Holographic Optical Elements Research Articles

Acoustic holographic lenses for transcranial focusing in an ex vivo human skull

The skull has long been an obstacle for transcranial ultrasound therapy and neuromodulation, leading to waveform distortion and focal points misalignment. In this work, we propose a dual-focus transcranial ultrasound focusing method for ex vivo human skulls to bridge this barrier, which is demonstrated by using a 2 MHz single-element transducer placed outside the occipital bone, coupled to a 3D-printed acoustic holographic lens. The experimental results show that the proposed method allows for achieving high-precision single- and dual-focus ultrasound focusing through human skulls with the maximum target registration error less than one wavelength in water. The in-target ratio spans a range from 72% to 92%, with an average of 80.7%, while the out-of-target ratio varies from 0% to 43.9%, with an average of 18.3%. Additionally, the focal spots are substantially free of the skull-induced distortion, closely matching the ideal ones, and maintain a clearly identifiable circular focus shape. The method opens up a route toward the subsequent applications in clinical research and may enable to implement transcranial ultrasound therapy and neuromodulation.

Multifunctional computational fluorescence self-interference holographic microscopy

Fluorescence microscopy is crucial in various fields such as biology, medicine, and life sciences. Fluorescence self-interference holographic microscopy has great potential in bio-imaging owing to its unique wavefront coding characteristics; thus, it can be employed as three-dimensional (3D) scanning-free super-resolution microscopy. However, the available approaches are limited to low optical efficiency, complex optical setups, and single imaging functions. The geometric phase lens can efficiently manipulate the optical field’s amplitude, phase, and polarization. Inspired by geometric phase and self-interference holography, a self-interference fluorescent holographic microscope-based geometric phase lens is proposed. This system allows for wide-field, 3D fluorescence holographic imaging, and edge-enhancement from the reconstruction of only one complex-valued hologram. Experiments demonstrate the effectiveness of our method in imaging biological samples, with improved resolution and signal-to-noise ratio. Furthermore, its simplicity and convenience make it easily compatible with existing optical microscope setups, making it a powerful tool for observing biological samples and detecting industrial defects.

Loop corrections versus marginal deformations in celestial holography

Four-dimensional all-loop amplitudes in quantum electrodynamics and gravity exhibit universal IR singularities with a factorization structure. This structure is governed by tree amplitudes and a universal IR-divergent factor representing the exchange of soft particles between external lines. This Letter offers a precise dual interpretation of these universal IR-divergent factors within celestial holography. Considering the tree amplitude as the foundation of the celestial conformal field theory (CCFT), these universal factors correspond to marginal deformations with a construction in the CCFT. Remarkably, a novel geometric representation of these deformations through topological gauging provides an exact description of transitions within bulk vacuum moduli spaces which extends the celestial holography beyond the perturbative level. Our findings establish a concrete dictionary for celestial holography and offer a holographic lens to understand loop corrections in scattering amplitudes. Published by the American Physical Society 2024

Gradient descent optimization of acoustic holograms for transcranial focused ultrasound

Acoustic holographic lenses, also known as acoustic holograms, can change the phase of a transmitted wavefront in order to shape and construct complex ultrasound pressure fields, often for focusing the acoustic energy on a target region. These lenses have been proposed for transcranial focused ultrasound (tFUS) to create diffraction-limited focal zones that target specific brain regions while compensating for skull aberration. Holograms are currently designed using time-reversal approaches in full-wave time-domain numerical simulations. Such simulations need time-consuming computations, which severely limits the adoption of iterative optimization strategies. In the time-reversal method, the number and distribution of virtual sources can significantly influence the final sound field. Because of the computational constraints, predicting these effects and determining the optimal arrangement is challenging. This study introduces an efficient method for designing acoustic holograms using a volumetric holographic technique to generate focused fields inside the skull. The proposed method combines a modified mixed-domain method for ultrasonic propagation with a gradient descent iterative optimization algorithm. The findings are further validated in underwater experiments with a realistic 3D-printed skull phantom. This approach enables substantially faster holographic computation than previously reported techniques. The iterative process uses explicitly defined loss functions to bias the ultrasound field’s optimization parameters to specific desired characteristics, such as axial resolution, transversal resolution, coverage, and focal region uniformity, while eliminating the uncertainty associated with virtual sources in time-reversal techniques. The proposed techniques enable more rapid hologram computation and more flexibility in tailoring ultrasound fields for specific therapeutic requirements.

Design of a polarization-insensitive broadband achromatic metalens for mid-wave infrared detector.

