Nonlinear Transmission Of Ps-Pulses Through Optical Fibers

Abstract

Nonlinear transmission of ps- pulses through optical fibersB. Valk, W. Hodel and H.P. WeberInstitute of Applied Physics, University of Bern, CH-3012 BernSwitzerlandAbstractIntense ps- pulses are spectrally broadened after transmission through a singlemode fiber.The obtained spectra showed a strong sensitivity to the temporal symmetry and polarizationof the input pulses.IntroductionIn the past few years a lot of work has been done on the subject of nonlinear pulse pro-pagation in optical fibers. The combined effect of self -phase -modulation (SPM) and group -ve-locity- dispersion (GVD) can lead to optical solitons in the anomalous dispersion region' andin the normal dispersion regime it offers the possibility of pulse compression2.In the visible, an analytical solution of the nonlinear wave equation including disper-sion is not possible. Additionally, the modification of the output spectrum by effects likeselfsteepening',`` and random birefringence in non polarization maintaining fibers' is diffi-cult to predict. Most published experiments were performed with ps- pulses of medium intensi-ties where a comparision with theory was possible ,'. However, at high powers some unexpec-ted spectra were found'.Here we report about measured spectra of high intensity ps- pulses after transmissionthrough a singlemode fiber. These spectra were in general asymmetric and very sensitive tothe alignment of the dye laser and to the polarization of the input pulses.Experimental set upThe experimental set up is shown in Fig. 1. A cavity- dumped Rh6G dye laser was synchro-nously pumped by a cw frequency - doubled modelocked Nd:YAG laser (Quantronics). Pulses withpeak powers of up to 5 kW have been achieved with this system. From the shape of the auto -correlation trace we conclude that the laser emits exponential pulses of about 2 ps duration.The spectral width was 0.22 nm (FWHM) indicating that the pulses were not quite bandwidthlimited.