Vector Finite Element Method Research Articles

Effect of bending on photonic crystal fibre based surface plasmon resonance biosensor

In this study, the effect of bending on proposed PCF based SPR biosensor has been analysed by employing the Full vectorial Finite Element Method (FVFEM) with Perfectly Matched Layers (PMLs). The spectral interrogation method is chosen to calculate the sensitivity and the resolution of the proposed sensor structure. The blood components (water, cytop, blood plasma, white blood cell (WBC)) refractive index variations are used as a sample. Our numerical results have shown that the overall performance of the proposed sensor can be improved up to 63% by bending. Also, the resonance wavelength of the proposed sensor can be tuned by bending.

Crossings in photonic crystal fiber with hybrid core and design of broadband dispersion compensating photonic crystal fiber

A photonic crystal fiber (PCF) with sub-wavelength air inner core and Ge-doped concentric ring outer core is proposed. The full vector finite element method with perfectly matched layer is used for simulation. Mode crossing phenomenon which can be controlled through the hollow core diameter is investigated. A PCF with an effective compensated dispersion range of ±1.38 ps/nm/km from 1460 nm to 1637 nm wavelength is designed. The dispersion compensating PCF (DCPCF) can compensate for the dispersion and dispersion slope of a standard single mode fiber (SMF) at the same time. The kappa value matches very well with that of the commercial single mode fiber. Moreover, the figure of merits inside air core region of the proposed DCPCF is improved by 21.3 dB at 1550 nm wavelength compared to a hollow core photonic bandgap (PBG) fiber. This field enhancement can effectively reduce the material loss and the nonlinear accumulation in dispersion compensation fibers.

Performance analysis of octagonal photonic crystal fiber (O-PCF) for various communication applications

In this research work, a novel design of octagonal cladding with two elliptical cores in photonic crystal fiber (O-PCF) is studied for application in the terahertz (THz) frequency regime. There exists five layers octagonal figure in circular air holes (CAH) of cladding region with two elliptical shapes of core area are proposed in this research work. The O-PCF features of the fiber have been explored using full vector finite element method (FEM) with perfectly match layer (PML) boundary condition that have been used to confine the light inside the core region properly. Some supplementary significant fiber features for THz signal spread with low confinement loss, high core power fraction, scattering loss and single-mode PCF circumstances of the fiber have also been considered. Simulated results exhibition compares to the low effective material loss (EML) of 0.0153 cm−1, larger effective area of 5.95 × 10–8 m2, core power fraction of 79%, a low confinement loss and scattering loss such as 3.36 × 10–14 dB m−1 and 1.25 × 10–10 dB km−1 respectively at 1 THz frequency regime. To shorten design and smooth fabrication, only circular shaped air holes have been employed. Due to its promising characteristics, the proposed SM-OPCF waveguide provides efficient transmission of broadband terahertz signals. The suggested excellent designed of O-PCF can be used mostly for in nano-optics, biomedical signal processing, optical amplification, SONET and others communication areas.

Design and optimization of index guiding photonic crystal fiber-based gas sensor

Hydrogen sulfide(H2S) and methane(CH4) are flammable, toxic, and colorless gases that exist in oil rigs/refineries. The PCF based gas sensors can detect the concentration of chemical materials such as hydrogen sulfide and methane. This paper presents a hexagonal PCF for sensing these gases. Characteristics of the proposed structure have been investigated for the wavelength range of 1.1 μm–1.6 μm using the full vector finite element method (FEM). The numerical results show that using non-circular holes around the central ring holes and a higher number of ring holes improves sensitivity and confinement loss respectively. Eventually, the relative sensitivity is enhanced to 62.07% and 67.07% and also the confinement loss 2.33 × 10−9dB/m and 8.61 × 10−5dB/m at the wavelength of 1.33 μm and λ = 1.578 μm at which the CH4 and H2S have a strong absorption line, respectively.

