Tailoring focused optical vortices by using spiral forked plates.

ABSTRACT

We propose and experimentally demonstrate a single optical element, termed as spiral forked plates (SFPs), to simultaneously generate two tightly focused optical vortices (OVs). The key idea is to combine a spiral zone plate (SZP) and a forked grating (FG) through a logic XOR operation. Both theoretical and experimental results demonstrate that SFPs not only can completely suppress the undesirable zeroth (central) order diffraction, but also can further manipulate the topological charges (TCs) of the two resultant focused OVs by varying the TCs of the SZP and FG, following the so-called TC transformation rule. Thus, SFPs show promising potential for advancing the shrinking and integrating applications of orbital angular momentum superpositions.