Flexible Photonics Research Articles

Fabrication of PMMA/PEG/SnO2/SiC quaternary multifunctional nanostructures and exploring the microstructure and optical features for radiation attenuation and flexible photonics applications

Fabrication of PMMA/PEG/SnO2/SiC quaternary multifunctional nanostructures and exploring the microstructure and optical features for radiation attenuation and flexible photonics applications

Micromotor based on single fiber optical vortex tweezer

Optical micromotors are powerful tools for trapping and rotating microparticles in various fields of bio-photonics. Conventionally, optical micromotors are built using bulk optics, such as microscope objectives and SLMs. However, optical fibers provide an attractive alternative, offering a flexible photon platform for optical micromotor applications. In this paper, we present an optical micromotor designed for 3D manipulation and rotation based on a single fiber optical vortex tweezer. A tightly focused vortex beam is excited by preparing a spiral zone plate with an ultrahigh numerical aperture of up to 0.9 at the end facet of a functionalized fiber. The focused vortex beam can optically manipulate and rotate a red blood cell in 3D space far from the fiber end facet. The trapping stiffness in parallel and perpendicular orientations to the fiber axis are measured by stably trapping a standard 3-µm silica bead. The rotational performance is analyzed by rotating a trimer composed of silica beads on a glass slide, demonstrating that the rotational frequency increases with rising optical power and the rotational direction is opposite to the topological charge of the spiral zone plate. The proposed fiber micromotor with its flexible manipulation of microparticle rotation circumvents the need for the precise relative position control of multiple fiber combinations and the use of specialized fibers. The innovations hold promising potential for applications in microfluidic pumping, biopsy, micromanipulation, and other fields.

Flexibility, Dispersion Property, and Giant Sunlight Absorption of Monolayer MX2 (M = Zr, Hf; X = S, Se) and Related Janus MXY (M = Zr, Hf; X = S, Y = Se)

IVB–VIA transition metal dichalcogenides (TMDs) MX2 (M = Zr, Hf; X = S, Se) and related Janus MXY (M = Zr, Hf; X = S, Y = Se) have garnered significant attention due to their unique optoelectronic properties. To further explore their potential in flexible photonics, their mechanical, band dispersion, and optical dielectric properties using orbital hybrid theory are investigated. The results reveal that the out‐of‐plane linear compression resistance of these materials is considerably lower than their in‐plane resistance, primarily because van der Waals interactions are much weaker compared to ionic bond interactions. This characteristic makes them less susceptible to external pressure and torsional forces, positioning them as promising candidates for flexible optoelectronic devices. Furthermore, the presence of multiple energy bands at the same momentum state suggests a tendency toward metal–insulator transitions. Notably, the materials exhibit a high photon flux, indicating robust photoelectric conversion capabilities, making them suitable for applications in photoelectric transducers. This study not only deepens the understanding of the optoelectronic and mechanical properties of IVB–VIA TMD materials, but also offers theoretical guidance for the development and application of flexible optoelectronic devices based on IVB‐VIA TMDs and related Janus materials.

Flexible electronic-photonic 3D integration from ultrathin polymer chiplets

Integrating flexible electronics and photonics can create revolutionary technologies, but combining these components on a single polymer device has been difficult, particularly for high-volume manufacturing. Here, we present a robust chiplet-level heterogeneous integration of polymer-based circuits (CHIP), where ultrathin polymer electronic and optoelectronic chiplets are vertically bonded at room temperature and shaped into application-specific forms with monolithic Input/Output (I/O). This process was used to develop a flexible 3D integrated optrode with high-density microelectrodes for electrical recording, micro light-emitting diodes (μLEDs) for optogenetic stimulation, temperature sensors for bio-safe operations, and shielding designs to prevent optoelectronic artifacts. CHIP enables simple, high-yield, and scalable 3D integration, double-sided area utilization, and miniaturization of connection I/O. Systematic characterization demonstrated the scheme’s success and also identified frequency-dependent origins of optoelectronic artifacts. We envision CHIP being applied to numerous polymer-based devices for a wide range of applications.

Tunable Intracavity Coherent Up-Conversion with Giant Nonlinearity in a Polar Fluidic Medium.

