Search Results (117)

This research presents a novel square-shaped photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor, designed using the external metal deposition (EMD) technique, for highly sensitive refractive index (RI) sensing applications. The proposed sensor operates effectively over an RI range of 1.33 to 1.37 and supports both x- polarized and y-polarized modes. It achieves a wavelength sensitivity of 15,800 nm/RIU and 14,300 nm/RIU, and amplitude sensitivities of 11,584 RIU⁻¹ and 11,007 RIU⁻¹, respectively, for the x-pol. and y-pol. The sensor also reports a resolution in the order of 10⁻⁶ RIU and a strong linearity of R² ≈ 0.97 for both polarization modes, indicating its potential for precision detection in complex sensing environments. Beyond the sensor’s structural and performance innovations, this work also explores the future integration of artificial intelligence (AI) into PCF-SPR sensor design. AI techniques such as machine learning and deep learning offer new pathways for sensor calibration, material optimization, and real-time adaptability, significantly enhancing sensor performance and reliability. The convergence of AI with photonic sensing not only opens doors to smart, self-calibrating platforms but also establishes a foundation for next-generation sensors capable of operating in dynamic and remote applications. Full article

This study proposes the development of a dual-wavelength optical fiber sensor (DWOFS) that integrates two optical fiber structures in a multimode transmission line to measure the refractive index and temperature of a liquid concurrently. One structure is based on a refractive index sensor that utilizes surface plasmon resonance, comprising a 5 mm long single-mode fiber (SMF) section coated with chromium/gold (Cr/Au) films. The secondary structure employs a multimode interferometer with a 29 mm long no-core fiber (NCF) section covered with a thick layer of polydimethylsiloxane (PDMS) to measure temperature. The measurements obtained reveal two distinct drops in the transmission spectrum at approximately 600 nm and 1550 nm, respectively, enabling precise measurement of the two parameters. The sensor demonstrates a high degree of sensitivity to both refractive index and temperature, spanning the visible ($2770.30\mathrm{n}\mathrm{m}/\mathrm{R}\mathrm{I}\mathrm{U}$) and infrared $(-0.178\mathrm{n}\mathrm{m}/°\mathrm{C}$) regions of the spectra, respectively. Furthermore, the thermo-optical coefficient for water $({-0.9928\times 10}^{-4}\mathrm{R}\mathrm{I}\mathrm{U}/°\mathrm{C})$ was estimated. The proposed sensor offers a compact solution for the simultaneous measurement of refractive index and temperature in liquid samples for a variety of applications, including biological, environmental, and healthcare research. Full article

This paper focuses on the mathematical and numerical modeling of a non-classical macro fiber composite (MFC) piezoelectric transducer, MFC-P2, integrated with an aluminum cantilever beam for energy harvesting applications. It seeks to harness the transverse vibration energy in the environment to power small electronic devices, such as wireless sensors, where conventional power sources are inconvenient. The P2-type macro fiber composites (MFC-P2) are specifically designed for transverse energy harvesting applications. They offer high electric source capacitance and improved electric charge generation due to the strain developed perpendicularly to the voltage produced. The system is modeled analytically using Euler–Bernoulli beam theory and piezoelectric constitutive equations, capturing the electromechanical coupling in the d31 mode. Numerical simulations are conducted using COMSOL Multiphysics 6.29 to reduce the complexity of the mathematical model and analyze the effects of material properties, geometric configurations, and excitation conditions. The theoretical model is based on the transverse vibrations of a cantilevered beam using Euler–Bernoulli theory. The natural frequencies and mode shapes for the first four are determined. Depending on these, the resonance frequency, voltage, and power outputs are evaluated across a 12 kΩ resistive load. The results demonstrate that the energy harvester effectively operates near its fundamental resonant frequency of 10.78 Hz, achieving the highest output voltage of approximately 0.1952 V and a maximum power output of 0.0031 mW. The generated power is sufficient to drive ultra-low-power devices, validating the viability of MFC-based cantilever structures for autonomous energy harvesting systems. The application of piezoelectric phenomena and obtaining electrical energy from mechanical vibrations can be powerful solutions in such systems. The application of piezoelectric phenomena to convert mechanical vibrations into electrical energy presents a promising solution for self-powered mechatronic systems, enabling energy autonomy in embedded sensors, as well as being used for structural health monitoring applications. Full article

