Silica Fiber Bragg Gratings Research Articles

An optimum design of high sensitivity PMMA-coated FBG sensor for temperature measurement

Fiber Bragg grating (FBG) with silica material has limitations in measuring mechanical quantities such as strain and temperature, this happens because silica fibers are easy to break at higher transverse or axial strains. This deficiency can be overcome in several ways, one of which is by coating the silica FBG with a coating material made of metal or polymer. In this research, the FBG sensor has been designed by poly methyl methacrylate (PMMA)-coated FBG and silica. The finite element method (FEM) is used to analyze the electric field distribution on the surface of PMMA coated FBG with a coating thickness of 20 µm. Furthermore, the sensitivity of each coated FBG as a temperature sensor was measured in the range of 25 ℃ to 85 ℃ using coupled mode theory (CMT). From the design and analysis of coated FBG, it was found that FBG coated with PMMA material had the highest sensitivity of 395.73pm/℃. However, the FBG sensor coated with silica material has a sensitivity of 13.73 pm/℃. the shift obtained is also linear along with the temperature of 25 ℃ to 85 ℃.

Bragg grating in a flexible and stretchable coreless polymer optical fiber.

In this Letter, we propose and experimentally demonstrate fiber Bragg grating (FBG) fabrication in a flexible and stretchable coreless polymer optical fiber. The flexible polymer optical fiber is prepared with polydimethylsiloxane (PDMS). Femtosecond laser direct writing and slit beam shaping are used to form periodic grating structures in the fiber. The fabricated FBG exhibits a large strain measurement range and a blueshift response to temperature. Moreover, it offers low humidity sensitivity due to its low permeability toward water vapor. Taking advantage of the unique sensing performances of the PDMS fiber, the proposed FBG has considerable advantages over the traditional silica FBG devices for strain and temperature sensing.

Performance of Etched Silica FBG for Simultaneous Strain Temperature Measurement

In this paper, we have proposed an etched silica Fiber Bragg Gratings (FBGs) based interrogation technique using an optical spectrum analyser (OSA). The efficiency of the proposed system has extensively been investigated for measuring the temperature and strain simultaneously with higher sensitivity and accuracy covering a larger measurement range. A Single mode-Multi mode-Single mode fiber (SMS) which acts as a bandpass filter is employed in the circuitry for an efficient and fast interrogation technique. We recorded a remarkable enhancement in sensitivity of 20.30 pm/°C and 2.89 pm/μɛ over the temperature and strain range of 25–225 °C and 50–2050 μɛ, respectively. These data were recorded with the strain resolution of ±10 μɛ whereas the resolution for the temperature is ±0.50 °C. The experimental results show the capability of the sensor for measuring the strain and temperature simultaneously with higher intrinsic sensitivity and resolution. The performance of the proposed sensor has been compared with various reported techniques.

High sensitivity sapphire FBG temperature sensors for the signal processing of data communications technology

<p>This study has outlined the fiber bragg grating (FBG) temperature sensors signal processing for data communications by using OptiGrating simulation software. The reflectivity of the silica and sapphire fiber grating spectrum is reported against the grating wavelength for internal and external temperature variations. As well as apodized Gaussian reflectivity of the silica and sapphire fiber grating spectrum is simulated and clarified against the grating wavelength for high temperature variations. The temperature sensitivity of sapphire FBG nearly 0.11 pm/<sup>0</sup>C, where its value is three times higher than silica FBG. It is observed that silica and Sapphire FBG sensors were tested up to 1000 <sup>0</sup>C by using Gaussian apodization type, side lobes in reflectivity spectrum are totally suppressed.</p>

Gold Nanoparticles Coated FBG Sensor Based on Localized SPR for Adulterated Honey Classification

Two types of fiber optics, namely macro etched silica single mode fiber (SMF) and Fiber Bragg Grating (FBG) (Bragg wavelength of 1550 nm and 1554 nm) had been used to detect various types of honey samples, such as Apis Dorsata Honey, Trigona Honey and Capilano Australian Honey. To study the effect of exposure period in open environment at room temperature, all honey samples were exposed in open environment at room temperature from 2 to 10 days. In comparison with macro etched SMF and FBG (λB=1554 nm), the FBG (λB=1550 nm) portrays an excellent sensing properties with sensitivity and selectivity of 33.56 dB/RIU and 24.07 dB/RIU respectively. The output of this work concludes that the quality of honey based on optical output power reduces up to 0.35% as period of exposure to the open environment increased.

