Tunable sum-frequency generation in modal phase-matched thin film lithium niobate rib waveguides

Noncritical birefringence phase-matched second harmonic generation in a lithium-niobate-on-insulator micro-waveguide for green light emission

Lithium niobate on insulator (LNOI) holds great potential for frequency conversion, where a variety of high-performance nonlinear devices based on different structures has been demonstrated. Here, we report on second harmonic generation (SHG) in MgO-doped LNOI ridge micro-waveguides for efficient green light emission, via an exact type-I noncritical birefringence phase matching (BPM). The LNOI micro-waveguide has a cross section of ∼3×4 μm2, featuring low coupling loss with lens fiber. The normalized conversion efficiency from a continuous-wave (cw) pump to its second harmonic is measured to be 37%/Wcm2 in a single-pass configuration. The device shows both relatively high efficiency and a void of periodic poling, offering a potential solution for efficient and scalable green light sources and frequency converters.

High-efficiency second harmonic generation in a micro-resonator on dual-layered lithium niobate

High-quality micro-resonators on thin-film lithium niobate (TFLN) have emerged as an ideal platform for on-chip nonlinear optical applications due to their strong light confinement and excellent natural nonlinear optical properties. Here, we present high-efficiency second-harmonic generation (SHG) in micro-resonators on a TFLN based on the modal phase matching and natural quasi-phase matching. By optimizing the phase-matching conditions through thermal tuning, we demonstrate an on-chip SHG efficiency of 149,000%/W in the low power regime. Furthermore, we achieve an absolute conversion efficiency of 10.3% with a 0.3 mW pump power. Our work paves the way toward future efficient on-chip frequency conversion of classical and quantum light without the need for poling of the LN films.