Phase Holograms Research Articles

Intraocular lens simulator using computational holographic display for cataract patients.

To develop and validate a holography based vision simulator for the demonstration of expected postoperative vision corresponding to monofocal and multifocal intraocular lenses (IOL) to cataract patients before surgery. An artificial eye model is used to measure the optical performance of different IOL types. The resultant aberrations and degradations are then modeled using phase holograms and shown to subjects on a holographic display. We measure the contrast and resolution loss, halos around the light sources, and point spread function (PSF) corresponding to three different IOLs. We tested the holography based vision simulator on 13 healthy subjects and 6 cataract patients. Monofocal, bifocal, and trifocal IOLs exhibited a contrast decrease of 5%, 42%, and 45% and a resolution limit of 4.49, 4.00, and 4.00 lp/mm (using 0.05 MTF criteria), respectively. Monofocal IOLs have the best resolution and contrast at the optimal focus distance, and multifocal lenses offer extended depth-of-field but exhibit prominent halos and reduced contrast/resolution. We confirmed that the visual functions of IOLs could be successfully modeled using phase holograms and simulated using a holographic display without using a physical IOL. Patients can experience the effects of different IOL options prior to surgery, which helps with IOL selection, expectation management, and patient satisfaction.

Preparation of Panchromatic Silver Halide Emulsion to Fabricate High Efficiency Multiplexed Volume Phase Holograms for Solar Concentration Application

Volume Phase Gratings (VPG) are often recorded using holographic emulsions such as photopolymer, Dichromated Gelatin (DCG), and silver halide. We employed silver halide emulsion to record the VPG in monochromatic red wavelength for solar concentration purposes. According to the Braggs condition, the recorded VPG's diffraction efficiency reaches its peak at the recorded angle and wavelength. For solar applications, we needed high diffraction efficiency over a wide angle and wavelength range. So, we captured multiplexed single VPG in our own panchromatic silver halide emulsion. The procedure of making panchromatic silver halide emulsion is described in depth. This technique is unique in that it achieves peak diffraction efficiency at broad wavelength and wide angle in a single multiplexed VPG. The panchromatic multiplexed VPG produced a high diffraction efficiency in wide-angle response with overall visible wavelengths. This study describes the high diffraction efficiency multiplexed VPG in its own manufactured panchromatic silver halide emulsion for solar concentrating applications.

High-speed arbitrary pure phase hologram generation method based on a specific multi-phase: publisher’s note

High-speed arbitrary pure phase hologram generation method based on a specific multi-phase: publisher’s note

High-speed arbitrary pure phase hologram generation method based on a specific multi-phase

This paper presents a novel design method, to the best of our knowledge, for the creation of computer-generated holograms (CGHs) with arbitrary phases based on a specific multi-phase. This approach combines the design, production, and fabrication of holographic phase structures and requires only their assembly according to specific phase values. The arrangement of eight different specific phase values enables the production of 2D and 3D holograms comparable in quality to random phase holograms obtained through optimized Gerchberg–Saxton (GS) algorithms and requires only one-sixth of the computational time. The results of simulations and experiments indicate that this method provides a convenient approach to designing, processing, manufacturing, and reproducing high-quality phase holograms. It has the potential for widespread use in holography.

Dynamic geometric phase holography based on in-plane switching liquid crystal

ABSTRACT Liquid crystal geometric phase modulation technology is expected to achieve thin, small and achromatic spatial light modulation, which in turn has the potential to achieve holographic displays with large field angles and high clarity. This article presents a continuous dynamic geometric phase liquid crystal spatial light modulation method based on in-plane switching (IPS) mode. The relationship between geometric phase modulation and driving voltage is calibrated by using interferometry. Two hundred fifty-six phase orders within the phase modulation range of 0~π/2 is achieved. Subsequently, a phase hologram with a modulation range of 0~π/2 was designed by combining the GS (Gerchberg-Saxton) algorithm and single Fourier transform, demonstrating the holographic display capability. This article provides a low-cost approach for dynamic geometric phase holographic display.

