Joint Dispersion Engineered Thin-Film PP-LNOI Waveguide for Broadband and Highly Efficient Frequency Conversion from Near-Infrared to Mid-Infrared

We propose and numerically study a robust near- to mid-infrared (MIR, @2.9 ~ 3.6 μm) difference frequency generation (DFG) in a designed periodically poled thin-film lithium niobate on insulator (PP-LNOI) waveguide. Optimized design of the geometrical parameters and temperatures yields joint dispersion engineering of the waveguide, which can lead to simultaneous quasi-phase-matching and group refractive index matching. Meanwhile, large nonlinearity can be maintained due to the tight mode confinement nature of LNOI. As a result, the trade-off between bandwidth and efficiency is mitigated and the DFG process in the proposed PP-LNOI waveguide possesses both broad bandwidth and high efficiency. We show that the conversion efficiency of ~ 35% W−1 is achieved with a 3-dB bandwidth covering the entire low-loss MIR window of 2.9 ~ 3.6 μm (700 nm) of the SiO2 substrate. Remarkably high conversion efficiency of more than 4000% W−1 within a sacrificed, but still reasonable, 3-dB bandwidth of more than 200 nm is also achieved. The central wavelength of the high efficiency band can be flexibly tuned by varying the geometrical width and poling period. Given the same length of device, the conversion efficiency and bandwidth can exceed those of the bulk PPLN platforms by two and one orders of magnitude, respectively. Our results show useful guidance to achieve MIR waves with broad bandwidth and high efficiency, and confirm the PP-LNOI a versatile platform for chip-scale MIR frequency conversion and its potential applications.