Properties Of Fiber Bragg Gratings Research Articles

Noise Signal Recognition and Noise Reduction Algorithm of Ships

Based on the study of the sensing property of fiber bragg grating (FBG) sensor network, this paper takes hybrid wavelength division/time division multiplexing sensor network with high-capacity FBG as the research object to study noise source, noise category and traditional noise reduction algorithm. In accordance with the characteristic of crosstalk accumulation noise in the network, this paper proposes LCEEMD-LWT signal processing method, which uses the local complementary ensemble empirical mean decomposition (LCEEMD) method for signal preprocessing, and then adopts LWT technology to refine high-frequency signal and solve the related problems. Then this paper put forwards detrended fluctuation analysis (DFA) to evaluate the sensing signal of high-capacity FBG, preprocesses the sensing signal by LCEEWD-LWT method, and conducts a temperature sensing experiment. The average temperature error of the demodulating system is reduced from 0.2923℃ to 0.2357℃, which not only overcomes the shortcoming that the traditional signal processing method is not meticulous for high-frequency signal processing, but also avoids the problem that the signal processing time is too long, exerting a good effect on the signal pre-processing of high-capacity FBG. The method in this paper has certain theoretical and technical reference value for the signal processing and the improvement of sensing property of high-capacity FBG sensing demodulating system in engineering application.

Enhanced high temperature properties of overexposed FBG fabricated by femtosecond laser

The high temperature properties of fiber Bragg gratings (FBGs) fabricated by overexposure using femtosecond laser phase mask technology are investigated. It is found that the overexposed FBG (FBG-II) has exhibited a temperature resistance of up to1000 °C and a reflection intensity of over 12 dB after air cooling treatment at 1000 °C for 5 h, as well as showing better high temperature stability than the unexposed gratings (FBG-I). Moreover, the temperature stability of FBG-II can be enhanced obviously through the rapid air cooling treatment after high temperature annealing, as well as the higher the air cooling rate, the more significant the effect. In addition, the wavelength hysteresis and spectral repeatability of the FBG-IIs can be significantly improved through the method. This research essentially provides a new approach to enhance the thermal properties of FBG and shows great potential in a harsh environment.

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.

Sensing applications of fiber Bragg gratings in single mode fibers with as-drawn 25 μm diameter cladding

The sensing properties of fiber Bragg gratings (FBG) inscribed in single mode fiber with a 5 μm diameter core and 25 μm diameter cladding are studied experimentally for temperature, strain, bending, and surrounding refractive index. Compared to normal single mode fiber, the diameter of this fiber is 5 times smaller and it stretches 14.5 times more at the same applied load. Therefore, it is much more flexible and stretchable, while maintaining excellent optical quality at wavelengths near 1550 nm. In addition to a core mode back reflection resonance, strong FBGs inscribed in this fiber show a relatively small number of narrow bandwidth (0.7 nm) cladding mode resonances separated in wavelength by 2.5–6 nm. This relatively coarse spectral comb can then be used to sense many different kinds of perturbations involving core and cladding modes. In particular, unlike cladding-mode based sensors made from tilted FBGs, all resonances are of the same azimuthal order as the core mode (i.e. HE1m). This feature makes these gratings particularly sensitive to bending which causes the appearance of new resonances and reduced amplitudes of the original ones, each by up to 10 dB/mm−1 of curvature. On the other hand, the temperature sensitivities of all modes are similar to that of standard fiber (around 11 pm/oC) while strain sensitivities are somewhat higher (1.6–1.7 pm/μstrain). The surrounding refractive index sensitivity is also increased (by a factor of 3) over normal fiber, mostly due to the increased modal dispersion of the modes of the thinner cladding. Furthermore, it is possible to serially multiplex different gratings at different wavelengths by interleaving their resonance combs and preserving each grating identity in the combined spectrum.

Promoting optical fibre sensor technology with educational experimental setup

This work shows the production steps of two optical fibre sensing setups which were specially designed for the activities of the 2018 Photonics Lab Open Day realized at the Federal University of Technology—Paraná in Brazil as a celebration of the first International Day of Light (16 May). The systems are based on the sensing properties of fibre Bragg gratings, a well-established photonic sensing technology but not covered in regular undergraduate Optics courses. The demonstrations of optical fibre sensing properties by means of funny scientific activities intended to stimulate high school and college students’ interest in science, seeking greater engagement of these students in the research projects developed at the University. Fibre Bragg ability of detecting mechanical vibration and temperature changes was used to measure the temperature of the attendee’s breath and vibrations produced during a short walk. Demonstrations were realized in a contest where students were challenged to walk smoothly over a flat surface instrumented with vibration sensors, as well as to blow into a tube containing the temperature sensor. Steps of the sensing systems implementation are provided in detail including aspects concerning to the choice of the apparatus design and the installation of the sensors.

