Computer-generated Hologram Algorithm Research Articles

High-throughput multiplexed fluorescence lifetime microscopy.

Fluorescence lifetime microscopy has been widely used in quantifying cellular interaction or histopathological identification of different stained tissues. A novel, to the best of our knowledge, approach for high-throughput multiplexed fluorescence lifetime imaging is presented. To establish a high-throughput fluorescence lifetime acquisition system, a uniformed illumination optical focus array was generated by a novel computer-generated hologram algorithm based on matrix triple product. This, in conjunction with an array detector and multichannel time-correlated single-photon counting, enables the full use of the acquisition ability of each detector. By utilizing interval segmentation of photon time detection, a high-throughput multiplexed fluorescence lifetime imaging is achieved. Experimental results demonstrate that this method achieves a fivefold increase in the collection throughput of fluorescence lifetime and is capable of simultaneous dual-target fluorescence lifetime measurement.

Investigating learning-empowered hologram generation for holographic displays with ill-tuned hardware.

Existing computational holographic displays often suffer from limited reconstruction image quality mainly due to ill-conditioned optics hardware and hologram generation software. In this Letter, we develop an end-to-end hardware-in-the-loop approach toward high-quality hologram generation for holographic displays. Unlike other hologram generation methods using ideal wave propagation, ours can reduce artifacts introduced by both the light propagation model and the hardware setup, in particular non-uniform illumination. Experimental results reveal that, compared with classical computer-generated hologram algorithm counterparts, better quality of holographic images can be delivered without a strict requirement on both the fine assembly of optical components and the good uniformity of laser sources.

Wavefront recording plane-like method for polygon-based holograms.

The wavefront recording plane (WRP) method is an algorithm for computer-generated holograms, which has significantly promoted the accelerated computation of point-based holograms. Similarly, in this paper, we propose a WRP-like method for polygon-based holograms. A WRP is placed near the object, and the diffracted fields of all polygons are aggregated in the WRP so that the fields propagating from the polygonal mesh affect only a small region of the plane rather than the full region. Unlike the conventional WRP method used in point-based holograms, the proposed WRP-like method utilizes sparse sampling in the frequency domain to significantly reduce the practical computational kernel size. The proposed WRP-like method and the analytical shading model are used to generate polygon-based holograms of multiple three-dimensional (3D) objects, which are then reproduced to confirm 3D perception. The results indicate that the proposed WRP-like method based on an analytical algorithm is hundreds of times faster than the reference full region sampling case; a hologram with tens of thousands of triangles can be computed in seconds even on a CPU, whereas previous methods required a graphics processing unit to achieve these speeds.

Reconfigurable Metasurface Hologram of Dynamic Distance via Deep Learning

Reconfigurable metasurfaces have been regarded as an emerging subfield of metasurfaces that can manipulate electromagnetic wave information in a smart manner. They stimulate a gradual transition in metasurface holography from passive to active elements. To date, intelligent dynamic holographic imaging schemes typically rely on iterative or data-driven methods to obtain holograms at a fixed imaging distance, which significantly hinders the development of intelligent dynamic holographic imaging in practical scenarios involving high demands for dynamic imaging distances. Herein, a computer-generated hologram algorithm with a dynamic imaging distance and a reconfigurable metasurface are proposed, which is referred to as a generator and physical diffractive network. Simulation results of time–distance division for three-dimensional imaging are provided to demonstrate the reliability and high efficiency of the proposed algorithm.

Phase dual-resolution networks for a computer-generated hologram.

The computer-generated hologram (CGH) is a method for calculating arbitrary optical field interference patterns. Iterative algorithms for CGHs require a built-in trade-off between computation speed and accuracy of the hologram, which restricts the performance of applications. Although the non-iterative algorithm for CGHs is quicker, the hologram accuracy does not meet expectations. We propose a phase dual-resolution network (PDRNet) based on deep learning for generating phase-only holograms with fixed computational complexity. There are no ground-truth holograms employed in the training; instead, the differentiability of the angular spectrum method is used to realize unsupervised training of the convolutional neural network. In the PDRNet algorithm, we optimized the dual-resolution network as the prototype of the hologram generator to enhance the mapping capability. The combination of multi-scale structural similarity (MS-SSIM) and mean square error (MSE) is used as the loss function to generate a high-fidelity hologram. The simulation indicates that the proposed PDRNet can generate high-fidelity 1080P resolution holograms in 57 ms. Experiments in the holographic display show fewer speckles in the reconstructed image.

