Glass Optical Fibers Research Articles

Translucent Concrete: Test of Compressive Strength and Transmittance

Translucent concrete allows light to pass through it because of the presence of optical fibers within the opaque concrete wall. Light is transmitted from one surface of the said wall to the other, because of the presence of optical fiber strands along the width of the wall, which allows light to pass through. The principal objective of this project is to design translucent concrete blocks with the use of glass optical fibers, and then analyze their various properties and characteristics. All tests further performed on our concrete samples and on the optical fibers as such were done to ascertain the improvements of the casted blocks over normal concrete blocks of the same size and with the same design ratios, and to ascertain the practical utility of using translucent concrete as a building material for green building development.

Low loss Ge-As-Se chalcogenide glass fiber, fabricated using extruded preform, for mid-infrared photonics

Chalcogenide glass fibers have attractive properties (e.g. wide transparent window, high optical non-linearity) and numerous potential applications in the mid-infrared (MIR) region. Low optical loss is desired and important in the development of these fibers. Ge-As-Se glass has a large glass-forming range to provide versatility of choice from continuously varying physical properties. Recently, broadband MIR supercontinuum generation has been achieved in chalcogenide fibers by using Ge-As-Se glass in the core/clad. structure. In the shaping of chalcogenide glass optical fiber preforms, extrusion is a useful technique. This work reports glass properties (viscosity-temperature curve and glass transition) and optical losses of Ge-As-Se fiber fabricated from an extruded preform. A robust cut-back method of fiber loss measurement is developed and the corresponding error calculation discussed. MIR light is propagated through 52 meters of a fiber, which has the lowest loss yet reported for Ge-As-Se fiber of 83 ± 2 dB/km at 6.60 μm wavelength. The fiber baseline loss is 83-90 dB/km across 5.6-6.8 μm, a Se-H impurity absorption band of 1.4 dB/m at 4.5 μm wavelength is superposed and other impurity bands (e.g. O-H, As-O, Ge-O) are ≤ 20 dB/km. Optical losses of fiber fabricated from different positions of the extruded preform are investigated.

Structural Analysis of a Cavitary Region Created by Femtosecond Laser Process

Femtosecond laser machining has been applied for creating a sensor function in silica glass optical fibers. Femtosecond laser pulses make it possible to fabricate micro structures in processed regions of a very thin glass fiber line because femtosecond laser pulses can extremely minimize thermal effects. With the laser machining to optical fiber using a single shot of 210-fs laser at a wavelength of 800 nm, it was observed that a processed region surrounded a thin layer which seemed to be a hollow cavity monitored by scanning electron microscopy (SEM). This study aims at a theoretical investigation for the processed region by using a numerical analysis in order to embed sensing function to optical fibers. Numerical methods based finite element method (FEM) has been used for an optical waveguide modeling. This report suggests two types modeling and describes a comparative study on optical losses obtained by the experiment and the numerical analysis.

Mode coupling in glass optical fibers and liquid-core optical fibers by three methods

We test Slemon and Wells's function and recently reported Hurand et al.'s (Appl. Opt., 50, 492–499, 2011) function for calculation of coupling characteristics in step-index optical fibers against experimental measurements and against calculations by a related method that is based on the power flow equation. Compared are the coupling length Lc (which is the fiber length where the equilibrium mode distribution is achieved) and length zs (where steady-state distribution is achieved) in three step index glass optical fibers as well as a liquid core optical fiber. The two functions, while simpler to apply being just algebraic formulas, are less accurate over a wide range of numerical apertures. It is also shown that fibers with same coupling coefficient can have much different coupling characteristics.

A novel image-guided FT-IR sensor using chalcogenide glass optical fibers for the detection of combustion gases

An optical-fiber-based sensor suitable for the detection of combustion gases was designed and experimentally implemented with state-of-the-art sensitivity and capabilities. The system can not only provide imaging capability, but also provide spectral capability of the field of view (FOV) center guided by the imaging. The sensor employs a Fourier transform infrared (FT-IR) spectrometer, coupled with chalcogenide glass optical fiber, and a specially designed infrared optic lens. A special kit provided by Bruker Optics is connected on the spectrometer to focus the infrared beam from the lens at the entry of the fiber. It was tested in situ, in real time, under real-world conditions. Since each gas shows a characteristic optical emission spectrum, it is possible to detect selectively and quantitatively the presence of gases in combustion environment by analyzing mid-IR spectra. Spectral investigation techniques based on spectral shape band intensities and areas are tested to find the most effective tool for monitoring combustion gases. A comparison with experimental data has demonstrated that this sensor is well designed to study gases coming from combustion processes.

