Search Results (6,809)

This paper proposes and experimentally demonstrates a fiber ring laser (FRL) salinity sensing system based on a Sagnac loop (SL) formed by a tapered polarization-maintaining fiber (TPMF). The operating principle is that salinity modulates the birefringence of the polarization-maintaining fiber (PMF), causing a shift in the interference wavelength of the SL transmission spectrum, while the FRL narrows the optical spectrum and enhances the signal-to-noise ratio (SNR). In the experiment, the SL consists of a 20-cm-long PMF with a tapered waist diameter of 10.86 μm. Over the salinity range of 0‰ to 30‰, the sensitivity of the laser-based sensing system is 97 pm/‰, which agrees well with the 93 pm/‰ sensitivity obtained using a broadband light source (BBS), and the salinity exhibits a good linear relationship with the wavelength shift, with a coefficient of determination (R²) of 0.997. Meanwhile, the ring laser cavity improves the SNR of the sensing system from 22 dB to approximately 54 dB, and compresses the 3-dB bandwidth from 1.75 nm to 0.06 nm. Further adopting the support vector regression (SVR) algorithm for linear regression modeling of the spectral data, the results show that the mean absolute error (MAE) decreases from 0.50‰ to 0.04‰, the root mean square error (RMSE) decreases from 0.54‰ to 0.11‰, and R² reaches as high as 0.99988. To the best of our knowledge, this is the first work that combines salinity laser sensing with an artificial intelligence algorithm. The proposed sensor leverages the narrow linewidth and high SNR advantages of the FRL together with the high-precision linear fitting capability of the SVR algorithm, achieving significantly improved accuracy for salinity measurement compared to conventional spectral demodulation. Full article

Lithium niobate on insulator (LNOI) has emerged as a promising platform for compact, low-loss phase modulators. The extant LNOI studies evaluate device performance almost exclusively through the Pockels effect, treating piezoelectric–photoelastic strain and thermo-optic drift as decoupled channels. Crucially, both mechanisms directly perturb the phase bias of a fiber-optic gyroscope (FOG), rendering them indispensable in sensing-oriented design. This work establishes a unified multiphysics model of an X-cut TFLN ridge phase modulator that self-consistently couples the electro-optic, piezoelectric–photoelastic, thermo-optic, and pyroelectric channels. The contributions of the four mechanisms are quantitatively decomposed under realistic FOG operating conditions, and the slab thickness, ridge-top width, and electrode gap are systematically optimized to balance modulation efficiency against environmental robustness. The co-optimization of the ridge geometry and electrode gap design maintains the EO overlap factor near 0.55, while reducing the half-wave voltage requirement. This results in a half-wave voltage length of V_πL = 1.65 V·cm at a 4.4 μm electrode gap. The optimized geometry and electrode gap (4.4 μm) are essentially temperature-independent: extracted from the Pockels modulation slope, V_πL remains stable at ≈1.65 V·cm (push–pull single-pass; within ~0.3%) across 25~85 °C. Furthermore, an externally imposed substrate temperature rise of 60 K (the upper end of the 25~85 °C FOG operating range) induces a mode-field-weighted thermal residual corresponding to approximately 27% of the Pockels modulation depth at an applied voltage of 5 V. The present study demonstrates that the DC-coupled operation of TFLN sensor-grade modulators is viable across the full FOG temperature range, without dedicated active temperature stabilization, and the residual thermal-bias offset is absorbed by the FOG’s standard closed-loop servo electronics. The results of the study provide quantitative design guidelines for high-performance, environmentally stable TFLN phase modulators in compact FOG systems. Full article

The development of new technologies enabling rapid, frequent, and reagent-free monitoring of kidney function is recognized as being of paramount importance. In this work, mid-(MIR) and near-infrared (NIR) spectroscopy were compared for the prediction of key renal biomarkers—creatinine, urea and albumin—using 54 serum solutions mimicking the biochemical profiles of five stages of chronic kidney disease (CKD). MIR spectra were acquired in a high-throughput microplate platform after a simple dehydration step, while the NIR spectra were obtained directly from liquid serum using a fiber optic probe. After evaluating several spectral pre-processing methods and targeted spectral regions, excellent regression models (R² > 0.9 for the best models) were obtained for the three biomarkers. MIR provided highly accurate urea predictions, whereas optimized NIR sub-regions enabled excellent estimation of creatinine and albumin. Both MIR and NIR, associated with supervised classification methods, enabled us to successfully distinguish healthy from diseased profiles and to identify the diseases state with AUC > 0.93. These findings highlight the complementary value of MIR and NIR spectroscopy for kidney disease assessment and their potential integration into point-of-care diagnostic systems. Full article

