Evaluation of coupling coefficients for laterally-coupled distributed feedback lasers

Dependence of coupling coefficient, κ, on laterally-coupled distributed feedback (LC-DFB) laser structure is investigated. In LC-DFB lasers, gratings are fabricated on and around the ridge after ridge-waveguide formation and, thus, neither epitaxial regrowth nor growth on corrugated substrates is required. For κ calculation, coupled-mode theory is used with the two-dimensional field intensity calculated using the imaginary-distance beam propagation method. Comparisons are made for LC-DFB lasers with different layer, ridge and grating structures and parameters that affect κ are identified. In addition, it is shown that LC-DFB structure is less sensitive to processing variations and, thus, more manufacturable than a conventional buried heterostructure DFB structure.