The classic Denisyuk recording method is commonly used to reproduce three-dimensional (3D) image of volume holography, but its diffraction efficiency is low, and white light irradiation is required to obtain high-brightness reproduced image. Aiming at the above problem, the diffraction characteristics of transmissive and reflective volume holographic gratings are analyzed by Kogelnik’s coupled wave theory. A two-step volume holographic recording method is proposed. Firstly, the transmissive volume hologram is recorded and then the reconstructed image is transferred to the reflective volume hologram. Finally, through this method, the brightness and field of view of the reproduced image are improved, and a clear and bright 3D image can be observed under natural light.
With the development of holography and nanomanufacturing technology, metasurfaces are playing an increasingly important role in the field of holography. We designed a silicon cylindrical structure based on the Huygens metasurface. By exciting the Mie electric dipole and magnetic dipole resonance of the silicon cylindrical structure, a high transmission efficiency of 84% can be achieved at a wavelength of 633 nm, and a full phase coverage of 0-2π can be obtained by adjusting the radius of the silicon cylindrical. We used the angular spectrum algorithm to obtain the phase distribution relationship between the object image and the metasurface, and designed the arrangement of the silicon cylinder metasurface. The simulation obtained a high-fidelity hologram, and the structure has a high transmission efficiency around the 633 nm spectrum. This method can realize metasurface holography with high transmission efficiency, and it can be applied in holographic imaging.
In this paper, a laser-assisted light-emitting diode (LED) car high-beam headlight for modern cars is proposed. The headlight employs the LED light as the main light source of the car high-beam headlights. Under certain circumstances, the auxiliary main light source of the laser light source is added. Laser light sources are widely used in the field of automotive lighting owing to their high energy efficiency, small size, and good directionality. However, in terms of its application in headlights, the laser itself has limitations, such as a narrow line width and instability. In addition, all laser high beams are afflicted by the problems of laser light sources, and their optical design complexity has increased significantly. Therefore, this study used the total internal reflection of the light cone to promote the uniform distribution of the LEDs. Moreover, the collimating lens is used for laser spot convergence, and the laser light source is positioned at the laser spot to coincide with the LED spot center. Finally, the aspheric lens is incorporated into the light distribution design of the headlight. This optical design ensures driving safety and leverages the advantages of a laser light source to enhance the vehicle high-beam lighting effect, while improving the optical system design and reducing its complexity.
With the rapid development of autonomous driving technology, the driving environment is becoming more and more complex, and higher requirements are put forward for car headlights. This paper proposes a smart headlamp with LED as the light source, Digital Mirror Device (DMD) as the core light distribution element, and free-form surface lens as the optical imaging element. The LED collimating outer lens is calculated by the theory of light refraction and reflection, and modeling and simulation are performed on it. Its optical efficiency meets the design requirements and achieves good light collection and collimation for the LED. According to the relevant specifications of the national standard and the structural characteristics of the DMD micromirror array. Using the principle of area segmentation to design standard patterns that meet national standards and DMD intelligent patterns in multiple traffic scenes; use theoretical calculations to obtain free-form surface imaging lenses. The processed LED light is modulated by DMD to form a specific intelligent pattern, and a free-form surface lens is used to achieve imaging and light distribution. The simulation analysis results show that the optical modulation performance of the system is good, and the optical efficiency meets the design requirements. A prototype of the intelligent light distribution system was built, and compared with the lighting effect after loading the standard pattern, its lighting index reached the national standard requirements, and the intelligent light distribution experiment under multiple intelligent scenes was completed. The system can flexibly load different lighting patterns to achieve clarity. Light projection.
Structured light illumination (SI) is a most commonly used method to realize super-resolution microscopy. However, resolution enhancement in multiple spatial directions requires multiple SI to reconstruct the image, a typical number of which is nine. This technology requires the CCD camera to record corresponding numbers of images, which takes a quite long time to record a sample. In this paper, we design an optical system to combine compressive sensing (CS) algorithm with SI to realize the fast super-resolution imaging. Coded exposure technique is used to sample the hologram formed by the diffraction of the object illuminated by SI and processed with CS algorithm later. In the process of collecting 9 images with SI, the CCD only exposes 5 times, which saves nearly half of the time and operation steps. After comparison in simulation, the resolution of the SI reconstructed image using 50% sampling CS is 0.12 times higher than that of the method without SI illumination, and is the same as the resolution of the SI reconstructed image using full sampling. The method and the system realize the fast super-resolution imaging.
Volume holograms can achieve concentration of sunlight, but it has shortcomings such as small concentration angle, dispersion, and complex production process of the volume holography material, which is difficult to mass produce. This paper proposes a method based on the metasurface concentrating sunlight. We analyzed the mechanism of volume holographic light focusing by Kogelnik coupling wave theory, which is greatly limited by wavelength selectivity. Utilizing the metasurface control mechanism on the wave front phase, the array arrangement that meets the light concentrating effect was designed. Simulation analysis shows that the metasurface can achieve light concentration in the visible light band with low dispersion.
Volume holograms can record and reproduce three-dimensional object. Compared with planar holograms, volume holograms can improve the resolution, stereo perception and realism of anti-counterfeiting, and realize three-dimensional anti-counterfeiting. In order to improve the diffraction efficiency and anti-counterfeiting effect of volume holographic anti-counterfeiting, this paper proposes a reflection volume holographic three-dimensional anti-counterfeiting method based on photopolymer. The diffraction characteristics and influencing factors are analyzed by Kogelnik’s coupled wave theory. Based on Piazzolla’s monomer diffusion model, the effects of exposure energy and exposure intensity on refractive index modulation and diffraction efficiency were studied. The simulation results show that the reflection volume holograms can achieve a greater refractive index modulation, with higher diffraction efficiency, stronger wavelength selectivity, which enhances the effect of three-dimensional anti-counterfeiting.
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