In recent years, silicon-based photodetectors have been extensively utilized in various optoelectronic applications due to their compatibility with standard CMOS processes. However, their efficiency in the visible to near-infrared range is limited by high surface reflection and weak absorption in thinner silicon layers. To address these challenges, this study investigates the use of surface photon-trapping microstructures to enhance light absorption in a thick Si-based PIN photodetector. This work presents a Si-based PIN photodetector incorporating a surface-integrated hexagonal inverted photon-trapping hole array, which significantly improves quantum efficiency across a broad spectral range. The device structure was optimized by finite-difference time-domain (FDTD) simulations examining the influence of hole diameter, shape, period and lattice arrangement, depth. Three photodetectors with varying hole configurations were fabricated using optical projection lithography. Specifically, devices with hexagonal hole arrays of diameter/period ratios of 1000/1200 nm and 830/1030 nm exhibited average reflectances of 8.32

With the increasing threat of soft-kill laser weapons to military optoelectronic systems, there is an urgent need for nonlinear laser protection technologies that combine high performance, long-term stability, environmental robustness, and operational sustainability. Conventional laser protection materials, whether liquid-based or solid-state, suffer from critical shortcomings including poor stability, low damage thresholds, limited environmental adaptability, and lack of recyclability. Here, we report a colloidal suspension based nonlinear laser protection system that overcomes these limitations. Using magnetic graphene oxide (MGO) dispersed in a high-viscosity, water-soluble polyethyleneimine medium, the system achieves exceptional stability (no sedimentation for over two months), a high laser damage threshold (>1.2 J/cm2), and green recyclability via magnetic recovery. At a concentration of 0.0219 mg/mL, the MGO colloidal suspension exhibits a minimum transmittance of 22.7% and an NOL capacity coefficient of 0.385 at 1064 nm. Its protective performance exceeded that of many existing NOL materials. The nonlinear absorption coefficients measured by Z-scan experiments reach up to 1.69×10−9 m/W. Furthermore, the material maintains stable performance at elevated temperatures (up to 75 °C) and after extended storage. This work demonstrates that colloidal suspensions represent a new class of practical laser protection media, offering a promising solution for defending military platforms against soft-kill laser threats.

As a high-performance acousto-optic (AO) material, Hg2Br2 single crystal (SC) has emerged as a highly promising candidate for various AO devices. In this study, the high-quality Hg2Br2 crystal with dimensions of phi 54 & times; 70 mm(3) were successfully grown through an optimized physical vapor transport (PVT) method. After clarifying the formation mechanism and interrelationship of quasi-crystalline interfaces, stripes and twins in the Hg2Br2 crystal growth process, the generation of defects during the crystal growth process was effectively suppressed by optimizing the growth parameters. Then, the optical properties, including laser-induced damage threshold (LIDT), refractive index, polarized transmission spectra, and angle-resolved polarized Raman spectra (ARPRS) were systematically investigated. The results demonstrate that Hg2Br2 SC not only exhibit excellent optical performance but also display pronounced optical anisotropy. Furthermore, the acoustic velocities corresponding to different acoustic modes were measured, followed by the determination of the elastic constant tensors and polar plots of acoustic velocity and slowness distribution. This analysis revealed an exceptionally low shear wave velocity of 276.78 m/s, which emerges as a key characteristic of this crystal. Using a home-built Mach-Zehnder interferometer system, the piezo-optic coefficients (pi(IJ)) and elasto-optic coefficients (p(IJ)) were experimentally determined for the first time, enabling the calculation of the acousto-optic figure of merit M-2 across various modes, with a maximum value of 2900 & times; 10(-18) s(3)/g. This work presents the first systematic characterization of the anisotropic optical and AO properties of Hg2Br2 SC. It not only confirms the broad potential of Hg2Br2 SC in AO applications but also lays a solid foundation for the optimization of future device performance and their practical implementation.

