Use of beacons in a WDM communication system

Apparatus, comprising:

• means for receiving a WDM communication signal having first and second beacon lines representing a first frequency comb;
• means for generating a second frequency comb;
• and
• means for locking the phases of the second frequency comb to the phases of the first frequency comb, wherein said means for locking is adapted to (i) lock the phase of a first comb line of the second frequency comb to the phase of the first beacon line and (ii) lock the phase of a second comb line of the second frequency comb to the phase of the second beacon line to substantially achieve a phase-lock between the first and second frequency combs.

Apparatus, comprising:

• a detector adapted to receive a WDM communication signal having first and second beacon lines representing a first frequency comb generated by a first optical-frequency comb source (OFCS);
• a second OFCS adapted to generate a second frequency comb;
• and
• a control circuit adapted to control the second OFCS such that (i) the phase of a first comb line of the second frequency comb is substantially locked to the phase of the first beacon line and (ii) the phase of a second comb line of the second frequency comb is substantially locked to the phase of the second beacon line.