Metalenses, boasting outstanding focusing efficiency and high-resolution imaging capabilities, have generated widespread usage in fields such as integrated optics, achromatic imaging, and optical holography. In this study, we have developed a broadband achromatic metalens within the detection range from 3 to 5 µm, and it has a numerical aperture (NA) of 0.71 with a remarkable maximum focusing efficiency of 63.8% at the focal plane within the specified bandwidth. We have further delved into the dispersion control mechanism that combines the geometric and transmission phases and optimized the constructed phase response simulation database using the particle swarm optimization (PSO) algorithm, ensuring a precise phase matching between the actual wavefront and the ideal focusing wavefront. This metalens with its ability to expand the array size has the potential to create a compact infrared imager, which holds significant importance in achieving efficient detection and integration within infrared detectors.

Augmented Reality and Virtual Reality: A New Way of Seeing the World

Technologies such as (AR) Augmented Reality &(VR) Virtual Reality, which provide immersive digital experiences, interactive environments, simulation, and engagement, have completely changed how we approach learning. However, in order to meet the huge demand in education, these technologies which are still in the emerging stage need to be heavily customized and heavily invested in. This thorough analysis seeks to contextualize the last few years of development of Virtual and Augmented Reality in the Education. For additional study, a total one thousand five hundred and thirty-six articles are chosen using text mining and theme analysis techniques. Based on earlier research on AR and VR in education, hypotheses were developed and are currently being processed and analysed to reveal the current development in literature via Augmented Reality and Virtual Reality, applications, benefits, and future directions. The findings show that wearable technology has contributed significantly to the exponential expansion in the use of Virtual and Augmented Reality in education in recent years. Results also highlight the need for faster adoption and customization of these technologies in educational institutions, based on secondary data. An increasing number of educational applications for the learning process are emerging as Virtual and Augmented Realityexp and quickly. It is advised that researchers stay up to date on the gaps in AR and VR’s Changeover to education &develop practical adaptation strategies to maximize the benefits of these technological development with significant developments in high-speed transmission and processing, AR &VR are developing as Display Platforms for Next Generation for more intimate human-digital interactions. Nonetheless, matching the extraordinary Human Vision Performance while keeping Near the Eye Display module tiny and lightweight presents unprecedented hurdles for optical engineering. Fortunately, new advances in Holographic Optical Elements HOEs and Lithography Enable Devices present novel approaches to overcoming these challenges in Virtual and Augmented Reality which would otherwise be problematic with traditional optics

Asymmetric Optical Scanning Holography Encryption with Elgamal Algorithm

This paper proposes an asymmetric scanning holography cryptosystem based on the Elgamal algorithm. The method encodes images with sine and cosine holograms. Subsequently, each hologram is divided into a signed bit matrix and an unsigned hologram matrix, both encrypted using the sender’s private key and the receiver’s public key. The resulting ciphertext matrices are then transmitted to the receiver. Upon receipt, the receiver decrypts the ciphertext matrices using their private key and the sender’s public key. We employ an asymmetric single-image encryption method for key management and dispatch for securing imaging and transmission. Furthermore, we conducted a sensitivity analysis of the encryption system. The image encryption metrics, including histograms of holograms, adjacent pixel correlation, image correlation, the peak signal-to-noise ratio, and the structural similarity index, were also examined. The results demonstrate the security and stability of the proposed method.

Higher-Dimensional Communications Using Multimode Fibers and Compact Components to Enable a Dense Set of Communicating Channels

Higher-dimensional communications are of interest for multiple reasons, including increasing the classical transmission capacity and, more recently, the quantum state transfer through fibers using the many modes within the fiber. For quantum communications, this enables an increase in the number of bits per photon, increasing quantum fidelity, increasing error thresholds and enabling hyperentanglement transfer, among other possibilities. A high-dimensional quantum state transfer can be transported through multimode fiber using the many modes available. However, this transfer of information through multimode optical fiber is limited by attenuation and mode coupling among the various spatial and polarization modes. Here, we consider how this mode coupling impacts the transfer process. We consider the fiber’s modal properties, including orbital angular momentum, modal group numbers, and principal modes. We also investigate and propose input and output optical components, as well as fiber properties, which better mitigate the deleterious effects of mode coupling. We use the WKB approximation to the scaler wave equation as a guidance to quantify this coupling and then implement corrections to this approximation using exact solutions to the scaler wave equation. We consider methods to circumvent this mode coupling using optical fiber designs, holographic optical components and devices that are commercially available today. Some of these components, such as the holographic gratings and lenses, could be implemented using flat optics.

Visual Illusion Created by a Striped Pattern Through Augmented Reality for the Prevention of Tumbling on Stairs.

