The Distributed Feedback (DFB) Laser (available in NIR and MIR) incorporates the grating within the laser diode structure itself (see Figure below). This structure coupled closely to the active region acts as a Bragg Reflector, selecting a single longitudinal mode as the lasing mode. If the active region has enough gain at frequencies near the Bragg frequency, an end reflector is unnecessary, relying instead upon the Bragg reflector for all optical feedback and mode selection.

What is the difference between DFB laser and DBR laser?

DBR Laser is Distributed Bragg Reflector Laser. Similar to DFBs, DBR Lasers has an internal grating structure. However DFB lasers incorporate the grating structure continuously along the active region (gain region), while DBR lasers place the grating structure(s) outside this region (see Figure 4). In general a DBR can incorporate various regions not typically found in a DFB that yield greater control and tuning range.