Confinement Loss Research Articles

Highly Sensitive Bilirubin Biosensor Based on Photonic Crystal Fiber in Terahertz Region

An unstable bilirubin level in the human blood causes many dangerous health problems, such as jaundice, coronary artery disease, ulcerative colitis, and brain lesions. Therefore, the accurate and early detection of bilirubin concentrations in the blood is mandatory. In this work, a highly sensitive biosensor based on photonic crystal fiber (PCF) for monitoring bilirubin levels is proposed and analyzed. The sensor parameters, including relative sensitivity, effective mode area, confinement loss, and effective material loss, are calculated. The geometrical parameters are studied, and a modal analysis of the suggested sensor is carried out using the full-vectorial finite element method (FEM). The fabrication tolerance of the geometrical parameters is also studied to ensure the fabrication feasibility of the reported design. High sensitivities of 95% and 98% are obtained for the x-polarized and y-polarized modes, respectively. Furthermore, a small material loss of 0.00193 cm−1, a small confinement loss of 2.03 × 10−14 dB/cm, and a large effective mode area of 0.046 mm2 are achieved for the y-polarized mode. It is believed that the presented sensor will be helpful in health care and in the early detection of bilirubin levels in the blood.

High-Sensitivity Early Detection Biomedical Sensor for Tuberculosis With Low Losses in the Terahertz Regime Based on Photonic Crystal Fiber Technology

Tuberculosis is one of the most contagious and lethal illnesses in the world, according to the World Health Organization. Tuberculosis had the leading mortality rate as a result of a single infection, ranking above HIV/AIDS. Early detection is an essential factor in patient treatment and can improve the survival rate. Detection methods should have high mobility, high accuracy, fast detection, and low losses. This work presents a novel biomedical photonic crystal fiber sensor, which can accurately detect and distinguish between the different types of tuberculosis bacteria. The designed sensor detects these types with high relative sensitivity and negligible losses compared to other photonic crystal fiber-based biomedical sensors. The proposed sensor exhibits a relative sensitivity of 90.6%, an effective area of 4.342×10−8m2, with a negligible confinement loss of 3.13×10−9cm−1, a remarkably low effective material loss of 0.0132cm−1, and a numerical aperture of 0.3462. The proposed sensor is capable of operating in the terahertz regimes over a wide range (1 THz–2.4THz). An abbreviated review of non-optical detection techniques is also presented. An in-depth comparison between this work and recent related photonic crystal fiber-based literature is drawn to validate the efficacy and authenticity of the proposed design.

Effect of Overburden Depth and Stress Anisotropy on a Ground Reaction Caused by Advancing Excavation of a Circular Tunnel

The assumption of the Convergence–Confinement Method (CCM) is the analysis of the interaction behavior of the support and ground of a deep circular tunnel under an isotropic stress field. Aiming to improve this method, this paper proposes a discussion on the influence of the overburden depth and stress anisotropy. To consider the influence of the overburden effect, the ground reaction in different depths due to tunnel advancing excavation is investigated. Under anisotropic stress conditions, the analytical solutions of the stress/displacement in the plastic and elastic regions of this ground reaction can also be suitable for theoretical analysis in a consistent manner. The key factor in this study is the use of confinement loss, which can not only describe the simulation of tunnel advancing effects but also become a superimposed value of the incremental procedure. In addition, the calculation spreadsheets can be used to estimate and implement the theoretical analytical solutions into executable computational solutions. To check the validity of the analytical solution, finite element analysis is used to examine the distribution of stress/displacement around the tunnel, especially the distribution along the overburden pressure line in the circular tunnel cross-section. Comparing the analytical solution calculated by the incremental procedure with the result of the numerical analysis shows a consistent trend.

A Mid-Infrared Ultrawide-Bandwidth Single-Polarization Single-Mode Fiber Based on a Twin-Tube Structure

