Chinese Optics Letters, Volume. 23, Issue 7, (2025)
Optical Orbital Angular Momentum Transformation Based on Nonlinear Forked Gratings [Early Posting]
We fabricated a three-dimensional nonlinear photonic crystal in a Sr0.61Ba0.39Nb2O6 (SBN) crystal using femtosecond laser direct writing of ferroelectric domain structures. The crystal features three layers of fork-shaped gratings, each oriented differently. These gratings convert an incident vortex beam into a second-harmonic Gaussian beam in specific directions. By altering the vortex beam's topological charge, we can control the emission direction of the second-harmonic beam, enabling flexible, all-optical switching and manipulation. This work provides a foundation for controlling photon angular momentum in nonlinear optical frequency conversion processes.