Bragg Grating Research Articles

Customized femtosecond laser-inscribed superstructure fiber Bragg grating: A novel approach to decoupling temperature and strain.

This paper introduces a novel technique to simultaneously measure temperature and strain using a single 5 mm femtosecond laser-inscribed superstructure fiber Bragg grating (SFBG). This SFBG enables improved spectral capabilities, resulting in side-resonances within the optical spectrum. The characteristics of the device depend on three key factors: the length of the SFBG, the inscribed FBG’s periodic perturbations, and the length of the uninscribed sections that compose the entire structure. Initially, mathematical expressions were derived to calculate the separation between the central peak and a resonance on each side, which plays a crucial role in determining the sensor’s response. Then, a series of complete simulations using OptiGrating software, and a theoretical analysis were performed to comprehend the functioning of this superstructure. Subsequently, the fabrication process employed a femtosecond laser following a point-by-point inscription. Finally obtaining a comprehensive study on the principle, design, simulation, and implementation of the proposed SFBG. The sensitivities of the central Bragg wavelength and the distance between central peak and first-order resonance when applying temperature and strain were calibrated. The results yielded sensitivities for the central Bragg peak of 10.58 pm/°C and 1.1598 pm/µɛ, while the peak-to-resonance distance had sensitivities of 0.3495 pm/°C and 0.03052 pm/µɛ. The different response of both magnitudes makes it possible to distinguish the contributions of strain and temperature within short distances, having the possibility to improve measurements in sensing applications. This study finally provides a critical insight into the design process, as it aligns with the theoretical expectations.

Optical fiber fronthaul segment in open radio access 5G networks: enhanced performance utilizing AFBG

In open Radio access network (oRAN) 5G networks, a fronthaul segment between virtual Distribution unit (vDU) edge cloud and other external Remote radio units (RRUs) sites is very important to transmit high data rate to achieve 5G requirements. Performance parameters such as Quality factor (Q-factor) and Bit error rate (BER) of an optical fiber fronthaul segment are the main important parameters to enhance latency and bit rate. An Apodized fiber bragg grating (AFBG) is utilized with different apodization profiles to optimize linewidth of an optical signal leading to enhance performance. The designed AFBG is used with a data rate of 25 Gb/s optical Ethernet module at the vDU edge cloud to optimize the linewidth of the optical signal between the vDU and the RRU in the fronthaul optical fiber segment. The AFBG is investigated at different connections pre, post, and symmetrical connections, where different apodization functions are used in the AFBG design. It is found that the best results for the maximum Q-factor and minimum BER are 9.2 and 2.72e− 21, respectively, obtained from uniform function in the symmetrical connection. Finally, the proposed model linewidth is 0.408 nm, which is better than 1.56 nm that is evaluated by related work.

An FBG-based optical pressure sensor for the measurement of radial artery pulse pressure.

One of the diagnostic tool for clinical evaluation and disease diagnosis is a pulse waveform analysis. High fidelity radial artery pulse waveforms have been investigated in clinical research to compute central aortic pressure, which has been demonstrated to be predictive of cardiovascular diseases. The radial artery must be inspected from several angles in order to obtain the best pulse waveform for estimate and diagnosis. In this study, we present the design and experimental testing of an optical sensor based on Fiber Bragg Gratings (FBG). A 3D printed device along with the FBG is used to measure the radial artery pulses. The proposed sensor is used for the purpose of quantifying the radial artery pulse waveform across major pulse position point. The suggested optical sensing system can measure the pulse signal with good accuracy. The main characteristic parameters of the pulse can then be retrieved from the processed signal for their use in clinical applications. By conducting experiments under the direction of medical experts, the pulse signals are measured. In order to experimentally validate the sensor, we used it to detect the pulse waveforms at Guan position of the wrist's radial artery in accordance with the diagnostic standards. The findings show that combining optical technologies for physiological monitoring and radial artery pulse waveform monitoring using FBG in clinical applications are highly feasible.

