Method of curved composite hologram generation with suppressed speckle noise

Phase unwrapping algorithm for images with local high-density noise

Due to undersampling and the local phase with local high-density noise, it is still difficult to develop a robust phase unwrapping algorithm. In order to resolve this issue, here, we propose what we believe to be a novel multiple path-following phase unwrapping (MPIPU) algorithm based on the shearing interference principle to recover the undersampling phase (non-noise). By calculating the unwrapping coefficient k, the phase iteration filling algorithm based on least-squares is developed for the high-density noise region in order to reconstruct the three-dimensional surface topography of interferometric synthetic aperture radar (InSAR) data. The proposed algorithm takes advantage of the MPIPU's ability to fill in the missing phase with fitting data and can successfully suppress the error transfer caused by the blocky noise phase iteration process. Several experiments are conducted using both simulated and actual InSAR image data. The experimental findings show that the proposed method can achieve robust phase unwrapping performance on a phase of local high-density noise.

Holographic near-eye display system with large viewing area based on liquid crystal axicon

In this paper, a liquid crystal axicon based holographic near-eye display system with large viewing area is proposed. The viewing area of the system is extended by implementing the liquid crystal axicon. The error diffusion algorithm is used to calculate the computer-generated hologram (CGH). When incident on the liquid crystal axicon placed at the back focal plane of Fourier lens, the reconstruction light modulated by the CGH is deflected into two directions resulting in a viewing area extension. Meanwhile, to illustrate the potential of the proposed system, two-dimensional viewing area extension is demonstrated. It combines the frequency spectrum shift with the proposed system and achieves a double expansion of the horizontal viewing area and three-times expansion of the vertical viewing area. Feasibility of the proposed system is verified by optical experiments. The proposed system has potential applications in holographic augmented reality (AR) display.

Real scene acquisition and holographic near-eye display system based on a zoom industrial endoscope

In this paper, we propose a real scene acquisition and holographic near-eye display system based on a zoom industrial endoscope. By controlling the driving current of the liquid lens, the working distance and focal length of the zoom industrial endoscope can be tuned accordingly. Thus, the object at different depths can be captured. Then, the sub-sampling algorithm is used to generate the hologram. By adjusting the hologram sampling rate of the objects with different depths, the holographic near-eye 3D display can be realized. Experimental results demonstrate that the working distance of the zoom industrial endoscope can be tuned from 20 mm to 200 mm with the driving current changing from 80 mA to 190 mA. With the proposed system, the human eye can intuitively see the depth relationships among the real objects. The proposed system is expected to be applied to 3D display and industrial inspection fields.

Color curved hologram calculation method based on angle multiplexing

In this paper, a method of color curved hologram calculation based on angle multiplexing is proposed. The relationship between the wavelength, center angle and sampling interval of the curved holograms is analyzed for the first time by analyzing the reconstruction process of the curved holograms with different wavelengths. Based on this relationship, the color curved holograms are calculated by compensating phase to the complex amplitude distribution of the planar holograms. To eliminate the chromatic aberration, the curved holograms of different objects with the same color channel are respectively used for angle multiplexing and phase compensation, and then the color composed curved hologram is generated. Different color objects without chromatic aberration can be reconstructed by bending the composed curved hologram into different central angles. The experimental results verify the feasibility of the proposed method. Besides, the application of the proposed method in augmented reality display is also shown.

Large field-of-view holographic display by gapless splicing of multisegment cylindrical holograms

A holographic three-dimensional (3D) display is a recognized and ideal 3D display technology. In the field of holographic research, cylindrical holography with the merit of 360° field of view (FOV) has recently become a hot issue, as it naturally solves the problem of limited FOV in planar holography. The recently proposed approximate phase compensation (APC) method successfully obtains larger FOV and fast generation of segment cylindrical hologram (SCH) in the visible light band. However, the FOV of SCH remains limited due to its intrinsic limitations, and, to our best knowledge, the issue has not been effectively addressed. In this paper, the restricted conditions are first analyzed for the generation of SCH by the APC method. Then, an FOV expansion method is proposed for realizing a large FOV holographic display by gapless splicing of multi-SCH. The proposed method can successfully obtain larger FOV cylindrical holograms and effectively eliminate the splicing gaps; its effectiveness is verified by the results of numerical simulation and optical experiments. Therefore, the proposed method can effectively solve the FOV limitation problem of the APC method for the generation of SCH in the visible band, realize a large FOV 3D display, and provide a useful reference for holographic 3D display.

Conical holographic display to expand the vertical field of view

Recently, cylindrical holographic display technology as a 360-degree display technology has attracted much attention. However, all the studies are based on the field of view (FOV) in the azimuth direction, and the issue of FOV in the vertical direction has never been discussed. In this paper, a new holographic display is proposed to expand the vertical FOV by a conical holographic diffraction model, in which the object plane is the outer cylinder and the observation plane is a part of the cone. In this proposed method, the proposed diffraction model is firstly established by the Rayleigh-Sommerfeld diffraction formula, and then the convolution and FFT are used for a fast diffraction calculation. The correctness and effectiveness of our proposed method are verified by the simulation of Young's interference and the numerical reconstructions from the complex amplitude and encoded holograms, respectively. In addition, an accurate relationship between the conical inclination angle and the vertical FOV expansion is analyzed, and the simulation results show that our proposed method can significantly expand the vertical FOV by 0.4 of the original object. Therefore, the issue of the vertical FOV in cylindrical holography is deeply discussed and successfully addressed for the first time.

Holographic Display System to Suppress Speckle Noise Based on Beam Shaping

In this paper, a holographic system to suppress the speckle noise is proposed. Two spatial light modulators (SLMs) are used in the system, one of which is used for beam shaping, and the other is used for reproducing the image. By calculating the effective viewing angle of the reconstructed image, the effective hologram and the effective region of the SLM are calculated accordingly. Then, the size of the diffractive optical element (DOE) is calculated accordingly. The dynamic DOEs and effective hologram are loaded on the effective regions of the two SLMs, respectively, while the wasted areas of the two SLMs are performed with zero-padded operations. When the laser passes through the first SLM, the light can be modulated by the effective DOEs. When the modulated beam illuminates the second SLM which is loaded with the effective hologram, the image is reconstructed with better quality and lower speckle noise. Moreover, the calculation time of the hologram is reduced. Experiments indicate the validity of the proposed system.

Focus issue introduction: 3D image acquisition and display: technology, perception, and applications

This feature issue of Optics Express is organized in conjunction with the 2020 OSA conference on 3D image acquisition and display: technology, perception and applications which was held virtually in Vancouver from 22 to 26, June 2020 as part of the imaging and sensing congress 2020. This feature issue presents 29 articles based on the topics and scope of the 3D conference. This review provides a summary of these articles.