Dimension Evolution of Self-Assembled Organic Microcrystal for Laser and Polarization-Rotation Function.

Multidimensional integrated micro/nanostructures are vitally important for the implementation of versatile photonic functionalities, whereas current material structures still suffer undesired surface defects and contaminations in either multistep micro/nanofabrications or extreme synthetic conditions. Herein, the dimension evolution of organic self-assembled structures 2D microrings and 3D microhelixes for multidimensional photonic devices is realized via a protic/aprotic solvent-directed molecular assembly method based on a multiaxial confined-assisted growth mechanism. The 2D microrings with consummate circle boundaries and molecular-smooth surfaces function as high-quality whispering-gallery-mode microcavities for dual-wavelength energy-influence-dependent switchable lasing. Moreover, the 3D microhelixes with smooth surfaces and natural twistable characteristics act as active photon-transport materials and polarization rotators. These results will broaden the horizon of constructing multidimensional microstructures for integrated photonic circuits.

Organoboron Polymorphs with Different Molecular Packing Modes for Optical Waveguides.

Organoboron compounds offer a new strategy to design optoelectronic materials with high fluorescence efficiency. In this paper, the organoboron compound B-BNBP with double B←N bridged bipyridine bearing four fluorine atoms as core unit is facilely synthesized and exhibits a narrowband emission spectrum and a high photoluminescence quantum yield (PLQY) of 86.53 % in solution. Its polymorphic crystals were controllable prepared by different solution self-assembly methods. Two microcrystals possess different molecular packing modes, one-dimensional microstrips (1D-MSs) for H-aggregation and two-dimensional microdisks (2D-MDs) for J-aggregation, owing to abundant intermolecular interactions of four fluorine atoms sticking out conjugated plane. Their structure-property relationships were investigated by crystallographic analysis and theoretical calculation. Strong emission spectra with the full width at half maximum (FWHM) of less than 30 nm can also be observed in thin film and 2D-MDs. 1D-MSs possess thermally activated delayed fluorescence (TADF) property and exhibit superior optical waveguide performance with an optical loss of 0.061 dB/µm. This work enriches the diversity of polymorphic microcrystals and further reveals the structure-property relationship in organoboron micro/nano-crystals.

Ultra-Wide Modulation and Reversible Reconfiguration of a Flexible Organic Crystalline Optical Waveguide Between 645 and 731 nm.

Flexible organic crystalline optical waveguides, i.e., delivering input or self-emit lights through various dynamic organic crystals, have attracted increasing attentions in the past decade. However, the modulation of waveguide outputs relies on chemical design and substituent modification, being time-consuming and laborious. Here we report an elastic organic crystal that displays long-distance light transducing capability up to 2.0 cm and ultra-wide modulation of crystalline optical waveguides between red (645 nm) and near infrared (731 nm) in both the pristine and the elastically bent states based on a pre-designed self-absorption effect. The flexible organic crystalline optical waveguides can be precisely and reversibly reconfigured by controlling irradiation point. In addition, deep red amplified spontaneous emissions (ASE) that are able to transduce through a 5.0 mm bent crystal with an ultra-low optical loss coefficient of 0.092 dB/mm has been attained. To the best of our knowledge, this is the first report of flexible organic ASE waveguides. The present study not only provides a simple yet effective strategy to remarkably modulate flexible organic crystalline optical waveguides but also demonstrates the superiority of laser over normal emission as flexible optical communication elements.

Achieving Near-Unity Red Light Photoluminescence in Antimony Halide Crystals via Polyhedron Regulation.

Exploration of efficient red emitting antimony hybrid halide with large Stokes shift and zero self-absorption is highly desirable due to its enormous potential for applications in solid light emitting, and active optical waveguides. However, it is still challenging and rarely reported. Herein, a series of (TMS)2SbCl5 (TMS=triphenylsulfonium cation) crystals have been prepared with diverse [SbCl5]2- configurations and distinctive emission color. Among them, cubic-phase (TMS)2SbCl5 shows bright red emission with a large Stokes shift of 312 nm. In contrast, monoclinic and orthorhombic (TMS)2SbCl5 crystals deliver efficient yellow and orange emission, respectively. Comprehensive structural investigations reveal that larger Stokes shift and longer-wavelength emission of cubic (TMS)2SbCl5 can be attributed to the larger lattice volume and longer Sb⋅⋅⋅Sb distance, which favor sufficient structural aberration freedom at excited states. Together with robust stability, (TMS)2SbCl5 crystal family has been applied as optical waveguide with ultralow loss coefficient of 3.67 ⋅ 10-4 dB µm-1, and shows superior performance in white-light emission and anti-counterfeiting. In short, our study provides a novel and fundamental perspective to structure-property-application relationship of antimony hybrid halides, which will contribute to future rational design of high-performance emissive metal halides.

