Light Manipulation Research Articles

Plate-like Guanine Biocrystals Form via Templated Nucleation of Crystal Leaflets on Preassembled Scaffolds.

Controlling the morphology of crystalline materials is challenging, as crystals have a strong tendency toward thermodynamically stable structures. Yet, organisms form crystals with distinct morphologies, such as the plate-like guanine crystals produced by many terrestrial and aquatic species for light manipulation. Regulation of crystal morphogenesis was hypothesized to entail physical growth restriction by the surrounding membrane, combined with fine-tuned interactions between organic molecules and the growing crystal. Using cryo-electron tomography of developing zebrafish larvae, we found that guanine crystals form via templated nucleation of thin leaflets on preassembled scaffolds made of 20-nm-thick amyloid fibers. These leaflets then merge and coalesce into a single plate-like crystal. Our findings shed light on the biological regulation of crystal morphogenesis, which determines their optical properties.

Extreme Optical Anisotropy in the Type-II Dirac Semimetal NiTe2 for Applications to Nanophotonics

Compared to artificial metamaterials, where nano-fabrication complexities and finite-size inclusions can hamper the desired electromagnetic response, several natural materials like van der Waals crystals hold great promise for designing efficient nanophotonic devices in the optical range. Here, we investigate the unusual optical response of NiTe$_2$, a van der Waals crystal and a type-II Dirac semimetal hosting Lorentz-violating Dirac fermions. By {\it ab~initio~} density functional theory modeling, we show that NiTe$_2$ harbors multiple topological photonic regimes for evanescent waves (such as surface plasmons) across the near-infrared and optical range. By electron energy-loss experiments, we identify surface plasmon resonances near the photonic topological transition points at the epsilon-near-zero (ENZ) frequencies $\approx 0.79$, $1.64$, and $2.22$ eV. Driven by the extreme crystal anisotropy and the presence of Lorentz-violating Dirac fermions, the experimental evidence of ENZ surface plasmon resonances confirm the non-trivial photonic and electronic topology of NiTe$_2$. Our study paves the way for realizing devices for light manipulation at the deep-subwavelength scales based on electronic and photonic topological physics for nanophotonics, optoelectronics, imaging, and biosensing applications.

In the Infinite Pool: The Cinematic Spectatorship of Sleep Has Her House (2017)

Scott Barley’s Sleep Has Her House is a recent landmark of experimental cinema, combining recent trends in the landscape and slow cinema movements to produce a painstakingly crafted meditation on nature and the viewer’s gaze upon it. Characterized by its manipulation of light and temporality, the film draws upon the various modes of viewing established by preceding experimental movements, as exemplified by the work of Warhol, Deleuze, and Brakhage, amongst others, to test the relationship between viewer and viewed. The film’s further environmental concerns, as filtered through its landscape focus, are explored through the recent writings of Plumwood, Kimmerer, and Heidegger and their concerns with animacy and human–nature relations. The result is a film that tests the relationship between man and environment through its manipulation of viewing and seeing, prompting a more animate and holistic view of the natural world.

Spin Hall Effect of Light via Momentum-Space Topological Vortices around Bound States in the Continuum.

Optical bound states in the continuum (BICs) are exotic topological defects in photonic crystal slabs, carrying polarization topological vortices in momentum space. The topological vortex configurations not only topologically protect the infinite radiation lifetime of BICs, but also intrinsically contain many unexploited degrees of freedom for light manipulation originating from BICs. Here, we theoretically propose and experimentally demonstrate the spin Hall effect of light in photonic crystal slabs via momentum-space topological vortices around BICs. The strong spin-orbit interactions of light are induced by using the topological vortices around BICs, introducing both wave-vector-dependent Pancharatnam-Berry phase gradients and cross-polarized resonant phase gradients to the spinning light beam, which lead to spin-dependent in-plane-oblique lateral light beam shifts. Our work reveals intriguing spin-related topological effects around BICs, opening an avenue toward applications of BICs in integrated spin-optical devices and information processing.

Plasmonic Sensing and Switches Enriched by Tailorable Multiple Fano Resonances in Rotational Misalignment Metasurfaces.

