Fiber-coupled plug-and-play heralded single photon source based on Ti:LiNbO$_3$ and polymer technology

Abstract: A reliable, but cost-effective generation of single-photon states is key for practical quantum communication systems. For real-world deployment, waveguide sources offer optimum compatibility with fiber networks and can be embedded in hybrid integrated modules. Here, we present the first chip-size fully integrated fiber-coupled Heralded Single Photon Source (HSPS) module based on a hybrid integration of a nonlinear lithium niobate waveguide into a polymer board. Photon pairs at 810nm (signal) and 1550nm (idler) are generated via parametric down-conversion pumped at 532nm in the $\mathrm{LiNbO_3}$ waveguide. The pairs are splitted in the polymer board and routed to separate output ports. The module has a size of $(2 \times 1)\, \mathrm{cm^2}$ and is fully fiber-coupled with one pump input fiber and two output fibers. We measure a heralded second-order correlation function of $g_h^{(2)}=0.05$ with a heralding efficiency of $\eta_h=4.5\, \mathrm{\%}$ at low pump powers.