Oct 13, 2022
Designing Cell phone Camera Lenses Part 2: Optomechanical Packaging with OpticsBuilder
This blog is the second of a 3-part series discussing the challenge of smartphone lens modules, from the conception and design to the manufacturing and analysis of structural deformation. It provides a walkthrough introduction to how to edit optics from an optical system in CAD and how to analyze a system with Ansys Zemax OpticsBuilder after adding mechanical components. The showcase example is a smartphone lens system which consists of five lenses, a cover glass and an infrared filter. The main task we tackle is to extend these lenses with complex edges, so they can be fitted into a mechanical mounting.
After the optical system was optimized in Ansys Zemax OpticsStudio, the system is converted into a.ZBD file with the Prepare for OpticsBuilder tool.
The two main important points to consider when using Prepare for OpticsBuilder are, firstly, that a sequential optical system will be converted into a non-sequential system secondly that in the File Loading setting of the Prepare for OpticsBuilder feature, the Read-only box should be unticked if the mechanical engineer should have the rights to edit the core optical properties.
Edit Optics with CAD
Classic mounting edges can be directly added within OpticsBuilder using the Add Mounting Edge feature. To add complex mounting edges to the lenses the Creo Parametric native sketch tool can be used.
To edit the first set of lenses, they are opened in their file (Assembly tab> right-click on part>Open). Next, an additional sketch is drawn onto the side of the lens. By appending a centerline to the optical axis of the lens, the sketch can be revolved around the lens.
The modified lenses are then inserted back into the assembly, so the fine adjustment of the complex edges can be done by modifying the sketches directly in comparison with the neighboring lenses and onto the Barrel. As marked in the image below, there are still gaps considered for the Baffle rings, which will be implemented in the next section.
Add and adjust the mechanical components
As the four Baffle rings, required for this design, are off-the-shelf components they can be directly inserted into the optomechanical assembly with the Creo Parametric native insert tool (Model Tab -> Assemble -> Assemble A). After that, they can be directly positioned with the Object Placement tool.
The Barrel and Front Baffle need to be modified slightly so that the mechanical assembly can simulate the optical aperture which was defined in OpticStudio and the Beam clipping can be kept to a minimum. In section A of the image below the clipped beam a displayed in purple. In section B, the diameter of the mechanical aperture on the barrel was slightly increased and, as a result, there is no visible clipping of the beam by the optomechanical system.
After a first visual check, the optical Performance can be analyzed in depth with the OpticsBuilder Analysis tools
Optical Performance Analysis with OpticsBuilder
To validate the Optomechanical system with the OpticsBuilder Analysis tools, the three delta values can be investigated and compared to the Baseline values (explained below).
The spot size delta is calculated from the absolute value of the difference between OpticsBuilder Baseline and OpticsBuilder modified configurations. While the Baseline configuration only contains optics and aperture surfaces, the modified configuration also contains mechanical geometry. As the spot size has a green checkmark, the modified configuration has the same value as the baseline configuration, or the difference is negligible.
Beam Clipping 1.04%
Rays that hit a detector in the OpticsBuilder baseline configuration, but do not hit a detector in the OpticsBuilder modified configuration are considered clipped. The percentage of clipped rays is defined by taking the ratio of the flux that does not hit a detector in the OpticsBuilder modified configuration to the flux that does hit the detector in the OpticsBuilder baseline configuration multiplied by 100. As the Baffle rings should prevent the rays from propagating through the upper parts of the assembly a minor amount of beam clipping is tolerated.
When traced rays in the OpticsBuilder modified configuration take unintended paths to a detector, they contribute to image contamination. An unintended path is any path that did not exist in the OpticsBuilder baseline configuration ray trace. In the image above the rays which contribute to the image, contamination is marked orange. The amount of image contamination is negligible, hence the green checkmark next to the Image Contamination Delta on the Results Window.
In addition to the Deltas, the CAD user can also investigate the actual change of the Spot Characteristics. The initial Spots from the non-sequential OpticStudio file are considered the OpticsBuilder Baseline and the Current Output includes the influence of the mechanical components. The spot for Field 3 is shown in the image below.
As a next step, the optomechanical system can be reviewed with the optical engineer and the optical performance properties analyzed. If needed the optomechanical system can either be improved with the CAD system or exported back into OpticStudio with the Export.ZBD file feature* or declared as completed and sent further.
*Important to note from here is also that because the optics were edited with a CAD feature, they are not solely optical components anymore. So, they can be either defined as CAD Part: Creo Parametric or CAD Part: STEP.
If the Optomechanical system is declared as completed by both the Optical and the Mechanical Engineer, the system can be exported from Creo Parametric as a STEP Assembly and moved further to FEA Software, such as Ansys Mechanical, to generate FEA Datasets for the OpticStudio STAR Module.
Find the full article and downloadable sample files on our Knowledgebase here.
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