Measuring the topological charge of a vortex beam via the self-rotating beam phase

We proposed a method to measure the topological charge of a vortex beam by using the self-rotating beam phase in this Letter. We investigated the far-field intensity patterns of the vortex beams passing through a phase hologram of the self-rotating beam with n = +2 theoretically and experimentally. The results demonstrate that the far-field intensity patterns cannot exhibit bright stripes when the topological charge of the vortex is positive (i.e., n ⋅ l > 0) and the calculated ratio relationship ξ can be used to identify the topological charge of the vortex beam. Differently, it can be found that the far-field intensity patterns exhibit several bright stripes when the topological charge of the vortex is negative (i.e., n ⋅ l < 0) and the number N of the bright stripes is equal to |l|−1(l represents the topological charge of the vortex beam). The experimental results are in good agreement with the theoretical ones. This method may inspire further research in the field of self-rotating beams.

Determination of optimal directions of the wave vector of the phase holographic grating in cubic photorefractive crystal

The dependence of the change in the components of the inverse permittivity tensor of a cubic photorefractive Bi12SiO20 crystal on the direction of the wave vector of holographic grating in the crystal coordinate system has been studied. It is shown that, when recording a phase hologram, the largest change in the refractive index of Bi12SiO20 crystal is attained when the holographic grating wave vector is oriented along symmetrically equivalent 111 directions. The maximum possible modulation amplitude of the refractive index of a holographic grating with the wave vector oriented along the 110 directions is found to exceed that in the case of orientation along the 100 directions. The components of the inverse permittivity tensor of Bi12SiO20 crystal were calculated taking into account that a phase hologram is recorded under linear electro-optic, photoelastic, and inverse piezoelectric effects.

Phase unwrapping in digital holography based on SRDU-net

In digital holographic measurement, the hologram phase is extracted using an inverse tangent function, resulting in a wrapped phase that is constrained to be (-π,π]. However, the phase contains the height information of the object, which is crucial for accurate measurement of the object contour. Therefore, a digital holographic phase unwrapping method based on SRDU-Net (Separable-Residual-Dense-Inverted U-Net) is proposed in this paper. The SRDU-Net network is constructed by introducing depth-separable convolution, inverted residuals and dense blocks with U-Net as the network framework to achieve high-precision hologram phase recovery. This network adopts depth-separable convolution instead of traditional convolution, combines the inverse residual connection to construct a lightweight convolution structure, and defines dense blocks with this structure to form a lightweight grouped deep convolution network. Meanwhile, the Leaky ReLU activation function is used to introduce the learning rate mechanism to optimize the network parameters with Huber and MSE (mean square error) as the combined loss function. The simulated phase dataset is used to train the network, the trained network model is tested for speckle noise immunity, and phase unwrapping experiments are performed on the collected holograms of the test samples. The results show that SRDU-Net improves the SSIM by 0.1% and reduces the RMSE by 86% over Res-UNet (Residual-UNet). Therefore, the proposed method can realize high-precision recovery of digital holographic wrapped phases, and has a good robustness to phase unwrapping of holograms containing a high degree of speckle noise.

Storage Optimization of Transmission Holographic Gratings in Photohydrogels.

