Single-mode distributed feedback and microlasers based on quantum-dot gain material

Quantum-dot gain material fabricated by self-organized epitaxial growth on GaAs substrates is used for the realization of 980-nm and 1.3-μm single-mode distributed feedback (DFB) lasers and edge-emitting microlasers. Quantum-dot specific properties such as low-threshold current, broad gain spectrum, and low-temperature sensitivity could be demonstrated on ridge waveguide and DFB lasers in comparison to quantum-well-based devices. 980-nm DFB lasers exhibit stable single-mode behavior from 20°C up to 214°C with threshold currents < 15 mA (1-mm cavity length). Utilizing the low-bandgap absorption of quantum-dot material miniaturized monolithically integrable edge-emitting lasers could be realized by deeply etched Bragg mirrors with cavity lengths down to 12 μm. A minimum threshold current of 1.2 mA and a continuous-wave (CW) output power of >1 mW was obtained for 30-μm cavity length. Low-threshold currents of 4.4 mA could be obtained for 1.3-μm emitting 400-μm-long high-reflection coated ridge waveguide lasers. DFB lasers made from this material by laterally complex coupled feedback gratings show stable CW single-mode emission up to 80°C with sidemode suppression ratios exceeding 40 dB.