Jin Guo-Fan

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.

Rigorous electromagnetic design of finite-aperture diffractive optical elements by use of an iterative optimization algorithm

We propose a rigorous electromagnetic design of two-dimensional and finite-aperture diffractive optical elements (DOEs) that employs an effective iterative optimization algorithm in conjunction with a rigorous electromagnetic computational model: the finite-difference time-domain method. The iterative optimization process, the finite-difference time-domain method, and the angular spectrum propagation method are discussed in detail. Without any approximation based on the scalar theory, the algorithm can produce rigorous design results, both numerical and graphical, with fast convergence, reasonable computational cost, and good design quality. Using our iterative algorithm, we designed a diffractive cylindrical lens and a 1-to-2-beam fanner for normal-incidence TE-mode illumination, thus showing that the optimization algorithm is valid and competent for rigorously designing diffractive optical elements. Concerning the problem of fabrication, we also evaluated the performance of the DOE when the DOE profile is discrete.

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.

Holographic Grating Formation in Cationic Photopolymers with Dark Reaction

We propose a new formula to describe the dynamics of holographic grating formation under low intensity pulse exposures in cationic photopolymers, in which the dark reaction contributes dominantly to the grating strength. The formula is based on the living polymerization mechanism and the diffusion-free approximation. The analytical solution indicates that the grating formation time depends on the termination rate constant, while the final grating strength depends linearly on the total exposure energy. These theoretical predictions are verified experimentally using the Aprilis HMC-400 μm photopolymer. The results can provide guidelines for the control and optimization of the holographic recording conditions in practical applications.

Holographic Grating Formation in Photochromic Diarylethene-Doped Polymeric Thin Films

We introduce a model to describe real-time grating formation in holographic photochromic diarylethene-doped polymeric thin films. This model, which combines photochromic chemical reaction with the coupled-wave theory, indicates that the grating recording time depends on the molecular absorption coefficient of molecules and the quantum yield of the photochromic reaction at a certain holographic recording intensity. The model is validated by comparing its predictions with the experimental results in which photochromic molecule 1,2-bis(2-methyl-5-(4-formylphenyl)-3-thienyl) perfluorocyclopentene doped PMMA films were used.

Compact First-Order Polarization Mode Dispersion Compensator Based on Birefringent Crystals

We report a new first-order polarization-mode-dispersion (PMD) compensator based on birefringent crystals and magneto-optic polarization controllers. The compensator shows the response time of 150 μs, insertion loss smaller than 3 dB, and maximum differential group delay of 44.6 ps. Compared to the first-order PMD compensators reported so far, our PMD compensator exhibits fast response time, low insertion loss, compact size, broad bandwidth, and immunity to environmental vibrations.

Nonlinear Blind Equalization for Volume Holographic Data Storage

We investigate the nonlinear blind equalization for volume holographic data storage channel. Base on the recurrent neural network channel model, we describe a novel blind equalizer for the volume holographic data storage system to improve the bit error rate and hence to make the storage densities achievable. The experimental results also indicate that a significant improvement in the bit error rate to 2.55×10−3 is possible with the nonlinear blind equalization.

Optimal Design of an Achromatic Angle-Insensitive Phase Retarder Used in MWIR Imaging Polarimetry *

Dielectric gratings with period in the range from λ/10 to λ/4 with λ being the illumination wavelength not only exclude higher order diffractions but also exhibit strong dispersion of effective indices which are proportional to the wavelength. Moreover, they are insensitive to the incident angle of the illumination wave. With these features, we can design a true zero-order achromatic and angle-insensitive phase retarder which can be used as the polarization state analyzer in middle wave infrared (MWIR) imaging polarimetry. A design method using effective medium theory is described, and the performance of the designed phase retarder is evaluated by rigorous coupled wave analysis theory. The calculation results demonstrate that the retardance deviates from 45° by < ±1.6° within a field of view ±10° over the MWIR bandwidth (3–5 μm).

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.