Birefringence Changes Research Articles

Left and Right‐Handed Light Reflection and Emission in Ultrathin Cellulose Nanocrystals Films with Printed Helicity

AbstractNatural polymers, particularly plant‐derived nanocelluloses, self‐organize into hierarchical structures, enabling mechanical robustness, bright iridescence, emission, and polarized light reflection. These biophotonic properties are facilitated by the assembly of individual components during evaporation, such as cellulose nanocrystals (CNCs), which exhibit a left‐handed helical pitch in a chiral nematic state. This work demonstrates how optically active films with pre‐programmed opposite handedness (left or right) can be constructed via shear‐induced twisted printing with clockwise and counter‐clockwise shearing vectors. The resulting large‐area thin films are transparent yet exhibit pre‐determined mirror‐symmetrical optical activity, enabling the distinction of absorbed and emitted circularly polarized light. This processing method allows for sequential printing of thin and ultrathin films with twisted layered organization and on‐demand helicity. The complex light polarization behavior is due to step‐like changes in linear birefringence within each deposited layer and circular birefringence, different from that of conventional CNC films as revealed with Muller matrix analysis. Furthermore, intercalating an achiral organic dye into printed structures induces circularly polarized luminescence while preserving high transmittance and controlled handedness. These results suggest that twisted sequential printing can facilitate the construction of chiroptical metamaterials with tunable circular polarization, absorption, and emission for optical filters, encryption, photonic coatings, and chiral sensors.

Tunable and Switchable Thermochromism in Cholesteric Liquid Crystalline Elastomers.

Thermochromic materials have found widespread commercial use in packaging as temperature indicators. Often, these products utilize leuco dyes that are mixed into conventional polymeric resins to prepare coatings or films that exhibit temperature-dependent color change. Here, we consider a distinctive approach to thermochromism via the selective reflection of liquid crystalline elastomers that retain the helicoidal structure of the cholesteric phase (CLCEs). Upon heating, the order of the CLCEs reduces and approaches zero, resulting in a change in birefringence as well as material thickness, both of which manifest as changes in the selective reflection to heating. This examination systematically prepares CLCEs capable of reversible thermochromic response as a function of cross-link density and liquid crystalline composition. A particular focus of this examination is the preparation of CLCEs composed of chiral and achiral liquid crystalline monomers that reduce the strength of the mesogen-mesogen interaction and accordingly reduce the nematic-isotropic transition temperature. The low birefringence of some of the CLCE compositions facilitates thermochromic reflection tuning, followed by switching.

All‐Optical Excitatory and Inhibitory Synapses Based on Reversible Photo‐Induced Phase Transition in Single‐Crystal CsPbBr3 Perovskite

AbstractThe hardware‐level construction of artificial synapses, mimicking the functionality of biological synapses, is widely acknowledged as a pivotal stride in artificial intelligence systems. Particularly, establishing all‐optical artificial synapses for neuromorphic computing, leveraging on‐chip optical interconnects instead of conventional wired connections, has garnered widespread attention. Here, high‐quality CsPbBr3 single crystals are synthesized, and intriguing relaxation processes associated with reversible photo‐induced phase transition (PIPT) are observed, leading to a corresponding change in the birefringence effect. The birefringence change is systematically analyzed by an optical system. The relaxation time of reversible PIPT is similar to the behavior patterns of biological synapses, enabling the device to mimic synaptic features. The device successfully mimics excitatory/inhibitory synaptic behaviors such as EPSP/IPSP, PPF, SDDP, SFDP, and SIDP by using 1310 nm signal. Furthermore, the device continues to exhibit excitatory/inhibitory synaptic functionality when 940 and 1550 nm signals are applied, achieving multi‐wavelength synaptic behaviors. The all‐optical devices have the advantages of low crosstalk, fast signaling, and wide optical bandwidth, which lays the foundation of all‐optical hardware for neuromorphic computing systems.

