Removal of surface-normal spot beam from on-chip 2D beam pattern projecting lasers.

Abstract

Static arbitrary two-dimensional beam patterns have been demonstrated using on-chip size "integrable spatial-phase-modulating surface-emitting lasers," which use the band edge mode of a two-dimensional photonic crystal as an in-plane resonator, while the spatial phase of the lightwaves of the band edge mode are simultaneously modulated in a holographic manner by a local positional shift of holes from their lattice points. Meanwhile, the beam patterns include a spot beam in the surface-normal direction (0th-order beam), which corresponds to components of vertical diffraction of the band edge modes without spatial phase modulation. A promising method, used to remove the 0th-order beam, uses a structure that prohibits the vertical diffraction of band edge modes. For this purpose, we set the period of the virtual photonic crystal structure from the conventional Γ2 band edge to the Μ1 band edge, where vertical diffraction is prohibited. Moreover, the additional spatial phase modulation that cancels the in-plane component of the wavevectors of the lightwaves of the band edge modes at the Μ1 band edge are also imposed to output the beam patterns vertically. As a result, we successfully demonstrated two-dimensional beam patterns without a spot beam in the surface-normal direction.