Automated analysis of stable operation in two-section quantum dot passively mode locked lasers

In this paper, two-section mode-locked lasers consisting of monolithic quantum dot gain and absorber sections are studied as a function of absorber voltage, injected current to the gain region, and relative section lengths. We map the regions of stable mode-locking as measured by the electrical and optical spectra. A simple algorithm is presented that evaluates the quality of mode locking and allows automated characterization of devices. The relative advantages of increasing the absorber length compared to increasing the absorber reverse bias voltage are analyzed. Initial data indicate that doubling the absorber length from 1.4 to 2.8-mm in a 5 GHz repetition rate device increases the region of stable mode-locking by at least 25%, while increasing the absorber reverse bias can more than double the mode-locking regime. Nonetheless, in these devices, stable mode-locking over greater than a 100 mA bias range is realized with a grounded absorber making single bias control of a passively mode-locked semiconductor laser feasible.