THz near-field intensity distribution imaging in the 0.3 THz band using a highly sensitive polarization CMOS image sensor using a 0.35 μm CMOS process

In this paper, we propose a low-disturbance and fast terahertz (THz) near-field intensity distribution imaging method. The THz detector is fabricated using an oriented multiwalled carbon nanotube (CNT) thin film and a LiNbO3(LN) crystal to the thin film is attached. The CNT absorbs and converts THz waves into heat, and the birefringence change of the LN crystal owing to the heat is used. The birefringence change was measured with high sensitivity using a dual-polarizer configuration of a uniform polarizer and a polarization CMOS image sensor. The fabricated THz detector is a low-disturbance method because it does not use metal, and it can measure the THz distribution in the plane all at once, which is faster than the antenna scanning method. Using the proposed method, we have successfully imaged the THz near-field intensity distribution emitted from an impact avalanche and transit time diode oscillating at 0.278 THz.

Cardiac Pulsed Field Ablation Lesion Durability Assessed by Polarization-Sensitive Optical Coherence Reflectometry.

Pulsed field ablation uses electrical fields to cause nonthermal cell death over several hours. Polarization-sensitive optical coherence reflectometry is an optical imaging technique that can detect changes in the tissue ultrastructure in real time, which occurs when muscular tissue is damaged. The objective of this study was to evaluate the ability of a polarization-sensitive optical coherence reflectometry system to predict the development of chronic lesions based on acute changes in tissue birefringence during pulsed field ablation. Superior vena cava isolation was performed in 30 swine using a biphasic, bipolar pulsed field ablation system delivered with a nonirrigated focal tip catheter. Acute changes in tissue birefringence and voltage abatement were analyzed for each individual lesion. A high-resolution electroanatomical map was performed at baseline and 4 to 12 weeks after ablation to locate electrical gaps in the ablated area. A total of 141 lesions were delivered and included in the analysis. Acute electrical isolation based on the electroanatomical map was achieved in 96% of the animals, but chronic isolation was only seen in 14 animals (46%). The mean voltage abatement of lesions that showed recovery was 82.8%±14.6% versus 84.4%±17.4% for those that showed fibrosis (P=0.7). The mean acute reduction in tissue birefringence in points demonstrating fibrosis was 63.8%±11.3% versus 9.1%±0.1% in the points that resulted in electrical gaps. A threshold of acute reduction of birefringence of ≥20% could predict chronic lesion formation with a sensitivity of 96% and a specificity of 83%. Acute tissue birefringence changes assessed with polarization-sensitive optical coherence reflectometry during pulsed field ablation can predict chronic lesion formation and guide the ablation procedure although limited by the tissue thickness.

A macroscopic magneto-optical response resulting from local effects in ferronematic liquid crystals.

This study investigates the magneto-optical response of liquid crystals (LCs) with planar anchoring in the presence of γ-Fe2O3 magnetic nanoparticles (MNPs). This research demonstrates the formation of novel magnetic composite chains of LCs wrapped around γ-Fe2O3 MNP chains within the LC matrix under an applied magnetic field. These composite chains exhibit a distinct magneto-optical response, characterized by changes in birefringence and dichroism as the magnetic field direction is altered. Based on experimental findings, a two-subsystem model and an effective volume fraction of composite chains are proposed to describe the magneto-optical behavior of the γ-Fe2O3 MNP-doped LCs. The first subsystem comprises the LC matrix, which retains its inherent anisotropic optical properties and does not respond to the applied magnetic field. The second subsystem consists of the magnetic composite chains, which exhibit a distinct magneto-optical response due to their rotational alignment with the magnetic field. The difference in absorbance, 2αdd, which corresponds to dichroism, decreases with increasing magnetic field angle Θ, indicating a corresponding change in dichroism. This interplay between the two subsystems leads to the macroscopic magneto-optical response observed in the γ-Fe2O3 MNP-doped LCs. Due to the stability of the composite chains, the magneto-optical response is stable and can be reversed.