Sensitivity Enhancement of Methane Detection Based On Hollow Core Photonic Crystal Fiber

Monitoring methane (CH4) concentration is essential in many industrial and environmental applications. Emission of such gases is indeed important to detect for health, safety and environmental reasons. The major risk in all these areas is an explosion hazard, which may occur if methane reaches its Lower Explosive Limit (LEL) of5% concentration in air. For that reason, it is necessary to develop gas sensors to monitor that methane levels below this value. Due to a weak absorption of methane, this gas is difficult to detect using conventional methods.Hollow core photonic crystal fibers (HC-PBF) have emerged as a promising technology in the field of gas sensing. The strong interaction achievable with these fibers are especially advantageous for the detection of weakly absorbing regions of methane. In this paper, we investigated, by full vectorial finite element method (FV-FEM) in Rsoft CAD environment, the dependency of relative sensitivity on the fiber parameters and wavelength. Consequently, we introduced the optimal structureof an index guiding hollow core photonic crystal fiber capable of measuring methane concentrations down to 0.1%in air. The simulations showed that the sensing sensitivity increased with an increase in the core diameter and a decrease in the distance between centers of two adjacent holes.

Weighted adaptive finite-element method for 3D transient EM modelling

As we know, grid quality can produce big effect on the numerical precision of 3D forward modeling. How to generate high-quality grids becomes the key for high-accuracy EM responses. So we develop a weighted adaptive finite-element method based on hybrid posterior error estimation in combination with unstructured vector finite-element method and Backward Euler scheme. We introduce a weighting factor to adjust the relative weight of posterior errors defined by the continuities of normal current density and tangential magnetic field to create an effective mesh. The numerical experiments on a conductive cube model show that our algorithm performs better than the traditional adaptive method.

Pulsed Electromagnetic Cross-Well Exploration for Monitoring Permafrost and Examining the Processes of Its Geocryological Changes

This paper is dedicated to the topical problem of examining permafrost’s state and the processes of its geocryological changes by means of geophysical methods. To monitor the cryolithozone, we proposed and scientifically substantiated a new technique of pulsed electromagnetic cross-well sounding. Based on the vector finite-element method, we created a mathematical model of the cross-well sounding process with a pulsed source in a three-dimensional spatially heterogeneous medium. A high-performance parallel computing algorithm was developed and verified. Through realistic geoelectric models of permafrost with a talik under a highway, constructed following the results of electrotomography field data interpretation, we numerically simulated the pulsed sounding on the computing resources of the Siberian Supercomputer Center of SB RAS. The simulation results suggest the proposed system of pulsed electromagnetic cross-well monitoring to be characterized by a high sensitivity to the presence and dimensions of the talik. The devised approach can be oriented to addressing a wide range of issues related to monitoring permafrost rocks under civil and industrial facilities, buildings, and constructions.

Highly Sensitive Metamaterial Biosensor for Cancer Early Detection

A novel design of metamaterial biosensor for cancer early detection is proposed and analyzed. The suggested structure is based on two loops of hexagonal gold layers on a polyamide substrate. High field confinement is obtained in the sensing region with high absorption of 0.999 and high quality factor of 11.33 at f = 3.15 THz. The resonance frequency is sensitive to the sample refractive index variation. Therefore, high average sensitivity of 1649.8 GHz/RIU is achieved for cancer early detection through basal cell, breast cell, bervical cell, jurkat, MCF-7, and PC12. Further, high linear performance is obtained with good robustness against fabrication imperfection. The analysis is carried out using full vectorial finite element method.

Design and Simulation of Photonic Crystal Fiber for Liquid Sensing

A simple hexagonal lattice photonic crystal fiber model with liquid-infiltrated core for different liquids: water, ethanol and benzene, has been proposed. In the proposed structure, three air hole rings are present in the cladding and three equal sized air holes are present in the core. Numerical investigation of the proposed fiber has been performed using full vector finite element method with anisotropic perfectly match layers, to show that the proposed simple structure exhibits high relative sensitivity, high power fraction, relatively high birefringence, low chromatic dispersion, low confinement loss, small effective area, and high nonlinear coefficient. All these properties have been numerically investigated at a wider wavelength regime 0.6–1.8 μm within mostly the IR region. Relative sensitivities of water, ethanol and benzene are obtained at 62.60%, 65.34% and 74.50%, respectively, and the nonlinear coefficients are 69.4 W−1 km−1 for water, 73.8 W−1 km−1 for ethanol and 95.4 W−1 km−1 for benzene, at 1.3 µm operating wavelength. The simple structure can be easily fabricated for practical use, and assessment of its multiple waveguide properties has justified its usage in real liquid detection.

