Diffractive Components Research Articles

Study of the Dispersion Compensation Double-Layer Diffractive Optical Components Based on Metasurface and Grating, and Their Application in Augmented Reality Displays

We employed a double-layer coupled diffractive optical element, based on metasurfaces and diffraction gratings, which exhibits wavefront modulation and chromatic dispersion compensation. Utilizing this double-layer coupled diffractive optical element in the optical information transmission process of a diffractive waveguide allows for the transmission of color image information using a single-layer waveguide structure. Our results demonstrate that, under the conditions of a field of view of 47° × 47°, an entrance pupil size of 2.9 × 2.9 mm2, and an exit pupil extension size of 8.9 mm, the uniformity of the brightness for each monochromatic field reached 85%, while the uniformity of color transmission efficiency exceeded 95%.

Decoupling of Phase and Amplitude Channels with a Terahertz Metasurface Toward High‐Security Image Hiding

AbstractSteganography technology which conceals a message in a carrier to make it invisible is critical for information security. Conventional optical image steganography using diffractive optical components or spatial light modulators suffers from less encoding channel and bulky volume. The emergence of multifunctional metasurface that can manipulate abundant physical dimensions of optical fields allows the multi‐channel image steganography in a compact volume. Here, the image hiding in a metasurface is demonstrated by modulating the amplitude, phase, and polarization states of terahertz (THz) waves completely. Especially, the phase channel can decouple from the amplitude channel based on a Fresnel‐diffraction‐based algorithm. By directly measuring the phase distribution using the homemade THz focal plane imaging system, the number of transmission channels can expand from N to 2N. As a proof of concept, it is shown that the secret images can encode in the phase channel and subsequently extract by using different keys, such as polarization states, detection distances, and its combinations. Moreover, different hiding strategies with different attacker behaviors are also demonstrated. The decoupling of the phase and amplitude channels with a single metasurface may open an avenue toward innovative optoelectronic devices for optical image steganography, data storage, and terahertz communication.

Hydrodynamic performance of multi-chamber oscillating water columns in a caisson array

A theoretical model based on the linear potential flow theory and eigenfunction expansion-matching method is developed to analyze the interaction between water waves and multi-chamber oscillating water columns (OWCs) embedded in a caisson array. The semi-analytical solution consists of the diffraction and radiation components of periodic OWCs. The velocity singularity at the tip of the OWC chamber walls is resolved by implementing a Chebyshev polynomial expansion. The unknown expansion coefficients are determined by the continuity equations of velocity and pressure at the interface of subdomains. The semi-analytical solution is verified using the Haskind relation and the conservation law of wave energy flux. It is found that multi-chamber OWCs have higher hydrodynamic efficiency over a broader frequency bandwidth than traditional single- and dual-chamber OWCs. The maximum hydrodynamic efficiency η increases with increasing of chamber number (J), from 0.5 (J = 1) to nearly 1.0 (J = 8 and 12). It is also found that a larger incident wave angle leads to a narrower frequency bandwidth for energy capturing. Increasing the incident wave angle from π/3 to 5π/12 results in a decrease of the first cutoff frequency kc from 2.41 to 2.02, and therefore results in the energy capture bandwidth narrowing accordingly. Both constructive and destructive hydrodynamic interactions between caissons array and OWCs are observed over the tested frequency range. Interestingly, when configuration of the OWC chambers is reversed, the transmission coefficient remains unchanged.

Indicative significance of the interfacial interactions between pore surface and soluble organic matter on the shale oil mobility

The exploration and exploitation of shale oil resources enhance the necessity to characterize the mobility of the occluded oil in shales. Up to now, the understanding of the controlling factors of shale oil mobility has mainly come from molecular dynamics simulation but lacking in-depth research on actual shales. Therefore, in this study, the effects of mineral composition, soluble organic matter (SOM) composition and wettability on the shale oil mobility were studied by X-ray diffraction, N2 adsorption, mercury intrusion, contact angle, chloroform bitumen and group component detection methods, comprehensively. The results show that: (1) The asphaltene contents and (Asphaltenes × Aromatics)/(Saturates × Resins) negatively and positively correlate with clay and carbonate mineral contents, respectively, while the I/S and illite contents present opposite trend with (Asphaltenes × Aromatics)/(Saturates × Resins). These correlations indicate that the SOM that confined in the pores constructed with carbonate minerals and illite present better flow potential. (2) Both δVt and δSSA negatively correlate with asphaltenes and (Asphaltenes × Aromatics)/(Saturates × Resins). That is, less pores and surfaces can be released by extraction for the shales with more asphaltenes. Therefore, it can be concluded that asphaltene is a negative factor for shale oil seepage. Additionally, the larger pores present better flow condition for shale oil, even for asphaltenes. (3) Pore surface wettability also significantly affects the shale oil mobility. The hydrophobicity of the pore wall greatly inhibits the shale oil flow, especially for the mesopores and macropores. The pattern diagram was established to illustrate the effect of the interactions between pore surfaces and shale oil components on the movable potential. Based on our research, mineral composition, group composition and pore surface wettability are efficient parameters for the shale oil mobility evaluation based on the interfacial interaction theory, and the “sweet spots” for shale oil seepage of the Jiyang Depression are the shales with more illite, carbonate, saturates and relatively low lipophilicity.