The development of nonlinear optical limiting (NOL) materials with self-healing represents a significant new breakthrough in the field of optical limiting. Here, we innovatively prepare a novel self-healing NOL composites which is carbon nanotubes doped polydimethylsiloxane-boric acid crosslinked (CNTs-doped PDMS-BA, CPB), and achieve an excellent NOL performance. The dynamic network formed through transesterification between PDMS chains and BA enables efficient self-healing after mechanical damage, while CNTs ensure robust NOL properties. We experimentally measure the self-healing capability of CPB at different temperatures (25 degrees C, 50 degrees C, and 75 degrees C), demonstrating elevated temperatures can accelerate self-healing. Even if CPB is damaged by laser, it can still achieve self-healing by excising the damaged spot, enabling its recyclability. We also measure the transmittance of 1 and 2 mm-thick CPB with 0.54 and 0.62 mg/mL CNTs concentrations under a nanosecond pulse laser with a wavelength of 1064 nm. For the 2 mm-thick CPB at 0.62 mg/mL, the linear and minimum transmittance with NOL effects at 1064 nm are 62.6% and 27.2%, respectively. Furthermore, cycling performance of CPB show that the NOL performance only decrease by 5% within three cycles. These outstanding features highlight the practical adaptability and stability of CPB, and the high damage threshold also indicates that CPB is a promising NOL composites.

In recent years, relaxor ferroelectric single crystals (1-x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3) (PMN-xPT) have been widely investigated and attracted attention due to their excellent piezoelectric and electromechanical properties. Yet, their internal microdomain structure results in low transmittance, which limits their application in optical field. In this paper, 1% mol Sm-doped 0.7Pb(Mg1/3Nb2/3)-0.3PbTiO(3) (Sm-PMN-30PT) crystals were successfully grown by a modified Bridgman technique. Sm-3(+) induces nanoscale structural disorder in the crystal, significantly enhancing contribution of polar nanoregions (PNRs) to macroscopic properties. Piezoelectric, ferroelectric, and electro-optic performances were enhanced. Electromechanical coupling coefficients k(33) and k(t) reach 66% and 48%, respectively. Piezoelectric coefficient d(33) value of Sm-PMN-30PT crystal is 5800-6100 pC/N with 55 Hz test frequency. After poled along [110] direction, transmittance along [001] direction reaches 56%. Effective electro-optic coefficient gamma(c) is 240 pm/V at room temperature, and it can reach 1293 pm/V near the Curie temperature (109 degrees C). These results show that Sm-PMN-30PT single crystals could be ideal materials for piezoelectric and electro-optic devices.

Accurate simultaneous measurement of temperature, salinity, and axial strain is critical for advancing oceanography, aquaculture, biopharmaceuticals, and marine structural health monitoring, yet remains challenging due to severe cross-sensitivity among these parameters. In this paper, we have proposed and experimentally validated a novel forward Brillouin scattering (FBS)-based sensing method that uniquely utilizes the torsional-radial acoustic mode (TR2,m) in a simple direct sensing structure. The resulting FBS spectra exhibit strong signal amplitude and narrow linewidth. We perform the first systematic comparative analysis between our approach and two conventional sensing architectures, quantitatively examining their FBS spectra to establish the superiority of the direct scheme. Variations in temperature, salinity, and axial strain perturb the acoustic velocity, inducing distinct linear frequency shifts with well-separated sensitivity coefficients. By constructing a coefficient matrix and tracking the resonance peaks, we successfully decouple the three parameters, achieving measurement uncertainties of 0.28 degrees C for temperature, 0.18 % for salinity, and 14 mu epsilon for axial strain-to our knowledge, representing one of the highest accuracy levels reported for FBS-based multi-parameter sensing to date. This combination of high accuracy, simple structure, and effective decoupling offers a new method for optical fiber sensing in marine and biomedical applications.

To address sustainability and recyclability challenges in nonlinear optical limiting (NOL), we develop an eco-friendly magnetic graphene oxide (MGO)-water suspension. At 0.03 mg/mL, it exhibits strong NOL effects at 1064 and 532 nm, with maximum NOL capability coefficients of 0.535 and 0.556, and minimum transmittances of 0.225 and 0.229, respectively. Mie scattering is the primary mechanism. The suspension shows excellent dispersibility, stability, high damage threshold, and magnetically assisted recoverability, offering a promising material for practical NOL applications.

