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Exposing semiconductor lasers to external optical feedback can significantly affect their emission properties by, e.g., generating complex dynamics or enabling coherence control. When considering semiconductor multi-wavelength lasers, i.e., lasers designed to emit at two or more distinct wavelengths, feedback has been used to demonstrate emission switching between the different wavelengths. In particular, by controlling the phase shift in the feedback cavity, fast (nanosecond timescale) wavelength switching between two, three and even four of the lasing modes, separated by more than a THz, has been observed experimentally.
The wavelength control is not straightforward since the response of the laser depends on various parameters such as the differential gain between the modes or the cross-saturation parameters (or carrier population gratings). Based on a model relying on a multi-mode extension of Lang-Kobayashi rate equations, we explore the parameter space in terms of feedback strength, delay and modal phases, to identify regions suitable for wavelength switching. In this direction, we determine a feedback strength threshold and detect the appearance of dynamics with longer delays.
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