Bor Wang

Diffraction selectivity of holograms with random phase encoding

We have analyzed the lateral sensitivity of volume holograms based on random phase encoding. The diffraction characteristics are associated with induced two-dimensional destructive interference when the random phase plate, e.g. a ground glass, is laterally shifted. The random phase plate generates the first dimension of destructive interference, and the finite size of the hologram generates the second dimension of destructive interference. The former and the latter are responsible for the random phase multiplexing and the shift multiplexing of holographic storage, respectively. The developed analysis can be used to describe the shifting sensitivity of the hologram based on both random phase multiplexing and shift multiplexing.

Lateral shifting sensitivity of a ground glass for holographic encryption and multiplexing using phase conjugate readout algorithm

An encryption-selectable holographic storage algorithm with use of random phase encoding and angular multiplexing is proposed and demonstrated. The pattern for storage can be encrypted and multiplexed with use of a ground glass, which is also used to decrypt the pattern. A phase conjugation of the reference beam is used to generate phase conjugate waves of the stored patterns. The lateral shifting sensitivity of the ground glass used to decrypt the information is theoretically analyzed and is compared with experimental measurement. The shifting tolerance for various ground glasses under imperfection phase reconstruction in the decryption processing is studied.

Optical security using a random binary phase code in volume holograms

We propose a novel method for optical security by using a randomly selected binary phase code. The phase code is recorded with holographic volume gratings, and the recording material can be regarded as an optical lock, while the original phase code acts as the key. When an arbitrary phase code is used for decryption, the decryption probability is less than 10 210 when the phase code contains only five rows. The decryption probability decreases dramatically as the row number of the code or the threshold value increases. Furthermore, the security system performs good tolerance for data loss of the key. Both the theory and experiment are demonstrated.

Optical identification using a random phase mask

We propose a novel method for optical identification by using a random phase mask. The identification system is based on a holographic correlator used to verify the access phase mask. The random phase function of the mask works as a code for identification. The database is a holographic memory that records the complex amplitude image of the random phase mask through angle multiplexing. The cross talk between different masks is small and the main restriction of the capacity in this system is the dynamic range of the recording material. Both the theory and the experiment are presented.

Diffraction patterns for a transmission volume hologram under Bragg mismatch

We have presented simulations and experiments for 2-dimensional diffraction distributions of a transmission volume hologram. We sample the input pattern with a few elementary points and calculate the diffraction of the corresponding elementary grating. The simulations can describe well the diffraction pattern obtained in the experiment and can be used to predict the tolerance for angular deviation of the reading beam. The tolerance for angular deviation depends on its direction. It is affected by the Bragg degeneracy. The simulation results provide a clear picture of the spatial tolerance for reading a transmission volume hologram.

Optical encryption and holographic multiplexing in a volume hologram based on random phase encoding

In this report, we demonstrate and discuss a holographic storage system, where two holographic multiplexing methods are included: one is angular multiplexing and the other one is random phase multiplexing through a ground glass. The latter is responsible to the optical encryption when the stored pattern needs to be encrypted. We study the tolerance to the displacement of the ground glass in three-dimension. We find that it is a function of both the illumination area of the ground glass and the thickness of the volume hologram.

Encryption-selectable optical storage in LiNbO3

We demonstrate an encryption-selectable holographic multiplexing storage in LiNbO3. The storage of multiple holograms is based on angular multiplexing and random phase encoding. Phase conjugates of the reference beams are used to read out those stored patterns. The sensitivity of the displacement of the ground glass is analyzed theoretically.

Three-dimesional random phase encoding in volume holograms and the applications

Three dimensional shifting sensitivity of volume holograms based on random phase encoding using a ground glass has been theoretically analyzed. There are different shifting tolerances in different shifting directions, which include laterally horizontal, laterally vertical, and longitudinal directions. The shifting sensitivity depends on the diameter of the illumination region on the random phase plate, the thickness of the hologram and the distance between them. We apply the theoretical calculation to a degeneracy condition, a point object, and theoretically analyze the shifting tolerance of shifting multiplexing in holographic storage and holographic confocal microscope.

Improvement of the signal-to-noise ratio of a double random phase encoding encryption system

We investigate the tolerance to data loss of a double random phase encoding encryption system. The signal-to-noise ratio of the decrypted image is investigated when a part of the encrypted image is lost. The SNR can be enhanced by reducing the ratio of the sampling number of the image to the total sampling number when electronic implementation is performed. In optical implementation, the SNR can be increased by using a phase mask with higher spatial frequency. Both the theory and computer simulations are demonstrated.

Improvement of the shift tolerance in the double random phase encoding encryption system

Double random phase encoding technique is a valuable and effective method for optical image encryption. However, a precise alignment is required when optical setup is performed. In this paper, we investigate the shift tolerance property of the technique. The theory of the robustness to data loss of the encrypted image is proposed. According to the theory, we propose a simple and novel method to improve the shift tolerance of the decrypting phase mask. Both theory and computer simulation are presented.