Two laser types are commonly used in optical communication systems, the Fabry Perot laser (FP) and the
Distributed Feed Back laser (DFB). An FP laser is also known as a multi-longitudinal laser because its laser cavity
resonates at multiple regularly spaced wavelengths, Δλ=λ2/c. Figure 8a presents an FP laser’s spectral output,
notice the discrete regularly spaced wavelengths emitted from the laser. The spectral width of an FP laser is
measured at the –3dB point or the FWHM and is typically around 4nm. The FP laser’s greatest advantage is it’s
relatively low cost and is used for multimode, point-to-point direct links and low bandwidth networks