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1 Introduction FRT(FractionalFourierTransform )wasfirstlyintroducedbyNamiasin 1 980asamathematictoolinquantummechanics[1] .In1 993,MendlovicandOzaktasimplementedtheFRTatopticalfieldwhentheystudiedgradientindex (GRIN )fiber[2 ] andappliedthepuremathematicformulatio… 相似文献
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Rahul Bhatt Sanjay K. Mishra D. Mohan A.K. Gupta 《Optics and Lasers in Engineering》2008,46(6):428-439
A fast holographic wavefront sensor is proposed using a computer-generated hologram (CGH). This CGH is a multiplexed hologram of different Zernike mode–amplitude combinations, and is designed in such a manner as to get the corresponding spots on the detector according to the presence and strength of a particular aberration. Interference between the aberrated wavefront (with a single mode–amplitude combination) and the Fourier transform of an image with single bright pixel (defined as dot image) is numerically calculated for one hologram. Different mode–amplitude combination and corresponding different positions of bright pixels (dots) are taken to compute various holograms and then all the holograms are multiplexed to get the final hologram. When the aberrated wavefront with a particular mode–amplitude combination is incident onto the multiplexed hologram, the corresponding dot is generated in the Fourier plane. A lens performs the Fourier transform in optical domain and provides the instant detection of amplitude of the respective Zernike mode. The main advantage of the scheme is to avoid the need of any computations, which makes it really fast. The simulation results are presented with the cross-talk analysis for few Zernike terms. 相似文献
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This paper describes a simple method for making dual beam encoded extended fractional Fourier transform (EFRT) security holograms.
The hologram possesses different stages of encoding so that security features are concealed and remain invisible to the counterfeiter.
These concealed and encoded anticounterfeit security features in the security hologram can only be read through a key hologram.
Key hologram also facilitates in-built repositioning of security hologram. The method of fabrication, the principle of reconstruction
and the experimental results are presented.
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分数傅里叶变换计算全息 总被引:1,自引:0,他引:1
在计算全息和分数傅里叶变换的基础上提出了不对称分数傅里叶变换计算全息和双随机相位不对称分数傅里叶变换计算全息。在这种方法中,首先用一随机相位函数乘以输入图像信息,然后沿x方向实施α级次的一维分数傅里叶变换,再乘以第二个随机相位函数,最后,沿y方向实施β级次的一维分数傅里叶变换。采用迂回位相编码法对变换后的结果编码,绘出计算全息图。为了恢复原始图像,需要知道变换级次和随机相位函数。利用这种方法进行图像加密,使加密图像的密钥由原来两重增加到四重,从而提高了系统的保密性能。 相似文献
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Kenji Nagashima 《Optics & Laser Technology》2001,33(5)
Improvement of images reconstructed from 3D computer-generated holograms using 1D Fourier transform operations is presented. Required computing time for making 3D holograms is decreased when 1D Fourier transform method is used instead of 2D Fourier transform method, but reconstructed images from the holograms created by the 1D Fourier transform method are somewhat inferior in quality to the images by 2D Fourier transform method. In this paper, we propose a method that the disadvantageous properties of the holograms made by 1D Fourier transform are improved. We have performed two step improvements in this experiment. From the numerical experiments, the images that are reconstructed from the holograms created from 1D Fourier transform method show marked improvement. 相似文献