This article takes the user through the workflow of an optomechanical system from the design all the way to stray light analysis and optical performance validation. With a focus on the software mechanics and the conversion between Ansys Zemax software. Starting off in Zemax OpticStudio with the optical design, going into Creo Parametric 7 and Zemax OpticsBuilder which covers the optomechanical validation and finally using the Ansys Speos add-in of Creo Parametric 7 to perform further in-depth analysis such as Stray Light analysis.

Authored By Flurin Herren

Introduction

With the connection between Zemax and Speos under the Ansys umbrella, we continue our work in finding new and existing interoperability workflows which improves the design process of optomechanical systems. Our focus hereby lays on improving existing error prone optical-mechanical workflow, increasing the adaptability of individual steps to dynamically fight back on occurring roadblocks during the design process and reduce the time-to-market as a whole by reducing iteration steps.

Our show case example in this workflow is the Single Gauss 25mm, it is a high-performance system for camera applications with the main advantages of compact size and low distortion.

You can find the Single Gauss 25mm files in the Zemax installer:

• …\Documents\Zemax\Samples\OpticsBuilderCreo\Single Gauss 25mm

Ansys Zemax OpticStudio

We start off with the optimized optical system of the Single Gauss 25mm in OpticStudio sequential mode and analyze the Spot Sizes.

Here we got three field points and three Wavelengths which cover the visible range of this system. For the three Spot Sizes which include all three Wavelengths.

Here are the values from the first Spot Size, which can be looked up within the Text tab of the Analysis feature window.

RMS Spot Radius : 6.51744914E+00 µm RMS Spot X Size : 4.60853248E+00 µm RMS Spot Y Size : 4.60853249E+00 µm Max Spot Radius : 1.28474016E+01 µm

Another factor is the optical System STOP (SYS STOP) which the Optical Engineer has added. As the mechanical Parts have simulate the system STOP with a mechanical STOP, we will have to take that into consideration when designing the mechanical parts (This will be used for Ansys Zemax OpticsBuilder section in the Article, Workflowpoint1 (WP1)).

Additionally, we can also look up the Index of Refraction and the Abbe number if we set the Solve box of the Material parameters to Model (This will be used for the Ansys Speos section in this Article, Workflowpoint2 (WP2)).

From here on we can use the Convert To NSC Group tool in the File Tab of OpticStudio Seqeuntial Mode, which automatically converts our optical system to a non-sequential file and saves it with a NONSEQ postfix. As OpticsBuilder runs non-sequential ray traces, the Detector View in OpticStudio Non-sequential and OpticsBuilder should be same (This will be used for Ansys Zemax OpticsBuilder section in the Article, Workflowpoint3 (WP3)). On the image below we can see the Detector Viewer of Field 2:

After analyzing the optical system in sequential and non-sequential we can go ahead and convert the system into a .ZBD file which then can be imported into Creo Parametric. This can either be done within the sequential or the non-sequential mode of OpticStudio (If the user converts a sequential model to a .ZBD the conversion to a non-sequential system is automatically done by the Prepare for OpticsBuilder feature). The conversion can be done with the Prepare for OpticsBuilder feature in OpticStudio:

While packaging the optical system into a .ZBD file, we can set various parameters such as the User Inputs. The User Input section is used to declare how much variation will be allowed from the nominal system performance. These inputs will be used to compare the performance of the lens file to the ZBD after conversion (and before passing the system on to OpticsBuilder). These inputs will also be used as reference in Creo as performance targets for the mechanical engineer.

As a next step we can change into the CAD environment, in this example we will be using Creo Parametric 7.

Ansys Zemax OpticsBuilder

As a first step (Red1 Below, here the icon is greyed out because this step has already been carried out) we can import the .ZBD file into the CAD Platform within the OpticsBuilder tab.

Next, we can carry out an initial first Simulation (Red 2 above). This will create the first set of rays which help as a visual aid when adding and adjust the mechanical parts, additionally we can do a first initial check and compare the Detector Viewer with the once from OpticStudio Non-sequential.

Within the Simulation Dialog window, we can see the three allowable deltas Spot Size, Beam Clipping and Image Contamination. On the Spot Size value, we can show the Detector.

Compared to WP3 we are looking at the Field 2 and as we haven't added any mechanical parts which could influence the optical path the Spot Size is still unchanged.

• Spot Size

  • The RMS value of detector spot size delta averaged over all sources is reported in the spot size row in the Optical Performance Summary that is opened after a successful ray trace. The spot size delta is calculated from the absolute value of the difference between OpticsBuilder baseline and OpticsBuilder modified configurations. The OpticsBuilder baseline configuration only contains optics and aperture surfaces while the OpticsBuilder modified configuration also contains mechanical geometry.

• Beam Clipping

  • 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. 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.

• Image Contamination

  • 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. The percentage of image contamination rays is defined by the flux on an unintended path in the OpticsBuilder modified configuration divided by the flux on the OpticsBuilder baseline configuration multiplied by 100.

With these steps done we can go ahead and add mechanical parts to the optical system and so turn it into an optomechanical system.

Add Mechanical Parts

By saving the imported .ZBD file a Creo Assembly file is created, to which we can now add mechanical parts. The mechanical parts are created as native CAD Parts, so they are created with the normal Creo tools such as Sketch, Revolve and Extrude.

