Numerical analysis of reflection characteristics of cascaded non-uniform fiber Bragg gratings

Abstract

The paper is devoted to the simulation and reflectance performance of the cascaded non-uniform fiber Bragg gratings (FBG). In a FBG, periodically spaced regions in the fiber core are varied. FBGs are key enabling technologies for fiber optical sensing for their high sensitivity and potentially low cost. Uniform, chirped, phase-shifted and sampled FBGs can be used in the sensing systems. The cascaded FBG configuration is created by several sections where each section has a specific number of segments. In our simulations the transfer matrix method has been used assuming the entire grating made up of sections. Using this method the FBG reflectance spectra have been simulated in MATLAB. The simulated reflectances of FBGs with several sections alternating along the length of the FBG have been described. The simulation results show that the FGB reflectance at the Bragg wavelength and the reflectance bandwidth depend on the Bragg grating periodicity that means on the periodicity in the sections. The bandwidth and the amplitude reflectance at the Bragg wavelength for the length grating of 10 mm with several sections have been studied. The effects of sections of different Bragg grating periods and refractive index profiles (the Gaussian profile or the sinc profile) have been numerically investigated. From the simulations one can see that the maxima of the energy of FBGs reflected by several apodized sections depend on the grating length. Moreover, it has been found out that the undesirable sidelobes between main reflectance maxima can be partly suppressed by using an appropriately designed cascaded grating.

Apodized and chirped fiber Bragg gratings for optical communication systems: influence of grating profile on spectral reflectance

“…For this apodized index profile a considerable reduction of sidelobes was achieved and the bandwidth Bragg λ ∆ = 0.14 nm. Therefore, FBGs of this type are even better candidates for DWDM demultiplexers with low inter-channel interference as FBGs with Gaussian profile [8]. However the considerably reduced reflectance Bragg r = 32% may be the main disadvantage in comparison with the Gaussian-apodized FBG.…”

Optimal parameters for fiber Bragg gratings for sensing applications: a spectral study

“…Due to the tremendous potential of FBGs, the present work is focused on the design and optimization of grating parameters for uniform and apodized (Gaussian, hyperbolic tangent, apod1, sine, and raised sine) FBGs. Although some stand-alone reports are available on uniform [9][10][11][12][13] and apodized FBGs [14][15][16][17][18][19], but they are focused on one or two profiles (mostly Gaussian) or at only few specific grating lengths or index modulation values. Hence it is felt pertinent to undertake a comprehensive study to understand as to which apodized profile is ideal for sensing applications and what are the optimal grating parameters.…”

Graphical User Interface Calculator for FBGS Performance Optimization Based on New Window Formulas

“…The important feature of FBG sensors is that the sensed physical change is transmitted as a wavelength shift, giving reproducible measurements in spite of optical losses and intensity fluctuations [4]. Per contra, FBGs with uniform window profile show reflection spectrum with high side lobes, besides highly nonlinear dispersion characteristics, which makes them unsuitable for high performance applications [5]. Therefore, different window profiles have been recently developed and applied for FBGS technology as they provide superior filtering performance and low side lobe levels [6,7].…”