In radio-over-fiber (RoF) links, optical single-sideband (OSSB) modulation is an effective method to mitigate power fading caused by chromatic dispersion. However, its low modulation efficiency leads to suboptimal link performance. To address this, we propose a tunable optical carrier-to-sideband ratio (OCSR) OSSB modulation scheme based on a dual-electrode Mach–Zehnder modulator (DEMZM) in a Sagnac loop. Firstly, by adjusting the OCSR, higher radio-frequency (RF) transmission efficiency can be achieved. The experimental results demonstrate that the proposed link provides a 6 dB improvement in received RF power compared to conventional SSB modulation schemes. Furthermore, this approach effectively optimizes nonlinear distortions in the link, achieving a 12.14 dB enhancement in spurious-free dynamic range (SFDR). For tests conducted with a broadband signal featuring a 15 GHz carrier frequency and 500 MHz bandwidth, the optimal error vector magnitude (EVM) reaches 4.88%. Additionally, the link performance can be flexibly improved by adjusting the polarization controller configurations for each channel, making it suitable for multi-user application scenarios. Full article

In this paper, a comprehensive investigation into the single-mode capability of curved sapphire fiber is performed, ranging from theoretical simulation to experimental verification. The equivalent refractive index theoretical model for curved sapphire fiber is proposed based on stress–optic effects and the conformal mapping technique. According to the finite element method, when the radius of curvature is 0.02 m, the curved losses’ difference between high-order modes and the fundamental mode is as high as five orders of magnitude, demonstrating the best single-mode potential. In addition, the curving experiments of sapphire fiber and sapphire fiber Bragg grating are completed. The transmission spectrum of the curved sapphire fiber with a curving radius of 0.02 m is the closest to that of the single-mode fiber. As for curved sapphire fiber Bragg grating (CSFBG), the 3 dB bandwidth of reflection spectrum with the same radius of curvature is also the smallest, with a value of 3.7 nm. Furthermore, the temperature performance of the proposed CSFBG is measured from 22 °C to 1600 °C. The sensitivity is 37.88 pm/°C (@1600 °C), and the measurement accuracy is ±2.98 °C. This study provides theoretical support for single-mode signal transmission of curved sapphire fibers and facilitates high-precision sensing applications under extreme high-temperature conditions. Full article

Although optical fiber-based surface plasmon resonance (SPR) sensors have revolutionized real-time, label-free biosensing, conventional designs suffer from limited multi-analyte detection capabilities. This study utilizes the novel Pi (π)-configured dual SPR optical fiber sensor with two opposing side-polished surfaces, enabling plasmonic excitation for simultaneous multi-analyte detection. The proposed sensor leverages asymmetric metallic thin films such as Ag, Au, Cu, and hybrid configurations (metal + TiO₂) to generate two distinct resonance peaks, significantly enhancing detection versatility. Numerical simulations using the finite element method in COMSOL Multiphysics v6.3 demonstrate that the π-configuration achieves dual resonance dips at 982 nm and 1276 nm for Ag and Ag–TiO₂ films, 1040 nm and 1317 nm for Au and Au–TiO₂ films, and 977 nm and 1249 nm for Cu and Cu–TiO₂ films, respectively, for an analyte refractive index of 1.42. A peak spectral separation >125 nm was achieved for all the sensors for a refractive index range of 1.37–1.42, ensuring that the two dips are resolvable since the change in SPR wavelength is greater than or equal to the full width at half maximum, preserving dual-analyte capability and minimizing potential crosstalk. The results indicate that the π-configured dual SPR sensor utilizing silver and silver–TiO₂ sensing layers had the highest wavelength sensitivity of 12,600 nmRIU⁻¹ and 20,000 nmRIU⁻¹, respectively, slightly outperforming its gold and copper counterpart. The optimized metallic and hybrid nanostructured films ensure dual distinct peaks with high sensitivity, while maximizing refractive index resolution. This work presents the design of a π-configured SPR-based optical fiber sensor utilizing dielectric and multi-metallic thin films, thereby offering a breakthrough in multiplexed biosensing for applications in medical diagnostics, environmental monitoring, and chemical detection. Full article

