Bidirectionally injection-locked coupled microring GaN lasers

Coherent high-quality laser sources are important for a variety of photonic devices and applications, yet they are especially challenging for high-power semiconductor lasers, because high-power and single-mode lasing present conflicting requirements; high power drives nonlinear processes causing multimode lasing and instabilities. Here, we present a distributed feedback (DFB) microring laser coupled to a uniform ring, which displays single-mode lasing up to 10 times the threshold value. This is the first microring DFB laser in gallium nitride ($\mathrm{Ga}\mathrm{N}$) and the first monolithic coupled microring $\mathrm{Ga}\mathrm{N}$ lasers. Our work paves the way for future designs of high-quality high-power coupled lasers for applications, such as topological lasers, high-power monolithic frequency combs, optical clocks, gyros, sensing, and quantum systems.