Towards observation of sub-diffractive pulse propagation in photonic crystals

It is shown that sub-diffractive (self-collimating) propagation of ultrashort pulses of narrow light beams is possible in two dimensional planar photonic crystal slabs (in particular made with air holes in Si3N4 slab) where the sub-diffractive propagation of monochromatic beam of visible light has been demonstrated previously both theoretically and numerically. We found that the sub-diffractive propagations of the pulses of duration of more than 40 fs are indistinguishable from that of monochromatic beams. However, for the pulses with duration less than 40 fs their propagation peculiarities associated with asymmetric spatiotemporal misshaping, spatial and temporal broadening come into play. The effects are pronounced for the pulses of duration less than 20 fs. The phenomena are shown for both TM and TE polarized light by means of numerical integration of 2D Maxwell's equations with finite-difference time-domain technique.