Advanced Optical Applications Research Articles

Uniaxial alignment of perovskite nanowires via brush painting technique for efficient flexible polarized photodetectors

A polarization-sensitive and flexible photodetector was fabricated through the precise alignment of perovskite nanowires (NWs) using a brush coating technique. The alignment of the NWs was meticulously examined, considering various chemical properties of the solvent, such as boiling point, viscosity, and surface tension. Notably, when the NWs were brush-coated with toluene dispersion, the NWs were aligned in higher order than those processed from octane dispersion. The degree of alignment was correlated with the photodetector property. Especially, the well-aligned NW photodetector exhibited a two-fold disparity in current response contingent on the polarization direction. Furthermore, even after enduring 500 bending cycles, the device retained 80% of its photodetector performance. This approach underscores the potential of solution-processed flexible photodetectors for advanced optical applications under dynamic operating conditions.

Absorption of water molecules on the surface of stereocomplex-crystal spherulites of polylactides: An in-situ FT-IR spectroscopy investigation

The correlation between water molecules and polylactide was clarified. The crystallinity in stereocomplex (SC) crystal spherulites was investigated using microbeam wide-angle X-ray diffraction. The crystallinity was higher in the central region, and edge-on lamellae grew in a twisted manner. The hydrogen bonding in SC-crystal spherulites was evaluated via microbeam FT-IR spectroscopy in a humidity-controlled cell. The water-derived bands corresponding to OH vibration and HOH bending increased with increasing humidity. Microbeam FT-IR spectroscopy was used to evaluate the water absorption behavior of crystalline films depending on their position. Coarse-grained molecular dynamics simulations indicated that the number of adsorbed water molecules increased with decreasing crystallinity. In SC-crystal spherulites, water molecules are absorbed in both amorphous and crystalline regions but with greater difficulty in the crystalline regions. These insights into water molecule absorption on SC-crystal spherulite can facilitate the development of polylactide materials with controlled biodegradability for advanced medical and optical applications.

Tempering Multichannel Photon Emission from Emitter-Coupled Holographic Metasurfaces.

On-chip manipulation of photon emission from quantum emitters (QEs) is crucial for quantum nanophotonics and advanced optical applications. At the same time, the general design strategy is still elusive, especially for fully exploring the degrees of freedom of multiple channels. Here, the vectorial scattering holography (VSH) approach developed recently for flexibly designing QE-coupled metasurfaces is extended to tempering the strength of QE emission into a particular channel. The VSH power is demonstrated by designing, fabricating, and optically characterizing on-chip QE sources emitted into six differently oriented propagation channels, each representing the entangled state of orthogonal circular polarizations with different topological charges and characterized with a specific relative strength. We postulate that the demonstration of tempered multichannel photon emission from QE-coupled metasurfaces significantly broadens the possibilities provided by the holographic metasurface platform, especially those relevant for high-dimensional quantum information processing.

Crystal structure and elastic and phonon properties of realgar versus pressure

Realgar, α-As4S4 (space group P21/n), is one of the best-known arsenic sulfide minerals because of its extended use in the past as a red pigment and its employment in modern times for advanced optical and electronic technological applications. From a geological perspective, the main realgar deposits are hydrothermal and epithermal, but it is also a relevant phase found between the upper mantle and Earth's crust and therefore one of the main sources of arsenic. Despite this widespread use and interest, few experimental and theoretical studies have been focused on the characterization of the structural, elastic and vibrational properties of realgar, especially their variation with pressure. Some quantities, such as the cohesive energy between the As4S4 units and the elastic moduli, have never been reported in the scientific literature. The present work deals with a density functional theory investigation of the cited properties of realgar using the recently proposed PBEh-3c method, which was devised in particular to deal with crystalline solids characterized by weak van der Waals interactions. This approach is validated against the available crystal-chemical, mechanical and spectroscopic data from previous studies, finding a generally good agreement. The equation-of-state parameters of the energy versus unit-cell volume data were V 0 = 767.13 (9) Å3, B 0 = 15.73 (8) GPa and B′ = 9.1 (2), with the bulk modulus value (B 0) in good agreement with the value obtained from the elastic tensor analysis (B = 16.1 GPa). The cohesive energy was found to be about 146.1 kJ mol–1, a value that follows the typical ones of organic crystals. The present work provides new insights into this peculiar mineral that, from a mineralogical point of view, could be considered a prototype of a heterodesmic structure made by inorganic molecular clusters.

