Patricia Scully

Chemical tapering of polymer optical fibre

We introduce a novel method of chemically removing the cladding of PMMA based polymer optical fibre (POF) using organic solvents which can also be used to create etched tapers of any profile within lengths of POF or at fibre ends. The process is simple, inexpensive, low in chemical hazard and operator skill and has application to both improve the performance of numerous POF devices and allow conversion of silica devices to polymer. We give details of the etching processes involved and optical properties of the devices produced. We believe that this is the first application of this chemical process to the tapering of POF cores and suggest possible future applications of the technique.

Plastic Optical Fibre Sensors for Structural Health Monitoring: A Review of Recent Progress

While a number of literature reviews have been published in recent times on the applications of optical fibre sensors in smart structures research, these have mainly focused on the use of conventional glass-based fibres. The availability of inexpensive, rugged, and large-core plastic-based optical fibres has resulted in growing interest amongst researchers in their use as low-cost sensors in a variety of areas including chemical sensing, biomedicine, and the measurement of a range of physical parameters. The sensing principles used in plastic optical fibres are often similar to those developed in glass-based fibres, but the advantages associated with plastic fibres render them attractive as an alternative to conventional glass fibres, and their ability to detect and measure physical parameters such as strain, stress, load, temperature, displacement, and pressure makes them suitable for structural health monitoring (SHM) applications. Increasingly their applications as sensors in the field of structural engineering are being studied and reported in literature. This article will provide a concise review of the applications of plastic optical fibre sensors for monitoring the integrity of engineering structures in the context of SHM.

A novel technique for optical fiber pH sensing based on methylene blue adsorption

A novel fiber optic pH sensor is reported. The sensor is based upon surfacic adsorption of methylene blue dye, producing absorption in the evanescent field surrounding the sensing fiber. The sensor is based upon a 200 /spl mu/m diameter Plastic Clad Silica (PCS) fiber which has its cladding removed in order to expose its core. The linear range of operation is between pH 3 and pH 9 and its response time is considerably shorter than indicator based probes which measure spectral changes of pH sensitive chemicals. Effects of measurand ionic strength are shown to be negligible which is a further important advantage of this sensor over other optical fiber pH sensors. The sensor design is sufficiently flexible to allow it to be configured in probe (reflective) or in-line (transmissive) form. The latter allows the application of time domain reflectometry technique which may be used to achieve multipoint (distributed) sensing. >

Photochemistry of refractive index structures in poly(methyl methacrylate) by femtosecond laser irradiation

Femtosecond, subablation threshold photomodification of poly(methyl methacrylate) (PMMA) at 387 nm is explored to enable fabrication of optical components. Volatile fragment analysis (thermal desorption gas chromatography-mass spectrometry) and molecular weight distribution monitoring (size exclusion chromatography) suggest photochemical modification, involving direct cleavage of the polymer backbone and propagation via chain unzipping under formation of monomers, similar to the pyrolytic degradation of PMMA. Waveguides were produced in undoped, clinical-grade PMMA, showing an increased refractive index in the laser focal region (Dnmax=4x10(-3)).

Femtosecond laser irradiation of polymethylmethacrylate for refractive index gratings

Polymethylmethacrylate (PMMA) or Perspex is an inexpensive polymer widely used for making the cores of communications grade polymer optical fibres (POFs) and as a substrate for polymer optoelectronic devices and integrated waveguides. Periodic refractive index structures have been written in undoped PMMA using multiple pulses of 40 fs duration from a 1 kHz Ti:sapphire femtosecond laser operating at the fundamental (800 nm). A refractive index change (Δn) of 5 ± 0.5 × 10−4 was observed before the onset of striations. Optimization of writing conditions for refractive index modification of POF fibres or bulk undoped PMMA will enable structures such as Bragg gratings, long-period gratings, mode couplers, microlens arrays, and zone plates to be written.

