Bragg Grating Research Articles

Thulium doped all-fiber laser based on a double-cladding Bragg grating via femtosecond laser plane-by-plane writing technology

The fiber Bragg grating (FBG) is fabricated by the femtosecond laser writing technique with a plane-by-plane (Pl-by-Pl) method in the double-cladding fiber (DCF). The refractive index modified (RIM) region formed by this method is 12 μm × 8 μm in size. Due to the Pl-by-Pl method, high-order Bragg resonances with reflectance greater than 99% can be achieved. The fabricated high-quality FBG features a narrow full width at 3 dB bandwidth of approximately 0.45 nm, a high reflectivity above 99%, and almost no side-mode peaks. To investigate the application of fabricated FBGs, we have built a thulium-doped all-fiber oscillator with purely forward-pumped structures. A thulium-doped fiber laser (TDFL) at a central wavelength of 1953.79 nm was constructed by using the prepared fiber grating. The signal-to-noise ratio (SNR) is above 56 dB. When the pump power is 19 W, the total output power of the continuous wave is 4 W, and the output efficiency is 25.6%. In addition, the numerical calculation has been carried out to further optimize the output power. This work provides a possible approach for designing and implementing a continuous Tm-doped fiber laser with enhanced output efficiency.

Electron Radiation Impact on Long Period Gratings in Different Optical Fibers

Electron Radiation Impact on Long Period Gratings in Different Optical Fibers

Fiber Bragg Grating Strain Sensor With Extended Measurement Range via Strain Relief Ring

Fiber Bragg Grating Strain Sensor With Extended Measurement Range via Strain Relief Ring

A Highly Sensitive Strain Sensor Based on Hook-Shaped Core Long-Period Fiber Grating

A Highly Sensitive Strain Sensor Based on Hook-Shaped Core Long-Period Fiber Grating

Tunable all-fiber all-normal-dispersion mode-locked laser of cylindrical vector beams covering the range of 69 nm

We propose and demonstrate an ultra-wide tunable mode-locked all-fiber laser based on nonlinear amplifying loop mirror (NALM) with the output of cylindrical vector beams (CVBs). The tuning range covers from 1029 nm to 1098 nm through the intracavity nonlinear polarization evolution (NPE) filter effect. The switchable CVBs between radially and azimuthally polarized beams with mode purity above 90% are generated by incorporating a broadband few-mode long-period fiber grating (LPFG). It is the first time to realize mode-locked CVBs near 1100 nm and the widest spectral tuning range in all-fiber laser is achieved to our knowledge. The pulsed CVBs at 1098 nm have 3 dB bandwidth of 0.31 nm with a pulse duration of 358ps.The narrow-bandwidth pulse of less than 1 nm is obtained among the whole tuning process which is of high flexibility and high tuning precision by introducing what we believe to be novel tuning mechanisms of NPE into the NALM cavity. The wide-range tunable CVBs all-fiber mode-locked laser has potential applications in high-capacity optical communication, laser imaging, and fiber optic sensing fields.

High-sensitivity optical fiber seawater temperature and pressure sensor with a low-error demodulation method

Using a single optical microfiber (OM) sensor for multi-parameter sensing can lead to significant demodulation error due to ill-conditioned matrices and nonlinear response characteristics. To address these issues, this paper proposes a novel specially packaged optical microfiber coupler combined with a silver mirror (OMCM). OMCM is combined with a mechanically enhanced sensitivity fiber Bragg grating (FBG) to form a temperature-pressure sensor. The temperature sensitivity exceeds -1.7 nm/°C while the pressure sensitivity reaches 53.435 nm/MPa, with a depth resolution of 0.935 cm. According to the characteristics of the sensor spectrum, this paper proposes a new demodulation method, which combines machine learning methods with a traditional wavelength-tracking method to achieve low demodulation error. For temperature and pressure, the mean absolute percentage errors are 0.04% and 1.31%, respectively. This feature facilitates the detection of minute changes in shallow marine environments, lacustrine systems, and other aquatic habitats, thus making it highly suitable for applications such as underwater aquaculture and marine monitoring.

