Search Results (306)

To improve the efficiency and stability of the system, this paper proposes a monolithic integrated optical path design for a cavity optomechanical accelerometer based on a 250 nm top silicon thickness silicon-on-insulator (SOI) wafer instead of readout through U-shape fiber coupling. Finite Element Analysis (FEA) and Finite-Difference Time-Domain (FDTD) methods are employed to systematically investigate the performance of key optical structures, including the resonant modes and bandgap characteristics of photonic crystal (PhC) microcavities, transmission loss of strip waveguides, coupling efficiency of tapered-lensed fiber-to-waveguide end-faces, coupling characteristics between strip waveguides and PhC waveguides, and the coupling mechanism between PhC waveguides and microcavities. Simulation results demonstrate that the designed PhC microcavity achieves a quality factor (Q-factor) of 2.26 × 10⁵ at a 1550 nm wavelength while the optimized strip waveguide exhibits a low loss of merely 0.2 dB over a 5000 μm transmission length. The strip waveguide to PhC waveguide coupling achieves 92% transmittance at the resonant frequency, corresponding to a loss below 0.4 dB. The optimized edge coupling structure exhibits a transmittance of 75.8% (loss < 1.2 dB), with a 30 μm coupling length scheme (60% transmittance, ~2.2 dB loss) ultimately selected based on process feasibility trade-offs. The total optical path system loss (input to output) is 5.4 dB. The paper confirms that the PhC waveguide–microcavity evanescent coupling method can effectively excite the target cavity mode, ensuring optomechanical coupling efficiency for the accelerometer. This research provides theoretical foundations and design guidelines for the fabrication of high-precision monolithic integrated cavity optomechanical accelerometers. Full article

It is difficult to simultaneously achieve surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF) for noble metals. Herein, a composite substrate is demonstrated based on the rational construction of Ag nanoparticles (Ag NPs) and inverse opal polydimethylsiloxane (PDMS) for surface Raman fluorescence dual enhancement. The well-designed Ag nanoparticle (Ag NP)-decorated inverse opal PDMS (AIOP) composite substrate is fabricated using the polystyrene (PS) photonic crystal method and the sensitization reduction technique. The inverse opal PDMS enhances the electromagnetic (EM) field by increasing the loading of Ag NPs and plasmonic coupling of Ag NPs, leading to SERS activity. The thin shell layer of polyvinyl pyrrolidone (PVP) in core–shell Ag NPs isolates the detected molecule from the Ag core to prevent the fluorescence resonance energy transfer and charge transfer to eliminate fluorescence quenching and enable SEF performance. Based on the blockage of the core–shell structure and the enhanced EM field originating from the inverse opal structure, the as-fabricated AIOP composite substrate shows dual enhancement in surface Raman fluorescence. The AIOP composite substrate in this work, which combines improved SERS activity and SEF performance, not only promotes the development of surface-enhanced spectroscopy but also shows promise for applications in flexible sensors. 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

Compared to the traditional flip-chip bonded focal plane array, in high-density vertically integrated photodiode (HDVIP) focal plane technology, the thickness of the mercury cadmium telluride (MCT or Hg_1−xCd_xTe) layer serves as a more critical parameter. This parameter not only influences the efficiency of photon energy absorption but also defines the pn junction area, thereby affecting the magnitude of the dark current. Furthermore, it significantly impacts the manufacturability of via-hole etching and formation processes. This paper investigated the photonic crystal resonances and coherent perfect absorption (CPA) effect of a thin MCT layer in HDVIP by using COMSOL Multiphysics^® 4.3b and optimized the structure of the loop-hole photodiode device. The CPA, which is formed by this structure, achieves high absorption of illumination in a very thin MCT film. It is demonstrated that an absorption rate of infrared radiation of more than 95% with a wavelength during the 8 µm–10 µm range can be achieved in Hg_1−xCd_xTe (x = 0.225) with a thickness of only 1.5 µm–3 µm. The benefit of thinner MCT film is that it decreases the dark current of pn junction and reduces the technical difficulty of etching and metallization of the loop-hole photodiode. 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

Higher-order reflections from a cholesteric liquid crystal have been investigated for a long time after early observations of an oblique incidence of light. Even with the restriction of the required oblique geometry, wavelength tuning would make this property very attractive for photonic applications in the near-UV range of the electromagnetic spectrum. Unfortunately, this is quite difficult to achieve in cholesterics, and it has been obtained in special configurations that lead to the deformation of the helical structure. We show here that a new opportunity is provided by heliconical cholesteric liquid crystals and demonstrate that second-order Bragg resonance with high reflectivity and a narrow band can be produced by a light beam with intensity high enough to give rise to a significant optical torque with the consequent distortion of the helical structure. Exploiting the well-known properties of heliconical cholesterics under electric fields, we also demonstrate that the easy tuning of the second-order reflection band is achieved in the near-UV range. Full article

