Fig. 1. Geometric construction of the OPA for the OAM beam generation.

Fig. 2. Schematic drawing of the experiment setup. SL, seed laser; PA, pre-amplifier; FS, fiber splitter; PM, phase modulator; VDL, variable delay line; CFA, polarization-maintained cascaded fiber amplifier; CO, collimator; SP, small beam splitter; BE, beam expander; LC, liquid crystal; L, lens; PD, photodetector.

Fig. 3. Normalized PIB detected by the PD (a) open loop, (b) closed loop, and (c) their power spectral densities.

Fig. 4. Schematic drawing of observing the OAM beam emitting. HRM, high reflectivity mirror; L, lens; CCD, camera.

Fig. 5. Results of emitting the OAM beam when l = 0. (a) Phase structures of the OPA in the source plane, and the intensity distribution of the combined beam in the far field when the phase-sensing system was (b) turned off and (c) turned on.

Fig. 6. Results of emitting the OAM beam when l = −1, +1. (a1), (b1) Phase structures of the OPA in the source plane; (a2), (b2) accordingly experimental intensity distribution of OAM beams in the far field; (a3), (b3) accordingly theoretical intensity distribution; and (a4), (b4) phase distribution.

Fig. 7. Results of emitting the OAM beam when l = −2, −3. (a1), (b1) Phase structures of the OPA in the source plane; (a2), (b2) accordingly experimental intensity distribution of OAM beams in the far field; (a3), (b3) accordingly theoretical intensity distribution; and (a4), (b4) phase distribution.

Fig. 8. Results of presenting the OAM beam copier with l = −1. (a) Phase structures of the OPA in the source plane; (b) accordingly experimental intensity distribution of the OAM beam in the far field; (c) accordingly theoretical intensity distribution; and (d) phase distribution.