Reduction of lasing thresholds in circular photonic molecule microdisk lasers

Microdisk lasers have been attracting much attention since the 1990´s as extremely compact sources of light (McCall, 1992). Lasing in disks of 1-10mum diameter and 100-200 nm thickness, containing one or several quantum wells or layers of quantum dots has been achieved both with photopump and injection of current. The main features of such lasers are: (i) periodically spaced frequencies of lasing, (ii) ultralow thresholds, and (iii) predominantly in-plane light emission. The one disk lasing modes are identified as whispering-gallery (WG) ones confined at the rim due to almost total internal reflection. Description of the WG modes in the isolated disk has been done with many techniques ranging from a WKB analytical study to the FDTD numerical codes (Frateschi, 1996)