Non-Covalent Supramolecular 1D Alternating Copolymer in Crystal toward 2D Anisotropic Photon Transport.

To realize organic integrated optoelectronic circuits, there is a need for anisotropic optical waveguides at the micro/nanoscale. Anisotropic alignment of one-dimensional-ordered supramolecular structures composed of light-emissive π-conjugated molecules in a crystal may meet the requirements of such waveguides. Here, a bipyridyl-appended acrylonitrile-based π-conjugated molecule was designed, which produced a one-dimensional supramolecular polymer constructed through non-covalent bonding between a lone pair in bipyridyl and a σ-hole in 1,4-diiodo-2,3,5,6-tetrafluorobenzene. The one-dimensional copolymer of bipyridyl and 1,4-diiodo-2,3,5,6-tetrafluorobenzene is aligned horizontally with the two-dimensional crystal surface because of the angle-controlled supramolecular synthons. As a result of control over the non-covalent bonding direction, anisotropic photoluminescence and photon transport (optical waveguiding) characteristics are realized by orienting the transition dipole moment horizontally with respect to the two-dimensional surface. Compared with the loss coefficient αL =52 dB cm-1 for the long-axis direction of the two-dimensional platelet cocrystal, a very large difference of αS =2111 dB cm-1 is present in the crystal short-axis direction. The anisotropic waveguiding ability, αL /αS , is estimated to be 41, which is more than an order of magnitude greater than previously reported two-dimensional platelet crystal waveguides. This supramolecular synthon provides an approach to designing anisotropic photon transporters and highly regulated optical logic circuits.

Seven-layer analysis model of an optical waveguide excitation fluorescence microscopy.

In this paper, an optical waveguide evanescent field fluorescence microscopy is studied. Based on Maxwell's equation, a seven-layer theoretical analysis model is developed for the evaluation of an optical waveguide excitation fluorescence microscopy. The optical waveguide excitation fluorescence microscopy structure is systematically and comprehensively analysed at the wavelengths of 488, 532 and 646 nm for fluorescent dyes. The analysis results provide some useful suggestions, which will be beneficial to the research of an optical waveguide evanescent field fluorescence microscopy.

Low-Cost Distributed Optical Waveguide Shape Sensor Based on WTDM Applied in Bionics.

Bionic robotics, driven by advancements in artificial intelligence, new materials, and manufacturing technologies, is attracting significant attention from research and industry communities seeking breakthroughs. One of the key technologies for achieving a breakthrough in robotics is flexible sensors. This paper presents a novel approach based on wavelength and time division multiplexing (WTDM) for distributed optical waveguide shape sensing. Structurally designed optical waveguides based on color filter blocks validate the proposed approach through a cost-effective experimental setup. During data collection, it combines optical waveguide transmission loss and the way of controlling the color and intensity of the light source and detecting color and intensity variations for modeling. An artificial neural network is employed to model and demodulate a data-driven optical waveguide shape sensor. As a result, the correlation coefficient between the predicted and real bending angles reaches 0.9134 within 100 s. To show the parsing performance of the model more intuitively, a confidence accuracy curve is introduced to describe the accuracy of the data-driven model at last.

Influence of Ion Exchange Process Parameters on Broadband Differential Interference.

The paper presents theoretical analyses and experimental investigations of broadband differential interference in planar gradient waveguides made via K+-Na+ ion exchange in BK-7 glass. This technology, due to its large polarimetric dispersion, is especially useful for applications in differential interferometry. We discuss the influence of technological parameters on the operation characteristics of the structure in terms of sensor applications. The refractive index variation in the measured external surroundings affects the modal properties of TE and TM modes and the spectral distribution at the output of the differential interferometer. The optical system described in this work has been designed specifically for use in biological systems where variations in the index of refraction need to be measured.

A Dew-Condensation Sensor Exploiting Local Variations in the Relative Refractive Index on the Dew-Friendly Surface of a Waveguide.

