Widely‐Tunable Current‐Stable External Cavity Lasers Enabled by Sampled Multi‐Mode Waveguide Gratings

ABSTRACT Tunable laser diodes are pivotal to modern photonic technologies, including optical communications, high‐resolution spectroscopy, and frequency‐modulated continuous‐wave LiDAR. Most chip‐scale tunable lasers rely on microring‐resonator Vernier mirrors, in which current‐induced perturbations of the gain section and resonator‐assisted feedback can lead to mode competition and unstable light–current(LI) characteristics. Here, we resolve this bottleneck by introducing a vernier filtering based on sampled multimode waveguide gratings (SMWGs). The high side‐lobe suppression and strong wavelength selectivity of the SMWG Vernier reflector favor a dominant feedback peak during injection‐current sweeping, thereby suppressing current‐induced mode competition. The proposed laser achieves a tuning range from 1567 to 1630 nm, with a side‐mode suppression ratio exceeding 45 dB, fiber‐coupled output power up to 12 mW, and an intrinsic linewidth of 97.4 Hz. With all external‐cavity control currents held fixed, it exhibits a smooth LI response without observable mode‐hop‐induced power discontinuities. This work establishes a new performance benchmark for integrated tunable lasers, combining wide tunability, exceptional coherence, and robust mode stability, thereby enabling next‐generation coherent photonic systems.