Polymer Fiber Bragg Gratings Research Articles

Assessing Vehicle Wandering Effects on the Accuracy of Weigh-in-Motion Measurement Based on In-Pavement Fiber Bragg Sensors through a Hybrid Sensor-Camera System.

Weigh-in-motion (WIM) systems are essential for efficient transportation and monitoring parameters such as vehicle number, speed, and weight to ensure regulatory compliance and enhance road safety. Recently, WIM measurements using the Glass Fiber Reinforced Polymer Fiber Bragg Grating (GFRP-FBG) sensors have shown robustness and effectiveness. However, the accuracy of weight evaluation using the WIM systems based on GFRP-FBG sensors can be significantly influenced by the vehicle-wandering effect, which introduces uncertainties in wheel position determination and weight calculations. This paper assessed the impact of vehicle wandering on the accuracy of a WIM measurement system based on GFRP-FBG sensors by utilizing a new hybrid sensor-camera system that integrates roadside cameras and in-pavement GFRP-FBG sensors. The detailed methodology and framework of the developed hybrid system are introduced, followed by field testing on Highway I-94 in the United States. The field testing results indicate that by using the hybrid system, the wheel load detection accuracy of the WIM system based on GFRP-FBG sensors can be controlled to be a Type I or Type III WIM according to the ASTM 1318E-09 standard, with an average accuracy ranging from 87.83% to 94.65%. At the same time, when the wander distance is less than or equal to 9 cm, the developed WIM system proves to be very cost-effective as it only comprises two GFRP-FBG sensors, one temperature FBG sensor, and one camera. These findings indicate the practical potential to enhance the accuracy of WIM systems based on GFRP-FBG sensors designed for highways for low-coast, reliable, and accurate measurements by addressing vehicle wandering effects.

Potential of Discriminative Sensing of Strain and Temperature Using Perfluorinated Polymer FBG

Though the strain characteristics of fiber Bragg gratings (FBGs) inscribed in perfluorinated graded-index (PFGI) polymer optical fibers (POFs) have been reported, their temperature characteristics have not yet been detailed. In this paper, we experimentally investigate the temperature dependence of the Bragg wavelength of a PFGI-POF-FBG. With the increasing temperature, each peak of the FBG-reflected spectrum shifted to longer wavelength with different coefficients. The temperature coefficient of one of the clearest peaks was 0.09 nm/°C, which was eight times larger than those of FBGs in silica single-mode fibers and almost the same as those of FBGs in polymethyl methacrylate POFs. A temperature-independent but strain-dependent peak was also observed, which indicates the potential of discriminative sensing of strain and temperature.

Toward Commercial Polymer Fiber Bragg Grating Sensors: Review and Applications

Interest in polymer optical fiber Bragg gratings (POFBGs) arises from the different material properties and sensing modalities brought by polymers relative to silica. Polymer fibers typically offer twice the sensitivity to temperature of conventional silica fiber and increased sensitivity to strain overall. In addition, polymer fibers have higher elastic limits and as a result a larger range of operation for physical constraints. While some polymers are effectively humidity insensitive, others present inherent humidity sensitivity. Their organic properties also allow a variety of chemical processes to create (bio)chemical sensors, with the consequences of fiber breakage in situ being less hazardous than silica. These attributes have led to the use of POFBGs for applications that remain complex using silica fibers. This review paper covers the progress toward commercialization and the increasing number of specific applications.

Simultaneous detection of humidity and temperature through an adhesive based Fabry–Pérot cavity combined with polymer fiber Bragg grating

In this work we report the fabrication of a dual fiber sensor composed of an adhesive based Fabry–Pérot cavity combined with a polymer fiber Bragg grating (PFBG), for the simultaneous detection of humidity and temperature. The Fabry–Pérot structure was fabricated through a modified version of the self-written waveguide technology, by employing a no-core fiber, while the PFBG was inscribed in a flat-sides microstructured polymer fiber (mPOF) using the phase mask technology through the 248 nm UV laser. The combination of these two polymer based technologies allow an easy fabrication and provide an efficient route for the simultaneous detection of humidity and temperature with high resolution.

Largely tunable dispersion chirped polymer FBG.