The study has demonstrated a novel microcavity-based flexible photon up-conversion system using second harmonic generation (SHG) from a polar nematic fluidic medium doped with a laser dye. The idea is based on coherent light generation via stimulated emission (lasing) and simultaneous frequency doubling inside a microcavity. The polar nematic fluid equips very high even-order optical nonlinearity due to its polar symmetry and large dipole moment along the molecular long axis. At the same time, its inherent fluidic nature allows to easily functionalize the media just by doping, in the present case, with an emissive laser dye. The demonstrated system exhibits a giant nonlinear optical response to input light, while enabling spectral narrowing and multiple-signal output of up-converted light, which is not attainable through the simple SH-conversion of input light. Furthermore, the susceptibility of the liquid crystal offers dynamic modulation capabilities by an external stimulus, such as signal switching by the application of electric field or wavelength tuning through temperature variation. Such a brand-new type of simple coherent flexible up-conversion system must be promising as a new principle for easily accessible and down-scalable wavelength conversion devices.

An Ultrasensitive Perovskite Single‐Model Plasmonic Strain Sensor Based on Piezoelectric Effect

AbstractInterest in flexible photonics has been motivated by the development of artificial smart skins. In particular, coupling of photonics and mechanics can offer opportunities to realize ultrasensitive strain sensor, however, low‐cost fabrication of flexible sensing device with desired photonic functionality remains a challenge. Hereby, the study reports an ultrasensitive strain‐gauge sensor based on the poly(ethylenenaphthalate (PEN))/monocrystal Au/MgF2/CsPbBr3 nanorod/Al2O3/polyacrylonitrile (in short P/mAu/M/CPB@Al2O3@PAN), which are sensitive to nanoscale structure alterations of PEN substrate via the stress response of the single‐mode laser based on the piezoelectric‐effect. Wherein a low‐threshold single‐mode lasing (Pth ≈ 170 nJ cm−2) is achieved through coating Al2O3 on the CsPbBr3 nanorod, producing the higher quality factor (Q ≈ 1637) to guarantee a much higher sensitivity in sensing application. Reversible spectral regulating of ≈3 nm in single‐mode‐lasing wavelength, with a subnanometre scale resolution <0.4 nm and the wavelength sensitivity (Sλ) as high as 160 nm RIU−1, is validated in response to applied strain ranging from −1.31% to 1.31%. This work not only represents essential progress in construction of ultrasensitive and cost‐effective flexible photonic sensor, but also lays the foundation for the potential application in smart photonic skins.

Flexible nonlinear photonics of heterostructured MXene-derived quantum dots

High-quality V2C–VO2-heterostructured MXene-derived quantum dots (MQDs) were hydrothermally fabricated and characterized using microscopic, crystallographic, and spectroscopic methods. Open-aperture Z-scans were employed to investigate the nonlinear optical absorption of the MQDs irradiated using picosecond pulses at 532 nm. The results showed that the heterostructure converted the nonlinear optical behavior from saturable absorption to reverse saturable absorption. In individual V2C MQDs, saturable absorption was ascribed to the bleaching of ground-state free electrons, while in heterostructured V2C–VO2 MQDs, reverse saturable absorption was derived from two-photon-induced free-carrier absorption. The nonlinear absorption coefficient of the V2C–VO2 heterostructured MQDs was comparable to those of previously reported MQDs. This research could provide insight into the integration of heterostructured MQDs and promote the advanced photonics of MQDs and their applications in optoelectronic devices.

A Wearable Thin-Film Hydrogel Laser for Functional Sensing on Skin.

Flexible photonics offers the possibility of realizing wearable sensors by bridging the advantages of flexible materials and photonic sensing elements. Recently, optical resonators have emerged as a tool to improve their oversensitivity by integrating with flexible photonic sensors. However, direct monitoring of multiple psychological information on human skin remains challenging due to the subtle biological signals and complex tissue interface. To tackle the current challenges, here, we developed a functional thin film laser formed by encapsulating liquid crystal droplet lasers in a flexible hydrogel for monitoring metabolites in human sweat (lactate, glucose, and urea). The three-dimensional cross-linked hydrophilic polymer serves as the adhesive layer to allow small molecules to penetrate from human tissue to generate strong light--matter interactions on the interface of whispering gallery modes resonators. Both the hydrogel and cholesteric liquid crystal microdroplets were modified specifically to achieve high sensitivity and selectivity. As a proof of concept, wavelength-multiplexed sensing and a prototype were demonstrated on human skin to detect human metabolites from perspiration. These results present a significant advance in the fabrication and potential guidance for wearable and functional microlasers in healthcare.

Flexible Meso Electronics and Photonics Based on Cocoon Silk and Applications.