We propose a sensor technology for detecting dew condensation, which exploits a variation in the relative refractive index on the dew-friendly surface of an optical waveguide. The dew-condensation sensor is composed of a laser, waveguide, medium (i.e., filling material for the waveguide), and photodiode. The formation of dewdrops on the waveguide surface causes local increases in the relative refractive index accompanied by the transmission of the incident light rays, hence reducing the light intensity inside the waveguide. In particular, the dew-friendly surface of the waveguide is obtained by filling the interior of the waveguide with liquid H2O, i.e., water. A geometric design for the sensor was first carried out considering the curvature of the waveguide and the incident angles of the light rays. Moreover, the optical suitability of waveguide media with various absolute refractive indices, i.e., water, air, oil, and glass, were evaluated through simulation tests. In actual experiments, the sensor with the water-filled waveguide displayed a wider gap between the measured photocurrent levels under conditions with and without dew, than those with the air- and glass-filled waveguides, as a result of the relatively high specific heat of the water. The sensor with the water-filled waveguide exhibited excellent accuracy and repeatability as well.

Reflective Fiber Temperature Probe Based on Localized Surface Plasmon Resonance towards Low-Cost and Wireless Interrogation.

Reflection fiber temperature sensors functionalized with plasmonic nanocomposite material using intensity-based modulation are demonstrated for the first time. Characteristic temperature optical response of the reflective fiber sensor is experimentally tested using Au-incorporated nanocomposite thin films deposited on the fiber tip, and theoretically validated using a thin-film-optic-based optical waveguide model. By optimizing the Au concentration in a dielectric matrix, Au nanoparticles (NP) exhibit a localized surface plasmon resonance (LSPR) absorption band in a visible wavelength that shows a temperature sensitivity ~0.025%/°C as a result of electron-electron and electron-phonon scattering of Au NP and the surrounding matrix. Detailed optical material properties of the on-fiber sensor film are characterized using scanning electron microscopy (SEM) and focused-ion beam (FIB)-assisted transmission electron microscopy (TEM). Airy's expression of transmission and reflection using complex optical constants of layered media is used to model the reflective optical waveguide. A low-cost wireless interrogator based on a photodiode transimpedance-amplifier (TIA) circuit with a low-pass filter is designed to integrate with the sensor. The converted analog voltage is wirelessly transmitted via 2.4 GHz Serial Peripheral Interface (SPI) protocols. Feasibility is demonstrated for portable, remotely interrogated next-generation fiber optic temperature sensors with future capability for monitoring additional parameters of interest.

Donor-Acceptor-Donor 1H-Benzo[d]imidazole Derivatives as Optical Waveguides.

A new series of donor-acceptor-donor (D-A-D) structures derived from arylethynyl 1H-benzo[d]imidazole was synthesized and processed into single crystals with the goal of testing such crystals' ability to act as optical waveguides. Some crystals displayed luminescence in the 550-600 nm range and optical waveguiding behavior with optical loss coefficients around 10-2 dB/µm, which indicated a notable light transport. The crystalline structure, confirmed by X-ray diffraction, contains internal channels that are important for light propagation, as we previously reported. The combination of a 1D assembly, a single crystal structure, and notable light emission properties with low losses from self-absorption made 1H-benzo[d]imidazole derivatives appealing compounds for optical waveguide applications.

Ultralow-loss Optical Waveguides through Balancing Deep-Blue TADF and Orange Room Temperature Phosphorescence in Hybrid Antimony Halide Microstructures.

Harnessing the potential of thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) is crucial for developing light-emitting diodes (LEDs), lasers, sensors, and many others. However, effective strategies in this domain are still relatively scarce. This study presents a new approach to achieving highly efficient deep-blue TADF (with a PLQY of 25 %) and low-energy orange RTP (with a PLQY of 90 %) through the fabrication of lead-free hybrid halides. This new class of monomeric and dimeric 0D antimony halides can be facilely synthesized using a bottom-up solution process, requiring only a few seconds to minutes, which offer exceptional stability and nontoxicity. By leveraging the highly adaptable molecular arrangement and crystal packing modes, the hybrid antimony halides demonstrate the ability to self-assemble into regular 1D microrod and 2D microplate morphologies. This self-assembly is facilitated by multiple non-covalent interactions between the inorganic cores and organic shells. Notably, these microstructures exhibit outstanding polarized luminescence and function as low-dimensional optical waveguides with remarkably low optical-loss coefficients. Therefore, this work not only presents a pioneering demonstration of deep-blue TADF in hybrid antimony halides, but also introduces 1D and 2D micro/nanostructures that hold promising potential for applications in white LEDs and low-dimensional photonic systems.

An integrated optical waveguide micro-cantilever system for chip-based AFM.

