Nonlinear dynamics of a coupled twin-waveguide semiconductor laser with surface gratings

We propose and experimentally demonstrate a coupled twin-waveguide semiconductor laser featuring high-order slotted surface gratings to achieve a variety of nonlinear dynamics. The surface gratings serve as active distributed Bragg reflectors for selecting the lasing modes, while the nonlinear dynamics arise from mode coupling and carrier diffusion between the two identical waveguides. The coupling coefficient is designed to obtain coupled modes with a splitting frequency exceeding ten gigahertz, slightly higher than the relaxation oscillation frequency, thereby enhancing the nonlinear interaction between the modes due to the carrier density oscillation. By adjusting the mode frequency difference and the relaxation oscillation frequency through injection currents, we successfully achieve various controllable dynamic states, including periodic, quasiperiodic, and chaotic oscillations. A chaotic optical signal with inherent randomness is generated, reaching a maximum effective chaotic bandwidth exceeding 11 GHz with a flatness of 8.4 dB. Our approach offers a novel light source that can be fabricated using photolithography and regrowth-free processes, paving the way for mode engineering aimed at tailoring lasing actions in semiconductor lasers to generate nonlinear dynamics on-chip.