Temperature stability of static and dynamic properties of 1.55 µm quantum dot lasers

Static and dynamic properties of InP-based 1.55 µm quantum dot (QD) lasers were investigated. Due to the reduced size inhomogeneity and a high dot density of the newest generation of 1.55 µm QD gain materials, ridge waveguide lasers (RWG) exhibit improved temperature stability and record-high modulation characteristics. Detailed results are shown for the temperature dependence of static properties including threshold current, voltage-current characteristics, external differential efficiency and emission wavelength. Similarly, small and large signal modulations were found to have only minor dependences on temperature. Moreover, we show the impact of the active region design and the cavity length on the temperature stability. Measurements were performed in pulsed and continuous wave operation. High characteristic temperatures for the threshold current were obtained with T₀ values of 144 K (15 - 60 °C), 101 K (60 - 110 °C) and 70 K up to 180 °C for a 900-µm-long RWG laser comprising 8 QD layers. The slope efficiency in these lasers is nearly independent of temperature showing a T₁ value of more than 900 K up to 110 °C. Due to the high modal gain, lasers with a cavity length of 340 µm reached new record modulation bandwidths of 17.5 GHz at 20 °C and 9 GHz at 80 °C, respectively. These lasers were modulated at 26 GBit/s in the non-return to zero format at 80 °C and at 25 GBaud using a four-level pulse amplitude format at 21 °C.