Small Footprint and High Extinction Ratio Cladding-Modulated Bragg Grating Structure as a Wideband Bandstop Filter

This study presents a comprehensive numerical investigation of silicon Bragg grating (BG) waveguide structures with cladding modulation. The device design features a uniform silicon ridge waveguide with corrugated cladding on both sides. Two distinct architectures are explored: one where silicon serves as the cladding and another where gold (Au) is employed. Our detailed analysis uncovers compelling results for both configurations. The silicon corrugated cladding BG waveguide demonstrates a bandstop bandwidth of ~50 nm, accompanied by an extinction ratio (ER) of 7.98 dB. The device footprint is compact, measuring approximately 16.4 × 3 µm2. In contrast, the Au corrugated cladding BG waveguide exhibits exceptional performance, boasting a wideband bandstop bandwidth of ~143 nm and an impressive ER of 19.96 dB. Despite this enhanced functionality, the device maintains a reasonably small footprint at around 16.9 × 3 µm2. This investigation underscores the potential of Au corrugated cladding BG waveguides as ideal candidates for achieving high-spectral-characteristic bandstop filters. The significant improvement in bandstop bandwidth and ER makes them promising for advanced optical filtering applications.

Photoswitching the fluorescence of nanoparticles for advanced optical applications.

The dynamic optical response properties and the distinct features of nanomaterials make photoswitchable fluorescent nanoparticles (PF NPs) attractive candidates for advanced optical applications. Over the past few decades, the design of PF NPs by coupling photochromic and fluorescent motifs at the nanoscale has been actively pursued, and substantial efforts have been made to exploit their potential applications. In this perspective, we critically summarize various design principles for fabricating these PF NPs. Then, we discuss their distinct optical properties from different aspects by highlighting the capability of NPs in fabricating new, robust photoswitch systems. Afterwards, we introduce the pivotal role of PF NPs in advanced optical applications, including sensing, anti-counterfeiting and imaging. Finally, current challenges and future development of PF NPs are briefly discussed.

Three-dimensionally programmable soft crystals toward geometric phase photonics

Patterned monodomains of soft crystals enable programmable tuning in geometric phase photonics, showing prospects for application in flexible electronics and new displays.

Au nanopillar array prepared by selective etching of Au-Sr3Al2O6 vertically aligned nanocomposite thin films

Au nanostructures offer a wide range of applications such as surface-enhanced Raman spectroscopy, photovoltaics, and biosensors. Effective integrating well-controlled Au nanostructures on chip via a self-assembly process remains challenging as most of the Au nanostructures were prepared by either chemical synthesis methods or lithography patterning techniques. This study introduces a simple two-step approach for fabricating Au nanostructures on substrate with well controlled morphology and density. First, epitaxial Au-Sr3Al2O6 (SAO) vertically aligned nanocomposites (VANs) were deposited on SrTiO3 substrates. Second, by subsequently dissolving the water-soluble SAO matrix, various Au nanostructures ranging from 0D nanoparticles to 1D nanopillars are demonstrated. The Au morphology tuning is achieved by varying the deposition parameters of the VANs. This method eliminates the need of harsh chemical solutions and tedious lithography/patterning steps. These findings provide a novel strategy for tailoring the Au nanostructures and their optical properties, and, demonstrating on-chip integration for advanced optical device applications.