Plastic optical fibre sensors and devices

This paper considers the impact of recent developments in polymer optical fibre (POF) and its application in optical fibre sensors and optical measurement. A discussion of techniques developed for POF-based sensors and devices, and their applications includes sensors to measure flow, biofilm growth, turbidity, toxicity, humidity, rotation and fluorescence. Techniques to photoinduce refractive index changes and physical gratings into POF, and chemically to remove the cladding and taper plastic optical fibres are described, along with the use of fluorescent dye-doped plastic optical fibres (FPOF) in sensors and devices.

Pulse-duration dependency of femtosecond laser refractive index modification in poly(methyl methacrylate)

Refractive index modification of pure poly(methyl methacrylate) (PMMA) is investigated as a function of pulse duration using femtosecond lasers at 800 and 387 nm wavelength. It is observed that at 800 nm, the refractive index is modified more efficiently as the pulse duration decreases below 100 fs, whereas at 387 nm, efficient index modification is accomplished with longer, 180 fs pulses. Results suggest that three- and two-photon absorption is responsible for modification of pure PMMA at 800 nm and 387 nm, respectively. Repeated irradiation with short pulses of low laser fluence allows control of the photomodification via incubation, thus reducing bulk damage.

Sensing the fabric: To simulate sensation through sensory evaluation and in response to standard acceptable properties of specific materials when viewed as a digital image

This paper describes initial investigations, primarily from a textile and the related industries perspective, in developing and refining current fabric/texture simulation and interface design. We have considered the interactive possibilities of fabrics within a virtual environment using a simple haptic device, a commercially viable computer peripheral - Logitechs Wingman Mouse, which was developed by the Immersion Corporation for two dimensional (2D) exploration for the Games industry and desktop web navigation. Also, however because a majority of computer users are accustomed to using a mouse. The Wingman already has the facility to set up some simple mechanical variables to represent some of the more obvious tactile impressions in fabrics, e.g. denim for its overall roughness, and corduroy for its repetitive bumps. The results and issues involved are discussed in this paper.This paper presents a short review of the history surrounding the development of haptic feedback systems, from early manipulators and telerobots, used in the nuclear and subsea industries, to today’s impressive desktop devices, used to support real-time interaction with 3D visual simulations, or Virtual Reality. Four examples of recent VR projects are described, illustrating the use of haptic feedback in ceramics, aerospace, surgical and defence applications. These examples serve to illustrate the premise that haptic feedback systems have evolved much faster than their visual display counterparts and are, today, delivering impressive peripheral devices that are truly usable by non-specialist users of computing technology.

Automation and dynamic characterization of light intensity with applications to tapered plastic optical fibre

An automated chemical process for tapering highly multimoded plastic optical fibre tapers was developed. On-line monitoring was performed whilst varying the solvent composition to optimize taper formation, in order to obtain repeatable, optically clear and mechanically robust tapers in a minimum time period. A model of the process is presented in terms of fibre core radius and core/cladding refractive index. A relationship between core radius, cladding refractive index and numerical aperture was derived that had application for dynamic prediction and compensation of optical parameters. When characterized with a range of refractive indices, the tapered POF sensor exhibited two distinct regions: the water/alcohol region below 1.4 refractive index units, and the oil region above 1.4 suggesting the sensors use as an oil-in-water, or water-in-oil sensor. From 95% confidence limits, the accuracy of the POF was ±0.006 refractive index units (to 2 standard deviations) or 0.4% above 1.4. Tapered POF is sensitive to refractive index providing a cheap, easy-to-handle and rugged throwaway sensor for water and beverage process and quality monitoring.

A novel technique for on-line measurement of scaling using a multimode optical fibre sensor for industrial applications

Abstract The development of a novel on-line fibre optic sensor to measure the formation of scale and corrosion, as part of a study financed by the European Commission using sensitised, large diameter, polymer, multimode fibres is reported here. The consumption and discharge of water in industrial water systems are currently minimised. The circulation of such water causes the concentration of dissolved and suspended substances, promoting biofouling and scaling which can cost the industry several million Euros annually. Therefore, the development and validation of an on-line instrumentation and measuring technique regarding the scaling properties of aqueous process fluids and the laboratory trials is presented.