A novel chalcogenide As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> fiber based on a twin-tube structure is proposed and numerically studied for mid-infrared (MIR) single-polarization single-mode (SPSM) operation. The proposed fiber consists of two identical thin-wall tubes, which are located symmetrically inside the cladding. The simulation results show that the y-polarization fundamental mode (YPFM) can be well confined between the two tube walls near the fiber center, while all of the unwanted modes, including the x-polarization fundamental mode (XPFM) and all of the higher order modes (HOMs), are effectively suppressed due to huge confinement loss (CL). The SPSM operation can be maintained in the wavelength range from 3 to 10 μm, covering almost the entire transparency region of an As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> fiber, with the maximum YPFM CL of 8.63×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> dB/m at 10 μm. To the best of our knowledge, this is the first MIR fiber that can keep SPSM operation over such a wide wavelength region. Furthermore, the mode area of YPFM is quite small (e.g. 10.82 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the wavelength of 6 μm), which is beneficial to realize high nonlinearity. Besides, the bending induced CL increment of YPFM at 10 μm is only 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> dB/m even when the fiber bending radius is 1 cm. Owing to the simple structure and outstanding properties, the proposed fiber has practical applications in MIR photonics and nonlinear fiber optics.

Design and modeling of the nonlinear properties of octagonal lattice Ge20Sb5Se75 photonic crystal fibers

Most silica photonic crystal fibers have limited spectral broadening in the infrared region, making them less than ideal in terms of technological applications. In this work, we propose a new Ge20Sb5Se75 chalcogenide octagonal photonic crystal fiber that provides diverse dispersions with all-normal and anomalous regimes and multiple zero-dispersion wavelengths. The nonlinear properties are investigated over a wide wavelength range up to 14 µm by numerically solving Maxwell's wave equations using Lumerical Mode Solutions software. The full-vector finite-difference eigenmode method minimizes the losses so that low confinement losses in the short-wavelength region of 1 − 6 µm are found and nonlinear coefficients as high as thousands of W−1.km−1 are achieved. Three fibers with an all-normal dispersion profile and anomalous dispersion with one or three zero dispersion wavelengths are proposed for supercontinuum generation. The fibers provide small dispersion values of −0.88, 0.08, and 1.646 ps/(nm.km) at suitable pump wavelengths. Furthermore, the very small confinement loss of approximately 10−5 to 10−11 dB/m is the outstanding advantage of these optical fibers. A broadband spectrum with low input power is expected as a result of the proposed fiber-based supercontinuum generation.

Design and analysis of Hollow-core fiber with anti-resonant structure for Ethylene detection

An optical fiber for mid-infrared (mid-IR) guidance has long attracted great interest due to its wide range of applications especially in gas sensing. Ethylene gas is one of an important gas, which release from the fruit and flower, owing to their ripening process. Thus, the controlling and detection of ethylene gas is of interest for the storage and exportation of fruits and flowers. Gas detection using the hollow-core optical fiber (HCF) is a promising technique due to it intrinsic micro-channel structure that allows the gas to flow through the HCF for detection propose. Here, a hollow-core anti-resonant fiber (HC-ARF) is designed and optimized for mid-IR guidance for the purpose of ethylene detection. The HC-ARF includes 6 inner tubes which is optimized to achieve a low confinement loss at a wavelength of 3.2 µm (ethylene absorption wavelength). The simulation result shows that a confinement loss of 2 dB/m at the wavelength of 3.2 µm can be achieved when the fiber core diameter is 128 µm and the thickness and the diameter of inner tubes are 2 µm and 92 µm, respectively.

Highly sensitive plasmonic sensor based on eccentric-core photonic crystal fibers.

To further reduce the fabrication difficulty of optical fiber sensors and improve the sensing performance, this study introduced the surface plasmon resonance (SPR) effect into optical fiber sensing technology and designed an eccentric-core photonic crystal fiber (EC-PCF). We investigated the characteristics of the two fundamental modes in the fiber core and the surface plasmon polariton (SPP) modes on the surface of the gold film. We also investigated the influence of the structural parameters, such as gold film coating area and thickness, air hole diameter, and eccentricity, on the confinement loss and achieved a refractive index (RI) sensitivity of 31.25 μm RIU-1 in the RI range of 1.29-1.43, corresponding to a figure of merit (FOM) of 521.6 per RIU. When the resolution of the optical spectrum analyzer was 0.1 nm, the EC-PCF could achieve a refractive index resolution of 3.2 × 10-6 RIU. Moreover, we performed tests with two typical sensing types, one in which the sensor was directly in contact with adulterated gasoline to achieve kerosene-concentration detection, and another in which the sensor was coated with a layer of polydimethylsiloxane (PDMS), whose RI is sensitive to the temperature field, to achieve temperature sensing. The EC-PCF demonstrated excellent sensing performance and offers obvious manufacturing advantages, providing a new and easily fabricated structural design idea for optical fiber sensing.