A low-loss molybdenum plasmonic waveguide: perfect single-crystal preparation and subwavelength grating optimization

Abstract Plasmonic waveguides have attracted tremendous interest due to efficiently confining photons on the subwavelength spatial scale to be beating the propagation diffraction limit. Transition metal molybdenum (Mo) exhibits outstanding properties in light trapping and electromagnetic field confining, making it potentially valuable in 1.55 μm plasmonic waveguide applications. However, the reliable fabrication of high-quality Mo plasmonic waveguides is a significant challenge. A real-space micro-imaging study of the surface plasmon on Mo structures is still absent. In this study, we successfully prepared a single-crystalline Mo microrod waveguide structure and fabricated subwavelength gratings on it. The diffraction gratings were designed, optimized, and etched to excite the surface plasmon polariton behaviour of Mo for the first time. The grating-optimized Mo microrod single-crystal reveals highly efficient waveguide performance around near-infrared spectroscopy, exhibiting a long propagation length of 32 μm and a low transmission loss of 0.067 dB μm−1. The results provide an alternative to advanced materials research and optical device applications of plasmonic waveguide systems.

Preface to Special Issue on “Advanced Optical Applications and Visualization Technologies for Future Society II”

Preface to Special Issue on “Advanced Optical Applications and Visualization Technologies for Future Society II”

Towards Chiral Lasing from All-Solution Processed Flexible Perovskite Nanocrystal-Liquid Crystal Membrane.

Circularly polarized (CP) coherent light sources are of great potential for various advanced optical applications spanning from display/imaging to data processing/encryption and quantum communication. Here we report the first demonstration of CP amplified spontaneous emission (ASE)/lasing from a free-standing and flexible membrane device consisting of perovskite nanocrystals (PNCs) and cholesteric liquid crystal layers sandwiched within a Fabry-Perot cavity architecture. The chiral liquid crystal cavity enables the generation of CP light from the device. The device is completely solution-processable, and displays CP ASE with record dissymmetry factor (glum ) as high as 1.4, which is 3 orders of magnitude higher as compared with glum of CP luminescence of chiral ligand-capped colloidal PNCs. The device exhibits ultra-flexibility as the ASE intensity remains unchanged after repeated 100 bending cycles and it is stable for more than 3 months with 80% of its original intensity. Furthermore, the ultra-flexibility enabled the generation of ASE from various objects of different geometric surfaces covered with the flexible perovskite membrane device. This work not only demonstrates the first CP ASE from PNCs membrane with extremely high glum but also opens the door toward the fabrication of ultra-flexible, extremely stable, and all solution-processable perovskite chiral laser devices. This article is protected by copyright. All rights reserved.

An Analytical Model of Light Scattering by Birefringent Polycrystalline Dielectrics Using Perturbation of Maxwell's Equations

AbstractPolycrystalline materials have shown promise in advanced optical applications because of their unique optical and mechanical properties. Most polycrystalline materials have non‐uniform optical properties due to residual porosity, secondary phases, and/or crystalline anisotropies (e.g., birefringence). These optical inhomogeneities manifest as scattering that reduces the transparency of the polycrystal. Even in the case of a single‐phase polycrystal with negligible porosity, birefringence scattering will always be present whenever the crystal is anisotropic (non‐cubic). Multiple models for predicting birefringence scattering have been suggested in the literature that are successful in describing scattering loss in specific material systems. Here a first‐principles model of birefringent scattering that is applicable to any single‐phase, unaligned transparent polycrystal is derived. The model can treat grain size distributions and is not limited to a specific material system. The derivation culminates in an equation that describes birefringence scattering coefficient spectra using the single‐crystal refractive index tensor and chord length distribution (measured from a representative polished surface micrograph). The model should be useful for designing materials and characterization. For example, it can be used to predict transmissions of transparent polycrystals for a range of grain sizes or to characterize the average grain size using a transmission measurement.

Pyrolysis of Al-Based Metal-Organic Frameworks to Carbon Dot-Porous Al2 O3 Composites With Time-Dependent Phosphorescence Colors for Advanced Information Encryption.

