Feasibility study on the application of the quantum disk to the gain-coupled distributed feedback laser

Abstract

This numerical study investigated the possibility of using quantum disks in a gain-coupled distributed feedback (DFB) laser, specifically whether the laser would oscillate when the number of electrons in a disk (N/sub th/) is less than the maximum possible number of electrons in the disk (i.e., oscillate at a threshold material gain (g/sub th/) less than the maximum peak material gain for each quantum disk). The influences of the disk diameter and thickness, the number of disks stacked vertically in a layer (N/sub st/), the device length, the period perpendicular to the light propagation direction, and facet reflectivity on the g/sub th/, the threshold current density (J/sub th/), and the normalized gain-coupling coefficient (K/sub g/L) were also examined. When N/sub st/ is increased, g/sub th/ decreases to less than the value estimated when assuming that the product of g/sub th/ and N/sub st/ is constant. Although closely spaced disks are useful for reducing g/sub th/, there is an optimum disk distribution minimizing J/sub th/, and this distribution depends on the parameters described above. The J/sub th/ also depends on the disk size and is smallest when the diameter is 6 nm. The magnitude of K/sub g/L is about 0.76 and is independent of the height of the gain grating (i.e., N/sub st/), but it can be controlled by adjusting the disk diameter and the facet reflectivity.