Supercontinuum generation in higher order modes of photonic crystal fibre

Soliton behaviour in higher order electromagnetic (EM) modes in commercial highly nonlinear photonic crystal fibre (PCF) was investigated by mapping spatial and spectral emission. A femtosecond mode-locked Titanium:Sapphire laser was used to generate supercontinua within a set of higher-order electromagnetic modes by piezoelectric control of the spatial field input to the PCF. Coupling pump wavelengths within the normal dispersion regime for the fundamental EM mode into higher EM modes resulted in the emission of blue light, characteristic of higher order soliton fission, in higher order EM modes. Detailed spectral measurements across the spatial mode field output from the PCF, showed different spectral components of the generated continua occupying different spatial electromagnetic modes. In particular, the blue emission was found to be structured with spectral wavelengths at 440 nm and 450 nm associated with different spatial EM modes. These new measurements are the first to detail high order solitonic interactions in higher order electromagnetic modes and to record different spectral emission wavelengths associated with different higher order spatial modes. These results are not well matched to current theoretical models for supercontinuum generation developed for the fundamental EM mode. The lower zero dispersion wavelengths associated with higher EM modes in PCF enable previously undetected engagement of these modes in supercontinuum generation and propagation.