Abstract: A voltage controlled attenuator for an optical telecommunication system comprises an optical attenuator placed between an input and an output lens for obstructing the path of an incoming light beam. The attenuator has variable attenuation (reflection, absorption, etc.) which is controlled for maintaining a preset power of the outgoing light beam. To this end, a fraction of the outgoing signal is diverted to an output detector by reflecting off an end face of a lens, and processed for obtaining a control signal representative of the output power. The control signal actuates a dc motor which displaces the attenuator to a position corresponding to a preset output power.