Refractive Index and Temperature Sensor Based on D-Shaped Fiber Combined With a Fiber Bragg Grating

A novel D-shaped fiber structure combined with a fiber Bragg grating for refractive index (RI) and temperature sensing is proposed and experimentally investigated. Thanks to the etched cladding of D-shaped fiber, the resulting interference is strongly influenced by the surrounding refractive index. By monitoring the dip wavelength of D-shaped fiber structure, the refractive index can be measured. Theoretical analysis and simulations were conducted to investigate the cladding mode propagating behavior influenced by the surrounding RI. Combined with the temperature sensing property of fiber Bragg grating (FBG), the possibility of simultaneously measuring the RI and temperature relies on monitoring the resonance dip of the D-shaped fiber modal interferometer and the Bragg wavelength of the FBG. Experimental results showed that the RI sensitivity of −31.79 nm/RIU within the range of 1.333 ~ 1.428, and a temperature sensitivity of 28.7 pm/°C can be obtained. The proposed sensor with simple configuration, low cost and easy fabrication is suitable for refractive index and temperature sensing applications.

Characterizing the effect of femtosecond photo-treatment on the center wavelength of fiber Bragg gratings.

Various types of pre- and post-treatments to optical fibers are typically used to improve and/or change the properties of fiber Bragg grating (FBG). Here, we investigate experimentally the effects of NIR femtosecond (fs) laser pulses used for pre- and post-treatment on the refractive index of the fiber, and the resulting center wavelength shift of an fs inscribed FBG. We observe "red"-shift when applying a suitable pre-treatment, and both "blue"- and "red"-shifts when applying post-treatment. We characterize the photo-treatment parameters and compare to an FBG inscribed on a fresh fiber without any treatment. We also show that when the photo-treatment is saturated the result is a phase-shifted grating. Our results give further insight into the process of fs photo-treatments and quantify the effects in the case of fs FBG inscription.

Highly dispersion tailored properties of few mode fiber Bragg grating-based vibration sensor due to a perturbed apodization profile

A dispersion tailored properties of fiber Bragg grating (FBG)-based vibration sensor has been explored, assuming a highly perturbed apodization profile. Most of the FBG designed so far for vibration sensing applications are nonuniform. This paper deals with the modeling of perturbation as a more complicated chirp-type nonlinear apodization profile. It can significantly reduce the dispersion-induced signal distortion and side lobe intensity followed by the improvement of sensor performance. The study reveals that an accurate modeling of vibration sensor is quite feasible while opting the proposed apodization profile. FBG sensor parameters are optimized in such a way that the sensor may operate only under lowest order modes. To the author’s knowledge, sensing capability of FBG-based microaccelerometer having arbitrary chirp type of apodization profile has not been discussed before. It is assumed that small perturbation theory is valid while keeping the influence of microbend geometry in analysis. The standard matrix method is used to study dispersion characteristics due to the complicated apodized profile. The simulation results are validated with the experimental result for the known cases.

Magnetic field and temperature sensor based on a no-core fiber combined with a fiber Bragg grating

An optical fiber magnetic field sensor based on the no-core fiber (NCF) and magnetic fluid (MF) is proposed and demonstrated. By using the temperature sensing property of fiber Bragg grating (FBG), the magnetic field sensor with dynamic temperature compensation can be achieved. The transmittance of the NCF that is sealed in a capillary with MF is highly sensitive to the surrounding magnetic field. Experimental results show that the sensor has the magnetic field sensitivity of 9.2 pm/mT ranging from 0 to 9 mT and the temperature sensitivity of 11.9 pm/°C ranging from 15 to 45 °C. The prototype might be attractive due to its low fabrication cost and simple configuration, which are desirable features in magnetic field measurement.

