Implementing Optical Wavelet Filter By Grating

Wavelet transform can be used to analyze local signal or transient process. The new technique have conquered the disadvantage of Fourier analysis, which can effectively extract information from optical images or signals, and do multiscale analyzing through flexing and shifting.Wavelet transform is implemented in optical system through spatial filter in frequency domain, which is called optical wavelet transform. There are two advantages in using optical wavelet transform: parallelism and high speed real time. However, the error between input image and out put image is major concern for people, which is relevant to the chosen system and filter in the system.Placing filter on the Fourier plane in an optical 4f system is a usual way to implement optical wavelet transform. Film, holograph and grating can be used as the filter. Because the relationship between the grating parameters and the value of the wavelet spectrum is hard to get, people used film and holograph as the filter in the past, which could get a low precision. This thesis is supported by Nation Natural Science Fund item (No.60472037). In this article, we will talk about using grating as the filter to implement optical wavelet transform.In this thesis, the relationship between the grating parameters and the value of the wavelet spectrum is calculated firstly. Then the conclusion and analyzing error are emulated. Finally, the factors that affect the grating precision are discussed.Because the relationship is calculated through diffraction efficiency of the grating, firstly, vector and scalar quantity method are used to calculate diffraction efficiency respectively. Then the approximately equal conditions are analyzed. Finally, the relationship is obtained, and the relationship between the plane transmission grating parameters and the value of Mexico-hat wavelet is acquired.From the emulation results, we can conclude the quality of the output image is worse than input image, which is related with flex factor of wavelet. The smaller flex factor is, the better quality is. Comparing the best output image and the input image, we see that the figure of the output image is unchanged, however the difference with the input image can be distinguished for human eye. The disfigurement of grating from producing will affect the quality of the output image, too. Several factors are discussed in the article. This thesis discusses about using grating as filter to implement optical wavelet...