AUTHOR=Hansen Mikkel T. , Ulsig Emil Z. , Labbé Fabien , Madsen Magnus L. , Ding Yunhong , Rottwitt Karsten , Volet Nicolas 

TITLE=Efficient and robust second-harmonic generation in thin-film lithium niobate using modal phase matching

JOURNAL=Frontiers in Photonics

VOLUME=4

YEAR=2023

URL=https://www.frontiersin.org/journals/photonics/articles/10.3389/fphot.2023.1324648

DOI=10.3389/fphot.2023.1324648

ISSN=2673-6853

ABSTRACT=<p>A double-ridge waveguide is designed for efficient and robust second-harmonic generation (SHG) using the thin-film lithium-niobate-on-insulator (LNOI) platform. Perfect phase matching (PhM) is achieved between the fundamental waveguide mode at 1,550 nm and a higher-order mode at the second harmonic. The fabrication tolerances of the PhM condition are simulated using a finite-difference method mode solver, and conversion efficiencies as high as 3.92 W<sup>−1</sup> are obtained for a 1-cm long waveguide. This design allows access to the largest element of the second-order nonlinear susceptibility tensor, and represents a scalable alternative to waveguides based on periodically-poled lithium niobate (PPLN). The design has the potential for generating pairs of entangled photons in the infrared C-band by spontaneous parametric down-conversion (SPDC).</p>