An optical signal occupying one or more wavelengths. An optical data signal on each wavelength is modulated with a respective overhead (dither) signal, resulting in a respective dithered optical signal. The amplitude of a particular overhead signal used to modulate the corresponding optical data signal is chosen so that the RMS value of the overhead signal in the dithered optical signal is proportional to the average intensity of the optical data signal. The instantaneous frequency of each overhead signal is time-varying and each possible frequency belongs to a distinct set of frequencies which are all harmonically related to a fundamental frequency. The distinctness of each set of frequencies allows each overhead signal to be uniquely isolated from an aggregate overhead signal. The harmonic relationship among the frequencies allows improved accuracy of RMS detection at a receiver as well as reduced computational complexity, as each possible frequency for each overhead signal can be made to fall at the center of one of the frequency bins of a single FFT of reasonable size performed at a receiver. Methods and systems for generating and detecting such signals are disclosed.