Ultrabroadband second-harmonic generation based on a dispersion-engineered lithium niobate on insulator waveguide

Second-harmonic generation (SHG) is widely used for wavelength conversions in various applications including multi-wavelength lasers, imaging, and ultrafast optics. However, it remains a long-standing challenge to achieve both a broad SHG bandwidth and high efficiency due to the medium dispersion. Here, we propose an ultrabroadband efficient SHG on a lithium niobate on insulator (LNOI) platform by dispersion engineering. The waveguide cross section with two V-shaped grooves is carefully designed to minimize first- and second-order dispersion, which is feasible for current fabrication techniques. Due to the flattened dispersion, a record-high, to our knowledge, bandwidth-length product ( Δ λ ⋅ L ) of 2444 µ m 2 is achieved in a periodically poled 1.64-cm-long LNOI waveguide, which is four times the previously reported result. Such a scheme can also be generalized to SHG waveguides on other material platforms. Our results provide a new strategy of dispersion engineering for integrated photonics, and may be helpful for applications including frequency doubling, supercontinuum generation, and optical frequency combs.