Angular Tolerance Research Articles

Color arrestor pixels for high-fidelity, high-sensitivity imaging sensors

Abstract Silicon is the dominant material in complementary metal-oxide-semiconductor (CMOS) imaging devices because of its outstanding electrical and optical properties, well-established fabrication methods, and abundance in nature. However, with the ongoing trend toward electronic miniaturization, which demands smaller pixel sizes in CMOS image sensors, issues, such as crosstalk and reduced optical efficiency, have become critical. These problems stem from the intrinsic properties of Si, particularly its low absorption in the long wavelength range of the visible spectrum, which makes it difficult to devise effective solutions unless the material itself is changed. Recent advances in optical metasurfaces have offered new possibilities for solving these problems. In this study, we propose color arrestor pixels (CAPs) as a new class of color image sensors whose composite spectral responses directly mimic those of the human eye. The key idea is to employ linearly independent combinations of standardized color matching functions. These new basis functions allow our device to reproduce colors more accurately than the currently available image sensors with red-green-blue filters or other metasurface-based sensors, demonstrating an average CIEDE2000 color difference value of only 1.79 when evaluating 24 colors from the Gretag-Macbeth chart under standard illuminant D65. Owing to their high fidelity to the human eye response, CAPs consistently exhibit exceptional color reproduction accuracy under various spectral illumination compositions. With a small footprint of 860 nm height and 221 nm full-color pixel pitch, the CAPs demonstrated high absorption efficiencies of 79 %, 81 %, and 63 % at wavelengths of 452 nm, 544 nm, and 603 nm, respectively, and good angular tolerance. With such a high density of pixels efficiently capturing accurate colors, CAPs present a new direction for optical image sensor research and their applications.

Excellent angular and electrical performance damage tolerance of wave-absorbing laminate via gradient A-T-A design

Besides broadband electromagnetic wave absorption, electrical performance damage tolerance should be designed and evaluated to compete with advanced detection technologies. In this work, an A-T-A (absorption-transmission-absorption) design strategy with gradient electromagnetic parameters is proposed to enhance angular and electrical performance damage tolerance of wave-absorbing laminated structure in 6–18 GHz frequency band. The quartz fiber cloth with 700 μm periodic inter-bundle pores served as a transmission layer and was embedded into Fe3Co7/epoxy resin magnetic absorption film to improve the maneuverability of input impedance. Meanwhile, Fe3Co7 with a particle size between 10 and 30 μm can easily enter the inter-bundle pore to form periodic pattern, enriching the electromagnetic loss mechanisms. Two significant electromagnetic resonance peaks for the designed 5.3 mm thick gradient A-T-A laminated structure occur in the vicinity of 7 GHz and 15 GHz, realizing reflection loss less than −10 dB at an incidence angle of 0–40° in TE mode. When the penetrating damage area accounts for 20 %, effective absorption bandwidth almost covers 6–18 GHz. Therefore, gradient A-T-A structure provides an insight for realizing excellent angular and electrical performance damage tolerance.

Numerical Simulation of Metasurface Grating to Function as Polarization Modulator in Quantum Key Distribution Systems

Polarization modulation plays an important role in polarization encoding in quantum key distribution. By using polarization modulation, quantum key distribution systems become more compact and more vulnerable as one laser source is used instead of using multiple laser sources that may cause side-channel attacks. Metasurfaces with their exceptional optical properties have led to the development of versatile ultrathin optical devices. They are made up of planar arrays of resonant or nearly resonant subwavelength pieces and provide complete control over reflected and transmitted electromagnetic waves opening several possibilities for the development of innovative optical components. In this work, the Si nanowire metasurface grating polarizer is designed by COMSOL Multiphysics Software to operate in the visible region and transmit the transverse magnetic polarization of light. The same structure can be rotated by different angles, i.e., 90o, 45o, and -45o to mimic the function of polarization modulation in quantum key distribution systems. The designed structure has an extinction ratio of ~ 60000 and a wide angular tolerance range of (-20o - 20o).