Flexible electronics, applicable to enlarged health, AI big data medications, etc., have been one of the most important technologies of this century. Due to its particular mechanical properties, biocompatibility, and biodegradability, cocoon silk (or SF, silk fibroin) plays a key role in flexible electronics/photonics. The review begins with an examination of the hierarchical meso network structures of SF materials and introduces the concepts of meso reconstruction, meso doping, and meso hybridization based on the correlation between the structure and performance of silk materials. The SF meso functionalization was developed according to intermolecular nuclear templating. By implementation of the techniques of meso reconstruction and functionalization in the refolding of SF materials, extraordinary performance can be achieved. Relying on this strategy, particularly designed flexible electronic and photonic components can be developed. This review covers the latest ideas and technologies of meso flexible electronics and photonics based on SF materials/meso functionalization. As silk materials are biocompatible and human skin-friendly, SF meso flexible electronic/photonic components can be applied to wearable or implanted devices. These devices are applicable in human physiological signals and activities sensing/monitoring. In the case of human-machine interaction, the devices can be applicable in in-body information transmission, computation, and storage, with the potential for the combination of artificial intelligence and human intelligence.

Photonics-powered augmented reality skin electronics for proactive healthcare: multifaceted opportunities.

Rapid technological advancements have created opportunities for new solutions in various industries, including healthcare. One exciting new direction in this field of innovation is the combination of skin-based technologies and augmented reality (AR). These dermatological devices allow for the continuous and non-invasive measurement of vital signs and biomarkers, enabling the real-time diagnosis of anomalies, which have applications in telemedicine, oncology, dermatology, and early diagnostics. Despite its many potential benefits, there is a substantial information vacuum regarding using flexible photonics in conjunction with augmented reality for medical purposes. This review explores the current state of dermal augmented reality and flexible optics in skin-conforming sensing platforms by examining the obstacles faced thus far, including technical hurdles, demanding clinical validation standards, and problems with user acceptance. Our main areas of interest are skills, chiroptical properties, and health platform applications, such as optogenetic pixels, spectroscopic imagers, and optical biosensors. My skin-enhanced spherical dichroism and powerful spherically polarized light enable thorough physical inspection with these augmented reality devices: diabetic tracking, skin cancer diagnosis, and cardiovascular illness: preventative medicine, namely blood pressure screening. We demonstrate how to accomplish early prevention using case studies and emergency detection. Finally, it addresses real-world obstacles that hinder fully realizing these materials' extraordinary potential in advancing proactive and preventative personalized medicine, including technical constraints, clinical validation gaps, and barriers to widespread adoption.

Stretchable, stable, and structural color reversible enabled by mesoscopic regulation and design for flexible photonic crystal mechanical sensors

This paper reports a flexible mechanical sensor developed by combining an opal photonic crystal and a flexible medium through UV curing technology. Under the action of external force, the deformation of the flexible medium causes the change of the photonic crystal lattice constant, which leads to the displacement of the reflection peaks, thus realizing the detection of the deformation of the film. The flexible medium is mixed by photoinitiators and polymer monomers, and its mechanical properties are directly related to the mass fraction of photoinitiators and polymer monomers. The results show that the film can reach a maximum strain of about 180% when the mass fraction of photoinitiator is 3% and the volume ratio of the polymer functional monomers is 8:2. In addition, for the responsiveness test of the sensor under tensile, the results show that at 0%, 26%, and 78% of tensile strain, its structural color is blue-shifted sequentially, and its spectral peaks are 668 nm, 535 nm, and 488 nm, respectively. Finally, the sensor is applied to the detection of acoustic waves in air, and it is found that its spectral response peaks can be obtained for acoustic waves of different frequencies (250–650 Hz), and a spectral peak at 500 Hz. This flexible photon sensor has the potential to match the acoustic resistance of water. It will greatly expand the response research of ocean exploration in the low frequency range.

Biaxial strain tuned upconversion photoluminescence of monolayer WS2

Monolayer tungsten disulfide (1L-WS2) is a direct bandgap atomic-layered semiconductor material with strain tunable optical and optoelectronic properties among the monolayer transition metal dichalcogenides (1L-TMDs). Here, we demonstrate biaxial strain tuned upconversion photoluminescence (UPL) from exfoliated 1L-WS2 flakes transferred on a flexible polycarbonate cruciform substrate. When the biaxial strain applied to 1L-WS2 increases from 0 to 0.51%, it is observed that the UPL peak position is redshifted by up to 60 nm/% strain, while the UPL intensity exhibits exponential growth with the upconversion energy difference varying from − 303 to − 120 meV. The measured power dependence of UPL from 1L-WS2 under biaxial strain reveals the one photon involved multiphonon-mediated upconversion mechanism. The demonstrated results provide new opportunities in advancing TMD-based optical upconversion devices for future flexible photonics and optoelectronics.

