Photonic Crystal Fiber Structure Research Articles

The effect of photonic crystal fibre structure on the performance of Mach-Zehnder interferometer fibre optic gas sensors

A compact refractive index (RI) sensor, based on the Mach-Zehnder Interferometer (MZI), has been developed and experimentally evaluated for the highly sensitive detection and quantification of gases (Helium, Methane, and Carbon Dioxide). The RI sensor utilizes a variety of fibre types: Single Mode Fibre (SMF), Photonic Crystal Fibre (PCF), and Hollow-Core Photonic Crystal Fibre (HC-PCF). In order to fabricate the MZI sensors, a short length of sensing fibre was positioned between a lead-in and a lead-out single mode fibre (SMF) with an air gap at each interface. Three types of sensors were fabricated using this configuration employing 4 mm stub of: (i) PCF, (ii) 10 µm HC-PCF, and (iii) 20 µm HC-PCF as the sensing elements. The performance of these sensors, for detecting and measuring the quantity of gas present, were compared. The transmission spectrum of MZI sensors are formed by interference between the cladding and core modes. These transmission signals correspond to the frequency components in the sensor’s Fast Fourier Transform (FFT) spectrum. The effect of gap distance on the number and amplitude distribution of the modes was examined in an effort to optimize the design elements. The resulting fiber sensors can measure the RI of a gas-filled cavity and they showed high-sensitivity to helium, methane, and carbon dioxide. The highest RI sensitivity of 3210 nm/RIU was demonstrated in the RI range of 1.0000347-to-1.000449 by a sensor with a 4 mm long sensing stub element of 10 µm HC-PCF. Cyclic tests with the group of gases demonstrated that the measurements are highly repeatable. The measurement response and recovery times for all sensors were determined, and it was concluded that the 20 µm HC-PCF sensor has the fastest response/recovery time and the PCF sensor has the slowest. This research illustrates that the sensors fabricated by the proposed method have potential for improving the ability to detect and quantify pure gases. Additionally, the sensors are highly sensitive to low percentages of CO 2 , making them suitable for greenhouse gas measurement.

The sensing characteristics of microstructure-core photonic crystal fiber filled with liquid based on Sagnac interferometer

A highly-sensitive temperature sensor based on the Sagnac interferometer embedded with a microstructure-core photonic crystal fiber (PCF) has been demonstrated and studied. The PCF structure with the micro holes distributed on its core is designed and the unique core is called microstructure core. All the air holes of the PCF are assumed to be filled with a temperature-sensitive liquid whose thermo-optic coefficient is much higher than that of the background material. The mode field distribution and effective refractive index are calculated based on finite element method (FEM). The influences of the structural parameter d3 of the micro holes on the sensing characteristics are analyzed. The sensitivity of the designed PCF sensor increases as the diameter d3 increases and the average sensitivity is up to 21.05 nm/ °C as the temperature varies from 28.35 °C to 46.35 °C. The sensing characteristics are also discussed by just filling the air holes on the fiber cladding with the temperature-sensitive liquid and removing the air holes on the microstructure core.

A high linearity refractive index sensor based on D-shaped photonic-crystal fiber with built-in metal wires

We proposed a D-shaped photonic crystal fiber refractive index sensor based on surface plasmon resonance for the detection of refractive-index (RI) liquid analytes between 1.27 and 1.37. In contrast to the common D-shaped structure photonic crystal fiber, three metal wires were added between the D-surface and top level air holes in our design, which prevent the analytes from contacting the metal. It is particularly suitable for detecting some analytes which are easy to react with metal. The sensing performance of D-shaped photonic crystal fiber was studied by the finite element method. Simulation result shows that the sensor has a very good linearity. The adjusted R2 values of resonance wavelengths fitting lines are 0.9996 in 1.27−1.32. The sensitivity of the designed sensor can be as high as 11,500 nm/RIU, and a high resolution of 8.7 × 10−6 RIU is achieved when na = 1.36.An average sensitivity of 8,846.67 nm/RIU in the sensing range 1.27−1.32, and 10,812 nm/RIU in 1.33−1.37 with high linearity is obtained. The D-shaped optical fiber usually realizes the sensing function by coating a metal film, but the method of adding metal wires has rarely been reported before. Owing to the high linearity, high resonance intensity and sensitivity, the proposed sensor can find important applications in environmental, biological and biochemical analytes detection.