This study innovatively presents a hollow-core anti-resonant fiber integrating double-tube nesting and a single-layer anti-resonant wall. Featuring an exclusive two-layer cladding configuration along with an outer cladding circular ring, it differs significantly from traditional fibers. After careful parameter optimization, at 1.55 μm wavelength, the fiber shows excellent performance. Its confinement loss drops to 0.00088 dB/km, 1–2 orders lower than traditional ones. The proportion between the loss of the lowest higher-order mode and that of the fundamental mode reaches 19,900, indicating excellent single-mode performance. In the case of a bending radius of 11–14.2 cm, the x-polarization loss is below 0.001 dB/km, showing good bending resistance. Through structural comparisons, this paper quantitatively reveals the effects of the anti-resonant wall, cladding tube, and outer cladding ring on fiber performance. From the practical fiber-drawing process, it thoroughly analyzes the impact of the outer connecting tube’s offset angle on fiber performance. This research provides crucial theoretical support for new hollow-core fiber design, manufacture, and application, and is expected to drive technological innovation in this field. Full article

The increasing demand for high-precision, real-time sensing in various fields has spurred the development of optical fiber grating sensors (OFGSs). This study reviews the research field of OFGSs, exploring their historical development, current trends, and future opportunities through scientometric analysis utilizing CiteSpace. The research landscape has grown exponentially since the early studies on fiber Bragg gratings and long-period fiber gratings in the 1990s. Bibliometric data reveal that engineering, optics, and instrumentation dominate OFGS research, with emerging interdisciplinary applications in environmental, biological, and medical sensing. Key contributors have advanced OFGSs through femtosecond laser inscription, novel materials, and intelligent system integration, as reflected in co-citation and keywords analyses. Trends such as AI-driven optimization, surface plasmon resonance, and 3D printing signal shift toward adaptive, multifunctional sensing systems capable of addressing diverse challenges. This review also maps the evolution of OFGS research, transitioning from foundational strain and temperature sensing to sophisticated systems for structural health monitoring, biomedical diagnostics, and robotics. Despite global disruptions, the field’s recovery highlights its critical role in advancing sensing technologies. By combining thematic insights from co-citation and keyword analyses, this study identifies both established directions and transformative opportunities, providing a holistic understanding of OFGS research and its trajectory. Full article

Ultrafast fiber lasers have shown exceptional performance across various domains, including material processing, medical applications, and optoelectronic communication. The semiconductor saturable absorber mirror (SESAM) is a key enabler of ultrafast laser operation. However, the narrow wavelength range and limited modulation depth of conventional SESAMs pose challenges to further advancing ultrafast fiber laser technology. To address these limitations, we explored the integration of guided mode resonance (GMR) effects to enhance light–matter interaction within the absorption layer. By incorporating subwavelength dielectric film gratings onto the cap layer of SESAMs, we excited GMR and formed a microcavity structure in conjunction with the distributed Bragg mirror (DBR). This design significantly improved the absorption efficiency of InAs quantum dots. The experimental results demonstrate that the modulation depth of the SESAM increased from 6.7% to 17.3%, while the pulse width was reduced by 2.41 times. These improvements facilitated the realization of a high-quality, stable ultrafast fiber laser. This study not only broadens the application potential of ultrafast lasers in diverse fields but also offers a practical pathway for advancing SESAM technology toward industrial-scale deployment. Full article