K3B6O10Br (KBB) is a novel nonlinear optical (NLO) crystal for 355 nm ultraviolet (UV) laser generation. The second-order NLO properties of KBB crystals have been widely studied, however, their third-order NLO properties have rarely been investigated. The third-order NLO properties of crystals determine the ability of the laser output for frequency conversion. In this work, the nonlinear absorption coefficient (β) and nonlinear refractive index (n2) of KBB were investigated by Z-scan technique under different intensities at 532 and 355 nm. We observed that β increased with the increasing laser intensity at both 532 and 355 nm, suggesting that KBB is mainly associated with defect-state-assisted sequential two-photon absorption (TPA) process. The value of n2 > 0 indicates that KBB is a self-focusing crystal, and n2 increases with increasing laser intensity. The correlation of shorter wavelengths with higher β and n2 values confirms the strong third-order nonlinear response of the KBB crystal in the UV band. Moreover, the transient absorption spectra demonstrated that KBB underwent excited-state absorption (ESA) under laser excitation. Building upon these findings, an energy-level model of defect-state-assisted sequential TPA in KBB is proposed.

Objective Organic dyes (e. g., rhodamine B, methylene blue), widely used as raw materials in textile, printing, and other industries, have attracted increasing attention because of their environmental residues and associated ecotoxicological effects. Piezo-photocatalysis has emerged as an important strategy for the degradation of organic pollutants. Existing methods for monitoring dye mass concentration during piezo-photocatalytic processes, such as spectrophotometry, liquid chromatography, and electrochemical detection, are limited by complicated procedures, notable measurement errors, and the inability to achieve true in-situ monitoring. Forward Brillouin scattering (FBS) is a physical phenomenon involving energy exchange between optical and transverse acoustic fields through elasto-acoustic coupling, which shows unique advantages in optical fiber sensing and microstructure characterization. Fiber-optic FBS sensing systems exhibit notable strengths such as compact size, rapid response, high sensitivity, corrosion resistance, lightweight properties, and immunity to electromagnetic interference, making them particularly valuable for extreme environmental monitoring and in-situ detection. Therefore, we propose a novel FBS-based in-situ monitoring method using polyimide (PI)-coated optical fibers to track dye degradation. Compared with conventional detection techniques, this approach effectively overcomes technical limitations such as mechanical interference and operational complexity. It holds significant application potential in the study of piezo-catalysis, photocatalysis, and their synergistic mechanisms, providing a reliable tool for in-situ mass concentration monitoring in the industrial application of green catalytic technologies. Methods Variation in RhB solution mass concentration alters the liquid acoustic impedance, which in turn directly influences the radial acoustic modes excited within the optical fiber. As a result, a linear correlation can be established between the FBS peak linewidth and RhB mass concentration, enabling quantitative determination of the dye mass concentration. An experimental setup (Fig. 1) based on FBS in a PI-coated optical fiber is established to measure FBS spectra and study the proposed RhB solution mass concentration sensing method. The R0,7 and R0,8 modes are chosen for coefficient calibration based on standard selection criteria, including high sensitivity, good signal-to-noise ratio, and a well-defined Lorentzian spectral profile. Therefore, this study adopts R0,7 as the parameter for analyzing the mass concentration-dependent characteristics of FBS spectra. To validate the feasibility of the proposed measurement method and avoid coincidental results, RhB solutions at 0, 5.00, and 7.50 mg/L are measured. The mass concentration variations obtained through the linewidth-conversion formula are compared with the actual mass concentration changes to determine the measurement error. Finally, a fiber-optic sensing system (Fig. 7) is constructed for in-situ monitoring of solution mass concentration throughout the piezoelectric-photocatalytic dye degradation. In a typical piezoelectric-photocatalytic experiment, RhB solution serves as the simulated pollutant, barium titanate (BTO) nanoparticles act as the catalyst, and an ultrasonic cleaner combined with a 385 nm UV lamp provides mechanical vibration and light irradiation to the reaction system. During this process, the BTO nanoparticles facilitate RhB degradation through the synergistic effect of ultrasonic vibration and UV light, leveraging the coupled piezoelectric and photocatalytic mechanisms. Results and Discussions In this paper, we propose a novel in-situ monitoring method for dye degradation based on the FBS effect in PI-coated optical fibers. In the coefficient calibration experiment for RhB solution mass concentration, the normalized linewidths of the FBS peaks excited by two acoustic modes show a decreasing trend with increasing mass concentration. Both modes show significant linear relationships between the FBS peak linewidth and RhB mass concentration (Fig. 3). The linewidth-mass concentration coefficient for the mode is (-26.67 +/- 0.9) kHz/(mg/L) with a goodness-of-fit of 0.991. In the mass concentration measurement validation experiment, the proposed method yields linewidth differences of 0.128 MHz between state 2 and state 1, and 0.195 MHz between state 3 and state 1 (Fig. 4). Using the coefficient of-26.67 kHz/(mg/L) in the linewidth-conversion formula, the measured mass concentration changes are calculated as 4.80 mg/L and 7.31 mg/L, respectively. Compared to the actual mass concentration changes of 5.00 mg/L and 7.50 mg/L, the measurement errors are 0.20 mg/L and 0.19 mg/L (retaining two significant figures), showing good agreement with the theoretical error of 0.19 mg/L. The slight discrepancies between the experimental and theoretical values may be attributed to coefficient estimation errors, rounding during data processing, and minor temperature fluctuations. In addition, the power stability of the sensor is evaluated in an 8 mg/L RhB solution. The standard deviation of the linewidth for the mode remains below 0.05 degrees o, confirming excellent repeatability and stability. In the final in-situ monitoring experiment for piezoelectric photocatalytic dye degradation, the FBS technique tracks the real-time linewidth evolution of the excited FBS peak. The linewidth of the selected mode increases monotonically with degradation time, corresponding to a reduction in RhB mass concentration from 21 mg/L to about 4.4 mg/L over 8 h (Fig. 8), validating the effectiveness of the proposed method. Conclusions In this paper, we propose a novel in-situ monitoring method for piezoelectric-photocatalytic dye degradation based on PI fiber FBS. By detecting acoustic property changes in the PI fiber coating induced by RhB solution mass concentration variations, this method enables high-precision, real-time monitoring of the piezoelectric-photocatalytic degradation process. Experimental results reveal a strong linear correlation between the FBS spectral linewidth of various radial acoustic modes in the PI fiber and the RhB mass concentration. The linewidth-mass concentration coefficient of the mode reaches (-26.67 +/- 0.9) kHz/(mg/L) (R2 >0.99), with a measurement uncertainty of 0.19 mg/L. In a BTO catalytic system synthesized via hydrothermal method, this approach successfully accomplishes continuous 8 h in-situ real-time monitoring under ultrasonic-UV synergistic conditions. The non-invasive in-situ technique eliminates interference with the reaction system caused by traditional sampling methods, thus maintaining high consistency between catalyst mass concentration and reaction kinetics. Furthermore, the all-fiber sensing design eliminates complex pretreatment steps such as centrifugation and sampling, reducing single measurement time to 20 degrees o of conventional spectrophotometry while improving monitoring efficiency. Benefiting from the strong electromagnetic-interference resistance of optical signals, this technique enhances measurement accuracy by approximately 57 degrees o compared to spectrophotometry, effectively reducing systematic errors. In this paper, we offer a high-precision, non-invasive in-situ analytical tool for studying reaction kinetics in piezoelectric catalysis, photocatalysis, and synergistic piezoelectric-photocatalytic systems. The proposed method shows promising potential for advancing mechanistic studies and practical applications of green catalytic technologies, offering new technical support for environmental remediation and sustainable development.