NIR to visible upconversion in double – clad optical fiber co-doped with Yb^3+/Ho^3+

Spectroscopic properties of a fabricated double – clad, off-set core antimony - germanate optical glass fiber co-doped with Yb3+/Ho3+ has been investigated. Upconversion luminescence of holmium ions at the wavelengths of 549 nm (5S2 (5F4) → 5I8) and 658 nm (5F5 → 5I8) was obtained as a result of the energy transfer between Yb3+ and Ho3+ ions. Glass characterized by highest intensity of upconversion luminescence (1Yb2O3/0.5Ho2O3 mol%) was used as core of double-clad optical fiber. Upconversion amplified spontaneous emission in the fabricated double – clad, off-set core optical fiber was obtained. The intensity emission ratio red (5F5→5I8)/green (5S2 (5F4)→5I8) of the fabricated optical fiber is several times higher than in bulk glass. Reabsorption of the ASE signal along the fiber resulting from Ho3+: 5S2(5F4) → 5I8,5F5 → 5I8 transitions transition was observed.

High concentration Yb-Er co-doped phosphate glass for optical fiber amplification

We present the fabrication and characterization of two high concentration Yb3+-Er3+ co-doped double clad phosphate glass optical fibers (named A and B for short) manufactured by preform drawing, with the preform being obtained by the rod-in-tube technique. Optical amplification was demonstrated by core pumping 27 mm of fiber A (7/25/70 μm and NA = 0.17 between core and inner cladding) with a laser diode at 976 nm, achieving a 10.7 dB internal gain, i.e., 4.0 dB cm−1, for small signal input at 1535 nm. Amplification was also demonstrated in a cladding-pumped counter propagating configuration using both fibers A and B (12/48/140 μm and NA = 0.08). A maximum internal gain of 18.5 dB was achieved with 8 cm of fiber B, corresponding to an amplification of 2.3 dB cm−1, for small signal input at 1535 nm.

Fabrication and Spectroscopic Analysis of Yb–Tm Co-Doped Nano-Phase Separated Yttrium–Germanium–Aluminium–Phospho–Silicate Composite Glass Optical Fibers

A new class of Yb-Tm co-doped nano-phase separated yttrium germanium aluminium phospho silica composite optical fiber has been fabricated using a modified chemical vapour deposition process with a solution doping technique in order to achieve more intense up-conversion luminescence in visible region. A strong 474 nm up-conversion luminescence, along with three peaks at 364, 650 and 790 nm of Tm3+, have been detected under excitation at 975 nm. The observation of a 474 nm strong up-conversion emission in comparison with other three emission peaks is explained using energy transfer coefficient values obtained from kinetic model of energy transfer up-conversion process. The strong up-conversion emission (474 nm) of yttrium-germanium-aluminium-phospho-silica composite optical fibers compared to yttrium aluminium silicate composite fiber is detected due to the high value of third energy transfer coefficient (W-3) associated with the 474 nm emission. Tm-Yb doped nano-engineered optical fibers would be suitable for efficient power tunable 474 nm light source for several applications.

All-glass extrinsic Fabry-Perot interferometer thermo-optic coefficient sensor based on a capillary bridged two fiber ends.

An all-glass extrinsic Fabry-Perot interferometer (EFPI) is demonstrated for thermal-optic coefficient (TOC) of water, glycerol, and their mixture (volume ratio of 1:1). The compensation for the thermal expansion of Fabry-Perot (FP) cavity is realized by assembling a glass capillary and optical fibers through a CO2 laser welding. The thermal responses of EFPIs are tested in air at different cavity lengths of 578.6μm, 911.7μm, and 1520.3μm, respectively. The corresponding refractive index errors induced by thermal expansion of FP cavity are negligible, which are demonstrated to be 4.33×10-6 RIU/°C, 4.13×10-6 RIU/°C, and 3.45×10-6 RIU/°C when temperature increases from 20.03°C to 60.78°C. The thermal-optic coefficients of water, glycerol, and their mixture are measured to be -1.5×10-4 RIU/°C, -2.3×10-4 RIU/°C, and -2.0×10-4 RIU/°C, respectively. Our study suggests a potential use of this sensor for TOC measurements of liquids with the advantages of low costs and robustness.

Etching of multimode optical glass fibers: A new method for shaping the measuring tip and immobilization of indicator dyes in recessed fiber-optic microprobes

We describe a new procedure for making recessed tips on multimode optical glass fibers. The method is based on etching fiber tips in 40% hydrofluoric acid for defined immersion times. As the etching velocity decreases radially from the core center in multimode graded index fibers, a recess can be formed in the tip of flat-cut tapered or untapered fibers. Etched fiber tips showed improved focussing of excitation light coupled into the fiber at the opposite end, and very efficient excitation of thin layers of optical indicators immobilized into the recess. The sensor chemistry is well protected when immobilized in recessed fiber tips and allows the construction of O2 microoptodes with improved mechanical stability that can measure repeatedly even in very cohesive biofilms, tissue and dry soil.