Occlusion Culling for Wide-Angle Computer-Generated Holograms Using Phase Added Stereogram Technique

A computer-generated hologram (CGH) allows synthetizing view of 3D scene of real or virtual objects. Additionally, CGH with wide-angle view offers the possibility of having a 3D experience for large objects. An important feature to consider in the calculation of CGHs is occlusion between surfaces because it provides correct perception of encoded 3D scenes. Although there is a vast family of occlusion culling algorithms, none of these, at the best of our knowledge, consider occlusion when calculating CGHs with wide-angle view. For that reason, in this work we propose an occlusion culling algorithm for wide-angle CGHs that uses the Fourier-type phase added stereogram (PAS). It is shown that segmentation properties of the PAS can be used for setting efficient conditions for occlusion culling of hidden areas. The method is efficient because it enables processing of dense cloud of points. The investigated case has 24 million of point sources. Moreover, quality of the occluded wide-angle CGHs is tested by two propagation methods. The first propagation technique quantifies quality of point reproduction of calculated CGH, while the second method enables the quality assessment of the occlusion culling operation over an object of complex shape. Finally, the applicability of proposed occlusion PAS algorithm is tested by synthetizing wide-angle CGHs that are numerically and optically reconstructed.

Liquid crystal integrated metadevice for reconfigurable hologram displays and optical encryption.

The ultimate goal of metasurface research in recent years is to apply metasurface to reality applications and improve the performance compared to its counterpart, namely conventional optical elements with the same function. Inspired by the application of electrically addressing spatial light modulator (EA-SLM) and based on the binary holographic algorithm, here we propose a reconfigurable metadevice integrated with the nematic liquid crystal (NLC). The smart metadevice directly uses the subwavelength antennas as the main contributor to the phase accumulation instead of the NLC layer. By applying different electrical modulation patterns on the NLC, the metadevice can realize the function of dynamic holographic display as traditional SLMs but features in smaller size, higher resolution and lager field of view. In addition, we improved the existing computer-generated hologram algorithm to generate three holograms with quantitative correlation and also propose a new optical encryption method based on our metadevice. The encryption method needs four elements in total to decrypt and can fully meets the requirements of the various encrypted content. We believe such metadevice paves the way for the new generation of micro-optical display and optical encryption devices.

Digital correlation of computer-generated holograms for 3D face recognition

Three-dimensional (3D) face recognition has been a crucial task in human biometric verification and identification. A digital correlation method of a computer-generated hologram (CGH) for 3D face recognition is proposed, which encodes 3D data into a 2D hologram for recognition. The 3D face models are preprocessed and compressed to into groups of feature points. The CGH templates corresponding to the 3D feature points are generated by point- and layer-oriented algorithms based on three different numerical algorithms to encode depth values into 2D holograms. A 2D digital correlation is performed between the CGH templates. It is demonstrated that the generated CGHs templates could be effectively classified based on the correlation performance metrics of discrimination ratio, peak-to-correlation plane energy, and peak-to-noise ratio. With the essence of the CGH algorithm being the conversion of 3D data to a 2D hologram, the proposed encoding and decoding method has great advantages in reducing computational efforts and potential applications in 3D face recognition, storage, and display.

Formulas of partially spatial coherent light and design algorithm for computer-generated holograms

Formulas of partially spatial coherent light are derived and its corresponding design algorithm is proposed for generating computer-generated holograms based on partially spatial coherent light. The partially coherent light is divided into two terms: spatially absolute coherent part and incoherent part. The former is propagated by angular spectrum method, while the latter is based on the optical transfer function. The related formulas are derived where the coherent function (degree of coherence) is related. A modified iterative algorithm is further developed for optimizing the phase distributions. Numerical simulations and optical experiments are both performed to verify the proposed algorithm. The results obtained by the proposed method and the traditional method are compared, and it is clear that the speckle contrasts in optical experiments are improved more than 46%, and the image quality is obviously improved. This method could also provide new applications for three-dimensional holographic display, beam shaping, and other wave-front modulation techniques.

Simple and fast calculation algorithm for computer-generated hologram based on integral imaging using look-up table.