High numerical aperture photonic crystal fiber with silicon nanocrystals core for optical coherence tomography

A simple photonic crystal fiber (PCF) structure with silicon nanocrystals (Si-nc) embedded in core is proposed. The influence of geometric parameters is numerically investigated and three high numerical aperture PCFs for optical coherence tomography are designed. The zero dispersion wavelengths are at 0.83 μm, 1.06 μm and 1.31 μm wavelengths which are used for ophthalmology, dermatology and dentistry, respectively. By introducing a circular rod composed of Si-nc in the center of core region, the numerical apertures are greatly improved, which are 0.61 at 0.83 μm wavelength, 0.65 at 1.06 μm wavelength and 0.66 at 1.31 μm wavelength, respectively. The transverse resolutions as high as 0.463 μm, 0.563 μm and 0.682 μm are obtained correspondingly. Moreover, the confinement losses are as low as 4.5 × 10−8 dB/km at 0.83 μm wavelength for PCF1, 3.8 × 10−7 dB/km at 1.06 μm wavelength for PCF2, 2.2 × 10−6 dB/km at 1.31 μm wavelength for PCF3, respectively.

Photonic crystal fiber based terahertz sensor for cholesterol detection in human blood and liquid foodstuffs

Low density lipoprotein (LDL) cholesterol is the leading cause of heart diseases, peripheral artery diseases, and stroke. An accurate, flexible, and efficient detection process is very urgent for identifying the cholesterol. In this context, an octagonal shaped hollow core with eight head star cladding structured photonic crystal fiber (PCF) has been proposed in this paper for cholesterol sensing in liquid analytes (human blood, cocking oil, liquid foods, etc.). The sensing performances of proposed PCF are evaluated through the COMSOL multiphysics software where the finite element method (FEM) has been used as a solver. The numerical investigation of the presented PCF structure exhibits highly sensitive characteristics for cholesterol detection in liquid samples and the proportion is 98.75% at 2.2 THz frequency. It also reveals negligible confinement loss of 3.14 × 10−20 cm−1 and low effective material loss of 0.0008 cm−1 at the same operating point. Furthermore, the commercial development feasibility of designed PCF in the existing manufacturing environment and other crucial optical properties such as effective area, dispersion, numerical aperture are also discussed in detail.

Analysis of Photonic Crystal Fibers Using Full Vectorial Finite Difference Method (Dept.P)

The full-vectorial finite difference method (FV-FDM) is applied to perform modal solution to photonic crystal fibers (PCFs). The effects of geometrical parameters of the circular and elliptical holes on the effective index, the dispersion and the effective mode area of the fundamental mode have been studied. PCF structure showing dispersion of 0+1.288 ps/nm.km over the wavelength range from 1.3 um to 1.8 um has been reported. The applicability of using PCF as a pressure sensor has been discussed.

Low dispersion and confinement loss photonic crystal fiber for orbital angular momentum mode transmission

In this paper, we design a novel type of photonic crystal fiber (PCF) with a kind of typical micro-structure in its innermost cladding area, which can totally transmit 26 orbital angular momentum modes (OAMs). Over a bandwidth of 300 nm from 1.5 to 1.8 μm, this new type PCF shows a great improvement in dispersion property when it is compared with the total internal reflection PCF for reference. Moreover, other mode properties are also calculated and listed in curves, including effective indices, confinement loss and nonlinear coefficient. And basing on the test results, we further ameliorate the micro-structure and cladding of previous PCF structure and propose two effective ways to reduce the dispersion and confinement loss respectively. One is to insert typical type of micro-structure; the other is to change the arrangement and size of air holes in the cladding area. We finally propose an optimized structure which can support 30 OAM modes with the application of the two ways. Results show the optimized structure performs very well and achieves great progress in terms of dispersion and confinement loss.

