In this work, arbitrary micro phase-step digital holography with optical interferometry and digital image processing is utilized to obtain information about an image of a three-dimensional object and encrypting keys. Then, a computer-generated hologram is used for the purpose of holographic encryption. All information about the keys is required to perform the decryption, comprising the amplitude and phase distribution of the encrypting key, the distance of image reconstruction, zero-order term elimination, and twin-image term suppression. In addition to using identifiable information on different image planes and linear superposition processing hidden within the encrypted information, not only can we convey an important message, but we can also achieve anticounterfeiting. This approach retains the strictness of traditional holographic encryption and the convenience of digital holographic processing without image distortion. Therefore, this method provides better solutions to earlier methods for the security of the transmission of holographic information.

This paper proposes a novel phase-shifting digital in-line holography with computer-generated holograms (CGHs) to achieve the goal of encryption via multiple-key encoding. Multiple keys will also be required in order to complete the decryption. These keys include the amplitude and the phase distribution of the primary encryption key, the reconstruction distance of the image, and the phase value modulated via micro phaseshifting interferometry. Experiments in this research have proved that the decryption would not be possible without a primary key. The autocorrelation between the original and the decrypted images shows very high similarity.

Digital holographic encryption is an important information security technology. Traditional encryption techniques require the use of keys to encrypt information. If the key is lost, it is difficult to recover information, so new technologies that allow legitimate authorized users to access information are necessary. This study encrypts fingerprints and other data using a deterministic phase-encoded encryption system that uses digital holography (DPDH) and determines whether decryption is possible using a convolutional neural network (CNN) using the U-net model. The U-net is trained using a series of ciphertext-plaintext pairs. The results show that the U-net model decrypts and reconstructs images and that the proposed CNN defeats the encryption system. The corresponding plaintext (fingerprint) is retrieved from the ciphertext without using the key so that the proposed method performs well in terms of decryption. The proposed scheme simplifies the decryption process and can be used for information security risk assessment.

Conventional dark-field digital holographic microscopy (DHM) techniques require the use of specialized optics, and, thus, obtaining dark-field images with high contrast has a high cost. Herein, we propose a DHM system that uses an interference-dark-field technique for improving image contrast. Unlike conventional dark-field DHM, the proposed technique does not require expensive and specialized optical elements, or a complicated optical setup, to obtain dark-field images. The proposed technique employs a pure optical basis method to suppress scattering noise—namely, interference-dark-field—and mainly adopts an arbitrary micro-phase shifting method to achieve destructive interference for obtaining holograms. Under the framework of the proposed technique and through the observation of the USAF 1951 resolution target, the reconstructed image can retain the high contrast of the interference-dark-field DHM. The image contrast is enhanced by at least 43% compared to that which is obtained by conventional dark-field DHM. The resolution of the system can be as high as 0.87 μm. The proposed technique can switch between bright-field and dark-field DHM and prevents damage to the sample, which results from high-intensity illumination in conventional techniques.

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