Many advanced local and global optimisation techniques, such as Gradient, Simplex, Flip-flop, Needle, Genetic and Simulated annealing, have been successfully applied to optical thin-film design. Any optimisation algorithm applied to a particulardesign problem should firstly address the issue of choosing a reasonable starting design, which is always a big obstacle to an inexperienced designer. To find the true global optimised solution for a thin film design problem, we need to solve an array ofinterlinked multi-dimensional simultaneous equations. For more than just a few layers, until recently this has been a very difficult task, requiring the use of a supercomputer and highly skilled programming. By using orthogonal Latin Square theory and anexperimental design methodology into a search space reduction process, a Windows based program has been written that can operate on even a desktop personal computer. It can find the global optimum design for 23 layers design using any dispersive and lossy material within a period of several hours. Additionally this methodology (DGL-Optimisation, DGL is the short for D.G. Li) allows the use of target spectra such as s & p polarisation, with reflection and transmission simultaneously.
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