Index-guiding Photonic Crystal Fiber Research Articles

Simple method for characterization of photonic crystal fibers

We report on our experimental characterization of index-guiding photonic crystal fibers (PCF) from their far field intensity distribution. The algorithm presented below makes it possible to determine the geometrical parameters of the PCF (core diameter, air hole spacing and air hole diameter) from its far field pattern. We obtained good agreement with the manufacturer’s data for all fibers tested.

An estimation of far-field intensity distribution for photonic crystal fibers based on empirical relations

In this paper, we have reported the far-field intensity distribution for a varied configuration of air holes in the cladding region of the solid-core single-mode photonic crystal fibers (PCFs). Recently, an analytical approach based on the normalized frequency (V parameter) and normalized attenuation constant (W parameter) has been developed for index-guided PCF. Parameters V and W are frequently used in the design of conventional optical fibers. Using the empirical relations for the V parameter as well as W parameter of PCF, the dependence of the far-field intensity distribution on two structural parameters—the air hole diameter and the air hole pitch is calculated and presented. The results displayed here can find their utilization in the design and development of a sensor system based on PCFs for potential applications involving structural health monitoring, medicine, environmental monitoring sensors, and in certain areas of biology and chemistry.

Role of structural anisotropy in geometric birefringence of high-birefringence index-guiding PCFs: analysis by moment of inertia

We have studied the role of structural anisotropy on the geometric birefringence of four typical high-birefringence (HB) index-guiding photonic crystal fibers (PCFs) with the same air-silica structure and circular, ellipse, and rectangle air holes, respectively. The normalized difference between the moment of inertia ΔI in x and y direction of the PCF structure is utilized to quantificationally describe the structural anisotropy. We demonstrate that the phase birefringence B increases monotonously when the normalized ΔI rises in different cases of PCFs structures. In order to obtain high birefringence B, it can be an effective method to optimize the parameters of the structure to increase the normalized ΔI. This work can be not only a reference of founding the essence of geometric birefringence and proposing the optimal design of HB-IG-PCFs, but also an enlightenment for bringing the different method (compared to the finite element) into the investigation of PCFs.

Influences of asymmetrical geometric structures on the birefringence of index-guiding photonic crystal fiber

We have numerically investigated the influences of asymmetrical geometric structures on the birefringence of the index-guiding photonic crystal fiber (IG-PCF), by the finite element method. The structure of a reported highly birefringent (HB) PCF with artificial defect in the core is modified to destruct the symmetry. Our proposed structural modifications include elliptical air hole cladding, squeezing lattice of air holes, rotational elliptical air holes, and horizontally shifted air holes, in the cladding. It is found that the birefringence is sensitive to the modifications in different cases due to the different mechanisms. For 1550 nm wavelength, the optimized birefringence can be obtained to be 0.0328 by the elliptical air holes with the major semi-axis in the direction of the long side of the rectangular core region. Furthermore, for the HB-PCF by the asymmetric core shape, the structural factor restricting the further increase of birefringence is that continuous increase of asymmetry leading to the multi-core transmission. It seems to be that This work is not only a proposing of the optimal design of HB-PCF, but also a reference of founding the essence of geometric birefringence.

Ultra high birefringence and lower beat length for square shape PCF: Analysis effect on rotation angle and eccentricity

In this article, a circular air hole organized in a square manner cladding with porous core using elliptical holes index-guiding photonic crystal fiber (IG-PCF) has been proposed and numerically examined. The numerical study is obtained by using finite element method (FEM) inclusion with an electromagnetic absorption boundary perfectly matched layer (PML). Investigation process runs over a broader wavelength range near IR region from 1.20 µm to 1.80 µm for evaluating modal properties of proposed square shaped PCF. S-PCF expresses higher birefringence (2.2 × 10−3), high nonlinearity (23.46 W−1 km−1) along with lower beat length (553.86 µm) at the pumping wavelength λ = 1.20 µm. Core holes angle orientation and eccentricity are tuned for gaining higher birefringence. Furthermore, beat length, Veff, spot size, beam divergence are inquired in details. Finally, this research is focused on birefringence and nonlinearity behaviors are highly affected by angle effect and eccentricity.