In this paper, we propose an innovative approach based on the wavelength optimization of a light source for a simple, high-performance surface plasmon resonance (SPR) sensor utilizing comprehensive reflectance analysis in the angular domain. The proposed structure consists of a glass substrate, an adhesion layer of titanium dioxide, a silver plasmonic layer, and a 2D material. Analysis is performed in the Kretschmann configuration for liquid analyte sensing. Sensing parameters such as the refractive index (RI) sensitivity, the reflectance minimum, and the figure of merit (FOM) are investigated in the first step of this study as a function of the thickness of the silver layer together with the RI of a coupling prism. Next, utilizing the results offering a fused silica prism, the thickness of the silver layer and the wavelength of the light source are optimized for the structure with the addition of a 2D material, black phosphorus (BP), which is studied along different principal directions, the zigzag and armchair directions. In addition, a new approach of adjusting the source wavelength using a one-dimensional photonic crystal combined with an LED, is presented. Based on this analysis, for the reference structure at a wavelength of 632.8 nm, the optimized silver layer thickness is 50 nm, and the achieved RI sensitivity ranges from 193.9 to 251.5 degrees per RI unit (deg/RIU), with the highest FOM reaching 52.3 RIU⁻¹. In addition, for the modified structure with BP, the achieved RI sensitivity varies in the range of 269.1–351.2 deg/RIU at the optimized wavelength of 628 nm, with the highest FOM reaching 44.7 RIU⁻¹ for the zigzag direction. Due to the optimization and adjusting the wavelength of the source, the results obtained for the proposed SPR structure could have significant implications for the development of more sensitive and efficient sensors employing a simple plasmonic structure. Full article

Recently, Fano resonance modulators and photonic crystal nanobeam cavities (PCNCs) have attracted more and more attention due to their superior performance, such as high modulation efficiency and high extinction ratio (ER). In this paper, a silicon Fano resonance Mach–Zehnder modulator (MZM) based on a single arm coupled with a PCNC is theoretically analyzed, designed, and numerically simulated. By optimizing the coupling length, lattice constant, coupling gap, and the number of holes in the mirror/taper region, the ER of our MZM can achieve 34 dB. When the applied voltage of the MZM is biased at 4.3 V and the non-return-to-zero on–off keying (NRZ-OOK) signal at a data rate of 10 Gbit/s is modulated, the sharpest asymmetric resonant peak and the most remarkable Fano line shape can be obtained around a wavelength of 1550.68 nm. Compared with the traditional nanobeam cavities, along with the varying radii, our PCNC design has holes with a fixed radius of 90 nm, which is suitable to be fabricated by a 180 nm passive silicon photonic multi-project wafer (MPW). Therefore, our compacted lab-on-chip, resonance-based silicon photonic MZM that is coupled with a PCNC has the advantages of superior performance and easy fabrication, which provide support for photonic integrated circuit designs and can be beneficial to various silicon photonic application fields, including photonic computing, photonic convolutional neural networks, and optical communications, in the future. Full article

This study proposes a novel two-dimensional photonic crystal ring resonator for detecting dengue-induced changes in blood components such as platelets, haemoglobin, and plasma. By monitoring shifts in the central wavelength linked to refractive index variations, the structure offers highly sensitive and accurate detection. The Lorentzian peak cavity exhibits a high-quality factor, achieving sensitivity up to 1800 nm/RIU, underscoring its potential as a precise diagnostic tool against dengue. Full article

Integrated photonic biosensors are revolutionizing lab-on-a-chip technologies by providing highly sensitive, miniaturized, and label-free detection solutions for a wide range of biological and chemical targets. This review explores the foundational principles behind their operation, including the use of resonant photonic structures such as microring and whispering gallery mode resonators, as well as interferometric and photonic crystal-based designs. Special focus is given to the design strategies that optimize light–matter interaction, enhance sensitivity, and enable multiplexed detection. We detail state-of-the-art fabrication approaches compatible with complementary metal-oxide-semiconductor processes, including the use of silicon, silicon nitride, and hybrid material platforms, which facilitate scalable production and seamless integration with microfluidic systems. Recent advancements are highlighted, including the implementation of optofluidic photonic crystal cavities, cascaded microring arrays with subwavelength gratings, and on-chip detector arrays capable of parallel biosensing. These innovations have achieved exceptional performance, with detection limits reaching the parts-per-billion level and real-time operation across various applications such as clinical diagnostics, environmental surveillance, and food quality assessment. Although challenges persist in handling complex biological samples and achieving consistent large-scale fabrication, the emergence of novel materials, advanced nanofabrication methods, and artificial intelligence-driven data analysis is accelerating the development of next-generation photonic biosensing platforms. These technologies are poised to deliver powerful, accessible, and cost-effective diagnostic tools for practical deployment across diverse settings. Full article

