A new expression of partially coherent light is derived. The formula of the partially coherent optical field is consisted of two terms: spatially coherent part propagated by angular spectrum and incoherent part based on the optical transfer function. Both parts are related to coherent function (degree of coherence). Then a design method for computer generated hologram based on the theory of partially coherent light is proposed. The formation process of CGH is divided into angular spectrum and optical transfer function. Both numerical simulations and optical experiments are done to verify that speckle contrast of holographic reconstructed images is improved without sacrificing in PSNR compared to traditional method. The experimental results show that the speckle contrasts are improved more than 46%, and the image quality is obviously improved. This method can be applied on three-dimensional holographic display, beam shaping and other wave-front modulation techniques.
Computer-generated hologram (CGH) is a key technology in electro-holography systems. However, the huge computational complexity is a challenge for practical demands. In this paper, we propose an improved algorithm to accelerate CGH computation based on symmetric compressed LUT (SC-LUT) algorithm. In LUT calculation, the horizontal and vertical modulation factors is reduced to one-dimension arrays instead of dual one-dimension arrays. In hologram calculation, we introduce a one-time generation of color holograms method which is accelerated by matrix convolution operation. Numerical simulation results also show at least 13 times faster than existing algorithms without sacrificing the computation precision. The proposed algorithm accelerated by the graphic processing unit (GPU) is an effective method for fast calculation of CGH in color holographic display.
The liquid crystal spatial light modulator is able to provide flexible wavefront modulation, whereas its nonlinear and spatial varying phase response will influence the modulation accuracy. In this paper, a software based C++ algorithm are designed to calibrate these distortions regionally. Twyman-Green interference method is utilized for gray versus phase shift measurement. The curvature of cover glass is measured by phase shift algorithm. Finally the entire panel is divided into several local regions to overcome the spatial varying phase response. For each sub-region, the nonlinear phase response is calibrated by remapping table. For a Jasper 4K SLM panel, when three local regions are built, the root mean error of linear phase shift is reduced to approximate 0.1 rad. The calibrated SLM is applied for holographic display and the improvement ratios of structural similarity index reach 30.6%, 62.5%, and 43.6% for R, G, and B reconstructed components respectively.
The liquid crystal spatial light modulator (LC-SLM) is able to provide flexible wave front control, whereas its phase response distortions will influence the modulation accuracy. In this paper, we will provide a novel sub-regional phase response calibration method for minimizing these distortions. In our calibration method, the entire panel is divided into several local regions based on the similarity of phase response characteristic. Liquid crystal cells in one sub-region show the same phase response. The calibration method is theoretical analyzed and experimentally verified. For the entire Jasper 4K SLM panel, when three local regions are built, the root mean error of linear phase shifts is reduced to approximate 0.1 rad. The calibrated SLM is applied for holographic display and the structural similarity index of the assessment shows the improvement ratios reach 30.6%, 62.5%, and 43.6% for R, G, and B reconstructed components respectively. It also could be used for the calibration of various SLMs in the future.
Optical receiving antenna is usually positioned before the detector of an indoor visible light communication (VLC) system in order to collect more optical energy into the detector. Besides optical gain of the antenna, the field of view (FOV) plays also an important role to the performance of a VLC system. In this paper, the signal noise ratio (SNR) and inter-symbol interference (ISI) versus FOV of the antenna are simulated via Line-of-Sight (LOS) and non-Line-of-Sight (NLOS) links within a room with a size of 5m × 5m × 3m. Results show that, the blind area appears while the FOV is less than 40 deg. and the SNR reduces as FOV increases and keeps small when FOV is more than 70 deg.. Furthermore, the average power of ISI rises with the increase of FOV, and the rising trend is relatively moderate when FOV is below 50 deg., while there is a rapid increase between 50 deg. and 70 deg. and finally tends to be stable after 70 deg. Therefore, it is practical to determine the FOV of the optical receiving antenna in the scope of 40 to 50 deg. based on the installment of LED lights on the ceiling here so as to avoid the blind area, attain high SNR, and reduce the influence of ISI. It is also worthwhile in practice to provide an identifiable evidence for the determination of FOV of the optical antenna.