Compact, tunable microring resonator on a lithium niobate platform using etchless fabrication methods

Tunable microring resonators on a lithium niobate on insulator (LNOI) platform are demonstrated, making use of thick polymer strip-loaded waveguides and bound states in the continuum (BIC) to achieve compact devices without plasma etching. The racetrack resonator device, with a bend radius of 94 μm , demonstrates strong confinement for TM-polarized modes, enabling electro-optic modulation with a modest half-wave voltage–length product of 35 Vcm . The device achieves a loaded quality factor of 4.17 × 10 4 for TM polarization and also supports purely linear TE modes with a loaded quality factor of 1.1 × 10 4 through guiding in the polymer layer. This etch-free process simplifies fabrication while maintaining access to lithium niobate’s χ (2) nonlinearity, offering a scalable route for photonic integrated circuits that combine reduced footprint, effective electro-optic performance with future potential for polarisation diversity on-chip.