Temperature field reconstruction based on femtosecond laser prepared of multiwavelength fibre bragg grating array

Temperature field measurements are of great significance in industrial production, scientific research, and other fields. Contact temperature measurements usually achieve high spatial resolution by increasing the layout density of the sensors. However, in practical applications, achieving high-density sensor placement is often difficult. Therefore, when the number of sensors is limited, it is necessary to perform function fitting or interpolation of the temperature of the sampling points to reconstruct the temperature field distribution. This study proposed a temperature field reconstruction method based on femtosecond laser prepared multiwavelength fibre Bragg grating (FBG) array. A multiwavelength FBG array was prepared using the femtosecond laser phase mask method combined with stress stretching, and applied for measuring the temperature field distribution in a tubular high-temperature furnace. Cubic spline interpolation and backpropagation (BP) neural networks were used to construct two-dimensional temperature field models for the temperature field distribution data measured by the FBGs, and the prediction accuracies of the two models were compared. The test results show that the root mean square error of the temperature field distribution constructed using the BP neural network is 0.7333 °C, which is approximately 23.18% of the predicted results of the cubic spline interpolation model, indicating that it is a high-precision temperature field reconstruction method.

Performance Analysis of Gaussian Apodized Fiber Bragg Grating (GA-FBG) Dispersion Compensator for a Long Haul Optical Fiber Link

This examination gives a complete analysis of the GA-FBG, a generally involved grating for dispersion compensation across a 150 kilometer optical link, from each point. The essential objective of this study is to distinguish how long the GA-FBG can work as an independent dissemination reimbursement gadget and how well it acts in various compensation settings. In this review, the GA-FBG is utilized as an option in contrast to the exorbitant Dispersion-Reimbursing Fiber inside the association to give a more safe optical link. The investigation delves into three specific compensation methods and studies the GA-FBG grating boundaries in light of the relative abundance of real imperatives associated with a Fiber Bragg Grating (FBG) in the design phase. Using a Piece Blunder Rate analyzer to examine the streamlined links' exhibition highlights allows us to evaluate their productivity. Results show that the GA-FBG exhibits a common dispersion compensation adequacy when the link's channel boundaries are tuned. Using gearbox over distances easily exceeding 500 km, the balanced compensation strategy delivers a remarkable Q-factor respect. Utilizing OptiSystem programming, we validate the proposed system's functional viability. The results of our study indicate that the GA-FBG is capable of efficiently counteracting dispersion, leading to an optical link that is both more economical and effective, with significant potential for extended transmission ranges.

Improved optical contrast of plasmonic phase change memory using a Fabry-Perot cavity

As a promising technology to realize multilevel, non-volatile data storage and information processing, optical phase change technologies have attracted extensive attention in recent years. However, existing phase-change photonic devices face significant challenges such as limited switching contrast and high switching energy. This study introduces an innovative approach to tackle these issues by leveraging Fabry-Perot (F-P) cavity resonance and plasmon resonance techniques to enhance the modulation effect of phase change materials (PCMs) on the light. To the best of our knowledge, a novel device structure is proposed, featuring an elliptic nano-antenna placed on an F-P cavity waveguide composed of symmetric Bragg grating. This design exploits the enhanced electric field to achieve low power consumption and high contrast. The device enables crucial functions, including read, write, and erase operations, under all light conditions. Through the synergistic utilization of plasma and F-P cavity effects, an ultra-high switching contrast of around 70.6% is achieved. By varying the pulse power or duration, the proportion between the crystalline and amorphous states of the PCMs is altered, consequently modifying its refractive index. With its wide range of applications in optical storage and computing, the device holds significant potential for advancing these fields.

First-order Type A waveguides Bragg gratings with under-diffraction-limited periodicities and sub-millimeter length for NIR applications

First-order Type A waveguides Bragg gratings with under-diffraction-limited periodicities and sub-millimeter length for NIR applications

Spectral power stabilization against temperature variations in multimode fiber Bragg gratings

Fiber Bragg gratings (FBGs) have been extensively used for single-point and multi-point measurements, mostly inscribed in single-mode fibers. However, it is feasible to inscribe FBGs in multimode fibers, which resist bending and can perform discriminative sensing of multiple physical parameters. When using a simple experimental setup to measure the temperature dependence of the dip in the transmission spectrum, significant fluctuations in its spectral power can be observed. Therefore, this study shows that the temperature-dependent spectral power fluctuations in multimode FBGs can be mitigated using a reflectometric configuration with suppressed modal interference, leading to higher-reliability temperature sensing.

