Complete characterization of terahertz pulse trains generated from nonlinear processes in optical fibers

The measurement technique of frequency-resolved optical gating (FROG) is used to characterize the intensity and phase of terahertz pulse trains generated from nonlinear and dispersive interactions in optical fibers. We show that existing FROG retrieval algorithms are easily adapted to allow the retrieval of periodic pulse characteristics and, using synthetic pulse trains generated from numerical simulations, we demonstrate how FROG can differentiate between periodic pulse trains with fundamentally different intensity and phase characteristics, yet qualitatively similar autocorrelation functions and spectra. Experimental results are presented for the FROG characterization of a 0.3-THz sinusoidal beat signal from a dual wavelength laser source, a 2.5-THz train of dark solitons generated in a high-birefringence fiber, and a 0.6-THz bright polarization domain wall soliton train generated in an ultra-low birefringence fiber. These results are shown to be in good agreement with nonlinear Schrodinger equation simulations