Characteristics Of Fiber Bragg Gratings Research Articles

Research on Application of Fiber Bragg Grating Seepage Pressure Sensor in Soil Test

Combined with the pressure sensitive characteristics of corrugated diaphragm and the strain sensing characteristics of fiber Bragg grating (FBG), a kind of FBG sensor is developed to measure the seepage pressure change of soil in a small range. By carrying out the soil seepage flow monitoring test and the laboratory slope model test, and comparing the theoretical and measured values of these tests, it can be found that: it is feasible to apply FBG seepage pressure sensor to the seepage pressure monitoring of soil mass. The sensor can guarantee the validity and reliability of data in the medium-term or long-term monitoring process, and shows superior performance compared with conventional seepage pressure sensor. The FBG seepage pressure sensor has the characteristics of high sensitivity, stable long-term performance, high precision and strong real-time performance. It provides a new measurement method for the seepage pressure monitoring of soil mass within the range of 0 to 100 kPa.

Development and application of a borehole stress meter in rocks surrounding the roadway, based on optical-fiber sensing technology

Stress in rock masses is an important parameter in the design and construction of underground engineering, such as the design and maintenance of mine roadways and the design of mining working faces. It is also a fundamental force causing the deformation and failure of geotechnical engineering excavation. At present, the abutment-pressure monitoring technology of the surrounding rocks of the coal mine roadway in China is not intelligent and systematic and lacks some high-precision sensing instruments and multi-functional monitoring systems. The mechanical model of the rocks surrounding the borehole was constructed by theoretical analysis of problems in the stress monitoring technology for underground rock masses in coal mines. Additionally, the interaction between the surrounding rocks and the borehole stress meter was analyzed. The borehole stress meters for tubular-structure fiber Bragg grating (TS-FBG) and cystic-structure fiber Bragg grating (CS-FBG) were designed by combining the sensing principle and sensing characteristics of fiber Bragg grating, and the performance of the two kinds of fiber Bragg grating borehole stress meters was compared by laboratory test. The track roadway of the 14,301 tested working faces in the Shaqu Coal Mine was taken as an example, and the stress of the rocks surrounding the 14,301-track roadway was monitored in real time by CS-FBG borehole stress meter during the mining of the working face. The following conclusions are drawn from the field application. The rig-site utilization results revealed obvious stress growth and stress peak zones in the mining-stress change curves of each measuring point on the two sides of the 14,301-track roadway in the process of mining the tested working face. Additionally, there were four stages: rapid rise, uniform growth, rapid rise to the peak, and rapid decline. Maximum stress monitored by the second station was 18.5 MPa, and the influence range of stress was over 140 m. Maximum stress monitored by the first measuring station was 19 MPa, the influence range of stress was about 80 m, and the peak stress position was about 20 m in front of the coal wall. Rig-site utilization proved the design of the CS-FBG borehole stress meter to be reasonable. Performance was stable and reliable, and the successful operation of field monitoring achieved the expected effect.

Optical Phase/Frequency Demodulation Using Polarization-Maintaining Fiber Bragg Gratings

Conventional techniques for demodulating phase/frequency-modulated (PM/FM) optical signals either require a sophisticated frequency-stable laser or employ a discriminator with poor characteristics. Here, we present a simple, compact, and robust technique featuring high linearity over a wide bandwidth and low background noise. Our technique exploits the reflection characteristics of fiber Bragg gratings written in polarization-maintaining fibers to create a frequency discriminator, which is able to convert PM/FM signals into intensity-modulated (IM) signals. A simple theoretical analysis is presented to highlight the advantages of the scheme. Experimentally, the transfer characteristics of the demodulator are characterized, yielding a linear FM-to-IM conversion slope of 1.238 mV/Hz in a 0.2-nm (∼25 GHz) bandwidth. Highly linear operation up to an FM-modulation index of 1.2 has been achieved. Background-free operation is shown by demonstrating negligible carrier leakage and a 10-dB IM rejection. Finally, high fidelity in demodulating arbitrary PM/FM optical signals is demonstrated with a correlation coefficient of 0.99 and a confidence of almost 100%. This simple yet efficient technique can potentially find applications in optical communications, microwave photonics and radar/lidar technologies.

