Investigation of Intermodal Four-Wave Mixing for Continuous-Wave Photon-Pair Generation

We experimentally demonstrate the various intermodal and intramodal four-wave mixing processes in a few-mode fiber with three modes using non-degenerate pumps. We distinguish the processes by calculating their phase mismatch and identify the intermodal spontaneous four-wave mixing process that generates entangled photon pairs in various modes. We achieve this using continuous-wave beams and the seeding technique due to the low efficiency of the spontaneous four-wave mixing effect in the fiber. We seeded the Stokes and anti-Stokes waves and measured the spectral content of each mode while moving the seed away from the perfect phase-matched condition in the fiber under test. We observe that the closer the seed gets to the pumps, the higher the efficiency of the four-wave mixing process.