A distinctive method is used to achieve transverse-mode control by building and integrating a tunable liquid crystal (LC) mode filter on top of traditional vertical-cavity surface-emitting lasers (VCSELs). An LC cell is fabricated by injecting a type of nematic LC material (E7) in an annular groove patterned by SiO2. By electrically tuning the refractive index of the LC, a spatially dependent reflectivity profile can be achieved and optimized, which directly influences the threshold modal gain of each transverse mode provided by oxide-confined VCSELs. The flexible and accurate control performance of the LC mode filter structure have been demonstrated by the simulation results and our analysis. This design is a completely novel method to realize VCSELs with an accurate and real-time controllable transverse-mode, and it will probably play a significant role in the future.