Carcinogenic Chromium (VI) Sensing Using Transducing Characteristics of Fiber Bragg Grating and Physical Swelling of Hydrogel

Carcinogenic Chromium (VI) Sensing Using Transducing Characteristics of Fiber Bragg Grating and Physical Swelling of Hydrogel

Evaluation of the effectiveness of the effect of photosensitization on the spectral characteristics of the fiber Bragg grating

Currently, fiber Bragg gratings obtained on the basis of photoinduced optical fibers doped with a high concentration of germanium oxide are used as highly sensitive sensors. However, it is worth noting a significant drawback – the manufacturing technology of optical fibers doped with germanium is expensive. When recording Bragg gratings in a standard telecommunication fiber, where the molar concentration of germanium in the fiber core is from 3 % to 5 %, interference occurs due to very low and insufficient light sensitivity. Thus, an important role is played by solving the problem of low photosensitivity of standard telecommunication fibers for recording Bragg gratings. This paper presents the results of studies of the spectral characteristics of fiber Bragg gratings based on standard telecommunication fibers pre-saturated with hydrogen to increase photosensitivity. According to the results obtained, it was found that under the action of UV radiation in the presence of hydrogen, the photosensitivity of the fiber increases and the Bragg wavelength shift is associated with the saturation of the fiber with hydrogen, the effective modulation amplitude of the induced refractive index is equal to 1.2 with a refractive index of 1.438. This work proves that the VBR recorded in the S pre-saturated in hydrogen for 12 days is characterized by increased photosensitivity. The experimental results obtained make it possible to use a Bragg fiber array based on a standard telecommunications optical fiber saturated with hydrogen in the field of telecommunications, seismology, engineering geology as fiber-optic sensors of pressure, deformation, temperature, rotation and rotation, including in extreme environmental conditions

Properties of Fiber Bragg Grating in CYTOP Fiber Response to Temperature, Humidity, and Strain Using Factorial Design.

The characteristics of fiber Bragg grating (FBG) in cyclic transparent fluoropolymer (CYTOP) optical fiber have attracted more and more attention in recent years. However, different results of the FBG response to environmental parameters are reported. This work presents a three-variable two-level factorial experimental method to investigate the FBG response to temperature, humidity, and strain in CYTOP fiber. Two uniform FBGs are inscribed separately in CYTOP fiber with and without over-clad. With only eight measuring points, the interactions among three variable parameters are computed and the parameter sensitivities and cross-sensitivities are estimated. Similar temperature and strain sensitivities were found for both gratings, whereas significant cross-sensitivity between humidity and temperature was present only in FBG inscribed in CYTOP fiber with over-clad.

Pengaruh Sensitivitas Suhu Dengan Metode Couple-Mode Terhadap Fiber Bragg Grating Fiber Optik

The characteristics of Fiber Bragg Grating (FBG) related to change of reflection power and wavelength shift in the fiber optic due to changes in temperature. Furthermore, the refractive index alo affects the sensitivity of FBG. Using the Coupled-mode theory, the derivation of mathematical formula can be found to justify the effect of temperature in FBG. Also, the Coupled-mode theory is integrated numerically by the Transfer Matrix method to achieve the final equation of the effect of temperature in FBG. To obtain optimal results, several different parameter values are given to be analyzed. The results show that the temperatures are affecting the wavelength but have no effect on the peak of reflection power. In addition, by increasing the temperature and value of the refractive index will affect the enhancement of the sensitivity of FBG. These characteristics are a good opportunity to produce filters, sensors, or other applications by utilizing the characteristics of temperature in FBG.

Methods of hot wire creation for fiber-optical thermal anemometer

Subject of Research. The paper presents the study of various methods of optical radiation coupling from the fiber core into its cladding with the aim of creating a fiber-optic anemometer hot wire. The effectiveness of the described methods is evaluated by analyzing the obtained dependencies. Method. The structures of two optical fibers were studied, one of which was used to transmit an information signal, and the other — to create a hot wire. A Bragg grating was formed in the core of the first fiber, and a radiation coupling region was created in the second fiber. These fiber sections were aligned with each other and fixed by a tin-lead alloy. The temperature was measured by monitoring the spectral characteristics of fiber Bragg gratings inscribed by the phase mask method. The areas of radiation coupling were formed either by changing the fiber geometry using custom modes of the arc fusion splicer, or by creating a SMF-MMF-SMF transition. Main Results. Structures are developed which can be used as a hot wire of a fiber-optic anemometer sensitive element. The dependencies of the Bragg resonance wavelength shift on the pump laser power are obtained; the Bragg wavelength shift varies in the range from 0.15 nm to 3 nm as a result of a hot wire creation. The resulting curves are constructed after three experiments for each type of structure, taking into account the standard deviation. They make it possible to judge the effectiveness of various methods of radiation coupling. Comparative analysis of the studied methods is presented. Practical Relevance. The study describes the capabilities of fiber-optic anemometry when creating point and distributed sensors. The results of this work can be used in the areas where the creation of quasi-distributed and point diffusers is necessary, as well as partial or complete coupling of radiation from a fiber core.

