红外与激光工程

High capacity optical information encryption technology based on OAM holography and frequency shift

Zheng Wei, Zhang Di, Yuan Hao, Yu Nana, Xi Sixing, Wang Guilin, Ma Shuai, Wang Xiaolei, Lang Liying

2023, 52(7): 20230313. doi: 10.3788/IRLA20230313

[Abstract](131) [FullText HTML] (29) [PDF 3304KB](40)

Objective In order to improve the capacity and security of the optical encryption system, a new method based on OAM holography and frequency shift is proposed. Methods Since the orbital angular momentum eigenstates mathematically constitute a complete set of orthogonal basis vectors, the orbital angular momentum can be used to realize the encoding of multiple image information. This approach achieves parallel encryption of multiple images information using Fourier transform frequency-shift and OAM holography techniques, which eliminates the crosstalk between multiple image information. Firstly, several original images information are sampled, and the sampling constants is determined by the spatial frequency of the helical phase with different helical mode indexes, which is defined as the pixel width corresponding to 30% of the maximum amplitude modulus (Fig.3). Through this process, we obtained multiple different sampled images. The orbital angular momentum-preserving holograms are then generated by the coherent superposition of multiple sampled image information modulated by random phase, Fourier transform and frequency shift phase (Fig.4). Finally, the helical phases of different helical mode indexes are encoded into two orbital angular momentum preserving holograms, and two OAM selective holograms are obtained, they are superposed coherently to form the final OAM composite selected hologram (Fig.5). In decrypted process, the orbital angular momentum compound choice hologram is loaded onto the spatial light modulator, which is illuminated by a vortex beam containing a specific helical mode index and passes through a Fourier lens, a receiving device on the rear focal plane of the lens can receive a plurality of decrypted images (Fig.6). Results and Discussions Compared with other multi-image encryption algorithms, the proposed method can encrypt multiple image information of different sizes and types into a single hologram through two encryption processes, and no original information is displayed in the ciphertext image. The correlation of ciphertext image information in all directions is very low, which effectively reduces the statistical characteristics of highly correlated original image information, and can effectively resist statistical attacks based on pixel correlation, with high security (Tab.1, Tab.2). This encryption system has high encryption flexibility and great capacity. It can not only design different frequency shift factors to encrypt a group of multiple images information in parallel under the same helical mode index, but also has the advantages of high encryption flexibility and high encryption capacity, several groups of image information can also be encrypted by using different helical mode index. Conclusions In this method, the infinite OAM mode of the vortex beam are set as a new optical key, which greatly improves the security of the encryption system. In addition, due to the frequency-shift phase modulation, the size of the image to be encrypted is not limited by the number of pixels in the Spatial light modulator, which greatly improves the feasibility and effectiveness of optical realization of information encryption. The simulation results show that the proposed method has high safety, anti-noise and anti-shear capability (Fig.11, Fig.12).

Compressive sensing tomographic reconstruction of non-amplifying in-line hologram based on variable density downsampling in frequency domain

Wu Xiaoyan, Yu Yingjie, Bai Yuewei, Nie Li, Liu Kai, Pan Fangyu, Wang Xiaogang

2020, 49(S1): 20190500. doi: 10.3788/IRLA20190500

[Abstract](413) [PDF 2221KB](11)

A frequency-domain variable density downsampling method was applied to the reconstruction of compressive sensing tomography for non-amplifying in-line hologram. The purpose was to extract a small amount of information from the frequency-domain of non-amplifying in-line hologram and realize the reconstruction of compressed sensing tomography from a small amount of data in the frequency-domain of the hologram. Here, firstly it introduced the principle of combining three variable density downsampling with compressive sensing tomography reconstruction of hologram. Three kinds of variable density downsampling respectively were radial distribution, spiral distribution and exponential distribution variable density downsampling. Secondly, it carried out simulation and test experiments and analyzed the reconstruction quality of the methods for variable density downsampling combined with compressive holography. By experiments, it could be seen that:(1) three kinds of variable density downsampling could realize the extraction of a small amount of data for hologram in the frequency domain; (2) with the increase of sampling rate, the compression sensing tomography reconstruction quality of a small amount of data obtained by variable density reduction sampling was continuously improved; (3) under the sampling rate of less than 50%, exponential distribution downsampling had higher reconstruction quality than the other two methods (for example, in the case of low downsampling rate of 15%, the reconstruction quality of exponential distribution was more obvious than the other two methods); (4) under the sampling rate of more than 50%, the tomographic reconstruction quality of the three downsampling modes was relatively high and basically consistent.

Research on incoherent self-interference digital holography imaging technology

Zhang Minmin, Tian Zhenyun, Xiong Yuankang, Ma Fengying, Gong Qiaoxia, Pan Zhifeng, Du Yanli

2019, 48(12): 1224001. doi: 10.3788/IRLA201948.1224001

[Abstract](889) [PDF 2370KB](43)

An incoherent self-interference digital holography imaging system based on Michelson interferometer was reported. The system recorded the holograms of USAF1951 resolution target, onion epidermal cell and herbaceous stem crosscut. Reconstructing the captured hologram by three-step generalized phase shift can effectively eliminate zero-order images and twin images, and obtain a high resolution reconstructed image. The element three in group nine on the USAF1951 resolution target can be clearly seen, with a resolution of 645 lp/mm. The effect of diffraction distance on the quality of reconstructed image was studied by analyzing the relationship between them. Moreover, a 3D image of the object can be obtained by this system through reconstruction of the hair hologram.

Holography

NewsMore

Special IssueMore

DownloadMore

Main ColumnMore

LinksMore