(a) Measured excess loss for the silica PLC and 3D waveguides. (b) Measured intensity and phase of the device’s output waveguides without PEC, (c) with PEC. (d) Measured average azimuthal phase at each output waveguide. (e) Unwrapped azimuthal phase for each OAM mode. (f) Calculated OAM mode purity. (g–i) The measured intensity and phase for three OAM modes (ℓ=+1, –1, +6)11. OAM, orbital-angular momentum; PEC, phase-error correction.