Independent Control of Mode Selection and Power Extraction in Terahertz Semiconductor Lasers

Mode selection and power extraction are the core of single-mode semiconductor lasers, but generally, they restrict each other. A large gain area with high radiation efficiency is necessary for high output power but will induce more competitive modes and increase the threshold gain of the desired mode. Here, we demonstrate a novel laser cavity─an active distributed Bragg reflector (ADBR) and a grating coupler (GC) are monolithically integrated into a laser ridge─enabling independent control of mode selection and power extraction. The ADBR features a reflection peak with an extremely narrow bandwidth that releases the constraint on the cavity length, while the GC provides a controllable high radiation efficiency. The concept is implemented onto terahertz quantum cascade lasers, exhibiting robust single-mode emission with high output power and high operating temperature. Given the universality of the ADBR and GC, our concept can be utilized in different material systems at different wavelengths.