KEYWORDS: Image filtering, Optical filters, Digital filtering, Composites, Linear filtering, Spatial light modulators, Spatial filters, Phase only filters, Detection and tracking algorithms, Signal to noise ratio
This work evaluates real-time techniques for a novel concept of identifying weeds, location and extraction of outline features. THE proposed techniques are conducted by electro- optical methods and perform with the speed of light. The optical system is compact, easy to align and uses a small number of inexpensive components. Generating the 'right' filter for a pattern recognition problem is presented as an optimization process for which the filter performance is the function to be maximized. The genetic algorithm is introduce as a search procedure that uses a biologically motivated random choice as a tool to guide a highly exploitative search through the filter space for nonlinear correlation. The features of the genetic algorithm are ideal for a highly efficient and fast learning process. Computer simulations demonstrate very efficient pattern recognition and excellent discrimination.
A rotation invariant binary circular filter has been developed for optical pattern recognition. The filter is generated using an iterative numerical optimization method. The optimization is based on the genetic algorithm, which fits very well in optical systems due to its parallel nature. The features of the genetic algorithm provide a highly efficient and rapid learning process. During training, the parameters of a binary circular filter are selected to maximize the distinction between the target and other expected objects in the image. The genetic algorithm is searching through the complete filter space for the global solution, this is the filter with the best performance. These iteratively designed filters are good discriminators because they utilize all the spatial visual information about the target. The design of the rotation invariant filter does not require any a priori information about the target image. The rotation invariant filters are designed as binary circular filters to be suitable for real- time applications, when combined with spatial light modulators.
A new ellipsometric configuration suitable for in-situ studying of fast processes is proposed. This configuration eliminates the use of mechanically the use of mechanically rotating components. The light beam from a Zeeman laser is directed to a sample. The reflected light passes through two subsequent Brewster prisms and a polarizer. The plane of incidence of the first Brewster prism is perpendicular to the sample and to the incidence plane of the second Brewster prism. The intensities of the beams reflected from the prisms are proportional to the amplitudes of s- and p-total reflection coefficients of the sample, and the intensity of the beam transmitted through both the prisms and the polarizer contains information on their phase difference. The light from a Zeeman laser emerges as linearly polarized light whose plane of polarization rotates with the frequency of 1.2 MHz, therefore the signal on the detectors contains DC and AC components. The ellipsometric angle (Psi) is obtained from the ratio of the amplitudes of the AC signals from two detectors, whereas the ellipsometric angle (Delta) is obtained from a third detector. This ellipsometric system is fully automatic and free of any moving parts. The ellipsometer has a time resolution of approximately 1 microsecond(s) ec, and is not sensitive to low frequency noise. Theoretical calculations based on Jones matrix approach are presented as well as experimental results for a SiO2 layer on Si.
Pattern recognition using a coherent optical correlator has many advantages, including high speed operation at almost the speed of light and the implementation of parallel processing. The key part of an optical correlator is the so-called optical filter. Properly designed filter should clearly indicate the presence of desired features in an image to be detected. Therefore,the performance of an optical system relies essentially upon the performance of the filter. Much research have been conducted to improve the performance of optical correlators. Most approaches to the filter design, however, fall short of providing robustness to minute changes in the image. In this paper a new approach to the adaptive design of optical filters, which are both shift- and scale-invariant, is proposed. The filters are constructed in real-time in an optical pattern recognition system by an adaptive, iterative numerical approach. The design is formalized as an optimization procedure, for which the filter performance is the function to be maximized. During the training procedure filter parameters are selected to maximize the distinction between the target and other objects in the image. The latter problem is solved using the genetic algorithm. Filters obtained in this optimization procedure are good discriminators since they utilize all the visual information about the target. Computer simulations demonstrate high discrimination of the designed filters.
KEYWORDS: Gaussian beams, 3D modeling, Sensors, Polarization, Near field, Signal detection, Erbium, Optics manufacturing, Computer simulations, Near field optics
The interaction of a focused laser beam with a step on a conducting surface is investigated by a vector method. The 2-D problem is solved by using a model of fictitious current filaments, while 3-D problems are treated by using a model of fictitious dipoles as the sources of the scattered field. Computer simulations indicate a difference between the two polarization components (TE and TM), but with the samples investigated in this work, these differences are too small for practical measurements. The scattered field distribution is found to be strongly dependent on the step height relative to the observation plane and on its position relative to the beam waist. Thus, measurements of the intensity distribution in the observation plane can provide information about these parameters with high sensitivity. Experimental investigation confirms that the height of a step in the range λ/10 to λ/4 can be measured with an accuracy of 5%, including its sign (up or down). The position of the step with respect to the beam can be estimated with an accuracy of about 1/100 of spot size.
The reading signal of an optical disk relays on phase, amplitude and/or polarization changes induced on a
focused coherent light beam at the written (stored) domain boundaries (data) [1, 2, 3]. The interaction of light
with these storage media are usually treated under the assumption of plane wave illumination since an exact
mathematical analysis of focused beams is quite difficult [4]. In this work we show that very useful results can
be obtained by solving the scalar diffraction integral in the vicinity of a complex step function.
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