Polarization-mode coupling in birefringent fiber gratings.

Abstract

Polarization-mode coupling in birefringent fiber gratings is analyzed. The general expression for coupling coefficient components is also derived. It indicates that the polarization-mode coupling between any two linearly polarized (LP) core modes is possible by appropriately adjusting the grating parameters such as the grating tilt angle, the grating length, the orientation of the grating plane, the grating period, the birefringence, and the birefringent axis. It is analytically found that the complete ${\mathrm{LP}}_{01x}$-to-${\mathrm{LP}}_{01y}$ mode coupling and ${\mathrm{LP}}_{01x}$-to-${\mathrm{LP}}_{11y}$ mode coupling occur when fiber is pressed periodically. The ${\mathrm{LP}}_{01x}$-to-${\mathrm{LP}}_{11y}$ mode coupling in the linearly birefringent gratings created by pressing a two-mode fiber with a groove plate with a period of 80 µm at a tilt angle between 81.5° and 83.5° has also been experimentally demonstrated. The resonant ${\mathrm{LP}}_{01x}$-to-${\mathrm{LP}}_{11y}$ mode coupling in the birefringent gratings and their experimental transmission spectra were reasonably well predicted by the coupled-mode analysis.