Spectrally pure photon pair generation in asymmetric heterogeneously coupled waveguides

In this work, we develop a design methodology to generate spectrally pure photon pairs in asymmetric heterogeneously coupled waveguides by spontaneous parametric down-conversion. Mode coupling system of is used directly tailor the group velocity supermode achieve matching (GVM) that otherwise not allowed material dispersion. Design examples based on thin film lithium niobate are provided, demonstrating high spectral purity and temperature tunability. This approach versatile strategy applicable different materials structures, allowing more versatility single-photon source designs.