Fig. 1. Schematic of vortex beam mode measurement principle. (a) Gaussian beam; (b) vortex beam; (c) diffraction pattern; (d) measuring optical path

Fig. 2. Structural pattern of cubic phase grating

Fig. 3. Simulation results of vortex beam mode measurement under different topological charge values. (a) +2; (b) -2; (c) +4; (d) -4; (e) +6; (f) -6; (g) +8; (h) -8; (i) +10; (j) -10

Fig. 4. Diffraction patterns under different D values. (a) 0; (b) 1.0 mm; (c) 2.0 mm; (d) 3.0 mm; (e) 4.0 mm; (f) 4.2 mm; (g) 5.0 mm; (h) 6.0 mm; (i) 7.0 mm; (j) 8.0 mm

Fig. 5. Simulation results of LG beam after CPG diffraction under different topological charge values.(a) +10; (b) -10; (c) +20; (d) -20; (e) +30; (f) -30; (g) +40; (h) -40; (i) +50; (j) -50; (k) +60; (l) -60

Fig. 6. Experimental apparatus and experimental results. (a) Experimental device of vortex beam generation and pattern measurement; (b) forked grating loaded on SLM 1; (c) cubic phase grating loaded on SLM 2; (d) vortex beam with l=-10; (e) diffraction pattern of vortex beam with l=-10 after CPG diffraction

Fig. 7. Vortex beam patterns under different topological charge values. (a) 2; (b) 4; (c) 6; (d) 8; (e) 10

Fig. 8. Far field diffraction patterns of LG beam after CPG diffraction in different modes. (a) +2; (b) -2; (c) +4; (d) -4; (e) +6; (f) -6; (g) +8; (h) -8; (i) +10; (j) -10

Fig. 9. Diffraction patterns of LG beam after CPG diffraction at different D values. (a) 0; (b) 1.0 mm; (c) 2.0 mm; (d) 3.0 mm; (e) 4.0 mm; (f) 4.2 mm; (g) 5.0 mm; (h) 6.0 mm; (i) 7.0 mm; (j) 8.0 mm

Fig. 10. Diffraction experiment results of vortex beam after CPG diffraction under different topological charge values. (a) -10; (b) -20; (c) -30; (d) -40; (e) -50; (f) -60