Alcatel Cit

Stephane Morin

Jean-Luc Pamart

Roland Uhel

Francois-Xavier Ollivier

Franck Giraud

A particular embodiment comprises: a semiconductor laser; a Mach-Zehnder type modulator; an analog adder for adding a modulation signal representing binary data with a DC bias voltage; a coupler for taking off a fraction of the modulated light signal; a photodiode; an amplifier; a bandpass filter tuned to a frequency equal to the binary data transmission rate; an amplifier; an amplitude detector; an amplifier; and a microprocessor associated with an analog-to-digital converter and with a digital-to-analog converter to modify the bias voltage so as to cause the amplitude of the spectrum line extracted by the filter and the amplitude detector to remain below a fixed threshold value. The invention is applicable to digital data transmissions.

Apparatus for servo-controlling the bias voltage of a light source

A system for re-establishing the transmission quality of a digital information transmission link including amplifier equipments in the event of failure of one or more amplifier equipments includes, associated with at least one of the amplifier equipments, a gain control device for varying the gain of the amplifier equipment in order to compensate for deterioration of the receive signal-to-noise ratio following failure of at least one other amplifier equipment. An error corrector coder at the send end of the link operates on the digital information to be transmitted and an error corrector decoder at the receive end of the link operates on the received digital information. The error corrector code used by the error corrector coder and decoder reduces or eliminate residual errors at the receiving end associated with residual deterioration of the receive signal-to-noise ratio not compensated by varying the gain.

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Lannion, France

Stephane Morin