Full-vector Finite Element Method Research Articles

Design and analysis of surface-plasmon-resonance-based dual-cladding micro-structured fiber temperature and refractive index sensor

Combining the surface plasmon resonance(SPR) effect and the characteristics of dual-cladding micro-structured fiber(DC-MF), this study presents the design and analysis of a temperature and refractive index sensor. The performance of the sensor is analyzed by using the full-vector finite element method, and the structure parameters of the DC-MF and the thickness of the plasmonic material (ITO film), is optimized to achieve high sensitivity measurements of temperature and refractive index. Theoretical analysis results indicate that its maximal temperature and refractive index sensitivity can reach to 25.4 nm/°C and 46559.8 nm/RIU in −40 °C to −40 °C. Its average temperature and refractive index sensitivity is 22.53 nm/°C and 38292.3 nm/RIU in the temperature range from −40 °C to 0 °C, and the value is 7.03 nm/°C and 12591.7 nm/RIU in the temperature range from 0 °C to 40 °C. Besides, its operating wavelength shifts toward a long wavelength region (about 1.05 μm–2.25 μm) as the refractive index of analyte increases from 1.424 to 1.471.

Simulation of a Sensitive Mid-infrared (MIR) D-Shaped Optical Fiber Water Pollutant Sensor

In this work, an efficient optical sensor is proposed for the sensitive detection of various pollutants in water. The suggested optical sensor is based on an indium fluoride (InF3) glass fabricated as a D-shaped optical fiber. The polished surface of the D-shaped fiber is coated with a gold grating to induce the surface plasmon resonance (SPR). The SPR depends on the optical properties of the polluted water analyte in physical contact with the grating. The proposed optical SPR fiber sensor operates within the mid-infrared (MIR) range (3000–4500 nm) to detect any slight change in the water refractive index (RI) due to any pollutants. The full vectorial finite element method (FVFEM) is utilized to calculate the modal properties of the reported sensor. High sensor sensitivity of 17,834 nm/RIU (refractive index units) is achieved for the detection of dissolution of nitric acid (HNO3) in water at a concentration of 14% v/v (volume/volume). Additionally, the reported sensor detects the dissolution of hydrogen peroxide (H2O2) in water investigated at concentrations of 15% v/v and 30% v/v, with sensitivities of 12,308 nm/RIU and 17,143 nm/RIU, respectively. Further, suspending polystyrene beads of diameter 0.1 μm in the water at a concentration of 10% v/v gives a maximum sensitivity of 5333 nm/RIU. Therefore, the proposed sensor provides a promising approach for the detection of water pollutants in the MIR wavelength regime, rather than the weaker response in the near infrared.

THz dual-core liquid photonic crystal fiber with high negative dispersion

A novel photonic crystal fiber (PCF) design is proposed and analyzed with highly negative dispersion for THz applications. The reported PCF has TOPAS background material due to its low material loss in THz regime. Further, dual porous cores are constructed and selectively infiltrated with liquid crystal (LC) material to control the dispersion characteristics of the reported PCF. The basic operation of the suggested dual core LCPCF (DC-LCPCF) depends on the optical coupling between the supported modes of the two porous core regions in the THz regime to achieve high negative dispersion for the two fundamental polarizations: transverse electric (TE) and transverse magnetic (TM). The coupling can be switched between the TE and TM modes by applying an external electric field on the LC material via two metallic electrodes. The full vectorial finite element method (FVFEM) is utilized to study the dispersion characteristics of the DC-LCPCF structure. The obtained results reveal that the TE and TM modes have large negative chromatic dispersions of − 44.57 ps/THz/cm and − 30.59 ps/THz/cm at frequencies of 0.386 THz and 0.4027 THz, respectively. So, it will be a solution for further innovation of fiber devices in the THz regime.

