Modified superstructure fiber Bragg grating for a filter application

Performance of a modified superstructure fiber Bragg grating is carried out by; simulation using a Matlab and then by optisystem7. Results for these two simulations are compared with an experimental investigation for three special FBGs in addition to a standard one. These four FBGs have one, two, three, and four regions. For each region, Bragg wavelength is increased around 6nm, with constant spacing between every two regions. Laser reflectance (R) and transmittance (T) spectra and their corresponding number of peaks and their bandwidths are observed and analyzed in a constant temperature and strain. Results for this investigation indicate enhancement for the modified FBG to be an effective filter that can be employed for communication as well as sense. Filtering the transmitted signals could be satisfied in a simple and more efficiency than the traditional device.

Effect of Peak Tracking Methods on FBG Calibration Derived by Factorial Design of Experiment

We present a calibration procedure for a humidity sensor made of a fiber Bragg grating covered by a polyimide layer. FBGs being intrinsically sensitive to temperature and strain, the calibration should tackle three variables, and, therefore, consists of a three-variable, two-level factorial design tailored to assess the three main sensitivities, as well as the five cross-sensitivities. FBG sensing information is encoded in the reflection spectrum from which the Bragg wavelength should be extracted. We tested six classical peak tracking methods on the results of the factorial design of the experiment applied to a homemade FBG humidity sensor. We used Python programming to compute, from the raw spectral data with six typical peak search algorithms, the temperature, strain and humidity sensitivities, as well as the cross-sensitivities, and showed that results are consistent for all algorithms, provided that the points selected to make the computation are correctly chosen. The best results for this particular sensor are obtained with a 3 dB threshold, whatever the peak search method used, and allow to compute the effective humidity sensitivity taking into account the combined effect of temperature and strain. The calibration procedure presented here is nevertheless generic and can thus be adapted to other sensors.

Design and Analysis of Fiber Bragg Grating Sensor to Monitor Strain and Temperature for Structural Health Monitoring

In this paper, we have proposed a bragg grating based sensor to monitor health of civil structures at distinct temperatures. We have considered increased number of gratings with suitable refractive index to enhance sensitivity of fiber bragg grating sensor. Analysis of Bragg wavelength with respect to load and temperature is successfully studied. The simulation results reveal that when independently strain (50 units per simulation) and temperature (25 ℃) are increased uniformly, a linear shift in Bragg wavelength 0.064 nm and 0.347 nm is observed, respectively. Similarly, when both strain and temperature are increased (ε = 50 & T= 25 ℃) concurrently, a directly proportional relation is found in bragg wavelength (0.403 nm). The results verify the enhanced performance of as-proposed sensor, employing it could be potentially used in civil, bio-medical and military domains.

Pressure Sensitivity Improvement of Fiber Bragg Grating Sensor Using Cytop Fiber

Recent demand for using FBG as a pressure sensor in a different industrial application makes several types of research to be conducted to enhance the pressure sensitivity. This paper demonstrates a combination method to enhance pressure sensitivity. Firstly, in this work FBG with polymer fiber named perfluorinated monomer (CYTOP) was used with specific parameters. Secondly, this FBG was covered by a patch of thin polymer material. However, the strain, temperature, and pressure sensitivity were recorded and compared with bare silica FBG. The temperature effect was reduced by using the cascade FBG technique. By applying force on the grating and changing of refractive index; the Bragg wavelength was shifting, making the CYTOP FBG responds more efficiently than silica FBG. This responsivity was leading to an improvement in pressure sensitivity. Experimental results illustrate that the enhanced CYTOP FBG based pressure sensor achieves pressure sensitivity up to 93.5 pm/KPs with a resolution of 0.005 KPa, which was 1500 times higher than bare FBG. The advanced CYTOP FBG based pressure sensor can be functionalized in a technical application for instance, structural health monitoring, pressure of oil wells application, explosion wave, and prevention of erosion.