We proposed a simple and fast algorithm for computer-generated hologram (CGH) based on pinhole-type II using a look-up table. The method consists of two steps: in the first step, the unity amplitude diffraction pattern of the center pinhole on hologram plane is pre-calculated and stored as many sub-regions. Secondly, diffraction patterns for other pinholes are obtained by simply shifting and tiling the pre-calculated sub-regions, and the final CGH is obtained by adding them all together. The calculation time is short because only addition and multiplication of the stored diffraction pattern are required. In addition, the required memory space is small since only one diffraction pattern is stored. Numerical simulation and reconstruction are performed on both plane object and object with continuous depth profile to verify the proposed method. Result shows that the proposed method can easily achieve real-time hologram generation with several CPU threads running simultaneously.

Fast generation of computer-generated holograms using wavelet shrinkage

Computer-generated holograms (CGHs) are generated by superimposing complex amplitudes emitted from a number of object points. However, this superposition process remains very time-consuming even when using the latest computers. We propose a fast calculation algorithm for CGHs that uses a wavelet shrinkage method, eliminating small wavelet coefficient values to express approximated complex amplitudes using only a few representative wavelet coefficients.

Space bandwidth product enhancement of holographic display using high-order diffraction guided by holographic optical element.

A space bandwidth product (SBP) enhancement method for holographic display using high-order diffraction of a spatial light modulator (SLM) is proposed. Among numerous high order diffraction terms, the plus-minus first and the zeroth are adopted and guided by holographic optical elements (HOEs) to an identical direction with the same intensity. By using a set of electro-shutters synchronized with corresponding order component, the system acts as if three SLMs are tiled in the horizontal direction. To confirm the feasibility of using HOE as the guiding optics for the system, several optical characteristics of the recording material are measured before using them. Furthermore, a computer generated hologram algorithm is proposed for compensating the wavefront distortion caused by use of the HOE. The demonstrated system achieves a three-fold increase in SBP of a single SLM. The results are verified experimentally.

병렬 분산 컴퓨팅을 이용한 초다광원 3차원 물체의 홀로그램 고속 생성

컴퓨터 생성 홀로그램(CGH: computer-generated hologram) 기법은 일반적인 범용 컴퓨터(PC: personal computer)에서도 홀로그램을 쉽게 생성해주는 기술이다. CGH 알고리즘의 연산량은 생성하려는 홀로그램의 해상도 크기와 3D (three-dimensional) 물체의 광원 개수에 따라 결정되기 때문에, 초다광원 물체나 초고해상도 홀로그램을 생성하기 위해서는 방대한 양의 연산이 요구된다. 따라서 CGH 기법을 실용적으로 사용하기 위해서는 CGH 연산량을 줄이거나, 하드웨어의 연산 속도를 높이는 방법이 필요하다. 본 논문에서는 병렬 분산 컴퓨팅을 이용하여 초다광원 3차원 물체의 홀로그램을 고속으로 생성할 수 있는 시스템을 제안한다. 기존의 방법들은 주로 단일 PC를 이용하여 고속으로 CGH를 연산하는 방법을 사용했기 때문에 연산 능력을 증가시키는데 한계가 있었던 반면, 본 논문에서 제안하는 방법은 서버 PC가 일반적인 GPU가 장착되어 있는 다수의 클라이언트 PC들의 연산 능력을 효율적으로 사용하여 초다광원 물체에 대해 고속으로 CGH를 연산할 수 있다. 실험 결과, 제안하는 방법을 사용하면 157,771개의 광원을 갖는 초다광원 3차원 물체에 대해 1,5361,536 해상도를 갖는 홀로그램을 약 121ms로 생성할 수 있음을 확인할 수 있었다. 또한, 클라이언트 PC의 수를 증가시킬수록 디지털 홀로그램을 생성하는 시간이 줄어드는 것을 확인할 수 있었다. The computer generated hologram (CGH) method is the technology which can generate a hologram by using only a personal computer (PC) commonly used. However, the CGH method requires a huge amount of calculational time for the 3D object with a super multi-light source or a high-definition hologram. Hence, some solutions are obviously necessary for reducing the computational complexity of a CGH algorithm or increasing the computing performance of hardware. In this paper, we propose a method which can generate a digital hologram of the 3D object with a super multi-light source using parallel distributed computing. The traditional methods has the limitation of improving CGH performance by using a single PC. However, the proposed method where a server PC efficiently uses the computing power of client PCs can quickly calculate the CGH method for 3D object with super multi-light source. In the experimental result, we verified that the proposed method can generate the digital hologram with 1,5361,536 resolution size of 3D object with 157,771 light source in 121 ms. In addition, in the proposed method, we verify that the proposed method can reduce generation time of a digital hologram in proportion to the number of client PCs.

