Stray Light Analysis – Smartphone Camera

The goal of this example is to study the stray light of a smartphone camera system. Stray light refers to the ability for unintended sources of light to reach sensors in an optical system. These sensors can be either electronic (e.g., CMOS image sensors) or the human eye. The ability for unintended sources of light to reach sensors will degrade the performance of the optical system and must be accounted for in the system design.

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[[NOTES:]] Software Prerequisites

To be able to follow this example, the following tools need to be installed on your computer:

• Ansys Zemax OpticStudio 2024 R1 (optional for exporting the .odx file)
• Ansys Speos 2024 R1

Overview

Understand the simulation workflow and key results

Stray light analysis of an optical system and image quality assessment require consideration of the lens geometries and the optomechanical components that constrain them.

Stray light can originate from:

• Specular sources, such as Fresnel reflections off smooth optical surfaces or light entering the system from outside the intended field of view.
• Optical scattering (i.e., light that scatters from rough optical surfaces or as the result of volumetric inhomogeneities inside of the optics).
• Edge diffraction from an aperture.
• The optomechanical components in the system (i.e., reflection or scattering from optomechanical surfaces).

Stray light analysis involves identifying the various sources of stray light in an optical system and minimizing (or ideally eliminating) their impact. Simulation is key to conducting robust stray light analysis. Ansys Optics offers two software tools that support a comprehensive end-to-end stray light analysis workflow for designing high precision optical systems:

1. Ansys Zemax OpticStudio
2. Ansys Speos

Ghost analysis is typically performed in OpticStudio during the design of the free-floating lenses. It's the tool of choice for designing optical components and sub-systems. It is used to minimize the impact of Fresnel reflections off the smooth optical surfaces, enabling to optimize the location of ghost foci, determining the best surfaces to apply antireflection coatings, and more.

Leveraging from the Optical Design Exchange (.odx) format the stray light analysis process could then continue in Speos. The new file format enables seamless data transfer between OpticStudio and Speos.

Speos CAD-agnostic direct design modeler, allows engineers to consider, in addition to the optimized lens stack, the optomechanical components. It provides access to direct modeling functionality for quick CAD clean-up, design creation/modifications, parametric design, and/or material optimizations. It accurately simulate the light behavior and propagation through the digital model of an optical product, such as a cellphone camera. Combined with advanced stray light analysis capabilities, including support for Light Expert (LXP), sequence detection, ray path filtering, multi-sensor analysis, 3D Irradiance, and automation, it enables an end-to-end workflow for the design and stray light analysis of high-precision optical systems.

The complete camera system can be placed in a realistic virtual environment for performance analysis and final validation.

The interoperability workflow illustrates the process for analyzing stray light in a camera system using Ansys Optics tools. The steps include:

1. Optical Design and Optimization: This involves designing, optimizing, and tolerancing the lens system based on main path performance, such as Modulation Transfer Function (MTF) and Point Spread Function (PSF).
2. Ghost Image Optimization and Analysis: Focus on minimizing the impact of Fresnel reflections and determining critical lens faces for applying antireflection coatings.
3. System-Level Stray Light Analysis & Visualization
   1. a.) This step includes transferring the optical system from Zemax to Speos using "Optical Design Exchange" (.odx) and analyzing stray light at the system level, incorporating opto-mechanical components such as the lens barrel, mounting geometries, and housing.
   2. b.) Detection of critical Source positions: Identify all potential critical source positions inside and outside the intended Field of View (FOV) and assess light leakage for the entire system.
4. Analyze stray light paths and apply sequence filtering to identify the most critical objects causing stray light, with a specific focus on scattering from opto-mechanical components.
5. Minimization of Stray Light: Minimize stray light within the system by implementing design and material modifications on the surfaces identified as critical in the preceding steps.

Typically, steps 1 and 2 of the workflow are executed using Ansys Zemax OpticStudio. The subsequent articles offer an introductory exploration of the concepts and methodology behind stray light analysis:

• Introduction to stray light analysis - Part 1
• Introduction to stray light analysis - Part 2

This example primarily focus on the Speos part of the overall workflow. It involves the Optical Design Exchange functionality, stray light analysis concepts, and techniques utilizing Speos features, such as the Light Expert, Sequence Detection, and the 3D irradiance sensor.

