Variation of coupling coefficients by sampled gratings in complex coupled distributed-feedback lasers

We present an efficient method for an almost arbitrary variation of the complex coupling coefficient of distributed feedback lasers by using superstructure gratings, As shown by detailed transfer matrix model calculations the coupling coefficient can be reduced locally according to the duty cycle of a sampled grating. The additional supermodes caused by the superstructure can be strongly suppressed by choosing a small superperiod so that the supermodes are shifted apart from the gain curve. This novel approach for the realization of nonuniform coupling coefficients is applied to analyze experimentally the influence of the complex coupling strength on the performance of loss coupled InGaAs-InGaAlAs-InP-DFB lasers.>