Passive mode-locking in the cavity of monolithic GaN-based multi-section laser diodes

We demonstrate picosecond pulse generation in the blue-violet wavelength region by passive mode-locking in monolithic GaN-based ridge waveguide laser diodes with integrated absorbers. For cavity lengths between 1.5 and 0.45 mm we observe pulse repetition frequencies between 34 and 92 GHz, and pulse widths down to 3 ps at absorber biases around -10V and 0V. The quality of the pulses is related to a broad and homogeneous spectrum. At zero absorber bias passive mode-locking is only achieved in long cavities with absorbers smaller than 10% of the cavity length. A laser diode with a longer center absorber exhibits higher harmonics with supermode noise. We study samples from three epitaxial designs with different quantum well numbers and widths. The bias-dependent carrier lifetime in the absorber is determined by electroluminescence decay and decreases below 40 ps at large negative bias