High directionality of surface radiation for surface emitting distributed feedback lasers

Improving the directionality of surface radiation is the key to increase the output power and the differential quantum efficiency of grating-coupled surface-emitting distributed feedback lasers. We proposed a scheme to realize the high directionality of surface radiation. In the structure, the second-order grating is fabricated on the p-side of the epitaxial wafer. A SiO₂/Si₃N₄ multilayer reflector arranged above the grating is used to redirect the upward-diffracted beam. The design of the intermediate layer between the grating and the reflector is an important part of achieving high directionality, because the adjustment of its thickness can be used to phase the redirected light with the downward-diffracted light. The calculation results show that the directionality of this structural scheme can reach more than 98% which meets the device requirements. This design provides a reference for surface-emitting distributed feedback lasers with high performance and high stability.