What limitation of Fabry-Perot (FP) lasers is addressed by distributed feedback (DFB) lasers?

Distributed Feedback (DFB) lasers address the limitation of side modes that is often present in Fabry-Perot (FP) lasers. FP lasers typically have multiple longitudinal modes of oscillation, leading to the potential for side modes that can interfere with signal integrity and reduce performance in applications requiring stable and narrow spectral output.

DFB lasers, on the other hand, utilize a grating structure integrated within the laser cavity itself, which provides a means of wavelength stabilization and ensures that the laser operates predominantly at a single mode. This design effectively suppresses the generation of side modes, allowing for cleaner, more precise laser output essential in applications such as optical communication where signal quality and stability are critical.

The other limitations mentioned—wavelength tuning, temperature sensitivity, and cost efficiency—while relevant in different contexts of laser technology, do not directly relate to the specific improvement in mode stability that DFB lasers provide over FP lasers. DFB lasers can sometimes be more sensitive to temperature variations, particularly due to their narrow linewidth, but the primary enhancement they offer over FP lasers is a significant reduction in side mode interference.