The development and optimization of holographic materials represent a great challenge today. These materials must be synthesized according to the characteristics that are desirable in photonic devices whose application is the object of investigation. In certain holographic sensors and biosensors, it is essential that the recording material be stable in liquid media. Furthermore, the holographic gratings stored in them must have temporal and structural stability, so that they can act as transducers of the analytical signal. Therefore, it is essential to optimize its storage in terms of the chemical composition of the material and the optical parameters of recording. This work focuses on the study of the storage optimization of unslanted transmission volume phase holograms in photohydrogels based on acrylamide and N,N'-methylenebis(acrylamide). Hydrogel matrices, also composed of acrylamide and N,N'-methylenebis(acrylamide), with different degrees of cross-linking were used and analyzed by scanning electron microscopy and UV-visible spectroscopy. The best results in terms of diffraction efficiency were reached for hydrogel matrices with an acrylamide/N,N'-methylenebis(acrylamide) molar ratio between 19.9 and 26. This relationship was also optimized in the incubator solution used to incorporate the components necessary for the formation of the holograms in the hydrogel matrices. The maximum diffraction efficiency, about 35%, was achieved when using an incubation solution with an acrylamide/N,N'-methylenebis(acrylamide) molar ratio of 4.35. The influence of the physical thickness of the hydrogel layers, the intensity, and the exposure time on the diffraction efficiency was also investigated and optimized. In addition, the behavior of the hologram was analyzed after a washing stage with PBST. A simple model that considered the effects of bending and attenuation of holographic gratings was proposed and used to obtain the optical parameters of the holograms.

Multi frame holograms batched optimization for binary phase spatial light modulators

Phase retrieval methods used in computer generated holograms such as Gerchberg-Saxton and gradient descent give results which are prone to noise and other defects. This work builds up on the idea of time-averaging multiple hologram frames, first introduced in methods like One-Step Phase-Retrieval and Adaptive One-Step Phase-Retrieval. The proposed technique called Multi-Frame Holograms Batched Optimization uses the L-BFGS optimization algorithm to simultaneously generate a batch of binary phase holograms which result in an average reconstructed image of improved fidelity and fast algorithmic convergence, both in the Fraunhoffer and the Fresnel regimes. The results are compared to One-Step Phase-Retrieval and Adaptive One-Step Phase-Retrieval in simulation and experimentally, proving the superiority of the proposed approach. This technique can be easily extended to other spatial modulation methods.

Reaching the efficiency limit of arbitrary polarization transformation with non-orthogonal metasurfaces

Polarization transformation is at the foundation of modern applications in photonics and quantum optics. Notwithstanding their applicative interests, basic theoretical and experimental efforts are still needed to exploit the full potential of polarization optics. Here, we reveal that the coherent superposition of two non-orthogonal eigen-states of Jones matrix can improve drastically the efficiency of arbitrary polarization transformation with respect to classical orthogonal polarization optics. By exploiting metasurface with stacking and twisted configuration, we have implemented a powerful configuration, termed “non-orthogonal metasurfaces”, and have experimentally demonstrated arbitrary input-output polarization modulation reaching nearly 100% transmission efficiency in a broadband and angle-insensitive manner. Additionally, we have proposed a routing methodology to project independent phase holograms with quadruplex circular polarization components. Our results outline a powerful paradigm to achieve extremely efficient polarization optics, and polarization multiplexing for communication and information encryption at microwave and optical frequencies.

Design of Holographic Condenser Lens for Visible Light Lithography

Photolithography with visible light at λ = 405 nm utilizing the concept of nonlinear saturable absorption effect where the size of the spot is diminished to the nanometer scale as proposed by several researchers is an alluring proposition for cost-effective projection lithography. Costly conventional condenser lenses can be replaced by monochromatic aberration-free and cost-effective volume phase holographic lenses for visible light photolithography with enhanced resolution utilizing the concept of off-axis illumination. However, the diffraction efficiency of holographic lenses depends on the wavelength of illuminating light and the angle of illumination. Angular and spectral characteristics of volume phase holograms can be controlled by optimizing processing parameters. The results on the theoretical optimization of three important processing parameters, namely fringe spacing ( ∧ ), thickness of the film ( d ), and refractive index modulation ( Δ n ) in the light of coupled wave theory for recording holographic lenses of high diffraction efficiency at λ = 405 nm are presented. It is pointed out that a properly designed single holographic lens can be used for off-axis illumination of a photomask with a parallel beam of light, whereas a system of two identical holographic lenses cemented together has to be used to realize a condenser lens similar to a converging lens.

