Fig. 1. Schematic of the experimental setup for detecting the topological charge of optical vortex with an IMI.

Fig. 2. Far-field intensity patterns for vortex beams with different topological charges diffracted by (a) IMI and (b) MI with N=6. (a) and (b) are calculated by Eqs. (3) and (4), respectively.

Fig. 3. Distinctions between the two methods with (c) MI and (f) IMI. (a) and (b) The phase distributions of vortex beams with l=1 and l=7, respectively. (d₁) and (d₂) are the corresponding local phase distributions obtained by MI for l=1 and l=7, respectively. (e₁) and (e₂) are the corresponding far-field intensity patterns, respectively. (g₁), (g₂), (h₁), and (h₂) are the same as (d₁), (d₂), (e₁), and (e₂) but for IMI.

Fig. 4. Schematic overview of the setup for measuring OAM of the vortex beams.

Fig. 5. Experimental results of the far-field intensity patterns corresponding to Fig. 2(a).