Diffractive optical elements (DOEs) are intricately designed devices with the purpose of manipulating light fields by precisely modifying their wavefronts. The concept of DOEs has its origins dating back to 1948 when D. Gabor first introduced holography. Subsequently, researchers introduced binary optical elements (BOEs), including computer-generated holograms (CGHs), as a distinct category within the realm of DOEs. This was the first revolution in optical devices. The next major breakthrough in light field manipulation occurred during the early 21st century, marked by the advent of metamaterials and metasurfaces. Metasurfaces are particularly appealing due to their ultra-thin, ultra-compact properties and their capacity to exert precise control over virtually every aspect of light fields, including amplitude, phase, polarization, wavelength/frequency, angular momentum, etc. The advancement of light field manipulation with micro/nano-structures has also enabled various applications in fields such as information acquisition, transmission, storage, processing, and display. In this review, we cover the fundamental science, cutting-edge technologies, and wide-ranging applications associated with micro/nano-scale optical devices for regulating light fields. We also delve into the prevailing challenges in the pursuit of developing viable technology for real-world applications. Furthermore, we offer insights into potential future research trends and directions within the realm of light field manipulation.
The combination of Computer-Generated Holography (CGH) and deep learning has opened the possibility to generate both real-time and high-quality holograms. However, the widely-used data-driven deep learning method faces the problem of the large number of labeled training datasets generated by traditional algorithms, such as Gerchberg–Saxton (GS) iterative algorithm. It always takes a long time and limits the training performance of the network. In this work, we propose a model-driven neural network for high-fidelity Phase-Only Hologram (POH) generation. The Fresnel diffraction process is introduced as the physical model, which makes the network can automatically learn the latent encodings of POHs in an unsupervised way. Furthermore, the sub-pixel convolution upsampling method effectively improves the reconstruction quality. Once the training is completed, the POH of any two-dimensional image can be quickly generated. The calculation time is one to two orders of magnitude faster.
The Gerchberg–Saxton (GS) algorithm is a widely employed algorithm for phase-only hologram (POH) generation. However, the POHs which can strictly satisfy the amplitude constraints on the object and the holographic plane may not exist or be obtained, resulting in speckle noise and reduction of the reconstruction quality. Relaxing the amplitude constraint during the iterations is an effective method to solve the above problem. In this work, a GS-double amplitude freedom (GS-DAF) algorithm is proposed. The amplitude constraint relaxation is realized by both the combined amplitude constraint and the support constraint. The spherical initial phase and oversampling method are applied to further improve the optical reconstruction quality of the GS-DAF algorithm. An enhanced reconstruction quality with less speckle noise has been achieved.
KEYWORDS: 3D displays, Holography, Computer generated holography, Cameras, 3D modeling, 3D acquisition, 3D image processing, Image processing, Sensors, Optical simulations
One of the challenges that has been faced by holographic 3D display is the lack of 3D contents. To deal with the shortage of 3D contents, a 2D-to-3D algorithm is presented for the holographic 3D display. The 2D images are firstly classified into 3 categories by the features. The depth maps for different categories are obtained by different calculation models accordingly. The computer-generated holograms (CGHs) are calculated by the layer-based angular-spectrum approach. These CGHs can be reconstructed with obvious 3D depth cues in simulations and experiments.
Holographic three-dimensional (3D) display can reproduce the amplitude and phase of the wavefront, providing perfect reconstructions of real 3D scenes. The computer-generated hologram (CGH) for the 3D model is calculated by the layer-based angular-spectrum theory. The wavefront is encoded by the CGH which is uploaded on the phase-only spatial light modulator. In order to achieve holographic 3D display with the high-definition, the number of layers and the resolution of the 3D model are significantly important. In this work, the effects of the number of layers and the resolution on reconstruction quality are analyzed quantitatively, which provides a guidance for the design of holographic 3D display system. A high-definition 3D display system with a high-resolution 3D data module based on Kinect Azure is designed and built, realizing a high quality 3D display effect.
Reliable phase-only spatial light modulators (SLMs) are in demand for accurate phase modulation. However, the nonlinear optical response of liquid crystals and the limited manufacturing process can lead to the spatial nonuniformity of the phase modulation of the SLM. The transfer from the grayscale to the modulated phase can be different from the lookup table (LUT) shown in the SLM manual. The SLM should be measured for calibration. We propose a calibration method based on digital holography to calibrate the spatial nonuniformity of phase modulation of the SLM. Using a self-generated grating, the SLM involved system is converted to the calibration system based on the principle of digital holography. The in-situ strategy for low cost and efficient calibration was demonstrated with optical experiments using a 4K (3840 × 2160 pixels) phase-only SLM. The spatial nonuniformity was calibrated to decrease by more than 75% using only a beam splitter and an imaging sensor.
