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Highly directional surface radiation for surface emitting distributed feedback lasers

Improving the directionality of surface radiation is an important issue to increase the output power and the differential quantum efficiency of grating-coupled surface-emitting distributed feedback lasers. We proposed a method to realize the high directionality of surface radiation. Surface second-order gratings are fabricated on the p-side of the epitaxial wafer to provide feedback and surface radiation. High contrast gratings arranged above the surface grating are used to reflect the upward-diffracted light. The adjustment of the thickness of the intermediate layer between the grating and the reflector can be used to phase the reflected light with the downward-diffracted light. The calculation results show that the directionality of this structure can reach 92.5% which meets the device requirements. This design provides a reference for surface-emitting DFB lasers with high performance.