Development and study of Bragg fibres with a large mode field and low optical losses
Mikhail E. LikhachevS. L. SemjonovМ. М. БубновEvgenii M DianovV. F. KhopinM. Y. SalganskiiM.A. GurjanovA. N. GurjanovRaphaël JamierPierre VialeSébastien FévrierJean-Marc Blondy
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A silica Bragg fibre with optical losses lower than 10 dB km-1 is fabricated for the first time. The Bragg fibre manufactured by the MCVD method is intended for operation at a wavelength of 1.06 μm and has the mode-spot diameter 18.5 μm (the mode-spot area is 270 μm2). The fibre is considerably less sensitive to bending than step-index fibres and microstructure fibres with the same mode-spot size. The possibility of fabricating a Bragg fibre with the record mode-spot area (530 μm2 at the operating wavelength of 855 nm) for all-silica fibres is demonstrated.Keywords:
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An optical fibre sensor has been developed to measure particle concentration in water. The principle of operation is based on light being coupled between two parallel mounted fibres in the vicinity of the sensing region. The optical power is coupled by means of the evanescent field of the multimode fibres. A theoretical description of the light propagation mechanism in the fibre is presented which is extended to include the effect of attenuation of the evanescent wave in the measurand medium. Experimental results are also presented for yeast suspensions in water in the range 0-16 gl - 1 .
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An optical-fibre unit with a strain-relaxing effect is proposed for realising a highly reliable optical-fibre submarine cable. The basic design of the new type of optical-fibre unit means that optical fibres are not subjected to the same strain as the fibre unit directly when the unit is elongated. The test result of the strain-relaxing effect of an experimental optical-fibre unit was about 0.2%, and optical fibres returned to the original position in the fibre unit after the tension was released.
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Polymer optical fibre (POF) is a growing technology in short distance telecommunication due to its flexibility, easy connectorization, and lower cost than the mostly deployed silica optical fibre (SOF) technology. Microstructured POFs (mPOFs) have particular promising potential applica-tions in the sensors and telecommunications field, they could specially help to reduce losses in poly-mer fibres by using hollow-core fibres. However, mPOFs are intrinsically more difficult to cut due to the cladding hole structure and it becomes necessary to have a high quality polymer optical cleaver. In the well-known hot-blade cutting process, fibre and blade are heated, which requires electrical compo-nents and increases cost. A new method has recently been published to cut POF without the need for heating the blade/fibre, therefore electronically devices are not required if it is used a proper mechani-cal system. In this paper, we present a passive and portable polymer optical cleaver implemented with a mechanical system formed by a constant force spring and a damper.
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We demonstrate the performance of optical fibre dissolved oxygen (DO) sensor when subject to different core material and sizes. It was found that fluorescence emission from oxygen sensitive material coated at the end-face of an optical fibre DO sensor varies with core material and sizes. Glass core optical fibre provides higher emission when compared to plastic core optical fibre. Using glass core optical fibre, up to 20 meter of optical fibre length can be achieved compared to other reported work.
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The focus of this research was to design, optimise and deploy a practical multi-measurand sensor (MMS) for process monitoring of glass and carbon fibre preforms in an autoclave. The MMS design was based on the optical fibre-based extrinsic Fabry-Perot interferometric (EFPI) strain sensor. The EFPI sensor consisted of a pair of cleaved optical fibres, with a defined gap that were housed in a precision bore capillary. Interferometric interrogation was used to measure the cavity length hence, permitting the strain to be determined. The basic EFPI sensor design was modified in the following manner to enable multi-measurand monitoring.