The 5G network has the advantage of ultra-high transmission bandwidth, which will accelerate the developments of new three-dimensional (3D) communication systems. Computer-generated holographic display is an ideal solution for 3D communication because it could provide realistic 3D effect. Currently, only the amplitude of the wavefront, rather than the phase, is recorded by the traditional image capture system, which could not provide 3D information for the 3D computer-generated holographic display. Based on the light-field camera, a capture system employed in the computergenerated holographic display is developed. It could calculate position of every object point, and render the point-cloud model of the target 3D object. The layer-based angular-spectrum method is also employed in this capture system to calculate the computer-generated holograms (CGHs) of the 3D object. Simulations and experiments have verified that the proposed capture system is able to utilize the transmission bandwidth of 5G network. The proposed system realizes quasi real-time output of large size CGHs. The reconstruction quality of these CGHs is preferable. The proposed capture system for 3D holographic communication would have a broad application prospect through further optimizations and developments.
Phase-only holograms could be displayed with a single phase-only SLM free from the zero-order diffraction and the twin image. Addition of random phase to the object light in computer-generated holograms (CGHs) can widely diffuse the object light and to avoid its concentration on the CGH. But it causes speckle noise in the reconstructed image. Speckle reducing methods could be classified as iterative and non-iterative methods. Non-iterative methods are fast and effective, such as random displaced phase distribution (RDPD) and error diffusion (ED). The drawbacks are degradation of the reconstruction at different spatial frequencies.
Point spread function (PSF) works as the impulse response of optical reconstruction system. Its Fourier transform, optical transfer function (OTF), gives a set of coefficients for plane waves of various spatial frequencies and orientations. The evaluation of OTF could quickly determine which spatial frequency components are passed or attenuated for the CGH display. The non-iterative methods for speckle noise reduction on reconstructed images in spatial frequency domain is analyzed.
Metasurface is used to manipulate the optical field recently. In holography, the complex amplitude computer generated hologram can improve the quality of the reconstructed image. However, the current devices limit the application of complex amplitude modulation. Several works have been done for complex amplitude modulation by metasurface. In this work, a novel metasurface structure has been proposed to realize complex amplitude modulation. This kind of metasurface can modulate arbitrary complex amplitude. Furthermore, it has a thinner thickness, making it easier to fabricate.
The relationship between the transmission distance and the number of Fresnel zone plate rings is evaluated. The influence of different transmission distance and the number of Fresnel zone-plate rings are analyzed. Their parameters of the best reconstructed image are obtained. A point light source is taken as an example, a phase-only spatial light modulator with the resolution of 3840×2160 pixels and the pixel interval of 3.74 μm is used for experimental verification. The numerical simulation and optical experiment results show that the optimal reconstructed image has a transmission distance of 200 mm. Meanwhile, the optimal Fresnel zone ring number is 8 under the same conditions. This study provides the optimal parameters for the spatial light modulators with different size.
KEYWORDS: Holography, Volume holography, Optical storage, Data storage, 3D modeling, Data modeling, Data storage servers, Clouds, Holographic data storage systems, Systems modeling
Holographic data storage is expected to realize capacity of terabytes as well as fast data-transfer rate of Gbits/sec on a disk format. This kind of performance will be a potential solution for next-generation storage of big data in diversities of applications such as cloud servers and ultra-high definition systems. In this work, we analyze and optimize the axial response of the holographic data storage, aiming at maximizing storage density while suppressing the inter-page crosstalk on the reconstructed data pages. The optical model of the three dimensional hologram recorded in the medium is presented. Based on the reconstructed data page model, inter-layer crosstalk is also analyzed by use of orthogonal reference patterns. The signal to noise ratio and bit error rate of the reconstructed data page are improved. Experiments are conducted to obtain the axial shift selectivity curves and verify the predicted storage density and capacity of a holographic optical disk.
Partially coherent light source has been used in holographic display due to less speckle noise and lower cost. Different from laser, it has a low temporal and spatial coherence. The reconstructed image would be blurred by the illumination properties such as size, wavelength bandwidth and divergence angle range of partially coherent light source. However, due to the limitation of the pupil diameter and the human eye’s sensitive wavelength, the blur of the reconstructed image cannot be recognized within a confined limit. The mathematical model of diffraction intensity distribution for holographic display is derived. The relationship between the illumination properties of partially coherent light source and the reconstruction results is simulated. The results suggest a criterion for the maximum size, wavelength bandwidth and divergence angle range.
KEYWORDS: Light emitting diodes, 3D displays, Autostereoscopic displays, Monte Carlo methods, LED displays, Computer simulations, LED lighting, 3D vision
Stereo depth is the most important factor for the 3D experience when viewing an autostereoscopic display. In this paper, we investigate the influence of viewing distance and viewing angle on stereo depth. First, we build the ideal stereo depth model based on the physiological limitation. Second, we establish a wave aberration model based on diffraction theory. The simulation and experimental results agree with the theoretical analyses. The model is of significant importance for giving a guidance on display system designing.
Gold nanorod has generated great research interests due to its tunable surface plasmon resonance (SPR). The mechanism of the SPR effect on the enhancements of optical performance for the volume holographic polymer is investigated. The resonance wavelength is dependent on the aspect ratio of the nanorod. Theoretical model for the localized surface plasmon resonance effect are developed and simulated for the interactions between the photopolymer components and nanorods in the gold nanorod doped volume holographic photopolymer. The experimental evaluation of the material suggests a novel candidate for potential applications in high-density optical data storage and high-resolution holographic display.
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