title: Q-plates as higher order polarization controllers for orbital angular momentum modes of fiber.
abstract: We demonstrate that a |q|=1/2 plate, in conjunction with appropriate polarization optics, can selectively and switchably excite all linear combinations of the first radial mode order |l|=1 orbital angular momentum (OAM) fiber modes. This enables full mapping of free-space polarization states onto fiber vector modes, including the radially (TM) and azimuthally polarized (TE) modes. The setup requires few optical components and can yield mode purities as high as ∼30  dB. Additionally, just as a conventional fiber polarization controller creates arbitrary elliptical polarization states to counteract fiber birefringence and yield desired polarizations at the output of a single-mode fiber, q-plates disentangle degenerate state mixing effects between fiber OAM states to yield pure states, even after long-length fiber propagation. We thus demonstrate the ability to switch dynamically, potentially at ∼GHz rates, between OAM modes, or create desired linear combinations of them. We envision applications in fiber-based lasers employing vector or OAM mode outputs, as well as communications networking schemes exploiting spatial modes for higher dimensional encoding.
authors: P
authors: P
authors: Gregg
authors: M
authors: M
authors: Mirhosseini
authors: A
authors: A
authors: Rubano
authors: L
authors: L
authors: Marrucci
authors: E
authors: E
authors: Karimi
authors: R W
authors: RW
authors: Boyd
authors: S
authors: S
authors: Ramachandran