Single-shot dynamics of dual-comb generation in a polarization-multiplexing fiber laser.

Dual optical frequency combs have been a recurrent case of study over the last decade due to their wide use in a variety of metrology applications. Utilizing a single cavity laser to generate a dual comb reduces system complexity and facilitates suppression of common noise. However, a dual-comb regime in single cavity lasers tends to be more unstable and difficult to achieve. Therefore, having a better understanding about the way they are generated could improve and automate their generation and control. In this paper, we investigate the build-up dynamics and collision of dual comb in a polarization-multiplexing ring-cavity fiber laser using DFT (Dispersive Fourier Transform) method. We observe a bunch of meta-stable short-lived mode-locking states before the laser entered the dual-comb mode-locking state. The energy level of this short-lived initial pulses determines its evolution. If it decreases too much, the pulse will eventually collapse while if it stays above certain level, it will be successfully generated. The results presented in this paper increase the understanding of dual-comb generation inside a single cavity laser and may contribute in future attempts to increase the stabilization of this regime.

Polarization attractors driven by vector soliton rain.

Soliton rain is a bunch of small soliton pulses slowly drifting near the main pulse having the period of a round trip. For Er-doped fiber laser mode-locked by carbon nanotubes, for the first time, we demonstrate both experimentally and theoretically a new type of polarization attractors controllable by vector soliton rain. With adjusting the pump power, vector soliton rain takes the form of pulses with rotating states of polarization which enable transforming slowly evolving trajectories on the Poincaré sphere from the double-scroll spiral to the circle. The obtained results on controlling complex multisoliton dynamics can be of interest in laser physics and engineering with potential applications in spectroscopy, metrology, and biomedical diagnostics.

Isolator-free switchable uni- and bidirectional hybrid mode-locked erbium-doped fiber laser.

An Erbium-doped fibre ring laser hybrid mode-locked with single-wall carbon nanotubes (SWNT) and nonlinear polarisation evolution (NPE) without an optical isolator has been investigated for various cavity conditions. Precise control of the state of polarisation (SOP) in the cavity ensures different losses for counter-propagating optical fields. As the result, the laser operates in quasi-unidirectional regime in both clockwise (CW) and counter-clockwise (CCW) directions with the emission strengths difference of the directions of 22 dB. Furthermore, by adjusting the net birefringence in the cavity, the laser can operate in a bidirectional generation. In this case, a laser pumped with 75 mW power at 980 nm generates almost identical 790 and 570 fs soliton pulses with an average power of 1.17 and 1.11 mW. The operation stability and pulse quality of the soliton pulses in both unidirectional regimes are highly competitive with those generated in conventional ring fibre lasers with isolator in the cavity. Demonstrated bidirectional laser operation can find vital applications in gyroscopes or precision rotation sensing technologies.