Dissolved gas analysis (DGA) is a critical method for transformer fault diagnosis. Medium-to-high-temperature thermal fault is a key focus in transformer condition monitoring, with its characteristic gases primarily dominated by ethylene (C2H4) and ethane (C2H6). Traditional detection methods based on mid-infrared (MIR) band absorption spectroscopy face limitations in manufacturing maturity and high costs. C2H4 and C2H6 exhibit weak and severely overlapping absorption cross sections in the near-infrared region (NIR). The small absorption crosssections leads to significant noise, which in turn causes large errors in multispectral separation and makes it difficult to achieve high-precision cross-interference suppression. This study pioneers the application of Nonnegative Matrix Factorization (NMF) for cross-interference suppression. By decomposing mixed-gas secondary harmonics (2f) into products of the 2f of individual component gas and their concentrations, this method isolates individual gas signals from overlapping spectral bands. Furthermore, to address the issue that noise affects the accuracy of cross-interference suppression, a Noise-Suppressed NMF model is established through rigorous noisepropagation analysis. Experimental results demonstrate that, using a 3-meter absorption cell at 1683.25 nm, Noise-Suppressed NMF achieves average relative errors of -0.57 % for C2H4 and - 0.005 % for C2H6 across 15 calibrated C2H4 and C2H6 binary mixtures. Additionally, under severe cross-interference, absolute errors of 1.5 ppm for 40.6 ppm C2H4 and 2 ppm for 73.72 ppm C2H6 are attained. This work establishes a novel paradigm for resolving weak, highly overlapping NIR absorption bands, thereby enabling high-reliability, low-cost C2H4 and C2H6 quantification in industrial gas monitoring.