Dispersion Tailoring in Circular Photonic Crystal Fibers for Ultraflattened Dispersion

In order to tailor the dispersion characteristics and to control the dispersion slope of index-guiding photonic crystal fibers (PCFs), a new controlling technique is reported. Moreover, this technique is applied to design PCF with both near zero and ultraflattened dispersion in a large wavelength range. The birefringence of the fiber is also addressed as the field profile becomes elliptical in the designed fiber. In addition, how the inevitable imprecision introduced during the fabrication process affects the final dispersion profile is investigated. A finite difference method is used to analyze the dispersion properties and the birefringence characteristics of the PCF. Simulation results reveal that ultraflattened dispersion of 0 ± 1.5 ps/(nm.km) can be achieved over a bandwidth of 890 nm in the wavelength region of 1110–2000 nm along with polarization maintaining property.

Magnetic-Ionic-Liquid-Functionalized Photonic Crystal Fiber for Magnetic Field Detection

A compact optical fiber magnetic field sensor based on a magnetic-ionic-liquid-functionalized photonic crystal fiber (PCF) has been proposed and experimentally demonstrated. The magnetic field sensor was fabricated by splicing an index-guiding PCF having one magnetic-ionic-liquid-infiltrated (MIL-infiltrated) air hole in the innermost layer infiltrated with conventional single-mode fibers. The transmission spectral magnetic response of the proposed sensor have been measured and theoretically analyzed. Owing to the effective interaction between the MIL and transmission light as well as the controllable attenuation property of MIL, the magnetic field sensitivity reaches up to −0.01991 dB/Oe for a relatively linear magnetic intensity range of 0 to 440 Oe.

Comparative Analysis of Hexagonal Solid Silica and Nitro-benzene Filled Hollow Core Photonic Crystal Fiber

A comparative study of five ring solid core and nitrobenzene filled hollow core liquid filled photonic crystal fiber (PCF) are presented. Considering the same structure, one is used as solid silica and another one is filled with nitrobenzene in the core. Here the paper elaborates the confinement loss, dispersion properties and birefringence of an index-guiding PCF with asymmetric cladding designed and analyzed by the finite-element method. The proposed structure shows the low confinement loss in case of solid silica, negative dispersion in nitrobenzene filled hollow core PCF and high birefringence in both the cases. The calculated values shows flat zero confinement loss in 0.7 µm to 1.54 µm range, flat zero dispersion is achieved in solid core and -2000 ps/km-nm in nitrobenzene filled hollow core PCF and high birefringence in the range of 10-3 in nitrobenzene filled hollow core PCF. Results show the relative analysis at different air fill fraction.

Fiber Ring Laser Temperature Sensor Based on Liquid-Filled Photonic Crystal Fiber

A temperature sensor based on a fiber ring laser embedded with liquid-filled photonic crystal fiber (PCF) is proposed and experimentally demonstrated. High refractive index liquid is infiltrated into an index-guiding PCF to generate band gap-like effect then used as the laser filter and the sensing head simultaneously. With the temperature increasing, the emission wavelength of the fiber laser shifts to the shorter wavelength and the output intensity increases due to the band gaps’ movement. The temperature sensitivity −1.747 nm/°C and 0.137 dB/°C are obtained utilizing the wavelength modulation and the intensity modulation, respectively, with high signal-to-noise ratio (~55 dB), narrow 3-dB bandwidth (less than 0.08 nm) and good stability.

Analysis on Transition between Index- and Bandgap-guided Modes in Photonic Crystal Fiber

We calculate optical properties of guided modes of a hybrid-guiding photonic crystal fiber. The design and modeling of such hybrid-guiding PCF is made by replacing air holes with inserts of high refractive index material layer by layer in order. The optical properties such as mode intensity profile, mode dispersion, optical birefringence, confinement loss, and chromatic dispersion during transition of the guiding mechanism are analyzed and discussed. The guided modes in the hybrid-guiding region are also compared with those of reference index-guiding and bandgap-guiding photonic crystal fibers.

