Multiplex frequency conversion of femtosecond laser pulses in trefoil and quatrefoil channels of a holey fiber

We report that trefoil and quatrefoil silica channels with sizes ranging from 0.6 μm to as large as 4–5 μm in a holey fiber can strongly confine the light field and act as highly nonlinear waveguides. Supercontinuum emissions, efficient dispersive-wave generation and parametric four-wave-mixing processes were achieved in these channels with sub-nanojoule femtosecond Ti:sapphire laser pulses. Two dispersion curves corresponding to two orthogonal modes in each channel were simulated and used to explain the experimental results.