  Soliton self-compression is demonstrated during the propagation of high
spatial modes in hollow core fibers in the near-infrared spectral region,
taking advantage of their negative dispersion response. We have found that
there is always an optimum spatial mode to observe this phenomenon, compressing
the pulses down to the single-cycle regime without needing any external
compression device and with a consequent increase in the output peak power. Our
result is relevant for any ultrashort laser application in which few- or
single-cycle pulses are crucial.