ABSTRACT In recent years, relaxor ferroelectric single crystals (1‐x)Pb(Mg 1/3 Nb 2/3 )O 3 ‐xPbTiO 3 (PMN‐xPT) have been widely investigated and attracted attention due to their excellent piezoelectric and electromechanical properties. Yet, their internal microdomain structure results in low transmittance, which limits their application in optical field. In this paper, 1% mol Sm‐doped 0.7Pb(Mg 1/3 Nb 2/3 )‐0.3PbTiO 3 (Sm‐PMN‐30PT) crystals were successfully grown by a modified Bridgman technique. Sm 3 + induces nanoscale structural disorder in the crystal, significantly enhancing contribution of polar nanoregions (PNRs) to macroscopic properties. Piezoelectric, ferroelectric, and electro‐optic performances were enhanced. Electromechanical coupling coefficients k 33 and k t reach 66% and 48%, respectively. Piezoelectric coefficient d 33 value of Sm‐PMN‐30PT crystal is 5800–6100 pC/N with 55 Hz test frequency. After poled along [110] direction, transmittance along [001] direction reaches 56%. Effective electro‐optic coefficient γ c is 240 pm/V at room temperature, and it can reach 1293 pm/V near the Curie temperature (109°C). These results show that Sm‐PMN‐30PT single crystals could be ideal materials for piezoelectric and electro‐optic devices.

The advancement of solid-state nonlinear optical limiting (NOL) materials plays a crucial role in improving the practical applications of optical limiting technology. In this paper, we use a simple physical blending method to prepare what is, to our knowledge, a new solid-state NOL material: a reduced graphene oxide (rGO)/methyl red (MR) co-doped epoxy resin (rGO/MR-ER) film, which can be used to achieve excellent NOL effects. The optical limiting properties of rGO/MR-ER films were investigated under a fixed MR concentration of 1.07 mg/mL and varying rGO doping concentrations (0.0071, 0.0143, and 0.0214 mg/mL). The sample with an rGO concentration of 0.0071 mg/mL exhibits the strongest NOL effect, with a linear transmittance of up to 70.5% and a minimum transmittance of 39.1%. The nonlinear absorption coefficient, nonlinear refractive index, and third-order nonlinear optical susceptibility at a wavelength of 1064 nm are measured by Z-scan experiments. The results of the Z-scan experiments show that the rGO/MR-ER film has a large nonlinear absorption coefficient (6.41 ± 0.49 × 10-8 m/W). The rGO/MR-ER films exhibit other outstanding characteristics, including ease of fabrication and environmental friendliness. The proposed rGO/MR-ER film could be an excellent NOL material for optical limiting.

The fluorescence intensity ratio (FIR) technique has emerged as a pivotal approach in non-contact optical thermometry, offering substantial application potential. In this study, Y3Al5O12 (YAG) phosphors co-activated with Ce3+ and Cr3+ ions were successfully synthesized through a high-temperature solid-state reaction method. Spectroscopic analysis revealed efficient energy transfer between the dopant ions, manifesting as distinct luminescence intensity variations compared to their single-doped counterparts. Under 450 nm excitation, the system demonstrates prominently yellow-green emission from Ce3+ ions and well-resolved red emission from Cr3+ ions, ensuring excellent spectral discrimination. Capitalizing on the differential thermal response between the two luminescent centers, the developed system achieves remarkable temperature sensing performance. The FIR method yields a maximum relative sensitivity of 0.845 % K-1, maintaining sensitivity above 0.6 % K-1 throughout the 340-580 K range, coupled with exceptional temperature resolution below 0.03 K. Furthermore, we have engineered a novel FIR thermometry system incorporating 3D-printed spectral modules and fiber-optic phosphor encapsulation. The integrated system demonstrates superior sensing capabilities, reaching sensitivity values of 1.23 % K-1 in Cr3+ lifetime mode and 4.64 % K-1 in FIR mode. These results indicate that Ce/Cr codoped YAG has exceptional potential in multimodal optical thermometry applications.

