GaAs-based quantum dot (QD) semiconductor lasers at 1300 nm exhibit a number of benefits for use in metropolitan and local area networks. Low modulation-induced chirp attributed to small linewidth enhancement factor (LEF) in QDs overcomes some limitations in a directly-modulated laser compared to quantum well counterparts. Along with the temperature-insensitive low threshold current, these QD lasers demonstrate considerable prospects towards Peltier-free direct-modulation operation.
In this work, we experimentally investigate the temperature-dependence of the LEF as a function of injection current and wavelength in state-of-the-art 1300 nm In(Ga)As/GaAs QD lasers grown by molecular beam epitaxy. These structures demonstrate a large state separation and a comparatively small inhomogeneous linewidth. Gain is measured using the Hakki-Paoli method and carrier related mode shift is extracted by correcting for thermal effects.
Previous reports have described LEF values of 1-5 over smaller temperature ranges (20-85°C) than the GPON commercial specifications in 1300 nm In(Ga)As/GaAs QD structures.
Here, at temperature range of -10 to 85°C extending beyond GPON commercial window, it is shown that even at higher temperatures where contribution from the excited state transition is expected to increase the LEF, the measured LEF remains essentially zero. This is ascribed to the large gain from the ground state transition. Such a low LEF at elevated temperatures bodes well for the use of such structures in applications where feedback insensitivity may be important. By analyzing individual modes as a function of their individual lasing thresholds, we also describe an interplay of mode position and lasing linewidth.
Soroush A. Sobhani, David T. D. Childs, Kenichi Nishi, Keizo Takemasa, Mitsuru Sugawara, and Richard A. Hogg, "Temperature-insensitive zero linewidth enhancement factor in state-of-the-art In(Ga)As/GaAs quantum-dot lasers (Conference Presentation)," Proc. SPIE 10526, Physics and Simulation of Optoelectronic Devices XXVI, 1052602 (Presented at SPIE OPTO: January 29, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2290112.5751405774001.
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