We show how to tailor the depth of focus for an optical system using pupil functions obtained from a Fourier transform approach. These complex amplitude and phase pupil functions are encoded onto a single liquidcrystal spatial light modulator. Experimental results show excellent agreement with theory and indicate the power of this approach.
Fu ll in -situ c h arac te r iz ation of spatial ligh t m od u lators in an optic al c orre lator. Filte r ad aptation to ope ratin g c u rv e s Abs trac t.In this paper we present one method for the characterization of the spatial light modulators (SLMs) of a real-time Vander Lugt type of correlator. This correlator uses two SLMs: one to introduce the scene and a second to introduce the frequency-matched ® lter. The SLM characterization methods are in situ, that is in the correlator set-up. Illumination conditions are di erent for each SLM, and consequently di erent characterization techniques must be used in each case. For the characterization of the scene SLM a di raction method is used, while for the characterization of the ® lter SLM an interferometric technique is more convenient. Finally, we take into account the operating curves of scene and ® lter SLMs in the design of the ® lter in order to optimize the correlation peak.
In this paper we present some results on the research line of real-time correlation applied to optical pattern recognition. We present a real time optical correlator that uses two twisted nematic liquid crystal spatial light modulators (SLM). This kind of SLM produces phase and amplitude coupled modulation. Phase modulation is useful for the implementation of phase only filters (POF), but the coupled amplitude modulation affects its performance. We present a model to evaluate the response of the phase-only filter (POF) implemented on a modulator with a restricted modulation and we show results on the optimal implementation of POF on this restricted coding domain. The phase modulation is also used for the implementation of the scene by means of a phase-encoding algorithm. The performance of the phase-only filter has been improved for several performance criteria by the design of binary amplitude masks. We present a technique for the implementation of these optimized binary amplitude phase-only filters (BAPOF) using phase-mostly SLMs. Results obtained for the optimization of different criteria are presented. Finally, we present results on the application of these methods to color pattern recognition problems by a multichannel correlation.
In this paper we present one method for the characterization of the spatial light modulators (SLMs) of a real-time Vander Lugt type of correlator. This correlator uses two SLMs: one to introduce the scene and a second to introduce the frequency-matched filter. T h e S L M characterization methods are in situ, that is in the correlator set-up. Illumination conditions are different for each SLM, and consequently different characterization techniques must be used in each case. For the characterization of the scene S L M a diffraction method is used, while for the characterization of the filter S L M an interferometric technique is more convenient. Finally, we take into account the operating curves of scene and filter SLMs in the design of the filter in order to optimize the correlation peak.
We propose an input-image preprocessing method consisting of homogenization of the image to improve the discrimination capability of a correlation-based recognition process. This method is an approximation of the optimal filter. It offers the advantage that correlation with the preprocessed images can easily be implemented in an optical correlator working with phase-only spatial light modulators.
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