Patent ID: 7386018

Claim:
A mode-locked laser comprising: a master laser which generates master laser light; a mode-locked laser section including at least a modulating section, an amplifying section, and a bandwidth limiting section in an optical resonator, the bandwidth limiting section reducing mode partition noise; a signal generating section which generates a periodic signal serving for mode locking of said mode-locked laser section and to be applied to said modulating section, wherein said master laser light is input to the optical resonator of said mode-locked laser section to cause injection locking; said modulating section is one of an electro-absorption modulator and a saturable absorption modulator; a modulating section average current measuring section which detects an average current flowing through the modulating section of said mode-locked laser section; and an optical resonator length control section which controls an optical path length of the optical resonator of said mode-locked laser section, wherein said optical resonator length control section controls the optical path length of the optical resonator so that the average current measured by said modulating section average current measuring section is to be smaller than an average current that flows when no master laser light is input to said mode-locked laser section.