The diffraction-grating mirrors tend to reflect a narrower band of wavelengths than normal end mirrors, and this limits the number of standing waves that can be supported by the gain in the cavity. So DBR lasers tend to be more spectrally stable than Fabry–Perot lasers with broadband coatings.
In the context of laser design, diffraction-grating mirrors tend to restrict the wavelengths reflected, which in turn limits the number of standing waves that can be sustained within the cavity. As a result, DBR lasers exhibit greater spectral stability than Fabry–Perot lasers with broad-spectrum coatings.