Method of operating a semiconductor laser as a mode-locked semiconductor laser and devices for implementing the method

A method of operating a semiconductor laser including a branched cavity that extends over at least four individually actuatable regions, as a mode-locked semiconductor laser, the method comprising:

• providing a direct current to at least one of said regions, said direct current being greater than a transparency current;
• and
• providing an alternating current through said at least one of said regions, the amplitude of said alternating current together with the amplitude of said direct current exceeding a laser threshold current, said alternating current having a frequency related to the reciprocal of the round-trip time of light pulses generated in said cavity by said alternating current.