Polarization-dependent intermodal four-wave mixing in a birefringent multimode photonic crystal fiber

In this Letter, polarization-dependent intermodal four-wave mixing (FWM) is demonstrated experimentally in a birefringent multimode photonic crystal fiber (BM-PCF) designed and fabricated in-house. Femtosecond pump pulses at wavelengths similar to 800 nm polarized along one of the principal axes of the BM-PCF are coupled into a normal dispersion region away from the zero-dispersion wavelengths of the fundamental guided mode of the BM-PCF. Anti-Stokes and Stokes waves are generated in the 2nd guided mode at visible and nearinfrared wavelengths, respectively. For pump pulses at an average input power of 500 mW polarized along the slow axis, the conversion efficiencies eta(as) and eta(s) of the anti-Stokes and Stokes waves generated at wavelengths 579.7 and 1290.4 nmare 19% and 14%, respectively. For pump pulses polarized along the fast axis, the corresponding eta(as) and eta(s) at 530.4 and 1627 nm are 23% and 18%, respectively. We also observed that fiber bending and intermodal walk-off have a small effect on the polarization-dependent intermodal FWM-based frequency conversion process. (C) 2017 Optical Society of America