Vector Finite Element Research Articles

Ultrahigh-sensitivity label-free optical biosensor based on a silicon nanowire rectangular optical waveguide for lung cancer detection

An ultrahigh-sensitivity optical biosensor is proposed and analyzed for early detection of lung cancer based on a silicon nanowire rectangular optical waveguide (SNROW). Parametric optimization is performed to get high surface sensitivity with compactness of the device for label-free biosensing by two-dimensional vectorial finite element methods. The proposed device is very effective in early detection of lung cancer based on the examination of variation in thickness of the functionalization layer due to binding with target biomarkers. Waveguide surface sensitivity is calculated by measuring the change in index of refraction per unit adlayer thickness variation. The waveguide surface sensitivity is obtained at 0.167 nm−1 with a cross-sectional area of 1255 nm×670 nm for the SNROW-based biosensor.

A V-shape photonic crystal fiber polarization filter based on surface plasmon resonance effect

In this paper, a V-shape photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance (SPR) effect is proposed. With the full vector finite element method, the V-shape photonic crystal fiber polarization filter is designed, and the coupling characteristics between the core mode and surface plasmon polariton mode are analyzed. The simulation results show that the fiber parameters have significant effects on the shift and strength of the SPR wavelength. Moreover, the losses of the core modes along the Y and X polarization directions are 68904 dB/m and 858 dB/m at the SPR wavelength of 1550 nm, respectively. Finally, the extinction ratio and error-tolerant rate of extinction ratio are also analyzed. The proposed V-shape PCF polarization filter can achieve good filtering effect in the communication band and is easy to integrate with existing optical fiber communication and sensing systems.

Metal Nanowire Assisted Hollow Core Fiber Sensor for an Efficient Detection of Small Refractive Index Change of Measurand Liquid

In this article, a cost-effective hollow core fiber (HCF)-based refractive index (RI) sensor using surface plasmon resonance (SPR) is designed and demonstrated. The sensor consists of a metal nanowire inside an HCF along with the sensing medium of various refractive indices. SPR effect between polaritons and the guided core mode of designed HCF is exploited to enhance the sensing performance. A full vectorial finite element method (FEM) is used for the design and analyses of the sensing probes which exhibit very high sensitivities of 12,400 nm/RIU, 10560 nm/RIU, and 6400 nm/RIU for copper (Cu), gold (Au), and silver (Ag), respectively with a resolution of 1.61 × 10−6 RIU. Additionally, the influence of metal wire dimension is also investigated in this paper. The reported simple and low-cost sensor exhibits high sensitivity for liquid with refractive indices slightly higher than that of the dielectric tube, such as olive oil, turpentine, kerosene, chloroform, carbon tetrachloride, glycerol, and toluene.

Grating couplers for (Bloch) long-range surface plasmons on metal stripe waveguides

Gratings capable of incoupling an incident Gaussian beam into long-range surface plasmon polaritons (LRSPPs), propagating along a thin narrow Au stripe on a low-index cladding (fluoropolymer), or on a truncated 1D photonic crystal as a Bloch LRSPP, are investigated for potential biosensing application. The gratings are optimized, initially, through 2D modeling using the vectorial finite element method. Different 3D grating designs are then investigated through 3D modeling using the vectorial finite difference time domain method, including wide gratings on adiabatic and nonadiabatic flared stripes. Wide gratings on flared stripes have a larger area enabling size matching and coupling to larger incident beams, which facilitates optical alignments. We also investigate the effects of changing the size of the beam incident on the structures. Incoupling efficiencies of up to 25% at λ0=1310 are predicted for optimal gratings—such coupling efficiencies are among the highest reported to date for a structure of this kind. Similar grating designs are also examined as outcoupling structures, capable of coupling (Bloch) LRSPPs into a perpendicularly emerging Gaussian beam. The absorptance, reflectance, and transmittance of the structure were also calculated. Structures were fabricated on a multilayer wafer supporting Bloch LRSPPs to verify design concepts.

