Key Takeaways & Executive Findings
- •• • Achieves a tuning range of ~51.8 nm with a tuning precision of ~0.03 nm, enabling dense wavelength-division multiplexing (DWDM) systems with 50 GHz channel spacing to be addressed without mode hops, directly reducing transceiver complexity and cost in optical networks. • • Delivers an intrinsic linewidth of ~1.21 MHz and a side-mode suppression ratio of 39.65 dB, meeting the requirements for coherent optical communication and LiDAR, where narrow linewidth and high SMSR are critical for phase-sensitive detection and ranging accuracy. • • Demonstrates a maximum on-chip power of 102.7 μW at 1551.69 nm, sufficient for short-reach optical interconnects and chip-scale sensing, while the continuous tuning range of ~3.5 pm supports fine frequency tuning for atomic clocks and spectroscopy. • • Exhibits long-term mode-hop-free operation under DC voltage tuning from −30 V to +30 V, ensuring reliable operation in field-deployed systems where environmental perturbations would otherwise cause mode instability, thereby reducing the need for active feedback control.
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Abstract
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.
1. Introduction
Miniaturized wavelength-tunable lasers with narrow linewidth, wide tuning range, and high tuning speed are indispensable for optical communications, sensing, metrology, and quantum technology. Hybrid integration of semiconductor optical amplifiers (SOAs) with photonic integrated circuits (PICs) offers a compact, low-power solution. However, most on-chip tunable lasers rely on one or two tunable micro-ring resonators, which are limited by free spectral range (FSR) and out-of-band rejection ratio, making tuning precision at the 0.1 nm scale difficult to achieve. This bottleneck restricts their use in high-precision applications such as coherent detection and dense wavelength-division multiplexing.
Thin-film lithium niobate (TFLN) has attracted intense interest due to its ultra-wide optical transparency, strong electro-optic effect, and low-loss waveguides. Here, we demonstrate a hybrid integrated TFLN/III-V laser that overcomes the precision and range limitations of micro-ring-based designs. By combining Sagnac mirrors and unbalanced interferometers in an external cavity, we achieve a tuning range of ~51.8 nm, an intrinsic linewidth of ~1.21 MHz, and a tuning precision of ~0.03 nm. The cavity, fabricated using the PLACE technique, ensures single-mode operation and mode-hop-free tuning, providing a robust pathway for high-performance integrated lasers.
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ZHU Yiran, FU Botao, FANG Zhiwei, HU Qiyue, YU Jianping, SONG Yunpeng, MA Yu, WANG Min, JIA Kunpeng, XIE Zhenda, CHENG Ya (2026). A Hybrid Integrated High-Precision Tunable Semiconductor Laser. Opto-Electronic Advances (光电进展). https://doi.org/10.29026/oea.2026.250274
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Frequently Asked Questions
What is the measured intrinsic linewidth and how does it compare to commercial tunable lasers?
The intrinsic linewidth is ~1.21 MHz, extracted via a delayed self-heterodyne interferometer. This is comparable to commercial external-cavity diode lasers (typically 1–10 MHz) but achieved in a hybrid integrated format, offering significant size and power advantages.
What is the maximum on-chip power and what are the limitations for higher power operation?
Maximum on-chip power is 102.7 μW at 1551.69 nm. Higher power is limited by the SOA gain and coupling losses; however, the design allows for further optimization of the SOA and waveguide coupling to potentially reach milliwatt levels.
How does the laser perform under long-term operation and what is the mode-hop-free duration?
The laser exhibits long-term mode-hop-free operation, as measured by a wavemeter. Continuous tuning over ~3.5 pm and precise tuning steps of ~0.03 nm are maintained without mode hops, ensuring stability for extended periods.
What is the tuning range and precision, and how does it address the limitations of micro-ring resonators?
Tuning range is ~51.8 nm with a precision of ~0.03 nm. Micro-ring resonators typically struggle to achieve precision below 0.1 nm due to FSR limitations. The use of Sagnac mirrors and unbalanced interferometers provides a Vernier-like effect that enhances precision without complex control.
What are the fabrication tolerances and scalability prospects for this hybrid integrated laser?
The external cavity is built exclusively on single-mode-waveguide-based structures, ensuring fundamental-mode propagation and relaxing fabrication tolerances. The PLACE technique for TFLN enables low-loss waveguides, and the hybrid integration with SOAs is compatible with wafer-scale manufacturing, supporting scalability.
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