Depending on the system and the mechanical part, a part can either be partially created, added to the assembly and then adjusted or added directly as a finished part. The CAD user is completely free here to apply whichever strategy is more convenient in the given situation.

In this workflow here, the mechanical parts are already practically finished and then added to the optical system. 

To add the mechanical parts to the optomechanical assembly, which is now a native Creo assembly file as well as a .ZBD file, the Creo native Assemble tools can be used. After the parts have been added they can be aligned to the optical components with the Component Placement Tool. Within an optomechanical assembly it is advised to add the mechanical parts with reference to the optical components. 

After the mechanical parts are added, a next Simulation can be run in order to examine the influence of the mechanical parts onto the optical performance. 

• Note: The step of running a simulation to check the optical performance can also be done after adding any individual mechanical part. 

In the image below, it can be seen that the mechanical stop aperture which should be aligned with the optical stop (See Workflow point 1, WP1 in prior chapter) and is design within the Lens Mount Part, is clearly too small. Hence, the beam clipping and the increased Spot Size, which you can see as purple rays and within the Simulation Results.

To increase the diameter of the Lens Mount Part, the Part can be opened individually in the Creo Model Tree and the Sketch of the Revolved feature can be edited. After saving the Part, the Assembly will be updated automatically, and the mechanical stop is in reference to the optical stop.

If all the Allowable Deltas are checked and the Simulation Results are showing the green check marks, the optomechanical validation process is done and we can move on to Ansys Speos.

Ansys Speos

The main advantage here is that because Ansys Speos is also available as a Creo Parametric add-in as well as a Standalone software. The transition between the optomechanical assembly which has been created in Creo with the help of OpticsBuilder and the Speos is fairly quick, and the engineer does not require to change to another software.

There are three main steps to take in order to use the assembly in the Speos add-in section:

• Optical Properties; Speos specific material and surface properties have to be assigned.
• Speos Sources; Speos specific sources have to be added in order to carry out simulations.
• Speos Sensors; Speos specific sensors have to be added to analyze results.

The whole geometry of the optical and mechanical components can be reused and are automatically listed in the Speos Model tree.

Optical Properties

To apply optical properties, we need to differentiate between the optical components with a refraction index and the mechanical parts which only hold surface properties. As visible on the image below, the green framed settings are for the optical components. As soon as we set the Type optic, we can set the Index of Refraction and the Absorption value, the surface can be assumed as Optical Polished for normal optical components. The indices can be taken over from OpticStudio, see Workflow point 3 WP3.

The red framed properties settings are for the mechanical components. Therefore, we can set the Type to Opaque and for an inital simplification we can assume the reflection of anodized aluminum and set the reflectance to 50%. 

The orange framed setting is representing the option to use a Library Optical Surface, which is also possible in Ansys Speos.

Sources 

As this is a new analysis approach and the influence of the mechanical components on the optical performance has already been investigated with OpticsBuilder, we can go ahead and set new sources which the optomechanical assembly might experiences in a real-life application. An example would be any environmental source, such as the sun.

The two most common source types in Speos are Surface Sources which is a ray source coming from a actual part (In some scenarios, a small part can be imported to model a point source) and appears in the 3D view. Another approach would be to model a Ray File Source.

Sensors

Sensors which are the equivalent to OpticStudio and OpticsBuilder Detectors. Can be placed anywhere in or around the optomechanical assembly. Here we can mainly apply the Irradiance and the Intensity Sensor. The Irradiance shows the Illumination in Lux or the irradiance in Watt/m2. The Intensity Sensors shows the Radiant Intensity or the luminous intensity (in Candela).

 

After running a simulation, the incident light can be displayed onto the sensors and the optomechanical assembly can therefore be analyzed with a new toolset. In order to get more information on Ansys Speos and how any analysis approach may look like, please see the links after the Summery.

Summary

In order to summarize this workflow, let's look at a detailed overview in which the conversions between tools and entities have been marked with a letter:

• a: The Convert to NSC Group tool can be used to convert a sequential system to a non-sequential in OpticStudio.
• b: After the Prepare for OpticsBuilder tool (in OpticStudio, either sequential or non-sequential) the so generated .ZBD file can be transferred to a CAD Environment with OpticsBuilder.
• c: In order to send a .ZBD file back into OpticStudio (Including any added mechanical parts) the Export .ZBD file tool can be used (in OpticsBuilder).
• d: In order to load a new .ZBD file which has been edit by an OpticStudio user, the Update .ZBD file tool in OpticsBuilder can be used
• e: To convert an optomechanical assembly from the OpticsBuilder to Speos, the Optical Properties in the Speos tab have to be set up (See prior chapter)

Using the Ansys Zemax OpticsBuilder add-in for Creo Parametric, can bridge the gap between optical and mechanical design process and allows the CAD user to validate the influence of the mechanical design process directly on the optical performance. Additionally, we can also go beyond that with Analysis Possibilities of Ansys Speos in Creo.

Next Steps

In order to find out more regarding Ansys Speos, our colleagues at Speos are happy to provide you with more information.

• Ansys Speos for Creo Parametric Getting Started | Training
• Ansys Speos | Optical System Design Software