Background/Objectives: Optical coherence tomography (OCT) and OCT angiography (OCT-A) provide detailed measurements of retinal structure and vasculature; however, age-related differences in how these parameters correlate with one another remain poorly understood. We hypothesized that vascular–structural integration in the macula is more pronounced in adults than in children. Our aim was to characterize correlation patterns in pediatric and adult populations to inform the development of age-specific clinical interpretation guidelines. Methods: This prospective cross-sectional observational study enrolled 37 healthy children (age 1–17 years) and 28 healthy adults (age 18–65 years). Eyes with ocular or systemic conditions affecting the retina or prior intraocular surgery were excluded. Standardized OCT and OCT-A acquisition protocols provided structural and vascular measures. Univariable correlation analyses applied a stringent threshold (p < 0.001) to identify robust associations. Significant univariable results were entered into multivariable regression models adjusting for age, gender, intraocular pressure, and axial length. A Group-wise Linkage Proportion quantified the percentage of potential significant correlations among eight predefined anatomical parameter groups. Results: Ninety univariable correlations met p < 0.001. Fourteen correlations were shared across age groups, notably foveal avascular zone metrics and vessel density, showing very large negative correlations (r = −0.70 to −0.87). The pediatric cohort displayed 40 unique correlations, primarily linking optic nerve head flow indices to retinal nerve fiber layer thickness. Adults exhibited 36 unique correlations, dominated by macular vascular–thickness coupling concentrated in the parafoveal region. After multivariable adjustment, 52 of 90 associations remained significant. Adult-specific associations lost significance more frequently (58%) than pediatric-specific associations (43%), whereas correlations shared across both groups showed complete stability (100%). The Group-wise Linkage Proportion indicated pronounced macular vascular–structural coupling in adults (48.4%) versus near absence in children (1.2%). Conclusions: Retinal parameter correlation patterns show fundamental differences between pediatric and adult eyes. While optic nerve head-macular thickness relationships remain consistent across ages, adults exhibit mature, localized integration of macular vascular and structural parameters absent in children. These findings suggest that pediatric and adult OCT/OCT-A measurements may benefit from separate reference standards, although prospective validation is required before clinical implementation. Full article

We propose a time-delay signature suppressed broadband chaotic (TSBC) carrier generation scheme and theoretically investigate its performance in a dual-polarization bidirectional chaotic communication system based on synchronized vertical-cavity surface-emitting lasers (VCSELs). The TSBC scheme is implemented by combining fiber Bragg grating (FBG) feedback with an external electro-optic (EO) phase modulation loop to introduce synergistic nonlinear perturbations. The results demonstrate that the proposed TSBC scheme effectively suppresses the time-delay signature (TDS) to less than 0.03 while significantly enhancing the chaotic carrier bandwidth to over 23 GHz for each polarization channel. Meanwhile, high-quality chaotic synchronization can be achieved with laser parameter mismatches of approximately 30%. Finally, an aggregated 46 Gbit/s dual-polarization bidirectional chaotic transmission is demonstrated, which confirms the effectiveness and the potential of the TSBC dual-polarization bidirectional scheme for secure optical communication applications. Full article

Accurate pressure measurement under high-temperature conditions is challenging for silica-diaphragm-based fiber-optic Fabry–Perot (F-P) sensors because temperature causes both optical cavity length (OCL) baseline drift and pressure-sensitivity variation. In this work, a structurally simple and readily fabricated silica-diaphragm-based fiber-optic F-P pressure sensor was developed, and a neural-network-assisted compensation strategy was proposed to suppress the residual errors of conventional analytical compensation. A temperature-dependent response model was established to describe OCL drift and sensitivity variation. The OCL was demodulated from reflection spectra using an FFT-assisted dual-peak and MMSE refinement method, and static pressure measurements were performed over 25–400 °C and 0–2.4 MPa. Based on the experimentally verified response characteristics, a fitting-based compensation method considering both OCL drift and sensitivity variation was first implemented. A lightweight neural network was then constructed using the OCL variation, $\Delta \mathrm{O}\mathrm{C}\mathrm{L}$, and ambient temperature as physically meaningful input features. Compared with fixed-sensitivity compensation and drift-and-sensitivity fitting compensation, whose maximum full-scale errors were 7.10% F.S. and 2.74% F.S., respectively, the proposed method reduced the maximum error to 0.90% F.S. with an RMSE of 0.0045 MPa. Additional validation at the independent intermediate temperatures of 150, 250, and 350 °C further confirmed the generalization capability of the proposed NNC model between calibrated temperature gradients, achieving an overall RMSE of 0.0055 MPa and a maximum full-scale error below 0.77% F.S. The proposed approach provides a high-accuracy and practical solution for high-temperature pressure monitoring using simple fabricated silica-diaphragm F-P sensors. Full article

