We propose a multiwaveguide cavity which can significantly enlarge the mode volume of distributed feedback (DFB) cavity without increasing the cavity length. The cavity is constructed by combining λ/4 shifted DFB cavity with contra-directional couplers. Different from single-waveguide DFB cavity, the resonant mode is oscillating in multiple waveguides. A smaller threshold gain density is also obtained compared to single-waveguide DFB cavity. Theory model of the multiwaveguide cavity is established and finite-difference time-domain simulation is performed to verify the model.
Wide line detection plays an important role in image analysis and computer vision. However, most of the existing algorithms focus on the extraction of the line positions and length, ignoring line thickness and direction which can deepen our understanding of images. This paper presents a novel wide line detector using the ridge distribution feature and layer growth method. Unlike most existing edge and line detectors which use directional derivatives, our proposed method extracts the ridge target point and use the layer growth to find the line completely based on the isotropic nonlinear filter. Ridge points are detected by its distribution symmetry based on the isotropic responses via circular masks and orientation of the ridge is determined roughly. The ridge point is selected as a seed point, then growth layer by layer, to determine the width and orientation of the curvilinear structure accurately. Instead of point by point scanning, we label points in the growth region and adjust the scanning step adaptively which improve the method efficiently. The proposed method can detect the accurate width and direction of lines dynamically. This can provide great convenience for post-processing or for application requirements. A sequence of tests on a variety of image samples demonstrates that the proposed method outperforms state-of-the-art methods.
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