Tetra-core surface plasmon resonance based biosensor for alcohol sensing

A novel tetra core surface plasmon resonance (T-SPR) based photonic crystal fiber (PCF) biosensor is proposed for alcohol sensing and detection in near IR region. Alcohol compounds are commercial products and heavily used for different purposes. In this work, different groups of alcohol series like- methanol, ethanol, propanol, butanol, pentanol, and phenol. Therefore, the entire analysis is done by a full vectorial finite element method (FV-FEM) for 1.5–3.0 μm wavelength. In fact, we use chemically inert plasmonic material as - gold (Au) that helps to obtain maximum sensitivity and provide evanescent field and fused silica is used as the base material. Furthermore, an anisotropic perfectly matched layer (A-PML) is attached for declining nonphysical unwanted radiation conducted as absorbing boundary condition (ABC). The performances values of wavelength sensitivity, resolution and transmittance variance are reported as 40000 nm/RIU, 8.0 × 10−3 RIU and 1000 dB/RIU, respectively. In summary, the proposed T-SPR PCF can be widely applicable in fields of bio-optics and can prove it a tough competitor by its sensing performance.

Modified D-shaped SPR PCF polarization filter at telecommunication wavelengths

A compact surface plasmon photonic crystal fiber (PCF) polarization filter is proposed and analyzed at the two communication windows of 1.3 and 1.52 µm. The y-polarized mode can be filtered out at wavelength of 1.3 µm while the x-polarized mode can be excluded at λ = 1.52 µm using the same design. The effects of the geometrical parameters of the PCF on the polarization filter performance are studied by full vectorial finite element method. The numerical simulations reveal that the suggested polarization filter with a compact device length of 23 µm can achieve good crosstalk (CT) of − 46.4 and − 41.2 dB at the communication wavelengths of 1.3 and 1.52 µm, respectively. Further, bandwidths of 45 nm and 110 nm can be obtained around λ = 1.3 µm and 1.52 µm, respectively where the CT is better than − 20 dB. Therefore, the reported design has advantages in terms of low crosstalk, large bandwidth, short device length and multi-functionality.

Hollow core photonic crystal fiber for chemical identification in terahertz regime

Abstract A new kind of rectangular hollow core photonic crystal fiber (HC-PCF) has been proposed and analyzed in the terahertz regime to detect the chemical analytes. In this proposed HC-PCF a rectangular shaped air hole is used in the core and circular air holes are introduced in the cladding. Full vectorial finite element method (FEM) with perfectly matched layer (PML) boundary condition is used to investigate the guiding characteristics of the proposed HC-PCF. Our proposed PCF exhibits a high relative sensitivity and extremely low confinement loss for different chemical analytes. In addition, this proposed chemical sensor offers high birefringence, high numerical aperture and almost zero flattened dispersion over a wide frequency range. This proposed fiber can be used in chemical sensing as well as various polarization maintaining terahertz applications.

Highly sensitive photonic crystal fiber gas sensor

A novel design of circular photonic crystal fiber (C-PCF) gas sensor is presented and analyzed by full vectorial finite element method. The suggested structure has a spiral porous Core region to achieve high light interaction with the applied gas. The geometrical parameters of the proposed sensor are studied to achieve high sensor sensitivity. The introduced C-PCF offers high relative sensitivity of 72.04% at a wavelength of 1.33 μm. The reported gas sensor also offers a compact, accurate and useful tool for detecting harmful gases over a wide transmission band from wavelength of 1 μm to 1.8 μm.

