Calibrating a frequency difference between two or more lasers over an extended frequency range

This invention generally relates to lasers and more particularly this invention relates to optical heterodyne frequency generation. Methods and apparatus for calibrating a frequency difference between two or more lasers over an extended frequency range as well as optical signal generators that employ such an apparatus or method are disclosed. The lasers are tuned in coordination with respect to one or more readily characterized narrow frequency ranges to characterize one or more tuning parameters of each of the lasers over the extended frequency range. The apparatus may include first and second tuning controllers respectively coupled to the first and second lasers, an optical coupler optically coupled to the first laser and the second laser, a frequency detector coupled to the optical coupler and a controller coupled to the frequency detector and the temperature controllers. The controller may include a processor and a memory containing processor executable instructions for calibrating the two lasers in accordance with the method described above. Such a frequency calibration apparatus may be incorporated with the lasers into a signal generator apparatus.