Low-loss and high-sensitivity surface plasmon resonance sensor composed of microstructured optical fibers for wide visible-to-infrared and refractive index ranges

ObjectiveOptical fiber sensing technology develops rapidly and is widely used. In order to design a SPR sensor with better performance and easy production, a new type D-MOF sensor with low loss, high sensitivity and simple structure is proposed. MethodsThe full vector finite element method (FEM) was used to optimize the structure parameters by using the multi-physics analysis software COMSOL, and the performance of the structure was systematically analyzed. ResultsThe sensor operational wavelength spans the visible and infrared range (430 nm to 7200 nm). The refractive index detection range of 1.00–1.42, the maximum wavelength sensitivity and the optimal resolution are 60,000 nm/RIU and 1.67 × 10−6 RIU−1, respectively, and the maximum limiting loss peak is 64.99 dB/cm. In addition, MOF-SPR sensors have large tolerance and low sensitivity of structural parameters in actual manufacturing. It has great application potential in biosensing and other fields.

Dual-resonant-peak single-mode fiber surface plasmon resonance gas sensor with V-groove for methane detection

ObjectiveThe simple structure of single-mode fibers as a sensing platform circumvents the technical bottlenecks associated with manufacturing difficulties. Meanwhile, compared to photonic crystal fibers, they have lower manufacturing costs and can achieve similar performance to other types of fibers, providing greater possibilities for mass production. The V-groove in the SMF destroys the original symmetry of the fiber and renders the core mode energy leak controllable, consequently enhancing the sensitivity and confinement loss (CL) intensity of the core mode as well as the resolution. The composite nanolayer (gold gas-sensitive film) combines the advantages of both the materials and mutual gain to strengthen the detection ability and continuously outputs high-quality free electrons to promote mode coupling. MethodsA dual-resonant-peak single-mode fiber (SMF) surface plasmon resonance (SPR) gas sensor with a V-groove is designed for the sensitive detection of methane and analyzed by the full-vector finite element method (FEM). ResultsBy optimizing the structural parameters and polarization states, the SPR sensor can be operated in the concentration range between 0 % and 3.5 %, which can be spread across two transmission bands simultaneously with the maximum wavelength sensitivities being 12 nm/% and 8 nm/% and the corresponding resolution being 0.0083 % and 0.013 %, respectively. The tolerance of the structural parameters of the sensor is below 0.88 nm/μm to make manufacturing easier compared to conventional products. This sensor has good prospects and application potential in areas such as gas leakage diagnostics and environmental safety.

High Sensitivity and Wide Range Refractive Index Sensor Based on Surface Plasmon Resonance Photonic Crystal Fiber.

In order to detect the refractive index (RI) of high refractive index materials such as trichlorobenzene and aniline in the near-infrared and mid-infrared spectra and expand the detection range of the refractive index, a surface plasmon resonance (SPR) photonic crystal fiber (PCF) sensor based on an elliptical sensing channel is proposed for high refractive index detection. The fiber core and the analyte channel are surrounded by two types of air holes with different sizes. When the surface plasmon resonance effect appears at the interface between the fiber core and the elliptical sensing layer, obvious resonance peaks appear in the near-infrared and mid-infrared bands. The full vector finite element method (FEM) is used to study the sensing characteristics of the sensor and the influence of structural parameters on the resonance peak. The results demonstrate that the sensor achieves detection in the refractive index range of 1.41-1.58, in the wavelength range of 1600-3200 nm. The average wavelength sensitivity is 9217.22 nm/RIU, and the refractive index resolution is 10.85 × 10-6 RIU. The proposed sensor realizes high refractive index detection in the near-infrared and mid-infrared bands, and obtains an ultra-wide detection range and higher sensitivity. The sensor has broad application prospects in chemical detection, biomedical sensing and other fields, and provides a theoretical reference for the design of a photonic crystal fiber surface plasmon resonance sensor.

