Multiple-waveguide distributed feedback lasers

Coupled wave theory is used to examine the performance of lasers formed from an array of coupled stripe waveguides with a grating overlay. It is found that such lasers exhibit inherent longitudinal mode discrimination, and, if the number of coupled guides is small, inherent transverse mode discrimination as well. The conditions for such selectivity are examined in detail, and it is shown that the correct grating distribution to use is one in which the grating fills the overlap region between the coupled guides.