Realization and simulation of silicon-on-sapphire mid-infrared one-dimensional photonic crystal cavities

The mid-infrared (MIR) waveband is significant for chemical and biological sensing since it covers several atmospheric windows and molecular fingerprint regions. On-chip photonic integrated one-dimensional (1D) microcavities have great potential for high-performance mid-IR sensing because of their high sensitivity and compact structure. However, high-performance 1D microcavities based on the promising silicon-on-sapphire (SoS) MIR platform have not yet been designed or realized. Based on the photonic band structure induced by 1D photonic crystals (PhC), a high-performance Bragg reflector, an inward apodized Bragg grating, and a free spectral range (FSR)-free PhC microcavity integrated system operating in the MIR waveband were developed on the SoS platform. By carefully designing the period and penetration depth of the corrugation in the Bragg reflector, a stopband of 45 nm and an extinction ratio of −12 dB were achieved. The inward apodized Bragg grating was optimized by adjusting the apodization depth and the number of periods, resulting in a quality factor of 1043 at a wavelength of 3088.4 nm. Furthermore, introducing a Fabry–Pérot (F-P) cavity between two Bragg reflectors (with side-coupled light) and precisely tuning the stopband of the Bragg reflector and the FSR of the F-P cavity enabled the realization of an FSR-free PhC microcavity. This microcavity exhibited a single deep resonance dip with subnanometer bandwidth across a record-wide operational waveband from 3025 to 3200 nm, achieving a quality factor of approximately 5090. The MIR 1D PhC microcavities on the SoS platform hold great promise for high-performance gas detection and molecular sensing in future applications.

Radiation-Induced Wavelength Shifts in Fiber Bragg Gratings Exposed to Gamma Rays and Neutrons in a Nuclear Reactor

Radiation-Induced Wavelength Shifts in Fiber Bragg Gratings Exposed to Gamma Rays and Neutrons in a Nuclear Reactor

Anchor test and long-term monitoring of grouted anchors instrumented with Fiber Bragg Grating sensing technology

Geotechnical monitoring of anchors provides fundamental data for analysis and evaluation to ensure safe environment. The use of optic fiber sensing technology, especially Fiber Bragg Gratings, brings many advantages of optic fiber sensors, such as high measurement accuracy, real-time continualmonitoring of deformation, on-line access to data and resistance against electromagnetic interferences. This article deals with anchor tests instrumented with FBG deformation gauges of the root and the tendon of the pre-stressed strand anchor in a test field in the Central Bohemian Region. First, the anchor with three optic cables with FBG sensors for measurement of axial deformation was subjected to six loading stages of the anchor test. Most of the sensors measured values of axial deformation less than 200 με and the root mobilisation was observed. Then, the measurement continued by 26-day long-term monitoring and a trend of a small increase of deformations occurred.

A Skin-Attachable Flexible System Based on Fiber Bragg Gratings With Multisite Sensing Capacities for Mother and Fetus Health Monitoring

A Skin-Attachable Flexible System Based on Fiber Bragg Gratings With Multisite Sensing Capacities for Mother and Fetus Health Monitoring

Settlement Monitoring of Ultra-Long GIS in Substations Based on Weak Fiber Bragg Grating Array

Settlement Monitoring of Ultra-Long GIS in Substations Based on Weak Fiber Bragg Grating Array

Fast and High-Precision Shape Sensing Based on Dual-Comb Fiber Bragg Grating Array Demodulation

Fast and High-Precision Shape Sensing Based on Dual-Comb Fiber Bragg Grating Array Demodulation

Research of fiber Bragg gratings inscription by the method of translation of a laser beam relative to a phase mask

Research of fiber Bragg gratings inscription by the method of translation of a laser beam relative to a phase mask

Brillouin-Random Laser and Fiber Bragg Gratings for All-Fiber High-Resolution Sensing

Brillouin-Random Laser and Fiber Bragg Gratings for All-Fiber High-Resolution Sensing

Design Optimization of a Sensitivity-Enhanced Tilt Sensor Based on Femtosecond Fiber Bragg Grating

Design Optimization of a Sensitivity-Enhanced Tilt Sensor Based on Femtosecond Fiber Bragg Grating

Pd/WO3 Co-Deposited Tilted Fiber Bragg Grating for Fast Hydrogen Sensing

Pd/WO₃ Co-Deposited Tilted Fiber Bragg Grating for Fast Hydrogen Sensing

Long period fiber gratings in anti-resonant hollow core fiber

Abstract Long period gratings, based on anti-resonant hollow core fibers (AR-HCFs), are fabricated using a high-frequency CO2 laser pulse by carving periodic grooves. This device exhibits both axial strain and bending sensing characteristics. Benefiting from the low thermal sensitivity and radiation resistance characteristic of AR-HCFs, this grating can be utilized in extreme environments, particularly in the high-radiation environment, such as nuclear power plants and space shuttles. Additionally, due to the characteristics of AR-HCFs, including low latency, low dispersion, low nonlinearity, and high damage threshold, this device also serves for long-distance fiber communication and high-power laser pulse shaping.

