Complex-Coupled DFB Laser Using a Buried SiO2 Grating

In this letter, we report a distributed feedback (DFB) laser having a dielectric grating formed by SiO 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 of about 250 cm 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.