Phosphorescent materials with time-dependent phosphorescence colors (TDPCs) have great potential in advanced optical applications. Synthesis of such materials is attractive but challenging. Here, a series of carbon dot-porous Al2 O3 composites exhibiting distinctive TDPC characteristics is prepared by high-temperature pyrolysis of Al-based metal-organic frameworks NH2 -MIL-101(Al). The composite synthesized at 700 °C (CDs@Al2 O3 -700) shows an obvious change in phosphorescence color from blue to green after removing the excitation light of 280nm. Photophysical analysis reveals that two emission centers in CDs, namely carbon core and surface states, are responsible for the short-lived blue phosphorescence (96ms) and long-lived green phosphorescence (911ms), respectively. The combination of blue and green phosphorescence with different decay rates triggering the interesting TDPC phenomenon. CDs@Al2 O3 -700 has a significantly high phosphorescence quantum yield of up to 41.7% and possesses an excellent optical stability against water, organic solvents, and strong oxidants, which benefits from the multi-confinement of CDs by the porous Al2 O3 matrix through rigid network, strong space constraint, and stable covalent bonding. Based on the TDPC property, multilevel coding patterns composed of CDs@Al2 O3 are successfully fabricated for advanced dynamic information encryption.

(Invited) Microenvironment Responsiveness of Defect Photoluminescence of Locally Functionalized Single-Walled Carbon Nanotubes and Its Sensing Applications

Photoluminescence (PL) of single-walled carbon nanotubes (SWCNTs) in the near infrared (NIR) region is applicable to advanced optical applications such as bio-imaging and sensing. Local chemical functionalization (slight amount of chemical modification) of SWCNTs has been developed to introduce sp3 carbon defects in the sp2 carbon network of the tube walls for the luminescent defect formation.[1-3] The resultant locally functionalized SWCNTs (lf-SWCNTs) show defect PL (E 11* PL) with red-shifted wavelengths and increased quantum yields compared to original E 11 PL of pristine SWCNTs. For lf-SWCNTs, molecularly designed modifier molecules have enabled the defect PL wavelength modulation[4] and the sensing function creation.[5,6]Recently, we have reported the unique microenvironment responsiveness of defect PL of lf-SWCNTs; namely, the greater wavelength shifts of E 11* PL than E 11 PL by dielectric effects[7] and the PL shifting behavior modulation based on the chemical structure difference of the functionalized sites and the exciton localization effects[8] were observed. The microenvironment responsiveness of the defect PL was applied to the biological sensing application development.[9] To investigate protein detection/recognition functions of lf-SWCNTs, we introduced an avidin-biotin interaction with a selective and strong binding fashion at the functionalized sites of lf-SWCNTs. The lf-SWCNTs tethering biotin groups (lf-SWCNTs-b) were synthesized through diazonium chemistry, followed by its subsequent-modification. When neutravidin was mixed with a lf-SWCNTs-b solution, E 11* PL peak was red-shifted, indicating the higher polarity environment formation by the neutravidin adsorption on lf-SWCNTs-b. When avidin or streptavidin was used, wavelength shifting behaviors of E 11* PL of lf-SWCNTs-b were clearly changed depending on the used avidin derivatives. The results indicate the different polarity environment formation deriving from structural differences of each avidin derivative. Moreover, the detection signal enhancement was observed in a film device using lf-SWCNTs-b. Therefore, lf-SWCNTs have a high potential for development of advanced protein detection/recognition systems using NIR PL.[1] T. Shiraki et al. Acc. Chem. Res., 53, 1846 (2020). [2] S. Tretiak et al., Acc. Chem. Res., 53, 1791(2020) [3] Y. Wang et al. Nat. Rev. Chem., 3, 375 (2019). [4] T. Shiraki et al. ACS Nano, DOI: 10.1021/acsnano.2c09897 (2022). [5] T. Shiraki et al. Chem. Commun., 52, 12972 (2016). [6] S. Kruss et al, Angew. Chem. Int. Ed., 59, 17732 (2020). [7] T. Shiraki et al. Chem. Commun., 55, 3662 (2019). [8] T. Shiraki et al. J. Phys. Chem. C, 125, 12758 (2021). [9] T. Shiraki et al. Nanoscale, 14, 13090 (2022). Figure 1

Robust Strategy to Improve the Compatibility between Incorporated Upconversion Nanoparticles and the Bulk Transparent Polymer Matrix.

