G. Amouzad Mahdiraji

Copper-Graphene-Based Photonic Crystal Fiber Plasmonic Biosensor

We propose a photonic crystal fiber surface plasmon resonance biosensor where the plasmonic metal layer and the sensing layer are placed outside the fiber structure, which makes the sensor configuration practically simpler and the sensing process more straightforward. Considering the long-term stability of the plasmonic performance, copper (Cu) is used as the plasmonic material, and graphene is used to prevent Cu oxidation and enhance sensing performance. Numerical investigation of guiding properties and sensing performance is performed by using a finite-element method. The proposed sensor shows average wavelength interrogation sensitivity of 2000 nm/refractive index unit (RIU) over the analyte refractive indices ranging from 1.33 to 1.37, which leads to a sensor resolution of 5 × 10-5 RIU. Due to the simple structure and promising results, the proposed sensor could be a potential candidate for detecting biomolecules, organic chemicals, and other analytes.

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.

XPS and PIXE Analysis of Doped Silica Fibre for Radiation Dosimetry

The material characteristics of doped SiO2 fibre are studied, the electron traps in the product medium creating a situation attractive for their application in thermoluminescence (TL) radiation dosimetry. To date, rather limited research has been conducted towards gaining an essential understanding of the magnitude of TL signal and material characteristics of doped fibres. Characterization is being sought to ensure that the mechanism of TL yield in optical fibres is well understood, allowing a favourable well controlled production situation to be established. The intended end point is to specify dosimeters, not only for clinical dosimetry but also for their application in industrial/energy-industry settings. Investigation of the surface oxidation state of the Ge-doped SiO2 optical preform has been carried out using the X-ray photoelectron spectroscopy technique. In a further development using the fibre forming technology, particle-induced X-ray emission/Rutherford back scattering measurements have been employed to ascertain dopant concentrations of Ge-doped-cladding photonic crystal fibres (PCFs) with a view to improving TL yield. Present results concern uncollapsed and collapsed-hole-PCFs.

Latest developments in silica-based thermoluminescence spectrometry and dosimetry.

Using irradiated doped-silica preforms from which fibres for thermoluminescence dosimetry applications can be fabricated we have carried out a range of luminescence studies, the TL yield of the fibre systems offering many advantages over conventional passive dosimetry types. In this paper we investigate such media, showing emission spectra for irradiated preforms and the TL response of glass beads following irradiation to an 241Am-Be neutron source located in a tank of water, the glass fibres and beads offering the advantage of being able to be placed directly into liquid. The outcomes from these and other lines of research are intended to inform development of doped silica radiation dosimeters of versatile utility, extending from environmental evaluations through to clinical and industrial applications.

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.

Design of near infrared bandpass filter using all-solid photonic crystal fiber with parasitic bandgaps suppression

In this work, an approach of realizing fiber-based near infrared bandpass filter with parasitic bandgaps suppression is proposed. By doping the core of an all-solid photonic bandgap fiber with lower refractive index material, single-mode light is confined in the main bandgap centered at 1.0 μm wavelength region. Light guiding in higher order bandgaps is suppressed due to the coupling of light to the cladding region. The proposed design is suitable for realizing in-fiber single-band broadband light filter with possible applications in lasing, spectroscopy and optical communication.

Low-crosstalk semi-trench-assisted multicore flat fiber

250-m long 125-μm×315-μm size semi-trench-assisted multicore flat fiber is fabricated using undoped-secondary-cladding as the trench. Crosstalk at 630 nm is fully suppressed in the fiber with 4.2-μm and 27.5-μm core and pitch size, respectively.

Photonic Sensors: Glass Optical Fibers as Dosimeters

This article describes the effect of processing on the sensitivity of optical fiber based dosimeters. It argues that additional processing steps such as application of vacuum to collapse a fiber preform increases the amount of defect centers which would in turn act as radiation absorbers. Dosimeters based on photonic crystal fibers (PCFs), collapsed-hole PCFs, and Flat fibers are described. Coupled with suitable dopants, these fibers show promising performance as dosimeters.