Generation of linearly polarized orbital angular momentum modes in a side-hole ring fiber with tunable topology numbers.

A refractive index (RI) tunable functional materials infiltrated side-hole ring fiber (SHRF) is proposed to generate 10 LP OAM states with 6 topology numbers. On the basis of perturbation theory, the basis of the SHRF is demonstrated to be the LP modes. After a fixed propagation distance of 0.03 m, 0.009 m and 0.012 m, the phase difference between the odd and even LPx, LPx,y, LPx,y modes in the SHRF accumulate to ± π/2 respectively with na ranging from 1.412 to 1.44. Correspondingly, the output states are OAM x, OAM x,y, OAM x,y with a bandwidth of 380 nm, 100 nm and 80 nm respectively. The proposed fiber is easy to be fabricated with the mature fiber drawing technology and could facilitate the realization of all fiber based OAM system.