Universal Lateral Surface‐Grating Architecture for Violet‐to‐Green Single‐Mode Lasers

Single‐longitudinal‐mode semiconductor laser diodes (LDs) operating in the visible spectral range are critical for optical atomic clocks, retinal scanning displays, and high‐speed underwater optical communication. Visible LDs are typically based on III‐nitride semiconductors, yet robust single‐longitudinal‐mode control remains challenging because conventional buried‐grating designs require complex p‐GaN regrowth. Here, we demonstrate a regrowth‐free monolithic laterally coupled grating architecture, which integrates high‐order Bragg gratings that deliver wavelength‐selective distributed feedback (DFB) into a standard Fabry‐Pérot (FP) cavity. The device with optimized grating penetration depth achieves single‐longitudinal‐mode lasing at 450.2 nm, with a side‐mode suppression ratio (SMSR) of 34 dB and a continuous‐wave output power of 41 mW. This design was further applied to violet, cyan, and green FP LDs, yielding single‐longitudinal‐mode emission with low threshold current densities. These findings establish a practical route to visible single‐mode LD sources, eliminating the need to adopt conventional full‐cavity DFB laser configurations.