Continuously tunable orbital angular momentum generation using a polarization-maintaining fiber.

We demonstrate the generation of orbital angular momentum (OAM) in a two-mode polarization-maintaining (PM) optical fiber. We combine two linearly polarized modes of PM fiber to generate linearly polarized optical vortex beams with OAM. The average OAM can be finely varied by changing the phase between modes. We have quantitatively measured the resulting OAM to vary between ±1ℏ per photon while varying the relative phase between the LP_11e- and LP_11o-like fiber modes. The modal purity is 97%.