For the waveguide displays, low diffraction efficiency and narrow response bandwidth at high spatial frequency limit the development of coupling elements. In this paper, a dual-monomer, with higher and lower refractive index modulation separately, allyl propionate H-PDLC system is proposed. After experimental optimization, the diffraction efficiency of prepared high transmittance (more than 90% in the visible spectrum) H-PDLC gratings is up to 91%, and the response bandwidth is 99 nm at 973 lp/mm. By increasing the proportion of initiator and changing the radiation conditions, the diffraction efficiency is optimized to 75.4% and the response bandwidth is 29 nm at 2941 lp/mm. The experiments demonstrate that the high-frequency H-PDLC gratings have considerable application prospects as coupling elements for augmented reality optical waveguide display systems.
Lensless imaging technology can recover real scenes from highly multiplexed measurements without the focusing lens, effectively reducing the size and cost of the camera. Current reconstruction algorithms based on iterative optimization are hard to generate high-quality results due to the superposition and inevitable loss of the valid information. In order to improve the quality of the generated results, we propose a two-stage network. The first stage generates preliminary scene mapping results. The second stage uses a modified U-net network to construct a backbone network that suppresses the use of error information measured in the Point Spread Function (PSF). Meanwhile, the multiple attention modules are used at different scales of the network to extract the effective feature information in the PSF and reformulate the image information. In addition, a dual-scale discriminator structure is proposed to further improve the image quality. The results of experiments in the mask-based lensless imaging system captured dataset show that the method produces realistic results.
Diffusive photopolymer is one of the fastest developed fields on the application of the holographic optical storage, and has the advantages of huge data capacity and low coat. Based on the extended model of the nonlocal polymerization-driven diffusion, the photophysical mechanism of the dual monomer system in the photopolymer holographic material is introduced. The diffusion coefficient, polymerization rate and diffusion rate are determined experimentally to provide the conditional parameters in the model. Quantitative analysis of photopolymer formulation, refractive index modulation and diffraction efficiency. This analysis can improve material performance and provide a basis for the development of next-generation holographic storage materials. A nonlocal diffusion model is used to predict theoretically the grating evolution. The model has been developed to account for both nonlocal spatial and temporal effects in the medium, which can be attributed to polymer chain growth and corresponding polymeric kinetics equations are given. We find the relationship between these equations and refractive index modulation, and obtain a diffraction efficiency equation which is appropriate for transmission volume grating. The proportion of dual monomer in chemical reaction system was optimized, and the high optical transparency of photopolymer film were obtained.
In order to study the new holographic recording medium, four kinds of photopolymer materials containing TMPTA monomers are studied. The three-dimensional interference fringe information was successfully recorded in the photopolymer film samples, which proved that it has good holographic recording and high resolution ability. The experimental results show that when the recording angle is 30°, the diffraction efficiency is as high as 93.5%@532nm and the refractive index modulation is as high as 3.07×10-3. As a holographic recording medium, it has high resolution ability and high diffraction efficiency, the material is possible suitable for permanent storage of holograms and big data, besides it has strong advantages and potential applications in the large-scale 3D display, big data storage, holographic anticounterfeiting, holographic printing and other fields.
In order to study a new holographic recording medium, this paper prepares a kind of holographic photoinduced polymer material based on a double monomer and a composite photoinitiator. Add different photoinitiator, such as red bengal (RB), titanium (irgacure 784, Ti) and a mixture of the two in the photopolymer materials, and then perform holographic exposure. We found that the compound photoinitiator improved the diffraction efficiency, light sensitivity, and transmittance to some extent compared with a single photoinitiator. Combined with the diffusion kinetics, we studied the effects of the two kinds of photoinitiators on the photoinduced polymers, and the ratio of the composite photoinitiators was optimized. The holographic parameters such as diffraction efficiency under different exposure intensities, different exposure time, different thickness and different wavelength are tested, it is shown that the exposure conditions have a great influence on the diffraction efficiency. At the same time, this material is sensitive to both green light and red light. The experiment results show that the reconstructed image is clear and bright, which indicates that the photoinduced polymer is suitable for dual-wavelength multiplexing holographic storage.
In this paper, we reported a method to fabricate 2D hexagonal lattice Holographic Polymer-dispersed Liquid Crystal (HPDLC) grating with variable period by using cylindrical waves interfere with plane waves. In order to separate polymer from liquid crystal syrup, a 532nm laser with an exposure intensity of 16mw/cm2 was used to expose. Two steps exposure techniques was adopted in the experiment with the expose time of 2s and 60s in the separate steps to form the 2D gratings. In the second exposure step, the sample was rotated by anti-clockwise 60° to form 2D hexagonal lattice structure within H-PDLC grating. The theoretical equations for describing the variable period grating is analyzed. What’s more, the diffraction efficiency and other characteristics of this grating is also studied experimentally. The experimental result shows that fabricated grating with the continuously changing periods varying from 1.679 micrometer to 2.051 micrometer within the radius of 6 mm circle sample area, which is corresponded to the theoretical simulation quite well. The first-order diffraction efficiency was tested around18.3%. The intensity of transmission beam increased from 15.6% to 73% when applied with the driving voltage from zero to the maximum of 90 V. This 2D grating has the potential application in diffractive optics such as a tunable multi-wavelength organic laser device etc.
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