Role of UV fluence on the thermal regeneration characteristics of fiber Bragg gratings: experiment and analysis

In this paper, the effect of UV exposure time on the thermal regeneration characteristics of fiber Bragg gratings (FBGs) inscribed using 255 nm laser radiation is presented for the first time. This effect is studied in terms of reflectivity, refractive index (RI) modulation and thermal stability of the gratings. Type-I FBGs of RI modulation varying from 2.03 × 10−4 to 3.38 × 10−4 were inscribed in hydrogenated SMF-28 fiber by controlling UV exposure fluence from 0.9 kJ cm−2 to 28.8 kJ cm−2. Thermally regenerated gratings were fabricated from type-I FBGs by applying a step-annealing schedule up to 900 °C. The reflectivity of the regenerated FBGs increases with UV fluence and after reaching a maximum value of 46.05%, it decreases. The different behavior of the thermal regeneration characteristics of FBGs is linked with the stress developed inside the fiber during the writing of FBGs and their relaxation during thermal annealing. The theoretical calculations using the defect center and densification model provided an indirect novel approach to estimate the contribution of stress relaxation in thermal regeneration. The work presented in this paper is significant for optimizing the thermal regeneration of FBGs with the final aim of developing a highly reflective regenerated grating for high temperature sensing applications.

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.

Analysis of mode characteristics of fiber Bragg gratings in large-mode-area double-clad fibers

Fiber Bragg gratings (FBGs) in large-mode-area double-clad fibers (LMA-DCFBGs) are the key components for high-power all-fiber lasers. Mode characteristics analysis of LMA-DCFBGs is of great significance for mode selection and performance optimization for high-power fiber lasers. In this paper, the spectral characteristics of LMA-DCFBGs were studied theoretically and experimentally, and confirmed that there is a power conversion between the LP01 mode and the LP11 mode in LMA-DCFBGs. Then, the growth curves of coupling coefficients of LMA-DCFBG with an increasing irradiation dose of ultraviolet (UV) light were measured. The results demonstrated that coupling efficiency between the LP01 mode and the LP11 mode is independent of the polarization state of UV lasers. In high-power fiber lasers, according to the spectral characteristics of LMA-DCFBGs, it can be considered that mode selection of fiber lasers could be realized by a pair of FBGs inscribed in fibers with different structural parameters, and that the appropriate wavelength matching condition could effectively avoid the laser power conversion from the LP01 mode to the LP11 mode, which could improve the beam quality of the output laser.

Investigation on sensing characteristics of fiber Bragg gratings based on soft glass fibers

Soft glass fibers can transmit the wavelengths longer than 2μm, which can realize the sensors in mid-infrared waveband. Compared to the FBG sensors based on silica fibers, FBG sensors based on soft glass fibers have the advantages of high sensitivity. For the first time, the sensing characteristics of FBGs based on different soft glass fibers are analyzed and compared. The sensing characteristics of temperature, strain and pressure of FBGs based on tellurite, chalcogenide and fluoride fibers are numerically simulated and compared. By analyzing and comparing a series of sensitivity curves of FBGs, we get some conclusions. For temperature sensing, the FBG based on the As2S3 fiber has the highest sensitivity coefficient of 175.7 pm/°C, while the FBG based on the silica fiber has the lowest sensitivity coefficient of 11.3 pm/°C. The Bragg wavelengths are red-shifted with the increase of temperature. For strain sensing, the FBG based on the β-ZnS (CVD) fiber has the highest strain sensitivity coefficient of 2.76 pm/με, while the FBG based on the silica fiber has the lowest strain sensitivity coefficient of 1.22 pm/με. The Bragg wavelengths are red-shifted with the increase of strain. For pressure sensing, the pressure sensitivity of the FBG based on the As2S3 fiber is the highest and the Bragg wavelength has is red-shifted; the pressure sensitivity of the FBG based on the silica fiber is the lowest and the Bragg wavelength is blue-shifted. These results will be significant for optical sensing and fiber lasers in mid-infrared waveband.

Study on dynamic response measurement of the submarine pipeline by full-term FBG sensors.

The field of structural health monitoring is concerned with accurately and reliably assessing the integrity of a given structure to reduce ownership costs, increase operational lifetime, and improve safety. In structural health monitoring systems, fiber Bragg grating (FBG) is a promising measurement technology for its superior ability of explosion proof, immunity to electromagnetic interference, and high accuracy. This paper is a study on the dynamic characteristics of fiber Bragg grating (FBG) sensors applied to a submarine pipeline, as well as an experimental investigation on a laboratory model of the pipeline. The dynamic response of a submarine pipeline under seismic excitation is a coupled vibration of liquid and solid interaction. FBG sensors and strain gauges are used to monitor the dynamic response of a submarine pipeline model under a variety of dynamic loading conditions and the maximum working frequency of an FBG strain sensor is calculated according to its dynamic strain responses. Based on the theoretical and experimental results, it can be concluded that FBG sensor is superior to strain gauge and satisfies the demand of dynamic strain measurement.