Fiber Optic Fabry-Perot Magnetic Field Sensor With Temperature Compensation Using a Fiber Bragg Grating

Based on the characteristic of magnetic-controlled refractive index, magnetic fluid was used as a sensitive medium in fiber optic Fabry-Perot (F-P) cavity. Combined with the temperature sensing property of fiber Bragg grating (FBG), a novel fiber optic F-P magnetic field sensor with temperature compensation was proposed. The sensor probe has the advantages of simple structure, low cost, and high magnetic field measurement accuracy. Magnetic field and temperature can be simultaneously measured by the proposed sensor. Sensing mechanism and experimental results indicated that the temperature cross effect on magnetic field measurement can be effectively compensated using a FBG. The maximal magnetic field intensity is up to 600 Gs with a sensitivity of 0.04 nm/Gs and measurement resolution is 0.5 Gs.

Degradation of sensing properties of fiber Bragg grating strain sensors in fatigue process of bonding layers

Bonding layers, serving as the strain transmission mediums, may bring undesirable effects to the sensing properties of fiber Bragg grating (FBG) strain sensors during their fatigue process. To analyze the strain sensitivity and the reflected spectrum of FBG strain sensors in different fatigue stages of bonding layers, their strain sensitivities were derived according to strain transfer models. Resorting to T-matrix formalism, the affected reflected spectra were stimulated. Theoretical analysis results show that there is a gradual decline in the strain sensitivity during the stage of fatigue crack initiation, and that significant distortions emerge in the reflected spectrum during the stage of fatigue crack propagation. In addition, a cyclic loading fatigue test was conducted and the phenomenon observed in the test showed a good agreement with the theoretical prediction.

Theoretical and experimental study of refractive index sensors based on etched fiber Bragg gratings

In this work, a theoretical and experimental study of the effect of the etching process on the properties of fiber Bragg gratings (FBGs) used as refractive index sensors is presented. The theoretical study addresses the dependence of the effective refractive index on the cladding thickness of the etched FBG. The results of this study show that as the cladding thickness is reduced, the effective refractive index decreases exponentially. Based on this result, a simple analytic expression between the effective refractive index and the radius of the etched FBG was developed. Thus, the radius of the FBG after the etching process can be determined directly from the shift of the Bragg wavelength, without the need of extensive numerical simulations. Also, the sensitivity of the FBG sensor in characteristic environments of practical interest has been calculated as a function of the fiber radius, and found to be described by simple analytic functions. The time evolution of the Bragg wavelength during the etching process has also been investigated, both experimentally and theoretically. By means of detailed theoretical analysis of the experimental results, the heating and the etching rate of the FBG was calculated. Finally, the etched FBGs have been used as liquid level sensors for water and oil, having refractive indices lower and higher than the fiber core respectively. The analysis of the experimental results was based on the shift of the diffracted wavelength in the case of water and on the reduction of the reflected power in the case of oil.

Real time transverse-force sensor based on polarization properties of fiber Bragg grating and cross-sensitivity compensation

We present a new method for real-time transverse force sensor based on the measurement of the polarization properties of a uniform fiber Bragg grating (FBG) written into standard single mode fiber. Unlike the usual spectral analysis of FBG sensors, we demonstrate here that the amplitude of the first Stokes parameters of a uniform FBG in transmission can be used to obtain transverse force value. The influences of incident angle of linear polarized light launched into FBG on sensor performance are analyzed. Experimental results measured by means of a tunable laser source and a polarimeter are presented. We also propose a kind of grating structure with triangular-shaped transmission spectrum to reduce the influences of cross-sensitivity. The compensation effect can satisfy the requirements of the practical application with optimized grating parameters.

Evolution of polarization properties in circular birefringent fiber Bragg gratings and application for magnetic field sensing

The transmission and polarization properties of Fiber Bragg Grating (FBG) with Faraday Effect are studied in this paper. The evolutions of transmission spectrum for different circular birefringence, grating parameter (physical length, index modulation) and input polarizations are simulated with Jones Matrix method. It is demonstrated that the monitoring of the 3rd normalized Stokes parameter peak values provide a new magnetic field measurement. The magnetic field strength sensitivity value is 1.482×10−5/Gs by using the optical vector analyzer whose precision is 10−5 in experiment and a very good agreement between theory and experience is reported.

Sensing circular birefringence by polarization-dependent parameters in fiber Bragg gratings and the influence of linear birefringence

In this paper, we focus on the transmission and polarization properties of fiber Bragg grating (FBG) with magnetically induced circular birefringence. The evolutions with wavelength of transmission spectrum and the third Stokes parameter for different circular birefringence values are analyzed by implementing the Jones formalism. We demonstrate that the evolutions of polarization dependent parameters contain the information about the amount of circular birefringence. The influences of linear birefringence on these evolutions are analyzed for further practical research. The results show that for typical intrinsic linear birefringence values in FBG the influences are tolerable, while for lager linear birefringence values it maybe overwhelm the circular birefringence effect.