Design of an octagon structure dual-core photonic crystal fiber polarization beam splitter with a liquid crystal filled central hole

In this paper, an octagon structure dual-core photonic crystal fiber (OS-DC-PCF) polarization beam splitter (PBS) with a liquid crystal filled central hole is designed. The octagon lattice structure is simple and easy to fabricate. By filling the nematic liquid crystal into the central hole, the birefringence of the octagon structure can be enhanced, and the coupling lengths along the two polarization directions can be reduced. The full vector-finite element method is used to analyze the polarization and coupling characteristics, and the influences of different structural parameters on the extinction ratio (ER) of the PBS. The simulation results show that for the designed OS-DC-PCF PBS, the maximum ER is ∼91 dB, the splitting length is only 125μm, and the working bandwidth is up to 339 nm (1.493–1.832μm), covering the whole C+L+U communication bands. Moreover, it has good fabrication tolerances and anti-interference ability. It is believed that the designed OS-DC-PCF PBS can provide the critical device support for the future all-optical communication systems.

Low-Loss Nodeless Conjoined-Tube Anti-Resonant Hollow-Core Fiber

We propose a novel nodeless conjoined-tube hollow-core fiber (CT-HCF) with elliptical arcs as negative curvature boundaries to limit the leakage of transmitted light. The cladding nodes are effectively eliminated by the attachment of arcs to the outermost dielectric tube. Numerical simulations performed using the full-vector finite element method show that a significant reduction in fiber loss over a wide bandwidth can be obtained. The confinement losses for the proposed fiber are two orders of magnitude lower than those obtained for a typical CT-HCF. The total loss, including confinement loss and surface scattering loss, is also investigated. The proposed fiber shows a loss of less than 0.1 dB/km for a bandwidth of 450 nm, with a minimum loss of 6.58·10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> dB/m at 1.45 μm. Moreover, the proposed fiber exhibits good single-mode performance, with the higher-order mode extinction ratio reaching a maximum value of 39341 at 1.7 μm.

Design and numerical analysis of dual-core photonic crystal fiber-based biosensor

In this study, the coupling and the relative sensitivity characteristics of a Dual-Core photonic crystal fiber (DC-PCF)-based liquid sensor are evaluated by employing the full-vectorial finite element method (FV-FEM). The simulation results demonstrate that coupling length of the proposed sensor varies between 2[Formula: see text]mm and 0.2[Formula: see text]mm length at wide wavelength range (800–1600[Formula: see text]nm) for low index analytes (1.33–1.36). Besides, birefringence of order [Formula: see text] is reported. It is found that analyte with 1.36 index reaches higher sensitivity levels. On the other hand, the coupling length of the proposed sensor can be optimized with the ellipticity ratio of the central core hole. Bending analysis on coupling length and optical power fluctuations is also reported. It is found that the power flow in one core is increasing almost 90% towards the bending direction. The proposed structure with simple design parameters has a great potential in various biomedical applications including DNA detection and can also be employed as fiber-based refractometer in various sensing applications.

Au-TiO2 Coated Photonic Crystal Fiber Based SPR Refractometric Sensor for Detection of Cancerous Cells.