Distributed phase-matching measurement for dynamic strain and temperature sensing based on stimulated Brillouin scattering enhanced four-wave mixing

A Brillouin dynamic grating (BDG) can be used for distributed birefringence measurement in optical fibers, offering high sensitivity and spatial resolution for sensing applications. However, it is quite a challenge to simultaneously achieve dynamic measurements with both high accuracy and high spatial resolution. In this work, we propose a sensing mechanism to achieve distributed phase-matching measurement using a chirped pulse as a probe signal. In BDG reflection, the peak reflection corresponds to the highest four-wave mixing (FWM) conversion efficiency, and it requires the Brillouin frequency in the fast and slow axes to be equal, which is called the phase-matching condition. This condition changes at different fiber positions, which requires a range of frequency injection for the probe wave. The proposed method uses a chirped pulse as a probe wave to cover this frequency range associated with distributed birefringence inhomogeneity. This allows us to detect distributed phase matching for birefringence changes that are introduced by temperature and strain variations. Thanks to the single shot and direct time delay measurement capability, the acquisition rate in our system is only limited by the fiber length. Notably, unlike conventional BDG spectrum recovery-based systems, the spatial resolution here is determined by both the frequency chirping rate of the probe pulse and the birefringence profile of the fiber. In the experiments, an acquisition rate of 1 kHz (up to fiber length limits) and a spatial resolution of 10 cm using a 20 ns probe pulse width are achieved. The minimum detectable temperature and strain variation are 5.6 mK and 0.37 με along a 2 km long polarization-maintaining fiber (PMF).

AROMATIC POLYMER HAVING BOTH AZOBENZENE AND AZOMETHINE UNITS IN THE MAIN CHAIN AS AN EFFICIENT PHOTO-RESPONSIVE MATERIAL

Azobenzene and aromatic azomethine groups acting as versatile photoreversible optically switchable scaffolds attract much interest as efficient building blocks for the construction of light-responsive materials. The pronounced interest in light-sensitive polymers originates from their unique ability to become anisotropic after irradiation by polarized light. Despite the significant progress that has been made on the synthesis of either polyazobenzenes or polyazomethines, numerous challenges remain, and they have become the catalyst for the ongoing research. The polymer having both azobenzene and azomethine groups are fundamentally less developed. In this work, a strategy to the synthesis of the light-responsive polymer with azobenzene and azomethine units in the backbone is proposed. The polymer is prepared by condensation polymerization of octafluorobiphenylene-based bis-hydroxybenzaldehyde with aromatic meta-linked octafluorobiphenylene-based diamine. The structure of the polymer is characterized by Fourier transform infrared spectroscopy. The synthesized polymer can be solution-cast into flexible solid films with a tensile strength of 25 MPa. Furthermore, the polymer displays elevated glass transition temperatures (Tg), reaching 235 °C, and demonstrates an admirable thermal stability, retaining resilience at temperatures up to 390 °C. The polymer film underwent photoisomerization and exhibited changes in light-induced birefringence when exposed to 365 nm UV light and both polarized and unpolarized blue (405 nm) and green (532 nm) light. The ability to record optical information using polymer films in the form of diffraction gratings is demonstrated.

Functionalization of starches from Mexican Oxalis tuberosa using dual chemical modification

This study evaluated for the first time the effects of dual modification of native starch extracted from Mexican Oxalis tuberosa (NSO) by lipophilic substitution with octenyl succinic anhydride (OSA) at one concentration level (3%; MS-OSA) and crosslinking with sodium trimetaphosphate (STMP) at different concentrations (0.25%, 0.50%, 1.00%, 1.50%, 2.00%, and 2.50%, denoted as DMS-0.25, DMS-0.50, DMS-1.0, DMS-1.50, DMS-2.0, and DMS-2.50, respectively). The results showed that the dual modification proportionally decreased the degree of OSA substitution as the STMP concentration increased, as evidenced by the decrease in the Fourier transform infrared absorption band at 1570 cm−1, which is characteristic of vibrations of the carboxyl groups belonging to OSA. The amount of amylose gradually decreased after the double modification, favoring crystallinity. The microstructure of the dually modified granules presented rough-looking changes on the surface. No evident changes in birefringence were observed, maintaining the characteristic Maltese cross. The DMS-0.25 treatment induced an increase in maximum viscosity (1558.62 ± 1.94 mPa⋅s), which suggests greater stability of the interactions in the polymeric matrix. The double modification provided greater stability to the emulsions formed with the DMS-0.25, DMS-1.0, and DMS-2.0 treatments with respect to the native starch and MS-OSA. The DMS-1.0 and DMS-2.50 treatments improved the functional properties (water absorption index, water solubility index, swelling power, and lipid absorption index) compared with the native starch and other treatments. These enhanced properties make modified starches suitable for applications, such as controlled drug delivery systems in pharmaceuticals and improved texture and stability in food products.

