Unbroadened-spectrum chirped Modulation: effects of the chirp-inducing mechanism on the spectral broadening in LiNbO/sub 3/ Modulators

The spectrum of a chirped optical nonreturn-to-zero data stream obtained by an external Mach-Zehnder modulator (MZM) is analyzed. We demonstrate that it is possible to induce chirp without broadening the optical spectrum by employing an MZM with optical power unbalancing in the two waveguides. For standard chirped MZMs (different electric fields on the two arms), such as z-cut LiNbO/sub 3/ modulators, the broadening as a function of chirp factor is measured for comparison.