Full 3D FDTD analysis of transverse mode characteristics in surface relief VCSELs

We have analyzed transverse mode characteristics of 850-nm oxide-confined vertical-cavity surface-emitting laser (VCSEL) with shallow surface relief (SR) structure by finite-difference time-domain (FDTD) method. We have used FDTD solution software to complete the full 3D simulations, which costs us about 24 hours for every structure. The ring form SR structure has been located in the central of the topmost DBR, and the depth is 1/4 optical wavelength, which can suppress the higher mode from emitting to the maximum extent. We have simulated different inner diameter of the ring form structures on 10-μm oxide-confined VCSELs, and compared the transverse mode characteristics with that of ordinary VCSEL. Finally find the structure can effectively decrease far-field divergent and improve transverse mode performance. The most suitable inner diameter is 6.5-μm, and the full-width half-maximum of the far-field divergent angle is 5.5°, which provides guideline for actual device fabrication.