Pixels and resonators with blazed Littrow structures: Passive and non-Hermitian approaches

The confinement of light by Littrow blazed grating structures is explored for targeted device operation principles. For passive devices, these grating structures are explored in one and two-dimensional versions to study resonant pixel with sizes of about ten grating periods (for 4.5 μm-side), which retain a CMOS compatible design. The resonances are found to substantially enhance the weak silicon absorption at 940 nm, a wavelength of interest for, e.g., distance ranging and face recognition, and to achieve a 7.5° angular tolerance. The addition of gain and loss in generic Littrow structures that display an original dispersion made of crossing manifold is next considered, with a view to the issue of broad-area laser modal control.

Three-dimensional angular deviation and diffraction efficiency of a grating in Littrow-configuration ECDL

We consider in this paper the angular deviation and diffraction efficiency of the reflection gratings in Littrow-configuration for applications of external cavity diode laser using the rigorous coupled-wave analysis method. We consider the three-dimensional diffraction case in general, where the incidence plane is un-parallel with the grating vector, i.e. conical diffraction. The angular tolerance of arbitrary gratings under plane and conical diffraction are thus derived and presented. A typical blazed grating is chosen as an example to calculate its diffraction efficiency using the rigorous coupled-wave analysis method. Furthermore, we point out that the angular tolerance and reflection efficiency can be improved if the appropriate parameter settings are selected for Littrow-configuration devices, including incidence angle, diffraction order, grating period and blazed angle. Otherwise, a tiny slanting angle of the grating vector deviated from the incidence plane will deviate the feedback light away from entering the laser-diode-chip and halt laser oscillation in the external cavity. Finally, a general rule for the parameter settings in Littrow-configuration is provided as a benchmark.

Angle-Insensitive Ultrathin Broadband Visible Absorber Based on Dielectric-Semiconductor-Lossy Metal Film Stacks.

Ultrathin broadband absorbers with high efficiency, wide angular tolerance, and low fabrication cost are in demand for various applications. Here, we present an angle-insensitive ultrathin (<150 nm) broadband absorber with an average 96.88% (experiment) absorptivity in the whole visible range by utilizing a simple dielectric-semiconductor-lossy metal triple-layer film structure. The excellent broadband absorption performance of the device results from the combined action of the enhanced absorptions in the semiconductor and lossy metal layers exploiting strong interference effects and can be maintained over a wide viewing angle up to ±60°. Benefiting from the lossy metal providing additional absorption, our design reduces the requirement for the semiconductor's material dispersion and has great flexibility in the material selection of the metal layer. Additionally, the lithography-free nature of the proposed broadband visible absorber provides a high-throughput fabrication convenience, thus holding great potential for its large-area applications in various fields.

Deep neural network-enabled bifunctional terahertz metasurface design for absorption and polarization conversion

With the assistance of deep neural networks, a bifunctional metasurface (MS) was designed and optimized, i.e., a broadband absorber and a broadband polarization converter. The MS acts as a wide absorber when the vanadium dioxide (VO2) is in the metallic state and has an absorption bandwidth of 5.21 THz with an absorption rate ≥ 90%. In contrast, the MS acts as a linear–linear polarization converter when the top VO2 is in the insulating state and has a bandwidth of 3.7 THz with a conversion efficiency ≥ 90%. The bandwidth in both states is maximum compared to other bifunctional counterparts, while this bifunctional MS has good parametric and angular tolerance characteristics and low material cost. The proposed structure and design method of the bifunctional MS can provide a useful reference for the research of new multifunctional terahertz devices.

Angle-insensitive topological interface states in hybrid one-dimensional photonic crystal heterostructures containing all-dielectric metamaterials.

Topological interface states (TISs) in conventional one-dimensional (1D) photonic crystal (PhC) heterostructures strongly shift toward higher frequencies as the incident angle increases. This strong blueshift property of TISs intensively limits the operating angle ranges of TISs. Herein, we design two angle-insensitive photonic bandgaps (PBGs) in two hybrid 1D PhCs containing all-dielectric metamaterials. By cascading these two hybrid 1D PhCs to construct a hybrid 1D PhC heterostructure, we achieve an angle-insensitive TIS under transverse magnetic polarization. Empowered by the angle-insensitive property of the PBGs, the angular tolerance of the TIS reaches 69.65°, which is much higher than those of the TISs in conventional 1D PhC heterostructures. In addition, the angle-insensitive property of the TIS is robust against the layer thickness. Our work provides a viable route to achieving TISs with high angular tolerances and would facilitate the applications of photonic topological states.