Optoelectronic oscillators (OEOs) have emerged as indispensable tools for generating low-phase-noise microwave and millimeter-wave signals, which are critical for a variety of high-performance applications. These include radar systems, satellite links, electronic warfare, and advanced instrumentation. The ability of OEOs to produce signals with exceptionally low phase noise makes them ideal for scenarios demanding high signal purity and stability. In radar systems, low-phase-noise signals enhance target detection accuracy and resolution, while, in communication networks, such signals enable higher data throughput and improved signal integrity over extended distances. Furthermore, OEOs play a pivotal role in precision instrumentation, where even minor noise can compromise the performance of sensitive equipment. This review examines the progress in OEO technology, transitioning from classical designs relying on long optical fiber delay lines to modern integrated systems that leverage photonic integration for compact, efficient, and tunable solutions. Key advancements, including classical setups, hybrid designs, and integrated configurations, are discussed, with a focus on their performance improvements in phase noise, side-mode suppression ratio (SMSR), and frequency tunability. A 20-GHz oscillation with an SMSR as high as 70 dB has been achieved using a classical dual-loop configuration. A 9.867-GHz frequency with a phase noise of −142.5 dBc/Hz @ 10 kHz offset has also been generated in a parity–time-symmetric OEO. Additionally, integrated OEOs based on silicon photonic microring resonators have achieved an ultra-wideband tunable frequency from 3 GHz to 42.5 GHz, with phase noise as low as −93 dBc/Hz at a 10 kHz offset. The challenges in achieving fully integrated OEOs, particularly concerning the stability and phase noise at higher frequencies, are also explored. This paper provides a comprehensive overview of the state of the art in OEO technology, highlighting future directions and potential applications. Full article

Background: This review evaluates needle navigation technologies in minimally invasive cardiovascular surgery (MICS), identifying their strengths and limitations and the requirements for an ideal needle navigation system that features optimal guidance and easy adoption in clinical practice. Methods: A systematic search of PubMed, Web of Science, and IEEE databases up until June 2024 identified original studies on needle navigation in MICS. Eligible studies were those published within the past decade and that performed MICS requiring needle navigation technologies in adult patients. Animal studies, case reports, clinical trials, or laboratory experiments were excluded to focus on actively deployed techniques in clinical practice. Extracted data included the study year, modalities used, procedures performed, and the reported strengths and limitations, from which the requirements for an optimal needle navigation system were derived. Results: Of 36 eligible articles, 21 used ultrasound (US) for real-time imaging despite depth and needle visibility challenges. Computer tomography (CT)-guided fluoroscopy, cited in 19 articles, enhanced deep structure visualization but involved radiation risks. Magnetic resonance imaging (MRI), though excellent for soft-tissue contrast, was not used due to metallic tool incompatibility. Multimodal techniques, like US–fluoroscopy fusion, improved accuracy but added cost and workflow complexity. No single technology meets all the criteria for an ideal needle navigation system, which should combine real-time imaging, 3D spatial awareness, and tissue integrity feedback while being cost-effective and easily integrated into existing workflows. Conclusions: This review derived the criteria and obstacles an ideal needle navigation system must address before its clinical adoption, along with novel technological approaches that show potential to overcome those challenges. For instance, fusion technologies overlay information from multiple visual approaches within a single interface to overcome individual limitations. Additionally, emerging diagnostic methods like vibroacoustic sensing or optical fiber needles offer information from complementary sensory channels, augmenting visual approaches with insights into tissue integrity and structure, thereby paving the way for enhanced needle navigation systems in MICS. Full article

With the rapid advancement of information technology, the data demands in transmission rates, processing speed, and storage capacity have been increasing significantly. However, silicon electro-optic modulators, characterized by their weak electro-optic effect, struggle to balance modulation efficiency and bandwidth. To overcome this limitation, we propose an electro-optic modulator based on an all-fiber micro-ring resonator and a p-Si/n-ITO heterojunction, achieving high modulation efficiency and large bandwidth. ITO is introduced in this design, which exhibits an ε-near-zero (ENZ) effect in the communication band. The real and imaginary parts of the refractive index of ITO undergo significant changes in response to variations in carrier concentration induced by the reverse bias voltage, thereby enabling efficient electro-optic modulation. Additionally, the design of the all-fiber micro-ring eliminates coupling losses associated with spatial optical-waveguide coupling, thereby resolving the high insertion loss of silicon waveguide modulators and the challenges of integrating MZI modulation structures. The results demonstrate that this modulator can achieve significant phase shifts at low voltages, with a modulation efficiency of up to 3.08 nm/V and a bandwidth reaching 82.04 GHz, indicating its potential for high-speed optical chip applications. Full article

