ABSTRACT
Distributed feedback (DFB) laser was proposed and demonstrated by Kogelnik and Shank in a dye laser. Semiconductor DFB laser was first realized for AlGaAs/GaAs, and then for InGaAsP/InP material for 1.55 μm fiber transmission. These early stage DFB lasers were made on uniform corrugation grating for distributed reflection. The chapter describes some results of numerical calculations of the eigenvalue equation. The power intensity ratio of a main mode to a side mode S0/S1, which is called a side mode suppression ratio (SMSR), may be a direct index of single longitudinal mode operation. However, SMSR is not easily derived from the parameters of the DFB waveguide structure, since it depends on conditions of modulation and nonlinear effects such as gain saturation. The relation between SMSR and Δαh can be estimated from a multimode rate equation. Behavior of longitudinal mode below threshold can be analyzed by calculation of transmitting spectra using the equations.
