Abstract:We experimentally investigate the noise properties of picosecond supercontinuum spectra generated at different power levels in uniform and tapered photonic crystal fibers. We show that the noise at the spectral edges of the generated supercontinuum is at a constant level independent on the pump power in both tapered and uniform fibers. At high input power the spectral bandwidth is limited by the infrared loss edge, this however has no effect on the noise properties.

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We demonstrate how the gradient of the tapering in a tapered fiber can significantly affect the trapping and blueshift of dispersive waves (DWs) by a soliton. By modeling the propagation of a fundamental 10 fs soliton through tapered fibers with varying gradients, it is shown that the soliton traps and blueshifts an increased fraction of the energy in its DW when the gradient is decreased. This is quantified by the group-acceleration mismatch between the soliton and DW at the entrance of the taper. These findings have direct implications for the achievable power in the blue edge of a supercontinuum generated in a tapered fiber and explain observations of a lack of power in the blue edge.

Abstract:We use an asymmetric 2 m draw-tower photonic crystal fiber taper to demonstrate that the taper profile needs careful optimisation if you want to develop a supercontinuum light source with as much power as possible in the blue edge of the spectrum. In particular we show, that for a given taper length, the downtapering should be as long as possible. We argue how this may be explained by the concept of group-acceleration mismatch (GAM) and we confirm the results using conventional symmetrical short tapers made on a taper station, which have varying downtapering lengths.

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