Optical Communication : Optimising negative chirp of an electroabsorption modulator for use in high-speed optical networks

Optical networks using singlemode fiber rely on negative chirp to improve the transmission performance. In particular for an electroabsorption modulator (EAM) optimal chirp control is required when it is used to achieve various network functions in high-speed optical networks. An approach to modelling the negative chirp for the EAM is presented that is suitable to apply to a cross-absorption modulation scheme. A novel feature of this modelling process is that it allows cubic polynomials to incorporate the nonlinear coefficients of chirp describing the α-parameter related to the nonlinear transmission coefficients. In addition to the two-tone signal parameters (i.e. bias and modulating signal voltages), the model also includes wavelength-temperature-dependent absorption variation and the effects associated with the length of the device. It therefore enables accurate determination for the values of the nonlinear coefficients of the chirp responsible for the negative chirp of an EAM. Using this model an optimised range of ± 0.5 is obtained for the nonlinear coefficients of the chirp to exhibit negative chirp for specific values of nonlinear transmission coefficients (within a range of −10 and 2) at a reverse bias voltage of less than 2 V. Since negative chirp optimisation of an EAM can minimise the unwanted effects of dispersion on a singlemode fiber in high-speed optical networks an improvement of performance without employing expensive dispersion compensation management techniques can be achieved. Copyright © 2006 AEIT