Traditional transparent polymer nanocomposites combined with functional fluorescent inorganic nanofillers are promising for many advanced optical applications. However, the aggregation of the incorporated functional nanoparticles results in light scattering and will decrease the transparency of nanocomposites, which will restrain the application of the transparent nanocomposites. Herein, a robust synthesis strategy was proposed to modify upconversion nanoparticles (UCNPs) with polymethyl methacrylate (PMMA) to form UCNP@PMMA core@shell nanocomposites though metal-free photoinduced surface-initiated atom transfer radical polymerization (photo-SI-ATRP), and thus, the dispersity of UCNP@PMMA and the interface compatibility between the surface of UCNPs and the bulk PMMA matrix was greatly improved. The obtained PMMA nanocomposites possess high transparency and show strong upconversion photoluminescence properties, which promises great opportunities for application in 3D display and related optoelectronic fields. This strategy could also be applied to fabricate other kinds of functional transparent polymer nanocomposites with inorganic nanoparticles uniformly dispersed.

Modulation of orbital angular momentum of vortex beam based on ordered pinhole screens

Optical vortex phase beams have unique amplitudes and phase distributions, rendering them sensitive to the position and symmetry of modulating structures. This sensitivity can facilitate their applicability to optical communications. We propose a method for modulating the topological charge of input vortex beams using a pinhole screen. By changing the pinhole arrangement to match the phase of the vortex beam and considering the Fresnel diffraction theory, the transmission light field is calculated numerically. In addition, the intensity map of the adjustable topological charges is measured near the origin, with the experimental results suitably agreeing with the theoretical simulation results. The diffraction field modulated by spiral pinholes has various orbital angular momentum modes, including the increase and decrease of orbital angular momentum, especially when the incident vortex beam is more complex. The proposed method opens new possibilities for the use of vortex beams in advanced optical applications with improved capabilities and functionalities.

Nanotechnology-Enabled Polymer-Based Nanocomposite Hybrids for Advanced Optical Applications: A Review

Polymer nanocomposites (PNCs) are functional hybrids lying at the interface of organic and inorganic realm, whose high versatility offers numerous possibilities to develop tailor-made materials with advanced material behaviors. Accordingly, a considerate combination of optically effective additive and particle-stabilizing polymer often opens up unique design possibilities, thereby offering momentous lead in creating advanced functional materials for targeted techno-commercial applications. Accordingly, optically effective nanofillers characterized by particle size and dielectric constant of the surrounding medium-dependent surface plasmon resonance effects may induce entirely new optical functionalities (UV and visible light absorption, optical dichroism, spectral manipulation, photonic emission and so forth) in the polymeric host. Herein, we discuss the major causative factors, which enable nanostructured materials to exhibit unique properties, general introduction to nanotechnology-enabled polymer-based nanocomposites and present a comprehensive review on functional properties and related applications of PNCs, with special emphasis on optical functionalities (photonic absorption encompassing UV shielding, color switching and refractive index engineering and photonic emission covering photoluminescence and spectral manipulations). This review also sheds light on the effect of nature of filler, filler morphology, filler size and filler composition and dispersion homogeneity on optical behaviors of polymer nanocomposites.

Molecular and Supramolecular Designs of Organic/Polymeric Micro-photoemitters for Advanced Optical and Laser Applications.

