Efficient refinement algorithm for the synthesis of inhomogeneous optical coatings

An efficient first-order algorithm with an exact calculation of the gradients is described and applied to the refinement of inhomogeneous dielectric thin films. Numerical results calculated at normal and oblique angles of incidence are correlated with an important mathematical theorem. It is shown that, when appropriate conditions are satisfied, the synthesis process generates binary type solutions based on two materials, including classical multilayers.     

Efficient evolutionary algorithm for the thin-film synthesis of inhomogeneous optical coatings

We propose an efficient evolutionary approach for the thin-film synthesis of inhomogeneous optical coatings. The proposed approach consists of global and local strategies by integration of decreasing-based mutations and self-adaptive mutations by means of family competition and adaptive rules. Numerical results indicate that the proposed approach performs robustly and is competitive with other approaches. Our approach, although somewhat slower, is flexible and can easily be adopted to other application domains. Our approach is also able to generate homogeneous solutions with two materials available.     

Starting designs for the computer optimization of optical coatings

Several generic starting designs are used for the computer optimization of multilayer optical coatings. The first is a stack of many thin layers. Another, which is applicable to the needle-layer optimization method, is at least one thick layer. Examples include the following coatings: antireflection, beam divider, enhanced metallic reflector, dark mirror, and total internal reflection with prescribed differential phase shift.     

Optimum phase for rugate filter synthesis by Fourier transforms

An optimum phase is developed for the synthesis of rugate reflectors by a simple Fourier transform. This phase belongs to a complex function of the desired spectral characteristics and is usually a free parameter. In general, it receives much less attention than the function magnitude, which is not known exactly. The current work shows that phase shaping alone produces surprisingly good results and has other advantages in rugate filter synthesis. In addition, the operating mode of this design procedure is quite unusual and interesting in itself.     

蚁群算法结合微遗传算法优化设计多层雷达吸波涂层

针对多层雷达吸波涂层的结构特点,提出蚁群算法结合微遗传算法的全新优化设计方案.在给定最大厚度的约束条件下,在2～18GHz频率范围内,采用对不同频段给定不同吸收率的方案,对多层雷达吸波涂层进行了优化设计.实验数据表明,该融合算法获得的解比微遗传算法更为精确.这种融合算法为求解类似的组合约束优化问题提供了一种新的方法.     

可靠性优化的一种新的算法

建立了可靠性冗余优化模型,提出了一种基于粒子群优化算法的可靠性优化的新方法,该方法结合了遗传算法的思想。实例结果表明,粒子群算法比模拟退火算法和遗传算法效果好。     

Application of constrained optimization to the design of quasi-rugate optical coatings

The constrained optimization approach is applied to the design of quasi-rugate optical coatings. These coatings are defined as multilayers with no thin layers where refractive index profiles resemble rugate-type refractive index profiles and where spectral properties are typical for rugate filters. It is shown that all design problems that are usually solved using rugate filters can be solved successfully in the frame of quasi-rugate optical coatings. Comparison between quasi-rugate and two-component multilayer designs is provided.     

Application of the needle optimization technique to the design of optical coatings

The authors' experience with the application of the needle optimization technique to the design of optical coating is summarized. A physical interpretation of the technique is provided, and its main features are identified. Guidelines on the application of the needle optimization technique to various types of design problems are given.     

Genetic local search algorithm for optimization design of diffractive optical elements

We propose a genetic local search algorithm (GLSA) for the optimization design of diffractive optical elements (DOE's). This hybrid algorithm incorporates advantages of both genetic algorithm (GA) and local search techniques. It appears better able to locate the global minimum compared with a canonical GA. Sample cases investigated here include the optimization design of binary-phase Dammann gratings, continuous surface-relief grating array generators, and a uniform top-hat focal plane intensity profile generator. Two GLSA's whose incorporated local search techniques are the hill-climbing method and the simulated annealing algorithm are investigated. Numerical experimental results demonstrate that the proposed algorithm is highly efficient and robust. DOE's that have high diffraction efficiency and excellent uniformity can be achieved by use of the algorithm we propose.     