A dual-frequency broadband metasurface capable of generating four circularly polarized vortex beams with independently control of the topological charge and deflection direction is proposed. The broadband unit based top and bottom layer of the designed metasurface generate the vortex beams in the Ku band (10-20 GHz) and the Ka band (26-30 GHz), respectively. A custom-designed frequency selection surface is inserted to minimize the mutual interference. The far-field measurement experimental results confirm that the designed metasurface generates four vortex beams with the deflection directions of θL = -40°, θR = 20° and θL = -40°, θR = 30°across the broad bandwidth in the Ku and Ka band, respectively.

Significance:Interproximal caries detection is critical for effective dental treatment. We report an ultrathin lensed fiber-based manual scanning optical coherence tomography (OCT) needle probe to enables the direct imaging of the interproximal caries between two adjacent teeth. Aim:We aim to design and fabricate the ultrathin lensed fiber-based manual scanning OCT needle probe, and validate the performance of the proposed probe by applying it to the imaging of the phantom sample, the human skin tissue and the interproximal caries between two adjacent teeth. Approach:A homemade lensed fiber is packaged into a 21-gauge hypodermic needle to create a high-flexibility, ultrathin probe. A decorrelation algorithm is employed for image reconstruction based on manual scanning. The performances of the developed needle probe are experimentally measured. The probe is incorporated in a swept-source OCT system to image the phantom sample, the human skin tissue, and the interproximal caries between two adjacent teeth. Results:The working distance and focused spot diameter of the developed probe are measured to be 1.22 mm and 18.78    μ m , respectively. The correctly reconstructed OCT images of the phantom, skin tissue, and the tooth tissue demonstrate the performance of the developed ultrathin lensed fiber-based manual scanning OCT needle probe. The distinct structural difference between the healthy and abnormal teeth tissue validates the efficacy of the proposed method. Conclusion:We propose an ultrathin lensed fiber-based manual scanning OCT needle probe potentially useful for the interproximal caries detection. The design, fabrication, and performances of the developed needle probe are demonstrated. We address a critical issue in the caries diagnostics and offer a promising tool for the future clinical applications.

Thulium-doped zinc tungstate (ZnWO4: Tm) crystal is an important functional material, which has potential applications in the field of laser technology. However, the third-order nonlinear optical behavior and nonlinear optical limiting (NOL) properties of ZnWO4: Tm crystal have rarely been investigated. In this study, we have successfully grown ZnWO4 crystal doped with Tm3+ using the Czochralski method. We have measured the absorption, Raman, and X-ray diffraction spectra of the crystal, with absorption peaks corresponding to the energy transitions of Tm3+. Utilizing Z-scan technique at the wavelength of 1064 nm, we have determined the nonlinear absorption coefficients arising from two-photon absorption, the nonlinear refraction coefficients stemming from electronic Kerr effect, and the third-order nonlinear coefficients for the crystal. Furthermore, we have evaluated the NOL performance of the crystal by measuring its transmittance at three different thicknesses of 2, 4, and 6 mm. At the thickness of 6 mm, the crystal exhibits a maximum transmittance of 89.1% at low input fluence and a minimum transmittance of 54.2% at high input fluence. These experimental results suggest that the novel ZnWO4: Tm crystal holds potential as a promising new material for NOL at 1064 nm.

In this paper, a new method for temperature and refractive index (RI) simultaneous measurement by using the linewidths of forward Brillouin scattering (FBS) induced by torsional-radial acoustic modes (TR2,m) in optical fiber is proposed. The FBS induced by TR2,m with strong signal is detected by a new single-end reflective structure. We propose to measure temperature and RI simultaneously with high accuracy by using linewidths of two peaks of FBS corresponding to two TR2,m. In the proof-of-concept experiment, a thin polyimide-coated G657 fiber is used as sensing fiber, in which the thin coating not only provides high sensing sensitivity, but also achieves high mechanical strength. The experimental results show that the sensor has high temperature and RI measurement accuracy of 0.17 degrees C and 0.0005, respectively. The sensor with such new detection method, new detection structure and new sensing fiber possesses the benefits of high accuracy, high mechanical strength, and simplicity, which has many potential applications in the field of biomedicine and marine monitoring.

