Coated Fiber Bragg Grating Research Articles

Investigation of polyimide coated fibre Bragg gratings for relative humidity sensing

This paper reports the development of a polyimide coated fibre Bragg grating for relative humidity sensing. The humidity response was measured for several polyimide coatings including P84 and P84 HT. The P84 HT polyimide coating proved the most promising with a large coefficient of moisture expansion measured at 73.8 ppm/%rh. The effect of coating thickness and optical fibre diameter were also investigated.

Protective coatings of fiber Bragg grating for minimizing of mechanical impact on its wavelength characteristics

The paper deals with the scheme for the study of the Bragg wavelength shift dependence on the applied tensile force. Samples of fiber Bragg gratings with different coatings have been studied: the restored acrylate coating, the heatshrinkable fusion splice protection sleeve without metal rod, the heat-shrinkable fusion splice protection sleeve with a metal rod, the metal capillary, polyvinylchloride tube. For different coatings of diffractive structure, dependences of wavelength shift for the Bragg grating resonance have been obtained on the tensile strength applied to the ends of an optical fiber. It was determined that the studied FBG coatings give the possibility to reduce the mechanical impact on the Bragg wavelength shift for 1.1-15 times as compared to an uncoated waveguide. The most effective version of coated fiber Bragg grating is the heatshrinkable fusion splice protection sleeve with a metal rod. When the force (equal to 6 N) is applied to the 100 mm optical fiber area with the inscribed diffractive structure, the Bragg wavelength shift is 7.5 nm for the unprotected sample and 0.5 nm for the one coated with the heat-shrinkable fusion splice protection sleeve.

High Sensitive FBG Sensor for Equivalent Salt Deposit Density Measurement

Online monitoring of the contamination condition of power transmission line is important to prevent insulation from flashover. The conventional online monitoring methods are easily disturbed by the strong electromagnetic interference around the high voltage line. In this letter, Bragg wavelength of polyimide coated fiber Bragg grating (FBG) is found to be slightly restrained by the salt deposited on the polyimide surface. Based on the effect, a special designed FBG sensor is proposed for detecting equivalent salt deposit density (ESDD) on insulators of power transmission line. To improve the sensor sensitivity, multiple polyimide layers are coated on the naked FBG, and in the curing process a 0.15-N force is applied on the free end of FBG to form uniform layers. Experiment results show the restrain wavelength varies with the ESDD. The resolution can be improved with multiple polyimide layers.

Study on Fiber-optic Hydrogen Sulfide Gas Sensor

We describe a novel fiber-optic gas sensor which hydrogen Sulfide (H2S) gas can be detected by a silver coated fiber bragg grating (FBG). The H2S sensitive material Ag can be coated on the cladding surrounding surface of FBG by conventional silver mirror reaction. The scanning electron microscope (SEM) was applied to analysis the Ag film structure before and after the interaction with H2S gas. By conducting the experiment of Ag-coated optical sensor (AOS), the relation between the H2S gas concentration and absorption spectrum was built. Result shows that while the concentration alters from 0 to 9.32%, a linear response of AOS signal to H2S concentration was observed with the response sensitivity of 0.332 dBm/% and linearity R2=0.9966. Such H2S sensor is suitable for monitoring the H2S hazard as a one time disposable logging-while-drilling sensor.

Modeling of Hydrogel Coated Fiber Bragg Grating pHSensor

Modeling of Hydrogel Coated Fiber Bragg Grating pHSensor

Modeling of Hydrogel Coated Fiber Bragg Grating pHSensor

This paper present the modeling and simulation of the hydrogel coated FBG for pH sensor application. The hydrogel swelling was modeled by using Poisson-Nernst-Planck equation and mechanical equilibrium equation. The simulation was done by assuming that the hydrogel was coated on unetched fiber and etched fiber. The strain induced at the fiber core was analyzed using finite element method. It was found that at the region near the jacketed fiber, the strain is distributed nonuniformly. The non uniform area for etched fiber is shorter than that of unetched fiber. The Bragg wavelength shift due to strain of the etched fiber is much larger than that of the unetched fiber.