Solid Optical Fiber With Tunable Bandgaps Based on Curable Polymer Infiltrated Photonic Crystal Fiber

We demonstrated the realization and characterization of a solid photonic bandgap fiber (SPBF) with a compact size of about 10 mm and a high wavelength sensitivity of up to −4.034 nm/°C by means of fully infiltrating an ultraviolet curable polymer with a high refractive index of 1.515 into air holes of a photonic crystal fiber (PCF). To the best of our knowledge, it was the first time that the SPBF with tunable bandgaps was fabricated in the conventional index-guiding PCF. Compared with conventional fluid filled PBFs, the proposed SPBF can be stable to temperature and other environmental effects and maintain a large extinction ratio of more than 30 dB within a broad wavelength. The splicing between the SPBF and single mode fibers has been solved. Moreover, it is observed that the bandwidth of bandgap (G2) gradually broadens with the increase in temperature.

Simple technique to estimate macrobending losses in index guiding photonic crystal fibers

We report a simple and complete approach to estimate macrobending losses in index-guiding photonic crystal fibers with given optogeometrical parameters. The approach is based on a previously developed simpler formulation of their effective cladding indices valid in the entire single mode region of such fibers. To check the validity of our approach, we compare our results with those obtained by an earlier scalar effective index method which is not so easily accessible. We observe our results to match fairly well with the available results. Our approach should find wide attention by system designers for its ease of use.

Birefringence and large mode area analysis of segmented cladding index-guiding photonic crystal fibers

High birefringence and large mode area are the two paramount requirements of single-mode fibers to control polarization mode dispersion and nonlinear effects. We have investigated the birefringence, higher-order mode coupling loss of a fundamental mode (FM), and numerical aperture of index-guiding segmented cladding photonic crystal fibers in continuation to our previous analysis of the design for FM confinement and V parameter. High birefringence on the order of 10−4 to 10−3 over the near-infrared to short-wavelength infrared (0.75 to 2.3 μm) spectral range has been obtained. The finite difference time domain method has been used for simulation. The center defect in the lattice forms the core and the remaining part represents the cladding. With phosphate glass (ngl=1.56) as a base material, cladding consists of different segments formed by varying the air hole diameter resulting in strong form birefringence and reduced numerical aperture which leads to a large mode area. We inferred a relation between fiber symmetry and birefringence by varying the duty cycle of the designs. A significant reduction in beat lengths shows reduced power losses in the FM due to higher-order mode coupling.

Suspended Ring-Core Photonic Crystal Fiber Gas Sensor With High Sensitivity and Fast Response

We demonstrate the design and fabrication of an in-line evanescent field gas sensor based on a novel suspended ring-core photonic crystal fiber (PCF) to further overcome limitations in sensing capability. The suspended ring-core PCF is made by the stack-and-draw technique with a large central capillary of ~60µm and adapted small capillaries in a larger cladding tube. Sensing capabilities of two variations of the proposed suspended ring-core PCFs were investigated experimentally by detecting absorption lines of acetylene gas. The sensitivity of the two PCF structures was also numerically analyzed using a full-vectorial finite-element method. The dynamic response of the sensors was quantified in detail. The results demonstrated significant improvement in both sensitivity and response time of the suspended ring-core PCF as this special PCF can provide larger gas diffusion and higher overlap between the sensing species and the guided light than either a Ge-doped ring defect PCF or a conventional index-guided PCF.

Analysis of modal characteristics and thermal effects on photonic crystal fiber laser

In this paper, thermo-optics effects on fiber lasers based on index-guiding photonic crystal fibers (PCFs) are studied. The modal characteristics of the PCF lasers are discussed in terms of the thermal effects. Modal analysis of PCF has been done with help of plane wave expansion and supercell lattice methods. The thermal analysis is performed by obtaining the effective index of fundamental mode and core confinement factor (CCF) when the fiber laser was pumped. The results show that PCF laser structure has negligible modal sensitivity to thermal load in comparison to conventional fiber laser. Analyzing the mode performance of the fiber laser under thermal load shows that the assumed PCF laser at 80W/m pump power show ∼500° rise in temperature and 0.34% propagation constant variation in fundamental mode index and 0.04% CCF variation in fundamental mode.