In this work, we propose a hyperbolic metamaterials (HMMs)-based coreless fiber surface plasmon resonance (SPR) sensor. Leveraging the absence of a core in coreless fibers, the evanescent waves at the cladding–external solution interface couple more effectively into the solution, enabling surface plasmon resonance without any additional processing. To enhance sensitivity, we adopted a multimode–coreless–multimode (MCM) structure and grew layered hyperbolic metamaterials as the SPR-excitation-sensitive layer within the coreless region. Through finite element simulations, we optimized HMM parameters and fabricated high-performance HMM-SPR sensors. Test results demonstrate that the fabricated HMM-SPR sensor achieves an optimal refractive index sensitivity of 3703.33 nm/RIU, representing a 49.68% improvement over single-layer gold film SPR sensors. It successfully detects glucose solutions at varying concentrations with a sensitivity of 2671.25 nm/RIU. The high-sensitivity, structurally simple HMM-SPR sensor we proposed demonstrates broad application prospects in biosensing, environmental monitoring, food safety, and other fields. Full article

Accurate state-of-charge (SOC) estimation is essential for the safe and efficient operation of lithium-ion batteries. However, the weak voltage observability of lithium iron phosphate (LFP) batteries within the voltage plateau region limits the accuracy of conventional voltage-based methods. To address this issue, an electro–mechanical information fusion framework for SOC estimation is proposed. Fiber Bragg grating (FBG) sensors were employed to simultaneously measure the surface strain and temperature of prismatic LFP batteries. Experimental results showed that the strain signal exhibited a stronger correlation with SOC than the voltage signal, with an average absolute correlation coefficient of 0.92. A Thevenin equivalent circuit model combined with an adaptive forgetting factor recursive least squares (AFFRLS) algorithm was established for online voltage modeling, while a Mamba-based strain model was developed to capture the nonlinear temporal relationship between multidimensional sensing data and battery strain. The two models were further integrated with adaptive unscented Kalman filters (AUKFs) and fused through a dual-layer adaptive weighting strategy. Experimental results under the five operating conditions considered in this study demonstrated that the proposed method achieved average RMSE and MAE values of 0.98% and 0.80%, respectively, outperforming standalone voltage- and strain-based methods. Full article

Background: Hydroxychloroquine (HCQ) is widely used in systemic lupus erythematosus (SLE), yet cumulative exposure may result in progressive retinal toxicity. Structural biomarkers capable of identifying subclinical damage remain incompletely defined. Methods: In this cross-sectional controlled study, 60 female SLE patients receiving HCQ for ≥5 years (22 with clinically detectable maculopathy and 38 without) and 30 healthy controls underwent a comprehensive ophthalmologic assessment including spectral-domain optical coherence tomography (SD-OCT). Peripapillary retinal nerve fiber layer (RNFL) and macular thickness parameters were analyzed. Logistic regression and ROC analysis evaluated exposure-related risk. Results: Patients with clinically detectable maculopathy demonstrated significant superior and temporal RNFL thinning compared with patients with clinically undetectable maculopathy and controls (p ≤ 0.021). Inferior quadrant thinning was detectable in patients without ophthalmoscopic changes, suggesting subclinical neuroaxonal involvement. Parafoveal macular thinning was observed exclusively in the clinically detectable maculopathy group (p = 0.041). Cumulative dose >1000 g independently predicted toxicity (OR 3.84; 95% CI 1.72–8.56). The combined structural–exposure model demonstrated strong discrimination (AUC 0.89). Conclusions: HCQ-related retinal structural changes may be detectable on OCT in the absence of clinically apparent retinal findings. Our results support the concept of a dose-associated structural continuum in HCQ-related retinal injury, involving both inner retinal neuroaxonal parameters and parafoveal macular alterations. However, the cross-sectional design does not allow determination of the temporal sequence of inner versus outer retinal changes. Further longitudinal studies with combined inner and outer retinal layer-specific analysis are required before these findings can inform modifications to current screening strategies. Full article