Numerical analysis of a highly nonlinear microstructured optical fiber with air-holes arranged in spirals

• A spiral shape photonic crystal fiber deposition has been designed for nonlinear applications. • Numerical simulation proves that the proposed work gives the extremely high nonlinear coefficient. • It simultaneously offers a desirable optical property of numerical aperture. • The outcome indicates that the proposed PCF is few times more effective than the earlier reported fiber. • A strong candidate in supercontinuum generation and biomedical imaging applications. A spiral shape photonic crystal fiber (S-PCF) deposition with silicon nanocrystal has been designed for nonlinear applications. Full vector finite element method (FV-FEM) based commercially available software COMSOL Multiphysics® version 4.2 has been used here to investigate some essential optical characteristics. Numerical simulation proves that the proposed work gives the extremely high nonlinear coefficient of 2.28 × 10 5 W −1 km −1 and 2.56 × 10 5 W −1 km −1 for the X and Y polarization respectively, at wavelength λ = 1.00 µm. Moreover, it simultaneously offers a desirable optical property of numerical aperture (NA) of 0.54 and 0.56 at the same electromagnetic (EM) wave. The outcome indicates that the proposed PCF is approximately a few times more effective than the earlier reported fiber designs. The proposed PCF designed with circular shape holes and geometrical rhythms which remains enormously convenient in fabrication. This PCF structure provides a way to get the high nonlinearity with NA at the same time, which can find extensive applications in the optical signal processing as well as medical imaging.

Effect of plasmonic materials on photonic crystal fiber based surface plasmon resonance sensors

In this study, we proposed photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor with gold, bimetallic silver-gold and silver-graphene as active plasmonic layers. Proposed PCF structure with surrounded outer shell of two large analyte channels are studied with spectral interrogation method. Full vectorial Finite Element Method (FV-FEM) with Perfectly Matched Layers (PML) are assigned to investigate the resonance condition, resolution and sensitivities of proposed structures. According to spectral sensitivity analyses, maximum sensitivity reached up to 3000 nm/RIU for gold, 3500 nm/RIU for gold-covered silver and 4000 nm/RIU for graphene-covered silver. Meanwhile, the average sensitivities are around 2850 nm/RIU, 2650 nm/RIU and 3750 nm/RIU for gold, gold-covered silver and graphene-covered silver, respectively.

Extremely high birefringent and low loss microstructure optical waveguide: Design and analysis

In this paper a new kind of porous core microstructure fiber is proposed and analyzed for the efficient transmission of terahertz signal. We use hexagonal type air hole instead of conventional circular air hole to produce hexagonal structure in cladding. Rectangular shaped air holes are introduced in the core to provide higher birefringence than other structures. Full vector finite element method is used to investigate the guiding characteristics of that hybrid waveguide. The numerical analysis ensures that, the proposed fiber offers extremely high birefringence of 0.075 and ultralow effective material loss of 0.045 cm−1 simultaneously at optimum designing condition. Along with the excellent guiding characteristics this fiber exhibits very high power fraction of 47% and very low dispersion variation of 0.17 ps/THz/cm over 600 GHz frequency range. The proposed fiber can be easily fabricated by using the ongoing technology. We hope this microstructure fiber will be a good candidate in different polarization maintaining applications.

Design and Optimization of a Magnetically Levitated Inductive Reaction Sphere for Spacecraft Attitude Control

The inductive reaction sphere (RS) brings the benefit of simple, economical, and miniaturized design, and it is capable of multi-DOF torque generation. Thus, it is a suitable choice for the angular momentum exchange actuator in attitude control of micro-spacecrafts. To synthesize symmetric distribution of eddy currents and improve the speed and stability of rotation, a novel 4-pole winding design is proposed. However, the developed simplified analytical model shows that reduced pole number degrades the torque generation. To enhance the output torque of 4-pole RS, its curved cores and electromagnets are redesigned to enable the side teeth to be functional. As the analytical torque model for the RS with the slotted cores is not available, a constrained optimization problem is formulated, and the optimized parameters are calculated based on the prediction model from supported vector machine and finite element analysis. The lab prototypes are developed to validate the proposed design and test the speed performance. The experimental results show that the 4-pole RS prototype obtains a stable rotation over 700 rpm about X, Y and Z axis respectively with the angular momentum of 0.08 kg·m 2 /s, being superior to the 6-pole counterpart.

