| We study the dynamics of spatially modulated laser structures, which include distributed feedback (DFB) lasers with longitudinal modulation and semiconductor laser arrays with lateral modulation.; A time domain model is developed to describe the dynamics of DFB lasers. Uniform grating, {dollar}lambda{dollar}/4-shifted, chirped grating DFB (CG-DFB) semiconductor lasers, and CG-DFB fiber lasers are investigated. We found that a single section, asymmetric, linearly chirped DFB laser exhibits the dynamic behavior of high frequency, self-sustained pulsations. This high-frequency self-pulsating behavior, however, is absent in a uniform or symmetrically chirped DFB laser. The frequencies of these self-pulsations are multi-100 gigahertz in CG-DFB semiconductor lasers, and several gigahertz in CG-DFB fiber lasers. The physical mechanism is attributed to the mode beating between the two asymmetric, longitudinal modes with similar gain. The self-pulsation frequency depends on the coupling strength of the DFB laser. With sufficiently large coupling strengths, a terahertz self-pulsation frequency can be obtained. The effect of end mirror reflectivity on the self-pulsating behavior is also investigated in CG-DFB semiconductor lasers.; For CG-DFB fiber lasers, we develop both a full model and a simplified model. The simplified model is based on the averaging over the inverted population distributions. Both models produce similar self-pulsations, while the simplified model needs much less computing time.; For uniform grating DFB fiber lasers, we also study the effect of the intensity-dependent refractive index of the host material. This nonlinear index gives rise to a nonlinear phase shift, which could alter the dynamics in a high nonlinear index DFB fiber laser.; We finally study the dynamics of semiconductor laser arrays by characterizing both the spatio-temporal and the spatio-spectral behaviors of the field in the lateral dimension. An eight-stripe channeled-substrate-plannar (CSP) semiconductor laser array is modeled and analyzed. The analyses give rise to the conclusion that a closely spaced CSP array with strong optical coupling between array elements can be characterized by a gain-guided, broad area laser.; In summary, we conclude that multimode instabilities in spatially modulated laser structures can give rise to dynamic behaviors such as periodic self-pulsations, quasi-periodic self-pulsations and chaotic output. |
