Generation of Optical Vortices Using a Helical Fiber Bragg Grating

We present an effective method to generate optical vortices (OVs) by using a helical fiber Bragg grating (H-FBG) written directly on the few-mode fiber. The helical index modulation is obtained by rotating fiber during single-side UV exposure using a phase mask. A set of coupled-mode equations are formulated to analysis reflection characteristics of the H-FBG. We propose that stable OVs can be achieved with a proper design M-fiber, and the order of the OVs can be adjusted by tuning the resonant wavelength and the handedness of the H-FBG.