This article is part of a 3-series articles that will discuss the challenge of smartphone lens modules, from the conception and design to the manufacturing and analysis of structural deformation. This article is part two of the three-part series. It provides a walkthrough introduction on how to edit optics from an optical system in CAD and how to analyse a system with Zemax OpticsBuilder after mechanical components have been added. The show-case example is a smart phone lens system from a worldwide operating manufacturer which consist of five lenses, a cover glass and an infrared filter. The main objective is it to extend these lenses with complex edges, so they can be fitted into a mechanical mounting. Additionally using the optomechanical validation tools of Zemax OpticsBuilder to add and adjust mechanical components.

Designing Cell phone Camera Lenses Part 1: Optics
Designing Cell phone Camera Lenses Part 3: STOP analysis by using STAR module and ZOS-API

Authored By Flurin Herren

Introduction

After the optical system was optimized in OpticStudio, the system is converted into a ZBD. file with the Prepare for OpticsBuilder tool.

When an optical system is converted to a .ZBD file with Prepare for OpticsBuilder some points need to be considered. Firstly, as the ray tracing tools of OpticsBuilder are built on the OpticStudio non-sequential ray trace engine, a sequential optical system will be converted into a non-sequential system and then into a .ZBD. If the Prepare for OpticsBuilder tool is used in non-sequential the optical system is directly converted into a .ZBD file.

Secondly, that in the User Input section of the Prepare for OpticsBuilder tool, the Read-only box should be unticked if the mechanical engineer should have the rights to edit the core optical properties.

Additionally, can the OpitcStudio user edit various allowable deltas within the settings of the tool in order to set the boundaries of the optomechanical design process (further explained in the next section).

Edit Optics with CAD

As a first step the .ZBD file can be imported into the CAD Platform (here Creo Parametric 7), the initial optical system can be validated and then the next steps can be planned.

Part List:

1. Infrared Filter (A)
2. Lens (LB)
3. Lens (LC)
4. Lens (LD)
5. Lens (LE)
6. Lens (LF)
7. Cover Glass (G)

The geometrical prerequisites for the extended lens edges are that given mechanical baffle rings must be retained between them and the main mounting, which holds the optical system, and is denoted in this article as the Barrel, should be edited as little as possible. Ideally the Barrel should only be extended to hold the IR Filter (A) and the Cover Glass (G).

• Disclaimer: For display purposes the IR Filter (A) and the Cover Glass (G) are retained with the Barrel Assembly, in a real-life application these two components would very likely not be within the same optomechanical assembly as the lenses.

As a next step the optical performance, namely the spot size, beam clipping and the image contamination, are reviewed by executing a Simulation. As there are no changes made to the system, all the metrics should meet the allowable delta specification and a green checkmark should be displayed. 

After that the complex lens edges can be designed.

Add Complex Lens edges

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 an own file (Assembly tab>right click on part>Open). After that, an additional sketch is drawn onto the side of the lens. By appending a centerline to the optical axis of the lens, the so added sketch can be revolved around the lens.

In a next step the modified lenses are 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 (the Barrel can already be added here, as this makes the fine adjustment of the Complex Lens Edges easier). 

As marked on the image below, there are still gaps considered for the Baffle rings. These are the implement in the next chapter.

Add and adjust the mechanical components

As the four Baffle rings 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 directly positioned with the Object Placement tool.

The Barrel and Front Baffle need to be slightly modified so that the mechanical assembly can simulate the optical aperture which was defined in OpticStudio and the Beam clipping can be held to a minimum. See on the image below (Section A) the clipped beams in purple and on the right side (Section B), as the diameter of the mechanical aperture on the barrel was slightly increased, the newly simulated optomechanical system without any visible clipped beams.

After a first visual check, the optical Performance can be analyzed in depth with the OpticsBuilder Analysis tools.

Optical Performance Analysis with OpticsBuilder

In order 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).

Spot Size

The spot size delta is calculated from the absolute value of the difference between OpticsBuilder Baseline and OpticsBuilder modified configurations. While the OB Baseline configuration only contains optics and aperture surfaces, and the modified configuration also contains mechanical geometry. As the spot size has a green checkmark, the modified configuration has the same (Or the difference is neglectable) value as the baseline configuration.

Beam Clipping 1.04%

Rays that that hit a detector in the OpticsBuilder baseline configuration that do not hit any detector in the OpticsBuilder modified configuration are considered clipped. So, 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 divided by 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 in this system.

Image Contamination

Detector Viewer

Additionally, to the Deltas, the CAD user can also investigate the actual change of the Spots Characteristics. The initial Spots from the Non-sequential OpticStudio file are considered the OpticsBuilder Baseline and the Current Output does include the influence of the mechanical components. On the Image below the Field 3 can be observed.

Next Steps 

As a next step the optomechanical system can be review with the optical engineer and the optical performance properties analyzed. If needed the optomechanical system can either be improved with the CAD system, exported back into OpticStudio with the Export .ZBD file feature (*¹) or declared as completed and sent further.

(*¹) 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 the both the Optical and the Mechanical Engineer, the system can be exported from Creo Parametric as a STEP Assembly and moved further to a FEA Software, such as Ansys Mechanical, in order to generate FEA Datasets for the OpticStudio STAR Module. These Steps as elaborated in the third part of this Article series: 

• Designing Cell phone Camera Lenses Part 3: FEA and STOP Analysis with the STAR Module