Electromagnetic theory of distributed feedback lasers in periodic dielectric waveguides

A theory for distributed feedback lasers in transversely bound structures was developed, and the space harmonics approach was used to discuss the general properties of periodic structures. The coupled mode approach was employed to develop expressions for the threshold gain, longitudinal mode structure, and electromagnetic field distribution for distributed feedback lasers. Three basic structures are considered for distributed feedback lasers-thin film waveguides, diffusion waveguides, and fiber waveguides. Equations for the amplification of a waveguide mode that extends transversely over both regions with and without gain are derived. Analytical expressions are derived for coupling between modes in periodically perturbed dielectric waveguides. Sinusoidal perturbations of the electric permittivity and of the waveguide boundary are considered. Theoretical results indicate that an optimum design of distributed feedback lasers can be achieved by an appropriate choice of geometrical parameters.