Parametric Optimization for Low Loss Negative Curvature Hollow Core Fiber With Elliptical Tube

Negative curvature hollow core fiber (NC-HCF) with elliptical tubes is beneficial for low confinement loss (CL) due to the rich degree of freedom in tube curvature. In this paper, an empirical formula for optimizing the structural parameters of NC-HCF with elliptical tubes is presented, which is aimed at the minimum CL. It is obtained by analyzing the trade-off between the mode coupling induced loss and the gap induced leakage loss, according to the theory of mode coupling between core fundamental mode and tube ring mode, and the geometric arrangement. Consequently, a relationship between gap and elliptical tube diameter in the radial direction has been found to be 1/2, with corresponding formula validated by the numerical investigation and simulation for a wide wavelength range and different elliptical tube numbers. The parametric optimization formula provides a design guideline for low loss NC-HCF, which can be an effective tool for further exploration and application.

Recent progress of gold nanostructures and their applications.

For noble metals, such as gold (Au) and silver (Ag), it is well-known that surface plasmons of their nanocrystals have significant spatial confinement and propagation loss due to the strong damping effect and the scattering between the plasmons and phonons. Noble metal nanostructures are usually referred to as "plasmonic nanostructures" in many studies. Based on the resonance effect of surface plasmons, the electromagnetic field can be localized on the subwavelength scale, which induces a booming new field of nanophotonics. Among the various nanostructures, Au nanostructures have received extensive attention both in fundamental research and technological fields due to their unique localized surface plasmon characteristics. These characteristics include strong optical extinction, near-field enhancement, and far-field scattering. By changing either the morphological parameters or the surrounding medium of nanostructures, the localized surface plasmon resonance (SPR) of Au nanostructures can be tuned in a large spectral region from visible to near infrared (Vis-NIR) wavelength. Corresponding to the experimental research, there are several numerical techniques that enable modeling the optical characteristics of Au nanostructures in different shapes and assemblies. The most popular technique is the finite-difference time-domain (FDTD) method for modeling various nanostructures and nanoscale optical devices. The accuracy of the computational models has been proven by reliable experimental data. In this review, we focused on Au nanostructures of different morphologies, such as nanorods, nanocubes, nanobipyramids and nanostars. Then combined with FDTD simulations, we described the effect of morphological parameters and the surrounding medium on the SPR properties of Au nanostructures. More and more achievements indicate that the surface plasmon effect is promising in many technical fields. In the last part, we summarize some typical applications of plasmonic Au nanostructures, such as high sensitivity sensors, photothermal conversion with hot electron effects and photoelectric devices, as well as plasmonic nanolasers.

Optical properties of As2S3-based suspended-core photonic crystal fiber

In this paper, the nonlinear properties of photonic crystal fibers (PCF) with As2S3 substrate were analyzed numerically. With the suspended-core design, we achieve an anomalous dispersion regime with one or two zero-dispersion wavelengths, which is flat and has a small value at the investigated wavelength. The high nonlinear coefficient and very low confinement loss in the wavelength range of 1–3 µm, in comparison with other publications, are the outstanding advantages of these suspended-core PCFs. The highest nonlinear coefficient (28,527.374 W–1·km–1), smallest effective mode area (0.593 µm2), and low confinement loss (6.050 × 10–17 dB·m–1) at the wavelength of 1.55 µm were observed in the PCFs with a fiber diameter of 16.07 μm. Based on the numerical simulation results, we proposed two optimal structures suitable for supercontinuum generation.

Designing of Hollow Core Grapefruit Fiber Using Cyclo Olefin Polymer for the Detection of Fuel Adulteration in Terahertz Region

A grapefruit-shape hollow-core liquid infiltrated photonic crystal fiber (LI-PCF) is proposed and evaluated to identify the percentage of kerosene in adulterated petrol. The proposed hollow-fiber sensor is designed with Cyclo Olefin Polymer (Zeonex) and likely to be filled with different samples of petrol which is adulated by the kerosene up to 100%. Considering the electromagnetic radiation in THz band, the sensing properties are thoroughly investigated by adopting finite element method (FEM) based COMSOL Multiphysics software. However, the proposed sensor offers a very high relative sensitivity (RS) of 97.27% and confinement loss (CL) less than 10-10 dB/m, and total loss under 0.07 dB/cm, at 2 THz operating frequency. Besides that, the sensor also possesses a low effective material loss (EML), high numerical aperture (NA), and large Marcuse spot size (MSS). The sensor structure is fabrication feasible through existing fabrication methodologies consequently making this petrol adulteration sensor a propitious aspirant for real-life applications of petrol adulteration measurements in commercial and industrial sensing.

