There are three primary types of optical semiconductor resonant cavity devices, Fabry-Perot (FP), Distributed Bragg Reflector (DBR) and Distributed Feedback (DFB).
In DFB-LD devices a grating is fabricated in above or below the active layers (laser gain region) of the DFB devices, and has the same length as the active region.
A main difference between DBR and DFB LDs is that in DBRs, the grating is outside of the area of the active laser gain region.