Temperature and strain gradient monitoring of the buoyancy material curing reaction with a submillimeter spatial resolution fs-FBG array

Millimeter-scale temperature and strain gradient measurements are crucial for understanding the mechanical properties of buoyancy materials. In this paper, we successfully fabricated ultrashort and high-density fiber Bragg grating (FBG) array based on femtosecond laser point-by-point writing technology. By optimizing the energy and number of femtosecond laser pulse, and introducing secondary tilt apodization technology, submillimeter-spatial-resolution FBG arrays were prepared. To the best of our knowledge, this is the first application of femtosecond FBG array for high spatial resolution temperature and strain gradient in situ monitoring of buoyancy materials. FBGs exhibit excellent anti-chirp performance and achieve submillimeter spatial resolution curing monitoring under temperature and strain monitoring gradients of 2.6 °C/mm and 231 με/mm, respectively.

On-line cure monitoring of phenol formaldehyde resin using embedded fiber Bragg grating sensor

On-line cure monitoring techniques have shown advantages for identifying the stages of curing and can lead to smart curing process of resin system and its composites. In this study, an on-line measuring technique with fiber Bragg grating (FBG) sensors was used to gain clear understanding of the curing stages of phenolic resin, as well as to determine its chemical shrinkage level. The FBG sensors were embedded in phenolic resin and worked under temperature raising and isothermal conditions. Through the interface between FBG sensor and resin, curing shrinkage strain was transferred to the grating, changing the central wavelength of FBG and producing strain. The feasibility of FBG sensors for monitoring chemical shrinkage during curing was verified by employing epoxy and benzoxazine resins that exhibits low chemical shrinkage. For cure monitoring of phenolic resin, the results show that the strain signal can be corresponded to various responses, such as solvent volatilization, hydroxylation and dehydration condensation reactions during temperature raising curing process. Through these strain characteristics, the curing state of phenolic resin can be obtained, which degree of cure ranges from 0.05 to 0.9. In isothermal curing process of phenolic resin, an exponential correlation between chemical shrinkage induced compressive strain and degree of cure of resin was identified, indicating that the real-time compressive strain is proportional to the degree of cure of phenolic resin. By evaluating real-time curing shrinkage levels, the estimation of curing degree of phenolic resin can be achieved utilizing exponential correlation of curing degree and curing shrinkage level.

Recent advances in optical fiber grating sensors for detection of organic substances

The continuous development of society has led to the flourishing of environmental chemistry and biomedical fields, as well as to the research and development of novel functional materials and sensors. Some novel materials have excellent optical and biological/chemical properties and can be coupled with the optical fiber grating. The coupling between the materials and optical fiber grating can improve the performance due to the advanced materials can amplify the changing signals generated during the reaction with analytes of organic compounds. Despite the great achievements in the development of bio- and chemical-optical fiber grating sensors, there is no publicly available systematic review of the recent advances in the use of materials combined with optical fiber grating in organic substances sensing available in the literature since January 2016.Thus, we summarized the sensing principles of the bio- and chemical-optical fiber grating with and without surface plasmon resonance. We discussed the performance parameters such as sensitivity, selectivity, detection range, and low limit of detection for detection of organic substances including organic pollutants, life organics (glucose, hemoglobin, cancer markers, antibody-antigen, biotin and streptavidin, DNA, enzymes), microorganisms, and other organic substances. We analyzed the advantages and limitations of optical fiber grating sensors and presented challenges in their practical applications and future research directions.

Design of vibration sensors based on fibre Bragg grating type composites for earthquake detection and early warning application

Composite materials can be rapidly moulded using additive manufacturing processes due to their excellent mechanical and physical properties. Combining fibre Bragg gratings with composites results in high-performance fibre grating vibration sensors that address the limitations of electrical sensors and traditional materials. This study focused on developing a fibre optic acceleration sensor that utilizes a parabolic column made of silica gel. The sensor underwent fabrication, packaging, and calibration using a dedicated test system. Parametric calibrations and vibration detection tests were conducted to evaluate the performance of the system. The experimental results indicate that the sensor exhibits an intrinsic frequency of 70 Hz, a flat response range of 5 to 40 Hz, a linearity coefficient greater than 0.99, effective control of transverse interference, and exceptional low-frequency response, which improves the detection of vibration signals. Therefore, the sensor’s low intrinsic frequency and exceptional low-frequency response make it well-suited for detecting vibrations at low to medium frequencies.