Fano resonances that feature strong field enhancement in the narrowband range have motivated extensive studies of light-matter interactions in plasmonic nanomaterials. Optical metasurfaces that are subject to different mirror symmetries have been dedicated to achieving nanoscale light manipulation via plasmonic Fano resonances, thus enabling advantages for high-sensitivity optical sensing and optical switches. Here, we investigate the plasmonic sensing and switches enriched by tailorable multiple Fano resonances that undergo in-plane mirror symmetry or asymmetry in a hybrid rotational misalignment metasurface, which consists of periodic metallic arrays with concentric C-shaped- and circular-ring-aperture unit cells. We found that the plasmonic double Fano resonances can be realized by undergoing mirror symmetry along the X-axis. The plasmonic multiple Fano resonances can be tailored by adjusting the level of the mirror asymmetry along the Z-axis. Moreover, the Fano-resonance-based plasmonic sensing that suffer from mirror symmetry or asymmetry can be implemented by changing the related structural parameters of the unit cells. The passive dual-wavelength plasmonic switches of specific polarization can be achieved within mirror symmetry and asymmetry. These results could entail benefits for metasurface-based devices, which are also used in sensing, beam-splitter, and optical communication systems.

Observation of Vortex Hall Effect in Double Negative Index Materials

AbstractOptical orbital angular momentum (OAM) Hall effect requires the interaction between different angular momenta, which hosts great potential in the manipulation of light. Dozens of studies have revealed that this interaction depends on the materials that the waves pass through. Negative refraction has given rise to many exceptional phenomena in the past decades, which greatly inspires us to investigate the interaction between OAM and double negative index materials (DNMs). It is demonstrated that in‐plane optical vortex waves can exhibit transverse shift through DNM, and such a phenomenon is also called vortex Hall effect. From numerical calculations, a linear relationship is observed between the transverse shift and the topological charge l for a fixed wavelength. The transverse shift originates from the transition of the caustics of the vortex source through DNM. The general theory reported in this work can be applied in more than electromagnetic (EM) systems. Acoustic experiment is performed to support the proposed theory due to the equivalence between acoustic and EM systems. The vortex Hall effect is then observed experimentally utilizing acoustic space‐coiling metamaterials, which can be effectively regarded as DNM. This phenomenon will help to understand the superoscillations of the vortex source, as well as bring significant applications in on‐chip signal de‐multiplexing.

When Chirophotonic Film Meets Wrinkles: Viewing Angle Independent Corrugated Photonic Crystal Paper.

Light manipulation strategies of nature have fascinated humans for centuries. In particular, structural colors are of considerable interest due to their ability to control the interaction between light and matter. Here, wrinkled photonic crystal papers (PCPs) are fabricated to demonstrate the consistent reflection of colors regardless of viewing angles. The nanoscale molecular self-assembly of a cholesteric liquid crystal (CLC) with a microscale corrugated surface is combined. Fully polymerizable CLC paints are uniaxially coated onto a wrinkled interpenetrating polymer network (IPN) substrate. Photopolymerization of the helicoidal nanostructures results in a flexible and free-standing PCP. The facile method of fabricating the wrinkled PCPs provides a scalable route for the development of novel chirophotonic materials with precisely controlled helical pitch and curvature dimensions. The reflection notch position of the flat PCP shifts to a lower wavelength when the viewing angle increased, while the selective reflection wavelength of wrinkled PCP is remained consistent regardless of viewing angles. The optical reflection of the 1D stripe-wrinkled PCP is dependent on the wrinkle direction. PCPs with different corrugated directions can be patterned to reduce the angular-dependent optical reflection of wrinkles. Furthermore, 2D wavy-wrinkled PCP is successfully developed that exhibit directionally independent reflection of color.

The Effectiveness of Blue-Light-Emitting Glasses in Security Guards Exposed to Night Shift Work on Work-Related and General Fatigue: A Randomised Controlled Cross-Over Study.

