Search Results (179)

With the continuous advancement of optical fiber micromachining technology, C-type optical fibers have demonstrated significant potential in the field of optical fiber sensing. By partially or completely removing specific regions of the cladding, a “leakage window” is created, enabling interaction between the optical field and external substances. This structure has facilitated the development of various sensors. This paper reviews recent progress in the research and applications of C-type optical fibers in optical sensing. Based on sensing principles and application scenarios, C-type optical fiber sensors can be categorized into two main types: interferometric and photonic crystal types. This article discusses the fundamental operating principles and structural characteristics of each type, and provides a detailed comparison of their respective advantages and disadvantages. Studies have shown that sensors based on C-type fiber structures offer notable benefits such as simple fabrication, excellent mechanical performance, strong anti-interference capability, and high sensitivity. Therefore, they hold great promise for applications in intelligent monitoring, environmental detection, and healthcare. Finally, this review outlines future research directions for C-type fiber sensors. As technology continues to evolve, future studies are expected to focus on improving sensor stability, expanding application scenarios, and addressing challenges in current fabrication techniques. Full article

This article presents a comprehensive overview of recent advancements in photonic crystal fiber (PCF)-based sensors, with a particular focus on the surface plasmon resonance (SPR) phenomenon for biosensing. With their ability to modify core and cladding structures, PCFs offer exceptional control over light guidance, dispersion management, and light confinement, making them highly suitable for applications in refractive index (RI) sensing, biomedical imaging, and nonlinear optical phenomena such as fiber tapering and supercontinuum generation. SPR is a highly sensitive optical phenomenon, which is widely integrated with PCFs to enhance detection performance through strong plasmonic interactions at metal–dielectric interfaces. The combination of PCF and SPR technologies has led to the development of innovative sensor geometries, including D-shaped fibers, slotted-air-hole structures, and internal external metal coatings, each optimized for specific sensing goals. These PCF-SPR-based sensors have shown promising results in detecting biomolecular targets such as excess cholesterol, glucose, cancer cells, DNA, and proteins. Furthermore, this review provides an in-depth analysis of key design parameters, plasmonic materials, and sensor models used in PCF-SPR configurations, highlighting their comparative performance metrics and application prospects in medical diagnostics, environmental monitoring, and chemical analysis. Thus, an exhaustive analysis of various sensing parameters, plasmonic materials, and sensor models used in PCF-SPR sensors is presented and explored in this article. Full article

To enhance the sensing performance of fiber-optic magnetic field sensors, we explored the design, optimization, and application prospects of a D-type fiber-optic magnetic field sensor. This D-type PCF-SPR sensor is metal coated on one side (the metal used in this study is gold), which serves as the active metal for SPR and enhances structural stability. Magnetic fluid is applied on the outer side of the gold film for SPR magnetic field sensing. Six internal air holes arranged in a hexagonal shape form a central light transmission channel that facilitates the connection between the two modes, which are the sensor’s core mode and SPP mode, respectively. The outer six large air holes and two small air holes are arranged in a circular pattern to form the cladding, which allows for better energy transmission and reduces energy loss in the fiber. In this paper, the finite element method is employed to analyze the transmission performance of the sensor, focusing on the transmission mode. Guidelines for optimizing the PCF-SPR sensor are derived from analyzing the fiber optic sensor’s dispersion curve, the impact of surface plasmon excitation mode, and the core mode energy on sensing performance. After analyzing and optimizing the transmission mode and structural parameters, the optimized sensor achieves a magnetic field sensitivity of 18,500 pm/mT and a resolution of 54 nT. This performance is several orders of magnitude higher than most other sensors in terms of sensitivity and resolution. The SPR-PCF magnetic field sensor offers highly sensitive and accurate magnetic field measurements and shows promising applications in medical and industrial fields. Full article

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

The refractive index is an important optical property of materials which can be used to understand the composition of materials. Therefore, refractive index sensing plays a vital role in biological diagnosis and therapy, material analysis, (bio)chemical sensing, and environmental monitoring. Conventional optical refractive index sensors based on optical fibers and ridge waveguides have relatively large sizes of a few millimeters, making them unsuitable for on-chip integration. Photonic crystals (PCs) have been used to significantly improve the compactness of refractive index sensors for on-chip integration. However, PC structures suffer from defect-introduced strong scattering, resulting in low transmittance, particularly at sharp bends. Valley photonic crystals (VPCs) can realize defect-immune unidirectional transmission of topological edge states, effectively reducing the scattering loss and increasing the transmittance. However, optical refractive index sensors based on VPC structures have not been demonstrated. This paper proposes a refractive index sensor based on a VPC Mach–Zehnder interferometer (MZI) structure with a high forward transmittance of 0.91 and a sensitivity of 1534%/RIU at the sensing wavelength of λ = 1533.97 nm within the index range from 1.0 to 2.0, which is higher than most demonstrated optical refractive index sensors in the field. The sensor has an ultracompact footprint of 9.26 μm × 7.99 μm. The design can be fabricated by complementary metal–oxide semiconductor (CMOS) fabrication technologies. Therefore, it will find broad applications in biology, material science, and medical science. Full article