Reconfigurable Geometrical Phase Spatial Light Modulator Using Short‐Pitch Ferroelectric Liquid Crystals

AbstractThis article presents an approach to achieve a fast and analog geometrical phase modulation based on the optical axis rotation of the defect‐free Deformed Helix Ferroelectric Liquid Crystal (DHFLC) with a short pitch. This study demonstrates a Spatial Light Modulator (SLM) prototype with a feature size of 3 µm without Fringe Field Effect (FFE), having a phase depth of 1.9π, fast switching time (<250 µs) at a low operating voltage (<7 V), and high diffraction efficiency (>77%). The high phase modulation depth is achieved by developing DHFLC with a cone angle of up to 85˚, which is inherently immune to FFE. The ellipticity is minimized by using a compensation film that can suppress the changes in birefringence under the applied electric field. The proposed SLM is promising in applications such as a real‐time hologram and dynamic beam steering in Light Ranging and Detector (LiDAR).

A Polarimetric Fiber Ring Laser Incorporating a Coupled Optoelectronic Oscillator and Its Application to Magnetic Field Sensing

A novel configuration for a polarimetric fiber ring laser incorporating a coupled optoelectronic oscillator (COEO) is proposed and experimentally demonstrated, and its application to magnetic field sensing is studied. The COEO-based polarimetric fiber ring laser has two mutually coupled loops: the fiber ring laser loop and the OEO loop. In the fiber ring laser loop, longitudinal modes break up into orthogonal polarization modes because of birefringence. The frequency of the polarization mode beat (PMB) signals is determined by the cavity birefringence. In the OEO loop, a microwave signal with its frequency equal to the PMB signal is generated. By feeding the oscillation mode to modulate the optical loop, mode-locking can be achieved, rendering the mode spacing of the laser equal to the frequency of the oscillating OEO mode. We can estimate the birefringence variation by measuring the oscillating frequency of the COEO. To validate the proposed sensing system, a circular birefringence change is introduced in a magneto-optic crystal via the Faraday rotation effect. Then, the magnetic field sensing is implemented. Such configuration can achieve single longitudinal oscillation and realize high-speed and high-precision measurements.

Azobenzene–N-salicylideneaniline based aromatic polymers as efficient light-responsive materials

We propose a strategy for the synthesis of light-responsive polymers with azobenzene and N-salicylideneaniline units as the backbone. The polymers were prepared by condensation polymerization of tetrafluorobenzene- or octafluorobiphenylene-based bis-hydroxybenzaldehydes with aromatic meta-linked octafluorobiphenylene-based diamines. A model azo-azomethine-based dye was synthesized to confirm the formation of imine bonds between the bis-hydroxybenzaldehyde used in this study and aromatic amine (2-aminophenol). The synthesized polymers were successfully solution-cast into flexible solid films with a tensile strength of approximately 20 MPa, high values of Tg (>235 оС) and good thermal stability (up to 365 °C). Photoisomerization and light-induced birefringence changes in the polymer films were achieved upon photoirradiation with typical UV light at 365 nm, and by using both polarized and non-polarized blue and green light. Finally, we demonstrated the ability of the developed polymer films to record optical information in the form of diffraction gratings.

Ferroelectric Domain Wall Engineering Enables Thermal Modulation in PMN-PT Single Crystals.