This study aimed to evaluate the effectiveness of glasses that emit blue light in reducing the need for recovery, general fatigue, and stress levels in security guards who work night shifts. Light manipulation is seen as a promising strategy to mitigate complaints related to shift work, such as sleepiness and impaired cognitive performance. In a randomized controlled cross-over study design, 86 Dutch security guards used light-emitting glasses (exposure duration: 30 min) during night shifts in a five week period versus a five week control period without glasses. Measurements (Need for Recovery Scale; Checklist Individual Strength; stress level assessed by a fitness tracker) were performed at baseline, at five weeks, and again at 11 weeks. The chronotype was measured at baseline as a potential covariate. A mixed model for repeated measure analyses showed no significant reduction in the need for recovery, nor a reduction in general fatigue scores, during the intervention period. Paired Samples T-Test analyses showed no significant changes in stress levels for the intervention period. Conclusively, blue light exposure using light-emitting glasses for security guards during night shifts showed no directly measurable effect on the reduced need for recovery, overall fatigue, and stress levels.

End-to-end joint optimization of metasurface and image processing for compact snapshot hyperspectral imaging

Traditional snapshot hyperspectral imaging systems generally require multiple refractive-optics-based elements to modulate light, resulting in bulky framework. In pursuit of a more compact form factor, a metasurface-based snapshot hyperspectral imaging system, which achieves joint optimization of metasurface and image processing, is proposed in this paper. The unprecedented light manipulation capabilities of metasurfaces are used in conjunction with neural networks to encode and decode light fields for better hyperspectral imaging. Specifically, the extremely strong dispersion of metasurfaces is exploited to distinguish spectral information, and a neural network based on spectral priors is applied for hyperspectral image reconstruction. By constructing a fully differentiable model of metasurface-based hyperspectral imaging, the front-end metasurface phase distribution and the back-end recovery network parameters can be jointly optimized. This method achieves high-quality hyperspectral reconstruction results numerically, outperforming separation optimization methods. The proposed system holds great potential for miniaturization and portability of hyperspectral imaging systems.

Decoherence of photon entanglement by transmission through brain tissue with Alzheimer's disease.

The generation, manipulation and quantification of non-classical light, such as quantum-entangled photon pairs, differs significantly from methods with classical light. Thus, quantum measures could be harnessed to give new information about the interaction of light with matter. In this study we investigate if quantum entanglement can be used to diagnose disease. In particular, we test whether brain tissue from subjects suffering from Alzheimer's disease can be distinguished from healthy tissue. We find that this is indeed the case. Polarization-entangled photons traveling through brain tissue lose their entanglement via a decohering scattering interaction that gradually renders the light in a maximally mixed state. We found that in thin tissue samples (between 120 and 600 micrometers) photons decohere to a distinguishable lesser degree in samples with Alzheimer's disease than in healthy-control ones. Thus, it seems feasible that quantum measures of entangled photons could be used as a means to identify brain samples with the neurodegenerative disease.

Programmable Wavefront Control in the Visible Spectrum Using Low-Loss Chalcogenide Phase-Change Metasurfaces.

All-dielectric metasurfaces provide unique solutions for advanced wavefront manipulation of light with complete control of amplitude and phase at sub-wavelength scales. One limitation, however, for most of these devices is the lack of any post-fabrication tunability of their response. To break this limit, a promising approach is employing phase-change materials (PCMs), which provide fast, low energy, and non-volatile means to endow metasurfaces with a switching mechanism. In this regard, great advancements have been done in the mid-infrared and near-infrared spectrum using different chalcogenides. In the visible spectral range, however, very few devices have demonstrated full phase manipulation, high efficiencies, and reversible optical modulation. In this work, a programmable all-dielectric Huygens' metasurface made of antimony sulfide (Sb2 S3 ) PCM is experimentally demonstrated, a low loss and high-index material in the visible spectral range with a large contrast (≈0.5) between its amorphous and crystalline states. ≈2π phase modulation is shown with high associated transmittance and it is used to create programmable beam-steering devices. These novel chalcogenide PCM metasurfaces have the potential to emerge as a platform for next-generation spatial light modulators and to impact application areas such as programmable and adaptive flat optics, light detection and ranging (LiDAR), and many more.

