Broadband III‐V/Lithium Niobate Actively Mode‐Locked Lasers

ABSTRACT Chip‐scale optical frequency combs (OFCs) enable integrated solutions for various applications among optical communications, LiDAR, spectroscopy, and radio frequency signal generation. Among integrated OFC platforms, III‐V semiconductor mode‐locked lasers provide gigahertz repetition rates but often suffer from limited power and tunability due to narrow driving current ranges. Hybrid integration with thin‐film lithium niobate (TFLN) has been explored to address these limitations, but previous III‐V/TFLN mode‐locked lasers exhibited narrow spectral widths, constrained by gain bandwidth and cavity dispersion. This work demonstrates broadband III‐V/TFLN integrated actively mode‐locked lasers at the telecom band, leveraging a broadband multiple‐quantum‐well reflective semiconductor optical amplifier (RSOA). A mode‐locked laser with a high‐reflectivity TFLN mirror generates a 45‐nm‐span spectrum with a 10‐dB bandwidth of 19.1 nm and a beat‐note contrast exceeding 60 dB, while another laser with a low‐reflectivity RSOA output facet achieves an off‐chip output power of 26 mW with a 10‐dB bandwidth of 11.4 nm. Numerical simulations based on the Haus's master equation and the generalized nonlinear Schrödinger equation confirm the role of slight inhomogeneous gain in supporting stretched‐state pulse solutions and overcoming dispersion‐limited spectral narrowing. This work demonstrates outstanding spectral performance and provides a promising route toward broadband, high‐power OFC sources for integrated photonic applications.