In this paper, we present a printed circuit board (PCB) inspection system based on using Hausdorff distance for image alignment and defect detection. In addition, we apply support vector machine (SVM) for the defect classification and the metal classification in this system. The three major components in the proposed PCB inspection system consist of image alignment, defect detection, and defect classification. In image alignment, a coarse-to-fine search technique is applied to accelerate the speed of finding the minimal Hausdorff distance between the reference and the inspection images. For defect detection, we calculate the Hausdorff distance of every pixel in the inspection image as the first step and compare the result with a predefined threshold. For the cases where the computed Hausdorff distance is greater than the threshold, the location of that pixel is labeled as a defect suspect. The existence of defect then can be confirmed by merging the nearby suspects into one object. For defect classification, the local image features are extracted and passed to support vector machine for training and identifying defect types. In this work, we focus on distinguishing the type of a defect as one of open, short, pinhole, over-etch, or under-etch types. Support vector machine can be applied to metal classification as well. At the current stage, we supply support vector machine with RGB color information as the feature vector for metal classification. Experimental results show that the Hausdorff distance based method detects defects in a printed circuit board efficiently and accurately, and the support vector machine approach also gives satisfactory results for both defect and metal classifications.
This study presents a novel high-efficiency electro-optic (EO) light modulator whose operation is based on the attenuated total reflection effect, in which the surface plasmon wave is excited by an incident waveguide light wave. The EO light modulator is fabricated using a nonlinear optical polymer material that is a side-chain EO polyimide with 2-[N-ethyl-4-(tricyanovinyl)anilino]ethanol chromophore. The modulator is characterized, and its performance tested, in terms of the thickness and dielectric constant of the polymer thin film, the EO coefficient, the insertion loss, and the modulation index. Additionally, the dynamic response of the EO light modulator is fully investigated and discussed.
In this research, experiments and optical simulations have been carried out to study the effect of bevelled sidewalls and geometric shapes on the light extraction efficiency of GaN LED chips. Besides the conventional rectangular chips, hexagonal LED chips were experimentally processed for the fist time on a novel island-like GaN substrate. The bevelled sidewalls could be naturally formed on the chips during the growth of GaN islands by HVPE technology. The results of simulations and experiments are consistent with each other, and show that the output power of LED will be improved doubly when the sidewalls were beveled on the chip. The light output from hexagonal LED chips is also proved better than that from conventional rectangular chips.
A novel high efficiency electro-optic polymer light modulator based on waveguide-coupled surface plasmon resonance (WCSPR) is presented. The modulator consists of a five-layer system: dielectric layer/metal film/electro-optic (E-O) polymer layer/metal film/air. By combining WCSPR based on attenuated total reflection (ATR) method and Pockels effect from poled E-O polymer, we demonstrate that this kind of modulator operated with less applying modulation voltage, less optical insertion loss, and easy alignment compared to other light modulation techniques. Also, in this paper the theoretical derivation of WCSPR, the optimum design concerning the relation between the efficiency of modulator and E-O layer thickness, and the fabrication process of the E-O polymer light modulator are presented. This modulator is shown to allow a greater degree of modulation for a given voltage with working point chosen near the midst of WCSPR mode in the visible range.