Fiber Bragg Grating Parameters Research Articles

Reconstruction of phase-shifted fiber Bragg grating parameters using genetic algorithm over thermally-modulated reflection intensity spectra

This paper presents a numerical method for the inverse extraction of the multiple physical parameters of phase-shifted fiber Bragg gratings (FBGs). In the proposed approach, the reflection intensity spectra produced by two known temperature distributions are taken as objective functions and a genetic algorithm is then employed to perform an iterative search for the corresponding parameters of the phase-shifted FBG, including the grating period, the grating position, the grating length, the refractive-index modulation depth, the apodize factor, and the phase-shift position. The numerical results confirm that the proposed method successfully synthesizes the parameters of phase-shifted FBGs with various structures with a high degree of accuracy. Furthermore, the method has the advantages of simplicity, low cost and a nondestructive nature. Accordingly, the method is suitable for widespread application in the fiber communications and fiber laser components fields.

Reshaping periodic light pulses using cascaded uniform fiber Bragg gratings

The authors demonstrate the use of cascaded uniform fiber Bragg gratings (FBGs) for the generation of periodic optical pulses with arbitrary waveform. It is a significantly simplified structure compared to complex FBG shapes. The pulse shaping is based on splitting of the input pulses by low-reflecting FBGs into a number of replicas and their superposition with proper amplitude, time delay, and phase shift that depend on the FBG parameters. The reflection amplitude and phase of each grating are unambiguously determined by the needed pulse shape. This method was experimentally verified for converting sinusoidally phase-modulated radiation of continuous-wave laser diode into a Gaussian pulse train with a pulsewidth of 30 ps. A method for controlling the parameters of FBGs during their fabrication process is also presented. It is done by measuring the spectral interference between the reflections from the FBGs and the fiber end by an optical spectrum analyzer and performing a fast Fourier transform. The method allows correction of the FBGs until the needed parameters are obtained during the writing process, as well as at any time after that.

Reconstruction of chirped fiber Bragg grating parameters and phase spectrum using two thermally modulated intensity spectra and a genetic algorithm

This study presents a synthesis method for reconstructing the multiple parameters such as grating position, length, period profile, refractive index modulation, and phase response of a chirped fiber Bragg grating (FBG) and its phase spectrum using two thermally modulated reflection intensity spectra and a genetic algorithm. In the proposed approach, the FBG parameters are determined using the genetic algorithm and are then used to reconstruct the phase response. The advantages of the proposed method include its simplicity, low cost, and nondestructive nature. Furthermore, the proposed method does not require a prior knowledge of the sign of the chirp of the grating period distribution of FBGs.

The synthesis of multiple parameters of arbitrary FBGs via a genetic algorithm and two thermally modulated intensity spectra

This paper describes the use of a genetic algorithm and two thermally modulated fiber Bragg grating (FBG) reflection intensity spectra to perform the inverse extraction of multiple physical parameters of arbitrary FBGs, including the grating period, grating position, grating length, chirped direction, and refractive-index modulation. The developed numerical approach is applied to synthesize the parameters of uniform and chirped FBGs. The experimental results confirm the ability of the proposed method to recover the grating period, grating length, grating position, refractive-index modulation depth, and apodize factor of a 10-mm-length uniform FBG. The proposed method is suitable for fiber communication applications and smart structure-monitoring systems.

Small signal intensity modulation of external cavity lasers with fiber Bragg gratings

The small signal intensity modulation (IM) of a hybrid soliton pulse source (HSPS) utilizing Gaussian apodized fiber Bragg grating (FBG) is described using electric field approach. The HSPS is modeled by a time-domain solution of the coupled-mode equations. It is shown that type of external cavity is important effect on resonance peak spectral splitting (RPSS) in IM response as well as effect of laser and FBG parameters. It is also shown that the RPSS can be suppressed by using linearly chirped Gaussian apodized FBG as an external cavity insted of Gaussian apodized FBG.

Performance Analysis of the Fiber Bragg Grating Interrogation System Based on an Arrayed Waveguide Grating

In this paper, we analyze the performance of the fiber Bragg grating (FBG) interrogation system based on an arrayed waveguide grating (AWG) device. The spectrum of light reflected from the FBG sensor is analyzed using an AWG, which acts as a coarse spectrometer. Using measurement points from the AWG channels, the original spectrum of the sensing element is reconstructed by means of curve fitting. The measurement system is modeled in the LabView environment, which allows the modification of the FBG and AWG parameters and simulating the measurement process. This, in turn, allows the quantification of the measurement errors resulting from the nonlinearity of the particular FBG/AWG configuration, and allows the optimization of the system design for the particular measurement errors permitted. In addition to the simulations of the proposed measurement system, we provide details of the laboratory evaluation.

Local coupling-coefficient characterization in fiber Bragg gratings.

We propose a new method for characterizing the local parameters of fiber Bragg gratings. This method combines measurement of the complex impulse response by optical low-coherence reflectometry and reconstruction of the complex coupling coefficient by layer peeling. Application of the method to a nonhomogeneous grating shows that the local coupling coefficient can be precisely determined with an axial resolution below 20 microm and a maximum error of less than 5% for amplitude and phase, respectively.

Accurate characterization of fiber Bragg grating index modulation by side-diffraction technique

The performance of fiber Bragg grating (FBG) devices is determined by spatial distribution of FBG parameters. For many applications, like chirped FBG used for dispersion compensation, it is sufficient to control these parameters with spatial resolution of around 1 mm. We improve the sensitivity and accuracy of the side-diffraction FBG characterization at the cost of reducing the spatial resolution and demonstrate simultaneous measurement of fiber grating refractive index modulation with accuracy of 2/spl middot/10/sup -6/, grating period variation with accuracy of 5 pm, and spatial resolution of /spl sim/1 mm. The group delay ripple of a chirped FBG calculated from our side-diffraction characterization is in a good agreement with spectroscopic measurements.