Acting like thermal resistances, ferroelectric domain walls can be manipulated to realize dynamic modulation of thermal conductivity (k), which is essential for developing novel phononic circuits. Despite the interest, little attention has been paid to achieving room-temperature thermal modulation in bulk materials due to challenges in obtaining a high thermal conductivity switching ratio (khigh /klow ), particularly in commercially viable materials. Here, room-temperature thermal modulation in 2.5mm-thick Pb(Mg1/3 Nb2/3 )O3 -xPbTiO3 (PMN-xPT) single crystals is demonstrated. With the use of advanced poling conditions, assisted by the systematic study on composition and orientation dependence of PMN-xPT, a range of thermal conductivity switching ratios with a maximum of ≈1.27 is observed. Simultaneous measurements of piezoelectric coefficient (d33 ) to characterize the poling state, domain wall density using polarized light microscopy (PLM), and birefringence change using quantitative PLMreveal that compared to the unpoled state, the domain wall density at intermediate poling states (0< d33 <d33,max ) is lower due to the enlargement in domain size. At optimized poling conditions (d33,max ), the domain sizes show increased inhomogeneity that leads to enhancement in the domain wall density. This work highlights the potential of commercially available PMN-xPT single crystals among other relaxor-ferroelectrics for achieving temperature control in solid-state devices.

High‐Electron‐Mobility Transistor‐Inspired Freestanding AlGaN/GaN/AlN Optical Waveguide for High‐Pressure Sensing Applications

Herein, a high‐pressure sensor based on freestanding high‐electron‐mobility transistor (HEMT)‐inspired optical waveguide comprising AlGaN/GaN/AlN layers on silicon carbide (SiC) substrate is proposed and studied for harsh environment applications using finite element method (FEM). The working principle of the sensor is based on the change in birefringence due to applied pressure. Further, the transmission spectra for different wavelengths are evaluated. For the best possible outcomes, the dip wavelengths under different values of pressure are tracked and studied for different gallium nitride (GaN) core thicknesses. After optimizing GaN core thickness and AlGaN ratio, the sensor displays a good linear response within the pressure range of 90–150 MPa. The two dip wavelength shifts demonstrate maximum spectral sensitivities of −209.6 and 180 pm MPa−1, respectively, for the pressure range of 90–150 MPa within the communication wavelength regime of 1500–1600 nm. By considering the features such as cost‐effectiveness, portability, simple design, and easy detection process, the proposed pressure sensor is optimum for harsh environment measurements and studies.

Optical curvature sensor based on polarization characteristics of optical fiber.

Curvature measurement plays an important role in various applications. An optical curvature sensor based on polarization characteristics of optical fiber is proposed and verified by experiments. The direct bending of the fiber causes a change in birefringence, which results in a change of Stokes parameters of the transmitted light. The large curvature measurement range of tens to more than 100 m-1 has been realized in the experiment. For micro bending, a cantilever beam structure is used to achieve a sensitivity of up to 12.26/ m-1 and a linearity of 99.49% in the measurement range of 0 to 0.15 m-1, with a resolution of up to 10-6 m-1 order of magnitude, which reaches the level of the latest report. The method with the advantages of simple fabrication, low cost and good real-time performance gives a new development direction to the curvature sensor.

Transverse vibration modes analysis and acoustic response in optical fibers

Fiber optic sensors are often used as acoustic sensors to detect sound waves because of their apparent advantages, such as anti-electromagnetic interference and strong adaptation to the environment. The transverse vibration mode of the fiber caused by the acoustic wave can be obtained, and the principle of the optical fiber sensor to detect the acoustic wave signal was explored by using a simple model. It is found that the acoustic wave can effectively cause the change in birefringence of the fiber only when the number of azimuthal modes is 2, and the acoustic wave was detected by using a fiber sensor. It is found, by analyzing the detection mechanism, that the spectral width is proportional to the acoustic impedance of the surrounding medium, and the acoustic interaction between the TR22 mode and the surrounding medium is much weaker than that of the TR21 mode. This provides a theoretical basis for the detection of acoustic signals by fiber optic sensors.