We demonstrate a largely tunable dispersion fiber Bragg grating (FBG) inscribed in a microstructured polymer optical fiber (mPOF). The bandwidth of the chirped FBG (CFBG) was achieved from 0.11 to 4.86nm, which corresponds to a tunable dispersion range from 513.6 to 11.15ps/nm. Furthermore, thermal sensitivity is used to compensate for the wavelength shift due to the applied strain. These results demonstrate that a CFBG in a POF is a promising technology for future optical systems.

Strain Sensitivity Enhancement of a Sensing Head Based on ZEONEX Polymer FBG in Series With Silica Fiber

This study presents the use of a sensing device composed of an all ZEONEX-480R polymer fiber Bragg grating, in series with a silica fiber, for the control/enhancement of the strain sensitivity. The results show that the amount of strain imposed in the total gauge length is unequally distributed in each fiber section. The low Young's modulus and diameter of the polymer fiber employed, compared to the silica one, leads to a higher strain density in the former. Additionally, the control of the length of each fiber section plays also an important role on the distribution of strain in each fiber. Theoretical results show that higher strain sensitivities are easier to achieve for short and long polymer and silica fiber lengths, respectively. Experimental characterization of a sensing head composed by a 2.6 cm polymer optical fiber and different lengths of silica fiber, led us to control and improve the strain sensitivity of the sensing device.

Optical sensors for bond-slip characterization and monitoring of RC structures

Bond-slip is an important interaction between steel and concrete in reinforced concrete (RC) structures and other civil engineering constructions. It is essential to understand and to characterize, at local level, this stress transference mechanism. In particular its behavior for monotonic and cyclic demands, the parameters that influence this mechanism, and how it is affected by different deterioration factors. Therefore, characterizing and monitoring the bond-slip mechanism is essential for the safety assessment of RC structures, more specifically determining the reinforcing bars slippage inside the concrete, and therefore the stress and strain distribution in RC members. In this work, two optical fiber sensors are presented, based on silica and polymer fiber Bragg gratings (FBGs), which were implanted inside a concrete block specimen and subjected to a pull-out test. After 6 days of curing, the pull-out test was recorded and the displacement incurred during the test was also monitored with a traditional electric sensor; for comparison with the data acquired with the two optical sensors. The results obtained confirm the viability and advantages of the optical sensors, evidenced by their higher resolution and far lower dimensions (allowing them to be embedded into the concrete) when compared with their electronic counterparts. The straightforward implementation and use of the optical sensors show very promising results when used in civil engineering structures.

Strain Sensitivity Control of an In-Series Silica and Polymer FBG.

This work reports on the use of an in-series silica and polymer fiber Bragg grating (FBG) to control the FBG strain sensitivities and enhance in the case of the polymer fiber Bragg grating (PFBG). Due to differences in the Young’s Modulus of the fibers employed, the amount of strain is unequally distributed in each fiber section. By acting on the silica fiber length, it was possible to control the strain sensitivity of the two FBGs, allowing a polymer FBG strain sensitivity much higher than the one found in the elementary fiber to be obtained. The influence of the diameter of the polymer fiber on the strain sensitivities of the FBGs was also investigated. Results have shown that, besides the strain sensitivity control, an even greater improvement in the PFBG strain sensitivity can be achieved.

All-polymer fiber-optic pH sensor.

A novel all-polymer fiber-optic pH sensor using a UV-cured pH-sensitive hydrogel, poly(ethylene glycol) diacrylate (PEGDA), coated on a polymer fiber Bragg grating was developed. The PEGDA increased in volume according to the pH value of the surrounding fluid, which subsequently induced a lateral stress in the polymer fiber Bragg grating. The proposed pH sensor exhibits a pH sensitivity of up to -0.41 nm/pH and a fast response time of 30 s.

Etched Polymer Fibre Bragg Gratings and Their Biomedical Sensing Applications.

Bragg gratings in etched polymer fibres and their unique properties and characteristics are discussed in this paper. Due to the change in material and mechanical properties of the polymer fibre through etching, Bragg gratings inscribed in such fibres show high reflectivity and enhanced intrinsic sensitivity towards strain, temperature, and pressure. The short-term and long-term stability of the gratings and the effect of hysteresis on the dynamic characteristics are also discussed. The unique properties and enhanced intrinsic sensitivity of etched polymer fibre Bragg grating are ideal for the development of high-sensitivity sensors for biomedical applications. To demonstrate their biomedical sensing capabilities, a high-sensitivity pressure transducer that operates in the blood pressure range, and a breathing rate monitoring device are developed and presented.

