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In holographic three-dimensional (3D) display, phase-only spatial light modulators (SLMs) can only accept pure phase modulation signals, often leading to amplitude distortion in the reconstructed image and inaccurate object reconstruction. This paper presents a new modulating phase encoding method with amplitude compensation. Based on the imaging characteristics of phase digital holograms, the object light amplitude variation is extended to the nonlinear region of the first-order Bessel function to maximize the intensity of the reconstructed 3D image. The amplitude distortion of the reconstructed image is effectively eliminated by pre-distortion treatment of the light amplitude. Numerical simulations and optical experiments validate the presented method.

We present a bidirectional phase compensation for curved hologram generation in holographic displays. The proposed bidirectional phase compensation can enlarge the central angle of the curved hologram twice as that of the traditional method which is one-directional phase compensation. Due to the positive relationship between the angle of a curved hologram and its view angle, our proposed method is expected to double the view angle compared with the traditional method. Both numerical simulation and optical experiment results verify the validity and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

In a classical metasurface-based holographic display system, a clear holographic reconstruction image can be obtained only in the back-focal-plane of the lens. However, when the receiving plane deviates from the focal plane, the reconstructed holographic image suffers from degradations that limit the quality of the images. Hence, we propose a novel metasurface-based holographic display to realize clearly continuous imaging within the specified position range by superimposing the meta-axilens phase. It can effectively relieve the alignment requirements of the imaging system. Firstly, the parameters and properties of all-dielectric meta-atom is analyzed. Then we compare and demonstrate two sets of metasurface-based optical elements (meta-axicon, meta-lens, and meta-axilens), made by silicon meta-atoms working at 610 nm. Furthermore, we show that the metasurface hologram with the axilens phase can form a series of the relatively clear holographic images away from the focal plane. Our proposal suggests a method to reconstruct holographic wavefront in different planes simultaneously, and one can find their application domain, such as 3D biological imaging, spectroscopy, optical information storage, and encryption.

Holography can produce the most real three-dimensional (3D) image, and is considered as the ultimate 3D display technology. However, compared with other display technologies, it has not been practically available in video display so far due to low refresh rate. To realize dynamic holographic display, photosensitive material doped liquid crystal (LC) has been discovered and deeply investigated because of superior photorefractive and photoelectric properties. In this work, we present a dynamic holographic display using LC film doped with perovskite (CsPbBr3) nanocrystal (NC) as the photorefractive material. The dependence of diffraction efficiency and response time on doping concentration, recording beam power and applied voltage are investigated. A maximum diffraction efficiency of 18% has been achieved under a low electric field intensity of 0.45 V/μm and the shortest build-up time of grating is 5.5 ms. The system can realize a video display with 60 Hz refresh rate in red, green and blue colors, which demonstrates the feasibility of applying perovskite NC doped LC film in dynamic holographic display.

In this paper, a method of speckle noise suppression for holographic zoom display based on layered-pixel-scanning (LPS) algorithm is proposed. Different from the traditional algorithm, the proposed method suppresses the speckle noise based on a new algorithm design and light source optimization. The LPS algorithm is designed to calculate the phase-only hologram of the 3D object. By extracting the initial complex hologram of the 3D object and scanning the hologram by pixel, the errors of the complex amplitude can be reduced as much as possible. Then a hologram subsampling method based on the LPS algorithm generated is proposed, so the scaling of the reproduced image can be achieved easily. At the same time, the pattern with different random phase is generated and loaded on the spatial light modulator so that the reconstructed light can be optimized. When the optimized light irradiates on the phase hologram of the object, the reconstructed image with suppressed speckle noise can be displayed. The experimental results show that the proposed method has an excellent reproduction effect. Moreover, the feasibility and unique advantages of the proposed method in the holographic augmented-reality display, zoom display and multi-plane display have been proved. We believe that this method can promote the application of the holographic display.

Holography can produce the most real three-dimensional (3D) image, and is considered as the ultimate 3D display technology. However, compared with other display technologies, it has not been practically available in video display so far due to low refresh rate. To realize dynamic holographic display, photosensitive material doped liquid crystal (LC) has been discovered and deeply investigated because of superior photorefractive and photoelectric properties. In this work, we present a dynamic holographic display using LC film doped with perovskite (CsPbBr3) nanocrystal (NC) as the photorefractive material. The dependence of diffraction efficiency and response time on doping concentration, recording beam power and applied voltage are investigated. A maximum diffraction efficiency of 18% has been achieved under a low electric field intensity of 0.45 V/μm and the shortest build-up time of grating is 5.5 ms. The system can realize a video display with 60 Hz refresh rate in red, green and blue colors, which demonstrates the feasibility of applying perovskite NC doped LC film in dynamic holographic display. [ABSTRACT FROM AUTHOR]