Dual-band highly-sensitive SPR photonic crystal fiber sensor based on birefringence analysis

In this paper, a dual-band highly-sensitive D-shaped photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) is proposed and numerically analyzed. Au-TiO2 grating is deposited on the flat surface of D-shaped PCF, thus surface plasmon resonances are excited to detect the change of refractive index (RI) of analyte. Rabi-like splitting spectrum is achieved by the introduction of a small air hole in the fiber. Besides spectrum analysis, it is found that the resonance wavelengths can be located by the abnormal change of birefringence. Moreover, complete coupling and incomplete coupling of the guided mode and plasmonic mode can be distinguished from our simulation results. The influences of structural parameters are also analyzed systematically. Simulation results show that the two loss peaks have different RI detection ranges, and the maximum sensitivity reaches 26700 nm/RIU. The proposed sensor could be applied widely in biomedical and chemical fields.

Acoustic Birefringence Changes in the Base Metal and Heat Affected Zone of ASTM 1020 Steel under Plastic Deformation and Fatigue

This paper deals with metallographic studies and ultrasonic investigations of acoustic birefringence in the base metal and heat affected zone of welded specimens of ASTM 1020 steel under uniaxial tension and low-cycle fatigue. We examined microstructural changes on the surface using optical microscope. It was found that development of slip bands differs in the base metal and heat affected zone. The ultrasonic pulse echo method was used for the determination of acoustic birefringence and velocities of ultrasonic shear waves. The differences in the change in velocities in the base metal and in heat affected zone were revealed. Acoustic birefringence was found to change monotonously in the base metal under fatigue as well as in the base metal and heat affected zone under uniaxial tension. For heat affected zone, during fatigue, acoustic birefringence was found to change non-monotonously up to cycle ratio of 0.3 and decrease monotonously after cycle ratio of 0.3. Based on the relationship between relative number of loading cycles, or plasticity resource, and acoustic birefringence, ultrasonic techniques were proposed for assessing damage.

Phase transformation in some hexahydrated metal(II) fluorogermanates and fluorotitanates: Optical and differential scanning calorimetry studies

• Single crystals of hydrated fluorides CoGeF 6 ∙6H 2 O, FeGeF 6 ∙6H 2 O, CoTiF 6 ∙6H 2 O, ZnTiF 6 ∙6H 2 O were grown. • Twinning, birefringence and heat capacities indicate a phase transition of the first order from trigonal to monoclinic symmetry. • Small values of the change in entropy and birefringence accompany the phase transition of CoGeF 6 ∙6H 2 O and FeGeF 6 ∙6H 2 O, and rather large values are typical for CoTiF 6 ∙6H 2 O and ZnTiF 6 ∙6H 2 O. Graphical abstract_Synopsis!!! Polarization-optical observations of (001) section of an ABF 6 ∙6H 2 0 crystals: a − optically isotropic rhombohedra phase ( T > T 0 ). Twin pattern in the studied crystals at Т < Т 0 : b − CoGeF 6 ∙6H 2 O; c − FeGeF 6 ∙6H 2 O; d − FeTiF 6 ∙6H 2 O; e − CoTiF 6 ∙6H 2 O; f − ZnTiF 6 ∙6H 2 O.

Birefringence induced by antiferroelectric switching in transparent polycrystalline PbZr0.95Ti0.05O3 film

The most characteristic functional property of antiferroelectric materials is the possibility to induce a phase transition from a non-polar to a polar phase by an electric field. Here, we investigate the effect of this field-induced phase transition on the birefringence change of $PbZr_{0.95}Ti_{0.05}O_{3}$. We use a transparent polycrystalline $PbZr_{0.95}Ti_{0.05}O_{3}$ film grown on $PbTiO_{3}/HfO_{2}/SiO_{2}$ with interdigitated electrodes to directly investigate changes in birefringence in a simple transmission geometry. In spite of the polycrystalline nature of the film and its moderate thickness, the field-induced transition produces a sizeable effect observable under a polarized microscope. The film in its polar phase is found to behave like a homogeneous birefringent medium. The time evolution of this field-induced birefringence provides information about irreversibilities in the antiferroelectric switching process and its slow dynamics. The change in birefringence has two main contributions, one that responds briskly (~ 0.5 s), and a slower one that rises and saturates over a period of as long as 30 minutes. Possible origins for this long saturation and relaxation times are discussed.