A Photonic crystal fiber with large effective refractive index separation and low dispersion.

A photonic crystal fiber (PCF) structure with a ring-core and 5 well-ordered semiellipse air-holes has been creatively proposed. Through a comparison between the structures with a high refractive index (RI) ring-core and the structure without, it conclude that a PCF with a high RI ring-core can work better. Schott SF57 was elected as the substrate material of ring-core. This paper compares the effects of long-axis and short-axis changes on the PCF and selects the optimal solution. Especially TE0,1 mode’s dispersion is maintained between 0 and 3 ps / (nm · km) ranging from 1.45 μm to 1.65 μm. This property can be used to generate a supercontinuum with 200 μm long zero dispersion wavelength (ZDM). In addition, Δneff reaches up to 10−3, which enables the near -degeneracy of the eigenmodes to be almost neglected. The proposed PCF structure will have great application value in the field of optical communications.

Ultrahigh sensitivity refractive index biosensor based on gold coated nano-film photonic crystal fiber

A high sensitivity gold coated circular nano-film photonic crystal fiber (PCF) biosensor based on surface plasmon resonance (SPR) is proposed. Finite element method (FEM) has been applied to simulate and analyze the sensing performance of the proposed circular structure. The highest sensitivity response and birefringence of 45003.05 nm/RIU and 1.9 × 102 are obtained respectively, where the operating refractive index (RI) analyte range is 1.33–1.40 and the gold layer thickness is 50 nm. It is the maximum sensitivity response where the RI analyte range is 1.33–1.40. Changing the gold layer thickness, the sensitivity response of 48269.50 nm/RIU is achieved for 70 nm gold layer where the operating gold layer thickness range is 40 nm to 90 nm. In short, the suggested circular SPR PCF structure can be broadly applicable in RI sensing applications for its outstanding sensitivity response, simple compact structure design and tunable performance.

Development of a photonic crystal fiber for THz wave guidance and environmental pollutants detection

In recent years, photonic crystal fiber (PCF) in the THz regime has gained popularity very swiftly for wave guidance and sensing applications. The optical properties of PCF can be controlled by the fine tuning of the geometrical parameters. In this context, PCF geometry has been developed for THz wave propagation as well as for environmental pollutants sensing applications. The proposed PCF structure contains a circular manner sectored cladding and square shaped core which is inserted by four square lattices. The finite element method based COMSOL multiphysics v.5.3a software has been used to design and characterize the optical properties rigorously for both applications. Numerical outcomes of developed PCF have significantly improved in both cases because of strategic geometry selection and parameters optimization. The simulated results render high sensitivity of 90 ± 1% for all the tested analytes at optimum condition, besides, ultra-low effective material loss (EML) of 0.009 cm−1 and flattened dispersion of ±0.05 ps/THz/cm are obtained at wave guiding environment. Moreover, implementation possibilities in the existing fabrication environment, physical attributes and comparative performance analysis are also stated in this article.

Ring-based coil structure photonic crystal fiber for transmission of Orbital Angular Momentum with large bandwidth: Outline, investigation and analysis

A unique, spectacular design of Photonic Crystal Fiber (PCF) is discussed in this paper to introduce one of the highest numbers of Orbital Angular Momentum (OAM) modes for the very first time with a very large bandwidth of 1,900 nm. Three layers of convoluted coiled structure air cavities formed the cladding region. The optimal design of PCF is used to derive the OAM properties. Finite Element Method (FEM) is used to examine and calculate the fundamental optical characteristics. The result of simulation supports 56 OAM modes with flat dispersion variation. Most of the OAM modes for confinement loss are below 10−8 dB/m where the lowest value is 1.7407×10−11 dB/m at wavelength 1,100 nm for HE11,1 mode. The non-linear coefficient and numerical aperture are lower than 4 W−1km−1 and 0.17, respectively. These splendid optical characteristics ensure the addressed design as a striking competitor for OAM transmission with large bandwidth and many other relevant optical communications. It can be used in long haul communication, encoding and Mode Division Multiplexing (MDM).

