Porous Optical Fiber Research Articles

Low-Loss Polytetrafluoroethylene Hexagonal Porous Fiber for Terahertz Pulse Transmission in the 6G Mobile Communication Window

Hexagonal porous optical fiber without a central defect is proposed and numerically analyzed with the finite element method (FEM) for transmitting terahertz (THz) electromagnetic wave pulse. In experiments, the transmission characteristics of polytetrafluoroethylene (PTFE) hexagonal porous optical fibers were measured using a THz time-domain spectroscopy (THz-TDS) system. To precisely estimate the effective material loss (EML), we measured the refractive index and absorption coefficient of PTFE in the THz range to use them in FEM analyses, and the EML of the porous fiber was estimated to be lower than that of a bulk rod as large as by a factor of 2 in the frequency range from 0.1 to 0.33 THz. In experiments, we measured the transmission characteristics of both the porous fibers and the bulk rod, to confirm a significant improvement in THz wave transmission nearly by an order of magnitude in the 6G telecommunication window, showing a better performance than theoretical estimations.

Graded index porous optical fibers – dispersion management in terahertz range.

A graded index porous optical fiber incorporating an air-hole array featuring variable air-hole diameters and inter-hole separations is proposed, fabricated, and characterized in a view of the fiber potential applications in low-loss, low-dispersion terahertz guidance. The proposed fiber features simultaneously low modal and intermodal dispersions, as well as low loss in the terahertz spectral range. We experimentally demonstrate that graded index porous fibers exhibit smaller pulse distortion, larger bandwidth, and higher excitation efficiency when compared to fibers with uniform porosity.

Sol-Gel Synthesis of Palladium-Doped Silica Nanocomposite Fiber Using Triton X-100 Micelle Template and the Application for Hydrogen Gas Sensing

Palladium-doped silica nanocomposites were synthesized via a sol-gel technique combined with a template of Triton X-100 micelle. The freshly prepared sol sample of Pd-doped silica nanocomposites was investigated by TEM. Determined from the TEM image, the sizes of the Pd nanoparticles are narrowly distributed, which are around 30 nm in diameter. The prepared sol solution of the sample was injected into a Tygon Microbore Autoanalysis tubing. After 14 days gelatinization, a transparent porous optical fiber was obtained. The response of the fiber to hydrogen gas was tested by using a fiber-optic spectrometric method. The palladium-doped silica nanocomposite fiber is sensitive upon exposure to hydrogen gas and the response is reversible. This palladium-doped silica nanocomposite fiber can be applied as a new kind of hydrogen gas sensor

Porous glass optical fiber sensor as an end-of-service indicator for respiratory cartridges

Sections of porous glass optical fibers were fabricated and characterized. They were found to show a significant drop in light transmittance when exposed to solvent vapors. A sensor has been developed that uses these porous fibers to detect the saturation of activated charcoal inside cartridges. The sensor is sensitive to toluene vapors at a few thousand ppm. Various approaches for increasing this sensitivity are proposed.

Sol-gel derived porous silica as a constituent material for designing optical fiber chemical sensors

AbstractSol-gel processes were developed to prepare nano porous silica materials. The obtained porous sol-gel silica (PSGS) materials have been used as constituent materials in designing optical fiber chemical sensors. A PSGS membrane coated on the surface of an optical fiber was used as a transducer for sensing humidity level in air. A PSGS membrane doped with an ammonia indicator dye has been coated on an optical fiber to sense ammonia in air. Both of the coating based sensors are reversible and fast response. In the tested range, relative humidity (RH) in air down to 3% can be detected with the PSGS coated fiber optic sensor. The fiber optic ammonia sensor with ammonia indicator doped PSGS coating can be used to sense ammonia in air down to sub-ppm level. PSGS has also been used as a constituent material in preparing porous silica optical fibers. The obtained porous optical fibers have been used to design optical fiber chemical sensors for sensing humidity, ammonia and volatile organic compounds. A CuCl2 doped PSGS fiber has been tested for sensing ammonia in a high temperature gas sample. Ammonia in the high temperature air gas diffuses into the PSGS fiber, reversibly reacts with CuCl2 doped in the PSGS fiber to form a complex. The formed complex was detected with fiber optic spectrometric method. This sensor can detect ammonia in a high temperature (450 °C) air gas stream down 0.3 ppm. Techniques of preparing PSGS, coating PSGS on an optical fiber, making a porous optical fiber with PSGS as a constituent material will be presented. Examples of optical fiber sensors using PSGS coatings and a PSGS fiber as transducers for gas sensing are presented.

Recent progress in intrinsic fiber-optic chemical sensing II

Intrinsic fiber-optic chemical sensors, in which an optical fiber, or a section of fiber, plays a role in the transduction of chemical concentration information into optical information, have been reported in the scientific literature since 1946. This paper presents a very brief summary of early work in the field, and reviews the progress that has taken place in both passive (evanescent-field refractometric or spectroscopic) and active (chemically modified cores or cladding) sensing since 1989. Intrinsic fiber-optic refractometry continues to attract attention because of its simple geometry and its compatibility with a variety of hostile sensing environments. Evanescent-wave spectroscopic sensors have gained acceptance in some of the same fields as refractometric sensors, but are restricted to use in special environments because of stiff competition from plain ‘end-coupled’ spectroscopic approaches. Fluorimetry and surface-enhanced Raman spectroscopy (SERS) are two subfields in which direct evanescent spectroscopy remains strong. Coating-based sensors have made the most rapid progress. Recent reports include the development of hydrocarbon sensors based on refractive-index-changing polymer coatings, and numerous examples of coatings doped with fluorescent and absorptive sensor dyes. Core-based sensors, particularly those based on porous optical fibers, have undergone a great deal of development over the past few years. The first reports of intrinsic fiber-optic chemical sensor products involve these sensors. In general, intrinsic sensors have attracted increased attention over the past few years, primarily as a result of the interest in the sensing community at large in distributed and multiplexed sensing methodologies. These sensors offer the promise of true distributed measurements, in-line multiplexing and continuous large-scale production.

Sol-Gel and RF Sputtering Thin Film Coatings for Fiber Optic Sensor Applications

ABSTRACTThin film coating techniques appear to have many advantages over other techniques for immobilization and incorporation of chemical indicators to optical waveguides in developing dye based fiber optic chemical sensors. We have fabricated thin films of composites by using sol-gel and RF sputtering techniques. Different organic and inorganic indicators were immobilized in these films and incorporated into optical waveguides for sensor applications. A fiber optic pH sensor has been developed by introducing pH indicators into a silica matrix and coated as a thin film onto a porous glass fiber by a sol-gel technique. Also, a hydrogen gas fiber optic sensor has been developed by using a RF sputtered WO3/Pd coated porous optical fiber.

Porous optical fibers for high-sensitivity ammonia-vapor sensors

A new porous glass optical fiber has been developed for use as a sensor for the detection of ammonia vapors at low concentrations. The porous structure that remains after selective heat treatment, phase separation, and chemical leaching of a borosilicate glass imparts a high surface area to the fiber core. Ammonia vapors permeating into the porous zone, which is pretreated with a reversible pH dye indicator, produce a spectral change in transmission. The resulting pH change is measured by in-line optical absorbance and is proportional to the ambient-ammonia concentration. Ammonia-vapor concentrations as low as 0.7 part in 10(6) have been detected.