As a two-dimensional material at the nanoscale, optical metasurfaces have excellent and flexible optical field control methods. In particular, the application of the concept of bound states in the continuum (BIC) enables optical metasurfaces to achieve resonance effects with high quality factors (Q factor). In comparison to plasmonic metasurfaces, all dielectric metasurfaces can effectively reduce the Ohmic losses in the structure. In this study, we propose a q-BIC metasurface with a high quality factor (maximum Q factor of 247), which is all dielectric and symmetry-breaking, and investigate the enhancement effect of this structure on optical chirality in the near-infrared band. In the simulation and experiment, the transmission spectra of the structure in the near-infrared band exhibited differences at different light source incidence angles when illuminated with circularly polarised light of varying rotation directions (external chirality). The maximum far-field circular dichroism (CD) achieved was 0.17 in the simulation and 0.038 in the experiment. Subsequently, the near-field chirality enhancement of the structure was investigated, which has the potential to increase the optical chirality of the incident light by up to 22 times. Furthermore, the introduction of a chiral medium to a non-chiral metasurface results in a chiral transfer effect, enabling the achievement of circular dichroism beyond the intrinsic capabilities of the individual substances involved (maximum CD = 0.0055). The high-Q factor of the all-dielectric metasurface paves the way for a plenty of potential applications in optical chiral fields, including chiral sensing, ultra-sensitive analysis of biomaterials and soft matter.

Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) single crystal has been applied in many fields due to its excellent piezoelectric properties, but the optical properties remains to be explored. Here, the rhombohedral phase PMN-0.15 PT and 1 % Sm doped PMN-0.15 PT single crystal (Sm-PMN-0.15 PT) were grown by the Bridgman method. The crystal structure was investigated by X-ray diffraction, HRTEM, Raman spectra and second harmonic generation (SHG) microscopy. Combined with the characterization of dielectric, ferroelectric and electro-optic effects, we revealed the dynamic response of polar nanoregions (PNR) and phase transition to the electro-optic properties of crystals. The results demonstrate that the doping of Sm3+ ions can effectively reduce the Curie temperature (Tm) from 57 degrees C to 38 degrees C while maintaining high dielectric response characteristics. The Kerr electro-optic coefficient of PMN-0.15 PT and Sm-PMN-0.15 PT can reach 2.55 x 10-16 m2/V2 at 48 degrees C and 3.40 x 10-16 m2/V2 around 38 degrees C respectively. Due to the influence of PNR, the peak value of the Kerr electro-optical coefficient measured in the cooling process is higher than that measured in the heating process. The Sm-PMN-0.15 PT has a wide operating temperature range close to room temperature and stable response of frequency, rendering it promising candidate for application in electro-optic devices.

In this study, a novel temperature and axial strain simultaneous measurement method based on forward-Brillouinscattering (FBS) direct detection structure is proposed and verified by experiments. The sensing mechanism exploits acoustooptic interactions that generate transverse acoustic waves through torsional-radial acoustic modes, which exhibit strong FBS signals and narrow spectral linewidths. By using the distinct temperature and axial strain dependencies of the FBS resonance peaks, two such modes are selected from the spectrum to form a sensitivity matrix, enabling decoupled dual-parameter measurement. Comparative experiments demonstrate that the proposed direct-detection scheme achieves superior measurement accuracy over the conventional Sagnac loop (SL) configuration, alongside a significantly simplified optical architecture. Experimental results validate the high performance of the system, achieving measurement uncertainties as low as 0.11 C-degrees in temperature and 11 mu epsilon in axial strain, derived from frequency shifts of the selected torsional-radial acoustic modes. The FBS direct detection structure, designed for simultaneous measurement of temperature and axial strain, holds broad application prospects in fields such as mechanical engineering, aerospace engineering, civil engineering, and environmental monitoring.