Rotation angle sensor based on magnetostrictive materials and fiber Bragg gratings

We present a sensor concept for measuring rotation angle based on magnetostrictive materials and fiber Bragg grating strain sensors. The fiber optic strain sensors are used to measure strain in developed in the magnetostrictive rods due to the rotating permanent magnets. The measured strain is related to the angle of rotation. Numerical modeling was performed to investigate the response of magnetostrictive rods due to different angular orientation of magnets. A prototype based on a pendulum was designed to measure the angle with respect to the direction of gravity. Experimental evaluation of its performance revealed a large amount of hysteresis present in the strain data. Finally, we provide some suggestions for further improvement of the design to improve performance and reduce the amount of hysteresis.

Soil water potential measurement using fiber-optic sensing technique

Accurate measurement of soil water potential or suction is crucial for hydrology and geotechnical engineering. Inspired by recent advances in fiber-optic sensing techniques, we develop an innovative geophysical method for measuring the soil suction by using fiber Bragg grating (FBG), named FBG-suction method. In this study, working principles and theoretical background associated with the FBG-suction method are discussed. For verification purposes, a series of laboratory-scale tests including calibration, suction measurement, and evaporation monitoring are performed on two clayey soils of low to high plasticity under different degrees of saturation. The calibration and measurement results demonstrate the efficacy and accuracy of the developed method for measuring a wide range of soil suction. The curves of soil saturation with suction obtained by WP4C and FBG-suction method are comparable and reflect the difference in the water retention capacity of the tested soils. Additionally, the evaporation monitoring results show that the FBG-suction method can measure the low suction during the drying process and accurately obtain the high suction above the measuring range of the PST-55 psychrometer. The findings affirm the scientific viability of the fiber-optic sensing technique for acquiring the spatial distribution of water potential or suction in unsaturated soils and provide a novel perspective for future investigations into the spatiotemporal evolution characteristics of in-situ unsaturated soil under climate change. As interdisciplinary collaborations continue to advance, it becomes increasingly apparent that methods based on fiber-optic sensing have the potential to revolutionize traditional approaches to characterizing dynamic subsurface processes.

Design of Multistage Fiber Bragg Grating (FBG) with Variable Filter Parameters

Design of Multistage Fiber Bragg Grating (FBG) with Variable Filter Parameters

A Fiber-Only Optical Vibration Sensor Using Off-Centered Fiber Bragg Gratings

A Fiber-Only Optical Vibration Sensor Using Off-Centered Fiber Bragg Gratings

A new gas detection technique through cross-correlation with a complex aperiodic FBG

Optical cross-correlation is a technique that can achieve both high specificity and high sensitivity when deployed as the basis for a sensing technology. Offering significant gains in cost, size and complexity, it can also deliver significantly higher signal-to-noise ratios than traditional approaches such as absorption methodologies. In this paper, we present an optical cross-correlation technology constructed around a bespoke customised Fiber Bragg Grating (FBG). Exploiting the remarkable flexibility in design enabled by multiple aperiodic Bragg gratings, optical filters are devised that exactly mimic the absorption features of a target gas species (for this paper, acetylene C2H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$C_2H_2$$\\end{document}) over some waveband of interest. This grating forms the heart of the sensor architecture described here that employs modulated optical cross-correlation for gas detection. An experimental demonstration of this approach is presented, and shown to be capable of differentiating between different concentrations of the C2H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$C_2H_2$$\\end{document} target gas. Furthermore these measurements are shown to be robust against interloper species, with minimal impact on the detection signal-to-noise arising from the introduction of contaminant gases. This represents is a significant step toward the use of customised FBGs as low-cost, compact, and highly customisable photonic devices for deployment in gas detection.