An optical waveguide cantilever system with a tip is introduced as the displacement detection system of chip-based atomic force microscopy (AFM) system. A chip-based AFM on optical waveguide is demonstrated with sensitivity of up to 4.0 × 10-2 nm-1 , which is mainly constructed by a 210 nm thick optical waveguide cantilever with a nano-tip. The nano-tip is a height of 1.2 µm and diameter of 140 nm. This integrated on-chip system provides a displacement range of approximately ±0.4 µm, which makes it possible for the device to be used for AFM imaging and pays the way for further performance improvement.

The Real-Time Validation of the Effectiveness of Third-Generation Hyperbranched Poly(ɛ-lysine) Dendrons-Modified KLVFF Sequences to Bind Amyloid-ß1-42 Peptides Using an Optical Waveguide Light-Mode Spectroscopy System.

The aggregation of cytotoxic amyloid peptides (Aß1-42) is widely recognised as the cause of brain tissue degeneration in Alzheimer's disease (AD). Indeed, evidence indicates that the deposition of cytotoxic Aß1-42 plaques formed through the gradual aggregation of Aß1-42 monomers into fibrils determines the onset of AD. Thus, distinct Aß1-42 inhibitors have been developed, and only recently, the use of short linear peptides has shown promising results by either preventing or reversing the process of Aß1-42 aggregation. Among them, the KLVFF peptide sequence, which interacts with the hydrophobic region of Aß16-20, has received widespread attention due to its ability to inhibit fibril formation of full-length Aß1-42. In this study, hyperbranched poly-L-lysine dendrons presenting sixteen KLVFF at their uppermost molecular branches were designed with the aim of providing the KLVFF sequence with a molecular scaffold able to increase its stability and of improving Aß1-42 fibril formation inhibitory effect. These high-purity branched KLVFF were used to functionalise the surface of the metal oxide chip of the optical waveguide lightmode spectroscopy sensor showing the more specific, accurate and rapid measurement of Aß1-42 than that detected by linear KLVFF peptides.

Micromechanically-Powered Rolling Locomotion of a Twisted-Crystal Optical-Waveguide Cavity as a Mobile Light Polarization Rotor.

We demonstrate mechanically-powered rolling locomotion of a twisted-microcrystal optical-waveguide cavity on the substrate, rotating the output signal's linear-polarization. Self-assembly of (E)-2-bromo-6-(((4-methoxyphenyl)imino)methyl)-4-nitrophenol produces naturally twisted microcrystals. The strain between several intergrowing, orientationally mismatched nanocrystalline fibres dictates the pitch lengths of the twisted crystals. The crystals are flexible, perpendicular to twisted (001) and (010) planes due to π⋅⋅⋅π stacking, C-H⋅⋅⋅Br, N-H⋅⋅⋅O and C-H⋅⋅⋅O interactions. The twisted crystals in their straight and bent geometries guide fluorescence along their body axes and display optical modes. Depending upon the degree of mechanical rolling locomotion, the crystal-waveguide cavity correspondingly rotates the output signal polarization. The presented twisted-crystal cavity with a combination of mechanical locomotion and photonic attributes unfolds a new dimension in mechanophotonics.

Elastic Organic Crystals Based on Barbituric Derivative: Multi-faceted Bending and Flexible Optical Waveguide.

Elastic organic single crystals with light-emitting and multi-faceted bending properties are extremely rare. They have potential application in optical materials and have attracted the extensive attention of researchers. In this paper, we reported a structurally simple barbituric derivative DBDT, which was easily crystallized and gained long needle-like crystals (centimeter-scale) in DCM/CH3 OH (v/v=2/8). Upon applying or removing the mechanical force, both the (100) and (040) faces of the needle-like crystal showed reversible bending behaviour, showing the nature of multi-faceted bending. The average hardness (H) and elastic modulus (E) were 0.28±0.01 GPa and 4.56±0.03 GPa for the (040) plane, respectively. Through the analysis of the single crystal data, it could be seen that the van der waals (C-H⋅⋅⋅π and C-H⋅⋅⋅C), H-bond (C-H⋅⋅⋅O) and π⋅⋅⋅π interactions between molecules were responsible for the generation of the crystal elasticity. Interestingly, elastic crystals exhibited optical waveguide characteristics in straight or bent state. The optical loss coefficients measured at 627 nm were 0.7 dBmm-1 (straight state) and 0.9 dBmm-1 (bent state), while the optical loss coefficient (α) were 1.5 dBmm-1 (straight state) and 1.8 dBmm-1 (bent state) at 567 nm. Notably, the elastic organic molecular crystal based on barbituric derivative could be used as the candidate for flexible optical devices.

