Theoretical analysis of the generation of multiple wavelengths by pulsed serrodyne modulation

A technique that can expand the number of wavelengths while keeping the spacing of the wavelengths constant is in great demand for wavelength-division-multiplexing (WDM) optical communications. We have developed such a technique by employing a fibre loop that contains a pulsed serrodyne modulator (i.e., a serrodyne phase modulator for pulsed light). The modulator shifts the envelope of the discrete spectrum while maintaining the mode positions of the spectrum, and the loop combines the shifted spectra into a broad spectrum. Using that technique, we have experimentally generated ~100 wavelengths with an equal spacing of 0.1?nm (or 12.5?GHz) from ~3 input wavelengths. In this article, we numerically simulate the broadening of the spectrum and confirm that it agrees well in shape and size with that in the experiment, which indicates that our theoretical model is suitable for understanding the experimental results. Employing the same model, we find that the number of wavelengths is increased markedly when the compensation of the fibre dispersion is achieved appropriately.