Expanding THz Vortex Generation Functionality with Advanced Spiral Zone Plates Based on Single‐Walled Carbon Nanotube Films

AbstractOptical elements based on nanomaterials are becoming major avenues to satisfy the technological requirements of compact, lightweight, and tunable elements of the emerging terahertz (THz) field. A new generation of diffractive components integrating specific geometry with additional features (flexibility, stretchability, rotation, and other approaches for tuning properties) extends the functionality of wavefront control. Here, an innovative approach is demonstrated to control the THz wavefront via a layered composition of spiral zone plates (SZPs) with tunable mutual orientation and scaling. As a proof of concept, the SZP is designed using Laguerre‐Gauss mode analysis with further fabrication and experimental characterization of the resultant vortex beams. For each single SZP, a flexible element is proposed based on a thin film of single‐walled carbon nanotubes deposited on a stretchable substrate. Thus, this diffraction element can be tuned not only by rotation (along the azimuthal direction), but also by its stretching (in the radial direction). The spatial tuning of the developed SZPs (spiral zone plates) opens up an efficient, convenient, and highly customizable approach for the manipulation of vortex beams.

Tandem neural network-assisted inverse design of highly efficient diffractive slanted waveguide grating.

Virtual reality devices featuring diffractive grating components have emerged as hotspots in the field of near-to-eye displays. The core aim of our work is to streamline the intricacies involved in devising the highly efficient slanted waveguide grating using the deep-learning-driven inverse design technique. We propose and establish a tandem neural network (TNN) comprising a generative flow-based invertible neural network and a fully connected neural network. The proposed TNN can automatically optimize the coupling efficiencies of the proposed grating at multi-wavelengths, including red, green, and blue beams at incident angles in the range of 0°-15°. The efficiency indicators manifest in the peak transmittance, average transmittance, and illuminance uniformity, reaching approximately 100%, 92%, and 98%, respectively. Additionally, the structural parameters of the grating can be deduced inversely based on the indicators within a short duration of hundreds of milliseconds to seconds using the TNN. The implementation of the inverse-engineered grating is anticipated to serve as a paradigm for simplifying and expediting the development of diverse types of waveguide gratings.

DiffraPy: An open-source Python software for seismic diffraction imaging

Seismic diffraction events, often overlooked as noise in conventional seismic imaging methods, contain valuable high-resolution information about subsurface structures and heterogeneities. Furthermore, the diffractive component of the wavefield is masked by the stronger reflection events. Although the literature presents innovative methods for separating diffracted events from the total wavefield, there are currently limited options of open-source alternatives in seismic diffraction processing and imaging. In this study, we introduce DiffraPy, an open-source Python package specifically designed for performing both conventional and diffraction-oriented migrations. The main workflow involves implementing an anti-stationary phase filter in the Kirchhoff migration for enhancing energy outside the Fresnel zone. Additionally, we propose using the semblance matrix obtained from the dip field calculation as an additional weight in conventional migration. The code provides functionality for forward modeling seismic data, allowing for new testing and experimentation. We demonstrate the general workflow of the code using a toy model and evaluate its capabilities on a synthetic salt model. In both cases, the program successfully suppressed the majority of reflected energy in the diffraction-oriented image. The final image highlights the responses of small lenses, discontinuities, and faults, providing valuable insights into the subsurface for interpretation. Despite the method sensitivity to variations in the correct velocity model, we demonstrate that our code is capable of imaging diffractors even when utilizing incorrect migration velocities of up to 5%. Our wavenumber analysis reveals the diffraction image preservation of smaller wavelengths, indicating higher resolution compared to conventional products. Future implementations may include extension to 3D datasets and improve the computational efficiency of our code. We expect our code to offer the geosciences community the first freely accessible and well-documented Python alternative for testing, reproducing, and exploring diffraction imaging examples.

