Photonic Materials Research Articles

Advances in Photonic Materials and Integrated Devices for Smart and Digital Healthcare: Bridging the Gap Between Materials and Systems.

Recent advances in developing photonic technologies using various materials offer enhanced biosensing, therapeutic intervention, and non-invasive imaging in healthcare. Here, this article summarizes significant technological advancements in materials, photonic devices, and bio-interfaced systems, which demonstrate successful applications for impacting human healthcare via improved therapies, advanced diagnostics, and on-skin health monitoring. The details of required materials, necessary properties, and device configurations are described for next-generation healthcare systems, followed by an explanation of the working principles of light-based therapeutics and diagnostics. Next, this paper shares the recent examples of integrated photonic systems focusing on translation and immediate applications for clinical studies. In addition, the limitations of existing materials and devices and future directions for smart photonic systems are discussed. Collectively, this review article summarizes the recent focus and trends of technological advancements in developing new nanomaterials, light delivery methods, system designs, mechanical structures, material functionalization, and integrated photonic systems to advance human healthcare and digital healthcare.

Germanium-based ternary chalcogenide: An emerging low-dimensional material for nonlinear optics and ultrafast photonics

Germanium-based ternary chalcogenide: An emerging low-dimensional material for nonlinear optics and ultrafast photonics

High-efficiency, cryogenic-compatible grating couplers on an AlN-on-sapphire platform through bottom-side coupling.

Sapphire is a commonly used substrate for wide-bandgap III-nitride photonic materials. However, its relatively high refractive index results in low transmission efficiency in grating couplers. Here, we propose and demonstrate that the transmission efficiency can be significantly enhanced by bottom-side coupling. A metal reflector is deposited on the top side of the chip, and the fiber array is glued to the bottom side of the substrate. We experimentally achieve a transmission efficiency as high as 42% per coupler on an aluminum nitride (AlN) on a sapphire platform at the telecom wavelength. In addition, the grating couplers show a robust performance at a cryogenic temperature as low as 3 K for both transverse-electric (TE) and transverse-magnetic (TM) modes. Our results can be useful to a wide range of sapphire-based applications that require low coupling loss and cryogenic operation.

Selective passive tuning of cavity resonance by mode index engineering of the partial length of a cavity

Cavities in large-scale photonic integrated circuits (PICs) often suffer from a wider distribution of resonance frequencies due to fabrication errors. It is crucial to adjust the resonances of cavities using post-processing methods to minimize the frequency distribution. We have developed a concept of passive tuning by manipulating the mode index of a portion of a microring cavity, which we named mode index engineering (MIE). Through analytical studies and numerical experiments, we have found that depositing a thin film of dielectric material on top of the cavity or etching the material enables us to fine-tune the resonances and minimize the frequency distribution. This versatile method allows for the selective tuning of each cavity’s resonance in a large set of cavities in a post-fabrication step, providing robust passive tuning in large-scale PICs. We show that the proposed method achieves a tuning resolution below 1/Q and a range of up to 103/Q for visible to near-infrared wavelengths. Furthermore, this method can be applied and explored in various integrated photonic cavities and material configurations.

Dynamically mechanochromic, fluorescence-responsive, and underwater sensing cellulose nanocrystal-based conductive elastomers.

Utilizing cellulose nanocrystals (CNCs) to mimic biological skin capable of converting external stimuli into optical and electrical signals represents a significant advancement in the development of advanced photonic materials. However, traditional CNC photonic materials typically exhibit static and singular optical properties, with their structural color and mechanical performance being susceptible to water molecules, thereby limiting their practical applications. In this study, CNC-based conductive elastomers with dynamic mechanochromism, fluorescence responsiveness, and enhanced water resistance were developed by incorporating carbon quantum dots (C QDs) and hydrophobic deep eutectic solvents (HDES) into CNC photonic films via an in-situ swelling-photopolymerization method. Additionally, the abundant non-covalent and hydrophobic interactions within poly(HDES) endow the resulting poly(HDES)/C-CNC elastomer with excellent structural stability, ionic conductivity, and self-adhesive properties, allowing for encrypted information transmission in both air and aquatic environments. The design and application of poly(HDES)/C-CNC elastomers hold tremendous potential for various applications, including anti-counterfeiting labels, human-machine interactions, and wearable devices.

