Stable dual-wavelength operation in laterally coupled DFB lasers via waveguide induced detuning modulation

In this study, we propose and numerically demonstrate a novel surface-laterally-coupled dual wavelength DFB laser based on a horn-shaped ridge waveguide. The horn shaped waveguide produces a longitudinal effective index gradient while maintaining a strictly uniform grating period, producing a position-dependent local Bragg detuning, which physically separates the spatial distributions of the two modes and mitigates the gain competition. Concurrently, the lateral refractive index difference generates a position-dependent coupling coefficient, balancing the output intensities of the two lasing modes. The optical characteristics of the proposed structure are systematically investigated using the transfer matrix method (TMM) and time-domain traveling-wave (TDTW) model. The results demonstrate that the proposed structure can effectively enhance mode separation, modulate the modal intensity distribution, and maintain stable dual–wavelength emission under finite–current operation. This structure offers a regrowth-free, fabrication-friendly solution for high performance, integrated THz light sources.