Monolithic 1.58-micron InAs/InP quantum dash passively mode-locked lasers

Abstract

Monolithic InAs quantum dash 1.58-micron passively mode-locked lasers grown on an InP substrate are reported. A repetition rate of up to 18.5 GHz has been realized. The dashes-in-a-well (DWELL) active region consists of 5 stacks of InAs quantum dashes embedded in compressively strained Al_0.20Ga_0.16In_0.64As quantum wells separated by 30-nm undoped tensile-strained Al_0.28Ga_0.22In_0.50As spacers on both sides of the DWELL. 4 micron-wide ridge waveguides with cavity lengths in the range of 2.3 to 4 mm were fabricated with multiple electrically-isolated anode contacts. The modal gain and loss spectra of the InAs active region were then measured through the improved segmented contact method, and the characteristics that make InAs quantum dash materials system desirable for semiconductor mode-locked lasers were identified. The segmented waveguides were then reconfigured into mode-locked lasers by wire bonding the segments together to form separate gain and absorber regions utilizing the same DWELL active region. A highly reflective coating (95%) was applied to the mirror facet next to the absorber while the other facet was cleaved. To assist in the cavity design and to determine the relative length of the absorber and gain sections, a model for the cavity geometry of the twosection passively mode-locked lasers was studied and is based on a microwave photonics perspective. A new set of theoretical equations was used to find the optimal device layout using the measured modal gain and loss characteristics as input data.