VARIATION OF COUPLING-COEFFICIENTS BY SAMPLED GRATINGS IN COMPLEX COUPLED DISTRIBUTED-FEEDBACK LASERS

We present an efficient method for an almost arbitrary variation of th e complex coupling coefficient of distributed feedback lasers by using superstructure gratings, As shown by detailed transfer matrix model c alculations the coupling coefficient can be reduced locally according to the duty cycle of a sampled grating. The additional supermodes caus ed by the superstructure can be strongly suppressed by choosing a smal l superperiod so that the supermodes are shifted apart from the gain c urve. This novel approach for the realization of nonuniform coupling c oefficients is applied to analyze experimentally the influence of the complex coupling strength on the performance of loss-coupled InGaAs-In GaAlAs-InP-DFB lasers.