Computational analysis of vertical comb-drive microactuator with extended mirror for manipulation of light

Squeeze film damping is a dominant mechanism to examine the losses in the micro-opto-electro-mechanical systems. It plays an important role in understanding the dynamic performance of vertical-comb drive (VCD) microactuator. In the present paper, finite element method is used to estimate the Q factor and damping ratio at varying ambient pressures ranging from atmospheric (105 Pa) to vacuum (0.1 Pa) in COMSOL Multiphysics. The effect of ambient pressure on dynamic performance of the VCD is discussed in detail. Based on the applications, two different VCDs (VCD-L and VCD-SR) with extended micromirrors have been proposed in the current study for the manipulation of light. VCD-L having lower eigen frequency of 670 Hz can be used in laser and biomedical applications. VCD-SR with higher eigen frequency nearly 90 kHz has the potential use in a synchrotron radiation source. In addition, a parametric study is done to understand the performance of VCD for varying process parameters such as variable offset length among the comb fingers, spring dimensions, and orientation of single crystal silicon. For spring design, the von-Mises stress theory is preferred over maximum shear stress theory.

Atomic-Scale Confinement and Negative Refraction of Plasmons by Twisted Bilayer Graphene.

Moiré superlattices provide in-plane quantum restriction for light-matter interactions in twisted bilayer graphene (tBLG), leading to the exotic photon-Moiré physics and potential applications for light manipulation. Recently, our experiment identified a highly confined slow surface plasmons polaritons (SPPs) mode in tBLG. Here, we demonstrate that the propagation of the slow SPPs mode in tBLG is spatially tailored and steered at deep subwavelengths. Analysis by the perturbation theory indicates that the coupling between the slow SPPs mode and the Moiré system is greatly strengthened, which regulates the wavefront at the atomic scale and makes tBLG serve as a universal optical metamaterial. Consequently, the negative refraction is achieved at the interface of monolayer graphene and tBLG, by which a metalens with a controllable focal length and an extremely high resolution up to 1/150 of wavelength is devised. Our work paves the way for constructing optical metamaterial at the atomic scale and develops future photon-Moiré interaction systems.

Optical Manipulation of Incident Light for Enhanced Photon Absorption in Ultrathin Organic Photovoltaics.

We attempted to improve the photon absorption of the photoactive layer in organic photovoltaic (OPV) devices by device engineering without changing their thickness. Soft nanoimprinting lithography was used to introduce a 1D grating pattern into the photoactive layer. The increase in photocurrent caused by the propagating surface plasmon-polariton mode was quantitatively analyzed by measuring the external quantum efficiency in transverse magnetic and transverse electric modes. In addition, the introduction of an ultrathin substrate with a refractive index of 1.34 improved photon absorption by overcoming the mismatched optical impedance at the air/substrate interface. As a result, the power conversion efficiency (PCE) of an ultrathin OPV with a 400 nm grating period was 8.34%, which was 11.6% higher than that of an unpatterned ultrathin OPV, and the PCE was 3.2 times higher at a low incident light angle of 80°, indicating very low incident light angle dependence.

Active Tuning and Anisotropic Strong Coupling of Terahertz Polaritons in Van der Waals Heterostructures.

Electromagnetic field confinement is significant in enhancing light-matter interactions as well as in reducing footprints of photonic devices especially in Terahertz (THz). Polaritons offer a promising platform for the manipulation of light at the deep sub-wavelength scale. However, traditional THz polariton materials lack active tuning and anisotropic propagation simultaneously. In this paper, we design a graphene/α-MoO3 heterostructure and simulate polariton hybridization between isotropic graphene plasmon polaritons and anisotropic α-MoO3 phonon polaritons. The physical fundamentals for polariton hybridizations depend on the evanescent fields coupling originating from the constituent materials as well as the phase match condition, which can be severely affected by the α-MoO3 thickness and actively tuned by the gate voltages. Hybrid polaritons propagate with in-plane anisotropy that exhibit momentum dispersion characterized by elliptical, hyperboloidal and even flattened iso-frequency contours (IFCs) in the THz range. Our results provide a tunable and flexible anisotropic polariton platform for THz sensing, imaging, and modulation.

Beyond Bounds on Light Scattering with Complex Frequency Excitations.