Low voltage dual-period liquid crystal grating with tunable diffraction efficiency

A low voltage dual-period liquid crystal (LC) grating with tunable diffraction efficiency is demonstrated. Different periods can be achieved by controlling the driving scheme. Diffraction efficiencies of 25.9% for the small-period LC grating and 20.9% for the large-period LC grating have been realized. The diffraction angle can be alternatively tuned, as well as the diffraction efficiency by applying voltage to the top or bottom in-plane switching (IPS) electrodes. The driving voltage of the tunable LC grating is as low as 4.8 V, which shows great potential for diffractive optics components.

Hydrodynamic performance of a self-protected hybrid offshore wind-wave energy system

The load-bearing capacity is a pivotal consideration in the design of offshore renewable energy structures. This paper aims to address the technical challenges associated with the additional wave loads caused by the integrated devices in a hybrid system for the multi-purpose utilization of coastal renewable energy. A self-protected hybrid wind-wave energy system is proposed, in which an oscillating water column (OWC) device is attached at a monopile foundation of an offshore wind turbine. In the meantime, the OWC is connected by a submerged horizontal perforated plate at its exterior shell, which is expected to minimize the wave loads on the system. The hydrodynamic performance of the system is investigated. A novel approach is developed to model the wave interaction with the hybrid system. This efficient approach removes the necessity of decomposing the wave-scattering field into diffraction and pressure-dependent radiation components. Detailed numerical computation is then conducted for both regular and irregular sea states. Various hydrodynamic properties related to the system, such as wave energy harvesting, wave force/moment, and free-surface elevation, have been evaluated. Numerical results manifest the feasibility of imposing a negligible effect on the high wave energy harvesting while reducing the high wave loads by manipulating the submerged horizontal perforated plate. The impact of the perforated plate on the dominant wave energy harvesting in the long-period region is found to be trivial. In contrast, it can affect the high bending moment in the short-period region, which causes a reduction of greater than 15%.

Measurement-Based Close-In Path Loss Modeling With Diffraction for Rural Long-Distance Communications

In this letter, we investigate rural large-scale path loss models based on the measurements in a central area of South Korea (rural area) in spring. In particular, we develop new close-in (CI) path loss models incorporating a diffraction component. The transmitter used in the measurement system is located on a hill and utilizes omnidirectional antennas operating at 1400 and 2250 MHz frequencies. The receiver is also equipped with omnidirectional antennas and measures at positions totaling 3,858 (1,262 positions for LOS and 2,596 positions for NLOS) and 4,957 (1,427 positions for LOS and 3,530 positions for NLOS) for 1400 and 2250 MHz, respectively. This research demonstrates that the newly developed CI path loss models incorporating a diffraction component significantly reduce standard deviations (STD) and are independent of frequency, especially for LOS beyond the first meter of propagation, making them suitable for use with frequencies up to a millimeter-wave.

Small angle approximation for the lidar return from clouds and fogs

The paper is aimed at the inter-comparison of the small angle approximation (SAA) for the lidar return with Monte Carlo calculations at small receiver field of views, where the SAA can be used for the evaluation of lidar signals from clouds and fogs. The diffraction component of light scattering by a local volume of a cloudy medium is fully taken into account and the geometrical part of light scattering field has been neglected. It has been found that the derived approximation provides useful approximation for the simulation of lidar signals from a cloudy medium close to its boundary, where the contribution of small-angle light scattering and propagation on the path from the cloud boundary to the observation point and back is significant. It has been found that the multiple light scattering enhancement factor A in the framework of the SSA for clouds with the same half - width parameter μ of the droplet size distribution depends just on two main parameters: optical depth τand the scale parameter s, which is equal to the ratio of the effective scattering angle to the receiver field of view.

Numerical study of feature-distribution effects foranti-reflection structured surfaces on binary gratings.

Suppressing Fresnel reflections from dielectric boundaries using periodic and random antireflection structured surfaces (ARSSs) has been vigorously studied as an alternative to thin film coatings for high-power laser applications. A starting point in the design of ARSS profiles is effective medium theory (EMT), approximating the ARSS layer with a thin film of a specific effective permittivity, which has features with subwavelength transverse-scale dimensions, independent of their relative mutual positions or distributions. Using rigorous coupled-wave analysis, we studied the effects of various pseudo-random deterministic transverse feature distributions of ARSS on diffractive surfaces, analyzing the combined performance of the quarter-wave height nanoscale features, superimposed on a binary 50% duty cycle grating. Various distribution designs were investigated at 633nm wavelength for TE and TM polarization states at normal incidence, comparable to EMT fill fractions for a fused silica substrate in air. The results show differences in performance between ARSS transverse feature distributions, exhibiting better overall performance for subwavelength and near-wavelength scaled unit cell periodicities with short auto-correlation lengths, in comparison to equivalent effective permittivity designs that have less complicated profiles. We conclude that structured layers of quarter-wavelength depth and specific feature distributions can outperform conventional periodic subwavelength gratings as antireflection treatments on diffractive optical components.