A surface plasmon resonance (SPR) refractometric sensor based on gold (Au) and titanium dioxide (TiO2) coated Photonic Crystal Fiber (PCF) is presented for the quick detection of various types of cancerous cells. The cancerous cells and their corresponding normal cells are both considered to be liquid cells each with their unique refractive index (RI). Normally these cells are found in liquid form in the suitable media (food) required to live the cancerous/normal cell lines. Also in our detection case, liquid samples are easy to pump into the sensing channel of the proposed PCF by employing either pressure or capillary forces.The proposed PCF sensor works on the SPR principle, with the Au coating serving as the plasmonic material. This sensor is investigated using the COMSOL Multiphysics software computational tool that is based on the full-vector finite element method (FEM). A TiO2 coating has been applied to enhance adhesion between the Au layer and the PCF surface. Above the Au coating, cancerous cells samples are filled into the PCF. When the core mode of the PCF is coupled with the surface plasmon polariton (SPP) mode under the specific resonance circumstances, SPR will occur on the interface of the gold-sample cell, and in the core mode, the loss peak is observed at the resonance wavelength. Cancerous cells samples have a distinct loss peak than normal cells samples therefore the cancerous cells can be diagnosed by measuring the shift in resonance wavelength corresponding to the loss peak of cancerous and their normal cells samples. The proposed sensor may identify various cancerous cells such as MDAMB-231, MCF-7, PC12, HeLa, and Jurkat for the diagnosis of breast cancer type-1, breast cancer type-2, adrenal glands, cervical, and blood cancer respectively. The computed wavelengths sensitivities of the proposed PCF are 9428.57nm/RIU, 10714.28nm/RIU, 7571.43nm/RIU, 5500nm/RIU, and 6000nm/RIU for the MDAMB-231, MCF-7, PC12, HeLa, and Jurkat cancerous cells, respectively. However, for various cancerous cells, the maximum amplitude sensitivity varies from -1387 RIU-1 to -1599 RIU-1. Moreover, the sensor resolution ranges between 0.93 ×10-5 RIU and 1.82 ×10-5 RIU with a 0.024 maximum detection limit. Because of its improved sensing capability, the presented SPR refractometric sensor is appropriate for the early detection of cancerous cells.

Design and analysis of a hexagonal circular photonic crystal fibre with ultra-high negative dispersion and low confinement loss

This paper proposes a Hexagonal Circular Photonic Crystal Fiber (HC-PCF) with uniform tiny air holes around the core, obtaining ultra-high negative dispersion, high Birefringence and low confinement loss. The modal properties of the HC-PCF are investigated using the full-vectorial-Finite Element Method (FEM) with a perfectly matched layer as the boundary condition. The numerical investigations show ultra-high negative dispersion of −25503 ps/nm.km, a birefringence of 1.36×10-2, a nonlinearity of 38.34w-1km-1 and a confinement loss of 4.95×10-3 dB km-1 at the wavelength of 1550 nm. Moreover, the proposed HC-PCF exhibits a high negative dispersion and multiple Zero Dispersion within the 800 to 2000 nm wavelengths range. Specifically, the high negative dispersion, low optical Confinement Loss, and multiple Zero Dispersion Wavelengths (ZDW) give the proposed HC-PCF high Power Spectral Density (PSD). These characteristics make the proposed fibre suitable for long-range telecommunication networks and optical sensing.

Terahertz photonic crystal fiber for sensing the creatinine level in the blood

In this work, THz photonic crystal fiber (PCF) is used to detect the creatinine level in the blood with high sensitivity. The sensing technique depends on increasing the light interaction with the analyte infiltrated into the air holes in the fiber core region. In this regard, most of the light power should be confined through the analyte region. This will increase the relative sensitivity coefficient that is proportional to the analyte power fraction. The operation of the suggested sensor is based on studying the light–analyte interaction at different creatinine concentrations by detecting the change of the analyte power fraction against the change of the creatinine level in the blood at the THz range 0.5–1.5 THz. The effective mode index (neff), effective material loss (EML), effective modal area (Aeff), and relative sensor sensitivity are calculated using the full vectorial finite element method. Additionally, the different geometrical parameters are studied to maximize the sensor’s sensitivity. The proposed THz-PCF has a 93% and 95% relative sensitivity for x- and y-polarized modes, respectively. Therefore, the suggested THz-PCF biosensor gives a promising usage in measuring the creatinine level in the blood.

Optical mid-infrared modulator based on D-shaped photonic crystal fiber and GST phase changing material

Photonic crystal fibers (PCFs) have recently attracted compelling attention because of their numerous applications, particularly in the mid-infrared (mid-IR) wavelength region. In this paper, we have presented and analyzed mid-IR optical modulator based on phase-changing material (PCM) known as germanium-antimony-tellurium (GST) and D-shaped PCF. The modulation process can be performed as the GST material’s phase undergoes a transition between amorphous (on) and crystalline (off) states. To analyze the proposed design numerically, full vectorial finite element method (FVFEM) is employed. Further, we studied the light propagation through the suggested structure using 3D finite difference time domain (FDTD) method. The optical losses of the fundamental transverse electric (TE) mode supported by the reported structure in the two GST states are studied. The obtained extinction ratio (ER) of the proposed modulator approaches 302.61 dB, whereas the insertion loss (IL) is less than 0.00014 dB throughout the wavelength range from 3 to 5.8 μm at a device length (LD) of 0.2 mm. Therefore, the suggested modulator can be utilized in photonic integrated circuits that require high ER, very low IL, and large optical bandwidth.

