In a Single Mode Laser, a grating is etched into the active region to force the operation of the laser at very specific wavelength determined by the grating periodicity. As a result, the laser emits on a single spectral setting which may be adjusted slightly by changing the temperature of the active region.

Continuous Single-Mode Lasers have a narrow linewidth which makes them the preferred solution for gas sensing. They can be tuned within a range that can reach up to 10 cm-1; there exists a variety of modulation schemes which can be used for different purposes. CW-DFB lasers are mostly used for spectroscopy.