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 use a SOI lens and assume an object 500 µm away from the substrate and 25 µm tall with its base point at the optical axis (see image below). In this section, our goal is to find the optimal image position, where a detector can be placed to produce the sharpest and brightest image of the object.

Circular aperture, which is located at the unit cell layer, is forced in imaging simulation.

Start Parameter Sweep

Option 1: 1D Sweep

With this option, you can run simulation using a 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.

SIMULATE module (imaging).

At the bottom of OBJECT SPACE section, 'Paraxial Parameters' 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!

Paraxial parameters based on lens maker's equation.

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.

[ Imaging Simulation ] All results are simulated at z = - detector distance.

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.

Peak intensity divided by FWHM for object base (h = 0). Left: tangential (T). Right: sagittal (S).

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.

Peak intensity divided by FWHM for object top (h = 25 µm). Left: tangential (T). Right: sagittal (S).

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.

2D sweep parameters.

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.

Peak intensity divided by FWHM (2D sweep). Left: tangential (T). Right: sagittal (S).

Check Point Spread Functions (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.

Point spread functions (PSFs) for object top (h = 25 µm). Left: tangential (T). Right: sagittal (S).