Quantitative Phase Contrast Microscopy with Optimized Partially Coherent Illumination

This paper presents a partially coherent illumination quantitative phase contrast microscopic (PCI-QPCM) prototype. In the PCI-QPCM prototype, the light scattered by a rotating diffuser is coupled into a multi-mode fiber, and the output light is used as the illumination for PCI-QPCM. The illumination wave has a constrained spectrum with a diameter of tens of micrometers, which can reduce speckle noise and will not broaden the dc term of the object wave. In the Fourier plane of the object wave, grating-masked phase shifters generated by a spatial light modulator (SLM) allow for measuring the intensity of the undiffracted and diffracted components of the object wave, as well as the phase-shifted interference patterns of the two. Quantitative phase images can be reconstructed from the recorded intensity images. The proposed PCI-QPCM was demonstrated with quantitative phase imaging of a transparent waveguide and a phase-step sample.

How petrophysical properties influence the seismic signature of carbonate fault damage zone: Insights from forward-seismic modelling

Seismic imaging is the most common tool to detect subsurface structures in continental and marine settings. Despite technological advancement, seismic analysis of carbonates is still challenging because they are strongly influenced by petrophysical heterogeneities, being this even more difficult when further heterogeneities are added by the presence of faults. In this work, unmigrated forward-seismic models are developed to understand the seismic response changes related to carbonate-bearing fault systems and their deformation behaviour. We focus on the carbonate ramp of the Majella Massif (central Italy), that is characterised by the presence of porous and faulted carbonate lithologies. This carbonate system represents an analogue of carbonate reservoirs worldwide. Field and laboratory data of fault rocks sampled at increasing distances from the slip planes highlight a damage zone/fault core architecture with a decreasing porosity approaching fault planes. This observation is also confirmed by the thin sections analysis and the calculation of the shear modulus. Seismic images of fault rocks presenting lower porosity than the host rock show weak diffraction hyperbolas while diffraction hyperbolas are more evident in the forward-seismic models of fault rocks with greater porosity than the host rock. Moreover, factors such as the variation in the dip angle of the fault or the thickness of the damage zone can enhance or reduce the hyperbolas. Performing the migration process to stacked sections would not provide evidence of increased porosity in the damage zone due to the suppression of the diffractive component. The presence of weak hyperbolas in unmigrated seismic images is thus interpreted as evidence of a lower porosity damage zone with respect to the host rock. This can be related to deformation mechanisms leading to porosity loss in the damage zone for porous rocks as observed in the study area. However, this could also be related to the confining stress or fracture filling that counteract the fracture-related porosity increase when faults are hosted by tight rocks.

Complex amplitude modulated holographic display system based on polarization grating.

We propose a holographic display system for complex amplitude modulation (CAM) using a phase-only spatial light modulator (SLM) and two polarization gratings (PG). The two sub-holograms of the complex-amplitude computed generated hologram (CGH) are loaded in different regions of SLM. Two diffractive components couple in space after longitudinal migration from the double PGs, and finally interfered through the line polarizer. The influence of the system error on the reconstructed image quality is analyzed, which provides a theoretical assessment for adding pre-compensation to CGH to compensate the system error. Moreover, on the base of the proposed system, a large depth of field and enlarged display area display is realized and the real-time display can be achieved because of the analytical complex-amplitude computed generated hologram. The optical experimental results show that the proposed system has high energy efficiency, and can provide high-quality holographic display with a large depth of field and enlarged display area.

