Final answer:
Fabry-Perot and DFB lasers are designed for single mode applications. Single mode lasers emit light in a specific wavelength with a narrow spectral width.
Step-by-step explanation:
Fabry-Perot and DFB (Distributed Feedback) lasers are designed for single mode applications. Single mode refers to a laser that operates with only one longitudinal mode, meaning that the laser emits light in a specific wavelength with a narrow spectral width.
In contrast, multi-mode lasers can emit light in multiple modes or wavelengths simultaneously. Single mode lasers are used in applications that require high spectral purity and narrow linewidth such as telecommunications, spectroscopy, and optical sensing.