Accurate calculation of computer-generated holograms using angular-spectrum layer-oriented method.

Fast calculation and correct depth cue are crucial issues in the calculation of computer-generated hologram (CGH) for high quality three-dimensional (3-D) display. An angular-spectrum based algorithm for layer-oriented CGH is proposed. Angular spectra from each layer are synthesized as a layer-corresponded sub-hologram based on the fast Fourier transform without paraxial approximation. The proposed method can avoid the huge computational cost of the point-oriented method and yield accurate predictions of the whole diffracted field compared with other layer-oriented methods. CGHs of versatile formats of 3-D digital scenes, including computed tomography and 3-D digital models, are demonstrated with precise depth performance and advanced image quality.

Fully computed holographic stereogram based algorithm for computer-generated holograms with accurate depth cues

We propose an algorithm based on fully computed holographic stereogram for calculating full-parallax computer-generated holograms (CGHs) with accurate depth cues. The proposed method integrates point source algorithm and holographic stereogram based algorithm to reconstruct the three-dimensional (3D) scenes. Precise accommodation cue and occlusion effect can be created, and computer graphics rendering techniques can be employed in the CGH generation to enhance the image fidelity. Optical experiments have been performed using a spatial light modulator (SLM) and a fabricated high-resolution hologram, the results show that our proposed algorithm can perform quality reconstructions of 3D scenes with arbitrary depth information.

1211 Development of Novel Computer Generated Hologram (CGH) for Short Pulse Laser Processing of Precise Micro Pattern Using Spatial Light Modulator

Complex micro- and nano-structure can be formed simply by generating complex electric fields holographically with a spatial light modulator (SLM) by liquid crystal on silicon (LCOS) technology. Processing patterns for micro-patterns to be desired are commonly generated by computer generated hologram (CGH). In this study, to realize the more precise micro-processing with highly flexible pattern by use of the LCOS-SLM, a novel CGH algorithm suitable to micrometer order processing is developed, into which the principle of a phase shift mask is applied. From the results of processing experiments to form micro holes and longitudinal ridges, the novel algorithm can provide more precise processing.

Semi-analytic texturing algorithm for polygon computer-generated holograms.

A texturing method for the semi-analytic polygon computer-generated hologram synthesis algorithm is studied. Through this, the full-potential and development direction of the semi-analytic polygon computer-generated holograms are discussed and compared to that of the conventional numerical algorithm of polygon computer-generated hologram generation based on the fast Fourier transform and bilinear interpolation. The theoretical hurdle of the semi-analytic texturing algorithm is manifested and an approach to resolve this problen. A key mathematical approximation in the angular spectrum computer-generated hologram computation, as well as the trade-offs between texturing effects and computational efficiencies are analyzed through numerical simulation. In this fundamental study, theoretical potential of the semi-analytic polygon computer-generated hologram algorithm is revealed and the ultimate goal of research into the algorithm clarified.

Fast calculation of computer-generated hologram for RGB and depth images using wavefront recording plane method

