Envelope and phase evolution of femtosecond pulses in hollow photonic-crystal fibres

Changes in the envelope and the evolution of the spectral phase and chirp of femtosecond pulses propagating through hollow fibres with a photonic-crystal cladding are experimentally studied. Envelope and phase distortions of ultrashort pulses transmitted through such fibres are shown to be controlled by the detuning of the carrier frequency of laser pulses from the central frequency of the passband in the transmission of the fibre. Near the passband edges, which map the edges of photonic band gaps of the fibre cladding, ultrashort pulses transmitted through the fibre display considerable envelope distortions, as well as frequency- and time-dependent phase shifts.