Evaluation of energy-to-data ratio of quantum-dot microdisk lasers under direct modulation

The energy-to-data ratio (EDR) was evaluated for quantum-dot based microdisk laser directly modulated without external cooling. The experimental values of EDR decrease with decreasing diameter of the microdisk and reach 1.5 pJ/bit for the smallest diameter under study (10.5 μm). In larger microdisks (with a diameter greater than 20 μm), the EDR varies in proportion to the square of the diameter. If this relationship were true for smaller microdisks as well, an EDR value of about 100 fJ would be achieved with a diameter of 4 μm. The observed deviation of EDR from the quadratic dependence on the diameter is associated with an increase in the threshold current density in smaller devices, which in turn may be caused by the contribution of nonradiative recombination on the microresonator sidewalls formed by deep etching.