Resonant Hydrophones Based on Coated Fiber Bragg Gratings

In this paper, we report on recent experimental results obtained with fiber-Bragg-grating (FBG) hydrophones for underwater acoustic detection. The optical hydrophones under investigation consist of FBGs coated with ring-shaped polymers of different size and mechanical properties. The coating materials were selected and designed in order to provide mechanical amplification, via judicious choice of their acousto-mechanical properties and by exploiting selected resonances occurring in different frequency ranges. Our underwater acoustic measurements, carried out within the range 4–35 kHz, reveal the resonant behavior of these optical hydrophones, as well as its dependence on the coating size and type of material. These experimental data are also in good agreement with our previously published numerical results. By comparison with bare (i.e., uncoated) FBGs, responsivity enhancements of up to three orders of magnitude were found, demonstrating the effectiveness of polymeric coatings in tailoring the acoustic response of FBG-based hydrophones.

A PDMS-Coated Optical Fiber Bragg Grating Sensor for Enhancing Temperature Sensitivity

We proposed a poly-dimethylsiloxane (PDMS)-coated fiber Bragg grating (FBG) temperature sensor for enhancing temperature sensitivity. By embedding the bare FBG in a temperature-sensitive elastomeric polymer, the temperature sensitivity of the proposed structure could be effectively improved by 4.2 times higher than those of the conventional bare-type FBG sensors due to the high thermal expansion coefficient of the PDMS. We analyzed the temperature-sensitivity enhancement effect with the increased Bragg wavelength shift in our structure and dependence on the temperature sensitivity with respect to the cross-section area of the PDMS.

Opto-acoustic behavior of coated fiber Bragg gratings

In this paper, we present the study of the acousto-optic behavior of underwater-acoustic sensors constituted by fiber Bragg gratings (FBGs) coated by ring-shaped overlays. Via full-wave numerical simulations, we study the complex opto-acousto-mechanical interaction among an incident acoustic wave traveling in water, the optical fiber surrounded by the ring shaped coating, and the FBG inscribed the fiber, focusing on the frequency range 0.5-30 kHz of interest for SONAR applications. Our results fully characterize the mechanical behavior of an acoustically driven coated FBG, and highlight the key role played by the coating in enhancing significantly its sensitivity by comparison with a standard uncoated configuration. Furthermore, the hydrophone sensitivity spectrum exhibits characteristic resonances, which strongly improve the sensitivity with respect to its background (i.e., away from resonances) level. Via a three-dimensional modal analysis, we verify that the composite cylindrical structure of the sensor acts as an acoustic resonator tuned at the frequencies of its longitudinal vibration modes. In order to evaluate the sensor performance, we also carry out a comprehensive parametric analysis by varying the geometrical and mechanical properties of the coating, whose results also provide a useful design tool for performance optimization and/or tailoring for specific SONAR applications. Finally, a preliminary validation of the proposed numerical analysis has been carried out through experimental data obtained using polymeric coated FBGs sensors revealing a good agreement and prediction capability.

Polymer‐coated fiber Bragg Grating Sensor for cryogenic temperature measurements

AbstractCryogenic temperature sensing has been demonstrated using Polymer coated Fiber Bragg Grating Sensor, and the experimental results are presented in this article. Teflon coating thicknesses of 20 and 40 μ applied on Fiber Bragg Gratings, inscribed in silica fiber (TFBG) are used for these studies. It was observed that the sensitivity of Teflon‐coated FBG has been enhanced three times compared to uncoated regular FBGs. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1154–1157, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25914

Optical detection of volatile organic compounds using selective tensile effects of a polymer-coated fiber Bragg grating

