Theoretical analysis of multi-transverse-mode characteristics of vertical-cavity surface-emitting lasers

Based on the finite-difference method, the multi-transverse-mode behaviours of vertical-cavity surface-emitting lasers (VCSELs) are investigated numerically. For two types of injection current with different contact radii, the transverse-mode competition, the spatial distribution of the carriers inside the active region of VCSELs and the carrier diffusion effects are investigated thoroughly. Results show that the spatial dependences of the optical modes and the current injection profile play important roles in determining the transverse-mode behaviours of VCSELs. It is found that a narrow disc contact or a centre-vicinity ring contact is favourable for the excitation of the fundamental mode, while the higher-order modes are benefited for a wide disc contact or a ring contact with larger contact radius; the carrier distribution shows nonuniformities in both the radial and the azimuthal directions when the spatial nonuniformities of the optical mode are considered. It further shows that the carrier diffusion also affects the laser modal competitions and the spatial hole burning (SHB) effects greatly by influencing the carrier spatial distribution.