Dual-State Absorber-Photocurrent Characteristics and Bistability of Two-Section Quantum-Dot Lasers

The peculiar behavior of the absorber photocurrent of two-section quantum-dot lasers with different gain-bandwidth chirping is studied numerically and by experiments. By biasing the absorber section of a strongly chirped laser with a self-generated positive voltage or with a reverse-bias, different emission-state lasing regimes also involving a smooth emission-state-transition from quantum-dot ground-state to excited state via simultaneous ground- and excited-state are observed. The gradual emission state and photocurrent transitions are simulated and are in excellent agreement with experiments. In contrast, in a medium-chirped laser a photocurrent and emission-state bistability with hysteresis is experimentally observed involving a transition from sole ground state to sole excited state. Thereby, no intermediate simultaneous dual-state emission regimes occur suggesting the exclusion of simultaneous dual-state emission and bistability. This peculiar bistable behavior is explained qualitatively and offers the potential to be exploited toward switching applications.