的思路,在激光武器、激光加工和激光手术等领域有广阔的应用潜力.     

Transient response optimization of vibrating structures by Liapunov's second method

Liapunov's second method is applied to minimize an integrated square performance measure for damped vibrating structures subjected to initial excitation. The method reduces the calculation of the performance measure and its derivatives with respect to design parameters to the solution of a set of linear algebraic equations. The computational effectiveness of the method is illustrated by applying it to the classical vibration absorber and to a cantilever beam carrying an absorber at its midpoint.     

Ultrasound-promoted preparation of polyvinyl ferrocene-based electrodes for selective formate separation: Experimental design and optimization

The selective separation of ions is a major technological challenge having far-ranging impacts from product separation in electrochemical production of base chemicals from CO₂ to water purification. In recent years, ion-selective electrochemical systems leveraging redox-materials emerged as an attractive platform based on their reversibility and remarkable ion selectivity. In the present study, we present an ultrasound-intensified fabrication process for polyvinyl ferrocene (PVF)–functionalized electrodes in a carbon nanotube (CNT) matrix for selective electro-adsorption of formate ions. To this end, a response surface methodology involving the Box–Behnken design with three effective independent variables, namely, PVF to CNT ratio, sonication duration, and ultrasonic amplitude was applied to reach the maximum formate adsorption efficiency. The fabricated electrodes were characterized using cyclic voltammetry, X-ray diffraction, Raman spectroscopy, and scanning electron microscopy (SEM). SEM images revealed that an optimized ultrasonic amplitude and sonication time provided remarkable improvements in electrode morphology. Through a sedimentation study, we qualitatively demonstrate that the main optimized conditions improved PVF/CNT dispersion stability, consequently providing the highest number of active surface sites for adsorption and the highest adsorption efficiency. The highest percentage of active electrode surface sites and the maximum adsorption efficiency were 97.8 and 90.7% respectively at a PVF/CNT ratio of 3, ultrasonication time of one hour, and 50% ultrasonic amplitude.