A fall on stairs can be a dangerous accident. An important indicator of falling risk is the foot clearance, which is the height of the foot when ascending stairs or the distance of the foot from the step when descending. We developed an augmented reality system with a holographic lens using a visual illusion to improve the foot clearance on stairs. The system draws a vertical striped pattern on the stair riser as the participant ascends the stairs to create the illusion that the steps are higher than the actual steps, and draws a horizontal striped pattern on the stair tread as the participant descends the stairs to create the illusion of narrower stairs. We experimentally evaluated the accuracy of the system and fitted a model to determine the appropriate stripe thickness. Finally, participants ascended and descended stairs before, during, and after using the augmented reality system. The foot clearance significantly improved, not only while the participants used the system but also after they used the system compared with before.

Solar Window Innovations: Enhancing Building Performance through Advanced Technologies

Building-integrated photovoltaic (BIPV) glazing systems with intelligent window technologies enhance building energy efficiency by generating electricity and managing daylighting. This study explores advanced BIPV glazing, focusing on building-integrated concentrating photovoltaic (BICPV) systems. BICPV integrates concentrating optics, such as holographic films, luminescent solar concentrators (LSC), Fresnel lenses, and compound parabolic concentrators (CPCs), with photovoltaic cells. Notable results include achieving 17.9% electrical efficiency using cylindrical holographic optical elements and crystalline silicon cells at a 3.5× concentration ratio. Dielectric CPCs showed 97.7% angular acceptance efficiency in simulations and 94.4% experimentally, increasing short-circuit current and maximum power by 87.0% and 96.6%, respectively, across 0° to 85° incidence angles. Thermochromic hydrogels and thermotropic smart glazing systems demonstrated significant HVAC energy savings. Large-area 1 m2 PNIPAm-based thermotropic window outperformed conventional double glazing in Singapore. The thermotropic parallel slat transparent insulation material (TT PS-TIM) improved energy efficiency by up to 21.5% compared to double glazing in climates like London and Rome. Emerging dynamic glazing technologies combine BIPV with smart functions, balancing transparency and efficiency. Photothermally controlled methylammonium lead iodide PV windows achieved 68% visible light transmission, 11.3% power conversion efficiency, and quick switching in under 3 min. Polymer-dispersed liquid crystal smart windows provided 41–68% visible transmission with self-powered operation.

Hybrid Optical Scanning Holography for Automatic Three-Dimensional Reconstruction of Brain Tumors from MRI using Active Contours

Hybrid Optical Scanning Holography for Automatic Three-Dimensional Reconstruction of Brain Tumors from MRI using Active Contours

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.

Comparison of the fractionated Nd: YAG 1064-nm picosecond laser with holographic optics and the fractional CO2 laser in atrophic acne scar treatment: a prospective, randomized, split-face study.

The 1064-nm picosecond laser with holographic optics demonstrated significant efficacy in treating atrophic acne scars. Picosecond lasers with fractionated optics have enabled the development ofa breakthrough skin rejuvenation method. The authors compared the fractionated, non-ablative neodymium-doped yttrium aluminum garnet 1064-nm picosecond laser with holographic optics and the fractional CO2 laser in treating atrophic acne scars. One side of each patient's face was randomly allocated and treated with three sessions of the 1064-nm picosecond laser with holographic optics at 2-month intervals. In contrast, the other side was treated with the fractional CO2 laser. Participants were followed up 3 months after the final session. The primary outcome included the physicians' evaluation using the ECCA grading scale and a four-point scale to assess improvement. The patients' assessment of progress, their overall satisfaction and preferences, and the side effects were also evaluated. No significant difference was observed between the two lasers in terms of the mean ECCA scores after treatments (P = 0.209). The physicians' improvement assessment was more significant for the fractional CO2 laser (P = 0.001). The patients' evaluation of improvement and subjective satisfaction were consistent with physicians' four-point scale results. The picosecond laser side had fewer adverse effects (P < 0.001). The fractionated, non-ablative Nd: YAG 1064-nm picosecond laser with holographic optics and the fractional CO2 laser were effective and safe in treating atrophic acne scars. Significantly better clinical outcomes were observed with the fractional CO2 laser, whereas fewer adverse effects were noted with the 1064-nm picosecond laser with holographic optics.

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.

Retinal projection display with realistic accommodation cue

Although retinal projection displays have the feature of being always in focus and no loss of image resolution, the lack of accommodation cue makes it difficult to perceive the depth correctly. In this paper, we proposed a retinal projection display system with realistic accommodation cue. The proposed system adds an optometric device to the conventional holographic optical element (HOE)-based retinal projection display. The optometric device detects the accommodation response of the human eyes to observe a real scene at different distances. According to the focused depth of the human eye, refocused images containing realistic focusing and defocusing information are generated through the light field refocusing technology. By establishing a focus depth-lookup table, the refocused images matching with the focused depth of human eye was presented to the human eye, so as to restore the retinal projection display with realistic accommodation cue. A proof-of-concept prototype based on the proposed structure was developed, and the experimental results presented retinal projection displays with realistic accommodation cue at a depth between 250 mm and 400 mm. The proposed system retains the characteristics of high resolution and free focusing while adding the accommodation cue. The developed prototype has great competitiveness in near-eye displays.

