Fig. 1. Generation of vortex beams by spiral phase plate

Fig. 2. Generation of vortex beams by fork grating

Fig. 3. Fork grating holograms with topological charges of -1，0，1，2 and 3

Fig. 4. Schematic of fork grating phase synthesis

Fig. 5. Rotation of polarization direction of linearly polarized light as it passes through liquid crystal cell

Fig. 6. Experimental setup for LG beam generated based on spatial light modulator

Fig. 7. Beam diffraction of different orders

Fig. 8. Optical vortex and corresponding fork gratings with topological charges of 1，2，5，10 and 20

Fig. 9. Optical vortex with topological charges from 30 to 100

Fig. 10. Fork grating holograms with topological charges of 3.2，3.4，3.6 and 3.8

Fig. 11. Optical vortex with fractional topological charges

Fig. 12. Measurement of topological charge of optical vortex with different OAM by interferometry

Fig. 13. Optical path for interferometry measurement of topological charge