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We studied the injection current dependence of room-temperature lasing spectra of a 1.3-μm self-assembled InAs/GaAs quantum-dot laser both experimentally and theoretically. Starting from the ground-state lasing with a few longitudinal modes, the spectra showed splitting, broadening, excited-state lasing, and quenching of the ground-state lasing as the current increased. We could explain this unique current dependence by numerical simulation based on our quantum-dot laser theory, taking into account the inhomogeneous and homogeneous broadening of the optical gain as well as the carrier relaxation processes in the spatially isolated quantum dots. Through the simulation, we found that the homogeneous broadening of the ground state is kept between 5 and 10 meV under the ground-state lasing, while it increases up to 20 meV under the excited-state lasing. [ABSTRACT FROM AUTHOR]

Uncooled 25 Gbit/s direct modulation of 1.3 µm DFB lasers is demonstrated. The 150 µm-long semi-insulating buried-heterostructure AlGaInAs quantum-well DFB lasers show clear eye-openings with dynamic extinction ratio of 5 dB up to 70°C. 13 km singlemode-fibre transmission experiments using the devices show low power penalty within 1.3 dB between 25 and 70°C. These characteristics are the first achievement by 1.3 µm directly modulated lasers. [ABSTRACT FROM AUTHOR]