Mechanical behaviour and practical adhesion at a bamboo composite interface: Physical adhesion and mechanical interlocking

Physical adhesion was experimentally determined by measuring contact angles with different liquids on bamboo and glass fibres, using the Wilhelmy technique, and by applying the acid–base theory for calculating the surface energy components and the theoretical work of adhesion. The mechanical strength of the interfaces was assessed by single fibre pull-out tests. In order to consider the real mechanisms of interfacial failure of natural fibre composites, the fibre matrix interfacial bond strength was characterised by the critical local value of interfacial shear stress, τd, and the radial normal stress at the interface, σult, at the moment of crack initiation. Both interfacial parameters are used for correlating thermodynamic work of adhesion and practical adhesion. Pull-out tests (taking into account friction), XPS, and profilometry techniques were used to study the influence of rough natural fibre surfaces on the interface between the fibre and a thermoplastic matrix, by comparing the mechanical behaviour at the interface of a smooth optical glass fibre with that of rough natural fibres. The results suggest that the physical and chemical compatibility between the bamboo fibre and the matrix does not improve substantially the composite performance if compared with glass composites. The relatively low off-axis strength of the bamboo fibres is suggested as the main reason for the low stress transfer capability at the fibre–matrix interphase. Furthermore, the pull-out process may be friction-dominated in bamboo fibre systems.

ChemInform Abstract: Preparation of High‐Purity Chalcogenide Glasses

AbstractReview: emphasis on glasses for optical fibers; 62 refs.

Computational Modeling of Hole Distortion in Extruded Microstructured Optical Fiber Glass Preforms

Extrusion of glass preforms that are used to draw microstructured optical fibers was simulated using computational mechanics. The study focused on a preform with a cross-section geometry that contains 36 holes arranged in three hexagonal rings. Symmetry allowed for the modeling of a 30° portion of the cross section, which included five holes within this reduced computational domain. The simulations took into account flow through an array of 13 feed holes, flow along five circular pins to create the holes, exit from the die, and the development of a constant profile for the cross section of the preform. The primary concern in the study was exploring the capacity of the model to reproduce the observed distortion of the extruded holes, i.e., the difference between the holes that develop and the negative of the pin arrangement, by taking into account the complexity of the flow. The key features that describe the model are viscous flow, uniform temperature, interface slip using the Navier friction model, and the assumption of a steady-state solution. Validation of the procedure was based on a comparison between the predicted cross section and an actual preform. The results show that distortion of the holes is rather sensitive to the level of friction, which provides insight into reducing the magnitude of distortion in future experimental work.

Upconversion emission in antimony–germanate double-clad optical fiber co-doped with Yb3+/Tm3+ ions

In the paper upconversion luminescence properties in Yb3+/Tm3+ co-doped antimony–germanate glass and double-clad optical fiber were studied. The concentration of lanthanides, which has shown the highest upconversion emission intensity at 478nm (1G4→3H6) and 650nm (1G4→3F4), is 1Yb2O3/0.1Tm2O3(mol%) as a result of exciting with a laser diode (976nm). The lifetime of 2F5/2 (Yb3+) level decreases from 781μs to 71μs in the presence of Tm3+ 0.1–0.75mol% respectively. Luminescence decay curve of glass co-doped with 1Yb2O3/0.75Tm2O3 suggests donor–donor fast migration followed by Tm3+→Yb3+ energy transfer. Glass characterized by highest intensity of upconversion luminescence (1Yb2O3/0.1Tm2O3mol%) was used as core of double-clad optical fiber made by modified rod-in-tube method. Mechanisms influencing differences in upconversion amplified spontaneous emission of the fabricated optical fiber and bulk glass were discussed. Reabsorption of the amplified spontaneous emission signal along the fibre resulting from Tm3+:3H6→1G4, transition was observed.

Glass beads and Ge-doped optical fibres as thermoluminescence dosimeters for small field photon dosimetry

An investigation has been made of glass beads and optical fibres as novel dosimeters for small-field photon radiation therapy dosimetry. Commercially available glass beads of largest dimension 1.5 mm and GeO2-doped SiO2 optical fibres of 5 mm length and 120 µm diameter were characterized as thermoluminescence dosimeters. Results were compared against Monte-Carlo simulations with BEAMnrc/DOSXYZnrc, EBT3 Gafchromic film, and a high-resolution 2D-array of liquid-filled ionization chambers. Measurements included relative output factors and dose profiles for square-field sizes of 1, 2, 3, 4, and 10 cm. A customized Solid-Water® phantom was employed, and the beads and fibres were placed at defined positions along the longitudinal axis to allow accurate beam profile measurement. Output factors and the beam profile parameters were compared against those calculated by BEAMnrc/DOSXYZnrc. The output factors and field width measurements were found to be in agreement with reference measurements to within better than 3.5% for all field sizes down to 2 cm2 for both dosimetric systems, with the beads showing a discrepancy of no more than 2.8% for all field sizes. The results confirm the potential of the beads and fibres as thermoluminescent dosimeters for use in small photon radiation field sizes.

