Lens-array based imaging system is a kind of the direct-view system that is currently a hot topic of research. In fact, the viewing parameters of this system have been one of the focuses of research since its invention. However, most current literature discussions are based on depth of field, spatial resolution, and field of view. Only a few documents or products use angular resolution, spatial resolution, and field of view as criteria. The angle resolution is one of the parameters in the human eye vision module. This article will try to discuss the hardware conditions for realizing the angular resolution in the LCD discrete pixel system and its influence on the 3D perception. The results show that the angular resolution is determined by the number of pixels in each sub-image and is proportional to the number of elemental images and is limited by the LCD pixel pitch.
The challenge of dynamic holographic video display based on spatial light modulator is that it requires a large spatial bandwidth product. A simple method is to reduce the size of a single pixel in conventional LCOS (liquid crystal on silicon , LCOS) device. However, with the pixel size shrinks, it also requires a corresponding reduction in thickness of liquid crystal cell, otherwise the fringe field effect between pixels will affect the modulation of normal pixel. A deep sub-wavelength metal grating with a Fabry-Perot resonance is used instead of the top electrode of LCOS to form a liquid crystal phase modulator in this paper. Different from traditional LCOS, which realizes the phase modulation by using the birefringence of the liquid crystal in liquid crystal cell, the birefringence of the liquid crystal in our device is used to modulate the conditions of the reflective boundary of the deep sub-wavelength metal grating, which in turn controls the amount of phase modulation of reflected light in grating slit. The TechWiz and CST Microwave Studios software are used in this paper. Observing the distribution of liquid crystal directors and electric field distribution. Recording the intensity of visible light reflection and observing whether the device can achieve phase modulation of 0 ~ 2π by changing the pixel pitch and grating structure parameters. The simulation results show that there is no significant change in the liquid crystal directors and electric field distribution in different pixel pitch, the device phase modulation is close to<sup> 2π</sup> , and it has a high reflectivity.
3D display requires a high-resolution, high-pixel playing system. This paper studies the video playback with single frame resolution of 16K × 8K . The bandwidth of display exceeds the current video display capability of 8K × 4K resolution. On the one hand, an appropriate system architecture needs to be built on the existing hardware level. 16 liquid crystal displays (LCDs) are used in this paper, with resolution of each LCD is 4K × 2K and size is 15.6 inches. Constituting a video display terminal array of 4 × 4 ,which the resolution is 16K × 8K . And a single-layer architecture with a fully decode is used. Decoding 16 channels of 4K signals on one host with i7-6800K and two video cards with NVS810 (both with 25GBps memory bandwidth) and deliver signals through 16 DP interfaces in parallel. On the other hand, under this architecture, running load of CPU and GPU, bus bandwidth and scheduling of dynamic storage capacity impose higher requirements on the encoding and decoding of video data. Comparative research between MPEG series and H.26X series coding standard has carried out in this paper. An inter-frame-based forward prediction (BFP) method is proposed. Finally, in the Win7 system, using mpeg-2 encoding standard, and decoding by using ffplay that achieves 16K video with 15Fps smooth playback. The effectiveness of the proposed method is verified. The proposed BFP method further reduces the decoding complexity of CPU.
Aiming at the great challenge for Computer Generated Hologram (CGH) duo to the production of high spatial-bandwidth product (SBP) is required in the real-time holographic video display systems. The paper is based on point-cloud method and it takes advantage of the propagating reversibility of Fresnel diffraction in the propagating direction and the fringe pattern of a point source, known as Gabor zone plate has spatial symmetry, so it can be used as a basis for fast calculation of diffraction field in CGH. A fast Fresnel CGH method based on the novel look-up table (N-LUT) method is proposed, the principle fringe patterns (PFPs) at the virtual plane is pre-calculated by the acceleration algorithm and be stored. Secondly, the Fresnel diffraction fringe pattern at dummy plane can be obtained. Finally, the Fresnel propagation from dummy plan to hologram plane. The simulation experiments and optical experiments based on Liquid Crystal On Silicon (LCOS) is setup to demonstrate the validity of the proposed method under the premise of ensuring the quality of 3D reconstruction，the method proposed in the paper can be applied to shorten the computational time and improve computational efficiency.
Spatial light modulator (SLM) is the core device of holographic display, which requires a large space-bandwidth product (SBP), especially needing a wide viewing angle. According to the grating theory, the scale of the holographic display unit should be close to the wavelength of light. The transmission resonances of deep metallic sub-wavelength grating structure, which is produced by the surface plasmon and Fabry-Perot (FP) resonance based on metal grating phenomenon of Wood's anomaly, especially the metal-insulator-metal (MIM) structure provides a theoretical and effective technique for enhancing the reflection resonances and can be used for implementing the holographic display unit technology. In this paper, we replace the top electrode layer of the LCOS with a metallic deep sub-wavelength grating structure and change the grating period, slit width and spacer thickness. The simulation results by aid of CST software are given, which demonstrate that the improved device with dielectric medium parameter within liquid crystal refractive rate range (1.4~1.7) can reach 0 to 2π phase modulation in the visible wavelength range. Moreover, it also decrease the difficulty of device processing.
