  Harmonic and Intermodulation distortions occur when a physical system is
excited with a single or several frequencies and when the relationship between
the input and output is non-linear. Working with non-linearities in the
Frequency domain is not straightforward specially when the relationship between
the input and output is not trivial. We outline the complete derivation of the
Harmonic and Intermodulation distortions from basic principles to a general
physical system. For illustration, the procedure is applied to the Single Mode
laser diode where the relationship of input to output is non-trivial. The
distortions terms are extracted directly from the Laser Diode rate equations
and the method is tested by comparison to many results cited in the literature.
This methodology is general enough to be applied to the extraction of
distortion terms to any desired order in many physical systems in a general and
systematic way.
