Abstract
Broadband tunable and low-noise integrated lasers are crucial components in modern optical communication and sensing systems. However, conventional Vernier structure-based external-cavity lasers suffer from a fundamental trade-off between Vernier free spectral range (FSR) and insertion loss. This constrains the laser performance, making it difficult to simultaneously achieve an enlarged tuning range and narrower linewidth. To address this limitation, we propose the inverse Vernier structure that resolves this compromise by superimposing a periodic suppression envelope onto the transmission response of the conventional Vernier structure while preserving the high transmission of the primary mode, effectively expanding the FSR of the overall system without introducing significant additional losses. As a proof of concept, we have experimentally validated a hybrid III–V/Si3N4 laser incorporating the proposed inverse Vernier structure. The device achieves a fourfold expanded Vernier FSR of 15.58 THz (140.7 nm), facilitating a wavelength tunability of 9.4 THz (82.3 nm) across the L- and U-bands and a narrow intrinsic linewidth of 88.8 Hz. In particular, the proposed inverse Vernier structure is flexibly compatible with diverse material platforms and configurations and poised to become a key enabler for widely tunable and narrow-linewidth hybrid integrated lasers. This work opens new avenues for applications requiring broadband tunability and high coherence, including high-speed coherent optical communication, high-resolution fiber sensing, and quantum communication technology.