Dynamical Complexity Induced by Frequency- dependent Optical Feedback in Dual-section Passive Mode-locked Quantum-dash Laser at ~ 1.55 µm (original) (raw)

Quantum nanostructure-based mode-locked (ML) dual-section semiconductor lasers have received much attention in recent years due to their potential applications in high-speed optical telecommunications and clocking. Particularly, passively mode-locked lasers subject to optical feedback or optical injection possess a rich diversity of dynamical regimes including lasing wavelength bistability, dropout dynamics and dark pulses due to their broadband gain and fast carrier dynamics. These processes are characterized by a large number of quite different characteristic time scales, which determine the quality of mode-locked pulses and the dynamical behavior of the laser in general. Instabilities need to be identified and studied, with a view to their suppression and exploitation in telecommunication networks. In this work, we present experimental studies of complex nonlinear dynamics in mode-locked quantum-dash lasers subject to frequency dependent optical feedback with fixed filtering. Filtered or dispersive optical feedback offers advantages over conventional optical feedback as its provides specific controllable spectral content of feedback to manipulate the laser dynamics, specifically by varying the filter bandwidth and detuning from the free running mode-locked frequency, without introducing attenuating optics in the feedback loop. In addition, we discuss how the various dynamical regimes of the mode-locked laser with filtered optical feedback depend on the filter bandwidth and frequency and also how the presence of particular dynamical states can induce a significant change in the timing jitter of a mode-locked pulse train. We suggest that the dynamics are manipulated and controlled by changes in phase-amplitude coupling, and thus strong carrier dependence of the index on carrier density and varying with dispersive optical feedback. Physically, when the free running mode-locking frequency is on the blue side of the filter center frequency then the feedback induces a red-shift in frequency with reduced phase-amplitude coupling factor α. Our technique provides a simple and low cost way to effectively control the Rf dynamics of the mode-locked laser diode and here its uses as an optical clock, lidar or frequency comb.

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