Air Holes In Core Research Articles

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.

Dual polarized surface plasmon resonance refractive index sensor via decentering propagation-controlled core sensor

Refractive index (RI) is a unique attribute of bio-analytes which highly relies upon their concentrations or the activity/infectivity of the microbes. In this paper, a dual-polarized surface plasmon resonance (SPR) RI sensor based on a decentered propagation-controlled core photonic crystal fiber (PCF) has been studied. Fine-tuned light guidance is realized by scaling down the core air holes. The external surface of the fiber is metalized with a thin gold layer that maximizes the chemical stability by reducing the chances of oxidation. The deposition of the core from the central position reduces the core to analyte distance resulting in efficient coupling as well as greater sensitivity. Finite element method (FEM) based numerical investigation warrants promising sensing performances in wavelength and amplitude interrogation methods. The proposed sensor is viable for the RI range from 1.33 to 1.39, where it demonstrates the highest wavelength sensitivities of 13,700 and 15,400 nm/RIU and highest amplitude sensitivities of 852 RIU-1 and 654 RIU-1 in x-and y-polarized modes, respectively. It also exhibits high sensor resolutions of 7.30 × 10−6 RIU and 6.49 × 10−6 RIU, and high figure of merits of 216 and 256 RIU-1 for x and y-polarized modes, respectively. Along with the liberty of selecting light sources, the highly sensitive nature of the sensor will enable accurate detections of different organic compounds and bio-molecules.

Design and analysis of low loss porous-core photonic crystal fiber for terahertz wave transmission

We present a low loss hexagonal-core porous Photonic Crystal Fiber (PCF) for wave propagation in terahertz (THz) range. The cladding contains circular air holes whereas the core consists of elliptical air holes. As background material, Cyclo-Olefin Copolymer (COC) (also known as TOPAS) was used because in the terahertz range (0.1–2 THz), it shows a constant refractive index. The design has been analysed by using FEM-based COMSOL software for a particular frequency range and by varying radius along the x-axis. We observed that at radius of 8 µm and an operating frequency of 0.9 THz, the proposed fiber exhibits low effective material loss of 0.0697 cm−1 and low confinement loss in the order of 10−3 cm−1. Moreover, we did a complete analysis of the transition of core air holes from elliptical to circular.

Magnetic field sensor with truncated honeycomb photonic crystal fiber: analysis under the variations in magnetic fluid composition and temperature for high performance in near infrared

A photonic crystal fiber (PCF)-based magnetic field sensor is simulated and analyzed by using a honeycomb fiber without the first ring of air holes where the core air hole is filled with a magnetic fluid which is surrounded by a gold layer. The variation of the refractive index with the magnetic field at a fixed wavelength (1557 nm) is considered for the study. The sensor is based on variation of the transmission loss of optical power with the magnetic field. The real part of the effective index increases with the magnetic field. The simulation and analysis is carried out at (i) three different temperatures (t = 24.3 °C, 40 °C, and 60 °C) and, (ii) for different values of the volume fractions (c = 1.21%, 1.48%, 1.52%, and 1.93%) of Fe3O4 particles in a magnetic fluid solution. All the concerned values of magnetic fluid refractive index are adapted from the previously-reported experimental work. The detailed analysis of the simulation results indicates that the proposed PCF sensor has the capability of providing high sensitivity, ultrafine resolution, and low thermal sensitivity. The variation of Fe3O4 provides another crucial degree of freedom to further enhance the sensitivity of the magnetic field detection. The sensor can provide a sensitivity of 4.3763 dB/Oe and magnetic field resolution of 2.2850 × 10–3 Oe for a large enough range (∆H = 163.87 Oe) of magnetic field (28.58 Oe ≤ H ≤ 192.45 Oe).

Rectangular Porous-Core Photonic-Crystal Fiber With Ultra-Low Flattened Dispersion and High Birefringence for Terahertz Transmission

We propose a novel porous-core photonic crystal fiber (PCF) consisting of an asymmetric rectangular air-holes in core and six-ring hexagonal lattice circular air-holes in the cladding for achieving low loss polarization terahertz transmission in wide frequency range. By assuming TOPAS as the host material, finite element mothed (FEM) is used to investigate its properties. The near-zero flattened dispersion of -0.01±0.02 ps/THz/cm is achieved over a frequency range of 1.0-2.0 THz, as well as a high birefringence of 7.1×10-2 which can be useful for polarization maintaining applications. Also, critical parameters such as modal field distribution, effective modal loss, confinement loss, effective mode area, are discussed in detail. Further, fabrication possibilities are discussed briefly by comparing recent work on similar waveguide structures.

