Vertical-cavity surface-emitting lasers (VCSELs) with single-mode, single-polarization emission at a wavelength of 894.6 nm was demonstrated for miniaturized atomic clocks. Utilizing the direct-etched surface grating on the surface of VCSELs, the state of polarization of VCSELs was controlled and pinned over the whole current range. The Modal properties of VCSELs with grating structures was studied using a finite difference time domain (FDTD) method. We investigate modal loss behavior with respect to the variation of grating structural parameters for the optimization of VCSELs polarization characteristics.
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 Al0.98Ga0.02As 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.