Mode-locked chip-integrated diode lasers in the visible spectral range

Mode-locked miniaturized lasers in the infrared have been demonstrated through integration of laser diodes with low-loss photonic integrated circuits. However, additional challenges at shorter wavelengths, such as higher loss, smaller tolerances and availability of integrated saturable absorbers have prevented the realization of such lasers in the visible range. Here, we demonstrate the first hybrid integrated mode-locked diode laser in the visible (λ=640nm), based on a gallium-arsenide gain chip and a low-loss silicon nitride feedback chip. The laser is passively mode-locked using a saturable absorber, realized through electrical isolation of part of the gain section by focused ion beam milling. The laser shows a broad range of driving parameters that support stable mode-locking, achieving a maximum average output power of 3.2mW, with a spectral bandwidth of 1.5nm. Measurements reveal a repetition rate of 7.84GHz, with a corresponding Lorentzian RF linewidth component of 11.4kHz.