LED vs LASER

Major differences between LED & LASER optical sources for optic-fiber communication:

Parameter LED LASER
Wavelength Content : A monochromatic source consists of radiation of a single wavelength or a very small range of wavelength. Large Small (desirable; more monochromatic)
Spectral Width/Line Width : The wavelength interval over which the magnitude of all the spectral components is greater than or equal to a specified fraction of the total magnitude, Here, the fraction is (0.707)*P 50 nm < 5 nm
Principle of Emission Spontaneous; random photon emission (hence, not directional) Stimulated
Coherence : A constant phase difference between two waves Incoherent; since emission is spontaneous Coherent; since emission is stimulated; same phase as the stimulating photon
Output Power Low High
Directionality Low Highly directional
Speed of Operation Slow Faster
Numerical Aperture : determines the output pattern Higher Lower
Ease of Use Easier to use; less complex circuitry Complex circuitry; needs thermal & optical stabilization circuits due to light amplification
Lifetime Long Shorter
Cost Cheaper Expensive