Optimized thin-film-lithium-niobate photonic devices: enhancing integration and tunability (Invited Paper)

Thin-film lithium niobate (TFLN) platforms are increasingly recognized for their high second-order nonlinearity and excellent light confinement, facilitating efficient frequency mixing over millimeter-scale lengths. To overcome integration, coupling losses, and fabrication challenges, we have developed TFLN-based photonic platforms with adjustable thickness and user-friendly tapers. These platforms incorporate microguides transitioning from titanium-diffused waveguides to micrometer-thin suspended films, achieving coupling losses as low as 0.8 dB per facet with standard SMF28 fibers. A significant feature of these platforms is their high tunability: devices such as intensity modulators, polarization modulators, and frequency converters can be finely tuned via external controls like voltage, stress, or temperature. Key examples include a 200 µm Fabry-Perot micro-modulator with 60 pm/V tunability, a polarization modulator with 180° phase control, and a nonlinear frequency converter covering the C-band. Additionally, we introduce photonic-crystal-based sensors with 700 nm active lengths, supporting diverse applications from high-speed communications to artificial intelligence.