Eyebox expansion of a lensless near-eye display using diverging spherical wave illumination and a multiplexed holographic optical element

We expand the eyebox size of a lensless holographic near-eye-display (NED) using passive eyebox replication technique that incorporates a spatial light modulator (SLM) and a holographic optical element (HOE). In holographic NEDs, the space-bandwidth product (SBP) of the SLM determines the exit pupil dimensions and corresponding eyebox size. The base eyebox size is replicated in the horizontal direction by using the horizontal high-order diffractions of an SLM under spherical wave illumination and a multiplexed HOE combiner. When a digital blazed grating and a digital lens phase are added to the computed phase hologram sent to the SLM, two spatially separated, horizontal high-order diffraction terms with identical intensity and information can be uniformly formed without the zero-order term. When the eyebox size is expanded, the field-of-view (FOV) is not sacrificed; spherical divergence wave illumination alleviates the need for a tradeoff between FOV and eyebox size. The astigmatism introduced during HOE fabrication is counterbalanced by pre-correcting the target image using a computer-generated, holographic computation algorithm. The prototype system shows simple and effective, distortion-free eyebox expansion of a wide-angle, lensless, holographic NED.

High performance holographic video compression using spatio-temporal phase unwrapping

In this work, we present a high-performance holographic data compression technique. This approach is based in the temporal correlation found in a holographic video generated using an optimized random phase. This temporal correlation makes possible high levels of compression by using a spatio-temporal (ST) representation, partial phase unwrapping, and a lossless compression algorithm like DEFLATE. In this approach, two holographic videos are created using the optimized random phase (ORAP) technique and the Gerchberg-Saxton (GS) algorithm. The phase holograms corresponding to each frame of the videos are arranged into a ST representation, enabling spatial and temporal phase unwrapping. We test phase unwrapping along the spatial and temporal dimensions separately, followed by volume reduction after applying the DEFLATE lossless compression algorithm to the unwrapped phase in each case. The holographic video is then reconstructed from the compressed temporal and spatial unwrapped phase. The results demonstrate the high efficiency of the proposed method, with ORAP holograms achieving a compression percentage of 92.670 % after applying DEFLATE to a ST representation with partial phase unwrapping along the temporal dimension.

59‐1: Enhancing Brightness with Multi‐Color Holography

Holographic displays traditionally project full‐colored holograms time‐sequentially to achieve colored images. Time‐sequential image formation limits the achievable brightness levels. This work introduces a new method to achieve brighter images in holographic displays. Unlike the usual approach, our method allows three light sources to simultaneously illuminate the displayed holograms at different intensity levels. We optimize phase holograms along with the required intensity levels for each frame using our gradient‐descent based optimization pipeline.

Short-wavelength-infrared upconversion edge enhancement imaging based on a Laguerre-Gaussian composite vortex filter

Edge-enhanced imaging by spiral phase contrast has proven instrumental in revealing phase or amplitude gradients of an object, with notable applications spanning feature extraction, target recognition, and biomedical fields. However, systems deploying spiral phase plates encounter limitations in phase mask modulation, hindering the characterization of the modulation function during image reconstruction. To address this need, we propose and demonstrate an innovative nonlinear reconstruction method using a Laguerre-Gaussian composite vortex filter, which modulates the spectrum of the target. The involved nonlinear process spectrally transforms the incident short-wavelength-infrared (SWIR) signal from 1550 to 864 nm, subsequently captured by a silicon charge-coupled device. Compared with conventional schemes, our novel filtering method effectively suppresses the diffraction noise, significantly enhancing image contrast and resolution. By loading specific phase holograms on the spatial light modulator, bright-field imaging, isotropic, amplitude-controlled anisotropic, and directional second-order edge-enhanced imaging are realized. Anticipated applications for the proposed SWIR edge-enhanced imaging system encompass domains such as artificial intelligence recognition, deep tissue medical diagnostics, and non-destructive defect inspection. These applications underscore the valuable potential of our cutting-edge methodology in furthering both scientific exploration and practical implementations.

