Chip-integrated extended-cavity mode-locked laser in the visible.

Mode-locked lasers are of interest for applications such as biological imaging, nonlinear frequency conversion, and single-photon generation. In the infrared, chip-integrated mode-locked lasers have been demonstrated through integration of laser diodes with low-loss photonic circuits. However, additional challenges, such as a higher propagation loss and smaller alignment tolerances, have prevented the realization of such lasers in the visible range. Here, we demonstrate the first, to the best of our knowledge, chip-integrated mode-locked diode laser in the visible using an integrated photonic circuit for cavity extension. Based on a gallium arsenide gain chip and a low-loss silicon nitride feedback circuit, the laser is passively mode-locked using a saturable absorber (SA) implemented by focused ion beam (FIB) milling. At a center wavelength of 642 nm, the laser shows an average output power of 3.4 mW, with a spectral bandwidth of 1.5 nm at a repetition rate of 7.84 GHz.