Double-trench assisted thirteen-core five-mode fibers with low crosstalk and low non-linearity

Information technology has an increasingly strong demand for high-speed and large-capacity optical fiber networks. Space division multiplex(SDM) is a new generation of optical fiber communication technology which can be several times in communication capacity higher than the wavelength division multiplexing systems. In this paper, we present a kind of 13-core 5-mode fiber with double trench structure to meet the demand for high-speed and large-capacity information transmission in the future. In order to solve the crosstalk problem in SDM, a double-trench structure is adopted to better limit the light energy in the fiber core, thus reducing the crosstalk between cores and modes. The crosstalk and transmission characteristics of multi-core fiber are calculated and analyzed by the full vector finite element method and coupled power theory. After the optimization of structural parameters, the fiber can stably transmit LP<sub>01</sub>, LP<sub>11</sub>, LP<sub>21</sub>, LP<sub>02</sub> and LP<sub>31</sub> in the band of 1.3–1.7 μm; when the signal is transmitted at the 1.55 μm for 60 km, the inter-core crosstalks corresponding to the adjacent fiber cores in the above five modes are –122.37 dB, –114.76 dB, –106.28 dB, –100.68 dB and –92.813 dB, respectively; the effective refractive index difference between adjacent modes is greater than 1.026 × 10<sup>–3</sup>; inter-core and inter-mode crosstalk can be effectively suppressed. The corresponding non-linear coefficients of the 5-modes are 0.74 W<sup>–1</sup>·km<sup>–1</sup>, 0.82 W<sup>–1</sup>·km<sup>–1</sup>, 0.88 W<sup>–1</sup>·km<sup>–1</sup>, 1.26 W<sup>–1</sup>·km<sup>–1</sup>, 0.93 W<sup>–1</sup>·km<sup>–1</sup>, which can maintain low non-linear transmission. The structure of fiber is simple and compact, and the preform can be fabricated by vapor deposition method and stack method, then the 13-core five-mode fiber with low crosstalk and low nonlinear can be further drawn, which can be used in a long distance high-speed and large-capacity fiber transmission system.

Highly sensitive photonic crystal fiber liquid sensor in terahertz frequency range

We propose a highly sensitive hollow core photonic crystal fiber (HCPCF) for liquid sensing in the terahertz (THz) region. Asymmetrical rectangular shaped air holes in the cladding region along with Topas glass as a background material is used to get high sensitivity and low confinement loss. The full vector finite element method (FEM) is used to calculate relative sensitivity and other parameters of the proposed liquid sensor where frequency range is taken from 1 THz to 2 THz. The strut distance variations are also studied in this study to find out minimum strut length to make the proposed sensor fabrication friendly. Numerical analysis shows the maximum relative sensitivity of 91.42% for water, 92.55% for acetic acid and 94.03% for chloroform at optimal conditions along with the minimum confinement loss of 1.06 × 10−9cm−1 for water, 2.02 × 10−10cm−1 for acetic acid and 1.39 × 10−11cm−1 for chloroform. To the best of our knowledge, the proposed HCPCF sensor shows maximum relative sensitivity for liquid.

Large mode area single mode photonic crystal fiber with ultra-low bending loss

A novel asymmetrical structure of Photonic Crystal Fibers (PCFs) has been proposed in this article. The first ring consists of three big air holes which can confine the propagating mode in the core region. The second ring consists of twelve doped rods with two different diameters which can decrease the difference of refractive index between the core and the cladding in order to provide the large mode area. The third ring consists of eleven air holes to help the higher-order-modes (HOMs) to leak out. The bending properties of proposed fiber are investigated by full vector finite element method with an anisotropic perfectly matched layer. The numerical results show that the effective mode area of the FM of the proposed fiber is as large as 595.02 μm2 with small bending radius of 10 cm at the wavelength of 1064nm. The bending loss of fundamental mode (FM) is 9.884×10−5dB/m, while large bending loss for the high-order mode (HOMs) is 14.685dB/m. Moreover, the loss ratio can reach 1.45×105which can realize the effective and stability single-mode operation. Therefore, the novel fiber has potential application in high-power fiber lasers.

