Driven bright solitons on a mid-infrared laser chip.

Despite the continuing progress in integrated optical frequency comb technology, compact sources of short, bright pulses in the mid-infrared wavelength range from 3 to 12 μm so far remain beyond reach. The state-of-the-art ultrafast pulse emitters in the mid-infrared are complex, bulky and inefficient systems based on the downconversion of near-infrared or visible pulsed laser sources. Here we show a purely DC-driven semiconductor laser chip that generates 1-ps solitons at the centre wavelength of 8.3 μm at GHz repetition rates. The soliton generation scheme is akin to that of passive nonlinear Kerr resonators. It relies on a fast bistability in active nonlinear laser resonators, unlike traditional passive mode-locking, which relies on saturable absorbers, or active mode-locking by gain modulation in semiconductor lasers. Monolithic integration of all components-drive laser, active ring resonator, coupler and pump filter-enables turnkey generation of bright solitons that remain robust for hours of continuous operation without active stabilization. Such devices can be readily produced at industrial laser foundries using standard fabrication protocols. Our work unifies the physics of active and passive microresonator frequency combs while simultaneously establishing a technology for nonlinear integrated photonics in the mid-infrared.