EQUILIBRIUM MODE DISTRIBUTION IN W-TYPE GLASS OPTICAL FIBERS

Power flow equation is used to calculate equilibrium mode distribution in W-type glass optical fibers. It has been shown how the coupling length for achieving the equilibrium mode distribution in W-type glass optical fibers varies with the depth and width of the intermediate layer and coupling strength for different widths of launch beam distribution. W-type optical fibers have shown effectiveness in reducing modal dispersion and bending loss.

Mid-infrared supercontinuum covering the 1.4–13.3 μm molecular fingerprint region using ultra-high NA chalcogenide step-index fibre

Mid-infrared supercontinuum generation with a record-breaking spectral coverage of 1.4–13.3 µm is demonstrated by launching intense ultra-short pulses into short pieces of ultra-high numerical aperture step-index chalcogenide glass optical fibre consisting of a GaAsSe cladding and an As2Se3 core.

Brillouin scattering properties of lanthano-aluminosilicate optical fiber.

Utilizing measurements on a lanthano-aluminosilicate core optical fiber, the specific effects of lanthana (La2O3) on the Brillouin characteristics of silica-based oxide glass optical fibers are described. Lanthana is an interesting species to investigate since it possesses a wide transparency window covering the common fiber laser and telecom system wavelengths. As might be expected, it is found that the properties of lanthana are very similar to those of ytterbia (Yb2O3), namely, low acoustic velocity, wide Brillouin spectral width, and a negative photoelastic constant, with the latter two properties affording significant reductions to the Brillouin gain coefficient. However, lanthana possesses thermo-acoustic and strain-acoustic coefficients (acoustic velocity versus temperature or strain, TAC and SAC, respectively) with signs that are opposed to those of ytterbia. The lanthano-aluminosilicate (SAL) fiber utilized in this study is Brillouin-athermal (no dependence of the Brillouin frequency on temperature), but not atensic (is dependent upon the strain), which is believed to be, to the best of our knowledge, the first demonstration of such a glass fiber utilizing a compositional engineering approach.

Drawing of micro-structured fibres: circular and non-circular tubes

AbstractA general mathematical framework is presented for modelling the pulling of optical glass fibres in a draw tower. The only modelling assumption is that the fibres are slender; cross-sections along the fibre can have general shape, including the possibility of multiple holes or channels. A key result is to demonstrate how a so-called reduced time variable $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\tau $ serves as a natural parameter in describing how an axial-stretching problem interacts with the evolution of a general surface-tension-driven transverse flow via a single important function of $\tau $, herein denoted by $H(\tau )$, derived from the total rescaled cross-plane perimeter. For any given preform geometry, this function $H(\tau )$ may be used to calculate the tension required to produce a given fibre geometry, assuming only that the surface tension is known. Of principal practical interest in applications is the ‘inverse problem’ of determining the initial cross-sectional geometry, and experimental draw parameters, necessary to draw a desired final cross-section. Two case studies involving annular tubes are presented in detail: one involves a cross-section comprising an annular concatenation of sintering near-circular discs, the cross-section of the other is a concentric annulus. These two examples allow us to exemplify and explore two features of the general inverse problem. One is the question of the uniqueness of solutions for a given set of experimental parameters, the other concerns the inherent ill-posedness of the inverse problem. Based on these examples we also give an experimental validation of the general model and discuss some experimental matters, such as buckling and stability. The ramifications for modelling the drawing of fibres with more complicated geometries, and multiple channels, are discussed.

Mechanical characterization of optical glass fiber coated with a thin film of silver nanoparticles by nanoindentation

Optical glass fibers coated with Ag nanoparticles are proposed as alternative material within a system of root dental fillings for endodontic therapy, due to their potential mechanical and antibacterial properties. A group of glass fibers filaments was covered with Ag nanoparticles prepared by the chemical reduction method and immersed in a solvent of tetrahydrofuran (CH2)4O (THF). Nanoparticles achieve average size of 30nm of Ag nanoparticles diameters. At 1min of impregnation in THF on the surface of glass fiber cores, Ag nanoparticles formed thin films with better distributions with respect to the other impregnation times. Nano-mechanical properties such as hardness and elastic modulus were evaluated on the surface of optical glass fiber coated with Ag nanoparticles by nanoindentation using the continued stiffness measurements method. Hardness value was H=3.6±0.17GPa and elastic modulus was E=78.3±2.6GPa.