High-Reflectivity Force-Chromic Photonic Crystal Elastic Materials Based on Nanospheres within an Elastomer for Applications in Sensing and Textile Fields

High-Reflectivity Force-Chromic Photonic Crystal Elastic Materials Based on Nanospheres within an Elastomer for Applications in Sensing and Textile Fields

The Precise Synthesis of Ultradense Bottlebrush Polymers Unearths Unique Trends in Lyotropic Ordering.

Biomacromolecular networks with multiscale fibrillar structures are characterized by exceptional mechanical properties, making them attractive architectures for synthetic materials. However, there is a dearth of synthetic polymeric building blocks capable of forming similarly structured networks. Bottlebrush polymers (BBPs) are anisotropic graft polymers with the potential to mimic and replace biomacromolecules such as tropocollagen for the fabrication of synthetic fibrillar networks; however, a longstanding limitation of BBPs has been the lack of rigidity necessary to access the lyotropic ordering that underpins the formation of collagenous networks. While the correlation between BBP rigidity and grafting density is well established, synthetic approaches to rigidify BBPs by increased grafting density are underdeveloped. To address this gap in synthetic capability, we report the synthesis of novel macroinitiators that provide well-defined BBPs with an unprecedentedly high grafting density. A suite of light scattering techniques are used to correlate macromolecular rigidity with grafting architecture and density and demonstrate for the first time that poly(norbornene) BBPs exhibit long-range lyotropic ordering as a result of their rodlike character. Specifically, the newly reported ultradensely grafted structures, preparable on multigram scale, form hexagonal arrays while conventional BBPs do not, despite showing long-range spatial correlations. These results implicate the central role of density and entanglement in the solution phase assembly of BBPs and provide new fundamental insight that is broadly relevant to the fabrication and performance of BBP-derived materials, spanning biomedical research to photonic materials and thermal management technologies. Furthermore, these newly reported liquid crystalline BBPs provide a structural template to explore the untapped potential of the bottom-up assembly of semiflexible networks and are ultimately intended to provide a modular route to hierarchically structured biomimetic materials.

Discovering optical performance enhancers in perovskite materials through machine learning-based feature analysis.

Perovskites attract significant attention as a coating material in optical fiber sensing, but challenges remain due to the limited discovery of suitable materials and the high trial-and-error costs, resulting in only a few perovskites being used in optical sensing experiments. Addressing this issue, a novel systematic computational screening strategy for perovskites is established. This strategy is demonstrated to accelerate the discovery of perovskite coating materials that can enhance optical sensing sensitivity. These perovskites are defined in this study as optical fiber performance enhancers (POPEs). For the most accurate prediction results, 10 sampling methods combined with 10 classification algorithms are compared. Following 100 comparative experiments, the model using the SMOTE-ENN sampling methods and the label spreading (LS) algorithms shows 100% accuracy and precision in leaving-one-out cross-validation (LOOCV). However, this result should be supported with further experiments and numerical simulations. Finally, we feed 500 samples of photonic, piezoelectric, ferroelectric, magnetic, and other perovskite materials into the optimal model, resulting in 237 potential POPEs for the first time. Meanwhile, we predicted the probabilities of forming POPEs using 10 perovskites commonly used in the field of fluorescence sensing. The obtained values of probability of forming POPEs are all over 91%, which indirectly validates our screening strategy for perovskites is effective. These 237 POPEs show promising prospects for becoming the forefront materials in the next generation of fiber optic sensing technologies.

Synergistic color-changing and conductive photonic cellulose nanocrystal patches for sweat sensing with biodegradability and biocompatibility.

Given the ongoing requirements for versatility, sustainability, and biocompatibility in wearable applications, cellulose nanocrystal (CNC) photonic materials emerge as excellent candidates for multi-responsive wearable devices due to their tunable structural color, strong electron-donating capacity, and renewable nature. Nonetheless, most CNC-derived materials struggle to incorporate color-changing and electrical sensing into one system since the self-assembly of CNCs is incompatible with conventional conductive mediums. Here we report the design of a conductive photonic patch through constructing a CNC/polyvinyl alcohol hydrogel modulated by phytic acid (PA). The introduction of PA significantly enhances the hydrogen bonding interaction, resulting in the composite film with impressive flexibility (1.4 MJ m-3) and progressive color changes from blue, green, yellow, to ultimately red upon sweat wetting. Interestingly, this system simultaneously demonstrates selective and sensitive electrical sensing functions, as well as satisfactory biocompatibility, biodegradability, and breathability. Importantly, a proof-of-concept demonstration of a skin-adhesive patch is presented, where the optical and electrical dual-signal sweat sensing allows for intuitive visual and multimode electric localization of sweat accumulation during physical exercises. This innovative interactive strategy for monitoring human metabolites could offer a fresh perspective into the design of wearable health-sensing devices, while greatly expanding the applications of CNC-based photonic materials in medicine-related fields.

