Periodically poled lithium niobate ring resonators for efficient second-order optical nonlinear interactions

The large second-order optical nonlinearity of lithium niobate renders it attractive for optical frequency conversion, cascaded photon pair generation, optical frequency combs, and other applications. A key goal is to minimize the input power required to achieve the desired nonlinear effect. We are progressing toward this goal using three tools: poling an etched lithium niobate ring resonator to increase the effective interaction length; using a pulsed pump to reduce the average input power; and dispersion engineering the poled resonator segment to reduce temporal walk-off between the pump and the optical harmonic output. Here, we consider second-harmonic generation as a benchmark towards more advanced applications, such as supercontinuum generation via cascaded second-order nonlinear interactions. We discuss our progress, including measurements of second harmonic signals, with a detailed systems analysis. Our work is a step toward ultra-low power second-order nonlinear interactions.