In this paper, we propose an adjustable optical slit based on a phase type spatial light modulator (SLM). The adjustable optical slit consists of two polarized beam splitters and one SLM. The SLM is used to modulate the phase of light. A phase grayscale with specific structure is produced, where the middle phase is 0 and the phase on both sides is π. By changing the width of the slit grayscale, we can adjust the width of the slit easily. Our experiment shows that one-dimensional (1-D) slit and 2-D mask can be realized and the slit width can be tuned accordingly. The results verify its feasibility. The adjustment accuracy of slit can reach several microns, and the slit can also be laterally translated. The proposed device can be used not only in optical system or holographic display to improve the quality of the image, but also in spectrometers to select the specific spectral feature.

In this paper, a holographic display system with wide viewing area is proposed based on the effective area expansion of the SLM. The effective area of the SLM is calculated based on the viewing area characteristics and expanded by using two SLMs. Different from the traditional holographic system based on the parallel-arranged SLMs or curved-arranged SLMs, we calculate the effective areas of the SLMs and the effective hologram of the system can be generated based on the effective-viewing-area (EVA) algorithm. The proposed system uses a 4K SLM by seamlessly stitching the effective areas of two 2K SLMs. After the EVA is calculated, the size of the effective hologram is inversely calculated according to the EVA. So, the effective area of the hologram is increased, and the calculation of the wasted information is greatly decreased. With the proposed system, the reconstructed object with large viewing area can be realized. Moreover, the calculation time for generating the hologram is reduced significantly. Experimental results verify the feasibility of the proposed system. In the proposed system, the 2K SLMs are used as examples for splicing, when more high-performance SLMs are used, the viewing area will be further expanded, and the advantage of the calculation speed will be more obvious than the traditional splicing method. The proposed system can provide new references to the holographic display system based on multiple SLMs stitching.

In the point-based method, the aliasing phenomenon in the hologram plane is usually considered as a harmful phenomenon because it will degrade the reconstructed image quality. In this paper, the advantage of the aliasing phenomenon is employed to improve the reconstructed image quality of the phase-only hologram. Through analysis of the principle of this phenomenon, we proposed a method to improve the reconstructed image quality of the phase-only hologram. By controlling the strength of the aliasing, the amplitude distribution in the hologram plane can be turned into a nearly uniform distribution. It is helpful to generate an optimized phase-only hologram, which results in higher quality of the reconstructed image because the effect of lost information caused by abandon the amplitude part can be diminished. Moreover, a holographic see-through display system is designed to demonstrate the effectiveness of the proposed method.

In this paper, we propose a projection-type multiview holographic three-dimensional (3-D) display using a single spatial light modulator (SLM) and a directional diffractive device, where a phase-only Fresnel hologram is calculated and displayed on the SLM to reconstruct the multiview hybrid image of a 3-D object for providing the amplitude information of a multiview light field, and a directional diffractive device covered with many pixelated gratings is designed to guide different reconstructed perspectives into different viewing zones for expressing the phase information of the light field. Furthermore, a four-view directional diffractive device is fabricated by using the pixelated holographic exposure method, and its optical properties are also measured under a collimated illumination of the green reconstruction laser with the designed wavelength. In addition, an experimental verification system is constructed to demonstrate a four-view 3-D display. The recorded experimental results confirm that a crosstalk-free four-view light field is created, which is beneficial from the precise alignment between the directional diffractive device and the reconstructed image. Moreover, the capability of dynamic display with the proposed system is also tested by refreshing the SLM with the sequential holograms, and the captured videos show a promising potential for the real-time multiview holographic 3-D projectors.

In this paper, a holographic display system with wide viewing area is proposed based on the effective area expansion of the SLM. The effective area of the SLM is calculated based on the viewing area characteristics and expanded by using two SLMs. Different from the traditional holographic system based on the parallel-arranged SLMs or curved-arranged SLMs, we calculate the effective areas of the SLMs and the effective hologram of the system can be generated based on the effective-viewing-area (EVA) algorithm. The proposed system uses a 4K SLM by seamlessly stitching the effective areas of two 2K SLMs. After the EVA is calculated, the size of the effective hologram is inversely calculated according to the EVA. So, the effective area of the hologram is increased, and the calculation of the wasted information is greatly decreased. With the proposed system, the reconstructed object with large viewing area can be realized. Moreover, the calculation time for generating the hologram is reduced significantly. Experimental results verify the feasibility of the proposed system. In the proposed system, the 2K SLMs are used as examples for splicing, when more high-performance SLMs are used, the viewing area will be further expanded, and the advantage of the calculation speed will be more obvious than the traditional splicing method. The proposed system can provide new references to the holographic display system based on multiple SLMs stitching. [ABSTRACT FROM AUTHOR]

