Reversible and Tunable Second‐Order Nonlinear Optical Susceptibility in PZT Thin Films for Integrated Optics

Second‐order nonlinear optical processes enable a wide range of applications used in research and industry. The majority of available second‐order nonlinear devices however relies on bulk nonlinear crystals with low second‐order nonlinearity. By exploiting the advancements made in integrated optics, materials with large second‐order nonlinearity can enable efficient and small‐sized on‐chip nonlinear devices at low cost. Unfortunately, silicon and silicon nitride, mostly used for photonics integrated circuits exhibit negligible second‐order nonlinearity (χ(2)) and alternate materials have to be investigated. Lead zirconate titanate (PZT) thin films with high second‐order nonlinearity stand as a good candidate for on‐chip nonlinearity. An electric‐field induced tuning of χ(2) is demonstrated here in PZT thin films grown on glass substrates with a tuning efficiency of 3.35 pm V−2. Strong second‐harmonic generation is recorded and a very high dominant tensor component χzzz(2) of 128 pm V−1 is reported. The χ(2) of the PZT thin films can be reversed by poling with a DC electric field at room temperature. This opens avenues for highly efficient and tunable on‐chip nonlinear devices. The second‐order nonlinear properties of lead zirconate titanate (PZT) thin films grown on glass substrates were studied in second‐harmonic generation (SHG) experiments. By poling the thin films at room temperature, a tunable and reversible χ(2) is demonstrated. The PZT thin films can be directly grown on integrated waveguides using a low‐loss lanthanide‐based seed layer enabling a viable route for efficient on‐chip nonlinearity.