Second-harmonic generation of integer and fractional perfect vortex beams in laser-written lithium niobate nonlinear photonic crystals

Abstract

We propose and experimentally demonstrate the generation of second-harmonic (SH) perfect vortex beams (PVBs) in a χ(2)-amplitude-modulated lithium niobate (LN) nonlinear photonic crystal. The χ(2) structure is designed according to a radial phase-shifted spiral zone plate (RSSZP), which is fabricated through laser-induced χ(2) erasing technique in LN crystals. Such an RSSZP spatially modulates the amplitude of the SH field, thereby enabling the creation of SH PVBs. The radius of the generated SH PVB can be controlled by adjusting the phase-shift parameter of RSSZP. In experiments, we have successfully produced high-order integer and fractional PVBs at SH waves. Our work provides a compact approach for the nonlinear generation of SH PVBs for optical manipulation and quantum information processing.