Novel External Gold-Coated Side-Leakage Photonic Crystal Fiber for Tunable Broadband Polarization Filter

A kind of side-leakage photonic crystal fiber (SL-PCF) with external gold-coated film is proposed by introducing a leakage channel in the x polarization direction. The effects of air-holes diameters, gold film thickness, liquid filling, and different metal coating materials on the polarization characteristics of SL-PCF are analyzed using the full vector finite element method (FV-FEM). At resonance wavelengths of 1.41 and 1.59 $\mu$ m,the losses of x-polarized core mode are 725.74 and 1097.94 dB/cm, while that of y-polarized core mode are only 1.79 and 2.00 dB/cm. When the transmission length of SL-PCF is 1 mm, the bandwidth with extinction ratio better than 20 dB is up to 1410 nm, covering wide wavelengths from 1.09 to 2.5 $\mu$ m. Moreover, the direction of the polarization filter and its resonance wavelength can be effectively modulated by selectively filling the liquid into the cladding air-holes and changing the coating material.Furthermore, the introduction of side-leakage channel not only increases the mode birefringence, but also enhances the fiber's sensitivity to changes in external pressure, bending, and torque. Therefore, the proposed SL-PCF not only has important applications in fiber polarization filters, but also has broad application prospects in fiber sensors.

A photonic crystal fiber for liquid sensing application with high sensitivity, birefringence and low confinement loss

This research introduces a simple designed cost-effective photonic crystal fiber (PCF) for liquid sensing applications. A wide range of wavelengths (1.3μm-2μm) analyzes has been introduced to examine the effect of some design parameters especially for water as a liquid. In addition to water, the proposed model or structure shows how sensitive the human mucosa and glucose are at lower wavelength range (0.6μm-1.3 μm). By using the complete vector Finite Element Method (FEM), the statistical investigation has been performed and comparative performance analysis has been done between the proposed structure and previous structures. The holes in the core of the proposed structure are designed with diameters of different values and a circular shaped hole has been used to reduce fabrication complicacy. According to the calculated output, the proposed structure provides satisfactory performance in terms of sensitivity, birefringence, as well as confinement losses for water and at the same time, shows optimal sensitivity value for human mucosa is 47.31% and for glucose it is 47.59% at a lower wavelength. So simple and unique design of the proposed model can be used highly in relevant sensing applications especially in bio-sensing and chemical sensing applications.

Numerical analysis of photonic crystal fiber of ultra-high birefringence and high nonlinearity

A numerical analysis of a hexagonal PCF structure with four circular air hole rings around the core has been presented in this paper. By utilizing a full vectorial finite element method with perfectly matched layers, propagation properties such as birefringence, chromatic dispersion and confinement losses are numericaly evaluated for the proposed PCF structure. Specifically, birefringence of 2.018 × 10–2, nonlinear coefficients of 40.682 W−1 km−1, negative chromatic dispersion of − 47.72 ps/km.nm at 1.55 µm and − 21 to − 105 ps/km.nm at the telecommunication band of C-U have been reported.

Study of highly sensitivity metal wires assisted photonic crystal fiber based refractive index sensor

In this paper, a photonic crystal fiber (PCF) sensor based on surface plasmon resonance is proposed for refractive index (RI) sensing with improved sensitivity and resolution. In this design, solid core PCF with three layers of holes is used. Instead of a coating metal layer, we have used two metal wires at both sides of the outside layer of fiber to originate surface plasmon resonance for detection of RI of analyte effectively. Design and analyses have been performed by a Full vectorial finite element method (FV-FEM). Metals Cu, Au, and Ag have been used as plasmonic materials that exhibit higher wavelength sensitivity 7300 nm/RIU, 6200 nm/RIU, and 6100 nm/RIU, respectively. For Cu metal, we observe maximum amplitude sensitivity 597 RIU−1 with higher resolution 1.36 × 10–5 RIU for refractive index of range 1.31–1.36. However, the average sensitivity for Cu, Au, and Ag are 4320 nm/RIU, 4275 nm/RIU, and 3950 nm/RIU, respectively. The effect of air holes along with metal wires for sensitivity is also investigated. In results, copper has provided better sensitivity as well as resolution for a long-range analyte for this proposed RI sensor.