Design and characterization of rectangular slotted porous core photonic crystal fiber for sensing CO2 gas

In this article, we propose a rectangular slotted porous core photonic crystal fiber (RSPC-PCF) for sensing the CO2 gas. The RSPC-PCF is made of purely silica material with rectangular air holes in core and circular air holes in cladding. The COMSOL Multi-physics software with version 4.5.150 is used as a design and simulation tools. The effects of tuning the geometrical parameters have been numerically analyzed by using full-vector finite element method (FEM). The numerical results show the maximum relative sensitivity of 24% and minimum confinement loss of 0.0012 dB/m at 4 μm the absorption wavelength of CO2 gas. In addition, numerical aperture (NA) is also explored to check the light acceptance of the sensor. Since our proposed design is very simple having better sensitivity, it will be a suitable candidate for sensing the CO2 gas in the earth's atmosphere effectively.

Designing a dual steering wheel microstructured blood components sensor in terahertz wave band

We design a photonic crystal fiber (PCF) biosensor, based on the refractive index, capable of operating in terahertz (THz) region. This structure comprises a dual steering wheel (DSW) shape of large noncircular air–hole structure in the cladding region. This PCF is designed using rectangular structured air holes in core, and they are filled with blood components as analytes. We use the full-vectorial finite-element method to optimize the structural parameters and to characterize the proposed PCF. The simulation results demonstrate a high relative sensitivity for water, cytop, plasma, white blood cells, hemoglobin, red blood cells, sylgard184, biotin–streptavidin, polyacrylamide, and bovine serum albumin. As the practical sensor setup requires connecting a single-mode fiber with that of the PCF, we compute the effective area (Aeff), V-parameter (Veff), spot size (Weff), beam divergence (θ), and dispersion (β2) of the proposed PCF over the wide THz range. We envisage that the proposed fiber may not only be useful for the measurement of various blood components but also for polarization-preserving applications in the THz region.

Sensing of Illegal Drugs by Using Photonic Crystal Fiber in Terahertz Regime

Abstract Stimulant abuse enhances dopamine release, thereby causing increased excitation. Any extent of stimulant abuse can considerably harm the user. Thus, methods of detecting stimulants must be precise, accurate, and reliable. A novel terahertz (THz) photonic crystal fiber with a Topas substrate is designed and rigorously investigated for detecting liquid amphetamine, cocaine, and ketamine. The fiber structure has a pentagonal shape and comprises circular air holes in the core and cladding spatial extents. As shown in finite element simulation, the proposed fiber yields a high relative sensitivity of approximately 80 % when any of the liquid stimulants is infiltrated in the core air holes. At 1 THz operating frequency, the proposed fiber produces a large effective mode area, negligible confinement loss, and extremely low bending and effective material losses. Other THz waveguiding properties, such as core power fraction and total loss, are also studied. Lastly, a positive and negative 2 % fabrication tolerance is set to ensure seamless potential practical realization of the fiber.

Methanol-Filled Hybrid Photonic Crystal Fiber with High Birefringent and Negative Dispersion

A unique hexagonal lattice structure of silica-based solid core photonic crystal fiber (PCF) surrounded by array of air holes is proposed. The cladding portion of the structure consists of five rings where core is made up of 11 small rings filled with methanol. Three different-shaped structures are used to analyze the effect on PCF parameters where the first structure uses circular air holes in cladding and core, the second structure consists of circular air holes in cladding and elliptical air holes in core, and the last structure was designed by using elliptical air holes in both cladding and core. Optical properties birefringence, confinement loss, and negative dispersion have been found theoretically and compared. A novel and relatively simple approach depicts the results that attain high birefringence, low confinement loss, and negative dispersion. It is found that the presence of elliptic air holes instead of circular air holes in the core region and the cladding brings higher birefringence, low confinement loss, and highly negative dispersion.

Low loss and highly birefringent photonic crystal fibre for terahertz applications

A highly birefringent photonic crystal fibre, with horizontal arrangement of three elliptical air holes in the core and hexagonal arrangement of circular air holes in the cladding, has been proposed for transmission of terahertz waves. Guiding properties of the fibre have been rigorously investigated using finite element method with perfectly matched layer boundary conditions. It has been demonstrated that high birefringence of 0.08 can be achieved with low effective material loss of 0.03 cm−1 at 1.3 THz. Moreover, it has been shown that about 42 % of useful power flows through the elliptical core air holes. Near-zero flattened dispersion of 1.18 ± 0.01 ps/THz/cm is obtained for the x-polarisation mode of the fibre. Other important optical properties such as confinement, bending and total losses have also been investigated; further strengthening potential applicability of the proposed fibre for next-generation terahertz research.

