A DFB laser is a type of diode laser that generates resonance and oscillation in the cavity using diffraction gratings rather than mirrors. The laser’s purpose is to sharpen the output of conventional Fabry-Perot lasers. DBR lasers are among the earliest, if not the first, single-frequency lasers ever built. These are tunable single-mode diode lasers with a resonator made of a short piece of active fiber sandwiched between two Fiber Bragg Gratings. In comparison to the DFB laser, the DBR laser generates single frequency, phase-coherent photons at a specific wavelength.