Narrow-linewidth monolithic topological interface state extended laser with optical injection locking.

Narrow-linewidth lasers are essential for coherent optical applications, including communications, metrology, and sensing. Although compact semiconductor lasers with narrow linewidths have been demonstrated, achieving high spectral purity generally necessitates passive external cavities based on photonic integrated circuits. This study presents a theoretical and experimental demonstration of a monolithic optical injection locking topological interface state extended (MOIL-TISE) laser. By monolithically integrating a TISE laser with a micro-ring resonator on an AlGaInAs multiple quantum-well platform, the proposed device achieves efficient photon injection and linewidth narrowing. Experimental characterization indicates stable single-mode operation over a wide injection current range (65 to 300 milliamperes), exhibiting a side-mode suppression ratio exceeding 50 decibels. The laser's Voigt linewidth was reduced from 2 megahertz to 4.2 kilohertz, with an intrinsic linewidth of 983 hertz extracted from power spectrum density, underscoring the MOIL-TISE laser's promise for coherent communications and modulation-free quantum key distribution applications.