Holographic thermal mapping in volumes using acoustic lenses

Acoustic holographic lenses (AHLs) show great potential as a straightforward, inexpensive, and reliable method of sound manipulation. These lenses store the phase and amplitude profile of the desired wavefront when illuminated by a single acoustic source to reconstruct ultrasound pressure fields, induce localized heating, and achieve temporal and spatial thermal effects in acousto-thermal materials like polymers. The ultrasonic energy is transmitted and focused by AHL from a transducer into a particular focal volume. It is then converted to heat by internal friction in the polymer chains, causing the temperature of the polymer to rise at the focus locations while having little to no effect elsewhere. This one-of-a-kind capability is made possible by the development of AHLs to make use of the translation of attenuated pressure fields into programmable heat patterns. However, the impact of acousto-thermal dynamics on the generation of AHLs is largely unexplored. We use a machine learning-assisted single inverse problem approach for rapid and efficient AHLs’ design to generate thermal patterns. The process involves the conversion of thermal information into a holographic representation through the utilization of two latent functions: pressure phase and amplitude. Experimental verification is performed for pressure and thermal measurements. The volumetric acousto-thermal analyses of experimental samples are performed to offer a knowledge of the obtained pattern dynamics, as well as the applicability of holographic thermal mapping for precise volumetric temperature control. Finally, the proposed framework aims to provide a solid foundation for volumetric analysis of acousto-thermal patterns within thick samples and for assessing thermal changes with outer surface measurements.

Ultra-robust informational metasurfaces based on spatial coherence structures engineering

Optical information transmission is vital in modern optics and photonics due to its concurrent and multi-dimensional nature, leading to tremendous applications such as optical microscopy, holography, and optical sensing. Conventional optical information transmission technologies suffer from bulky optical setup and information loss/crosstalk when meeting scatterers or obstacles in the light path. Here, we theoretically propose and experimentally realize the simultaneous manipulation of the coherence lengths and coherence structures of the light beams with the disordered metasurfaces. The ultra-robust optical information transmission and self-reconstruction can be realized by the generated partially coherent beam with modulated coherence structure even 93% of light is recklessly obstructed during light transmission, which brings new light to robust optical information transmission with a single metasurface. Our method provides a generic principle for the generalized coherence manipulation on the photonic platform and displays a variety of functionalities advancing capabilities in optical information transmission such as meta-holography and imaging in disordered and perturbative media.

P‐50: Multi‐depth‐SGD Based Tilted Plane Diffraction Propagation for Holographic Near‐eye Displays

To facilitate the practical application of wearable holographic near‐eye displays, the propagation between non‐parallel planes is essential for the hologram generation of off‐axis projection onto the holographic‐optical‐element (HOE) based combiners. However, existing methods, particularly the angular spectrum rotation‐based approach for generating tilted plane holograms, encounter challenges such as gradient loss when integrated with the stochastic gradient descent (SGD) algorithm. In this paper, we present a novel method for generating a tilted plane hologram using multi‐depth‐SGD, effectively mitigating the gradient loss issue.

P‐230: Late‐News Poster: Enhancement of the color uniformity of a VHOE‐waveguide‐based AR eyewear display through drive signal management scheme

In this paper, we present an enhanced approach‐a drive signal management scheme employed on a micro‐display device of optical engine to retune the color uniformity of an Augmented Reality (AR) eyewear display with a the Volume Holographic Optical Elements (VHOEs)‐based waveguide. Our method streamlines multiplexing complexity, necessitating just one optical waveguide and three RGB gratings to attain a full‐color eyewear display with nearly a 16° horizontal field of view (FOV) and less than 3% ΔELab color non‐uniformity.

Design for a virtual reality head-mounted display with holographic pancake optics

A design for a head-mounted display using holographic optical elements (HOEs) and pancake optics is presented. The pancake optics assembly consists of a circular polarization, quarter-wave film, and a coated 50/50 (semi-transmissive and semi-reflective) aspherical lens. The HOE and pancake optics combination was employed to reduce the volume of the system. For this design, the effective focal length was 10.901 mm, the field of view was 30 deg, and the f-number was 3.633. In terms of image quality, the modulation transfer function (MTF) values for all fields exceeded 0.3 at 65 lp/mm. The MTF values for all fields under the tolerance error also exceeded 0.3 lp/mm. The maximum optical distortion was less than 2%. The impact of the efficiency of diffracted and non-diffracted light on the visibility was analyzed to select the appropriate reflectance for the coating of the 50/50 aspherical lens and the highest hologram diffraction efficiency to achieve the best visibility.