Sensitivity-enhanced two-dimensional bending sensor based on single-mode fiber measurement

A sensitivity-enhanced two-dimensional bending sensor using four-core fiber (FCF) transition to realized single-channel demodulation of seven-core fiber Bragg grating (FBG) is proposed. A section of FCF was added between the single-mode fiber (SMF) and the seven-core fiber (SCF), and the thermal diffusion technology (TDT) was used so that the signal of the SMF could be transmitted to the three side cores of the SCF through the FCF. Then, a 45° reflective circular cone (45° RCC) is fabricated at the end of the SCF, enabling the coupling of the symmetrical side core signals of the SCF. By inscribing the FBGs with different reflection wavelengths on the side cores of the SCF, the signals of each side core can be distinguished during single-channel demodulation. Monitoring the reflection wavelength shifts of the FBGs on the SCF can realize two-dimensional bending measurements. Furthermore, through the differential operation of the symmetrical side cores, the bending sensitivity can be enhanced while eliminating temperature crosstalk. The proposed sensor with high integration, high sensitivity, and reduced crosstalk, is expected to be applied in the field of structural inspection or interventional medical treatment.

Strain and Temperature Sensing Based on Different Temperature Coefficients fs-FBG Arrays for Intelligent Buoyancy Materials.

The temperature and strain fields monitoring during the preparation process of buoyancy materials, as well as the health status after molding, are important for mastering the mechanical properties of buoyancy materials and ensuring the safety of operators and equipment. This paper proposes a short and high-density femtosecond fiber Bragg grating (fs-FBG) array based on different temperature coefficients fibers. By optimizing the parameters of femtosecond laser point-by-point writing technology, high-performance fs-FBG arrays with millimeter level gating length and millimeter level spatial resolution were prepared on two types of fibers. These were successfully embedded in buoyancy materials to achieve in-situ online monitoring of the curing process and after molding. The experimental results show that the fs-FBG array sensor has good anti-chirp performance and achieves online monitoring of millimeter-level spatial resolution. Intelligent buoyancy materials can provide real-time feedback on the health status of equipment in harsh underwater environments. The system can achieve temperature monitoring with an accuracy of 0.56 °C and deformation monitoring with sub-millimeter accuracy; the error is in the order of micrometers, which is of great significance in the field of deep-sea exploration.

A Novel Inserting Pilot Radio over Fiber System without the Bit Walk-Off Effect for the Generation and Distribution of Frequency 16-Tupling Millimeter Waves by Mach–Zehnder Modulators

A novel inserting pilot scheme to generate and distribute a frequency 16-tupling millimeter wave (MMW) radio over fiber (ROF) system without the bit walk-off effect via Mach–Zehnder modulators (MZMs) is proposed. The operation principle is analyzed and the feasibility of our proposed scheme is verified by simulation test. The main part of our scheme is a ±8th-order sidebands generator (SG), which is constructed by four MZMs connected in parallel. In the back-to-back (BTB) transmission case, by properly adjusting the voltage and initial phase of the radio frequency (RF) drive signals of the MZMs, ±8th-order sidebands are generated by the SG. In the data transmission case, the data signal is first split into two beams, one of which modulates the RF drive signal with an electrical phase modulator (PM) while the other is amplified by an electrical gainer (EG), and then the two beams are combined into one and used as the composite RF drive signal of the MZMs. By adjusting the modulation index of the PM and the gain of the EG, the data signal can only be modulated to the +8th-order sideband of the output of the SG. The optical carrier from the continuous wave (CW) laser is split into two paths: one is sent into the SG, and the other is used as a pilot signal. The output signal of SG is combined with the pilot signal and is transmitted to the base station (BS) via optical fiber. At the BS, the pilot signal is filtered out by a fiber Bragg grating (FBG) and used as the carrier for the uplink for carrier reuse. After filtering out the pilot, the signal from the FBG, which is composed of ±8th-order sidebands, is injected into a photodetector, and a frequency 16-tupling MMW with downlink data is generated. The key parameters’ influence on the bit error rate (BER) and Q factor in the system is also analyzed. Our scheme can not only effectively overcome the bit walk-off effect caused by optical fiber chromatic dispersion and greatly increase the fiber transmission distance but can also effectively improve the performance and the tunability of system. Therefore, it has important application prospects in ROF systems.