This paper presents a method of haze removal and computer-generated holographic display of degraded images in coal mine. Firstly, the image enhancement of underground coal mine is realized by using the dark channel prior haze removal algorithm, which greatly weakens the shielding of coal dust and water mist in the roadway environment. Next, using the computer-generated hologram algorithm based on angular spectrum diffraction, the phase only hologram is generated with the haze removal image as the input. The peak signal-to-noise ratio (PSNR) of the reconstructed image of the red channel is 65.47dB, the PSNR of the reconstructed image of the green channel is 64.98dB, the PSNR of the reconstructed image of the blue channel is 65.78dB, and the average PSNR is 65.41dB. The simulation results show that high-quality reconstructed image can be obtained by combining dark channel prior and computer-generated hologram, and the image enhancement of underground coal mine is realized.
Belt conveyor is one of the main transportation equipment in coal mine. The belt is easy to tear in production. If the tear damage of belt surface cannot be detected in time, it may lead to serious production accidents. In this paper, a belt tear detection method based on industrial camera monitoring is proposed, which can identify the belt tear in time and output the quantitative evaluation result. After filtering the image, Canny edge detection algorithm is used to identify the tear region. A sliding window is used to evaluate the degree of damage area and further determine the control of belt conveyor. Experiments show that the average processing time of a single frame image is 0.4s, which can meet the needs of real-time detection in the production.
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 order to improve the effect, clarity and resolution of anti-counterfeiting, this paper proposes a method of reflection volume holographic three-dimensional (3D) anti-counterfeiting. This method adopts reflection volume holographic interference recording of 3D object to achieve 3D anti-counterfeiting. The principle of reflection volume holography was analyzed by using Kogelnik’s coupled wave theory. A reflection volume holographic anti-counterfeiting recording optical path based on a monochromatic laser was constructed. Photopolymer is used as the volume holographic recording material, and a metal school badge is used as the object. Experimental results show that the reflection holographic gratings can record and reproduce 3D object, and the 3D shape of the reproduced image is consistent with the object, which improves the effect of anti-counterfeiting.
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.
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.
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