We propose a polarization multiplexing structure based on multilayer reflective polarized volume holographic gratings(PVGs) to improve the field of view and brightness of the augmented reality ...waveguide display. The multilayer structure forms the splicing of different response bandwidths by stacking PVGs with different periodic components, and realizes the expansion of the wavelength (angle) bandwidth. The polarization multiplexing structure controls the polarization of the diffracted light by controlling the rotation direction of the liquid crystal pitch in the liquid crystal material, so that both left-hand and right-hand circularly polarized light are diffracted to enhance efficiency. Based on these two structures, the wavelength bandwidth of PVG is increased by 40 nm, the angular bandwidth is increased by 10° and the diffraction efficiency is nearly doubled. In order to verify the feasibility of these two structures, we use the holographic waveguide display with OLED as the image source. The demonstrated waveguide prototype shows a complete display with a diagonal field of view of 55°. The brightness of virtual image was measured as high as 1100 cd/m 2 with a transparency of 72% for ambient light.
Selective laser melting (SLM) is an important method of additive manufacturing (AM). However, due to the large temperature gradient, defects such as pores and inclusions are easily visible during the ...printing process, affecting the forming quality and internal mechanical properties of the parts. This paper proposes a lase-SAFT detection method based on longitudinal wave to detect internal defects in additive parts. The mathematical model of the laser-SAFT algorithm is developed, and simulation research on the quantitative detection technique of AM 316L steel’s internal defects is conducted. A de-artifact approach based on wave mode and flight duration is presented to increase the accuracy of imaging results. The detecting impact of double-defect within the AM 316L steel is also modelled. Finally, the SAFT imaging of various locations and sizes of defects in the AM 316L steel, as well as the SAFT imaging detection of double-defect, are accomplished.
This work proposes a green light-sensitive acrylate-based photopolymer. The effects of the preparation conditions for the waveguide applied volume holographic gratings (VHGs) were experimentally ...investigated. The optimum preparation conditions for holographic recording were revealed. After optimization, the peak of VHG diffraction efficiency reached 99%, the diffractive wavelength bandwidth increased from 13 nm to 22 nm, and the corresponding RIM was 0.06. To prove the wide application prospect of the acrylate-based photopolymer in head-mounted augmented reality (AR) displays, green monochromatic volume holographic waveguides were fabricated. The display results showed that the prototype was able to achieve a 28° diagonal FOV and possessed a system luminance of 300 cd/m
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Planar waveguide structure has benefits to expand the exit pupil of the near-eye display. To achieve a uniform output luminance within the expanded exit pupil, a specific distribution of diffractive ...efficiency (DE) should be set for the out-coupling grating. In this paper, a physical model is built to study the DE distribution of out-coupling grating with consideration of the whole field of view. Compared to the previous works, which only considered the central view angle, this model is more consistent with the actual situations to realize a uniform imaging output for a waveguide-based near-eye display system. Also, a planar waveguide with two holographic volume gratings as the in- and out-coupling gratings is fabricated to verify the proposed DE distribution. In experiments, a spatial light modulator is applied as the spatial luminance modulator, and the coupling grating with the proposed DE distribution is fabricated by the holographic interference exposure setup. The results show a high consistency between the simulation and the experiment.
The paper presents the characterization of the field of view (FOV) in a holographic waveguide display (HWD) with a broadband spectrum image source. The influences of parameters such as grating ...slanted angle of volume holographic grating (VHG), grating period, and effective refractive index are systematically analyzed. We optimized the parameters and calculated the maximum FOV of monochromatic and chromatic HWD. A multilayered VHGs structure is proposed to enlarge the FOV effectively without additional cost and optical design. We also build a rigorous simulation model to verify the feasibility of the multilayered structure. The theoretical maximum FOV of monochromatic and chromatic HWD are presented after optimization.
