Inter-modal four-wave mixing study in a two-mode fiber

We demonstrate efficient four-wave mixing among different spatial modes in a 1-km long two-mode fiber at telecommunication wavelengths. Two pumps excite the LP₀₁ and LP₁₁ modes, respectively, while the probe signal excites the LP₀₁ mode, and the phase conjugation (PC) and Bragg scattering (BS) idlers are generated in the LP₁₁ mode. For these processes we experimentally characterize their phase matching efficiency and bandwidth and find that they depend critically on the wavelength separation of the two pumps, in good agreement with the numerical study we carried out. We also confirm experimentally that BS has a larger bandwidth than PC for the optimum choice of the pump wavelength separation.