Comparison of static and dynamic characteristics of 1550 nm quantum dash and quantum well lasers.

Compared to quantum well (QW) lasers, lower dimensional quantum dot (QD) or quantum dash (QDash) devices demonstrate superior performances, owing to their quantized energy levels and increased carrier confinement. Here, we report the systematic comparison of static and dynamic properties of long wavelength (1550 nm) QDash and QW lasers. For the QDash lasers, a higher maximum operating temperature and lower temperature dependence was achieved for long cavities, although the threshold current densities were larger than the QW reference devices. The lasing characteristics for QDashes are significantly improved following the application of a high reflectance (HR) coating on the rear facets. The QDash lasers also exhibit three orders lower dark current, of 45 µA/cm under -1 V reverse bias. Small signal modulation on the 4 × 550 µm Fabry-Perot cavities yields a modulation efficiency of 0.48 GHz/√mA and a maximum 3-dB bandwidth of 7.4 GHz for QDashes, slightly larger than that for the QW devices. Meanwhile, a stronger damping effect was observed for the QDash lasers due to their lower differential gain.