Twisting effect on LP11 mode in optical fibers

We study the light propagating in a dual mode optical fiber with torsional mechanical stress. By twisting the fiber and distinguishing the LP01 and LP11 modes using wavelength-scanning spatially and spectrally resolved imaging technique (S2 Imaging), we show the twist induced mode variation of the intensity distribution and phase pattern of the fiber. The linear and nonlinear variation of the mode rotation with the physical twist of the fiber is observed and discussed. The experimentally obtained LP11 mode intensity fluctuation of the fiber is also presented. The mechanism provides a way to control the fiber mode pattern, which may find potential use in long-range robust transmission of mode division multiplexing.