Experimental investigation of a parabolic pulse generation using tapered microstructured optical fibres

Abstract

It has been shown that the parabolic pulses can be generated under certain conditions within normally dispersive optical amplifiers by exploiting the interplay between gain, nonlinearity and dispersion. Passive means to generate parabolic pulses have also been exploited and in previous experiments it has been investigated e.g. in a comb-like profiled dispersion decreasing fibre or using single conventional dispersion decreasing optical fibres. Tapered microstructured optical fibres represent an alternative way to produce the required dispersion decreasing fibre. This method is ideal for producing metre-length tapers needed to efficiently generate parabolic pulses starting from femtosecond pulses.In this paper we experimentally and numerically demonstrate the possibility of parabolic pulse generation in a normally dispersive microstructured optical fibre taper. The microstructured optical fibre that was initially in the anomalous dispersion regime was tapered to achieve normal dispersion values. The fibre parameters were measured and the taper's parameters determined to obtain a desirable linear taper profile. Using novel tapering facility we fabricated 1.8m long taper. The experimental study of parabolic pulse generation has been compared with the numerical simulations. The pulse propagating through the taper was characterized using linear FROG method. A qualitative agreement between the results of experiment and simulation was demonstrated. The consistent convergence towards the parabolic pulse at the taper's output is observed with increasing in the input pulse power levels. The quality of the parabolic pulses was quantified using a misfit parameter, which reached value of 0.0032, when maximum power level has been applied. It has been shown that the initial pulse FWHM of 0.59ps has been shaped into a pulse of 1.22ps FWHM (which has a root mean square error against the parabolic fit of 0.0032). These results suggest the possibility of achieving better parabolic pulses if the optimum launching conditions can be achieved or longer taper fabricated