Demonstration of Intermodal Four-Wave Mixing by Femtosecond Pulses Centered at 1550 nm in an Air-Silica Photonic Crystal Fiber

In this paper, we demonstrated experimentally the intermodal four-wave mixing effect by launching femtosecond pulses centered at 1550 nm into deeply normal dispersion region in the fundamental guided-mode of an air-silica photonic crystal fiber with two zero dispersion wavelengths. When intermodal phase-matching condition is satisfied, the energy of the pump waves at 1550 nm in the fundamental guided-mode is converted to the anti-Stokes waves around 1258 nm and Stokes waves around 2018 nm both in the second-order guided-mode. When femtosecond pulses at input average power P_av of 90 mW are propagated inside 22-cm-long photonic crystal fiber, the conversion efficiencies η_as and η_s of the anti-Stokes and Stokes waves generated are 8.5% and 6.8%, respectively. We also observed that the influences of the fiber bending and walk-off effect between the fundamental and second-order guided-modes on intermodal four-wave mixing-based frequency conversion process are very small.