Computer generated hologram of asymmetry fractional Fourier transform

A new optical encryption technique based on computer-generated hologram (CGH) and fractional Fourier transform (FRT) is presented. And the algorithm of making asymmetry FRT CGH is provided in this paper. In this method, the fractional Fourier transform of the input image is performed by two one-dimensional FRT with different orders in the x and y directions in cascade. With Lohmann III detour phase encoding method and computer plotting program, the transformed image is encoded and fabricated into CGH on the computer. Then a piece of asymmetry fractional Fourier transform CGH (AFRTCGR) of original input image is obtained. In order to reconstruct the encoded image, a special fractional Fourier transform systems with two special cylinder lens' are needed. Namely, only when the transform order in each direction is respectively matched with that of the asymmetry fractional Fourier transform CGH, can the encoded image be reconstructed exactly. Because of its particularity of image reconstruction, it is regarded as a new optical security system and can be used in anti-counterfeiting. When it is used to encrypt image or to anti-Counterfeit, anticounterfeiting intensity can be improved greatly. So it has very high applying value.