In this example, we will examine the 2D representation of an InP microdisk laser on an SOI system.
As shown in the image above, the structure consists of a silicon waveguide adjacent to a SOI microdisk. The system will be pumped at 1.2 um and is designed to lase at 1.5um.
Open the simulation file microdisk.fsp and run it. The images below are obtained using the analysis group object called "spectral time snapshots". The analysis group object contains a number of frequency monitors which utilizes the apodization feature, to record the simulation result at different wavelengths. The images below are a comparison of the real part of the electric field at 1500 nm using linear scale and at 1200 nm using log scale. When the pump signal originally comes into the waveguide and touches the InP disk, it is hard for the light to propagate any distance into the microdisk as the disk is incredibly lossy. Level populations invert where the light is most intense, and this eventually drives the material to transparency. At this point, light can travel further into the medium; this can be observed from the images below. For the 1500nm light we do not have light propagating all the way around the disk initially (see t=15ps), as the disk is very lossy. But by the end of the simulation (t=45ps), we have achieved transparency, where we have equalized the level populations at levels 1 and 2.
15 ps, 1500nm, linear scale
15 ps, 1200nm, log scale
45 ps, 1500nm, linear scale
45 ps, 1200nm, log scale
Run the script file microdisk_analysis.lsf to generate plots of level populations at different locations of the simulation, recorded using time monitors. The image below shows significant difference in behavior of level populations depending on the position of data collection. The result obtained from the monitor that is close to the input waveguide, therefore pumped really hard, immediately equalizes the level populations and eventually end up with small but constant level population inversion between levels 1 and 2. Dynamics of level populations at the opposite side of the disk is fairly different and the inversion is smaller. The majority of the disk is driven to transparency, acting as a laser cavity, where the majority of the gain occurs near the input waveguide.
The image below, on the left is a zoomed in plot of the level populations obtained from the point time monitor near the input waveguide. The image on the right shows the level populations obtained from the monitor on the upper part of the microdisk.