Comparative analysis of silica fiber Bragg grating and chalcogenide fiber Bragg grating

Sensing performance of silica fiber Bragg grating (FBG) and chalcogenide FBG are compared in presence of apodization functions. The Bessel and Gaussian apodization functions are chosen in this analysis. These fibers are compared on the basis of their sensitivity, detection accuracy, quality parameter and sidelobe suppression ability. Reflectivity equations established from couple modes equations by matching fields at interfaces. For considered apodization profiles, it is observed that the sidelobe suppression ability and sensitivities are nearly same in both chalcogenide and silica fiber Bragg grating. Chalcogenide-based fiber Bragg grating with Bessel apodization function have narrower full width half maxima (FWHM) value that’s why its detection accuracy and quality parameter is maximum in comparison of other considered cases. Hence for sensing application purpose chalcogenide-based fiber Bragg grating in presence of Bessel apodization function is appropriate.

Correlation between glass viscosity and the high-temperature lifetime of silica fiber Bragg gratings directly written by a femtosecond laser

We report our investigation on the correlation between glass viscosity and the lifetime of femtosecond laser written silica fiber Bragg gratings (FBGs) at high temperatures. The FBGs are made by a direct, point-by-point writing method using an 800-nm Ti:sapphire femtosecond laser. It shows that the femtosecond laser inscribed FBGs in the commercial silica fibers can survive under high-temperature up to 1150 °C. An empirical formula of FBG thermal lifetime τ (in second) versus glass viscosity η (in dPa·s), τ=0.27η0.32, is deduced. Both our experimental results and the previously reported work on femtosecond laser induced photo-defects is in good agreement with such a formula, indicating its effective prediction on the thermal stability and thermal decay of such a type of FBG at high temperatures.

Half-Watt Tm3+-Doped Fluoride Fiber Laser at 785 nm

All-fiber single-transverse-mode laser oscillators operating at 785 nm were demonstrated by splicing a 0.1 mol% Tm 3+ -doped fluoride fiber with a core diameter of 4 μm and a numerical aperture of 0.07 to a pair of silica fiber Bragg gratings. About 500 mW of continuous-wave single transverse mode laser output at 784.5 nm with a 3-dB spectral bandwidth of 0.2 nm was obtained by upconversion pumping a 3-m-long gain fiber at 1125 nm. Our experiments show that the ground-state absorption of Tm 3+ at 785 nm is the origin of low efficiency in previous reports. The efficiency of this all-fiber laser can be improved by using a gain fiber with an optimized overlap between the laser, the pump, and the fiber core, and employing new pumping schemes that deplete the ground state sufficiently.

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.

Large strain detection of SRM composite shell based on fiber Bragg grating sensor

There may be more than 2% strain of carbon fiber composite material on solid rocket motor (SRM) in some extreme cases. A surface-bonded silica fiber Bragg grating (FBG) strain sensor coated by polymer is designed to detect the large strain of composite material. The strain transfer relation of the FBG large strain sensor is deduced, and the strain transfer mechanism is verified by finite element simulation. To calibrate the sensors, the tensile test is done by using the carbon fiber composite plate specimen attached to the designed strain sensor. The results show that the designed sensor can detect the strain more than 3%, the strain sensitivity is 0.0762 pm/με, the resolution is 13.13με, and the fitting degree of the wavelength-strain curve fitting function is 0.9988. The accuracy and linearity of the sensor can meet the engineering requirements.

Graphene diaphragm integrated FBG sensors for simultaneous measurement of water level and temperature

A graphene diaphragm integrated silica fiber Bragg grating (FBG) based sensor head was developed for simultaneous determination of water level and temperature. This new design used two FBG sensors with uniform grating made of SMF-28 fiber with 1550nm of central wavelength, bandwidth of 0.5nm, 4mm length and 90% reflectivity. The response of the sensor to water level was monitored in terms of Bragg wavelength shift, which is proportional to the strain. Upon immersing inside the water column, the diaphragm gets deformed due to a strain originated from the water level imposed hydrostatic pressure. A linear response of the sensor head was achieved for water level in the range of 0–100cm. The FBG based sensor head revealed high detection sensitivity ∼24.84 pm/cm. The temperature measurement sensitivity of the sensor was 13.31 pm/°C in the range of 27–77°C. The water level detection sensitivity was found to reduce with increasing thickness of the graphene diaphragm.

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.

A self-referenced optical intensity sensor network using POFBGs for biomedical applications.

This work bridges the gap between the remote interrogation of multiple optical sensors and the advantages of using inherently biocompatible low-cost polymer optical fiber (POF)-based photonic sensing. A novel hybrid sensor network combining both silica fiber Bragg gratings (FBG) and polymer FBGs (POFBG) is analyzed. The topology is compatible with WDM networks so multiple remote sensors can be addressed providing high scalability. A central monitoring unit with virtual data processing is implemented, which could be remotely located up to units of km away. The feasibility of the proposed solution for potential medical environments and biomedical applications is shown.

