Mostafa Ghomeishi

Challenges and Solutions in Fabrication of Silica-Based Photonic Crystal Fibers: An Experimental Study

Abstract The fabrication process of photonic crystal fibers based on a stack-and-draw method is presented in full detail in this article. In addition, improved techniques of photonic crystal fiber preform preparation and fabrication are highlighted. A new method of connecting a handle to a preform using only a fiber drawing tower is demonstrated, which eliminates the need for a high-temperature glass working lathe. Also, a new technique of modifying the photonic crystal fiber structural pattern by sealing air holes of the photonic crystal fiber cane is presented. Using the proposed methods, several types of photonic crystal fibers are fabricated, which suggests potential for rapid photonic crystal fibers fabrication in laboratories equipped with and limited to only a fiber drawing tower.

Enhancing the radiation dose detection sensitivity of optical fibres

A method for improving the thermoluminescence (TL) yield of silica-based optical fibres is demonstrated. Using silica obtained from a single manufacturer, three forms of pure (undoped) fibre (capillary-, flat-, and photonic crystal fibre (PCF)) and two forms of Ge-doped fibre (capillary- and flat-fibre) were fabricated. The pure fibre samples were exposed to 6 and 21MeV electrons, the doped fibres to 6MV photons. The consistent observation of large TL yield enhancement is strongly suggestive of surface-strain defects generation. For 6MeV irradiations of flat-fibre and PCF, respective TL yields per unit mass of about 12.0 and 17.5 times that of the undoped capillary-fibre have been observed. Similarly, by making a Ge-doped capillary-fibre into flat-fibre, the TL response is found to increase by some 6.0 times. Thus, in addition to TL from the presence of a dopant, the increase in fused surface areas of flat-fibres and PCF is seen to be a further important source of TL. The glow-curves of the undoped fibres have been analysed by computational deconvolution. Trap centre energies have been estimated and compared for the various fibre samples. Two trap centre types observed in capillary-fibre are also observed in flat-fibre and PCF. An additional trap centre in flat-fibre and one further trap centre in PCF are observed when compared to capillary fibre. These elevated-energy trap centres are linked with strain-generated defects in the collapsed regions of the flat fibre and PCF.

Sensitive Fibre-Based Thermoluminescence Detectors for High Resolution In-Vivo Dosimetry.

With interest in the potential of optical fibres as the basis of next-generation thermoluminescence dosimeters (TLDs), the development of suitable forms of material and their fabrication has become a fast-growing endeavour. Present study focuses on three types of Ge-doped optical fibres with different structural arrangements and/or shapes, namely conventional cylindrical fibre, capillary fibre, and flat fibre, all fabricated using the same optical fibre preform. For doses from 0.5 to 8 Gy, obtained at electron and photon energies, standard thermoluminescence (TL) characteristics of the optical fibres have been the subject of detailed investigation. The results show that in collapsing the capillary fibre into a flat shape, the TL yield is increased by a factor of 5.5, the yield being also some 3.2 times greater than that of the conventional cylindrical fibre fabricated from the same perform. This suggests a means of production of suitably sensitive TLD for in-vivo dosimeter applications. Addressing the associated defects generating luminescence from each of the optical fibres, the study encompasses analysis of the TL glow curves, with computerized glow curve deconvolution (CGCD) and 2nd order kinetics.

Study on dielectric function models for surface plasmon resonance structure.

The most common permittivity function models are compared and identifying the best model for further studies is desired. For this study, simulations using several different models and an analytical analysis on a practical surface Plasmon structure were done with an accuracy of ∼94.4% with respect to experimental data. Finite element method, combined with dielectric properties extracted from the Brendel-Bormann function model, was utilized, the latter being chosen from a comparative study on four available models.

Kinetic analysis of IgM monoclonal antibodies for determination of dengue sample concentration using SPR technique.