We demonstrated a novel selective chemical sensing approach by incorporating a poly(dimethylsiloxane) (PDMS)-coated fiber Bragg grating (FBG) structure for optically detecting various volatile organic compounds (VOC's). When the proposed structure is exposed to a nonpolar solvent, a tensile stress is induced between the coated PDMS and the optical fiber by a VOC-dependent swelling effect of the PDMS, which results in a Bragg wavelength shift dependent on the concentration and the type of VOC's. Because of no need of an etching process of a fiber cladding, the proposed PDMS-coated FBG can be used as a simple, convenient, and durable chemical sensing element with a high sensitivity, compared with conventional FBG sensors requiring an evanescent wave coupling.

Polymer coated fiber Bragg grating thermometry for microwave hyperthermia

Measuring tissue temperature distribution during electromagnetically induced hyperthermia (HT) is challenging. High resistance thermistors with nonmetallic leads have been used successfully in commercial HT systems for about three decades. The single 1 mm thick temperature sensing element is mechanically moved to measure tissue temperature distributions. By employing a single thermometry probe containing a fixed linear sensor array temperature, distributions during therapy can be measured with greater ease. While the first attempts to use fiber Bragg grating (FBG) technology to obtain multiple temperature points along a single fiber have been reported, improvement in the detection system's stability were needed for clinical applications. The FBG temperature sensing system described here has a very high temporal stability detection system and an order of magnitude faster readout than commercial systems. It is shown to be suitable for multiple point fiber thermometry during microwave hyperthermia when compared to conventional mechanically scanning probe HT thermometry. A polymer coated fiber Bragg grating (PFBG) technology is described that provides a number of FBG thermometry locations along the length of a single optical fiber. The PFBG probe developed is tested under simulated microwave hyperthermia treatment to a tissue equivalent phantom. Two temperature probes, the multiple PFBG sensor and the Bowman probe, placed symmetrically with respect to a microwave antenna in a tissue phantom are subjected to microwave hyperthermia. Measurements are made at start of HT and 85 min later, when a 6 degrees C increase in temperature is registered by both probes, as is typical in clinical HT therapy. The optical fiber multipoint thermometry probe performs highly stable, real-time thermometry updating each multipoint thermometry scan over a 5 cm length every 2 s. Bowman probe measurements are acquired simultaneously for comparison. In addition, the PFBG sensor's detection system drift over 10 h is measured separately to evaluate system stability for clinical applications. The temperature profiles measured by the two probes simultaneously under microwave HT are in good agreement showing mean differences of 0.25 degrees C. The stability of the detection system is better than 0.3 degrees C with response times of the PFBG sensor system of 2 s for each scan over ten points. The single fixed multipoint fiber thermometry capability compares favorably with the scanning Bowman probe data. This offers an enabling alternative to either scanning or bundled single point temperature probes for distributed thermometry in clinical applications.

Design parameter evaluation of a metal recoated Fiber Bragg Grating sensors for measurement of cryogenic temperature or stress in superconducting devices

There are plenty of complex physical phenomena which remain to be studied and verified experimentally for building an optimized superconducting magnet. The main problem for experimental validations is due to the unavailability of suitable sensors. This paper proposes a Fiber Bragg Gratings (FBG) sensor for this purpose which allows access to the local temperature/stress state. To measure the low temperature (20 K), FBG can be recoated with materials having high thermal expansion coefficient (HTCE). This can induce a thermal stress for a temperature change, which in turn increases the sensitivity of the sensor. The performance of such sensors has been experimentally studied and reported in earlier paper [Rajinikumar R, Suesser M, Narayankhedkar KG, Krieg G, Atrey MD. Performance evaluation of metallic coated Fiber Bragg Grating sensors for sensing cryogenic temperature. Cryogenics 2008;48:142–7]. This paper aims at evaluation and determination of different design parameters like coating materials, coating thickness, grating period and the grating length for design of better performance FBG sensor for low temperature/stress measurements.