Waveguide design for a TFLN platform at 1064 nm for applications in spacecom and spectroscopy

Thin Film Lithium Niobate (TFLN) is a promising platform for applications at 1064 nm, including spectroscopy, metrology, and space communications through free space optics links, enabling high throughput wireless communication. However, compared with the 1550 nm optical window, TFLN waveguide cross-section optimization around 1 μm is more complex and lacking. Here, numerical simulations are carried out to compare etched and rib-loaded waveguides with an etched rib-loaded geometry, focusing on phase modulator performance in terms of optical losses and modulation efficiency, through the parameter. Absorption and scattering losses are considered, with the latter more severe at 1064 nm compared to 1550 nm, and calculated via the Payne-Lacey model, where waveguide roughness is estimated via atomic force microscopy and visible spectrum measurements. Polarization mixing, affecting both etched geometries, is also assessed in 90 degree curves by simulating the refractive index variation of the fundamental TE and TM modes and through FDTD simulations. Results indicate that while the fabrication of etched rib-loaded guides is more complex, the polarization mixing effect is reduced and lower losses are exhibited at high EO modulation efficiency.