Fluorescence sensor for volatile trace explosives based on a hollow core photonic crystal fiber

A novel hollow core photonic crystal fiber (HC-PCF) volatile trace explosive sensor based on the fluorescence quenching was proposed, which was made by coating the allyl tetraphenylethylene (AL-TPE) fluorescence nanofilm onto the inner surface of a HC-PCF core air hole. The theory of the fluorescence quenching was used to analyze the principle of explosives sensing. The effects of the refractive index (RI) and thickness of the fluorescence film on the light intensity at the core inner wall were analyzed theoretically and numerically. The results show that when the RI of the fluorescence film was close to 1.45 and the thickness was close to 150 nm, the normalized intensity of the light field energy at the core inner wall was 9.72%. The HC-PCF fluorescence explosive sensor was fabricated by a multiple cleaving filling technique and a pressure driven coating method. The experimental results show that the sensitivity of 2,4,6-trinitrotoluene (TNT) detection was 0.309/ppb and the minimum detection limit was 0.340 ppb for the sensor with a film thickness of 155 nm. The response time (T90) of 2,4-dinitrotoluene (2,4-DNT) was 120 s for the sensor with a film thickness of 110 nm.

Porous photonic-crystal fiber with near-zero ultra-flattened dispersion and high birefringence for polarization-maintaining terahertz transmission

One unique kind of porous-core photonic crystal fiber (PCF) is proposed with elliptical air-holes in core, and round-corner hexagonal air-holes in cladding, for efficiently transmitting polarization-maintaining terahertz waves. Dispersion, birefringence, effective material loss (EML) and confinement loss are investigated by using the full-vector finite element method (FV-FEM) with anisotropic perfectly matched layers. The numerical results indicate that its near-zero ultra-flattened dispersion (-0.01±0.06 ps/THz/cm) and birefringence higher than 7.0×10−2 (highest birefringence of 7.4×10−2 at 1.2 THz) can be achieved simultaneously over almost the same frequency range of 0.75–1.6 THz, with a low EML (0.08 cm−1 at 1.2 THz) and a low confinement loss (3.2 × 10-13 cm−1 at 1.2THz). Important modal properties, such as power fraction and effective mode area, are discussed, and the tolerance in fabrication is analyzed to indicate the feasibility of the proposed terahertz waveguides with PCF structure in manufacturing.

Design of terahertz spectroscopy based optical sensor for chemical detection

In this article, a new design of circular cladding with a rotated-hexacore in photonic crystal fiber (RH-CPCF) has been suggested for chemical sensing application in the THz regime. The five layers circular cladding and two layers rotated-hexacore in circular shape are designed here. All numerical results are obtained with a procedure of finite element method and perfectly match layered boundary condition in terahertz (THz) wave propagation. After the simulation result, the proposed RH-CPCF shows the high relative sensitivity is 76.44%, 77.16% and 73.20% for three chemicals such as Ethanol (n = 1.354), Benzene (n = 1.366) and Water (n = 1.330) at 1 THz. On the other hand, the low confinement losses are 2.33 × 10−03 dB/m, 3.07 × 10−06 dB/m and 2.84 × 10−02 dB/m for same in three chemicals at 1 THz. Moreover, effective area, effective mode index and total power fraction in core air holes are also briefly described here. In addition, this proposed circular photonic crystal fiber (RH-CPCF) can be used especially for chemical sensing in biomedical, industrial quality control, material research, micro-optics and many communication applications in THz technology.

Highly birefringent, low loss single-mode porous fiber for THz wave guidance

Abstract In this letter, authors have proposed a circular structured photonic crystal fiber for low-loss terahertz waveguiding. Transmission characteristics of the photonic crystal fiber (PCF) have been conducted by implementing a perfectly matched layer (PML) in the boundary using finite element method. Power transmitted through the core has been improved by tuning the geometries of the core air holes. The proposed design at the porosity of 80% and a diameter of 304 µm has reported a very low effective material loss of 0.046 cm−1. In the meantime, it reduces the maximum bulk absorption material loss by ∼77%. Moreover, the utmost birefringence of 0.057 is derived at the frequency f = 1.01 THz. Properties like, power fraction of the core air holes, responses of the effective material loss on the basis of the geometric parameter, power fraction with respect to diameter, have been also reported and well discussed.

