Ultra-wideband non-degenerate guided wave biphoton source in the near and mid-infrared

Abstract: Latest applications in ultrafast quantum metrology require bright and broadband biphoton sources with one photon in the mid-infrared and the other in the visible to near-infrared. However, existing sources based on bulk crystals are limited in brightness due to the short interaction length and allow only limited dispersion engineering. Here, we present an integrated PDC source based on a Ti:LiNbO$_3$ waveguide that generates broadband biphotons with central wavelengths at $860\,\mathrm{nm}$ and $2800\,\mathrm{nm}$. Their spectral bandwidth exceeds $25\,\mathrm{THz}$ and is achieved by simultaneous matching of group velocities and cancellation of group velocity dispersion for the signal and the idler field. We provide an intuitive understanding of the process by studying the behavior of our source at different temperatures and pump wavelengths, which agrees well with simulations.