Ramie is a valuable natural fiber resource. The fabric made of ramie fiber has distinctive natural characteristics, and its products are widely favored in the international market. Because the cellulose fiber in ramie is closely adhered by a viscous material composed of pectin, hemicellulose, and lignin, mechanical stripping and processing is needed to obtain primary ramie fiber for downstream use. To address the production challenges posed by high labor intensity and the scarcity of small, direct-feeding ramie decorticators in hilly and mountainous regions, this study designed and optimized a spiral ramie decortication component that integrated functions of ramie stalk crushing, xylem removal, outer shell scraping, and phloem separating and throwing. The three-dimensional model of the ramie stripping component was crafted with SolidWorks software, and subsequent modal analysis and dynamic simulation studies were conducted using Abaqus software. The Box–Behnken experimental design method was used to construct a mathematical model describing the effects of the decorticating drum rotation speed and the decorticating gap on the fiber percentage of fresh stalk, and the optimal operating parameters were determined accordingly. The research findings indicated that the component’s initial ten natural frequencies span from 234.41 to 431.70 Hz, which do not overlap with the external excitation frequencies, thus ensuring that no resonance phenomenon occurs during the operation process, meeting the design requirements for the ramie decortication operation. Under dynamic load conditions, the ramie decorticator can efficiently perform the task of ramie fiber decortication, and the stress and strain experienced by the device meet the established design specifications; by optimizing operating parameters, the optimal operating conditions were determined to be the speed of feeding and crushing parts (SFCP) of 100 r/min, the speed of separating and throwing parts (SSTP) of 400 r/min, the gap of feeding and crushing parts (GFCP) of 8 mm, and the gap of separating and throwing parts (GSTP) of 0 mm. Experimental results indicated that under this optimal parameter combination, the fiber percentage of fresh stalk of the spiral ramie decorticator can reach 5.03%, with a relative error of less than 3% compared to the theoretical model prediction value, thus confirming the accuracy of the model prediction. This study establishes a robust technical basis for the development of a convenient decortication technology for ramie fibers. However, this technique is more suitable for small growers, especially in hilly areas, to achieve large-scale applications, schemes must be reevaluated based on production efficiency. Full article

Magnetic resonance imaging (MRI) currently serves as the primary diagnostic method for glioma detection and monitoring. The integration of neurosurgery, radiation therapy, pathology, and radiology in a multi-disciplinary approach has significantly advanced its diagnosis and treatment. However, the prognosis remains unfavorable due to treatment resistance, inconsistent response rates, and high recurrence rates after surgery. These factors are closely associated with the complex molecular characteristics of the tumors, the internal heterogeneity, and the relevant external microenvironment. The complete removal of gliomas presents challenges due to their infiltrative growth pattern along the white matter fibers and perivascular space. Therefore, it is crucial to comprehensively understand the molecular features of gliomas and analyze the internal tumor heterogeneity in order to accurately characterize and quantify the tumor invasion range. The multi-parameter quantitative MRI technique provides an opportunity to investigate the microenvironment and aggressiveness of glioma tumors at the cellular, blood perfusion, and cerebrovascular response levels. Therefore, this review examines the current applications of advanced multi-parameter quantitative MRI in glioma research and explores the prospects for future development. Full article

In this paper, a highly sensitive methane (CH₄) sensor based on light-induced thermoelastic spectroscopy (LITES) and a T-shaped quartz tuning fork (QTF) with hydrogen (H₂) and helium (He) enhancement techniques are reported for the first time. The low resonant frequency self-designed T-shaped QTF was exploited for improving the energy accumulation time. H₂ and He were utilized as surrounding gases for the T-shaped QTF to minimize energy loss, thereby enhancing the sensitivity of the LITES sensor. Additionally, a fiber-coupled multi-pass cell (FC-MPC) with a 40 m optical length was utilized to improve the optical absorption of CH₄. The frequency response of the T-shaped QTF with different concentrations of H₂ and He was investigated, and the Q factor in the H₂ and He environment increased significantly. Compared to operating QTF in a nitrogen (N₂) environment, the signal amplitude was enhanced by 2.9 times and 1.9 times in pure H₂ and He environments, respectively. This enhancement corresponded to a minimum detection limit (MDL) of 80.3 ppb and 113.6 ppb. Under different CH₄ concentrations, the T-shaped QTF-based H₂-enhanced CH₄-LITES sensor showed an excellent linear response. Furthermore, through Allan deviation analysis, the MDL of the T-shaped QTF-based H₂-enhanced CH₄-LITES can reach 38 ppb with an 800 s integration time. Full article

