Abstract. Some image encryption systems based on modified double random phase encoding and joint transform correlator architecture produce low quality decrypted images and are vulnerable to a variety of attacks. In this work, we analyse the algorithm of some reported methods that optically implement the double random phase encryption in a joint transform correlator. We show that it is possible to significantly improve the quality of the decrypted image by introducing a simple nonlinear operation in the encrypted function that contains the joint power spectrum. This nonlinearity also makes the system more resistant to chosen-plaintext attacks. We additionally explore the system resistance against this type of attacks when a variety of probability density functions are used to generate the two random phase masks of the encryption-decryption process. Numerical results are presented and discussed.
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We describe a first-and-second-diffractive-order intraocular lens ((1,2)DIOL) within the class of hybrid refractive-diffractive designs for intraocular lenses (IOLs) and analyse its properties of focus extension and compensation of longitudinal chromatic aberration (LCA), particularly for lenses with low addition. Power, energy efficiency and their wavelength dependence are extended from monofocal IOL and conventional bifocal zeroth-and-first-diffractive-order IOL ((0,1)DIOL) to (1,2)DIOL of low addition. Compensation of LCA is experimentally assessed in optical bench through the through-focus energy efficiency of three Tecnis IOLs with red, green and blue illuminations: ZA9003 (monofocal), ZKB00 (bifocal (0,1)DIOL with + 2.75 D add) and Symfony ZXR00. We prove Tecnis Symfony ZXR00 IOL can be considered an example of (1,2)DIOL design of low addition, with LCA compensation in both the distance and intermediate foci, whereas the bifocal (0,1)DIOL does not compensate in the distance focus. However, the energy efficiency of (1,2)DIOL for wavelengths other than the design wavelength is markedly more asymmetric.
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