Direct Method Solution of 3-D Magnetotelluric Modeling Using Vector Finite Element Method

As exploration is forced into more difficult areas with complex three-dimensional (3-D) structural environments, the importance of 3-D magnetotelluric (MT) modeling is essential for the correct interpretation of MT data. To reduce the complexity of the calculations introduced by 3-D models, iterative forward calculation of MT response functions is used as basis for inversion of 3-D MT data. This paper proposes an alternative procedure for making reliable 3-D MT modeling codes for forward calculation that is not only effective but also accurate. This is accomplished by using a direct method to solve the linear systems arising from the discretization process in the vector finite element approach. The vector finite element method is known for its capability of overcoming difficulties in modeling caused by possible jumps of normal components across discontinuities of material properties. Meanwhile, by using a direct method rather than an iterative method, the process of solving the linear equations does not suffer from slow convergence. Here, we present a comparison between our modeling codes and codes based on a different approach. In the resulting 3-D MT responses it was found that the proposed method has high accuracy.

Modelling and simulation of a porous core photonic crystal fibre for terahertz wave propagation

A porous core photonic crystal fibre based on conventional hexagonal lattice cladding is proposed for propagating terahertz radiation. The structure is designed and theoretically investigated using full vectorial finite element method. Simulation results show that at 300 µm core diameter, with a high porosity of 85%, and an operating frequency of 1.3 THz, the proposed fibre reduces the bulk absorption loss of cyclic olefin copolymer (TOPAS) by about 81%, which corresponds to an ultra-low effective material loss value of 0.039 cm−1. Furthermore, the proposed fibre shows near zero dispersion coefficient of 0.47 ps/THz/cm with an extremely small variation of 0.05 over a broad 1.3 THz bandwidth; with confinement and bending losses investigated and found to be negligibly low. It is anticipated that the proposed waveguide can potentially be used for short range transmission of terahertz radiation in the communication window.

A dispersion engineered silica-based photonic crystal fiber for supercontinuum generation in near-infrared wavelength region

We report computational modeling of photonic crystal fibers in silica glass for near-infrared supercontinuum generation. Optical parameters like chromatic dispersion, nonlinearity and the effective area of the fundamental mode have been computed and tailored by using a full vectorial finite element method. At pump wavelength of 1300 nm, a flat-top dispersion profile has been obtained with very low dispersion value + 0.6402 ps/nm/km in the anomalous region. The reported structure offers high nonlinear coefficient 26.27W−1. km−1with effective mode area 4.78 μm2 at the pump wavelength. An ultra-broadband supercontinuum spanning, from 0.67 μm up to 2.4 μm can be easily achieved by the proposed fiber of 37 cm length using a 63 fs secant laser pulse source with 8 kW peak power in the near-infrared wavelength region. Such type of fiber can be advantageous in the field of near-infrared spectroscopy, optical communication, gas sensing, medical, frequency metrology, optical coherence tomography, and food quality control.

Detection of harmful food additives using highly sensitive photonic crystal fiber

This paper presents three different structures of index guided hexagonal shaped Hollow Core Photonic Crystal Fiber (HC-PCF) specially designed for sensing harmful food additives like Saccharin, Sorbitol and Butyl Acetate. The proposed PCFs have three distinct combinations of hexagonal and/or circular airholes at the innermost cladding layer and in the core region. A comparative study among the proposed structures reveals that the introduction of the hexagonal airholes at the innermost cladding layer increases the sensitivity. Also, the addition of the large circular airholes at the outermost layer reduces the confinement loss in all three structures. The diameters of the airholes of the innermost and outermost layer of the cladding region are gradually varied to optimize the PCFs. The numerical inquiry reveals that the optimized best structure shows relative sensitivity of 88.75%, 87.37% and 86.72% for Saccharin, Sorbitol, and Butyl Acetate respectively at the operating wavelength of 1.33 μm. The performances of the proposed structures are also investigated using Ethanol as the sensed sample for the purpose of comparison with previously reported works. The comparison shows that the introduced fibers outperform most of the recent works. Numerical analyses of the proposed structures are conducted using Full Vectorial Finite Element Method (FV-FEM).

