Temporal Stability and Spectral Accuracy Enhancement of the Spectro-Temporal Analyzer

Abstract

The advent of the time-stretch technology, together with the high-speed photodetector, enables ultrafast spectrum analysis in the form of spectro-temporal analyzer, such as the amplified dispersive Fourier transform (ADFT) and the parametric spectro-temporal analyzer (PASTA). Leveraging the MHz to GHz frame rate, such a spectro-temporal analyzer is capable of observing certain ultrafast or non-repetitive events, such as the birth of mode-locking. However, since it always requires a large amount of dispersion, the spectral accuracy will be greatly degraded by the temporal instability, including the temperature-induced timing jitter and the cavity-induced frequency jitter, which hinder the practical application of such an ultrafast spectroscopy technique. To enhance the temporal stability and thereby spectral accuracy, two active control schemes are introduced here: the temperature feedback control for the long fiber link, and the phase-locked loop for the short laser cavity. As a result, the temporal stability is greatly enhanced, and the spectral accuracy is improved from 1.6 to 0.04 nm over a 5-h period of time. This stabilization process is an essential step for the practical application of spectro-temporal analyzers, such as the ADFT and particularly the PASTA.