SiN loaded thin film lithium niobate waveguides for the generation of spectrally uncorrelated photon pairs

Silicon nitride (SiN) loaded thin film lithium niobate (TFLN) is an emerging integrated photonics platform, which benefits from the simplified etching process of SiN as well as the favorable optical properties of lithium niobate (LN). Depositing a layer of SiN facilitates the fabrication of sub micron-sized waveguides on TFLN, dispersion properties of which can be tailored for efficient spontaneous parametric down-conversion (SPDC), giving rise to the desired biphoton state. In this work, we focus on this aspect and explore SiN loaded TFLN waveguides for the generation of spectrally uncorrelated photon pairs based on type-II phase-matched SPDC process. We perform extensive simulations and optimize the waveguide geometry to avoid lateral mode leakage and satisfy group index matching condition, required to achieve a spectrally factorizable photon pair state with high generation efficiency, which remains tolerant to imperfections in the fabrication. For this optimized waveguide design, we compute joint spectral intensity and report spectrally pure photons with high purity (>97% ). Such a novel source of uncorrelated photon pairs will serve as a crucial resource for various quantum optics tasks.