Intrinsic Discrepancy of Multi-Soliton Interferogram in Dispersive Fourier Transform Measurements Due to Impulsive Response of Fast Electronics

Time-stretched dispersive Fourier transform (TS-DFT) technique has been widely used for studying transient soliton dynamics due to its unique capability of direct time-frequency mapping of ultrafast pulses in the real time. Particularly, multi-soliton structures that are ubiquitous in ultrafast lasers have been routinely analyzed using TS-DFT technique, giving concurrently spacing and relative-phase information during soliton interactions. While the TS-DFT signal recorded by the fast electronics would inevitably deviate from the genuine spectral interferogram, the consequent discrepancies have not, however, been systematically interrogated yet. In this work, we performed detailed comparisons between the temporal TS-DFT signal of multi-soliton structures (with tunable spacings and phases) and their genuine spectral interferograms measured using optical spectrum analyzer. We revealed that due the impulsive response of the detection system, the retrieved relative-phases from the TS-DFT signal could have non-trivial discrepancies from their actual values, even though the bandwidth of the detection electronics is a few times broader than that of the TS-DFT signal. Our findings can help to provide clearer insights in multi-soliton dynamics using TS-DFT technique.