Characterization of Polymer Fiber Bragg Grating With Ultrafast Laser Micromachining

We report that the main photosensitive mechanism of poly(methyl methacrylate)-based optical fiber Bragg grating (POFBG) under ultraviolet laser micromachining is a complex process of both photodegradation and negative thermo-optic effect. We found experimentally the unique characteristics of Bragg resonance splitting and reunion during the laser micromachining process providing the evidence of photodegradation, while the mean refractive index change of POFBG was measured to be negative confirming further photodegradation of polymer fiber. The thermal-induced refractive index change of POFBG was also observed by recording the Bragg wavelength shift. Furthermore, the dynamic thermal response of the micromachined-POFBG was demonstrated under constant humidity, showing a linear and negative response of around −47.1 pm/°C.

High Intrinsic Sensitivity Etched Polymer Fiber Bragg Grating Pair for Simultaneous Strain and Temperature Measurements

A sensing configuration for simultaneous measurement of strain and temperature with enhanced intrinsic sensitivity based on a fiber Bragg grating (FBG) pair with one grating inscribed in the etched and the other in unetched polymer fiber region is demonstrated. A poly (methyl methacrylate) based single-mode polymer fiber is etched to different diameters, and it is observed that etching can lead to change in the material properties of the fiber, such as Young’s modulus and thermal expansion coefficient, which can play a vital role in improving its intrinsic sensing capabilities. Thus, exploiting the different strain and temperature sensitivities exhibited by etched and unetched polymer FBGs, strain and temperature can be simultaneously measured with very high sensitivity. Experimental results show that rms deviations of ± 8.42 $\mu \epsilon $ and ± 0.39 °C for strain and temperature, respectively, in a real simultaneous measurement. The effect of individual thermal and strain sensitivity coefficients on measurement accuracy is also analyzed.

Etching Process Related Changes and Effects on Solid-Core Single-Mode Polymer Optical Fiber Grating

Etching process related material and mechanical changes on solid-core single-mode polymer optical fiber (POF) and their influence on the characteristic properties of polymer fiber Bragg gratings (PFBGs) are studied. A poly(methyl methacrylate)-based POF is etched to different diameters, and it is experimentally demonstrated that etching can lead to a change in the Young's modulus of the fiber. It is found that etching process induced material changes of the polymer fiber can enhance the reflectivity and inherent sensitivity of PFBGs. It is demonstrated that gratings based on etched POF exhibit higher reflectivity with a shorter exposure time compared with unetched ones. Highest reflectivity of 98.54% is observed within 7 seconds of exposure for a diameter of 85 $\mu\text{m}$ . The stability of fabricated Bragg gratings is also studied. By tailoring the etching diameter of POF, Bragg gratings with high sensitivity and high reflectivity can be fabricated.

Industrial and medical applications of fiber Bragg gratings (Invited Paper)

The uses of optical fibers are numerous, and over the past few decades, they have extended from optical fiber communications to a wide variety of sensing applications. In particular, fiber Bragg grating (FBG) sensors inscribed in single-mode optical fibers offer significant advantages over more conventional electrical sensors and have been successfully deployed in many different industries. In this Review, we review the applications of intrinsic FBG pressure and flow sensors in oil and gas and the deployment of FBG sensing networks in railways. The promising prospect of using polymer FBGs in wearable medical devices is also described.

Graphene-Based D-Shaped Polymer FBG for Highly Sensitive Erythrocyte Detection

Graphene-based silica fiber-optic sensors, with high sensitivity, fast response, and low cost, have shown great promise for gas sensing applications. In this letter, by covering a monolayer of p-doped graphene on a D-shaped microstructured polymer fiber Bragg grating (FBG), we propose and demonstrate a novel biochemical probe sensor, the graphene-based D-shaped polymer FBG (GDPFBG). Due to the graphene-based surface evanescent field enhancement, this sensor shows high sensitivity to detect surrounding biochemical parameters. By monitoring the Bragg peak locations of the GDPFBG online, human erythrocyte (red blood cell) solutions with different cellular concentrations ranging from 0 to $10^{\mathrm {\mathbf {4}}}$ ppm were detected precisely, with the maximum resolution of sub-ppm. Such a sensor is structurally compact, is clinically acceptable, and provides good recoverability, offering a state-of-the-art polymer-fiber-based sensing platform for highly sensitive in situ and in vivo cell detection applications.

