Enhanced Carrier Confinement and Mode Discrimination for Laterally-Coupled DFB Lasers

Reducing carrier leakage is the key to obtain laterally coupled distributed feedback (DFB) lasers with high injection efficiency. We proposed a device structure with slots fabricated between the ridge and gratings to form a good confinement on carriers. The incorporation of slots also makes the grating morphology easier to fabricate. To evaluate the dependence of coupling efficient on main structural parameters, four grating samples with different sizes are studied with FDTD Solutions. Calculation results indicate that slots with a width of
$0.1\!-\!0.3\;\mu{m}$
is suitable for the device. And, changing the lateral width of the grating can be used as a direct method to adjust the coupling strength. In addition, the carrier distribution and optical field distribution of the device were simulated with Crosslight PICS3D, and the results show that compared with the traditional laterally-coupled gratings, this structure can strengthen the competitive advantage of fundamental mode and enhance the mode discrimination of the device. This structural design provides ideas and references for improving the injection efficiency and mode stability of laterally-coupled DFB lasers.