The output from a laser is monochromatic, this means that it is

A monochromatic laser emits only one wavelength i.e. single frequency & therefore reduces or does not contribute to chromatic dispersion.

Note: Monochromatic Dispersion results from the spectral width of the emitter i.e. the spectral width determines the number of different wavelengths that are emitted by the LED or laser. One way to reduce chromatic dispersion is to narrow the spectral width.

Laser:

• The laser is the abbreviation of Light Amplification by the Stimulated Emission of Radiation.
• It is a device that creates a narrow and low-divergent beam of coherent light, while most other light sources emit incoherent light, which has a phase that varies randomly with time and position. 
• The principle of a laser is based on three separate features:

           a) stimulated emission within an amplifying medium, 

           b) population inversion of electronics and 

           c) an optical resonator.

These are based on the principle of population inversion at a junction as explained in below figure

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