We present a denoising method based on wavelets and generalized cross validation and apply these methods to image denoising. We describe the method of modified wavelet reconstruction and show that the related shrinkage parameter vector can be chosen without prior knowledge of the noise variance by using the method of generalized cross validation. By doing so, we obtain an estimate of the shrinkage parameter vector and, hence, the image, which is very close to the best achievable mean-squared error result--that given by complete knowledge of the underlying clean image.
We investigate the oscillation characteristics of active modulated periodic slabs such as those used for distributed feedback (DFB) lasers. In particular, we examine the effect of modulation wave number on the threshold gain and oscillation frequency of these structures by employing the vector coupled-mode approximation. Significant changes in threshold gain are found for large modulation indices and moderate couplings as compared to the unmodulated case. Small changes in the oscillation frequency are also noted. Methods for lowering threshold gain are suggested.
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