Simultaneous Type-0 and Type-I Optical Parametric Oscillation in Submicron Poled Thin-Film Lithium Niobate

We demonstrate dual optical parametric oscillations in a thin-film lithium niobate microring resonator enabled by polarization-insensitive submicron periodic poling. Under degenerate backward quasi-phase matching, the counter-propagating signal and idler wavevectors cancel, such that the phase-matching condition is determined solely by the pump wavevector. As a result, a single submicron poling period simultaneously supports both Type-0 (TM $\rightarrow$ TM + TM) and Type-I (TM $\rightarrow$ TE + TE) parametric interactions in the same device. Temperature-controlled resonance alignment further enables selective activation of either polarization channel. We observe optical parametric oscillation with thresholds of 290\,{\textmu}W for the Type-0 process and 3\,mW for the Type-I process, both comparable to state-of-the-art on-chip OPO thresholds. These results establish submicron poled TFLN as a compact and reconfigurable platform for polarization-diverse parametric light generation.