Infrared All-Dielectric Metasurface Beam Splitter Based on Transflective Structures

Beam splitters are widely applied in various optical systems as a common beam-splitting device. The conventional stereoscopic and flat-type beam splitters greatly limit the packaging and integration of optical systems due to their large size and restricted emitting direction. Recently, beam-splitting devices made of various transmissive or reflective metasurfaces have shown the potential to overcome these challenges. However, in optical systems such as machine vision, these single-ended beam splitters increase the design complexity of the signal feedback link due to the limitation of the beam-splitting path direction. Here, we proposed and numerically simulated a transflective all-dielectric metasurface beam splitter by applying incompletely transmissive structural designs to the metasurface and using the transmission phase modulation mechanism. It can realize the beam separation for arbitrarily polarized incident light on the same side of the normal at both transmissive and reflective ends with a single-layer unit cell arrangement structure and has a similar emergence angle. The results reveal that at 1550 nm, the angular tolerance bandwidth is about 32°, the total splitting efficiency is over 90%, and the splitting ratio is approximately 1:1. After comparison and verification of simulation results, this transflective metasurface beam splitter is hopeful to be applied in new compact optical systems that require real-time signal feedback, such as coaxial light sources and photoelectric sensing.

Micro-dispenser-based optical packaging scheme for grating couplers.

Due to their sub-millimeter spatial resolution, ink-based additive manufacturing tools are typically considered less attractive than nanophotonics. Among these tools, precision micro-dispensers with sub-nanoliter volumetric control offer the finest spatial resolution: down to 50 µm. Within a sub-second, a flawless, surface-tension-driven spherical shape of the dielectric dot is formed as a self-assembled µlens. When combined with dispersive nanophotonic structures defined on a silicon-on-insulator substrate, we show that the dispensed dielectric µlenses [numerical aperture (NA) = 0.36] engineer the angular field distribution of vertically coupled nanostructures. The µlenses improve the angular tolerance for the input and reduces the angular spread of the output beam in the far field. The micro-dispenser is fast, scalable, and back-end-of-line compatible, allowing geometric-offset-caused efficiency reductions and center wavelength drift to be easily fixed. The design concept is experimentally verified by comparing several exemplary grating couplers with and without a µlens on top. A difference of less than 1 dB between incident angles of 7° and 14° is observed in the index-matched µlens, while the reference grating coupler shows around 5 dB contrast.

Deep neural network-aided design of terahertz bifunctional metasurface

Based on the insulator-to-metal phase transition of vanadium dioxide (VO2), we present a bifunctional metasurface (MS), which can be switched between the two working states, i.e., a broadband absorber and a broadband polarization converter. When the top VO2 is in the metallic state, the MS can work as an absorber, which has an absorption bandwidth of 3.53 THz with an ≥90% absorption rate; and conversely, when the top VO2 is in the insulating state, the structure can function as a polarization converter, which exhibits a bandwidth of 3.0 THz with a ≥90% conversion efficiency. The overlapped bandwidth of the two states is the widest when compared with the other bifunctional counterparts. Meanwhile, this bifunctional MS has good angular and parametric tolerance characteristics. In the MS’s design, the deep neural network (DNN) is also utilized to assist us in optimizing the structural parameters efficiently. The proposed structure and design method of the bifunctional MS may provide a valuable reference for new multifunctional terahertz devices.

Visible-mid infrared ultra-broadband and wide-angle metamaterial perfect absorber based on cermet films with nano-cone structure

Abstract Metamaterial absorbers over a broadband spectrum with high absorption, good angular tolerance, and easy configurations have essential importance for optical and optoelectronic devices. In this study, a hybrid metamaterial absorber comprising multilayered cermet thin films (multi-cermet) with tapered structure is designed and experimentally demonstrated. Combining optical interference of multi-cermet films and optical field localization of nano-cone structures, the average absorbance of both simulation and measurement are more than 98% in an ultrabroad bandwidth (300–3000 nm), and the proposed absorber shows a good angular tolerance as well. The composite process of two easy-operated and efficient methods, colloidal lithography, and magnetron sputtering, is employed for large-area fabrication. In addition, owing to flexible polyimide substrate, the proposed absorber also shows good bending and heating resistance, which reflects its potential in engineering application.

