Optical Image Self-convolution And Rotation Manipulation

Pattern recognition is of great value in application to biological imaging,infrared detection and so on.Using digital imaging processing,we can realize the pattern recognition and the feature extraction by computers.However this method has poor performance on objects with a large number of calculation and less obvious feature,such as transparent phase objects.Optical method with advantages of real time and parallel processing play a significant role in imaging process.In recent years,commercial spatial light modulator(SLM)which can improve the efficiency of correlation recognition greatly is developing rapidly and used to produce various types of phase screens to complete spatial filter.Based on SLM,the aim of pattern recognition technology expands from recognizing the existence of target object to extracting the feature and information carried by images.However,previous works all force on the recognition of intensity objects and pay less attention on complex amplitude objects(objects with intensity and phase distribution simultaneously).In this paper,we obtain self-convolution of intensity images and complex amplitude images by second harmonic generation(SHG)happening in frequency domain.In this process,a nonlinear crystal(PPLN)is placed on Fourier plane of 4f system to realize SHG of frequency spectrum of images.Based on intensity and phase modulation,we prepare intensity clovers and clovers with complex amplitude by SLM.Comparing the experimental convolution results of clovers with different phase distribution,we find that the power of self-convolution peak depends on the extent of conjugate symmetry of complex amplitude images,and hence proving that our setup can be used to detect conjugate symmetry.We also demonstrate that optical images can be processed in real time with programmable SLM.In addition,this scheme will find potential in infrared remote sensing.As a light modulation device,the spatial light modulator is widely used to produce orbital angular momentum(OAM)beams which is applied in optical communication,optical information process,quantum optics and so on for its special phase structure.The technique of digital spiral imaging(DSI)relies on the theory that eigenstates of OAM form a complete orthogonal basis,therefore any optical images can be decomposed into a superposition of these bases.In our paper,using SLM,the images can be rotated and reflected by modulating the phase spectrum of Laguerre-Gaussian(LG)modes which are eigenstates of OAM based on DSI.The scheme presented in this work may find potential applications in optical pattern process,optical remote sensing and so on.