In this paper, we present a concept for speckle reduction using optical superposition instead of temporal superposition. The proposed speckle reduction method does not contain any mechanical movement nor time-multiplexing technique. Therefore, the system is stable and free from the frame rate degradation or additional computation load. In addition, the angle diversity method is adopted with the proposed method to intensify the speckle reduction. In order to apply the angle diversity method, the required minimum angle difference is analyzed theoretically. To realize the proposed speckle reduction concept, the system is implemented with practical optical components. The system includes an echelon, which is a stair-shaped glass and a static diffuser. The echelon is employed to decrease the spatial coherence of the incident beam. The static diffuser imposes the band-limited random phases on each of the split beams that have passed through the echelon. Also, the static diffuser is used to combine mutually incoherent split beams into a single speckle-reduced beam. The proposed speckle-reduced light source is applied to the holographic display to demonstrate the speckle reduction effect. Experimental results show that the speckle contrast of the reconstructed image is reduced by 55%. [ABSTRACT FROM AUTHOR]

The reconstruction quality of computer-generated holographic display is subject to distortions, which are caused by manufacture defects and misalignments of optical elements. Distortion correction based on precision optics is costly and time-consuming. In this paper, a numerical distortion-correction method based on the angular spectrum algorithm is proposed. A wavefront acquisition system using a camera and the four-step phase-shifting algorithm is employed for calculating the distorted distributions. A wavefront correction system using the spatial light modulator is developed for eliminating distorted distributions. Effective distance, calculation time and iterations, and limitations of the method are discussed. The proposed method is robust in reducing distortions in computer-generated holographic display. [ABSTRACT FROM AUTHOR]

In this paper, we propose a projection-type multiview holographic three-dimensional (3-D) display using a single spatial light modulator (SLM) and a directional diffractive device, where a phase-only Fresnel hologram is calculated and displayed on the SLM to reconstruct the multiview hybrid image of a 3-D object for providing the amplitude information of a multiview light field, and a directional diffractive device covered with many pixelated gratings is designed to guide different reconstructed perspectives into different viewing zones for expressing the phase information of the light field. Furthermore, a four-view directional diffractive device is fabricated by using the pixelated holographic exposure method, and its optical properties are also measured under a collimated illumination of the green reconstruction laser with the designed wavelength. In addition, an experimental verification system is constructed to demonstrate a four-view 3-D display. The recorded experimental results confirm that a crosstalk-free four-view light field is created, which is beneficial from the precise alignment between the directional diffractive device and the reconstructed image. Moreover, the capability of dynamic display with the proposed system is also tested by refreshing the SLM with the sequential holograms, and the captured videos show a promising potential for the real-time multiview holographic 3-D projectors. [ABSTRACT FROM AUTHOR]

A light-field 3-D display (LFD) reproduces light rays or wavefront as if there are real objects, and a perfect 3-D display that satisfies all the depth cues in human vision becomes possible. By reproducing both horizontal and vertical parallaxes, i.e., full-parallax, an LFD reconstructs a real or virtual image in 3-D space. A rich 3-D experience can be provided to viewers, and moreover, multiple viewers can share the same reproduced 3-D image. A technology called holographic stereogram (HS) is the integration of ray-based and wavefront-based methods, and has been applied to LFD. Hardcopy HS has already been commercialized. The technology of HS is helpful also for an interactive LFD; a full-parallax LFD using a projector and a holographic screen that modulates the directions of light rays is based on the principle of HS. In this case, accurate registration between the projected image and the holographic screen is necessary, and it is achieved by projecting some test patterns and capturing them with a calibration camera. As a full-parallax LFD can reproduce real images in midair between the screen and viewers, it is possible to realize interactive 3-D touch interface. If a user touches the 3-D real image floating in the air, the reproduced light is scattered by the user’s fingertip. The scattered light is detected by a color image sensor placed behind the holographic screen, and can be employed to detect the user’s touch. In this system, the reproduced 3-D images and the 3-D touch detection are associated with each other, and thus, we do not have to worry about the complicated registration between them. The identification of the user’s interaction is simple, because the color information of the 3-D image can be used for this purpose. Some experimental results of the 3-D touch-sensing display are introduced, and possible applications of this technology are discussed as well. [ABSTRACT FROM AUTHOR]

