March 29, 2018

How to assess out-of-field rejection in LensMechanix

How to assess out-of-field rejection in LensMechanix

To ensure that a mechanical design protects the integrity of an optical system, light sources that exist beyond the specified field of view must be analyzed. These sources can impact optical performance after the mechanical components have been integrated into the model by causing stray light, loss of contrast, or flaring. LensMechanix enables mechanical engineers to add additional sources of light to optomechanical models and assess impacts on performance. Mechanical engineers can quickly identify what parts of the mechanical system need to be changed to preserve the optical performance.

Assess optical performance with LensMechanix tools

Monitor spot size
LensMechanix monitors changes in spot size using the same calculations and detector types that OpticStudio uses. For example, when a file is converted from sequential to non-sequential in OpticStudio, detectors are added for each source and centered about the field’s centroid at the image plane. When LensMechanix loads a sequential file, the same process occurs. Using the same process and calculations ensures that mechanical engineers use the same data that optical engineers use. Mechanical engineers can be confident that when they look for a change in spot size between the baseline ray trace and full ray trace, they’ll be able to easily interpret the results reported in the Optical Performance Summary (OPS). The baseline ray trace and the full ray trace compare the spot sizes before and after the mechanical components are added, so you can easily determine if the mechanical components are causing a problem.


An out-of-field source is added in LensMechanix to check for image contamination


Consider beam clipping and image contamination
Beam clipping and image contamination are both important analyses to run when analyzing for stray light after the optical and mechanical design has been integrated. Beam clipping looks at light paths that follow unintended paths and miss the detectors. The important thing to ask is: What is considered an intended path? LensMechanix determines the intended paths from the OpticStudio baseline, which checks the optical set up before it’s loaded into LensMechanix. There are many tools that you can use to check for beam clipping, such as the Computational Domain which enables you to define which components are considered in the ray trace. By default, all sources are considered in the Computational Domain, including sources that are loaded in the optical system and those added within LensMechanix. You can easily remove sources from the Computational Domain, which doesn’t change the optical system, but it enables you to isolate a source’s contribution to the beam clipping calculation.

Similar to beam clipping, image contamination is light that follows unintended paths but it hits the detectors. Again, LensMechanix uses the same paths from the OpticStudio baseline to determine intended paths. These sources of image contamination can come from individual sources—but it can also come from reflections from components in the assembly.

When rays strike a mechanical object, power is lost on that surface. LensMechanix enables you to analyze the power incident on a surface. When a full ray trace is performed, the surface of the object will be tessellated and will display the amount of flux or irradiance that falls on the component. Tessellation resolution and color scale can be set prior to performing a full ray trace. After the ray trace is done, a color map will be applied to the surface of the component. You’ll see hotspots of flux or irradiance in the graphics area. A power scale bar is displayed in the graphics area to give you a general idea of how much power’s falling onto that particular component. Similar to beam clipping and image contamination, this provides an easy way to determine where you should make changes to the mechanical model.

Simulate out-of-field rejection with LensMechanix

There are several times when it’s particularly important to simulate out-of-field rejection in your designs. These include systems that take inputs from optical systems, such as autonomous vehicles or smart glasses. Many times, sources such as the sun or traffic lights are not included in an initial optical design, but they are present in the real world. Designing with out-of-field sources in mind is essential when it comes to safety and functionality.

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