Orbital Angular Momentum Modes From VCSELs Using Grayscale Photolithography

We present fabrication of dielectric micro-optical elements on VCSELs and characterization of emitted orbital angular momentum modes. Spiral phase plates are fabricated on the top facet of oxide-confined VCSELs using grayscale photolithography and dry etching silicon nitride. The refractive index of silicon nitride film is characterized using ellipsometry and atomic force microscopy is used to verify the fidelity of fabricated dielectric micro-optical elements. Orbital angular momentum modes with on-axis null are experimentally demonstrated. A novel circular rotation of intensity with propagation in the near-field is observed and is analyzed using Fresnel transfer function simulations.