Tailoring the spectro-temporal mode of photon pairs generated from interspatial-mode four-wave mixing

We investigate the spectro-temporal mode property of the photon pairs generated via interspatial-mode spontaneous four-wave mixing (FWM) in a few-mode fiber (FMF) that supports two linearly polarized spatial modes in the 1550 nm telecom band. The two pulsed pumps for the process are in distinct spatial modes, while the created signal and idler photon pairs are also occupying different spatial modes. By exploiting the unique inter-mode phase matching condition in the FMF, we can tailor the spectro-temporal mode structure of the photon pairs by changing the pulse duration (spectral bandwidth) of the two pumps. Especially, photon pairs with a nearly round-shaped factorable joint spectrum are experimentally realized. The techniques are valuable for generating and manipulating quantum states in multi-mode waveguides and exploiting the spatial degree of freedom in quantum information processing.