Realization of beam shaping using VCSEL incorporating a high-contrast subwavelength grating

In this paper, the far-field characteristic of the vertical-cavity surface-emitting laser (VCSEL) incorporating a highcontrast subwavelength grating (HCG) is analyzed by finite-difference time-domain (FDTD) method. Full three-dimensional simulations are carried out by utilizing FDTD solutions software. We study the parameters of HCG made from GaAs/AlOx which is defined by wet oxidation of an Al_0.98Ga_0.02As spacer layer. We have simulated HCG-VCSELs with different HCG periods and oxide aperture diameters. Various far-field patterns including single-lobe, double-lobe, triple-lobe shapes are obtained with the designed HCG-VCSEL. More interestingly, by tuning the HCG periods and the oxide aperture diameter, the far-field emission patterns transform from double-lobe to single-lobe shapes. By proper design of the two parameters, one can obtain Gaussian-like beam outputs, double-lobe or multi-lobe beams. The fullwidth half-maximum (FWHM) of the far-field divergent angle of the Gaussian-like fundamental mode obtained with grating periods of 23 and oxide aperture diameter of 8 μm is less than 5 degree. This opens a new path for engineering a VCSEL's emission properties and provides guideline for actual device fabrication.