Study Of Measuring Grating Parameters With Transmission Spectrum And Design Of Perfect Anti-reflection Coating

Present, there are two method to measure the grating parameters, among which are the direct method and the indirect method. But equipments the former use are expensive and the technique demand is high, at the same time, generally certain equipment only can measure one parameter, and what's more the elements measured are often destroyed. With the development of the optimization algorithm, people pay more attention on indirect method and measuring grating parameters with ellipsometry has been brought bout in theory, but because the ellipsometry is so sensitive to the grating parameters that report about it's test conditions hasn't been seen. The measure to transmission spectrum is simple stable and precise, at the same time, determining grating parameters with transmission spectrum have achieved preliminary success. This method gain and settle data with computer, and record the spectrum of the gratings at the same time, which not only improvethe accuracy of the data, but also save the labor of the operator. In addition it has the virtue of no destroy no perturbation and easily promote.Anti-reflection Coating are mostly used to reduce absorbing and scatting of the light. Presently there are mainly single layer AR coating and multiplayer AR coating, and sub-wave grating as well, but their fabrications is complex, and opt to limited wave light and incidence angle, which impose restrictions on their use. Base on effective medium theory, the design to wide incident angle range and incident wave light is brought forward, with the structure of two mediums distributed nested.The main contents of the dissertation are: the transmission spectrum is obtained according to certain grating model with the Fourier Model method, based on which the Gaussian noises are added to it to get the simulated measuring value of transmission spectrum. From estimated function, suitable optimization algorithm is selected, and the range of the grating parameters is defined, then the desiring value of the parameters is searched. Further, making using of the symmetric efficiency ration to search the gating parameters is proposed, which reduces spectrum's sensitivity to grating parameters, and achieves the preliminary success. A multiplayer AR coating applied to broad incidence angle and visible light is designed. To make this design practical, then with the effective medium theory, two mediums are distributed nested to form many units and every layer in the multiplayer AR coating can be represented by a unit. Lastly, optimization algorithm is used to improve the efficiency of the designed AR coating.