ConspectusFor optical and electronic applications of supramolecular assemblies, control of the hierarchical structure from nano- to micro- and millimeter scale is crucial. Supramolecular chemistry controls intermolecular interactions to build up molecular components with sizes ranging from several to several hundreds of nanometers using bottom-up self-assembly process. However, extending the supramolecular approach up to a scale of several tens of micrometers to construct objects with precisely controlled size, morphology, and orientation is challenging. Especially for microphotonics applications such as optical resonators and lasers, integrated optical devices, and sensors, a precise design of a micrometer-scale object is required. In this Account, we review the recent progress on precise control of microstructures from π-conjugated organic molecules and polymers, which work as micro-photoemitters and are suitable for optical applications.After the introduction on the importance of the control of the hierarchical structures from molecular assembly, we review supramolecular methodology for assembling molecules and supramolecules to form microstructures such as spheres and polygons with precisely controlled morphology and molecular orientations. The resultant microstructures act as anisotropic emitters of circularly polarized luminescence. We report that synchronous crystallization of π-conjugated chiral cyclophanes forms concave hexagonal pyramidal microcrystals with homogeneous size, morphology, and orientation, which clearly paves the way for the precise control of skeletal crystallization under kinetic control. Furthermore, we show microcavity functions of the self-assembled micro-objects. The self-assembled π-conjugated polymer microspheres work as whispering gallery mode (WGM) optical resonators, where the photoluminescence exhibits sharp and periodic emission lines. The spherical resonators with molecular functions act as long-distance photon energy transporters, convertors, and full-color microlasers. Fabrication of microarrays with photoswitchable WGM microresonators by the surface self-assembly technique realizes optical memory with physically unclonable functions of WGM fingerprints. All-optical logic operations are demonstrated by arranging the WGM microresonators on synthetic and natural optical fibers, where the photoswitchable WGM microresonators act as a gate for light propagation via a cavity-mediated energy transfer cascade. Meanwhile, the sharp WGM emission line is appropriate for utilization as optical sensors for monitoring the mode shift and mode splitting. The resonant peaks sensitively respond to humidity change, absorption of volatile organic compounds, microairflow, and polymer decomposition by utilizing structurally flexible polymers, microporous polymers, nonvolatile liquid droplets, and natural biopolymers as media of the resonators. We further construct microcrystals from π-conjugated molecules with rods and rhombic plates, which act as WGM laser resonators with light-harvesting function. Our developments, precise design and control of organic/polymeric microstructures, form a bridge between nanometer-scale supramolecular chemistry and bulk materials and pave the way toward flexible micro-optics applications.

Review of Microbottle Resonators for Sensing Applications

Microbottle resonators (MBR) are bottle-like structures fabricated by varying the radius of an optical fiber. MBRs can support whispering gallery modes (WGM) by the total internal reflection of the light coupled into the MBRs. MBRs have a significant advantage in sensing and other advanced optical applications due to their light confinement abilities in a relatively small mode volume and having high Q factors. This review starts with an introduction to MBRs’ optical properties, coupling methods, and sensing mechanisms. The sensing principle and sensing parameters of MBRs are discussed here as well. Then, practical MBRs fabrication methods and sensing applications are presented.

Ligand-protected nanocluster-mediated photoswitchable fluorescent nanoprobes towards dual-color cellular imaging.

Development of robust multi-color photoswitchable fluorescent probes is critical for many optical applications, but it remains a challenge to rationally design these probes. Here, we report a new design of Förster resonance energy transfer-based dual-color photoswitchable fluorescent nanoparticles (DPF NPs) by taking advantage of the distinct properties of ligand-protected gold nanoclusters (AuNCs). Detailed photophysical studies revealed that ultrasmall-sized AuNCs not only act as the FRET donors due to their intrinsic fluorescence properties, but also play a significant role in regulating the photochromic and aggregate properties of spiropyran through ligand-spiropyran interactions. These DPF NPs exhibit a high fluorescence on/off ratio (∼90%) for both green and red fluorescence emission, and good reversibility during cycled photo-stimulation. Cell imaging experiments showed that DPF NPs could specifically accumulate in lipid droplets, and enable photoswitchable dual-color imaging in living cells. Moreover, by labeling mitochondria with a green-emitting marker, we demonstrated that DPF NPs can distinguish different targets based on dynamic and static fluorescence signals at the sub-cellular level in two emission channels reliably. This study provides a new strategy for designing robust photoswitchable fluorescent probes by modulating the properties of photochromic dyes through ligand-protected nanoclusters, which can be generalized for the development of other photoswitch systems towards advanced optical applications.