System for transmitting optical data

DETAILED DESCRIPTION Also, the aim of the invention is to propose a transmission system which is more flexible to use and which is easier to optimize for each type of optical link and for each transmission distance.
To be more precise, the invention consists in a system for transmitting an optical signal in the form of an optical carrier wave modulated as a function of an input binary electrical signal, a clock rate defining successive time cells delimiting in the input signal first or second modulation levels, said device including a first electro-optical modulator adapted to respond to said input electrical signal by supplying a controlled phase optical signal having optical power modulated between low levels and high levels respectively corresponding to said first and second modulation levels of the input signal, and a phase shift within each time cell that contains a low power level and which precedes or succeeds a cell that contains a high power level, said system including a second electro-optical modulator controlled by said input signal and optically coupled to the first electro-optical modulator to apply complementary power and/or phase modulation to said controlled phase optical signal so as respectively to modify its extinction ratio and/or to apply a transient "chirp" to it.
To facilitate setting the modulation characteristics of the system, the first electro-optical modulator preferably does not apply any transient "chirp" to the controlled phase optical signal.
This latter condition can be met by using a "Mach-Zehnder" interferometer structure with "push-pull" control.
To be more precise, in this embodiment of the invention, the first electro-optical modulator includes: a "Mach-Zehnder" interferometer structure wherein an input optical guide splits into two branches to guide two partial waves, said two branches combining again to form an output guide, respective electrodes being provided to apply electrical fields to said two branches, and a control circuit for applying to the electrodes respective control voltages having DC components between modulation components in phase opposition, said DC components being such that in the absence of modulation components said partial waves interfere destructively