NiCo2O4 is widely used in traditional battery and supercapattery due to its extremely high capacitance value. Herein, the in-situ hydrothermal method has been optimized in order to utilize its own ...charge storage capacity. NiCo2O4 nanosheet thin films with four different morphologies (wrap, neuron, daisy, and tablet shape) are synthesized on Ni foam surface without mechanical stress damage. In the absence of interference from conductive agents and binders, these NiCo2O4 nanosheet thin films with different morphologies provide various conducive channels for charge transfer and more sites for redox reactions achieve better energy storage properties. Particularly, the daisy shape NiCo2O4 nanosheets have the highest capacity (C g−1) of 972.5 (2 M KOH) at 1 A g−1 comparing to others. Furthermore, after subjecting it to 1800 cycles of cyclic stability testing at 40 A g−1, its capacity (C g−1) remarkably increased to 1433.5. In addition, using the daisy shape NiCo2O4 nanosheets thin film and activated carbon, a supercapattery is assembled. The results exhibit that it has an impressive performance of 39.8 W h kg−1 at 750 W kg−1 comparing to other works, which demonstrates that our in-situ hydrothermal synthesized daisy shape NiCo2O4 nanosheet has significant potential in the field of energy storage.
•NiCo2O4 nanosheet thin films with four different morphologies (wrap, neuron, daisy, and tablet shape) are synthesized on Ni foam.•The in-situ hydrothermal method has been optimized in order to utilize NiCo2O4’s charge storage capacity.•The daisy shape NiCo2O4 nanosheets exhibited capacity of 972.5 C g−1 at 1 A g−1.•The daisy shape NiCo2O4 nanosheets//activated carbon exhibited energy density of 39.8 W h kg−1.
We present a volume holographic waveguide display by dispersing gold nanoparticles (Au-NPs) in acrylate-based photopolymer. The diffractive bandwidth and diffraction efficiency (DE) of the volume ...holographic grating (VHG) applied for waveguide displays are characterized and analyzed through both the simulations and experiments. The results show that the wavelength bandwidth of the VHG can be enlarged to 30 nm with a corresponding refractive index modulation (RIM) increased to around 0.08 by dispersing the Au-NPs with a concentration of 0.012 g/ml into the acrylate-based photopolymer. Finally, the green monochromatic waveguide display system with 30° horizontal field of view (FOV) is realized.
Augmented reality (AR) displays are gaining attention as next-generation intelligent display technologies. Diffractive waveguide technologies are progressively becoming the AR display industry's ...preferred option. Gradient period polarization volume holographic gratings (PVGs), which are considered to have the potential to expand the field of view (FOV) of waveguide display systems due to their wide bandwidth diffraction characteristics, have been proposed as coupling elements for diffraction waveguide systems in recent years. Here, what we believe to be a novel modeling method for gradient period PVGs is proposed by incorporating grating stacking and scattering analysis utilizing rigorous coupled-wave analysis (RCWA) theory. The diffraction efficiency and polarization response were extensively explored using this simulation model. In addition, a dual-layer full-color diffractive waveguide imaging simulation using proposed gradient period PVGs is accomplished in Zemax software using a self-compiled dynamic link library (DLL), achieving a 53° diagonal FOV at a 16:9 aspect ratio. This work furthers the development of PVGs by providing unique ideas for the field of view design of AR display.
The field of view of waveguide display systems based on volume holographic gratings is often limited by the grating diffraction response bandwidth, which still cannot meet people's needs for large ...field of view displays. In order to expand the viewing angle of the waveguide display, the influencing factors of the viewing angle of the waveguide display are analyzed based on the strictly coupled wave theory model, and a double‐layer volume grating waveguide structure that can effectively expand the diffraction response bandwidth is proposed. The grating is prepared by the variable‐angle fractional exposure method, and the holographic waveguide display system is built. The results show that the horizontal and vertical viewing angles of the display system can be expanded to 33° and 22°, respectively, and the diagonal viewing angle is 40°.
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