Ultrafast tunable lasers using lithium niobate integrated photonics

TL;DR

This paper presents low-noise, tunable lithium niobate integrated photonic lasers with narrow linewidth and high-speed frequency tuning, enabling advanced applications like coherent LiDAR and environmental sensing.

Contribution

It introduces a hybrid integrated platform combining silicon nitride and lithium niobate for ultrafast, narrow-linewidth, and frequency-agile lasers with demonstrated LiDAR ranging capabilities.

Findings

Achieved narrow linewidth of 3 kHz in integrated lasers.

Demonstrated 12 PHz/s electro-optic tuning speed.

Performed proof-of-concept FMCW LiDAR with 15 cm resolution.

Abstract

Recent advances in the processing of thin-film LNOI have enabled low-loss photonic integrated circuits, modulators with improved half-wave voltage, electro-optic frequency combs and novel on-chip electro-optic devices, with applications ranging from 5G telecommunication and microwave photonics to microwave-to-optical quantum interfaces. Lithium niobate integrated photonic circuits could equally be the basis of integrated narrow-linewidth frequency-agile lasers. Pioneering work on polished lithium niobate crystal resonators has led to the development of electrically tunable narrow-linewidth lasers. Here we report low-noise frequency-agile lasers based on lithium niobate integrated photonics and demonstrate their use for coherent laser ranging. This is achieved through heterogeneous integration of ultra-low-loss silicon nitride photonic circuits with thin-film lithium niobate via direct wafer bonding. This platform features low propagation loss of 8.5 dB/m enabling narrow-linewidth lasing (intrinsic linewidth of 3 kHz) by self-injection locking to a III-V semiconductor laser diode. The hybrid mode of the resonator allows electro-optical laser frequency tuning at a speed of 12 PHz/s with high linearity, low hysteresis and while retaining narrow linewidth. Using this hybrid integrated laser, we perform a proof-of-concept FMCW LiDAR ranging experiment, with a resolution of 15 cm. By fully leveraging the high electro-optic coefficient of lithium niobate, with further improvements in photonic integrated circuits design, these devices can operate with CMOS-compatible voltages, or achieve mm-scale distance resolution. Endowing low loss silicon nitride integrated photonics with lithium niobate, gives a platform with wide transparency window, that can be used to realize ultrafast tunable lasers from the visible to the mid-infrared, with applications from OCT and LiDAR to environmental sensing.