Sensitivity analysis of steering-wheel gas sensor against diverse core air hole sizes and core materials in terahertz wave band

We design a photonic crystal fiber (PCF) based gas sensor, which works based on evanescent field, by introducing a steering-wheel shape of large noncircular air-hole structure in the cladding region. Further, using the full-vectorial finite element method (FEM), we compute the relative sensitivities of the proposed sensor as 83% and 91% when the operating frequencies are 1THz and 0.5THz, respectively. The proposed sensor is suitable for detecting any kind of chemical and biological gases.

Effects of Triangular Core Rotation of a Hybrid Porous Core Terahertz Waveguide

Abstract In this paper, we investigate the effects for rotating the triangular core air hole arrangements of a hybrid design porous core fiber. The triangular core has been rotated in anti-clockwise direction to evaluate the impact on different waveguide properties. Effective Material Loss (EML), confinement loss, bending loss, dispersion characteristics and fraction of power flow are calculated to determine the impacts for rotating the triangular core. The porous fiber represented here has a hybrid design in the core area which includes circular rings with central triangular air hole arrangement. The cladding of the investigated fiber has a hexagonal array of air hole distribution. For optimum parameters the reported hybrid porous core fiber shows a flat EML of ±0.000416 cm−1 from 1.5 to 5 terahertz (THz) range and a near zero dispersion of 0.4±0.042 ps/THz/cm from 1.25 to 5.0 THz. Negligible confinement and bending losses are reported for this new type of hybrid porous core design. With improved concept of air hole distribution and exceptional waveguide properties, the reported porous core fiber can be considered as a vital forwarding step in this field of research.

Porous core photonic crystal fibre for ultra‐low material loss in THz regime

An extremely low-loss porous core circular photonic crystal fibre is presented for terahertz (THz) wave guidance. Much of attention is given to the geometries of the fibre to increase the fraction of power transmitted through core air holes. The finite-element method has been used to compute the modal characteristics of the fibre. Simulation results exhibit an ultra-low material loss of −0.05 cm−1 which is one-fourth of the bulk material loss and almost half of the useful power goes through core air holes at a frequency f = 1 THz. Besides, single-mode properties, confinement loss and dispersion of the fibre are rigorously discussed. The proposed fibre can be fabricated using capillary stacking or sol–gel technique and is useful for transmission applications in the THz frequency band.

Extremely low-loss, dispersion flattened porous-core photonic crystal fiber for terahertz regime

A porous-core octagonal photonic crystal fiber (PC-OPCF) with ultralow effective material loss (EML), high core power fraction, and ultra flattened dispersion is proposed for terahertz (THz) wave propagation. At an operating frequency of 1 THz and core diameter of 345 μm, simulation results display an extremely low EML of 0.047 cm−1, 49.1% power transmission through core air holes, decreased confinement loss with the increase of frequency, and dispersion variation of 0.15 ps/THz/cm. In addition, the proposed PCF can successfully operate in single-mode condition. All the simulations are performed with finite-element modeling package, COMSOL v4.2. The design can be fabricated using a stacking and drilling method. Thus, the proposed fiber has the potential of being an effective transmission medium of broadband THz waves.

Design of Broadband Porous-Core Bandgap Terahertz Fibers

Fibers that operate by the photonic bandgap effect guide light only within a limited frequency range and broadband transmission is highly desirable for the terahertz (THz) frequency range. A semi-analytical approach is used for the design of broadband porous-core bandgap THz fibers based on a honeycomb and Kagome lattice of air holes. We show how the design approach allows a fast and accurate determination of the mode indices for different sizes of the core air holes. In particular, a reduction of the central air hole size from that of the cladding air holes allows both fibers to operate within the first bandgap, enabling broadband transmission within the frequency range of 0.7–2 THz. These fibers will be promising for THz wave transmission.

Proposal for a low loss porous core octagonal photonic crystal fiber for T-ray wave guiding

We propose a porous-core octagonal photonic crystal fiber for low-loss terahertz (THz) waveguiding. Great attention is given to the geometries of the fiber inside the core to increase the fraction of power transmitted through the air holes. At an operating frequency f=1 THz, this design exhibits a low effective material loss which is approximately 0.05 cm−1 or 0.2 dB/cm. In addition to the confinement loss, some other properties like the power fraction of the core air holes, responses of the effective material loss, and power fraction with respect to frequency have been also reported. This design is useful for efficient transmission of broadband terahertz radiation.