This research introduces a biosensor utilizing surface plasmon resonance in a photonic crystal fiber (PCF) configuration. PCF uses fused silica as the base material, with a layer of gold placed over the U-channels in the cross-section of the fiber to create a surface plasmon resonance. There are three different sizes of internal fiber optic air hole diameters, with a larger channel circle below the u-channel for the formation of an energy leakage window. COMSOL software 6.0 assisted us in tuning the fiber optic structure and performance for the study, and the structural parameters analyzed mainly include the channel circle diameter, the channel circle spacing, the profundity measurement of the polished layer, and the nanoscale size variation of metal films. The results of the simulation study show that the optical fiber sensor achieves refractive index (RI) responsiveness across the 1.30 to 1.41 range, and in the RI interval of 1.40 to 1.41, the sensor exhibits the largest resonance peak shift, and its highest sensitivity reaches 10,200 nm/RIU, and the smallest full width at half peak (FWHM) corresponds to the RI of 1.34 with a value of 4.8 nm, and the highest figure of merit (FOM) corresponds to the RI of 1.34 with a value of 895.83 (1/RIU). COMSOL 6.0 simulation software, was used to simulate the changes in blood refractive index corresponding to different glucose concentrations, and the detection performance of the sensor for different concentrations of glucose was tested. Then, the results show that the glucose concentration in 75 mg/dL–175 mg/dL with RI detection sensitivity is 3750 nm/RIU, where the maximum refractive index sensitivity is 5455 nm/RIU. It shows that the sensor can be applied in the field of biomedical applications, with its convenience, fast response, and high sensitivity, it has great potential and development prospect in the market. Full article

A high-sensitivity surface plasmon resonance (SPR) dual-parameter sensor based on photonic crystal fiber (PCF) is proposed for simultaneous measurement of magnetic field and temperature. The grooves on the right and upper sides of the PCF, serving as distinct detection channels, are filled with magnetic fluid and polydimethylsiloxane, respectively, enabling high-sensitivity detection of magnetic field and temperature. The structure parameters and sensing characteristics of the proposed sensor are investigated based on the finite element method. Numerical results indicate, within the wavelength range of 850–1050 nm, that the sensor achieves a high magnetic field sensitivity of 86 pm/Gs under x-polarization in the range of 100–600 Gs, and exhibits a temperature sensitivity of −2.63 nm/°C under y-polarization within the temperature range of 20–40 °C. Furthermore, the detection precision and applicability of the sensor in actual measurement applications could be further enhanced in the future by introducing surface-enhanced Raman scattering technology. Full article

This paper aims to enhance the sensitivity of fiber-optic surface plasmon resonance (SPR) sensors by innovatively applying TRIZ (Theory of Inventive Problem Solving). To identify the key challenges faced by current SPR sensors, methods such as functional analysis, causal analysis, and the Nine-Window method are employed. Utilizing TRIZ tools, including Technical Contradiction, Physical Contradiction, the Smart Little Man method, and object–field analysis, innovative solutions are proposed, involving transparent indium tin oxide (ITO) thin films, an asymmetric photonic crystal fiber structure with elliptical pores, and titanium dioxide (TiO₂) thin films. Experimental results reveal a significant improvement in sensitivity, with an average of 9961.90 nm/RIU and a peak of 12,503.56 nm/RIU within the refractive index range of 1.33061 to 1.40008, representing a 456% increase compared to the original gold-film fiber-optic SPR sensor. These findings have potential applications in biosensing, environmental monitoring, and food safety. Full article

Photonic crystals, which are important functional materials, are formed by the periodic arrangement of materials with different dielectric constants that have photonic bandgaps and localization properties. Their preparation methods are primarily physical and chemical. Physical methods include mechanical drilling, layer-by-layer stacking, and precision processing. Chemical methods primarily involve colloidal self-assembly methods. Various colloidal crystal self-assembly methods have been reported, each with its own advantages and disadvantages. Photonic crystals have important applications in many fields, such as optical communications, information technology, energy, biomedicine, and sensors, including high-performance optical fiber fabrication, photonic chip development, and solar cell efficiency enhancement. This paper reviews the latest progress in the preparation of photonic crystals using physical and self-assembly methods. Currently, the preparation and application of photonic crystals have made significant achievements; however, there are still challenges in terms of preparation accuracy, efficiency, cost, and application integration technology. With the future development of science and technology, breakthroughs are expected in novel structural development, preparation process optimization, and cross-field integration, which will continue to promote the progress of photonic crystals and social development. Full article

