Fig. 1. Principle diagram of mode measuring for vortex beam. (a) Gaussian beam; (b) vortex beam; (c) diffraction pattern

Fig. 2. Structural patterns of gradually-changing-period gratings. (a) Grating with gradually-changing-period amplitude; (b) grating with gradually-changing-period phase; (c) vortex beams

Fig. 3. Simulation patterns of mode measuring for vortex beams. (a) Diffraction results of vortex beam measurement with amplitude grating when l=±1, ±2, ±3, ±4; (b) partially magnified diffraction pattern

Fig. 4. Diffraction results of vortex beam measurement with phase grating when l=±10, ±20, ±30

Fig. 5. Experimental link diagram of generation and mode measurement of vortex beam

Fig. 6. Simulation and experimental results of vortex beam generation when l=+1, -2, -3, +8

Fig. 7. Simulation and experimental results of mode measurement for vortex beams using phase grating when l=+1, -2, -3, +8

Fig. 8. Diffraction experimental results of mode measurement for vortex beam using phase grating when l=+16,+20,+30