Complex-Coupled DFB Laser Using a Buried SiO$_{2}$ Grating

In this letter, we report a distributed feedback (DFB) laser having a dielectric grating formed by SiO$_{2}$ and InP to explore both the large refractive index difference and the partial gain coupling. Epitaxy lateral overgrowth by metal–organic chemical vapor deposition is conducted to grow the top p-type InP waveguide layer in the dielectric grating template. An index coupling coefficient $\kappa$ of about 250 cm$^{-1}$ is estimated on the laser vertical waveguide structure. The insulating nature of the dielectric grating also partially blocks the injection current flow and modulates the optical gain of the active quantum-well region underneath it. A prototype DFB laser was fabricated and showed a stable single-mode operation with a sidemode suppression ratio larger than 47 dB measured at room temperature and continuous-wave operation. The technology developed can also be used for other applications that require high efficiency grating structures.