2.2. Imaging
In imaging simulation, you can simulate the lens for a point source. Click the information icon (
) next to 'GENERAL' on top of the software to see details about the geometry and parameters used for imaging simulation. To image, we will assume an object 500 µm away from the substrate and 25 µm tall with its base point at the optical axis (see image below). Our goal is to find the optimal distance to place a detector that produces the sharpest and brightest image of this object.
Sweep Parameter(s)
Option 1: 1D Sweep
With this option, you will run simulation using sweep on one parameter.
Step 1: Point Source at Object Base
To start with, we will sweep the detector distance for a point source corresponding to the object base; a case with no off-axis aberrations. Enter values in the fields as shown in the image below. For Object Height, make sure to put 0 to create a point source at the object base.
At the bottom of OBJECT SPACE section, '' will appear (see image below). The values of these parameters are automatically calculated through the lens maker's equation. These values, although they are based on paraxial approximation, provide useful insights for us to come up with some simulation parameters. For example, we took advantage of the value s' = 55.2 µm to decide the sweep range 50 - 60 µm of Detector Distance. Once you have filled in all the fields, click RUN SIMULATION to simulate your metalens for imaging!
Once the simulation has completed, open the ANALYZE module. You will see tangential (y-direction) and sagittal (x-direction) results as a function of detector distance.
Simulation results:
Peak Intensity: highest value of intensity.
y or x at Peak Intensity: y- or x-position at the peak intensity.
Peak Intensity / FWHM: peak intensity divided by FWHM.
Airy Radius: average value of Airy radius from both sides of PSF.
If any of the values could not be evaluated, it appears as a missing data point in the plot. From the results of 'peak intensity divided by FWHM', we pick detector distance 56 µm at which the image of the object's base point is sharpest and brightest. We will need to run another simulation to check if this is still true for the object top; a case with off-axis aberrations.
Step 2: Point Source at Object Top
Click SIMULATE in the sidebar and change the value of Object Height to 25 µm - since our object is 25 µm tall. This will simulate the lens for the point source at the object top. Run simulation and open ANALYZE module. From the results of peak intensity divided by FWHM, we confirm that the detector distance 56 µm still gives us the sharpest and brightest image for object top.
Option 2: 2D Sweep
Alternatively, you can also sweep two parameters at once. To do that, select the sweep parameters and enter values as shown in the image below. With all other user inputs same as Option 1: 1D Sweep, run simulation.
In ANALYZE module, results are visualized in 2D colormap figures. Below image is the peak intensity divided by FWHM, which shows that the sharpest and brightest image can be formed at the detector distance 56 µm.
Check PSFs
It is a good practice to check PSFs after sweep. Go back to SIMULATE module and uncheck 'Simulate with Parameter Sweep'. For Object Height, enter either 0 (object base) or 25 µm (object top). Enter the found optimal value 56 µm for Detector Distance and run simulation. In ANALYZE module, you will see PSFs corresponding to the point source you used. Below image shows PSFs for object top.
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