METHOD AND APPARATUS FOR REDUCING THE AMPLITUDE MODULATION OF OPTICAL SIGNALS IN EXTERNAL CAVITY LASERS

摘要

The present invention concerns a laser apparatus (200) comprising an external cavity laser (ECL) in which the optical signal is modulated by an electrical modulation signal with the purpose of modulating in frequency the laser output signal. The modulation in frequency produces in turn a modulation of intensity (power) of the laser output signal, also denoted amplitude modulation (AM). A method is described of control of the AM amplitude of a signal emitted by an ECL that comprises a gain medium (205), a phase element (206) with variable transmissivity induced by the modulation and a spectrally selective optical filter (209) and that selects and keeps the AM amplitude below a certain desired value or minimizes such value. A control method and a laser apparatus (200) are also described in which the reduction of the AM component of the output power is achieved by acting on the gain of the gain medium of the ECL in such way that the variation of transmissivity caused by the modulation applied to a phase element (206) is at least partially compensated by a corresponding variation of the gain current of the gain medium so as to reduce or to minimize the variation of the loop gain of the laser cavity induced by the modulation.