Time-dependent phenomena in plasma-assisted chemical vapor deposition of rugate optical films

The plasma-assisted chemical vapor deposition technique was used to produce thin-film structures with both sinusoidally and stepwise varying refractive-index profiles. The refractive index of the SiO(x)N(y) system used in the fabrication was found to be time dependent following a stepwise change in reactant gas flows or initiation of the plasma. This time dependence has been quantified using in situ ellipsometry and was found to have components with exponential and linear dependences. The time dependence of water vapor partial pressure in the system was identified as the cause of the linear dependence. Allowance for the time-dependent effects has improved the agreement between the calculated spectral response and the measured result for a broadband high-reflectance mirror consisting of an arithmetic progression of discrete layers.     

一种新的星图中星获取算法

提出一种新的星图中星获取算法——极值点法,利用最小二乘向量机(LSSVM)对原始星图的局部区域作灰度曲面最佳拟合,在拟合曲面上求解灰度极大值的像素点,获得星的中心点的初步位置。以初步位置为基础的星图像素聚类加速了星图中星的获取过程。以模拟星图中星的精确中心位置为参考,计算在不同噪声条件下测量位置与最近参考位置的距离平方倒数和的均值,优化 LSSVM 参数。为获得最佳星获取性能,卷积核为5×5像素的高斯LSSVM参数(σ2, γ)取(17,1.25)。该极值点法与矢量法相比,效率相当,但性能更好。     

Ion-beam etching for the precise manufacture of optical coatings

We propose using ion-beam etching as an additional tool for the accurate control of the thickness of thin films during the manufacture of sensitive optical multilayer coatings. We use a dual ion-beam sputtering system in the deposition and etch modes. In the deposition mode both the assist and sputtering ion beams are used to produce dense films at deposition rates in the range of 0.1-0.3 nm/s. In the etch mode, only the assist ion beam is used to remove material at a rate of less than 0.1 nm/s. A very high precision in the layer thicknesses can be obtained by alternating between deposition and etch modes. We observed that etching did not significantly affect the surface quality and the uniformity of the coatings. We introduced etching into our current manufacturing process and demonstrated its potential for the fabrication of several optical multilayer systems with performances that are very sensitive to the thickness of their layers.     

OpenFilters: open-source software for the design, optimization, and synthesis of optical filters

The design of optical filters relies on powerful computer-assisted methods. Many of these methods are provided by commercial programs, but, in order to adapt and improve them, or to develop new methods, one needs to create his own software. To help people interested in such a process, we decided to release our in-house software, called OpenFilters, under the GNU General Public License, an open-source license. It is programmed in Python and C++, and the graphical user interface is implemented with wxPython. It allows creation of multilayer and graded-index filters and calculation of reflection, transmission, absorption, phase, group delay, group delay dispersion, color, ellipsometric variables, admittance diagram, circle diagram, electric field distribution, and generation of reflection, transmission, and ellipsometric monitoring curves. It also provides the refinement, needle, step, and Fourier transform methods.     

Comparison of algorithms used for optical characterization of multilayer optical coatings

Two algorithms used for the on-line and off-line characterization of multilayer optical coatings are experimentally compared using test samples produced by two different deposition processes and different monitoring approaches. One of these algorithms, called the triangular algorithm, demonstrates its superiority in all considered situations. We performed experiments with multilayer samples formed by high-density thin films, which allowed us to neglect possible errors in the film refractive indices and concentrate only on errors in the thicknesses of the layers of the produced coatings.     

Hard UV-curable organo-mineral coatings for optical applications

Organically-modified silicate incorporating various amounts of zirconium precursor was synthesized via a sol-gel route. The material was deposited as thin films on PMMA substrates and densified by UV-curing. Mechanical properties were measured by nanoindentation and data were recorded continuously as a function of the penetration depth during the loading-unloading cycles. Values of hardness and Young modulus were found in the range 340-440 MPa and 4-6 GPa, respectively. It was shown that these values could be tailored by varying the relative amount of zirconium in the layer. The material exhibited a very elastic behaviour that was related to its high degree of cross-linking assessed by infrared spectroscopy. Results were compared with measurements published by various groups on related materials. The mechanical and optical properties of the samples made this class of materials promising as hard coatings for optical applications.