DOCTORAL CANDIDATE
Gayathri Vinod

SUPERVISORS
Prof. Christelle Monat, École Centrale de Lyon (EC Lyon)
Dist. Prof. Arnan Mitchell, RMIT University (RMIT)
Dr. Sebastien Cueff, École Centrale de Lyon (EC Lyon)
Prof. Thach Nguyen, RMIT University (RMIT)

Physics, Photonics, Nonlinear Optics, Nonlinear Photonics, Integrated Optics, Lithium niobate, Nano and Micro fabrication

Despite the potential of nonlinear optics for all-optical information processing, no ideal nonlinear material has yet emerged to complement silicon photonics. Lithium niobate (LiNbO₃), with both second-order (χ²) and third-order (χ³) nonlinearities, is useful for electro-optic modulation and all-optical signal processing. Recently, thin-film lithium niobate (TFLN) on insulator wafers has become a promising platform for integrated nonlinear optics. It enables tightly confined waveguides, enhancing nonlinear effects and allowing dispersion engineering—crucial for efficient broadband processes like supercontinuum generation and optical frequency combs. RMIT and INL have developed a complementary approach to high-performance thin-film lithium niobate (TFLN) devices by using a patterned strip of another material, such as silicon nitride (Si₃N₄), instead of etching the lithium niobate itself. This method enables low-loss guided modes, avoids LN patterning, and still provides tight mode confinement (A_eff ~2 µm²) and dispersion engineering—both essential for nonlinear optics. While lithium niobate on insulator (LNOI) has been widely used in the telecom band, TFLN remains underexplored in the mid-IR, despite LN’s transparency up to ~5 µm, a range relevant for sensing biomolecular fingerprints in defence and environmental applications. The PhD objectives are:

(1) Design and fabricate low loss waveguides and high-quality factor resonators (microrings, racetracks or photonic crystal cavities) on TFLN grown on sapphire in collaboration with the industrial partner 3D oxides within the MIRLIN ANR project, and ILM, a partner in the project. The strip-loading approach will be pushed to its limits using various dielectric materials for the strip (SiN, Al2O3, PCM…) and other types of oxide materials.
(2) Benchmark the optical devices developed on this new material platform both in the near-IR and mid-IR wavelength ranges against devices fabricated using more traditional TFLN that is commercially available
(3) Explore the opportunities offered by the integration of phase change materials onto TFLN structures, for either optically “writing” guided wave optics chip-based devices on demand and/ or creating tunable devices.
(4) Develop periodic poling on the TFLN platform, as per the expertise of RMIT, for quasi-phase matching of nonlinear processes.
(5) Use the developed high-Q resonators and waveguides as building blocks to create efficient nonlinear devices in the near-IR but also in the mid-IR band.