Metamaterials-based broadband absorption in long-wave infrared frequency enabled by multilayered ENZ films on metal-coated patterned silicon.

Large-scale, and high-throughput produced devices with strong ultrabroadband absorption and high angular tolerance are in demand for applications such as thermal imaging, energy harvesting, and radiative cooling. Despite long-standing efforts in design and fabrication, it has been challenging to achieve all these desired properties simultaneously. Here, we create a metamaterial-based infrared absorber fabricated from thin films of epsilon-near-zero (ENZ) materials grown on metal-coated patterned silicon substrates that exhibit ultrabroadband infrared absorption in both p- and s-polarization at angles ranging from 0° to 40°. The results show that the structured multilayered ENZ films exhibit high absorption (> 0.9) covering the entire 8∼14 µm wavelengths. In addition, the structured surface can be realized via scalable, low-cost methods on large-area substrates. Overcoming the limitations on angular and polarized response improves performance for applications such as thermal camouflage, radiative cooling for solar cell, thermal image and et., al.

Designing the Self-Assembly of Arbitrary Shapes Using Minimal Complexity Building Blocks.

The design space for self-assembled multicomponent objects ranges from a solution in which every building block is unique to one with the minimum number of distinct building blocks that unambiguously define the target structure. We develop a pipeline to explore the design spaces for a set of structures of various sizes and complexities. To understand the implications of the different solutions, we analyze their assembly dynamics using patchy particle simulations and study the influence of the number of distinct building blocks, and the angular and spatial tolerances on their interactions, on the kinetics and yield of the target assembly. We show that the resource-saving solution with a minimum number of distinct blocks can often assemble just as well (or faster) than designs where each building block is unique. We further use our methods to design multifarious structures, where building blocks are shared between different target structures. Finally, we use coarse-grained DNA simulations to investigate the realization of multicomponent shapes using DNA nanostructures as building blocks.

Laser Constructing Short‐Range Disordered Metagratings for Visible Near‐Infrared Polarization‐Independent Absorption

AbstractSubwavelength‐structured metasurfaces working in visible and near‐infrared bands present a high challenge in large‐scale device fabrication. In this study, a scalable, high‐efficient, and low‐cost laser‐induced nanopatterning technique is exploited to fabricate a kind of short‐range disordered metagratings, which enables broadband polarization‐independent absorption in the visible to near‐infrared wavelength. The short‐range disorder of the laser‐induced nanogratings originates from the laser‐induced thermal effect and can be spontaneously organized during laser nanopatterning. The unique disorder can break the unidirectional characteristics of the nanogratings, which empowers the metagratings to excite coupled resonance modes. This helps to achieve near‐perfect absorption in the visible to near‐infrared band (400–1100 nm) with an excellent angular tolerance (up to 60°) and average absorptivities of 96.3% and 93.5% under the TM and TE modes, respectively. These low‐cost metagratings can potentially inspire wide applications in the fields of solar cells, sensing, and thermal emitters.

Symmetric nonconfocal Fabry–Perot cavity with a stable long optical path length and improved tolerance for angular alignment

Engineering of optical alignment tolerance between a laser source and a Fabry–Perot (FP) cavity is of great importance in optimizing a laser analysis system and saving costs in the additional alignment task. We propose a modification of the conventional confocal FP (CFP) cavity–a symmetric nonconfocal FP (SNFP) cavity with two identical spherical mirrors separated by a distance equal to half of the common radius of curvature. Numerical analysis of the two cavities reveals that the SNFP cavity has better off-axis stability and much better angular misalignment tolerance than the CFP cavity, even with a longer optical path length (OPL). The SNFP cavity provides a six-transit path length for a basic cavity mode that supports a 1.5-fold long OPL within the same volume as the CFP cavity, which is favorable for applications requiring limits on the footprint and weight of the cavity. In addition, a ray-tracing simulation with a disk-type source having an angular Gaussian distribution (α = β = 5 deg) reveals that the emission beam profile from the SNFP cavity is narrower than that from the CFP cavity. These results are expected to help reduce cavity loss and to improve alignment efficiency between the laser source and the FP cavity.

