Mid-infrared light generation in a lithium niobate microdisk without any periodic poling structure

Whispering gallery resonators (WGRs) represent a class of optical devices capable of achieving optical parametric oscillation (OPO) with low thresholds. When combined with periodic poling technology, they enable output at any wavelength within the transparency range of lithium niobate (LN). However, the integration of poling technology invariably introduces additional fabrication steps, thereby prolonging the resonator preparation cycle. We propose mid-infrared laser output from a lithium niobate microdisk without any poling structure, based on Type I and modal phase matching. The microdisk exhibits a Q-factor of 1.23 × 10⁶, can generate idler wavelengths up to 4101 nm, and achieves a nonlinear conversion efficiency of approximately 4.2%. This approach circumvents the necessity for poling processes, thereby streamlining the fabrication workflow. Furthermore, it provides a viable solution for the efficient production of LN-based MIR compact light sources.