An Interfacial‐Assembled Self‐Supporting Nanofilm Induced by Strong Intermolecular Interaction between Silk Fibroin and Lysozyme

AbstractOrganic ultrathin nanofilms are increasingly favored in a wide range of applications, including flexible photonics and electronics, smart skin devices, sensing, and bioinspired designs, due to their high flexibility, chemical activity, and stimuli‐responsiveness. To create large‐area, robust, and freestanding nanofilms efficiently, a protein interfacial cooperative assembly technique that utilizes silk fibroin and lysozyme as building blocks is developed. The strong intermolecular interaction between these two proteins, coupled with the abundant intra‐ and intermolecular β‐sheets, confers remarkable mechanical robustness to the nanofilms with thicknesses as low as 50 nm. Consequently, these nanofilms exhibit the unique ability to stand freely in the air and can be conformally transferred to substrates of different types and topographies, forming stable, and versatile nanocoatings. The advantageous attributes of their ultrathinness, large‐scale homogeneity, robustness, and rapid and tunable responsiveness facilitate the construction of ultrasensitive photonic architectures and organic–inorganic hybrid multilayers with outstanding optical and mechanical properties. It is envisioned that these all‐protein‐based robust nanofilms with unique nanoscale effects can be easily integrated into various advanced technological platforms to enable adaptive, multifunctional, and intelligent systems with exceptional mechanical strength.

Wrinkled Graphene Structure and Localized Surface Plasmon Resonance Induced Stretchable White Random Lasers Based on GLN‐functionalized 2D WS2 Quantum Dots

AbstractThis study presents investigations into the fabrication, characterization, and performance analysis of stretchable white random lasers based on 2D glutamine(GLN)‐functionalized WS2 quantum dots (QDs) enhanced by the integration of Au nanoparticles (NPs) and a wrinkled graphene structure. Wrinkled graphene holds the potential for achieving transient population inversion through electron collisions. Incorporating Au NPs introduces localized surface plasmon resonance (LSPR), which enhances the light‐matter interaction, resulting in reduced lasing thresholds. The GLN‐functionalized WS2 QDs exhibit strong photoluminescence emission, and their integration with a wrinkled graphene structure and Au NPs creates a synergistic effect that enhances the emission efficiency and enables the realization of white random lasing. The extensive characterization and analysis of the emission spectra under different deformation ratios provide valuable insights into the tunability and reliability of these devices, as well as the importance of light trapping due to the wrinkled graphene structure. The findings of this study underscore the significant potential of LSPR and wrinkled graphene structure induced stretchable and white random lasers based on 2D GLN‐functionalized WS2 QDs. These lasers may have a promising application in the field of flexible and wearable photonics, which is a critical step towards the development of next‐generation optoelectronic devices with improved performance.

Flexible photonics in carbon and glass fiber reinforced polymers for new multifunctionality: Exploring the advances, challenges, and opportunities

Flexible photonics, characterized by their planar design and integrated features, have surfaced as a promising technology to unlock new possibilities for multifunctionality within fiber reinforced polymer composite materials. A comprehensive review of current progress, challenges, and opportunities associated with flexible photonic integration into carbon and glass fiber reinforced polymers is provided. A systematic examination of the literature has revealed several flexible photonic technologies that have demonstrated potential for integration in composite components to monitor performance in manufacture, service, and reuse. The review highlights the advantages and limitations of the current state-of-the-art in flexible integrated photonics for making assessments of compatibility with carbon and glass fiber reinforced polymer structures. By examining proof-of-concept demonstrations, the improved performance and novel functionalities that can be achieved for industrial applications are identified. The challenges associated with the integration process, such as durability and scalability are discussed in the context of the manufacturing processes required to create composite components. The concept of integrating flexible photonics in composite structures is relatively new, hence the paper closes by highlighting opportunities for further research and development in this field.

Polymer-Waveguide-Integrated 2D Semiconductor Heterostructures for Optical Communications.

