Selective excitation of LP01 and LP11 polarization modes in a birefringent optical fiber using a Wollaston prism

Abstract

Controllable excitation of spatial and polarization modes is of high importance in numerous applications, such as nonlinear optics, mode division multiplexing, interferometric measurements or sensing. We propose an effective method for selective excitation of different combinations of modes from LP01 and LP11 groups in a birefringent fiber. In the proposed method, the mode selection is realized with only a Wollaston prism, a rotatable polarizer and a half-wave plate, which ensures the possibility of high-power operation, low wavelength dependence, and tunability. Our approach makes it possible to excite almost all possible combinations of the LP01 and LP11 polarization modes and to continuously tune the relative coupling efficiencies of different modes by transverse shifting of the Wollaston prism. We demonstrate experimentally that the suppression rate of the unwanted modes with respect to the targeted mode exceeds 20 dB, and discuss the system configurations ensuring the highest possible coupling efficiencies for specific modes combinations. As example applications we show direct soliton and supercontinuum generation in the LP11 mode, broadband conversion of a supercontinuum from the LP01 to LP11 mode, broadband generation of vortex beams, gain tunability of intermodal four-wave mixing and cross-polarization four-wave mixing.