Mid-IR quantum dot cascade VCSEL: feasibility study and feature extraction.

Quantum cascade lasers with quantum dot (QD) active regions have been developed to overcome the drawbacks of quantum-well-based cascade lasers. Low threshold current and enhanced bandwidth characteristics of QD lasers can be combined with promising energy-efficient features of vertical cavity surface emitting lasers (VCSELs) through introducing the novel, to the best of our knowledge, concept of a QD cascade VCSEL (QDC-VCSEL). Design steps and predicted features of a QDC-VCSEL operating at 4.5 µm wavelength are discussed in this paper, where the cavity and active region are optimized for TE mode using a high contrast grating design. Laser characteristics are investigated by developing rate equations for the cascade scheme. Threshold and L-I characteristics are obtained at different temperatures. Also, the dependency of threshold current, slope efficiency, and modulation bandwidth on design parameters, mainly the carrier tunneling time, is studied. Results exhibit output peak powers of ∼2 and ∼0.5 at 150 and 273 K, respectively. In addition, threshold current increment and modulation bandwidth reduction are observed with the increase in tunneling time.