Generative Adversarial Neural Networks Model of Photonic Crystal Fiber Based Surface Plasmon Resonance Sensor

Photonic crystal fibers (PCF) for specific applications are designed and optimized by both industry experts and researchers. However, the potential number of design combinations and flexible propagation features are offering a wide range of application areas, resulting in an exponential increase in the search space. This issue combined with the speed of the commonly used full vectorial finite element method (FV-FEM) simulators causes the task to take a significant amount of time. As stated in the previous works, artificial neural networks (ANN) can be employed to predict the result of numerical simulations much faster. However, there are two issues with the methods proposed previously: the required number of samples for training and the generality of these methods. In this article, we propose the use of generative adversarial networks (GAN) to augment the real dataset to train an ANN model. The experimental analysis suggested that the proposed combination not only accurately predicts the confinement loss even with limited amounts of data but also GAN can be used to improve existing methods in the literature. Moreover, the proposed system can also predict the confinement loss over a range of analytes and wavelengths in a completely new geometric configuration and generic enough not to require any additional tuning when used in a new dataset. This property is demonstrated by experimenting on an existing PCF dataset, which the proposed system surpassed the accuracy of the method proposed for it.

Semi-analytical approach for calculation of intercore crosstalk in multicore fibers

In this paper, a semi-analytical method to calculate intercore crosstalk (ICXT) in bent and twisted multicore fibers (MCFs) is proposed. The modified refractive index of bent MCF is first computed using geometrically exact beam theory (GEBT) and conformal mapping technique. The computed refractive index profile is used to obtain mode field profiles of bent MCF by solving the wave equation using vectorial finite element method in COMSOL. To take twisting of MCF into account, outer cores of the MCF are approximated to be helically bent around the central core. Using the mode field profiles, mode coupling coefficient between the MCF cores is calculated for different bend radii which is then used to calculate ICXT by using closed form analytical expressions reported in the literature. The ICXT values obtained using our proposed approach are in very good agreement with the experimental values reported in the literature. The effect of change in core pitch and change in relative refractive index contrast of MCF on the mode coupling coefficient between the MCF cores is analysed. The influence of twisting rate of MCF on the ICXT values for different bend radii is studied and it is shown that, ICXT is constant with respect to twisting rate of MCF for bending radii greater than the critical bending radius of the MCF. The proposed approach is also extended to calculate ICXT between different modes of trench assisted few-mode MCF (FM-MCF). The ICXT values obtained for the trench assisted FM-MCF follow the expected trend.

Numerical analysis of photonic crystal fibre with high birefringence and high nonlinearity

Abstract A four-ring microstructure photonic crystal fibre with a descending air hole ring cladding is presented. Numerical analysis of the structure is done using full vectorial finite element method with perfectly matched layer (PML) boundary condition. It is demonstrated that it is possible to achieve at 1.55 µm confinement loss of 2.767 × 10−5 dB/m, birefringence of 0.00346 and a nonlinear co-efficient of 41.77 km−1 W−1. Also, chromatic dispersion realised suggests a tuneable zero dispersion at 0.9–1.1 µm wavelength range.

Ultra-short and dual-core photonic crystal fiber polarization splitter composed of metal and gallium arsenide

Two ultra-short polarization beam splitters (PBSs) based on surface plasma resonance (SPR) are designed for wavelengths of 1.31 and 1.55 μm. The center of the PCF has an oval hole filled with gold and the first layer of the air holes around the core is filled with the nematic liquid crystal (NLC) to enhance birefringence. In this work, the full vector finite element method is used to optimize the structural parameters. Two sets of parameters with extinction ratios of 114.02 and 111.86dB and lengths of 14.52328 and 11.02418μm are designed at wavelengths of 1.31 and 1.55 μm respectively. The results reveal that the beam splitters with broadband and short fiber length have important prospects in communication applications.