Precision-Microfabricated Fiber-Optic Probe for Intravascular Pressure and Temperature Sensing.

Small form-factor sensors are widely used in minimally invasive intravascular diagnostic procedures. Manufacturing complexities associated with miniaturizing current fiber-optic probes, particularly for multi-parameter sensing, severely constrain their adoption outside of niche fields. It is especially challenging to rapidly prototype and iterate upon sensor designs to optimize performance for medical devices. In this work, a novel technique to construct a microscale extrinsic fiber-optic sensor with a confined air cavity and sub-micron geometric resolution is presented. The confined air cavity is enclosed between a 3 µm thick pressure-sensitive distal diaphragm and a proximal temperature-sensitive plano-convex microlens segment unresponsive to changes in external pressure. Simultaneous pressure and temperature measurements are possible through optical interrogation via phase-resolved low-coherence interferometry (LCI). Upon characterization in a simulated intravascular environment, we find these sensors capable of detecting pressure changes down to 0.11 mmHg (in the range of 760 to 1060 mmHg) and temperature changes of 0.036 °C (in the range 34 to 50 °C). By virtue of these sensitivity values suited to intravascular physiological monitoring, and the scope of design flexibility enabled by the precision-fabricated photoresist microstructure, it is envisaged that this technique will enable construction of a wide range of fiber-optic sensors for guiding minimally invasive medical procedures.

Multimodal Functional Analysis Platform: 2. Development of Si Opto-Electro Multifunctional Neural Probe with Multiple Optical Waveguides and Embedded Optical Fiber for Optogenetics.

We have developed a Si opt-electro multifunctional neural probe with multiple waveguides and embedded optical fiber for highly accurate optical stimulation. The Si opt-electro multifunctional neural probe had 16 recording sites, three optical waveguides, and metal cover for suppressing light leakage. The other opt-electro multifunctional neural probe had an optical fiber in the trench of the probe shank, which leads to fewer damages to tissues. We evaluated the electrochemical properties of the recording sites and confirmed that the neural probe had suitable characteristics for neural recording. We also demonstrated the optical stimulation to the neurons expressing ChR2 using our probe. As a result, we succeeded in multisite optical stimulation and observed that no light leakage from the optical waveguides because of the metal cover. From in vivo experiments, we successfully recorded optically modulated local field potential using the fabricated Si neural probe with optical waveguides. Moreover, we applied current source density analysis to the recorded LFPs. As a result, we confirmed that the light-induced membrane current sinks in the locally stimulated area. The Si opto-electro multifunctional neural probe is one of the most versatile tools for optogenetics.

Hollow Core Bragg Fiber-Based Sensor for Simultaneous Measurement of Curvature and Temperature.

In this paper, the hollow core Bragg fiber (HCBF)-based sensor based on anti-resonant reflecting optical waveguide (ARROW) model is proposed and experimentally demonstrated for simultaneous measurement of curvature and temperature by simply sandwiching a segment of HCBF within two single-mode fibers (SMFs). The special construction of a four-bilayer Bragg structure provides a well-defined periodic interference envelope in the transmission spectrum for sensing external perturbations. Owing to different sensitivities of interference dips, the proposed HCBF-based sensor is capable of dual-parameter detection by monitoring the wavelength shift. The highest curvature sensitivity of the proposed sensor is measured to be 74.4 pm/m-1 in the range of 1.1859-2.9047 m-1 with the adjusted R square value of 0.9804. In the meanwhile, the best sensitivity of temperature sensing was detected to be 16.8 pm/°C with the linearity of 0.997 with temperature range varying from 25 to 55 °C. Furthermore, with the aid of the 2 × 2 matrix, the dual demodulation of curvature and temperature can be carried out to realize the simultaneous measurement of these two parameters. Besides dual-parameter sensing based on wavelength shift, the proposed sensor can also measure temperature-insensitive curvature by demodulating the intensity of resonant dips.

Recent Advances in Generation and Detection of Orbital Angular Momentum Optical Beams-A Review.

Herein, we have discussed three major methods which have been generally employed for the generation of optical beams with orbital angular momentum (OAM). These methods include the practice of diffractive optics elements (DOEs), metasurfaces (MSs), and photonic integrated circuits (PICs) for the production of in-plane and out-of-plane OAM. This topic has been significantly evolved as a result; these three methods have been further implemented efficiently by different novel approaches which are discussed as well. Furthermore, development in the OAM detection techniques has also been presented. We have tried our best to bring novel and up-to-date information to the readers on this interesting and widely investigated topic.