Time-frequency diffraction acoustic modeling of the Epidaurus ancient theatre

This work provides an in-depth investigation on the effect of sound diffraction in the acoustics of the ancient theatres, with reference to the theatre of Epidaurus. It is increasingly evident that in such theaters, sound diffraction at the edges of the multiple tiers generates significant source signal amplification. Especially for the distant listener positions, an accumulation (“avalanche”) effect from lower tier diffracted energy is identified. This study examines a 3D model of an elementary slice of the seating benches (“koilon”), evaluating the generated sound field in the time, frequency, and spatial domains. The analysis accounts for direct, reflected, diffracted and mixed reflected – diffracted paths and the theatre’s acoustic response is numerically evaluated in various positions along the koilon slice, accurately matching to in-situ measurements. The contribution of the diffracted sound to the total sound field is identified through a detailed and novel analysis of energy-based acoustic parameters, via the time and frequency responses as well as of the spatial parameters relating to listener-perceived effects. In all cases, the contribution of sound diffraction components is examined via its contribution to speech intelligibility from signals generated in the theatre’s orchestra and from a virtual reconstruction of the stage-scenic building.

Chiral liquid crystal based holographic reflective lens for spectral detection.

Flat optics based on chiral liquid crystal (CLC) can be achieved using holographic polarization recording with the help of a photoalignment technique to vary the orientation of the optical axis in a thin CLC layer. A variety of reflective diffractive optical components with high efficiency and polarization selectivity can be realized employing this technique. In this work we discuss the use of CLC diffractive lenses in a spectrometer. The functionalities of two mirrors and a linear grating used in a traditional spectrometer are combined into a single holographic CLC component. Circularly polarized light entering through the slit can be reflected and projected onto a linear detector by the CLC component, with over 90% efficiency. This excellent optical functionality can be achieved with a micrometer thin CLC layer, offering the opportunity for device integration.

Hyperchromatic lens doublets with an extremely small equivalent Abbe number employing diffractive elements and refractive materials with exceptional dispersion properties.

Hyperchromatic systems are characterized by strong longitudinal chromatic aberrations that are quantitatively described by very small equivalent Abbe numbers. In this contribution, doublet systems are systematically studied with the aim of obtaining extreme values for the equivalent Abbe numbers. Both purely refractive combinations and hybrid systems of diffractive and refractive components are considered. Chromatic axial splitting is determined as a function of the optical powers of the individual components as well as the dispersion properties of the materials involved. In order to determine actual implementable configurations for extremely small equivalent Abbe numbers, a systematic ray-trace analysis is performed in addition to paraxial studies, taking into account geometric constraints on lens curvatures and considering also complete, continuous dispersion curves. As extreme values for systems with appropriate imaging quality, an equivalent Abbe number of υ~=-2.5 is obtained for the purely refractive approach, and υ~=0.4 for the hybrid case, which is more than 8 times smaller than the absolute value of a single diffractive lens.

Diffraction Imaging of the Fractured Crystalline Basement, Lancaster Field, UK

In this paper, we demonstrate the application of seismic diffraction imaging technology to map the distribution of faults within Hurricane Energy’s operated, fractured basement fields, offshore West of Shetland. After the reprocessing of legacy 3D seismic data in 2018, it became apparent that the reflection seismic image had limited ability to image the intra-basement structure. Intra-basement imaging is crucial for understanding the distribution, frequency and geometry of intra-basement structures which directly influence production trends in fractured basement reservoirs. Diffraction imaging is a novel seismic processing technique that can produce high-resolution images of small-scale scattering subsurface events by extracting and focusing the diffractive component of the total wavefield to its subsurface origin. Analysis of the diffraction imaging seismic volume alongside well data and other seismic products can complement conventional seismic attributes and enhance the interpretational value of the seismic data. This paper shows how the intensity of the diffraction image varies from location to location across the Rona Ridge and is seen to have a strong, positive correlation with observed well productivity. As such, the application of this technology shows great promise to provide additional information for detailed analysis of Hurricane Energy’s fractured basement reservoirs and can facilitate new well placement and trajectory design.

Rapid direct laser writing of microoptical components on a meltable biocompatible gel

Microoptical components are coming of age in a wide range of applications: lab-on-a-chip, imaging, detection… There are a large number of fabrication technologies capable of producing high quality individual components and their arrays. However, most of them require high-end and costly equipment, complex and time-consuming fabrication, harmful chemicals, resulting in expensive final products. Here we present a technology capable of producing high quality microoptical components, using low-end direct laser writing on a biocompatible, environmentally friendly hydrogel, without any waste substances. The gel is locally and controllably melted while surface tension forces shape the optical component, following the laser beam profile. The process is so quick that a single microlens is fabricated in less than a second, and can be used instantly without any further processing. The technology is neither subtractive nor additive, and the base material is simply displaced producing a smooth surface. We have been able to fabricate individual microlenses and their arrays (positive, negative, aspheric), gratings and diffractive components. The technology is tested by generating unique, difficult to counterfeit QR-codes. Turnaround time is fast and makes the technology suitable both for rapid prototyping and serial production.