Dual-polarized highly sensitive surface-plasmon-resonance-based chemical and biomolecular sensor.

As the research work in surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) is getting tighter, a perfectly circular-shaped PCF with elliptical air holes is proposed where the performance parameters are improved significantly. The performances among our designed elliptical, circular, and rectangular air holes are compared, and the best result is achieved with the elliptical air holes. The technique used for the investigation is the finite element method, and for the simulation of data COMSOL Multiphysics 5.3a software is used. The method covers a wider range of the optical spectrum from 0.59 to 1.05 µm. The highest confinement loss achieved through our design is 340 dB/cm. The wavelength sensitivity and amplitude sensitivity are 13,000 nm/RIU and ${1189.46}\;{{\rm RIU}^{ - 1}}$1189.46RIU-1, respectively. The sensor resolution is ${7.69} \times {{10}^{ - 6}}$7.69×10-6 for our proposed design. The proposed sensor also achieved a maximum birefringence of ${2.8} \times {{10}^{ - 3}}$2.8×10-3, which is, to our knowledge, the highest birefringence reported so far for a PCF-SPR sensor. This enables the fiber to be operated in a dual-polarized mode. The RI for the analyte ranges from 1.33 to 1.40. Based on all the characteristics, the proposed PCF structure can be used effectively for chemical and biomolecular sensing.

D-Shaped Photonic Crystal Fiber–Based Surface Plasmon Resonance Biosensors with Spatially Distributed Bimetallic Layers

This paper deals with the development and analysis of D-Shaped photonic crystal fiber (PCF) biosensors using surface plasmon resonance (SPR). A thin metal layer is deposited on the outer flat surface of the PCF that behaves as the plasmonic material. Analyte is filled in the outermost peripheral region of metal layer. Finite element method (FEM) with perfectly matched layer (PML) is applied to analyze the proposed sensors. Mode analysis is performed on the proposed structures to evaluate various parameters of SPR-based PCF sensors. Three D-shaped PCF structures have been proposed with silver (Ag), gold (Au) and two-half layers of both (Ag-Au) on its flat surface. The first two structures are analyzed to the range of wavelength where the SPR will occur to facilitate understanding of the third structure. It is observed that the structures with one metal have only one sensitive plasmonic peak whereas the structure with two metal layers has two sensitive plasmonic peaks, making it suitable candidate for two-molecule sensing present in a sample analyte. Good sensitivities and resolutions are achieved for both plasmonic peaks.

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.

Photonic crystal fiber based wide-range of refractive index sensor with phase matching between core mode and metal defect mode

A high sensitivity wide range surface plasmon resonance (SPR) refractive index sensor based on photonic crystal fiber (PCF) has been proposed in this paper. The finite element method (FEM) is used to calculate and analyte the structure of PCF. The optical properties of the PCF are investigated by adjusting the refractive index of liquid analyte. By optimization, the fiber sensor achieves a high linearity refractive index sensitivity of 0.9979 and 1931.03 nm / RIU over a refractive index range from 1.350 to 1.460 and achieves a short PCF length of 1 mm. It is allowed the sensor to be small enough to be integrated into inspection equipment,and expected to gain important applications in the fields of biological monitoring, environmental monitoring, and chemical production.

New photonic crystal fiber structure with high birefringence for liquid sensing

提出一种用于液体传感的光子晶体光纤的结构和设计方法。将六边形光子晶体光纤的纤芯区域设计成2个椭圆空气孔，分别填充水和乙醇，进而比较两种光子晶体光纤结构的传播特性。采用全矢量有限元法对所设计光子晶体光纤结构的双折射、相对灵敏度、限制损耗、非线性系数进行数值分析，对光纤各项参数的优化及纤芯椭圆结构参数进行调整，结果表明：当椭圆率为0.6时，纤芯填充乙醇的光子晶体光纤PCF2在波长1.55 nm处相对敏感度可达到72.506 7%，同时限制损耗可以降至10⁻⁸级。所设计的模型可用于传感和生物传感研究及应用。

