Lithium niobate tantalate mixed crystals: a versatile platform for nonlinear quantum processes

Many quantum optical applications in spectroscopy, communication and signal analysis rely on spectrally-engineered nonlinear optical interactions to target specific wavelengths or bandwidth. Here, in an established material platform like lithium niobate the achievable wavelength and bandwidth combinations are usually limited by the material’s dispersion and its birefringence. In this regard, mixed crystals of lithium niobate tantalate (LNT) promise a novel material platform, because they allow tuning the birefringence, which is central for type II phase matching devices. Crucially, LNT offers crystal compositions without any birefringence, which still retain their second-order optical nonlinearity. Despite recent progress in the growth and fabrication of LNT, so far no works have investigated the unique properties of LNT for use in electro-optics, nonlinear or quantum optics. In this study, we explore nonlinear optical devices based on LNT for broad- and narrowband nonlinear optical interactions based on recently measured Sellmeier coefficients. Most interestingly, we find that compositions without birefringence allow the design of broadband, degenerate type II phase matching sources spanning the whole near- to mid-infrared range by only changing the poling period and pump wavelength. Such devices are not easily realizable in pure lithium niobate or lithium tantalate. This could potentially allow for more flexible light sources and nonlinear devices in quantum metrology, quantum spectroscopy and quantum communication.