In this example, we show how to use the angular distribution of radiated power from an LED or OLED to create a rayset in ASAP. The rayset can then be used to study the incoherent emission from a macroscopic device. We perform this calculation for an unpatterned layer structure and then for a patterned structure.
The files oled1.fsp, oled2.fsp and oled.lsf can be used for this example. The file oled1.fsp contains a multilayer without patterning, while the file oled2.fsp contains the same structure with a photonic crystal patterning, as shown above.
The script file oled.lsf can be used to run either the patterned or the unpatterned case. To switch between the two, modify the following line of oled.lsf
# Choose the name of the template fsp file. In this example, the file should # either oled1 or oled2, but can be changed to run the user's own file. basefilename = "oled1";
The script and fsp files makes the following assumptions
- The structure is symmetric with respect to x--x and y--y. This allows us to save simulation time by using symmetric and anti-symmetric boundary conditions.
- The position of the dipole with respect to the photonic crystal lattice in the x-y plane does not modify angular distribution of radiation. While this is certainly not completely true, it is sufficient for the purposes of this example. In reality, a number of simulations with different dipole positions in the x-y plane would have to averaged.
The script file oled.lsf performs the calculation in three parts. In general, running the simulations takes the most time, but this step only has to be performed once. The steps are:
- Run 3 simulations, each with a dipole oriented along the x, y and z axes in order to construct response of an incoherent, isotropic ensemble of dipole emitters.
- Perform a projection to the far field for each dipole orientation to calculate the angular distribution of radiation for an incoherent, isotropic ensemble of dipole emitters.
- Export the angular distribution to ASAP as an incoherent rayset. This will create an inr file that can be read into ASAP.
You can choose which steps to perform in the script file oled.lsf by modifying the following lines
# Choose which components to run (1 for yes, 0 for no) # The first time, each component needs to be run rerun_simulations = 1; rerun_analysis = 1; rerun_asap_export = 1;
The analysis step creates the following figures of the near field and the angular distribution of radiation
Unpatterened, patterned near field
Unpatterened, patterened far field
The rayset is created by exporting the angular distribution data to an inr file (oled1.inr and oled2.inr). The emitting rays are distributed randomly across a region of the emission layer that is defined in the following lines of oled.lsf
# Choose the size and position of the emission region when exporting to ASAP x1_asap = -0.25e-3; x2_asap = 0.25e-3; y1_asap = -0.25e-3; y2_asap = 0.25e-3; z_asap = 0; # Choose how many copies of the original rayset to export N_export = 10;
Once these files have been exported, the file OLED_MODEL_wDir.inr can be used to run an ASAP simulation of a finite sized chip. To switch between the emission pattern of oled1.fsp and oled2.fsp, simply modify the following lines of OLED_MODEL_wDir.inr, replacing the text oled1 (or OLED1) with oled2 (or OLED2).
$IF (LOADRAYS) GT 0.5 THEN !! load rays via text file $ECHO NONE $CASE LOWER $read oled1 $case upper $ECHO FLUX TOTAL 1 !! save rayset to binary dump file for reuse DUMP OLED1.DIS $ELSE !! reuse an existing binary dump file EMITTING DATA OLED1.DIS
The following results are calculated, showing the illumination pattern at the surface of the chip, as well as the angular distribution of radiation. Note that the effect of the photonic crystal pattern is not visible at the surface of the LED, but is clearly visible in the angular emission pattern. Depending on the application, this could be an important consideration when choosing to use whether to use photonic crystal patterning to increase the light extraction efficiency.