Pixel size limit in holographic memories

The bandwidth of holographic recording in LiNbO3 (Fe doped) in the 90° geometry is studied theoretically and experimentally. The wide holographic bandwidth of LiNbO3 makes it possible to record submicrometer pixels and reconstruct them by phase conjugation in a holographic memory system. This approach reduces the system cost and increases the system storage density. We demonstrate the recording and the phase-conjugate reconstruction of various pixel sizes down to 1 μm × 1 μm . The signal–noise ratio and the bit-error rate are examined

Robot autonomous navigation

Autonomous vehicle navigation is a very popular research area in the vision and control field. Based on Prof. Dickmanns' philosophy, we implement a navigation algorithm on thc small robot. The robot can rely on its eyes (the camera mounted on thc top of the robot) and control its wheels to walk through the sub-basement hallways of Caltech Moore Lab building. The speed we achieve is robot's mechanical maximum speed 0.5 m/s

Volume Holographic Hyperspectral Imaging

A volume hologram has two degenerate Bragg-phase-matching dimensions and provides the capability of volume holographic imaging. We demonstrate two volume holographic imaging architectures and investigate their imaging resolution, aberration, and sensitivity. The first architecture uses the hologram directly as an objective imaging element where strong aberration is observed and confirmed by simulation. The second architecture uses an imaging lens and a transmission geometry hologram to achieve linear two-dimensional optical sectioning and imaging of a four-dimensional (spatial plus spectral dimensions) object hyperspace. Multiplexed holograms can achieve simultaneously three-dimensional imaging of an object without a scanning mechanism

Folded shift multiplexing

Shift multiplexing is a holographic recording method that uses a spherical reference wave. We extend the principle to a thin slab of holographic material that acts as a waveguide. Total internal reflection folds the reference spherical beam in one dimension. We demonstrate that the shift selectivity with the folded spherical beam is independent of the slab thickness but depends instead on the numerical aperture of the coupled spherical wave. A shift selectivity of 0.5 µm has been achieved with a 1-mm-thick LiNbO3 crystal and 50 high-definition data pages are recorded with this method

Read/write holographic memory versus silicon storage

This paper compares the read/write holographic memory with silicon storage on issues of cost, density, size and speed. With a photorefractive crystal on top of a silicon interface, the holographic memory is of cost efficiency, volume compactness and fast data accessing. Key challenges to implement the competitive holographic memory are discussed

A Ring Signature Trust Model for Project Review Based on Blockchain Smart Contract

The traditional offline review model of grid projects has the problems of high cost, high risk and low efficiency, making the project review insecure and inefficient. What is worse, the review data of a grid project are generally stored in a central database, which is vulnerable to attacks and not highly trustable. To solve the problems, this paper proposes a ring signature trust model based on smart contract, an important blockchain technology, for project review. The blockchain technology was introduced to build an online review platform for grid projects, greatly saving human and financial resources. Then, the consensus efficiency was improved with a trust-based node consensus mechanism. Besides, the ring signature was integrated with smart contract to allow review experts to submit their results anonymously, ensuring the fairness and impartiality of grid project review. On this basis, an efficient review system was established for grid projects, and a secure review environment was created, so that the review results will not be tampered with. The case analysis proves that the proposed method can effectively solve the problems of traditional grid project review, making the review system more secure and efficient. The research findings provide decision and theoretical supports for grid project review

Diffraction from deformed volume holograms: perturbation theory approach

We derive the response of a volume grating to arbitrary small deformations, using a perturbative approach. This result is of interest for two applications: (a) when a deformation is undesirable and one seeks to minimize the diffracted field's sensitivity to it and (b) when the deformation itself is the quantity of interest and the diffracted field is used as a probe into the deformed volume where the hologram was originally recorded. We show that our result is consistent with previous derivations motivated by the phenomenon of shrinkage in photopolymer holographic materials. We also present the analysis of the grating's response to deformation due to a point indenter and present experimental results consistent with theory