Design of Photonic Crystal Fiber Capable of Carrying Multiple Orbital Angular Momentum Modes Transmission

For the traditional photonic crystal fibers with circular air holes, rectangular air holes are added to the fiber cladding. The periodic arrangement of the inner rectangular air holes allows the fiber structure to better match the annular mode field distribution of the vortex beam. The fiber structure was analyzed and calculated by COMSOL Multiphysics 5.4 finite element software, and the characteristics of fiber were analyzed, such as the dispersion, confinement loss, effective mode area and nonlinear coefficient. The results reveal that the photonic crystal fiber structure capable of carrying 50 orbital angular momentum (OAM) modes at the wavelength of 1.15 to 2.0 μm (850 nm). The effective refractive index difference Δneff between vector modes can reach 1 × 10-3, and larger difference can effectively separate the vector modes and improve the transmission performance of OAM modes. Moreover, the fiber has good performance, such as flat dispersion distribution of the low-order modes, low confinement loss below 10-9 dB·m-1, large effective mode field area and small nonlinear coefficient in the 850 nm wavelength range. Therefore, this fiber structure can be applied to the high-capacity communication system of fiber multiplexing OAM. In addition, the good characteristics of this fiber structure are of great significance for the transmission of vortex beam in fiber.

Design of an elliptical air-hole dual-core photonic crystal fiber for over two octaves spanning supercontinuum generation

A highly birefringent polarization-maintaining dual-core photonic crystal fiber (DC-PCF) structure with elliptical air holes around the cores has been designed for possible supercontinuum generation over two octaves spanning a spectral bandwidth in the 400- to 1800-nm wavelength range. The supercontinuum (SC) spectrum covers the near-UV, visual, and near-infrared regions of electromagnetic spectra when a hyperbolic secant pulse of 50 fs duration, 322 mW average power, and 80 MHz repetition rate corresponding to 4.03 nJ energy is launched into the DC-PCF around a 1060-nm pumping wavelength. The generated SC spectrum satisfies the necessary requirements for applications in biophotonics, telecommunications, and frequency metrology.

Simultaneous measurement of magnetic field and temperature based on surface plasmon resonance in twin-core photonic crystal fiber

Dual-parameter measurement method of magnetic field and temperature based on Surface Plasmon Resonance (SPR) in a twin-core photonic crystal fiber (PCF) is proposed. After platting a silver-graphene layer on the central hole, we infiltrate magnetic fluid (MF) into the hole to manipulate the twin-core structure. Based on the combined use of plasma resonance effect and twin-core PCF, the simultaneous measurement of magnetic field and temperature is achieved by observing the loss-peak shifts appear in output spectra. Moreover, by filling a mixture of chloroform and toluene into the cladding air holes around the right core, not only the temperature sensitivity is improved, but two different sensing mechanisms can be formed simultaneously, so that light propagation in the two cores would not interact with each other. Through dual-parameter demodulation method, the magnetic-field sensitivity and temperature sensitivity can reach up to 0.44nm/mT and −0.37nm/∘C, respectively. Such dual-core PCF structure has simple preparation process and good stability, which is applicable to measure multiple environmental parameters.

Numerical investigation on a new designed hollow-core photonic crystal fiber with large modal separation

We investigate the characteristics of optical modes in a new designed hollow-core photonic crystal fiber (PCF) with large modal separation. The large effective refractive index difference between the adjacent second-order vector modes can be maintained higher than 0.001 within the wavelength range from 1 to 2 μm. The maximum value can arrive 0.01199 between HE21 and TM01 mode at 2 μm. The fundamental mode of the proposed PCF has flat dispersion in a wide spectral range, which can be applied on wideband supercontinuum generation. The influence on the characteristics by the PCF structure has also been investigated. The increase of the size of the central air hole and the duty cycle affects the flatness of the dispersion curve to some extent. Our simulated results could provide an optimized fiber structure for the experimental study on stable transmission of vector modes.