There are many 3D data structures for computing diffraction field, the description based on 3D point-cloud is the elemental method of other descriptions, the diffraction field of 3D scene can be thought as the superposition of the diffraction field of each sampled light point and other descriptions can be thought as grouping with point-cloud by different way. The paper focuses on devising a computation method of 3D Fresnel field which is based on Fresnel diffraction field propagation reversibility. The proposed method combines the reversibility of Fresnel propagation and the requirement of sampling spacing by Nyquist criterion, i.e. to find the best space positions to optimize the number of sampling points and the reconstruction for the 3D Fresnel field. The method can be applied to reduce the computational complexity and improve computational efficiency.
In this paper, a novel phase retrieval algorithm is presented which combines the advantages of the Transport of Intensity Equation (TIE) method and the iteration method. TIE method is fast, but its precision is not high. Though the convergence rate of iteration method is slow, its result is more accurate. This algorithm consists of Iterative Angular Spectrum (IAS) method to utilize the physical constraints between the object and the spectral domain, and the relationship between the intensity and phase among the wave propagation. Firstly, the phase at the object plane is calculated from two intensity images by TIE. Then this result is treated as the initial phase of the IAS. Finally, the phase information at the object plane is acquired according the reversibility of the optical path. During the iteration process, the feedback mechanism is imposed on it that improve the convergence rate and the precision of phase retrieval and the simulation results are given.
Meta-surface offers an innovative approach to manipulate light with anomalous capabilities. We discuss the possibility of inserting a specially designed gradient meta-surface into the pixel architecture of the liquid crystal on silicon (LCOS) for the purpose of optimizing the diffraction efficiency of LCOS-based holography. The pixels in LCOS with feature size approaching the order of visible light wavelength could provide large diffraction angle, unfortunately, scaling down the pixel size would reduce the efficiency of the first diffraction we desired. The metal-insulator-metal (MIM) structure served as the unit cell of meta-surface consists of three layer, i.e., the subwavelength metal nanobrick with varying geometrical parameter and the continuous metal film separated by the insulator layer. A linear phase gradient is exhibited by the unit cells in each pixel period. When illuminated by a polarized incident light, the MIM structure, where a magnetic resonance is created at a particular frequency, can offer an anomalous reflection with high-efficiency and acts as a flat blazed grating. Finally, the light are supposed be diverted to the desired first diffraction. The properties of potential metal, such as Au, Ag, and Al, served as the plasmonic material and suitable insulator have been studied to configure the MIM structure accurately. Investigations are numerically carried out to observe the effects on the distribution of liquid crystal director with TechWiz Software and to obtain the relative diffraction efficiency by using FDTD software. Compared with the conventional LCOS device, the optimization of the diffraction efficiency has been achieved by our proposed structure.
In classical compressive holography (CH), which based on the Gabor holography setup, two nonlinear terms are inherent in the intensity recorded by a 2D detector arrays, the DC term and the squared field term. The DC term (the term at the origin) can be eliminated by filtering the Fourier transform of the interference irradiance measurements using appropriate high-pass filter near the zero frequency. The nonlinearity caused by the squared field term can be neglected and modeled as a error term in the measurement. However, the above assumptions are significantly limited, which yields the degradation of reconstruction quality. In this paper, an novel scheme using phase-shifting method is presented. To accurately recover the complex optical field caused by the propagation of the object, without the influence of the DC term and the squared field term, a very effective method for removing these two terms is introduced. The complex optical field of the 3D object and the complex optical field at the detector plane can be precisely represented by a linear mapping model. The complex optical field at the recorder plane is obtained by phase-shifting interferometry with multiple shots. Then, the corresponded complex optical field at the detector plane can be successfully extracted from multiple captured holograms using conventional four phase-shifting interferometry. From such complex optical field at the record plane, including the amplitude and phase information, the complex optical field of the 3D object can be reconstructed via an optimization procedure. Numerical results demonstrate the effectiveness of our proposed method.
In the design and development of Liquid Crystal on Silicon (LCoS), one can predict possible problems and propose
according solutions with calculating the director and optical characteristics of the liquid crystal. The optical property of
LCoS is calculated with the Finite-Difference Time-Domain Method (FDTD) in this paper. The diffraction characteristics
are exactly analyzed with incident plane wave and the computational space terminations are provided by a combination
of the perfectly matched layer (PML) and periodic boundary conditions (PBC). The influences on optical properties of
LCoS with different interpixel gap, pretilt angle and thickness are studied. The result shows that diffraction efficiency is
greatly affected by the thickness of cell. It’s significant and offer reference for the design and manufacture of LCoS.