Complex-coupled DFB lasers based on a current modulation concept

Pure gain-coupled DFB lasers and complex-coupled DFB lasers based on a current modulation concept is investigated. An n-doped current blocking layer is formed either directly on top of the active region or on top of the InGaAsP index-modulation grating. The blocking layer causes a spatial modulation of the carrier concentration at the active region, forming a gain-grating. The addition of the n-doped current blocking layer did not cause any deterioration in either the I-L or I-V curves. The stop band, which can be clearly observed in the index-coupled and the complex-coupled DFB lasers, cannot be distinguished in the pure gain-coupled DFB lasers, suggesting that the current blocking layer is sufficient to incorporate gain-coupling mechanism to the DFB lasers. The gain- and complex-coupled DFB lasers exhibit significant improvement in single mode yield and susceptibility to optical feedback compared to index-coupled DFB lasers