Firstly, a fibre Bragg grating (FBG) was inscribed on one of the optical fibres that were destined to be housed in the capillary; the end-face of this cleaved optical fibre was sputter coated with Au/Pd to produce a reflective surface. This FBG is in a relatively strain-free condition and only responds to temperature. Secondly, a technique was developed to manufacture optical-quality end-faces of the capillary and this too was sputter coated with Au/Pd. Thirdly, secondary cleaved optical fibres were packed around the lead-in optical fibre of the EFPI sensor with a defined (secondary) cavity thus, permitting transmission/reflection FTNIR spectroscopy. Finally, cleaved secondary optical fibres were also secured to the lead-in fibre and these served as Fresnel reflection sensors. The interrogation of the MMS was carried out using a conventional fibre-coupled multi-channel FTNIR spectrometer. The feasibility of monitoring strain, temperature, cross-linking kinetics and refractive index simultaneously during the processing of glass and carbon fibre preforms was demonstrated.
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This paper presents a general overview of a number of optical fibre sensor systems which have been developed and used in advanced fibre-reinforced composites for in-situ process and condition monitoring. The in-situ process monitoring techniques were optical-fibre-based evanescent wave spectroscopy, transmission near-infrared spectroscopy and refractive index monitoring. The optical fibre sensors were successful in tracking the cure reaction. The condition monitoring of advanced fibre-reinforced composites was carried out using two intensity-based optical fibre sensor systems: an extrinsic multi-mode Fabry-Pérot sensor and Bragg gratings. In addition to this, the feasibility of using the reinforcing fibre as a light guide was demonstrated. These sensor systems were evaluated under quasi-static, impact and fatigue loading. The test specimens consisted of prepreg-based carbon-fibre-reinforced epoxy and glass-fibre-reinforced epoxy filament-wound tubes. Excellent correlation was obtained between surface-mounted strain gauges and the embedded optical fibre sensors. The feasibility of using these sensor systems for the detection of impact damage and stiffness reduction in the composite due to fatigue damage was successfully demonstrated.
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Optical fiber-based extrinsic Fabry-Perot interferometric (EFPI) sensors have been extensively deployed for sensing a number of measurands including temperature, strain, vibration and pressure. Their circular cross-section has made it relatively simple and attractive to embed them in advanced fibre reinforced composites (AFRCs) such as glass and carbon fibers. However, a typical construction of an EFPI consists of two optical fibers that are positioned and secured within a precision bore capillary. The relative outer diameters of the various key components are as follows: capillary = 300 micrometers ; optical fibre = 125 micrometers ; carbon and glass fibers = 8 and 14 micrometers respectively. This mismatch in relative diameters of the reinforcing and the sensor fibers can result in significant spatial distortion of the former. The location of the embedded sensing fibre in relation to the reinforcing fibre layers can also lead to the formation of resin-rich regions in the AFRC. These factors can have a detrimental effect on the compressive properties of the material. Therefore, there is significant attraction in reducing the overall diameter of the sensor. In this current paper, the feasibility of reducing the diameter of EFPI sensor design to that of the optical fibre is demonstrated via two techniques. The first technique involved the use of hydrofluoric acid to etch and create the Fabry-Perot cavity. In the second technique, the feasibility of using laser ablation to fabricate the Fabry-Perot cavity in silica and sapphire substrates is presented. The optical fibre-based Fabry-Perot cavity produced via acid etching was interrogated using white light interferometry.
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The ongoing development of a fibre optic voltage sensor requires a self-aligning fibre. We experimentally demonstrate fibre designs with preferential bending directions which self-align when coiled as part of a voltage sensor device. Such a fibre has much wider applications.
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This paper presents the design of the side-polished optical fibre sensor. The polished core on one side of the optical fibre excites the fluorescence phenomenon inside the tubes by emitting rays of light outside the optical fibre cor. The sensor constructed in this way can be used both in industry and in the medicine. This article discusses the ability to collect information about the condition of blood vessels in the human body, which is the intended practical use of the sensor. An important part of the design process is the selection of a suitable optical fibre, the bend radius and the length of the polished fibre fragment so as to obtain optimal power concentration in the investigated place. The entire process taking place in the optical fibre was simulated using the Ray tracing method with optimised fibre optic parameters.
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