Experimental Study and Analysis of a Polymer Fiber Bragg Grating Embedded in a Composite Material

The characteristics of polymer fiber Bragg gratings (FBGs) embedded in composite materials are studied in this paper and are compared with characteristics of their silica counterparts. A polymer FBG of 10 mm length which exhibits a peak reflected wavelength circa 1530 nm is fabricated and characterized for this purpose. A silica FBG with a peak reflected wavelength circa 1553 nm is also embedded in the composite material for a comparison study. The fabricated composite material sample with embedded sensors is subjected to temperature and strain changes and the corresponding effects on the embedded polymer and silica FBGs are studied. The measured temperature sensitivity of the embedded polymer FBG was close to that of the same polymer FBG in free space, while the silica FBG shows elevated temperature sensitivity after embedding. With an increase in temperature, spectral broadening was observed for the embedded polymer FBG due to the stress induced by the thermal expansion of the composite material. From the observed wavelength shift and spectral bandwidth change of the polymer FBG, temperature and thermal expansion effects in the composite material can be measured simultaneously.

Highly Reflective Fiber Bragg Gratings Inscribed in Ce/Tm Co-Doped ZBLAN Fibers

We report highly reflective fiber Bragg gratings (FBGs) photoinduced in the core of Ce/Tm co-doped ZBLAN fibers using a 248-nm excimer laser. We compare the characteristics of the FBGs inscribed in ZBLAN fiber to those produced in silica fiber. We also characterize the strain and temperature responses of ZBLAN FBGs and find that the wavelength can be strain- and temperature-tuned at rates that are 45% and 15% higher, respectively, compared to silica FBGs.

Acousto-Optic Effect in Microstructured Polymer Fiber Bragg Gratings: Simulation and Experimental Overview

A fine control of the microstructured polymer fiber Bragg grating spectrum properties, such as maximum reflected power and 3-dB bandwidth, through acousto-optic modulation is presented. For simulation purposes, the device is modelled as a single structure, comprising a silica horn and a fiber Bragg grating. For similar sized structures a good correlation between the numerical results and the experimental data is obtained, allowing the strain field to be completely characterized along the whole structure. It is also shown that the microstructured polymer fiber Bragg grating requires less effort from the piezoelectric actuator to produce modification in the grating spectrum when compared with a silica fiber Bragg grating. This technique has potential to be applied on tunable optical filters and tunable cavities for photonic applications.

Intrinsic Temperature Sensitivity of Fiber Bragg Gratings in PMMA-Based Optical Fibers

Thermal response of fiber Bragg gratings (FBGs) in polymethyl methacrylate-based optical fibers doped with trans-4-stilbenemethanol is studied at 0% relative humidity (RH) from -20°C to 60°C. The Bragg wavelength is found to negatively shift upon heating in a nonlinear manner. The higher the temperature, the larger the magnitude of wavelength shift is. The absolute value of calculated temperature sensitivity also increased with temperature. The sensitivity at room temperature is about -1 pm/°C, which is one order of magnitude lower than that measured at constant RH for polymer FBGs and that of silica FBGs. Such low temperature sensitivity challenges the common notion of high temperature sensitivity of polymer FBGs. In addition, it is found that the dependence of Bragg wavelength of the polymer FBGs on RH is nonlinear. Below 30% RH, the Bragg wavelength shift upon RH increase is minimal compared to that above 30% RH.

Single-frequency Ho^3+-doped ZBLAN fiber laser at 1200 nm

A single-frequency (SF) fiber laser at 1200 nm was developed with a distributed Bragg reflector (DBR) configuration by splicing a 22 mm long highly holmium-doped ZBLAN (ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF) fiber with a pair of silica fiber Bragg gratings. The linewidth was estimated to be less than 100 kHz based on the measured frequency noise. The relative intensity noise was measured to be <110 dB/Hz at the relaxation oscillation peak and the polarization extinction ratio was measured to be >19 dB. Our results highlight the exciting prospect that wavelength coverage of SF DBR fiber lasers can be expanded significantly by using rare-earth-doped ZBLAN fibers.

976 nm single-frequency distributed Bragg reflector fiber laser

A single-frequency distributed Bragg reflector (DBR) fiber laser at 976 nm was developed with a 2 cm long highly ytterbium-doped phosphate fiber and a pair of silica fiber Bragg gratings. More than 100 mW of linearly polarized output was achieved from the all-fiber DBR laser with a linewidth less than 3 kHz. The outstanding features of this single-frequency laser also include ultralow relative intensity noise and high wavelength stability. This fiber laser is an excellent seeder for high-power 976 nm narrow-linewidth laser amplifiers that can be used for efficient coherent blue-light generation through frequency doubling.