Research On Orbital Angular Momentum Holography Based On Bessel Gaussian Beam

Holography is a three-dimensional imaging technology based on the principles of interference and diffraction to record and reproduce the real objects.It can simultaneously reconstruct the phase information and the intensity information,so that has broad application prospects.Holography has important applications in fields such as three-dimensional display,image encryption and data storage.In recent years,orbital angular momentum(OAM)has been used as the information carrier in holography due to its high dimensionality and orthogonality,resulting in the ultra-wideband orbital angular momentum holography,named OAM holography.In this thesis,OAM holographic encryption technology based on Bessel Gaussian beam and OAM holographic watermarking technology based on Bessel Gaussian beam are studied.The main work and results are as follows:(1)An OAM holographic method based on Bessel-Gaussian beam is proposed,named BG-OAM holography.The existing design of OAM hologram is constrained by the selected OAM helical mode index,which leads to the cross-talk of different OAM modes at different sampling distances,that is,the larger the helical mode index is,the larger the sampling distance is.In order to overcome this problem,the OAM hologram based on Bessel-Gaussian beam is proposed in the thesis,named BGOAM holography.The Fourier transform of the Bessel-Gaussian beam is the perfect vortex mode with the fixed ring radius for different OAM mode,which can reduce the crosstalk on OAM multiplexing holography.In addition,due to the non-diffraction property of Bessel-Gaussian beam,BG-OAM holography can heal itself when encountering obstacles in the propagation process,which can improve the quality of holographic image reconstruction.The simulation and experimental results show that the scheme is feasible.On this basis,the application of BG-OAM holography in information encryption is considered.The results show that,compared with the OAM holography based on Laguerre-Gaussian beam(named LG-OAM holography),which only uses the degree of freedom of topological charge,this scheme uses more freedom of axial parameters of Bessel Gaussian beam,which improves the security of multiplexing holography.And by adding obstacles in the way of propagation,it also verifies that the restoration effect of this scheme is better under the same propagation distance.(2)An OAM holographic watermarking method is then proposed based on BG-OAM holography.The watermark system is divided into three stages: watermark preprocessing,watermark embedding,and watermark recovery.Firstly,OAM holography can be combined with Arnold scrambling for watermark preprocessing to improve the security of the watermark.Then,the watermark is embedded using discrete wavelet transform and singular value decomposition algorithm to demonstrate the imperceptibility of the watermark.Finally,the watermark is restored using the inverse transformation of the first two stages.In this thesis,a holographic watermarking scheme based on LG-OAM holography is realized by using the degree of freedom of the topological charge and a holographic watermarking scheme based on BG-OAM holography is realized by using the two degrees of freedom,the topological charge and the axial parameters.The simulation results indicate that the proposed watermarking scheme is feasible.Meanwhile,due to the use of OAM for holographic watermark design,multiple watermark images can be embedded into the same host image.The holographic watermarking scheme based on BG-OAM holography has higher security.In addition,the attacks,such as JPEG compression attack,noise attack and geometric attack are testified for the proposed watermarking scheme.The results show that the LG-OAM holographic watermarking scheme shows good robustness and can recover the original watermark pattern,while the BG-OAM holographic watermarking scheme is less robust to the geometric attacks.