Light scattering is one of the most established wave phenomena in optics, lying at the heart of light-matter interactions and of crucial importance for nanophotonic applications. Passivity, causality, and energy conservation imply strict bounds on the degree of control over scattering from small particles, with implications on the performance of many optical devices. Here, we demonstrate that these bounds can be surpassed by considering excitations at complex frequencies, yielding extreme scattering responses as tailored nanoparticles reach a quasi-steady-state regime. These mechanisms can be used to engineer light scattering of nanostructures beyond conventional limits for noninvasive sensing, imaging, and nanoscale light manipulation.

Ultralow-Loss Phonon Polaritons in the Isotope-Enriched α-MoO3.

α-MoO3, a natural van der Waals (vdWs) material, has received wide attention in nano-optics for supporting highly confined anisotropic phonon polaritons (PhPs) from the mid-infrared to the terahertz region, which opens a new route for manipulating light at the nanoscale. However, its optical loss hinders light manipulation with high efficiency. This work demonstrates that the isotope-enriched Mo element enables ultralow-loss PhPs in the α-MoO3. Raman spectra reveal that the isotope-enriched Mo element in the α-MoO3 allows different optical phonon frequencies by efficiently altering the Reststrahlen band's dispersion. The Mo isotope-enriched α-MoO3 significantly reduces the PhPs' optical loss due to efficient optical coherence, which enhances the propagation length revealed by infrared nanoimaging. These findings suggest that the isotope-enriched α-MoO3 is a new feasible 2D material with an ultralow optical loss for possible high-performance integrated photonics and quantum optics devices.

Generalized homogenization method for subwavelength periodic lattices.

Periodic photonic lattices based on Guided-Mode Resonance (GMR) enable the manipulation of the incident light, making them essential components in a plethora of optical elements including filters, sensors, lasers, and polarizers. The GMR is regarded as a resonance phenomenon in the resonant-subwavelength regime of periodic lattices. We present a method that homogenizes these periodic structures in the subwavelength regime and provides an appropriate analytical interpretation of the resonance effect. Here, we propose a technique based on utilizing the dispersion relation for homogenization, which can be applied to multi-part period lattices under oblique incidence. The effect of asymmetry and emergence of the odd/even modes, not considered in previous methods, will also be taken into account and discussed. As a result of this analytical procedure, resonance lines are obtained, which are useful in designing optical elements such as wideband/narrowband reflectors and polarizers.

Creating anisotropic topological phases within inversely designed photonic crystals

Photonic topological insulators endow flexible manipulation of light with high efficiency and robustness. The majority of previous research concentrated on isotropic topological states, with anisotropic topological states receiving less attention. In this study, we investigate anisotropic topological edge states in two-dimensional photonic systems for both the transverse magnetic (TM) and transverse electric (TE) modes. First, using the topology optimization method, photonic crystals (PCs) with maximized odd-order band gaps, from the first-order to the seventh-order, are created. An anisotropic topological phase transition is then obtained by shifting the primitive unit cell (UC) of the optimized PC along the horizontal direction by half of the lattice constant. Tightly localized anisotropic topological edge states are thus formed at the interface between the primitive and translated UCs. Finally, the transmission properties of the anisotropic topological edge states are numerically demonstrated. Our findings could aid in the development of topological photonic devices that offer reliable directional transmissions and radiations.

Light funneling by spin-orbit-coupled chiral particles on an arbitrary order exceptional surface

Optical systems at non-Hermitian exceptional points (EPs) have intriguing properties that promise novel applications in light manipulations. Here, we realize an arbitrary order exceptional surface (ES), i.e., a surface of arbitrary order EPs, in chiral particles that couple with each other via the photonic spin-orbit interaction mediated by a dielectric waveguide. The chirality of the particles enables selective excitation of the chiral dipole modes by linearly polarized light. The unidirectional coupling of the chiral dipole modes gives rise to the ES in the parameter space defined by the material loss and coupling distance of the particles. We apply the system to realize a light funnel that can convert free-space plane waves to guided waves and funnel the incident light energy into a ring resonator. The results can find applications in designing optical switches, on-chip conversion of guided waves, and harvest of light energy.