Mode-controlled four-wave-mixing in the birefringent microstructure fiber by femtosecond laser pulses

Birefringent microstructure fibers are shown to allow efficient gereration of anti-Stokes line emission as a result of four-wave-mixing in higher mode by using unamplified femtosecond Ti:sapphire laser pulses. Intense blue-shifted lines with different central wavelength were generated in the high-delta (i.e.high-air filling in the cladding) microstructure fiber with axis sizes 5.0 and 4.6 mu m by femtosecond laser pulses with 35-fs in duration, 820nm in central wavelength and 4nJ in energy per pulse. The experimental result shows that phase-matched four-wave mixing in higher-order modes of microstructure fibers allows unprecedentedly high efficiencies of anti-Stokes frequency conversion to be achieved for subnanojoule femtosecond laser pulses. The dependence factor of the four waves mixing in hirefringent microstructure fiber is compared and analyzed. Good agreement between the theory and experiment is achieved.