A Hybrid Integrated High-Precision Tunable Semiconductor Laser
Thin-film lithium niobate (TFLN) has emerged as a promising platform for integrated photonics due to its strong electro-optic and nonlinear properties. However, on-chip tunable lasers essential for optical communications, sensing, metrology, and quantum technology remain constrained by limited tuning range or precision, often requiring complex control strategies. This work demonstrates a hybrid integrated electro-optically tunable narrow-linewidth III-V laser on TFLN, achieving a tuning range of ~51.8 nm, an intrinsic linewidth of ~1.21 MHz, and a tuning precision of ~0.03 nm. The external cavity uniquely combines highly reflective Sagnac mirrors and a series of unbalanced interferometers, providing a spectral response that favors single-longitudinal-mode narrow-linewidth lasing. Experimental results show a maximum on-chip power of 102.7 μW at 1551.69 nm, a side-mode suppression ratio of 39.65 dB, and continuous tuning range of ~3.5 pm. The laser operates mode-hop-free over long periods, with a DC voltage tuning range of −30 V to +30 V. The external cavity, built exclusively on single-mode-waveguide-based photonic structures, ensures fundamental-mode propagation, enhancing stability and relaxing fabrication tolerances. The reformulated theory of semiconductor lasers provides design insights for hybrid integrated lasers and on-chip self-injection locked lasers. This work advances the development of high-precision, wide-range tunable lasers for next-generation photonic systems.