In this study, we present a thermal-aware design of a compact hybrid plasmonic grating (HPG) TE-pass polarizer on X-cut lithium niobate on insulator (LNOI) for fiber-optic gyroscopes (FOGs). In a three-dimensional simulation, the optimization of the trapezoidal sidewall angle (θ = 78°) and the thickness of the Ag grating (13 nm) yield a polarization extinction ratio of 36.2 dB at 1550 nm (with a peak of 41.4 dB at 1548 nm) within a sub-10 μm grating length. This represents a ~3–8 dB improvement over prior LNOI HPG polarizers at the same footprint. A multiphysics thermo-optic analysis over the wide industrial FOG envelope (from −45 to +85 °C) demonstrates that the operating-wavelength polarization extinction ratio remains within the range of 24.7–36.2 dB across the entire 130 K span (worst case 24.7 dB at −25 °C), constrained solely by a modest 10 pm/K Bragg detuning stemming from the pronounced (~5) thermo-optic anisotropy of LN. The insertion loss exhibits a negligible drift of merely 0.73 dB. A fabrication tolerance study identified the Ag thickness as the predominant budgetary constraint (±1 nm tolerance, PER dropping ~10 dB at the resonance edge), while the ridge width and oxide buffer demonstrated comparatively greater flexibility. The device, therefore, fulfills the criteria for FOG-grade polarization suppression across most of the operational temperature range. The −25 °C point is established at the 25 dB threshold, thereby providing concrete design guidelines for ensuring environmentally stable on-chip polarization control on LNOI. Full article

Tellurene has a wide bandwidth and low propagation loss at near-infrared wavelengths due to its nonlinear absorption coefficient. Therefore, we prepared tellurene–polyvinyl alcohol (Te-PVA) film as a saturable absorber in an Er-doped fiber laser by liquid phase exfoliation and spin-coating. The modulation depth was 5.25% and the saturation intensity was 17.02 MW/cm. The nonlinear optical properties of the film and its application in high-stability mode-locked operation were studied. A mode-locked pulse with a fundamental frequency of 8.48 MHz and a central wavelength of 1560.10 nm was obtained, with a signal-to-noise ratio which was greater than 75 dB. A traditional soliton mode-locked operation with a pulse width of 1.41 ps was achieved. In addition, eighth- and 19^th-harmonic mode-locked operations were obtained by adjusting the pump power and polarization controller. Our results show that Te-PVA film functioned as a saturable absorber which enabled harmonic mode-locking with an SNR of 75 dB in an Er-doped fiber laser. It is thus an excellent ultra-fast photonics material. Full article

We demonstrate a mechanism-oriented Surface-Enhanced Raman Scattering (SERS) platform based on a hybrid structure integrating monolayer molybdenum disulfide (MoS₂) and gold nanospheres (AuNSs) on an optical microfiber (MF). The microfiber serves as a whispering-gallery-mode (WGM) microcavity. Monolayer MoS₂, grown directly on the microfiber surface via chemical vapor deposition (CVD), provides a chemically active interface for molecular adsorption and charge-transfer-related chemical enhancement. Subsequently deposited AuNSs couple with the microfiber-supported WGM, leading to the formation of hybrid photonic–plasmonic modes. This coupling results in a narrowed scattering resonance and a localized electromagnetic hotspot near the AuNS–microfiber interface. The combined contribution of electromagnetic enhancement from the microfiber–AuNS hybrid cavity and chemical enhancement from the MoS₂ layer produces discernible Raman enhancement for Rhodamine 6G (R6G) molecules under proof-of-concept measurement conditions. This work provides a useful platform for studying SERS enhancement mediated by hybrid photonic–plasmonic modes and offers guidance for the future development of optimized fiber-based SERS sensors. Full article