VARIABLE FREQUENCY LASER LIGHT SOURCE DEVICE

PROBLEM TO BE SOLVED: To avoid a dead zone in a state where the frequency of COM signal light is fixed by controlling the frequency of the output light of a variable frequency light source based on frequency-shifted light and heterodyne signals obtained from side-band waves. SOLUTION: A side-hand wave generating section 2 is made to generate many side-band waves of known frequencies by inputting the output light of a reference-frequency light source 1 which is a frequency-stabilized light source using the absorption lines of atoms or molecules as a reference frequency to the section 2 and the side-band waves are outputted to a frequency follow-up control section 5. Part of the output light of a variable frequency light source 3 is inputted to an optical frequency shifting section 4 and the section 4 outputs 0-order light and +1-order light to the control section 5 by shifting the frequency of the output light. The control section 5 multiplexes the output light of the side-band wave generating section 2 upon that of the optical frequency shifting section 4, outputs heterodyne signals to the variable frequency light source 3 by photoelectrically converting the multiplexed light, and controls the frequency of the output light of the light source 3.