High-speed AlGaInAs multiple-quantum-well (MQW) electroabsorption modulated lasers (EMLs) based on identical epitaxial layer (IEL) integration scheme are developed for 40 Gb/s optical fiber communication systems. The electroabsorption modulator (EAM) section adopts a narrow high-mesa waveguide formed by inductively coupled plasma (ICP) dry etching technique, and a self-aligned planarization technique is employed to further reduce the device capacitance. Resonances are observed in the small signal modulation response of the packaged EML module, which are attributed to parallel-plate modes of the coplanar waveguide (CPW) transmission line used for modulation signal feeding and the residual reflection at the modulator facet, respectively. The influence of such resonances on the large signal eyediagram performance of the device is studied, and methods for their suppression are presented. Clear eye opening under 40 Gb/s non-return-to-zero (NRZ) modulation has been demonstrated for the optimized EML module.
We propose a novel automatic seeded region growing method based on gradient vector flow (GVF) for color image segmentation. YCbCr color space is selected to avoid the high correlation of RGB color space. First, a GVF field is constructed from an edge map of the input image. Then a scaler force field is derived from it by minimizing an energy functional iteratively. From the scalar field, we can select a set of seeds and get an initial segmentation via a straightforward downstream process. Finally, a region adjacency graph–based region merging is applied to merge similar neighboring regions into true results. Experimental results demonstrate that this method is insensitive to noises and efficient to multiple objects segmentation in color images.
Setting of initial contours is a critical problem of active contour models. Although gradient vector flow (GVF) has simplified them greatly compared to the traditional snake, additional work is still necessary. We propose a specific setting method based on vector field analysis. Some critical points in the force field are used to estimate curve deformation. These points seem like sources whose neighbor vectors emanate from them, therefore they can be regarded as inflated centers of deformable contours in GVF snakes. The proposed method detects these points and sets initial contours to contain all the ones in the object area and none of the others. It can prevent the contours from stabilizing on false boundaries in homogeneous regions or real boundaries of other objects. Several experimental results demonstrate that this method is robust and effective.
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