Despite significant progress, fabricating two-dimensional (2D) lithium niobate (LN)-based photonic crystal (PhC) cavities integrated with tapered and PhC waveguides remains challenging, due to structural imperfections. Notable, especially, are variations in hole radius (r) and inclination angle (°), which induce bandgap shifts and degrade quality factors (Q-factor). These fabrication errors underscore the critical need to address nanoscale tolerances. Here, we systematically investigate the impacts of key geometric parameters on optical performance and optimize a 2D LN-based cavity integrated with taper and PhC waveguide system. Using a 3D Finite-Difference Time-Domain (FDTD) and varFDTD simulations, we identify stringent fabrication thresholds. The a must exceed 0.72 µm to sustain Q > ${10}^7$; reducing a to 0.69 µm collapses Q-factors below ${10}^4$, due to under-coupled modes and bandgap misalignment, which necessitates ±0.005 µm precision. When an r < 0.22 µm weakens confinement, Q plummets to 2 × ${10}^4$ at r = 0.20 µm (±0.01 µm etching tolerance). Inclination angles < 70° induce 100× Q-factor losses, requiring ±2° alignment for symmetric modes. Air slot width (s) variations shift resonant wavelengths and require optimization in coordination with the inclination angle. By optimizing s and the inclination angle (at 70°), we achieve a record Q-factor of 6.21 ×${10}^6$, with, in addition, C-band compatibility (1502–1581 nm). This work establishes rigorous design–fabrication guidelines, demonstrating the potential for LN-based photonic devices with high nano-fabrication robustness. Full article

Vanadium dioxide (VO₂) is a well-known phase-change material that exhibits a thermally driven insulator-to-metal transition (IMT) near 68 °C, leading to significant changes in its electrical and optical properties. This transition is governed by structural modifications in the VO₂ crystal lattice, enabling dynamic control over absorption, reflection, and transmission. Despite its promising tunability, VO₂-based optical absorbers face challenges such as a narrow IMT temperature window, intrinsic optical losses, and fabrication complexities associated with multilayer designs. In this work, we propose and numerically investigate a single-layer VO₂-based optical absorber for the visible spectrum using full-wave electromagnetic simulations. The proposed absorber achieves nearly 95% absorption at 25 °C (insulating phase), which drops below 5% at 80 °C (metallic phase), demonstrating exceptional optical tunability. This behavior is attributed to VO₂’s high refractive index in the insulating state, which enhances resonant light trapping. Unlike conventional multilayer absorbers, our single-layer VO₂ design eliminates structural complexity, simplifying fabrication and reducing material costs. These findings highlight the potential of VO₂-based crystalline materials for tunable and energy-efficient optical absorption, making them suitable for adaptive optics, smart windows, and optical switching applications. The numerical results presented in this study contribute to the ongoing development of crystal-based phase-transition materials for next-generation reconfigurable photonic and optoelectronic devices. Full article

Kagome lattices have attracted significant research interest due to their unique interplay of geometry, topology, and material properties. They provide deep insights into strongly correlated electron systems, novel quantum phases, and advanced material designs, making them fundamental in condensed matter physics and material engineering. This work presents an efficient method for terahertz (THz) wave generation across the entire THz spectrum, leveraging high-quality-factor Kagome-shaped silicon photonic crystal resonators. In the proposed simulation-based approach, an infrared (IR) single-frequency wave interacts with an induced resonance mode within the resonator, producing a THz beat frequency. This beat note is then converted into a standalone THz radiation (T-ray) wave using an amplitude demodulator. Simulations confirm the feasibility of our method, demonstrating that a conventional single-frequency wave can induce resonance and generate a stable beat frequency. The proposed technique is highly versatile, extending beyond THz generation to frequency conversion in electronics, optics, and acoustics, among other domains. Its high efficiency, compact design, and broad applicability offer a promising solution to challenges in THz technology. Furthermore, our findings establish a foundation for precise frequency manipulation, unlocking new possibilities in signal processing, sensing, detection, and communication systems. 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