Polymer-based optical sensors represent a transformative advancement in biomedical diagnostics and monitoring due to their unique properties of flexibility, biocompatibility, and selective responsiveness. This review provides a comprehensive overview of polymer-based optical sensors, covering the fundamental operational principles, key insights of various polymer-based optical sensors, and the considerable impact of polymer integration on their functional capabilities. Primary attention is given to all-polymer optical fibers and polymer-coated optical fibers, emphasizing their significant role in “enabling” biomedical sensing applications. Unlike existing reviews focused on specific polymer types and optical sensor methods for biomedical use, this review highlights the substantial impact of polymers as functional materials and transducers in enhancing the performance and applicability of various biomedical optical sensing technologies. Various sensor configurations based on waveguides, luminescence, surface plasmon resonance, and diverse types of polymer optical fibers have been discussed, along with pertinent examples, in biomedical applications. This review highlights the use of biocompatible, hydrophilic, stimuli-responsive polymers and other such functional polymers that impart selectivity, sensitivity, and stability, improving interactions with biological parameters. Various fabrication techniques for polymer coatings are also explored, highlighting their advantages and disadvantages. Special emphasis is given to polymer-coated optical fiber sensors for biomedical catheters and guidewires. By synthesizing the latest research, this review aims to provide insights into polymer-based optical sensors’ current capabilities and future potential in improving diagnostic and therapeutic outcomes in the biomedical field. Full article

A method is developed to make an optical fiber that only transmits fully linearly polarized light and maintains the polarization state. The method for efficient ingesting laser into this fiber is also reported. Using an optical fiber with a prism head, we can compress a plane wave into the thin rectangular cross-section fiber, and the light intensity within the fiber is much larger than that of the incidence wave. Our finite-difference time-domain (FDTD) simulation results show that the compressed light in the fiber becomes fully polarized and maintains the polarization state, and can be well coupled out by the resonance rings. This method is suitable for developing highly efficient polarization-maintaining optical fibers in a much simpler way, for applications in photonic integrated circuits or optical sensors. Full article

A novel surface plasmon resonance (SPR) refractive index (RI) sensor based on the D-type dual-mode photonic crystal fiber (PCF) is proposed. The sensor employs a side-polished few-mode PCF that facilitates the transmission of the fundamental and second-order modes, with an integrated microfluidic channel positioned directly above the fiber core. This design minimizes the distance to the analyte and maximizes the interaction between the optical field and the analyte, thereby enhancing the SPR effect and resonance loss for improved sensing performance. Au-TiO₂ dual-layer material was coated on the surface of a microfluidic channel to enhance the penetration depth of the core evanescent field and tune the resonance wavelength to the near-infrared band, meeting the special needs of chemical and biomedical detection fields. The finite element method was utilized to systematically investigate the coupling characteristics between various modes and surface plasmon polariton (SPP) modes, as well as the impact of structural parameters on the sensor performance. The results indicate that the LP_{11b_y} mode exhibits greater wavelength sensitivity than the HE_{11_y} mode, with a maximum sensitivity of 33,000 nm/RIU and an average sensitivity of 8272.7 nm/RIU in the RI sensing range of 1.25–1.36, which is higher than the maximum sensitivity of 16,000 nm/RIU and average sensitivity of 5666.7 nm/RIU for the HE_{11b_y} mode. It is believed that the proposed PCF-SPR sensor features both high sensitivity and high resolution, which will become a critical device for wide RI detection in mid-infrared fields. Full article