A novel amplitude-modulated phase-only filter (AMPOF) is proposed for achieving improved correlation discrimination. The proposed AMPOF has an amplitude spectrum which is the inverse of a biased amplitude spectrum of the object function and a phase spectrum which is a complex conjugate of the phase spectrum of the object function. When compared with the phase-only filters, the AMPOF is found to have significantly superior correlation discrimination capability.
Amplitude information, if properly incorporated along with the phase, can be utilized to improve the discrimination efficiency. In this work, we introduce a novel amplitude modulated phase-only filter (AMPOF) that effectively utilizes both amplitude and phase information and, at the same time, avoids the operational difficulty of the inverse filters. To counter excessive energy absorption and, at the same time, to achieve a significantly uniform filter plane spectrum, one can formulate an AMPOF characterized by D{exp[−jϕ(u, v)]}/[|F(u, v)| + a], where 0 < D ⩽ 1 and a> D, and F(u, v) is the object spectrum with phase ϕ(u, v). Parameter a is useful in (i) overcoming the indeterminate condition, (ii) ensuring that the gain is less than unity, and (iii) suppressing noise or bandlimit the filter or both. To discriminate between the object and the filter, the correlation peak energy is normalized with respect to the total output energy. An AMPOF based correlator produces autocorrelation peaks, narrower as well as larger than those of the POF based correlator. Furthermore, it provides a larger value for the ratio of auto- and crosscorrelation powers. A computer-controlled LCTV and MOSLM can be used to store the appropriate filter. A binary AMPOF amplitude mask can be designed using a scheme1 used for fabricating a binary inverse Gaussian filter.
Several different approaches exist for obtaining a circularly uniform laser beam. The scope of most of these approaches is limited because, while some of these waste much of the input power, the other methods waste the spatial coherency of the beam during the process of conversion. We present the design of refracting beam-transforming systems1 which are not only easy to fabricate but are also highly efficient. The design considerations used in the design process ensure that the spatial and temporal coherency of the to-be-processed laser beam are preserved by the optical system. While one of the systems is designed to convert an annular Gaussian input beam into an equivalent circularly uniform beam, the other system converts a circularly Gaussian input beam into equivalent circularly uniform beams. The proposed systems are compared to the other existing designs in terms of performance efficiency and ease of fabrication.
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