The era of big data has presented new demands for mass data storage, and data storage security is critical to social stability and development. Holographic optical storage has not only become a powerful solution for mass data storage because of its high storage density, fast reading speed, and long storage life, but also provides an effective encryption means to ensure data storage security by utilizing the multi-dimensional modulated characteristics of light. Holographic encrypted optical storage has many advantages, including multiple adjustable parameters, a large key space, and a complex storage state in material. By modulating reference or information light, it can prevent unauthorized users from obtaining data and thus can provide a sufficient guarantee for safe data storage.

Since double-random phase encoding was first used in optical encryption in the early 1990s, holographic encrypted optical storage has developed rapidly. In general, encrypted optical storage can be divided into four categories. First, as shown in Fig. 2, holographic encrypted optical storage can be realized by amplitude modulation. Specific reference and information light encoded with different amplitudes are recorded in the same position of the material. Only the correct amplitude reference light can reconstruct the stored information when reading, whereas the wrong amplitude reference light will reproduce only a portion of the information of multiple data pages and interfere with each other, and thus the correct information will not be obtained. Second, as shown in Fig. 3, holographic encrypted optical storage is realized through phase modulation. Specifically, a random phase plate can be placed on the image plane and Fourier plane of the information light to realize phase encryption. Only by mastering the mask in the optical path can the information be accurately reproduced. Here, the same encryption process can be implemented for reference light. In addition, phase modulation can be extended to the Fresnel and fractional Fourier transform domains to increase the security of the encryption system. Third, as shown in Fig. 4, holographic encrypted optical storage can be achieved through polarization modulation. The polarization data page is used to represent the original data, and the polarization state modulation is performed on the polarization data page with the polarization mask to realize polarization encryption. The encrypted polarization information is then stored in the polarization response recording medium. Decryption requires using an inverse polarization mask to reconstruct the original data. Fourth, as shown in Fig. 5, encrypted optical storage can be realized through geometric attitude modulation of the optical path, specifically by changing the location, angle, and other parameters of the mask. To increase the security of encrypted storage systems, simultaneous encryption of multi-dimensional modulation parameters has become a trend and shown great potential.

Holographic encryption optical storage technology implements encryption at the physical storage level and has natural advantages in terms of data encryption. Currently, research on holographic encryption optical storage technology using phase modulation and geometric attitude has achieved fruitful results. However, the research on polarization holographic encryption optical storage and multi-dimensional integrated encryption optical storage technology remains insufficient. In addition, security analyses of holographic encrypted optical storage systems are scarce. Therefore, obtaining methods for reasonably evaluating the performance of holographic encrypted optical storage systems is of great significance.