Resonant waveguide vs Fabry-Perot cavity: A comparative study for CMOS spectral sensor technology

The ubiquitous use of versatile smart devices fuels a rapid growth in spectral sensor technology. Ambient Light Sensors (ALS), with 3–6 spectral channels in the visible and near-infrared are the most common version today. Their architecture comprises a pixel and a filter atop. While the compliance of the pixel to CMOS technology is built-in, the compliance of the filter in terms of materials and of process parallelism is not obvious. The process demand discards the pixel-scale variable-thickness Fabry-Perot solution, notably, and rather points to single-step nanophotonic structures whose pattern is specific to each ALS pixel/channel. In this study, we provide a performance comparison between two such candidate filters, the resonant waveguide (RWG) rejection filter, and the hybrid Fabry Perot (FP) band-pass filter. The evaluation is carried out in terms of spectral response, tunability, angular and polarization tolerance, and noise sensitivity, assessing the collective ability of an ALS array to retrieve spectral information. Through this analysis from the photon to the system, we pave a methodological frame for engineers and manufacturers facing a variety of application choices and sensing capabilities.

Perturbation approach to improve the angular tolerance of high-Q resonances in metasurfaces.

The interest in highqualityfactor (high-Q) resonances in metasurfaces has been rekindled with the rise of the bound states in the continuum (BIC) paradigm, which describes resonances with apparently limitlessly high quality-factors (Q-factors). The application of BICs in realistic systems requires the consideration of the angular tolerance of resonances, however, which is an issue that has not yet been addressed. Here, we develop an ab-initio model, based on temporal coupled mode theory, to describe the angular tolerance of distributed resonances in metasurfaces that support both BICs and guided mode resonances (GMRs). We then discuss the idea of a metasurface with a perturbed unit cell, similar to a supercell, as an alternative approach for achieving high-Q resonances and we use the model to compare the two. We find that, while sharing the high-Q advantage of BIC resonances, perturbed structures feature higher angular tolerance due to band planarization. This observation suggests that such structures offer a route toward high-Q resonances that are more suitable for applications.

Tamm plasmon polariton with high angular tolerance in heterostructure containing all-dielectric elliptical metamaterials

Tamm plasmon polariton (TPP) in heterostructure composed of a metal layer and a conventional one-dimensional photonic crystal (1DPC) strongly shifts toward shorter wavelengths as the incident angle increases. Such angle-sensitive property of TPP greatly limits the operating angular width of TPP-based optical devices. Very recently, researchers found that the angle dependence of the photonic bandgap (PBG) in 1DPC containing all-dielectric elliptical metamaterials (EMMs) can be flexibly tuned from angle-sensitive to angle-insensitive. Herein, we propose a heterostructure composed of a metal layer and a 1DPC containing all-dielectric EMMs to achieve a TPP with high angular tolerance. The angular tolerance of the TPP reaches 30.8°, which is much larger than those of the reported TPPs in heterostructures composed of a metal layer and a conventional 1DPC. Our work provides a feasible route to expending the operating angular width of TPP-based optical devices, such as filters, absorbers, lasers, and sensors.

Silicon metasurface embedded Fabry-Perot cavity enables the high-quality transmission structural color.

While nanoscale color generations have been studied for years, the high-performance transmission structural color, simultaneously equipped with large gamut, high resolution, and optical multiplexing abilities, still remains as a hanging issue. Here, a silicon metasurface embedded Fabry-Perot cavity is demonstrated to address this problem. By changing the planar geometries of meta-atoms, the cavities provide transmission colors with 194% sRGB gamut coverage and 141,111 DPI resolution, along with more than 300% enhanced angular tolerance. Such high density allows two-dimensional color mixing at the diffraction limit scale. Benefitting from the polarization manipulation capacity of the metasurface, arbitrary color arrangements between cyan and red for two orthogonal linear polarizations are also realized. Our proposed cavities can be used in filters, printings, optical storage, and many other applications in need of high quality and density colors.