The demand for high-speed and low-loss interconnects in modern computer architectures is difficult to satisfy by using traditional Si-based electronics. Although optical interconnects offer a promising solution owing to their high bandwidth, low energy dissipation, and high-speed processing, integrating elements such as a light source, detector, and modulator, comprising different materials with optical waveguides, presents many challenges in an integrated platform. Two-dimensional (2D) van der Waals (vdW) semiconductors have attracted considerable attention in vertically stackable optoelectronics and advanced flexible photonics. In this study, optoelectronic components for exciton-based photonic circuits are demonstrated by integrating lithographically patterned poly(methyl methacrylate) (PMMA) waveguides on 2D vdW devices. The excitonic signals generated from the 2D materials by using laser excitation were transmitted through patterned PMMA waveguides. By introducing an external electric field and combining vdW heterostructures, an excitonic switch, phototransistor, and guided-light photovoltaic device on SiO2/Si substrates were demonstrated.

A shear-lag model for laminated beams with extreme modulus mismatch between layers

Multilayer laminated beams, comprised of alternating stiff and soft layers, are widely used in flexible electronics and photonics. These structures exhibit complex mechanical behaviors that deviate from the Euler–Bernoulli beam theory under conditions of extreme inter-layer modulus mismatch. Extending beyond prior studies on trilayer beams, we present an analytical framework for laminated beams with arbitrary number of layers subjected to various bending conditions, and validate our theory with finite element analysis. We define an equivalent flexural rigidity, exploring its dependence on position and deformation, and systematically examine the impact of the number of layers, applied deformation, layer properties, and the layer aspect ratio.

(INVITED) Flexible photonics for biomedical applications: A review

Flexible photonics is a powerful tool that has emerged in last few decades to solve footprint and shape related limitations in photonic devices. Indeed, flexible photonic devices offer several key features: ability to adjust to complex shape surfaces, small footprint, high resilience to mechanical damage, immunity to electromagnetic interference. Thanks to these characteristics, these devices are very attractive for applications in the biomedical field. For instance, the flexibility allows optimal adhesion to the skin, or the reduced size facilitates the realization of wearable devices. In this paper, we will first present the characteristic of flexible photonic devices and discuss about the so far impact of flexible photonics in the biomedical field. Then, we will analyze the currently existing devices and the main used components, with a focus on the applications.

Integrated Flexible Microscale Mechanical Sensors Based on Cascaded Free Spectral Range-Free Cavities.

Photonic mechanical sensors offer several advantages over their electronic counterparts, including immunity to electromagnetic interference, increased sensitivity, and measurement accuracy. Exploring flexible mechanical sensors on deformable substrates provides new opportunities for strain-optical coupling operations. Nevertheless, existing flexible photonics strategies often require cumbersome signal collection and analysis with bulky setups, limiting their portability and affordability. To address these challenges, we propose a waveguide-integrated flexible mechanical sensor based on cascaded photonic crystal microcavities with inherent deformation and biaxial tensile state analysis. Leveraging the advanced multiplexing capability of the sensor, for the first time, we successfully demonstrate 2D shape reconstruction and quasi-distributed strain sensing with 110 μm spatial resolution. Our microscale mechanical sensor also exhibits exceptional sensitivity with a detected force level as low as 13.6 μN in real-time measurements. This sensing platform has potential applications in various fields, including biomedical sensing, surgical catheters, aircraft and spacecraft engineering, and robotic photonic skin development.

Full-color persistent room temperature phosphorescent elastomers with robust optical properties

Persistent room temperature phosphorescent materials with unique mechanical properties and robust optical properties have great potential in flexible electronics and photonics. However, developing such materials remains a formidable challenge. Here, we present highly stretchable, lightweight, and multicolored persistent luminescence elastomers, produced by incorporating ionic room temperature phosphorescent polymers and polyvinyl alcohol into a polydimethylsiloxane matrix. These prepared elastomers exhibit high optical transparency in daylight and emit bright persistent luminescence after the removal of 365 nm excitation. The homogeneous distribution of polymers within the matrix has been confirmed by confocal fluorescence microscopy, scanning electron microscopy, and atomic force microscopy. Mechanical property investigations revealed that the prepared persistent luminescence elastomers possess satisfactory stretchability. Impressively, these elastomers maintain robust optical properties even under extensive and repeated mechanical deformations, a characteristic previously unprecedented. These fantastic features make these persistent luminescence elastomers ideal candidates for potential applications in wearable devices, flexible displays, and anti-counterfeiting.