High-yield production of lignin nanoparticle photonic glasses.

Lignin has emerged as a sustainable alternative to fossil-based polymers in advanced materials such as photonics. However, current methods for preparing photonic lignin materials are limited by non-benign organic solvents and low production yields. In this work, we present a highly efficient process that enables the production of photonic glasses with yields ranging from 48% to 72%, depending on the size of the lignin nanoparticles obtained from herbaceous soda lignin, softwood kraft lignin, and hardwood organosolv lignin. The hydrodynamic diameter of lignin nanoparticles can be regulated by the rate of water addition to the lignin-ethanol solution. We demonstrate that this control over particle size allows for tailoring the color of the photonic glass across the visible spectrum.

Mechanical and thermal responsive chiral photonic cellulose hydrogels for dynamic anti-counterfeiting and optical skin.

Dynamic responsive structural colored materials have drawn increased consideration in a wide range of applications, such as colorimetric sensors and high-safety tags. However, the sophisticated interactions among the individual responsive parts restrict the advanced design of multimodal responsive photonic materials. Inspired by stimuli-responsive color change in chameleon skin, a simple and effective photo-crosslinking strategy is proposed to construct hydroxypropyl cellulose (HPC) based hydrogels with multiple responsive structured colors. By controlling UV exposure time, the structural color of HPC hydrogels can be effectively controlled in a full-color spectrum. At the same time, HPC hydrogels showcase temperature and mechanical dual-responsive structural colors. In particular, the microstructure of HPC hydrogels undergoes a transition from the chiral nematic phase to the nematic phase under the action of external stretching, leading to a significant reflection of circularly polarized light (CPL) to linearly polarized light (LPL). Given the diverse responsiveness exhibited by HPC hydrogels and their unique structural transition properties under external forces, we have explored their potential applications as dynamic anti-counterfeiting labels and optical skins. This work reveals the great possibility of using structural colored cellulose hydrogels in multi-sensing and optical displays, opening up a new path for the exploration of next-generation flexible photonic devices.

Nonlinear Refraction and Absorption in Polymers Used for Femtosecond Direct Laser Writing.

Direct laser writing (DLW) has been recognized as a unique technique for three-dimensional (3D) prototyping with resolution beyond the diffraction limit. One trend in DLW technologies is the use of polymers, given their favorable mechanical properties and optical quality, rendering them promising for the next generation of nonlinear photonic devices. However, absorptive properties that facilitate DLW processes may also hinder the performance of polymers as all-optical devices. Furthermore, the increasing use of ultrashort pulse lasers makes refractive index dispersion a factor of fundamental importance in studying candidate materials for broadband applications. Here, we study the suitability of resins commonly used in DLW for all-optical broadband applications. We provide linear and nonlinear refractive and absorptive spectra of acrylate-based resins with different compositions, and IP-S and IP-Dip from Nanoscribe. We found nonlinear refractive indices four times higher than reported values for fused silica, one of the most widely used photonic materials, and we evaluate the potential of these materials using group velocity dispersion and figures of merits as comparative metrics.

Flexible Photonic Materials and Devices: Synthetic Strategies, Sensing Properties, and Wearable Applications

AbstractWearable technology is becoming increasingly visible in the daily life for improving human health and performance. Flexible photonics is rapidly emerging as a promising platform for advancing the wearable technology. The development and innovative use of flexible photonic materials play crucial roles in designing flexible sensor devices for wearable applications. Here it is aimed to summarize the key advancements in developing flexible photonic materials and devices for wearable sensing applications. In turn the synthetic strategies, sensing properties, and wearable applications of flexible photonic materials and devices will be comprehensively discussed. Finally, it is attempted to give an outlook on the future challenges and research trends in this fascinating field.

