  A physical nonlinear dynamical model of a laser diode is considered. We
propose a feed-forward control scheme based on differential flatness for the
design of input-current modulations to compensate diode distortions. The goal
is to transform without distortion a radio-frequency current modulation into a
light modulation leaving the laser-diode and entering an optic fiber. We prove
that standard physical dynamical models based on dynamical electron and photons
balance are flat systems when the current is considered as control input, the
flat output being the photon number (proportional to the light power). We prove
that input-current is an affine map of the flat output, its logarithm and their
time-derivatives up to order two. When the flat output is an almost harmonic
signal with slowly varying amplitude and phase, these derivatives admit precise
analytic approximations. It is then possible to design simple analogue
electronic circuits to code approximations of the nonlinear computations
required by our flatness-based approach. Simulations with the parameters of a
commercial diode illustrate the practical interest of this pre-compensation
scheme and its robustness versus modelling and analogue implementation errors.