Non-iterative Fresnel phase-only hologram generation and multiplexing for dynamic 3D holographic display

The conventional approach to three-dimensional holographic displays involves the iterative generation of holograms, which is time-consuming and results in poor reconstruction quality. This paper proposes a novel non-iterative approach to generate 3D phase holograms using a full support optimized Fresnel random phase (FS-OFRAP) method, which combines the FS-OFRAP method and the idea of 3D object layering. The proposed method involves using the iterative Fresnel method to generate FS-OFRAPs of different planes, followed by the non-iterative generation of holograms corresponding to different layers using the 3D object layering strategy. Finally, the final phase hologram is obtained through superposition or multiplexing. Numerical and optical experiments demonstrate the effectiveness and advantages of the proposed 3D-FS-OFRAP method. This new approach has the potential to significantly improve the efficiency and quality of 3D holographic displays.

Rapid modulation of left- and right-handed optical vortices for precise measurements of helical dichroism.

Helical dichroism (HD), which is defined as the difference in optical absorption between chiral pairs of lights involving left-handed (LH) and right-handed (RH) optical vortices (OVs) carrying orbital angular momentum (OAM), is a promising way to characterize chiral materials. In the current major methods of OV generation using spatial light modulators (SLMs), the speed of OAM switching is typically as slow as 100Hz, which is comparable to low-frequency noise, making precise chiral detection difficult. Here, we theoretically propose and experimentally demonstrate a rapid modulation of the LH and RH OVs at around 50kHz. This modulation is achieved through a rapid modulation of circularly polarized lights carrying spin angular momentum (SAM), combined with a SAM-OAM conversion technique. We establish a theory not only for rapid OV modulation but also for HD measurements using the modulated OVs. We experimentally verify the theory using helical phase holograms drawn on a SLM as a pseudo-HD active sample. Our work addresses the limitations of current methods and offers a new avenue for precise HD measurements, paving the way for the development of sensitive chiral-optical spectroscopy techniques.

Band-amplified angle spectrum method for the phase hologram design to achieve high-quality holographic imaging in long distance

The angular spectrum method (ASM) is widely used in the design of computer-generated holograms (CGH) due to its strict adherence to the Helmholtz equations and the potential for accelerated computation using fast Fourier transform (FFT). However, when dealing with long distance propagation conditions, the reduction of effective spectral components and spectral aliasing will introduce significant computation errors, leading to a substantial degradation in holographic imaging quality. To achieve high-quality holographic imaging design in long distance, we introduce a novel angular spectrum computation method, the calculation process is divided into two steps: (1) First propagate a longer distance from the CGH plane to an intermediate plane. (2) Then continue to propagate to the observation plane after incorporating a spread spectrum phase factor to amplify the effective non-aliased bandwidth in the intermediate plane and eliminating the aliasing artifacts. Furthermore, the non-uniform fast Fourier transform (NUFFT) algorithm is adopted which allows for the flexible adjustments of the sampling interval and quantity in the spatial frequency domain, all while maintaining compliance with the Nyquist sampling theorem even in the context of bandwidth amplification. Both simulations and optical experiments are conducted to validate the feasibility and effectiveness of our proposed method.

High quality holographic 3D display with enhanced focus cues based on multiple directional light reconstruction.

Holographic display faces the trade-off between image quality and focus cues, resulting from the specific choice of phase distribution. In this Letter, we propose a speckle-free holographic display with enhanced focus cues by multiple directional light reconstruction. The uniform phase hologram is first generated by the gradient descent optimization algorithm. The blazed grating phase is used to steer the object light to a specific direction. Multiple sub-holograms with different blazed gratings are refreshed fast to reconstruct the images from different directions. Thus, the defocus blur is improved due to the separation of multiple spots on the defocus plane. The multi-plane reconstruction is also realized by pre-processing the depth images to eliminate image separation. The proposed method provides apparent focus cues while maintaining high image qualities, which is expected to realize comfortable holographic near-eye display in the near future.