Wu Minxian

Rigorous concept for the analysis of diffractive lenses with different axial resolution and high lateral resolution

We present a rigorous electromagnetic design and analysis of two-dimensional diffractive lenses (DLs) with different axial resolution and high lateral resolution. Without paraxial approximation, focusing characteristics of two kinds of DL, one with a long focal depth and a high lateral resolution, the other with high axial resolution and high lateral resolution, for f-numbers of 0.6, 1.0, 1.5, and 2.0 have been determined including the actual focal depth, the ratio between the focal depth of the designed DL and the focal depth of the conventional quadratic lens, and the spot size of the central lobe at the actual focal plane. Numerical and graphic results show that the designed DLs indeed have a long focal depth and a high lateral resolution, or high axial resolution and high lateral resolution by use of different preset focal depths.

Diarylethene Materials for Rewritable Volume Holographic Data Storage

The photochromic diarylethene, 1,2-bis(2-methyl-5-(4-formylphenyl)-thien-3-yl)perfluorocyclopentene (1a) is studied and its applicable potential in rewritable volume holographic data storage is verified. Holographic recording films of 10-µm thickness have been fabricated. The refractive index modulation (Δn = 1.15×10-3) between the open- and close-ring forms is detected to be large enough so that the films are suitable for the production of volume holographic storage. The experiments of angle multiplexing and rewriting holograms show that the materials are fit for volume holographic data storage.

Holographic grating formation in dry photopolymer film with shrinkage

An important issue in developing applications for photopolymers in holography is the effect of shrinkage on recording properties. In this paper, we introduce a model to describe real-time formation of a single grating in photopolymers at any geometrical angle, under the assumption that the shrinkage is in proportion to the polymerization. This model combines polymerization kinetics with the coupled-wave theory, explaining the shrinkage effect on the diffraction efficiency. The model is validated by comparing its predictions with the experimental results for a film of 99μm thickness.

Kinoform with 64 phase levels for use as an array generator.

A transmissive kinoform with 64 phase levels is demonstrated that is used as a beam array generator. This kinoform converts a single beam to a 5 x 5 beam array. The measured diffraction efficiency is 75.56%, near the designed value of 79.68%. The measured intensity difference among the different diffraction orders of the 5 x 5 beam array is 21.56%, and the designed value is 10.99%. The total aperture of the kinoform is 10 mm x 10 mm.

Multiplexing Nonvolatile Holograms in LiNbO3:Cu:Ce Crystals

A practical experimental system for two-centre recording by angular multiplexing and 90° geometry is designed with red and blue light. The erasure mechanism of lithium niobate crystals doubly doped with copper and cerium for two-centre recording is discussed and a modified decremental recording schedule for angular multiplexing is proposed subsequently. Finally, 50 nonvolatile holograms with almost the same diffraction efficiency are recorded.

Epoxy Resin-Photopolymer Composite with None-Shrinkage for Volume Holography

A novel photopolymer storage medium for holographic storage is presented. In particular, the refractive index of the monomer methyl methacrylate is much lower than that of the binder epoxy resin solidified by m-xylylenediamine, and the material can be developed into samples with dimension stability and high optical quality and thickness of several millimetres or more. Some none-polymeric macromolecule impurity is uniformly mixed into the medium to aid the monomer diffusing and to enhance the diffraction efficiency. A holographic recording medium of 0.8 mm thickness has been fabricated, and relative theoretical analysis and experiments are presented.

Numerical Analysis of Three-Dimensional Object Recognition with Digital Holography

We describe an intrinsic correlation peak of three-dimensional (3D) pattern recognition, which is higher than that of the two-dimensional (2D) pattern recognition and whose difference can reach up to five orders of magnitude in our numerical simulation. The relationship between the 3D objects and their recognition result is formalized and the comparison between the 3D and 2D pattern recognitions as well as the formers independency of the reconstruction distance is presented. Finally, the augmentation of the 3D pattern recognition sensitivity with the increasing surface complexity of the 3D object is also demonstrated.