Dissipative Kerr solitons in semiconductor ring lasers

Dissipative Kerr solitons are self-organized optical waves arising from the interplay between the Kerr effect and dispersion. They can form in nonlinear microresonators by deliberately tuning the parameters of the external pump laser, which provides the parametric gain for the proliferation of an ultrastable frequency comb. These miniaturized and battery-driven microcombs have become a disruptive technology for precision metrology, broadband telecommunication and ultrafast optical ranging. Here we report the experimental observation of dissipative Kerr solitons generated in a ring cavity with a fast semiconductor gain medium. The moderate quality factor of the ring cavity is compensated by the giant resonant Kerr nonlinearity of a quantum cascade laser, which is more than a million times larger than that in Si3N4. By engineering the dispersion of the cavity, we observe the formation of bright dissipative Kerr solitons in the mid-infrared range. Two independent techniques shed light on the waveform and coherence of the solitons and confirm a reconstructed temporal width of ~3 ps. In addition, background-free 3.7 ps soliton pulses are demonstrated by optically filtering out the dispersive wave. Our results extend the spectral range of soliton microcombs to mid-infrared wavelengths and will lead to integrated, battery-driven and turnkey spectrometers in the molecular fingerprint region.