Refractive index (RI) and temperature (T) are both critical environmental parameters for environmental monitoring, food production, and medical testing. The paper develops a D-shaped photonic crystal fiber (PCF) sensor to measure RI and T simultaneously. Its cross-sectional structure encompasses a hexagonal-hole lattice, with one hole selectively filled with toluene for temperature sensing. By coating the D-shaped surface of the PCF with a metal film and a MoS₂ film, the refractive index-detection channel is formed. Numerical results demonstrate that RI and T can be reflected in the same spectrum, without any interference caused by the two parameters with each other. At an environmental RI of 1.26–1.38, its maximum RI sensitivity is up to 5400 nm/RIU. At a temperature of 20–80 °C, its temperature sensitivity reaches −1.2 nm/°C. This design allows for a broad operational spectrum and an extensive measurement range, which makes it particularly suitable for applications requiring low-RI detection. Moreover, the resonance strength of the sensor is significantly enhanced by introducing a two-dimensional material MoS₂ on the D-surface. Specifically, it reaches 195,149 dB/m when RI = 1.34 at 30 °C. This is much higher than that of most previous studies, and the requirements for inspection equipment can be lowered in this case. These results are essential for progress in simultaneously detecting RI and T. Full article

Methane gas leakage can lead to pollution problems, such as rising ambient temperature. In this paper, the Vernier effect of a double D-shaped photonic crystal fiber (PCF) in a Sagnac interferometer (SI) is proposed for the accurate detection of mixed methane gas content in the gas. The optical fiber structure of the effective sensing in the sensing SI loop and the effective sensing in the reference SI loop are the same. Both of them adopt the polarization-maintaining photonic crystal fiber (PM-PCF) designed in this paper. The optical fiber structure of the effective sensing in the sensing SI loop deposited with the methane gas-sensitive film is polished to obtain a double-D structure. This operation makes it easier for methane gas to contact the sensitive film and realize the sensor’s repeated use. The sensing capability of the methane gas sensor was evaluated utilizing the finite element method (FEM). The numerical simulation results show that when the concentration of methane gas in the environment is 0~3.5%, the average sensitivity of two parallel Sagnac loops is 409.43 nm/%. Using Vernier effect cascade SI loops, the sensitivity of the sensor for detecting methane gas increased by four times. Without considering air and humidity, we provide a practical scheme for the development and design of high-sensitivity methane gas sensors. Full article

In this paper, we design and demonstrate an all-fiber-sensitive refractive index (RI) sensor based on the Mach–Zehnder interferometer (MZI). It is constructed by splicing two no-core fibers (NCFs) and a photonic crystal fiber (PCF) between two single-mode fibers (SMFs) to obtain an SMF–NCF–PCF–NCF–SMF composite structure (SNPNS). A study of the effect of varying PCF lengths on the RI reveals that the shorter the length, the higher the sensitivity. The maximum RI sensitivity of 176.9 nm/RIU is attained within the RI range of 1.3365–1.3767 when the PCF length in the SNPNS structure is 3 cm. Meanwhile, the sensor exhibits a high stability in water, with an RSD of only 0.0019% for the interference trough over a duration of two hours. This proposed sensing structure offers the advantages of a large extinction ratio, small size, low temperature sensitivity, and simple fabrication, exhibiting a great potential in RI measurements. Full article

A terahertz photonic crystal fiber with two sensing channels was designed. Graphene coated on the micro-grooves in the cladding was used as plasma material to introduce tunability. The dispersion relation, mode coupling, and sensing characteristics of the fiber were studied using the finite element method. Ultrahigh sensitivity of 2.014 THz/RIU and 0.734 GHz/°C were obtained for analytes with refractive index in the range of 1.33 to 1.4 and environment temperature in the range of 10–60 °C, respectively. Refractive index resolution can reach the order of 10⁻⁵. The dual parameter simultaneous detection, dynamic tunable characteristics, and working in the low-frequency range of terahertz enable the designed photonic crystal fiber to have application prospects in the field of biosensing. 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

A novel highly sensitive D-shaped photonic crystal fiber-based surface plasmon resonance (PCF-SPR) sensor for dual parameters of refractive index and temperature detecting is proposed. A PCF cladding polishing provides a D-shape design with a gold (Au) film coating for refractive index (RI) sensing (Core 1) and a composite film of silver (Ag) and polydimethylsiloxane (PDMS) for temperature sensing (Core 2). Comsol Multiphysics 5.5 is used to design and simulate the proposed sensor by the finite element method (FEM). The proposed sensor numerically provides results with maximum wavelength sensitivities (WSs) of 51,200 and 56,700 nm/RIU for Core 1 and 2 as RI sensing while amplitude sensitivities are −98.9 and −147.6 RIU⁻¹ with spectral resolution of 1.95 × 10⁻⁶ and 1.76 × 10⁻⁶ RIU, respectively. Notably, wavelength sensitivity of 17.4 nm/°C is obtained between −20 and −10 °C with resolution of 5.74 × 10⁻³ °C for Core 2 as temperature sensing. This sensor can efficiently work in the analyte and temperature ranges of 1.33–1.43 RI and −20–100 °C. Due to its high sensitivity and wide detection ranges, both in T and RI sensing, it is a promising candidate for a variety of applications, including chemical, medical, and environmental detection. Full article