Study on the Transmission Spectrum of Fiber Bragg Grating as Temperature Sensor

The temperature sensing characteristic of Fiber Bragg Grating (FBG) has been studied. The temperature sensing equation of FBG is revised. The accurate analysis results are obtained. The center wavelength drifts of the tested FBG are displayed in the screen of Optical Spectrum Analyzer (OSA).The experimental results show that the center wavelength of FBG is thermally red-shift with the rise of the temperature and blue-shift with the decrease of the temperature. The results are agree with the revised temperature sensing equation. It is noticed that the transmission spectrum width (SPEC-WD) of FBG fluctuates with the change of temperature. Nevertheless, the trend of the fluctuation is demonstrably towards increase, which perhaps is some potential auxiliary sensing function in future.

Study on hydrofluoric acid-based clad etching and chemical sensing characteristics of fiber Bragg gratings of different reflectivity fabricated under different UV exposure times

An experimental study on hydrofluoric acid (HF)-based clad etching and chemical sensing characteristics of fiber Bragg gratings (FBG) of different reflectivity fabricated under different UV (255 nm) exposure times is presented. Two FBGs of reflectivity 11% and 93% were inscribed by phase mask–based exposition of the photosensitive fibers by a 5.5 kHz repetition rate of 255 nm UV pulses for 15 s and 10 min, respectively. These two FBGs, employed in an HF-based clad etching experiment, revealed a much higher etching rate of 2.03 μm/min for the grating of reflectivity 11% as compared to 1.69 μm/min for the grating of reflectivity 93%. The performance of these etched FBGs were also studied for refractive index sensing of the chemicals ethanol and ethylene glycol under different fiber etching times, hence of different residual cladding diameter. It was observed that the same refractive index sensitivity for both the chemicals could be achieved under smaller etching time, i.e., larger residual cladding diameter, for the FBG with lower reflectivity. This differentiating behavior of FBGs under etching and sensing may be linked to the different degree of densification in fused silica fiber cladding under different UV fluence exposures.

Shaping the spectral characteristics of fiber Bragg gratings written in optical fiber taper using phase mask method

Shaping the spectral characteristics of fiber Bragg gratings written in optical fiber taper using phase mask method

Optical System Monitoring Based on Reflection Spectrum of Fiber Bragg Grating

Problem statement: This study presents fiber fault monitoring approaches for Fiber-to-the Home (FTTH) with a Passive Optical Network (PON). Current fiber fault monitoring approaches are difficult to be implemented due to its complexity and high loss as the amount of branches increase. Approach: A fiber fault monitoring scheme is proposed whereas Fiber Bragg Grating (FBG) is placed on each branch of the Optical Network Unit (ONU). The advantages of the scheme are that it is simple, low cost and efficient in monitoring fiber fault in ONU. FTTH based network design is simulated using Optisystemtem 8.0 in order to investigate the feasibility of the proposed scheme. Results: The reflection spectrum of Fiber Bragg Gratings (FBGs) with different spectrum shape, frequencies and amplitude is used to differentiate each optical network. The simulation result shows that the unique characteristic of fiber Bragg grating is able to distinguish each optical network for a 20 km Passive Optical Network (PON) system. Conclusion: This study suggests the implementation of Fiber Bragg Grating that is placed in each network instead of using Optical Time Domain Reflectometer (OTDR) for fiber fault monitoring.

大模场双包层光纤光栅的光谱特性

大模场双包层光纤光栅的光谱特性

Experimental investigation of link between growth and decay of fiber Bragg gratings

We report here an experimental investigation for establishing and quantifying a link between the growth and decay characteristics of fiber Bragg gratings. One of the key aspects of our work is the determination of the defect energy distribution from the grating characteristics measured during their fabrication. We observe a strong correlation between the growth-based defect energy distribution and that obtained through accelerated aging experiments, paving the way for predicting the decay characteristics of fiber Bragg gratings from their growth data. Such a prediction is significant in simplifying the postfabrication steps required to enhance the thermal stability of fiber Bragg gratings.

Study on Strain Transfer Characteristics of Fiber Bragg Grating Sensors

In this article, strain transfer characteristics of fiber Bragg grating (FBG) sensors is analyzed with finite element method axial strain distribution of each layer described, and influencing factors of the strain transfer obtained, including bonded length of the sensor, thickness as well as Young’s modulus of the adhesive. The calculation results are verified by tensile tests of metal specimens. The results reveal that at suitable bonding conditions, the FBG sensors have good sensing characteristics. In addition, it is also easy for the chirping phenomenon to occur if the bonded length is not sufficient. The strain transfer efficiency can be improved and the chirping phenomenon reduced by either increasing the bonded length or decreasing the grating length or thickness of the adhesive, or choosing the proper adhesive.