Reflection spectrum study and polarization effects on apodized fiber Bragg grating filter

Abstract

Spectrum properties of apodized fiber Bragg gratings (AFBGs) are well studied, in particular, when there is a need to reduce transmission side lobes. Otherwise, the polarization properties of these gratings are rarely reported when evaluating system performance. We analyze the reflected spectrum, the polarization-dependent loss (PDL), and the differential group delay (DGD) of an AFBG written in a single-mode fiber (SMF28). The evolution of these properties versus the grating parameters is studied based on the coupled mode theory. We mainly focus on the PDL and DGD maximum amplitudes and their wavelength separation. The simulation analysis is developed by means of the transfer matrix method. We demonstrate that the apodization function induces some asymmetry between the left and right parts of the PDL and DGD curves. The maximum amplitudes of the PDL and DGD converge to constant values versus birefringence but increase with grating length.