Twist effect and sensing of few mode polymer fibre Bragg gratings

For the development of the twist sensor based on few mode polymer optical fibre (POF) gratings, we investigated the twist effect of few mode (FM) POF Bragg gratings with large twist, and found the twist effect on reflection is highly mode dependent-insignificant on the fundamental mode and considerable on higher order modes, which seems closely related to the symmetry of modal field. In addition, Bragg wavelengths of both the fundamental mode and higher modes red-shift with the twisting and blue-shift with the twist releasing, and they almost display the similar response trend without any mode dependence. Further analysis found that the red-shift of the Bragg wavelength should be attributed to the redistribution of the pre-strain applied upon the POF, activated by twist. Finally, based on the reflection response to the twist, one kind of twist sensing scheme with few mode POF gratings has been demonstrated, showing great potential as a twist sensor.

INVITED] New advances in polymer fiber Bragg gratings

During the last years, fiber Bragg gratings (FBGs) written in polymer optical fibers (POFs) have been pointed as an interesting alternative to silica FBGs for applications in sensors and in optical access networks. In order to use such components in real applications, the manipulation of POFs, as well as the increase of quality in the production of FBGs has to be achieved. In this article some of the recent advances regarding these two aspects are reported and include recent developments to produce smooth POFs end face with high quality, benefiting the current splicing process and the inscription of high quality FBGs in a few seconds. Furthermore, additional characterizations to strain, temperature, pressure, and humidity are also shown.

Antiresonant guiding in a poly(methyl-methacrylate) hollow-core optical fiber

Strong antiresonant reflecting optical waveguiding is demonstrated in a novel poly (methyl-methacrylate) (PMMA) hollow-core fiber. The transmission spectrum of the fiber was characterized using a supercontinuum source and it revealed distinct resonances with resonant dips as strong as ∼20 dB in the wavelength range 480–900 nm, where PMMA has low absorption. The total propagation loss of the fiber was measured to have a minimum of ∼45 dB m−1 at around 500 nm. The thermal sensitivity of the fiber is 256 ± 16 pm °C−1, defined as the red-shift of the resonances per °C, which is three times higher than the sensitivity of polymer fiber Bragg gratings.

Bragg wavelength shift for irradiated polymer fiber Bragg grating

The effect of neutron-irradiation from a 5 Ci Am-241/Be-9 neutron source on the characteristics of Polymer Fiber Bragg Grating (PFBG) has been studied in the present work. The PFBG has been irradiated using fast neutrons with different doses range from 24 up to 720 Gy. The transmittance and reflectance of the PFBG have been recorded and interpreted before and after the irradiation. Results in this study showed that the neutron irradiation might cause a structural degradation of the polymer's main chain, which led to a shift in the Central Bragg Wavelength (CBW). In addition, the CBW increased from 4 pm to 14 pm when the neutron dose increased from 24 to 720 Gy. Moreover, no saturation has been observed in the CBW under the effect of the applied doses. Therefore, the PFBG of high Bragg wavelength is a suitable candidate for the use in the dosimetry systems.

Intrinsic High-Sensitivity Sensors Based on Etched Single-Mode Polymer Optical Fibers

The significance of etched single-mode polymer optical fibers and their potential for the development of high-sensitivity sensors are presented. A polymethyl methacrylate-based single-mode polymer optical fiber is etched to various diameters and it is observed that etching can lead to change in the material properties of the fiber, such as Young’s modulus and thermal expansion coefficient. This can play a vital role in improving the intrinsic sensing capabilities of sensors based on etched polymer optical fiber. To demonstrate that the modified material properties of the etched polymer fiber can enhance its intrinsic sensing capabilities, sensing characteristics of etched polymer fiber Bragg gratings for strain, temperature, and pressure are obtained. From the results, it is confirmed that the sensors based on etched polymer fibers exhibit high intrinsic sensitivity compared with un-etched ones. The potential of developing a sensing system for simultaneous measurement of strain and temperature is also demonstrated.