ABSTRACT Surface plasmon resonance (SPR) sensing is recently emerging as a valuable technique for measuring the binding constants, association and dissociation rate constants, and stoichimetry for a binding interaction kinetics in a number of emerging biological areas. This technique can be applied to the study of immune system diseases in order to contribute to improved understanding and evaluation of binding parameters for a variety of interactions between antigens and antibodies biochemically and clinically. Since the binding constants determination of an anti-protein dengue antibody (Ab) to a protein dengue antigen (Ag) is mostly complicated, the SPR technique aids a determination of binding parameters directly for a variety of particular dengue Ag_Ab interactions in the real-time. The study highlights the doctrine of real-time dengue Ag_Ab interaction kinetics as well as to determine the binding parameters that is performed with SPR technique. In addition, this article presents a precise prediction as a reference curve for determination of dengue sample concentration.

The thermoluminescence response of undoped silica PCF for dosimetry application

This work concerns the suitability of the undoped silica photonic crystal fibre (PCF) as ionizing radiation dosimeters. The dosimetric capabilities of PCF optical fibres in terms of thermoluminescence (TL) and dose response have been investigated and compared with the single mode fibre (SMF) subjected to 6 MeV electron irradiations. The PCF shows dose response linearity curves in a dose range familiar to conventional radiation therapy covering doses from 1 to 4Gy.

Study of Traps in Special Doped Optical Fiber Radiation Sensors via GlowCurve Analysis

Thermoluminescence dosimeters (TLDs) are widely used, serving the needs of various radiation applications. In recent times optical fibers have been introduced as alternatives to more conventional phosphor-based TLD systems, with many efforts being carried out to improve their thermoluminescence (TL) yield. While there have been extensive studies of many of the various TLD characteristics of optical fibers, including TL response, linearity, reproducibility, repeatability, sensitivity and fading, far more limited studies have concerned dependence on the type of TL activator used in optical fibers, promoting the TL mechanism. Present study focuses on TLD glow curves analysis for five different doped optical fibers that have been subjected to photon and electron irradiation. Trap parameters such as activation energy and frequency factors have been obtained from second order kinetics analysis, based on computerized glow curve deconvolution. An interesting observation is that co-doped fibers typically leads to enhanced TL characteristics, pointing to a need for optimization of the choice and levels in use of co-dopants.

Analysis of optical fibre defects using thermoluminescence glow curve method

Knowledge about defects inside the optical waveg-uides is necessary to control the loss during the communication. Therefore the investigation of glow curve can be significant important for improvement of communication systems. In this research, the defects of a cylindrical optical fibre with 8% germanium doped is studied, and then the deconvolution of thermoluminescence glow curve is presented for this case study. This study offers a zero level noise as a reference for each experiment. In order to have a high accuracy of glow curve, this reference can help to calculate the final glow curve properly.

Adhesive layer effect on gold-silica thin film interfaces for surface plasmon resonance modeling

For years the so called method surface plasmon resonance (SPR) and its application in biomedical and sensors is in the attraction point of theoretical and experimental scientist. However, the practical structure of this technique is usually different with the ones in the modeling. The simplified dielectric-metal-dielectric is been using in the modeling instead the practical dielectric-adhesive-metal-dielectric and definitely the effect of this extra adhesive layer is always eliminated. In this paper we prove that adhesive layer in the structure will affect the results. The decrease of the magnetic intensity in TM mode for the SPR is the proof for this hypothesis. For this purpose we have done mode analysis of the SPR structure for both simple and practical structures using COMSOL Multiphysics.

Spectroscopic Modeling of Single Element Plasma

A strategy for spectroscopic analysis of single element plasmas is through modeling. An experimental investigation or generation of a specified emission spectrum can be attempted based on the modeling results which are currently under investigating by many researchers in the world. In the emission spectroscopy, the K‐shell emission is more interesting than emissions from other shells due to their unique EUV and SXR frequencies that can be applied in various scientific and industrial applications. Population information of our model is based on a steady state kinetic code which is calculated for a given electron temperature and an estimated electron density. Thus for each single element plasma it needs large amounts of experimental or theoretical database. Depending on the parameter of the plasma, theories based on local thermodynamic equilibrium (LTE) and non‐LTE are considered. In the non‐LTE case, the Corona model is used and the total absolute number densities are calculated based on the ion densities ...