Recent Progress in Block Copolymer Self-Assembly for the Fabrication of Structural Color Pigments.

The self-assembly of block copolymers (BCPs) into photonic materials has garnered increasing interest due to the versatility and ease of fabrication offered by the synthesized building blocks. BCPs are highly tunable, with their self-assembled structures' size being adjustable by modifying the block lengths, molecular weight(Mw), and polymer composition. This review provides a concise summary of the use of BCPs as photonic pigments, which generate color through structural manipulation rather than relying on chemical pigmentation. These photonic crystal pigments manipulate light behavior, including interference, diffraction, and diffusion, to generate specific colors. BCPs are categorized into two types: linear block copolymers (LBCPs) and brush block copolymers (BBCPs), each involving different monomers that form photonic crystals(PCs). The structural evolution and advancements of BCPs in various practical applications are also explored. It concludes by suggesting that structural color(SC) pigments based on eco-friendly PCs may replace traditional chemical ones in fields such as printing ink, biosensing, chemical sensing, and adaptive photonic materials.

Transparent Composite for Cooperative Near‐infrared and X‐ray Imaging

AbstractThe advancement of imaging technology has significantly contributed to the progress in medical diagnosis and treatment, biomedical science, and various other fields. However, the visualization of comprehensive information on the imaged target remains a great challenge, especially for the complex biological system. Herein, it is proposed that the Cr3+‐doped transparent glass composite with near‐infrared (NIR) activity may gift a new possibility for achieving cooperative imaging. It presents remarkable photoluminescence (PL) and radioluminescence (RL) response in the NIR region, with ultra‐broadband tunable luminescence (full‐width half‐maximum from 47 to 263 nm), excellent external quantum efficiency (>50%), and robust RL thermal quenching resistance (83.85%@150 °C). Benefiting from these distinctive features, NIR imaging and high‐resolution X‐ray imaging with a spatial resolution exceeding 19 lp mm−1 are successfully realized. Furthermore, a cooperative imaging device is developed and its practical applications for simultaneously visualizing bone and blood vessels in biological targets are demonstrated. These findings represent a significant advancement in the field of NIR active photonic materials for cutting‐edge imaging technology.

Spatiotemporal Retention of Structural Color and Induced Stiffening in Crosslinked Hydroxypropyl Cellulose Beads.

Hydroxypropyl cellulose (HPC) is known for its ability to form cholesteric liquid crystalline phases displaying vivid structural colors. However, these vibrant colors tend to fade over time when the material dries. This issue is a major bottleneck to finding practical applications for these materials. Here this problem is overcome by producing free-standing, millimeter-sized HPC structurally colored beads with spatiotemporal color retention, facilitated by a glutaraldehyde crosslinker. By leveraging the well-known chemically induced stabilization of cholesteric liquid crystalline phases, stable structural colors are achieved for at least three weeks. The presence of glutaraldehyde significantly increases the mechanical stiffness, with Young's modulus rising from 0.3± 0.1GPa to 1.8± 0.2GPa. This integrated approach of creating free-standing photonic HPC beads offers a strategy for developing robust and durable photonic HPC materials with enhanced stability, advancing photonic material applications with spatiotemporal color stability.

Revolutionizing Fingerprint Detection: Ce3+ Doped SiO2-Zr2O3:Sr2+ Nanocomposites with Enhanced Luminescence and Selectivity.

Even though fingerprints remain one of the most reliable methods of identification, they are often lost during the recovery process. Accurate fingerprint recognition depends on the contrast between the ridges and substrate. On tough surfaces, such as glossy, colorful, and patterned materials, the contrast is harder to establish. Photoluminescent materials play a crucial role in forensic investigations as they enable the development of procedures that enhance image quality and increase the accuracy of findings from security institutions. Due to the strong emission in the red area at 620nm, the use of trivalent Rare Earth ions (RE3+) doped materials in this work is notable. Because of the unique properties and abundance of cerium, luminous materials based on SiO2-Zr2O3: Ce3+, Sr2+ prepared via sol-gel technique present a more practical alternative for use in criminal investigations compared to current photonic materials. The sample was further co-doped with synthetic (Safranin-O and crystal violet) as well as organic (curcumin and lycopene) photoluminescent dyes. The nanocomposites were examined using X-ray diffraction analysis (XRD), energy-dispersive X-ray analysis (EDX), dynamic light scattering (DLS), scanning electron microscopy (SEM), and photoluminescence spectroscopy (PL). In conclusion, this work highlights the qualities critical to obtaining higher-resolution latent fingerprint images for potential forensic applications.

