Reflection Spectra Of Bragg Gratings Research Articles

Gaussian-LM算法在光纤布拉格光栅反射光谱寻峰中的应用

Gaussian-LM算法在光纤布拉格光栅反射光谱寻峰中的应用

Suppression of side lobes in the fiber Bragg grating reflection spectrum

A revision of works on the methods of writing and apodization of fiber Bragg gratings (FBG) is presented. The possibilities of apodizing FBGs recorded by holographic methods with phase masks and Lloyd interferometer using laser radiation with a Gaussian intensity profile are considered. FBG reflection spectra are numerically simulated for different parameters of the writing beam and configurations of the experimental setup. Side-lobe suppression and FBG spectrum smoothing are experimentally demonstrated. It is shown that this effect is due to equalization of the average value of the induced refractive index in the FBGs. FBG applications, in particular, as frequency selectors in fiber lasers (tunable, narrow-band, and multiwavelength) are described.

Origin of Bragg reflection peaks splitting in gratings fabricated using a multiple order phase mask

We have studied the effect of waveguide alignment on the reflection spectrum of Bragg gratings fabricated using a multiple order phase mask. We have demonstrated that splitting of certain Bragg peaks observed in earlier experiments reported in literature is caused by formation of the gratings with different periodicities in the waveguide tilted with respect to the phase mask plane due to the interference of non-symmetrical diffraction orders. Analytical expressions for spectral separation of the split peaks have been derived and verified against the experimental data recently presented in literature. The analytical predictions were also confirmed by numerical simulations of intensity distributions behind the multiple order diffraction grating and its projection on the tilted waveguide.

Distributed Strain Reconstruction Based on a Fiber Bragg Grating Reflection Spectrum

Abstract In this paper, we present a synthesis of the parameters of the fiber Bragg grating (FBG) and the reconstruction of the distributed strain affecting the grating, performed by means of its reflection spectrum. For this purpose, we applied the transition matrix method and the Nelder-Mead nonlinear optimization method. Reconstruction results of the strain profile carried out on the basis of a simulated reflection spectrum as well as measured reflection spectrum of the FBG indicate good agreement with the original strain profile; the profile reconstruction errors are within the single digit percentage range. We can conclude that the Nelder-Mead optimization method combined with the transition matrix method can be used for distributed sensing problems.

Birefringence in optical fibers formed by proton implantation

Birefringence can be induced in silica-based optical fibers by ion implantation. In the present research, protons were implanted in single-mode optical fibers with two different energies, one being the energy with which the protons can just reach the center of the optical fiber core and the other being a slightly lower energy. The degree of birefringence was evaluated by measuring reflection spectra of Bragg gratings formed at the proton-implanted region of the optical fibers. The results confirmed that birefringence is induced by unidirectional densification along the projected range of protons formed in the fiber core and by densification of the fiber cladding. The induced birefringence reached three to ten times higher than that of a conventional birefringent fiber. The birefringence caused by ion implantation can be a versatile tool for manufacturing various optical fiber devices.

Fiber Bragg grating spectra in multimode optical fibers

Bragg gratings in optical fibers in multimode propagation are investigated theoretically by using the coupled-mode theory and considering two modes coupling. Bragg gratings in multimode fibers (MMFBGs) show multiple reflection peaks due to the coupling between all bounded modes. The reflection spectra depend on the excitation condition of the bounded modes. A numerical method based on the fourth-order Runge-Kutta formula is developed to solve the coupled equations. The reflection spectra of Bragg gratings with sinusoidal and square refractive index modulations were simulated. The asymmetric change of refractive index in the cross section is also considered here. The spectra characteristics and potential applications of these gratings are discussed.