Optical orbital angular momentum amplifier based on an air-core erbium doped fiber

We present for the first time broadband operation of an optical orbital angular momentum (OAM) erbium-doped fiber amplifier for lower order OAM modes based on an air-hole erbium-doped fiber designed and fabricated to provide significant mode splitting between the OAM │ l │ = 1 modes and the adjacent vector modes. Up to 15.7 dB gain is obtained using a cladding pumped amplifier configuration for OAM modes with topological charge │ l │ = 1 in the operational wavelength range 1545–1600 nm