Axial compression behavior of stub square concrete-filled steel tubes with regional defect

This paper investigated the axial compression behavior of stub square concrete-filled steel tubes with simulated local corrosion damage through a series of tests. The local corrosion damage was simulated by machining a regional defect on the tube. Aiming at the test specimens, the noteworthy observations were recorded, the load-shortening curves were developed, and the influence of the defect dimensions on the compressive performance of the specimens was discussed. The results revealed that the local defect on the steel tube can lead to the loss of confinement on the core concrete and the centroid offset of the specimen. Therefore, the increase in the defect sizes decreased the ultimate resistance of the specimen. When the local defect sizes reached 150 mm (length) × 112.5 mm (width) × 3.5 mm (depth), the ultimate resistance and the ductility of the specimen decreased to 88.2 % and 65.8 % of the intact specimens, respectively. Furthermore, based on the experimental study and the theoretical analysis, with consideration of the cross-sectional area loss and the confinement loss, a method was proposed to predict the ultimate resistance of the specimens with the local defect, which also can be adopted to evaluate the residual resistance of the locally corroded members in service.

Mid-infrared negative curvature hollow-core fiber with elliptically nested tubular structure

Arsenic triselenide chalcogenide negative curvature hollow-core fiber with ellipse-nested tubular cladding elements was numerically presented for the low-loss light guidance in the mid-infrared region. Confinement and total losses were calculated for the fiber with a five-tube design as low as 0.34 dB/km and 4.55 dB/km at 10.6μm, respectively. The single-mode light guidance characteristic of the proposed design was investigated, and a strong suppression on the higher-order modes shows that the fiber design favors the light guidance with the fundamental mode. A dispersion control study was carried out to optimize the primary design parameters to shift the zero-dispersion wavelength close to 10.6μm. The bending loss performance of the proposed design was analyzed in the targeted spectrum. The proposed negative curvature hollow-core fiber could be potentially used in low-loss guidance for high-power lasers and could also be utilized for several other applications, such as surgery and drug delivery in the mid-IR spectrum.

Bendable transmission line and amplifier of spoof surface plasmon polaritons at microwave frequencies.

A bendable transmission line (TL) of spoof surface plasmon polaritons (SSPPs) is presented, which can maintain good transmission performance despite of the deformation caused by bending. Such a TL consists of flexible dielectric substrate and ultrathin metallic strip with zigzag decorations that are designed to support the propagation of SSPPs with strong field confinement and low radiation loss. Furthermore, the proposed SSPP TL is used to excite an amplifier chip efficiently, reaching high and stable gains with nearly no degradation of amplification in the bending states. Numerical and experimental results are demonstrated to verify the bendable merits of both passive TL and active amplifier from 12 GHz to 18 GHz. The flexible and stable characteristics of this design may find utility in novel applications like wearable electronics and conformal plasmonic circuits in the microwave frequencies.

Design of photonic crystal fiber with large mode area for flat-top mode generation

We report a large mode area photonic crystal fiber with a flat-top mode field. The optical fiber has a multi-layer square structure with air holes and doped layer. A flat and top-hat-like mode intensity profile is provided through the reasonable design of the doped layer. The modal characteristics including effective mode area, dispersion, bending loss, confinement loss and field profile are investigated. The proposed fiber with a top-hat mode generation has potential applications in laser drilling, laser cleaning, imaging, spectroscopy, and so on.

High birefringence low loss low dispersion ring core photonic crystal fiber on terahertz band

Abstract A novel high birefringence low loss photonic crystal fiber (PCF) based on terahertz (THz) band is proposed in this paper. By constructing ring cores in core air holes and innermost cladding air holes, the characteristics of the PCF were studied in the band of 0.6–1.2 THz. The simulation results show that the birefringence characteristic of the fiber can reach 0.0514 at 0.6 THz under the optimal parameters. When working at an operating frequency of 1 THz, not only the birefringence characteristic is maintained at 0.044, but also the confinement loss is as low as about 10−6 dB/m, the dispersion of 0.272 ps/THz/cm and 0.49 ps/THz/cm, the effective mode field area reaches 0.981 μm2 and 0.745 μm2, and the single-mode operating characteristics can be maintained in the entire studied band.

