Time-stretch Dispersive Fourier Transform Research Articles

Revealing the buildup of dynamic mode-switchable frequency-shifted feedback laser based on photon–phonon interaction

Photon-phonon interaction (PPI) is an intriguing physical phenomenon in which the dynamic photon-phonon energy transfer allows the manipulation of acousto-optic properties in the media. Recently, there has been significant interest of PPI as it accompanies the conservations of energy and momentum processes. Mode-locking is a process in which temporal and spatial resonant modes establish stable synchronization through non-linear interactions. Here, we propose and reveal the buildup of a dynamic mode-switchable frequency-shifted feedback laser in which frequency shift and mode conversion are achieved based on PPI. Moreover, dynamic switching between LP11a/b mode and stable donut mode output is achieved and precisely controlled by PPI. Finally, by using the time-stretch dispersive Fourier transform (TS-DFT) detective system, we observe the transient dynamics established in frequency-shifted feedback (FSF) fiber laser, such as the direct evolution from continuous wave (CW) state to mode-locked state, CW state to multipulse state and subsequently to stable mode-locked state. All these findings would unveil the buildup of mode-locking mechanisms of dynamic mode-switchable FSF fiber lasers based on PPI with more degrees of freedom and unlock new possibilities in ultrafast laser-based technology, optical communication and light control.

Transient dynamics in mode-locked all-PM Er-doped fiber laser with NALM

In this study, we utilized the Time-Stretch Dispersive Fourier Transform (TS-DFT) method to explore rapid transient states in both time and frequency domains of an all-polarization-maintaining dispersion-managed figure-eight mode-locked laser with Nonlinear Amplifying Loop Mirror (NALM). We detail the different stages of build-up dynamics at varying pump powers, encompassing the Q-switching (QS) stage, transient single pulse formation, pulsation beating patterns, bound states, and the final transition to a single pulse state. Our findings reveal that the mode-locked bound state regime emerges from a single pulse stage following QS, different from previously reported directly resulting from QS pulses or relaxation oscillations. In a novel contribution to the field, we have experimentally demonstrated the transient single pulse stage of build-up dynamics and compared it with the fundamental mode-locked single pulse.

Single-shot observation of stretched-pulse buildup dynamics in an ultrafast fiber laser

Time-stretch dispersive Fourier transform (TS-DFT) technique offers a powerful way to investigate the non-repetitive formation dynamics of mode locking. Here we have unveiled the entire buildup dynamics of stretched pulse in a passively mode-locked fiber laser using TS-DFT technique. The entire buildup dynamics include relaxation oscillation, transient bound states, beating dynamics, intensity fluctuation and stable stretched pulse finally. These results provide a direct insight into the start-up dynamics of stretched pulse, which could be helpful for the understanding of mode locking formation mechanism.

Reconstruction in time-bandwidth compression systems

Recently, it has been shown that the intensity time-bandwidth product of optical signals can be engineered to match that of the data acquisition instrument. In particular, it is possible to slow down an ultrafast signal, resulting in compressed RF bandwidth—a similar benefit to that offered by the Time-Stretch Dispersive Fourier Transform—but with reduced temporal record length leading to time-bandwidth compression. The compression is implemented using a warped group delay dispersion leading to non-uniform time stretching of the signal's intensity envelope. Decoding requires optical phase retrieval and reconstruction of the input temporal profile, for the case where information of interest resides in the complex field. In this paper, we present results on the general behavior of the reconstruction process and its dependence on the signal-to-noise ratio. We also discuss the role of chirp in the input signal.