Compact and Ultrasensitive Temperature Sensor With a Fully Liquid-Filled Photonic Crystal Fiber Mach–Zehnder Interferometer

We propose a compact and ultrasensitive all-fiber temperature sensor based on an in-line fully liquid-filled photonic crystal fiber (PCF) Mach-Zehnder interferometer (MZI). It consists of a small piece of index-guiding PCF fully infiltrated by fluid and two standard single-mode fibers offset spliced with PCF. Two core modes LP01 and LP11 are conveniently used as optical arms to form the in-line MZI-type interferometer. Experimental and theoretical investigations of its response to temperature confirm that high temperature sensitivity up to -1.83 nm/°C could be realized with such a compact interferometeric PCF temperature sensor.

Generation of Raman sidebands aided by a CW Stokes signal

We experimentally demonstrate that adding a continuous wave Stokes signal to a picosecond pulse will significantly expand the spectra or help to generate broad cascaded Raman sidebands in an index-guided photonic crystal fiber when pumping in the normal dispersion regime. The generated twelve Raman peaks, spaced by ~13.2 THz, contain four Stokes and six anti-Stokes peaks, and spread over a broad spectrum range of 893–1491 nm. Each peak has a 3-dB line width smaller than 0.5 nm. The cascaded Raman sidebands make it promising to get the wavelength-tunable Raman sources.

Log-periodic-type photonic crystal fiber structures and their propagation characteristics

We propose some modifications in the conventional index-guided photonic crystal fiber (PCF) structure having circular holes of constant radii. In one of the proposed structures, the hole dimensions of the conventional PCF are modified such that the ratio of the radii of the holes in a particular layer with the nearest layer is constant while maintaining the same refractive index in all the holes. In the other structure, we propose to use different dielectrics in different layers of holes in the conventional PCF structure such that the ratio of the refractive index of the dielectric material in the holes in a particular layer with the nearest layer is constant. The simulations of the proposed structures are carried out using OptiFDTD simulator with full-vector mode solver using finite difference time domain method, and the results are compared with the conventional PCF structure having four layers of air holes. It is observed that the proposed structures exhibit lower waveguide dispersion and confinement loss than the conventional PCF structure over a wide range of wavelengths, making them suitable candidates for applications such as long-distance optical communications or high-data rate data transfer applications. One of the proposed structures exhibits large negative dispersion, and it can be used as a dispersion compensating fiber.

Index Guiding Photonic Crystal Fibers With Large Birefringence and Walk-Off

This paper presents the design of an index guided photonic crystal fiber which promises to yield very large birefringence (~2.22 ×10- 2). Important optical properties, such as birefringence, single modeness, optical confinement, fiber dispersion, walk-off, etc., have been studied employing numerical simulation through finite difference time domain scheme. The fiber also promises a very small walk-off near optical communication wavelength.

High sensitivity evanescent-field gas sensor based on modified photonic crystal fiber for gas condensate and air pollution monitoring

Flammable and/or toxic gas sensors can be used as safety measuring in gas production facilities, especially in oil rigs. The gas sensors detect gas leaks capable of causing fire, explosion, and toxic exposure. Here we proposed an index-guiding photonic crystal fiber for gas sensing that have a broad spectral transmission band and so is capable to detect more gas condensate components. The dependence of relative sensitivity and confinement loss on the fiber parameters is numerically investigated by finite element method (FEM). Introducing a hollow high index ring with an air hole in the center of fiber simultaneously enhances the relative sensitivity and achieves low confinement loss. In addition, we prove that increasing the diameter of holes located in the inner rings, improve the relative sensitivity and increasing the ring diameter holes located in the outer rings, greatly reduces the confinement loss. Placing hexagonal holes instead of circular holes in the innermost ring, the relative sensitivity is effectively enhanced. The relative sensitivity at wavelength of λ=1.33μm that is in the Methane absorption line is enhanced to value of 13.23%. The confinement loss is also improved to 3.77×10−6.