Numerical analysis of the highly non-linear and ultra-sensitive modified core of a photonic crystal fiber sensor for detection of liquid analytes

A design of the highly non-linear and ultra-sensitive modified core of a photonic crystal fiber (PCF) sensor is reported for the detection of various liquid analytes. The sensor design comprises three rings of a hexagonal lattice around the liquid-infiltrated hollow core. A steric-shaped hollow core design in PCF effectively optimizes the sensor’s sensitivity and performance. The design is analyzed numerically by using the full vector finite element method with perfectly matched layers to find a rigorous solution. The proposed PCF sensor exhibits ultra-high relative sensitivity, a high power fraction, high non-linearity coefficient, low confinement loss, ultra-low chromatic dispersion, compact effective mode area, and single-mode operation in a wider wavelength range, i.e., within visible and infrared wavelength regimes. At an operating wavelength of 1.0 µm, optimum relative sensitivities of 96.37%, 97.40%, and 99.82% with high non-linear coefficients of 78.0 W − 1 k m − 1 , 66.09 W − 1 k m − 1 , and 62.57 W − 1 k m − 1 and extremely low confinement loss of ∼ 10 − 10 d B / m are obtained for water, ethanol, and benzene analytes, respectively. Further, waveguiding characteristics of the PCF sensor endorse its usage for a range of liquid analyte detections. It is a simple design and can be fabricated using existing manufacturing technologies.

Analysis of Dual Core Photonics Crystal Fiber with Circular Sensing Ring for Biochemical Detection from Blood Samples

This paper presents a proposed structure of Dual core photonic crystal fiber (DCPCF) along with a circular sensing ring for biochemical detection. Numerical analysis, Confinement loss and Relative sensitivity of PCF sensor have been observed for biochemical detection using Maxwell’s equations with perfectly matched boundaries. The core region is filled with the patient's blood samples, and the light is confined through the core region. The circular sensing ring is utilized for trouble-free penetration to cope with biosensing applications. Since the occurrence of the blood samples is very in-differentiable in the human body, these sensors play a valuable role due to their trimness, small size, litheness, and isolated competence to identify diagonisive elements in human blood.

Ultralow confinement loss anti-resonant fibers designed by swarm intelligence

Anti-resonant fibers featured with multiple cladding tubes are promising light guiding media with a broadband low-loss transmission window in the optical spectrum. Herein, we numerically demonstrate anti-resonant fibers with ultra-low confinement loss and good single mode property, which is automatically designed by swarm intelligence. The basic idea of the particle swarm optimization algorithm is to find the optimal solution by the cooperation and information sharing among particles in the group. It is demonstrated that the particle swarm optimization algorithm can be utilized to design such anti-resonant fibers with multiple geometry parameters. By breaking the mirror symmetry of the fiber’s cross section, the coupling between the fundamental mode and cladding mode is further suppressed than the mirror symmetry one. As a result, ultra-low confinement loss as small as 2.2 × 10−8 dB/m can be achieved in simulation. Our results might facilitate the advanced applications of nested anti-resonant fibers in optical communication and high energy pulsed laser, etc.

Photonic Crystal Fiber Sensor for Detecting Sulfuric Acid in Different Concentrations

A high-performance photonic crystal fiber sensor for sulfuric acid detection is designed and investigated, undertaken through a full vector Finite Element Method on COMSOL Multiphysics software to establish the optical properties of effective refractive index, power fraction, relative sensitivity, confinement loss, chromatic dispersion, and propagation constant. Different aqueous sulfuric acid concentrations of 0%, 10%, 20%, 30%, and 40% were selected as the test analytes. The dimensions of two cladding rings of the hexagon- and circular-shaped air holes and a circular core hole denoted outstanding outcomes of relative sensitivity and confinement loss. At 1.1 µm optimum wavelength, 0%, 10%, 20%, 30%, and 40% sulfuric acid concentrations depict relative sensitivities of 97.08%, 97.67%, 98.06%, 98.39%, and 98.67%, respectively, and confinement losses of 1.32 × 10−12 dB/m, 4.11 × 10−12 dB/m, 1.46 × 10−12 dB/m, 6.34 × 10−12 dB/m, and 2.12 × 10−12 dB/m, respectively.