Material selection for efficient strain transfer in pavement monitoring using FBG sensors

ABSTRACT Fibre Bragg Grating (FBG) sensors are increasingly used to monitor road pavement infrastructures due to their sensitivity and resilience. However, challenges such as mechanical vulnerability and effective strain and stress transfer remain critical. This study addresses these challenges by evaluating the effectiveness of four distinct filling materials (bitumen mastic, polymeric resin, polymeric sealant and flexible polymeric sealant) for installing encapsulated FBG sensors in pavement grooves. An innovative laboratory testing methodology was developed to assess the suitability of these materials in ensuring accurate strain transfer and mechanical protection. Specifically, the research involved embedding FBG sensors in fibreglass rods and testing their performance with various filling materials under controlled conditions. Among the tested materials, the polymeric sealant exhibited the best performance, demonstrating only a minimal stiffness reduction of 5% and acceptable fatigue resistance, closely mimicking the behaviour of conventional asphalt mixtures. These findings offer valuable insights into the practical implementation of FBG sensors in pavement structures and highlight the critical importance of selecting appropriate embedding materials to preserve pavement integrity and ensure precise, long-term monitoring.

A temperature compensation method for fiber Bragg gratings using negative thermal expansive β-eucryptite packaging

Abstract Fiber optic sensing measurements hold significant potential for various applications, but temperature compensation of fiber Bragg grating (FBG) remains a formidable challenge. This paper introduces the utilization of β-eucryptite as an encapsulation material for FBG, exploiting its negative thermal expansion property to achieve temperature compensation. A two-point adhesive sealing technique was employed to affix FBG to the β-eucryptite substrate. While bare FBG and sensors encapsulated in 7075 aluminum alloy served as comparison. Experimental outcomes reveal that the FBG encapsulated in β-eucryptite exhibits temperature sensitivities of 1.67 pm °C−1 within the temperature ranges of −30 °C to 150 °C. In contrast, bare FBG and sensor encapsulated with 7075 aluminum alloy display temperature sensitivities of 10.46 pm °C−1 and 37.31 pm °C−1, respectively. The use of β-eucryptite for sensor encapsulation effectively reduces the temperature sensitivity of FBG. This temperature compensation method is straightforward yet promising and has great potential in aerospace and precision instrument measurement.

An Energy Modulation Interrogation Technique for Monitoring the Adhesive Joint Integrity Using the Full Spectral Response of Fiber Bragg Grating Sensors.

Adhesive joining has the severe limitation that damages/defects developed in the bondline are difficult to assess. Conventional non-destructive examination (NDE) techniques are adequate to reveal disbonding defects in fabrication and delamination near the end of service life but are not helpful in detecting and monitoring in-service degradation of the joint. Several techniques suitable for long-term joint integrity monitoring are proposed. Fiber Bragg grating (FBG) sensors embedded in the joint are one of the promising candidates. It has the advantages of being close to the damage and immune to environmental attack and electromagnetic interference. Damage and disbonding inside an adhesive joint will give rise to a non-uniform strain field that may bring about peak splitting and chirping of the FBG spectrum. It is shown that the evolution of the full spectral responses can closely reveal the development of damages inside the adhesive joints during tensile and fatigue failures. However, recording and comparing the successive full spectra in the course of damage is tedious and can be subjective. An energy modulation interrogation technique is proposed using a pair of tunable optical filters. Changes in the full FBG spectral responses are modulated by the filters and converted into a conveniently measurable voltage output by photodiodes. Monitoring damage development can then be easily automated, and the technique is well-suited for practical applications. Filter spectrum width of 5 nm and initial overlap with the FBG spectrum to give 40% of the maximum output voltage is found to be optimal for measurement. The technique is tested on embedded FBGs from different adhesive lap-joint specimens and successfully reflected the severity of changes in the full spectral shapes during the course of tensile failure. Moreover, the trends in these PD outputs corroborate with the V value previously proposed to describe the qualitative change in FBG spectral shape.