Changes in spectral properties of fibre Bragg gratings owing to bending

The effects of bending on the spectral characteristics of fibre Bragg gratings have been investigated at relatively small bend diameters for small form factor applications. Tests undertaken on Bragg gratings written in different types of singlemode optical fibre indicate that the fibre type influences the magnitude of observed changes. Shifts in the centre wavelength of ∼0.35 nm have been measured for a low bend loss fibre when the bend diameter was reduced to 6 mm. In contrast, no consistent trend could be observed for Bragg gratings in standard SMF-28 optical fibre as a function of bend diameter, despite the higher losses exhibited in this case.

磁光光纤光栅滤波器的全光时钟提取性能研究

The reflection spectra of polarization-mode conversed light in Magnetooptic Fiber Bragg Gratings(MFBGs) dependent on the magnetooptical coupling intensity is investigated.According to the magnetooptic coupled-mode theory combined with the propagation property of fiber Bragg grating,the magnetic control characteristics of the MFBGs are analyzed numerically.The 3 dB bandwidth tunable filter is obtained by adjusting the magnetooptical coupling intensity.The clock extraction of 40 Gbps RZ data signal by utilizing the comb filtering of MFBGs under bias magnetic fields is simulated and the jitter performance of the MFBGs is also analyzed.

Influence of the Grating Parameters on the Polarization Properties of Fiber Bragg Gratings

Due to the lateral inscription process, photo-induced birefringence is present in fiber Bragg gratings (FBGs) written into photosensitive single mode fiber. The birefringence value is generally too small to be perceived in the grating spectral response but it can lead to significant polarization dependent loss (PDL) and differential group delay (DGD) evolutions. In this paper, we first theoretically analyze the evolution with wavelength of PDL and DGD as a function of the grating parameters and the birefringence value. We demonstrate that the PDL and DGD evolutions with wavelength can be strongly enhanced by a modification of the grating parameters. Simulations carried out using the coupled mode theory and the Jones formalism are then confirmed by experiments conducted on FBGs written into photosensitive single mode fiber. Our work brings a complete characterization of polarization related phenomena in FBGs and presents a great interest for the evaluation of system performances and the design of gratings for specific applications, either for telecommunications or sensing purposes. In addition, based on the comparison between experimental and simulated evolutions, we are able to verify that the birefringence value is strongly dependent on the fluence of the laser used for the grating inscription.

Sensing properties of fiber Bragg gratings in small-core Ge-doped photonic crystal fibers

We report about fiber Bragg gratings (FBGs) inscribed in two different types of small-core Ge-doped photonic crystal fibers with a UV laser. Sensing properties of the FBGs were systematically investigated by means of demonstrating the responses of Bragg wavelengths to temperature, strain, bending, and transverse-loading. The Bragg wavelength of the FBGs shifts toward longer wavelengths with increasing temperature, tensile strain, and transverse-loading. Moreover, the bending and transverse-loading properties of the FBGs are sensitive to the fiber orientations. The reasonable analyses for these sensing properties also are presented.

Study of spectral and annealing properties of fiber Bragg gratings written in H_2-free and H_2- loaded fibers by use of femtosecond laser pulses

The spectral and annealing properties of a series of fiber Bragg gratings (FBGs) written in both H(2)-loaded and H(2)-free fibers by use of 800nm femtosecond laser pulse irradiation and created through a phase mask, have been investigated. It is found that type II FBGs inscribed in H(2)- loaded fibers exhibit superior spectral quality when compared with those written in H(2)-free fibers. Isochronal annealing tests shows that type II FBGs written in H(2)-free fibers have the highest thermal stability, followed (in order of stability) by H(2)-loaded type II, H(2)-free type I and then H(2)-loaded type I FBGs. The thermal stability of the H(2)-loaded type II FBGs can effectively be increased by using a high temperature pre-annealing treatment. After the treatment, type II FBGs written into both H(2)-free and H(2)-loaded fibers can sustain long-term annealing (for more than 12 hours) at temperatures of more than 1000 masculineC while their high reflectivities can still be maintained. This demonstrates the real potential of the FBGs developed and investigated in this work to be used as the ideal sensing elements for a series of high temperature measurement applications.