Highly sensitive SPR PCF biosensors based on Ag/TiN and Ag/ZrN configurations

We numerically present and analyze a surface plasmon resonance (SPR) bimetallic photonic crystal fiber (PCF) biosensor using full vectorial finite element method. The bimetallic configuration is based on Silver and (TiN or ZrN) as alternative plasmonic materials. The reported design relies on PCF with an external channel to house the analyte. The inner surface of the channel is coated by a silver layer followed by TiN or ZrN to protect the silver layer from oxidation. The proposed biosensor can be implemented to detect the unknown analytes, organic chemicals, biological analytes, and biomolecules via the sensitive resonant peaks to the analyte refractive index variations for both polarized modes with high linearity. In this study, a comparison is made between the Ag/TiN configuration and the Ag/ZrN counterpart in terms of sensitivity, losses, and linearity. The geometrical parameters are optimized to achieve high refractive index sensitivities of 7000 nm/RIU for quasi-transverse electric (TE) mode and 6900 nm/RIU for quasi-transverse magnetic (TM) mode, respectively for the Ag/TiN configuration. However, the quasi TE and quasi TM modes achieve high sensitivity of 5300 and 5400 nm/RIU, respectively using the Ag/ZrN configuration. The standard PCF fabrication technologies can be used to fabricate the proposed SPR PCF biosensors.

Весовой векторный метод конечных элементов и его приложения

Весовой векторный метод конечных элементов и его приложения

Multifunctional surface plasmon resonance photonic-crystal fiber polarization filter at telecommunication wavelengths

A compact surface plasmon photonic-crystal fiber (PCF) polarization filter is proposed and analyzed at the two communication windows of 1310 and 1490 nm, respectively. The x-polarized mode can be filtered out at the wavelength of 1310 nm, while the y-polarized mode can be excluded at λ = 1490 nm. Therefore, the reported PCF design can be used as x-polarized or y-polarized filters using the same design. The effects of the geometrical parameters of the PCF on the performances of the polarization filter are studied by the full vectorial finite-element method. The numerical simulations reveal that the suggested polarization filter with a compact length of 150 μm can achieve good cross talk (CT) of −78 and −80.7 dB at the communication wavelengths of 1310 and 1490 nm, respectively. Further, bandwidths (BW) of 97 nm and 580 nm can be obtained around wavelengths of 1310 and 1490 nm, respectively, where the CT is better than −20 dB. Therefore, the reported design has advantages in terms of low cross talk, large BW, short device length, and multifunctionality.

Corrections to “Simultaneously Achieving a Large Negative Dispersion and a High Birefringence Over Er and Tm Dual Gain Bands in a Square Lattice Photonic Crystal Fiber”

We proposed a novel photonic crystal fiber composed of a double-cladding square lattice that could be used in dual-band, Er and Tm optical gain bands, simultaneously supporting a large negative dispersion and a high birefringence. We theoretically investigated the light guiding property through the proposed photonic crystal fiber by using a vectorial finite-element method with a perfectly matched layer. By optimizing the structural parameters, we obtained an ultra-large negative dispersion of −20,186 ps/(nm·km) and a very high birefringence of 9.27 × 10−3 at the wavelength of 1.55 μ m in the Er gain band and a very large negative dispersion of −8,067 ps/(nm·km) and a high birefringence of 1.0 × 10−3 at the wavelength of 1.87 μ m in the Tm band. We further discussed the roles of waveguide parameters on the chromatic dispersion, its slope, and the birefringence of the fiber as well as the mode field diameter. The proposed fiber could be directly applied for dual-band dispersion and polarization control in fiber laser cavities as well as optical communications and sensors in the dual bands.