Chirp control of an electroabsorption modulator to be used for regeneration and wavelength conversion at 40 gbit/s in all-optical networking
Chirp control to produce low or negative values of chirp at the output of an electroabsorption modulator ( EAM) is an important mechanism for reducing the signal degradation due to chromatic dispersion in high- speed transmission over standard single- mode fibre. An analytical model for the chirp performance of an EAM capable of optical regeneration and simultaneous wavelength conversion operating at 40 Gbit/ s is derived. A chirp control approach is identified using this model by exploring the tradeoff between the alpha- parameter describing the chirp factor ( based on the nonlinear absorption coefficients) and bias voltage requirements of an EAM. In particular, an optimum range of bias voltage is determined to ensure reduced chirp operation when a two- tone signal ( i. e., comprised of bias and modulating voltages) is applied to the EAM. It is also demonstrated for large signal operation at 40 Gbit/ s that the optimum range of reverse bias voltage is between 0 and 2V to obtain low values for the chirp factor ( between + 1 and - 2) in order to facilitate the necessary chirp control in all- optical networking. In addition, it is identified that at 40 Gbit/ s higher positive values of the second- and third- order nonlinear coefficients of chirp must be avoided when operating at reverse bias voltages less than 1V.