Simultaneous Measurement of Temperature and Strain Based on Peak Power Changes and Wavelength Shift Using Only One Uniform Fiber Bragg Grating

Many efforts have been devoted to simultaneous measurements of strain and temperature by FBG sensors and several improving techniques have been resulted and implemented on the measurement. Most of them are based on two or more FBGs configurations or a single non-uniform FBG implementation. We propose simultaneous measurement of temperature and strain based on peak power changes and Bragg wavelength shifts using only one uniform fiber Bragg grating (FBG). We placed a ramp with the angle of θ, similar to a tilted cantilever beam, on an assumptive structure and stuck a uniform FBG on it. When a uniform strain applied to a structure, the cantilever beam converts it to a non-uniform strain distribution along with itself and consequently the uniform FBG. By creating this non-uniform strain distribution, the peak power of the reflection spectrum of the FBG will be sensitive to strain changes. In addition, the Bragg wavelength shift will be sensitive to both temperature and strain parameters. According to our simulation, temperature sensitivity of 14.15 pm/℃ is obtained for FBG sensor without any changes in the peak power. The strain sensitivity of 0.7837 pm/µε, and a nonlinear sensitivity according to a quadratic function for peak power variation are also observed.

Fiber Bragg Grating Wavelength Drift in Long-Term High Temperature Annealing

High-temperature-resistant fiber Bragg gratings (FBGs) are the main competitors to thermocouples as sensors in applications for high temperature environments defined as being in the 600–1200 °C temperature range. Due to their small size, capacity to be multiplexed into high density distributed sensor arrays and survivability in extreme ambient temperatures, they could provide the essential sensing support that is needed in high temperature processes. While capable of providing reliable sensing information in the short term, their long-term functionality is affected by the drift of the characteristic Bragg wavelength or resonance that is used to derive the temperature. A number of physical processes have been proposed as the cause of the high temperature wavelength drift but there is yet no credible description of this process. In this paper we review the literature related to the long-term wavelength drift of FBGs at high temperature and provide our recent results of more than 4000 h of high temperature testing in the 900–1000 °C range. We identify the major components of the high temperature wavelength drift and we propose mechanisms that could be causing them.

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.

Design Reliable Bus Structure Distributed Fiber Bragg Grating Sensor Network Using Gated Recurrent Unit Network

The focus of this paper was designing and demonstrating bus structure FBG sensor networks using intensity wavelength division multiplexing (IWDM) techniques and a gated recurrent unit (GRU) algorithm to increase the capability of multiplexing and the ability to detect Bragg wavelengths with greater accuracy. Several Fiber Bragg grating (FBG) sensors are coupled with power ratios of 90:10 and 80:10, respectively in the suggested experimental setup. We used the latest IWDM multiplexing technique for the proposed scheme, as the IWDM system increases the number of sensors and allows us to alleviate the limited operational region drawback of conventional wavelength division multiplexing (WDM). However, IWDM has a crosstalk problem that causes high-sensor signal measurement errors. Thus, we proposed the GRU model to overcome this crosstalk or overlapping problem by converting the spectral detection problem into a regression problem and considered the sequence of spectral features as input. By feeding this sequential spectrum dataset into the GRU model, we trained the GRU system until we achieved optimal efficiency. Consequently, the well-trained GRU model quickly and accurately identifies the Bragg wavelength of each FBG from the overlapping spectra. The Bragg wavelength detection performance of our proposed GRU model is tested or validated using different numbers of FBG sensors, such as 3-FBG, 5-FBG, 7-FBG, and 10-FBG, separately. As a result, the experiment result proves that the well-trained GRU model accurately identifies each FBG Bragg wavelength, and even the number of FBG sensors increase, as well as the spectra of FBGs, which are partially or fully overlapped. Therefore, to boost the detection efficiency, reliability, and to increase the multiplexing capabilities of FBG sensor networks, the proposed sensor system is better than the other previously proposed methods.

Design of a Sensor System Using Fiber Bragg Grating for Liquid Level and Liquid Density Measurement

In this work, a simple but versatile sensing system for very accurate sensing of liquid level and liquid density is presented. The sensor works based on basic strain sensitivity of Fiber Bragg Grating (FBG) and principle of liquid obeying Archimedes’ law of buoyancy. In this system, a cylindrical shaped mass suspended from a Fiber Bragg Grating and partially immersed in the liquid to be sensed. If the liquid level in the container or liquid density varies, that change the up thrust on the suspended mass and load on the Fiber will be changed accordingly. The change in the load on Fiber changes strain on the FBG and the reflected Bragg wavelength also changes. The proposed device with proper calibration should be able to carry out real time and nonstop liquid level and liquid density measurements. A mathematical analysis of the system considering liquid properties and geometrical structure of the suspended mass is presented here. Sensitivity of the system for liquid level monitoring is also reported. Achieved results shows the path for the utilization of the proposed sensor system for precise liquid density measurement and liquid level sensing in very large storage tanks used for commercial/residential applications.