New Insight into Industrial Lignin Intermolecular Force Heterogeneity Mitigation: Monodispersed Lignin Colloidal Sphere Synthesis and Full Biomass Photonic Material Preparation.

Industrial lignin is an underutilized resource from the pulping industry due to its high heterogeneity. The transformation of industrial lignin into monodispersed lignin colloidal spheres (LCSs) for the preparation of advanced biomass photonic materials is particularly appealing, because of their unique biocompatibility. However, the LCSs synthesized from industrial lignin generally show a wide size distribution and thus limit this specific application. To address the issue, selective functionalization was carried out to convert phenolic and aliphatic -OH groups into ester groups, decreasing the LCS size distribution to a monodispersing degree. Simulation analysis revealed that the functionalization had narrowed the difference of C-O linkage electron cloud distribution and led to a lignin polarity decrease. Additionally, atomic force microscopy (AFM) quantification of lignin proved a force distribution index (FDI) decrease from 0.38 to 0.11, which was consistent with the LCS polymer dispersity index (PDI) decrease from 0.182 to 0.05. The photonic materials can be readily prepared from monodispersed LCSs with the color precisely adjusted by controlling LCS particle sizes.

Engineering plasmonic charge kinetics and broadband photoelectrochemical spectral responses using a multi-resonant Au-TiO2 plasmonic particle grating-based optical resonator.

The plasmonic integrated semiconductor has widened the operational spectral region of semiconductors for light-matter interaction-driven solar energy harvesting applications. However, a specific plasmonic resonance has moderate light absorption and is only active in a specific width of the visible spectrum. We present a tailored plasmonic particle grating-based Au-TiO2 Schottky photoelectrode-based broadband absorber that operates in the extended spectral region of 400-800 nm due to the synergistic interaction of multi-resonant photonic and plasmonic modes of the plasmonic particle grating structure. In the visible spectrum, the proposed photoelectrode increased the incoming photon to electron conversion efficiency (IPCE%) by seven and five times more than TiO2 for TM (along the grating vector) and TE (perpendicular to the grating vector) incidence, respectively. The plasmonic response of the gold nanoparticle and the grating-coupled surface plasmon polariton (SPP)-guided mode resonance (GMR) are responsible for such increments. Ultrafast pump-probe spectroscopy verifies that the plasmon-GMR interaction causes extended plasmonic charge generation and lifetime. The kinetics of plasmonic-generated charges in grating-coupled SPP and LSPR was investigated through TM and TE polarized pump and probe excitation. Such findings are consistent with the observed PEC spectral responses under their respective polarization illumination. Therefore, our research provides a simple method for integrating photonic and plasmonic materials for innovative broadband spectrum responses in photovoltaic and energy harvesting applications.

Construction of Luminescent Terpyridine-Based Metallo-Bowties with Alkyl Chain-Bridged Dimerized Building Blocks.

Numerous metallo-supramolecules with well-defined sizes and shapes have been successfully constructed via the strong coordination interaction between terpyridine (TPY) moieties and ruthenium cations. However, the pseudo-octahedral geometry of <TPY-Ru-TPY> unit hampers the luminescent properties of such metallo-architectures, thus limiting their applications as optical materials. To address this issue, we herein use a flexible alkyl chain to bridge TPY building blocks, replacing conventional <TPY-Ru-TPY> linkage. The introduction of alkyl chain guides the self-assembly into desired architecture while simultaneously eliminating the quenching effects typically associated with the <TPY-Ru-TPY> linkage. More importantly, this design strategy enables the precise construction of bowtie-shaped metallo-supramolecules with significantly enhanced emission. The incorporation of alkyl chain linkage not only maintains structural integrity but also enhances optical performance, making these metallo-supramolecular assemblies highly promising for applications in advanced photonic and luminescent materials. This study offers a versatile approach to construct complex metallo-supramolecular architectures with desired optical properties.