In a three-dimensional display by a computer-generated hologram?(CGH), fast computation of CGH is required. In this paper, in order to accelerate CGH generation, the following two methods are used; the first method is band-limited double-step Fresnel diffraction. Compared with the convolution-based diffraction, such as angular spectral the proposed method requires less computational time and memory. The second method is a wavefront recording plane (WRP) method which reduces the calculation amount by placing WRPs in the vicinity of the object. We succeeded in speeding up CGH calculation by combining the two methods. Full Text: PDF References T. C. Poon (Ed.), holography and three-dimensional display: Principles and Applications, Springer (2006). CrossRef S. C. Kim and E. S. Kim, Effective generation of digital holograms of three-dimensional objects using a novel look-up table method, Appl. Opt. 47, D55–D62 (2008) . CrossRef K. Matsushima, H. Shimmel, and F. Wyrowski, Fast calculation method for optical diffraction on tilted planes by use of the angular spectrum of plane waves, J. Opt. Soc. Am. A. 20, 1755-1762 (2003). CrossRef M. Yamaguchi, H. Hoshino, T. Honda, and N. Ohyama, Phase-added stereogram: calculation of hologram using computer graphics technique, Proc. SPIE 1914, 25-31 (1993). CrossRef N. Okada, T. Shimobaba, Y. Ichihashi, R. Oi, K. Yamamoto, M. Oikawa, T. Kakue, N. Masuda, and T. Ito, Band-limited double-step Fresnel diffraction and its application to computer-generated holograms, Opt. Express 21, 9192-9197 (2013). CrossRef F. Zhang, I. Yamaguchi, and L. P. Yaroslavsky, Algorithm for reconstruction of digital holograms with adjustable magnification, Opt. Lett. 29, 1668-1670 (2004). CrossRef T. Shimobaba, N. Masuda and T. Ito, Simple and fast calclulation algorithm for computer-generated hologram with wavefront recording plane, Opt. Lett. 34, 3133-3135 (2009). CrossRef T. Shimobaba, H. Nakayama, N. Masuda and T. Ito, Rapid calculation of Fresnel computer-generated-hologram using look-up table and wavefront-recording plane methods for three-dimensional display, Opt Express 18 19504-19509 (2010). CrossRef J. Weng, T. Shimobaba, N. Okada, H. Nakayama, M. Oikawa, N. Masuda and T. Ito, Generation of real-time large computer generated hologram using wavefront recording method, Opt. Express 20, 4018-4023 (2012). CrossRef T. Shimobaba, T. Kakue, N. Masuda, Y. Ichihashi, K. Yamamoto and T. Ito, Computer holography using wavefront recording method, Digital Holography and Three-Dimensional Imaging(DH) DH2013, DTu1A. 2 (2013). CrossRef A. -H. Phan, M. -l. Piao, S. -K. Gil, and N. Kim, Generation speed and reconstructed image quality enhancement of a long-depth object using double wavefront recording planes and a GPU, Appl. Opt. 53, 4817-4824 (2014). CrossRef P. Tsang, W. -K. Cheung, T. -C. Poon, and C. Zhou, Holographic video at 40 frames per second for 4-million object points, Opt. Express 19, 15205-15211 (2011). CrossRef

다중 GPGPU를 이용한 컴퓨터 생성 홀로그램의 병렬화 구현

컴퓨터생성홀로그램은 수학적으로 모델링된 광학적인 현상을 컴퓨터로 연산한 것이다. 이때 방대한 량의 연산이 필요하기 때문에 실시간으로 고해상도의 홀로그램을 얻기 위해서는 고속 기법이 필요하다. 본 논문에서는 CGH를 위한 두 가지 병렬화를 제안한다. 첫 번째는 GPU 내에서 CGH 알고리즘을 병렬화하는 것이고, 두 번째는 다수의 GPU를 위한 병렬화이다. 제안한 알고리즘 구조는 CUDA를 이용하여 GTX780 Ti GPU에 구현하였다. 약 10K의 입체 정보를 이용하여 <TEX>$1,024{\times}1,024$</TEX>의 컬러 홀로그램을 생성하는데 약 106ms가 소요된다. Computer-generated hologram (CGH) is to mathematically model optical phenomenon with digital computer. Because it requires huge amount of computational power, a fast and high performance technique is needed. In this paper, we proposed two parallelizations for CGH calculation. The first is to parallelize CGH algorithm in a GPU (general processing unit) and the second is to parallelize multiple GPUs. The proposed algorithm was implemented in GTX780 Ti GPU. It calculates a <TEX>$1,024{\times}1,024$</TEX> hologram with 10K object points for about 24ms.

Noise Reduction in Digital Hologram Using Wavelet Transforms and Smooth Filter for Three-Dimensional Display

A noise reduction method of Fresnel computer-generated hologram (CGH) using wavelet transform and smooth filter is presented. Noise in hologram is very difficult to remove because an interference pattern is recorded on a digital camera during the digital processing. It also occurs in the reconstruction process, which is affected by discrete quantizing levels and optical experiment setup. So, we develop an algorithm that is capable of changing pixel values at different scales with imaginary or real value according to the requirements of each position in the hologram. A new algorithm is proposed to satisfy the above requirements using a mathematical transformation between the smooth filter function and mother wavelet function in a wavelet transform. In this paper, a theoretical model to predict the effect of noise is described and verified by the experimental results. Based on this, the resultant noises in the reconstructed image by Fresnel CGH algorithm are decreased clearly when spatial light modulator (SLM) for 3D object is placed at distance from 260 mm to 900 mm. The enhanced 3D images can be obtained from digital holograms using efficient noise reduction algorithm to apply this proposed model.