Single-mode operation of electrically pumped edge-emitting lasers through cavity coupling of high order modes
The output power of a typical single-mode semiconductor laser is limited by its narrow waveguide width required to cut off high-order spatial modes. Conventional techniques rely on engineering the waveguide without introducing higherorder modes. In contrast, this work utilizes the concept of coupled-cavity (CC) structures. A single-mode lasing is achieved by employing a multi-mode and a neighboring single-mode waveguide. The CC approach is based on the resonant coupling of the high-order mode in the wide waveguide to the fundamental mode of a narrower lossy waveguide. First, geometrical dispersion of the CC lasers, such as their width, spacing, and their sensitivity to the resonance, was investigated. After optimizing the design, edge-emitting-lasers were fabricated using high-efficiency GaAs-based structures. Optical mode control and single-mode operation of the design are demonstrated through fundamental optical characterization measurements. The output power curves for the single and CC designs show similar slope efficiencies suggesting the proposed method as a promising approach towards high-power single lateral mode operation of edge-emitting lasers.