Distributed-feedback grating used as a lateral-mode selector in phase-locked antiguided arrays

We show here, for the first time, that a distributed-feedback (DFB) grating can act as a lateral-mode discriminator if located below the active region of a phase-locked antiguided array. Spatial-mode selection from such a lower-DFB (LDFB) grating in a resonant antiguided structure (ROW-LDFB) relies on the fact that the optical field distribution below the active region is strongly array-mode dependent. In particular, it is shown that at and near resonance a ROW-LDFB structure strongly favors resonant-mode oscillation, while suppressing oscillation of high-order modes. ROW-LDFB devices thus accomplish both spatial- and frequency-mode selection in a single structure. Furthermore, for effective intermodal discrimination, there is no need for interelement loss or Talbot-type filters, thus eliminating all potential sources of self-pulsations.