High density lithium niobate photonic integrated circuits and lasers

Abstract Photonic integrated circuits are indispensable for data transmission within modern datacenters and pervade into multiple application spheres traditionally limited for bulk optics, such as LiDAR and biosensing 1 . New applications and higher performance are enabled by the diversification of optical waveguide materials past silicon-on-insulator. Of particular interest are ferroelectrics such as Lithium Niobate, which exhibit a large electro-optical Pockels effect enabling ultrafast and efficient modulation, but are difficult to process via dry etching 2 . For this reason, etching tightly confining waveguides - routinely achieved in silicon or silicon nitride - has not been possible. Diamond-like carbon (DLC) was discovered in the 1950s 3 and is a material that exhibits an amorphous phase, excellent hardness, and the ability to be deposited in nano-metric thin films. Its use today is pervasive, ranging from applications for hard disk surfaces 4 and medical devices 5 to low friction coatings for automotive components 6 . It has excellent thermal, mechanical, and electrical properties, making it an ideal protective coating. Here we demonstrate that DLC is also a superior material for the manufacturing of next-generation photonic integrated circuits based on ferroelectrics, specifically Lithium Niobate on insulator (LNOI). Using DLC as a hard mask, we demonstrate the fabrication of deeply etched, tightly confining, low loss photonic integrated circuits with losses as low as 4 dB/m and Q-factor as high as 10 · 10 6 . In contrast to widely employed ridge waveguides 7,8 , this approach benefits from a more than 1 order of magnitude higher area integration density while maintaining efficient electro-optical modulation, low loss, and offering a route for efficient optical fiber interfaces. As a proof of concept, we demonstrate a frequency agile hybrid integrated III-V Lithium Niobate based laser with sub-kHz linewidth and tuning rate of 0.7 Peta-Hertz per second with excellent linearity and CMOS-compatible driving voltage. Our approach can herald a new generation of high density ferroelectric photonic integrated circuits, in particular for applications in coherent laser based ranging 9 and beamforming 10 , optical communications 7 , and classical 11 and quantum computing networks 12 .