Random phase is always added to the object to diffuse the object light in computer-generated holograms. However, this addition causes considerable speckle noise in the reconstructed image. For improving the speckle noise problem, we propose a new method, which can reconstruct the 3-D object with higher image quality. A virtual intermediate plane is introduced between the object and the hologram plane. A three-dimensional object is first sliced into multiple layers according to their depth information. Then, each layer is added with uniform constant phase and propagates to the intermediate plane with an angular spectrum diffraction algorithm. Complex amplitude from each layer is added together as the desired distribution in the signal area in the intermediate plane. Then, the iterative Fourier transform algorithm is taken between the hologram and the intermediate plane to achieve the phase-only computer-generated hologram (CGH). Feasibility of the proposed method is verified with simulations and experiments. [ABSTRACT FROM PUBLISHER]

A novel approach for color holographic 3D displays employing several liquid crystal based spatial light modulators (SLM) is presented. A multicolor reconstruction is introduced into circular monochrome display architecture with horizontal-only-parallax through the use of space-division method (SDM). In the SDM active area of an SLM is divided into three regions generating the RGB component images by using color spatial filter composed of a three glass stripes that are attached to the front of each SLM. Relatively low complexity level of SDM enables to upgrade a horizontal-only-parallax monochrome display to a color one at the expense of image resolution. There is no reduction of remaining key performance parameters, i.e., image dimensions, refresh frame rate, and viewing angle are preserved with no increase of SLM number. In this paper, practical aspects of color imaging implementation, including filter mask design and hardware calibration, are considered. Developed procedures focus on major three effects, i.e., spectral calibration of response of highly dispersive SLM phase, spatial calibration of filter mask and numerical alignment of RGB imaging volumes. The presented experimental results of static and dynamic 3D reconstructions of computer generated holograms validate the performance of calibration procedures and the high color imaging quality of the display. [ABSTRACT FROM PUBLISHER]

A novel technique of simultaneously recording of multiple digital holograms with different lightings is proposed. The technique is based on optical scanning holography (OSH). In OSH, the object is raster scanned by a heterodyne interference pattern, and a single-pixel detector is applied to detect the scattered light. Subsequently, a complex hologram is obtained by removing the carrier and conjugate term. Based on the principle of light-path-reversal, the detector in OSH is found to play the role of a light source in conventional digital holography. As a result, simultaneously recording of multiple master holograms with different lightings can be achieved by using multiple detectors located at different positions. In the stereo-lighting reconstruction, the holograms with different lightings are superimposed with a weighting to generate a fusion hologram. Various desired lighting effect can thus be produced by modifying the weighting of the master holograms. The proposed technique may find novel applications in holographic display and holographic metrology. [ABSTRACT FROM PUBLISHER]

Dynamic holographic three-dimensional (3-D) display, which features reconstructing 3-D images with full depth cues has great potential in various fields such as medical, and military industries obtained a broad attention in the last decades. Combing parallel computation techniques, hologram synthesis algorithms are capable of calculating diffraction and interference pattern dynamically or even in real-time manner. In addition, the development of various types of optical modulators including liquid crystal (LC)-based, opto-acoustic-typed, digital micromirror devices (DMDs), and opto–opto materials made it possible that device can load and display such holographic patterns dynamically. In accordance with the progress of algorithms and modulators, we can expect that dynamic holographic 3-D display will be able to reconstruct 3-D images with real-time refresh rate, full color, wide viewing angle, and large image size, and the system will be commercialized in a near future. [ABSTRACT FROM PUBLISHER]

We present optical experimental results for a high-resolution three-dimensional (3D) holographic display system based on dense ray sampling and integral imaging capture. Holograms are generated based on re-sampling the rays from 2D images captured by an integral imaging system. In addition, we demonstrate a depth of field extension technique during the integral imaging capture by combining an amplitude modulated lens technique and a blind convolution approach. The optically reconstructed images of the holographic display system are shown and compared with conventional integral imaging-based holographic displays for different scenes. [ABSTRACT FROM PUBLISHER]

A video-rate optical holographic display is achieved by using an azo-dye-doped liquid crystal as the passive, updatable recording material. The response time of this material is measured in the order of several to tens of milliseconds, depending on recording beam intensities, polarization directions, and polarization states. A holographic video at a refresh rate of 25 Hz, sourced from a spatial light modulator, is demonstrated in the experiments. [ABSTRACT FROM PUBLISHER]

We propose a new method to compute the phase-only computer-generated hologram (CGH) that can modulate an image on a tilted plane. We used the fractional Fourier transformation to compute light propagation between the hologram plane and the tilted plane. The phase-only hologram was obtained by an iterative algorithm. We proposed a method to calculate the inverse optical propagation from the hologram plane to a tilted plane by coordinate rotation and a simple interpolation in the Fourier domain. The experimental results show that the projected image on the tilted plane can be reconstructed by a phase-only hologram generated by our iterative algorithm. We also show that the quality of the projected image on the tilted plane is better than the image projected by the phase hologram generated by traditional method. [ABSTRACT FROM PUBLISHER]

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.