Reduction of second- and third-order harmonic distortion by nonlinear absorption in gain-coupled distributed-feedback laser diodes

We have calculated the characteristics of second- and third-order harmonic distortion in gain-coupled distributed feedback (DFB) lasers using a set of three rate equations. In these calculations, the relaxation oscillation, nonlinear gain compression, and nonlinear loss compression are taken into account. We have found that modulation distortion due to nonlinear gain compression is reduced significantly in the gain-coupled DFB laser of absorptive-grating type. This improvement occurs because gain compression is compensated by loss compression within the grating.