Double-clad photonic crystal fibre for two-photon microscopy

Miniaturized and head-mountable scanning nonlinear fibre-optic microscopy offers an exciting opportunity for the visualization of brain activity on freely walking mice. One challenge in the creation of such miniaturized microscopes is the design of optical fibres capable of delivering ultrashort pulses without distortion and collecting fluorescence simultaneously and efficiently. A double-clad photonic crystal fibre (DCPCF) with 37-cell air holes arranged in hexagonal lattice in core is proposed. The full vector finite element method (FEM) is used for numerical analysis. Nearly zero dispersion of −0.34 ps/nm/km at 920 nm wavelength is finally achieved. The single-mode core with an NA of 0.53 at 920 nm wavelength is used to deliver the femtosecond excitation beam and the inner cladding with an NA of 0.54 at 532 nm is used to collect the two-photon fluorescence signal. The nearly zero dispersion, high NA and low nonlinearity will be beneficial to promote its application in two-photon microscopy.

Nearly Zero Ultra-Flattened Dispersion in Octagonal Photonic Crystal Fiber

The low confinement losses, relatively high nonlinearity, and wideband ultra-flattened chromatic dispersion are the crucial properties of the PCFs. Thus, in this research, a comprehensive study has been conducted to design a novel Octagonal PCF (Photonic Crystal Fiber) microstructure with an ultra-flattened dispersion profile through a vast range of optical communication band wavelengths with a large negative dispersion of nearly 0.6635 ps/nm/km at 1550 nm. This PCF design and simulative study have been made by using COMSOL multi-physics. The guiding features of the fiber have been analyzed numerically to solve the Maxwell equation of electromagnetic field by using the full vector finite element method with cylindrically perfect to match layer for strongly absorb the outgoing waves from the computational region. Moreover, Octagonal rings in the cladding region provide better confinement and flattened dispersion in O-band (1260 nm-1360 nm) and C-band (1530 nm-1565 nm) in comparison to honeycomb or hexagonal lattice structures. Our proposed model has a nearly zero ultra-flattened dispersion of ± 0.3028 ps/nm/km in a 1290 nm to 1620 nm with wavelength range (320 nm flat band) and low confinement loss is less than 10-7 dB/km in the entire band of interest. Furthermore, this research has been presented a 7.2 μm2 effective area which is smaller than other reported fibers at 1550 nm wavelength.

Design and optimization of a Micro-structured fiber temperature sensor based on surface plasmon resonance

Basing on surface plasmon resonance technology, a micro-structured fiber temperature sensor with a simple structure is proposed. It has a three core micro-structured fiber infiltrated with temperature-sensitive material (chloroform). Moreover, an ITO film is selected as the plasmonic material to stimulate surface plasmon resonance. A large number of numerical calculations are carried out by using the full vector finite element method, and the influence of structural parameters on the temperature sensitivity is analyzed. The results show that the temperature sensitivity can be improved by reducing D1 and the ITO thickness. By optimizing the parameters, the sensor has a maximum temperature sensitivity of 18 nm/°C. Moreover, the average temperature sensitivity can reach to 17.1 nm/°C(the corresponding wavelength sensitivity is 26771.7 nm/RIU) in the temperature range from −40 °C to 0 °C, and the average temperature sensitivity is 7.07 nm/°C (the corresponding wavelength sensitivity is 11343.9 nm/RIU) in the temperature range from 0 °C to 40 °C.

A low-loss polarization-maintaining terahertz fiber

A novel low-loss THz polarization-maintaining fiber is analyzed numerically. The proposed fiber consists of two small thin dielectric tubes nested in a large dielectric tube. Numerical simulations performed using the full-vector finite element method show that the difference between the effective refractive index of LPx01 and the adjacent modes is up to 10−2 orders of magnitude in the frequency range from 0.32 to 0.7 THz. At the same time, the proposed fiber has low loss characteristics, and the total loss of LPx01 is only 0.17 dB/cm at 0.35 THz. In addition, near-zero flat dispersion of 0.3 ± 0.36 ps/THz/cm can be achieved by adjusting the structural parameters of the fiber.

Efficient MIR crosstalk reduction based on silicon-on-calcium fluoride platform with Ge/Si strip arrays

Reduction of the crosstalk (CT) between contiguous photonic components is still a big challenge in fabricating high packing density photonic integrated circuits (PICs). Few techniques to accomplish that goal have been offered in recent years but all in the near-IR region. In this paper, we report a design for realizing a highly efficient CT reduction in the MIR regime, for the first time to the best of our knowledge. The reported structure is based on the silicon-on-calcium-fluoride (SOCF) platform with uniform Ge/Si strip arrays. Using Ge strips shows better CT reduction and longer coupling length (Lc) than the conventional Si based devices over a wide bandwidth in the MIR region. The effect of adding a different number of Ge and Si strips with different dimensions between two adjacent Si waveguides on the Lc and hence on the CT is analyzed using both full vectorial finite element method and 3D finite difference time domain method. An increase in the Lc by 4 orders of magnitude and 6.5 times are obtained using Ge and Si strips, respectively, compared to strips-free Si waveguides. Consequently, crosstalk suppression of − 35 dB and − 10 dB for the Ge and Si strips, respectively, is shown. The proposed structure is beneficial for high packing density nanophotonic devices in the MIR regime, such as switches, modulators, splitters, and wavelength division (de)multiplexers, which are important for MIR communication integrated circuits, spectrometers, and sensors.

Design of Single-Polarized Single-mode Photonic Crystal Fiber Without Air Holes in the Cladding

This study proposes a novel single-polarized single-mode (SPSM) photonic crystal fiber (PCF) without air holes in the cladding, and the silicon nitride holes and air holes in the core of the PCF are staggered. Based on the full vector finite element method, the birefringence characteristics with different hole sizes have been discussed in detail, and a SPSM-PCF is achieved through optimizing the core structure. Moreover, the extinction ratio, effective refractive index, dispersion, confinement loss and nonlinearity of the PCF are analyzed. Simulation results show that the PCF can obtain a high birefringence value of 2.142 × 10−3 , a large negative dispersion of −2750 ps/(nm · km), a low confinement loss of 1.57 × 10−7dB/m and a high nonlinear coefficient of 90.5W−1 · km−1 at the wavelength of 1.55 μm. In this paper, the proposed structure has the properties of high birefringence and high negative dispersion, which can be used in fiber laser, optical fiber sensing, dispersion compensation and other fields.

Ultra-high birefringence with tuneable double zero chromatic dispersion-PCF: a theoretical analysis

This work presents photonic crystal fibres made up of four hexagonal shape of four rings. Four structures have been designed and configured. The structures show improvement in optical properties consecutively to achieve the optimum configuration. The full vectorial finite-element method is adopted for this work. COMSOL Multiphysics is used for the simulation. The results show a birefringence of 1.308 × 10−2 at 1.55 µm and tuneable double zero dispersion at wavelengths of 0.99 µm and 1.8 µm for x-polarisation mode. Also, the chromatic dispersion of − 24.062 ps/km nm and nonlinear coefficient of 30.32 W−1 km−1 are obtained at a telecommunication wavelength of 1.55 µm. The proposed photonic crystal fibre can be beneficial in nonlinear and supercontinuum applications since photonic crystal fibres of double zero dispersion demonstrate higher power spectral densities than single zero dispersion.