Step 3a: Transfer ZOS lens design to Speos using the Optical Design Exchange

In step we utilize the new Optical Design Exchange (.odx) file format to import the lens design from Ansys Zemax OpticStudio into Ansys Speos. Both products are designed to seamlessly interoperate for this purpose, ensuring an efficient and smooth stray light analysis workflow. By using .odx, both sequential and non-sequential components can be exported.

Note that components including a Zemax Black Box cannot be exported.

In this example, we employ a streamlined and efficient lens system that has been designed and optimized for aberrations using Ansys Zemax OpticStudio in sequential mode.

The .odx file serves as a container storing information about the lens design, spectral material and coating properties, stop surface, and sensors. For more information about the content, supported surface, and object types, refer to the link .

The lens system (green) is added to the optomechanical parts (grey) and lens edges (yellow), which are already predefined in Speos.

Step 3b: Detection of all possible critical source positions in and outside of the intended FOV and light leakage for the complete system. Analyze the stray light path sequences and identify most critical objects causing stray light.

In this step we examine all potential critical source positions in a single simulation using a reverse ray-tracing approach. This powerful method involves sending rays from the imager through the camera system to the scene. It allows us to identify light leakage in the mechanical system as well. The Speos Monte-Carlo ray-tracing algorithm considers the material behaviors of all geometries. Additionally, we will categorize these areas based on criticality and the ray paths inside and outside of the camera FOV.

Within the camera's FOV, most light sources can undergo multiple reflections at optically polished lens surfaces, leading to ghost reflections and lens flare on the imager. Light sources outside the FOV can potentially cause stray light scattering on mechanical and optical parts. We will introduce a methodology to identify and analyze the root cause of certain forms of stray light in this system.

By leveraging the Speos Light Expert (LXP) and sequence detection capabilities, we can visualize and export these ray paths for a specific area in the intensity result.

Step 4: Analyze stray light path sequences and identify the most critical objects causing stray light for a specific sun position within the FOV.

In Step 4, we will identify and investigate the most critical ray path sequences, measured in terms of irradiance hitting the sensor, and identify object interactions responsible for stray light on the imager at the 20° sun position. This analysis leverages the features of Speos LXP and "Sequence Detection." Additionally, we utilize the 3D Irradiance sensor on the lens barrel to identify areas with a high irradiance load.

Step 5: Minimize stray light within the system by implementing design and material modifications on the surfaces identified as critical in the preceding steps.

In Step 5, we mitigate stray light by applying coatings to the most critical geometry faces identified in Steps 3b and 4. This involves the application of both antireflective, highly absorbing coatings and implementing design modifications on the optomechanical parts to minimize noise and enhance the overall optical system performance.

Run and Results

Instructions for running the model and discussion of key results

The following steps guide you through the workflow on how to analyze stray light in a smartphone camera system using Speos capabilities:

Step 3a: Transfer the optical system from Zemax to Speos using "Optical Design Exchange"

Duration: 5min (+40min simulation time)

As the initial step, generate a .odx file for the cellphone lens design in ZOS (Optional). Then, import the lens system into the optomechanical parts and lens edge, which are already predefined in Speos.

Finally, prepare the simulations for the next steps.

Notes:

If you don't have Ansys Zemax OpticStudio available, you can skip the .odx file generation and proceed to Step 3.

To enable .odx import in Speos you need to "Enable Beta features" in the Speos Options under the "Advanced" section.Open Speos-> Options -> Advanced and tick the checkbox "Enable Beta features".

1. Start Ansys Zemax OpticStudio24R1 and open the the "Lens @hyperfocal.zmx" project (located in "\ZOS\").
2. The button to start the "Export Optical Design to Speos" is found in the Export group under the Files tab. The generated .odx file is saved in the project folder.
3. Start Ansys Speos 2024R1 and open the “Stray Light Analysis - Smartphone Camera.scdocx “ project (located in “\Speos\”). The project includes several predefined sensors to speed up the simulation setup. An intensity sensor covering the halfsphere in front of the camera and an irradiance sensor representing the imager. Both sensors are set to layer “Sequence”, which is required to separate the ray path sequences in the simulation result.
4. Click on the “Optical Design Exchange" button in the Components group located under the “Light Simulation” ribbon.
5. A new "Optical Design Exchange Component.1" feature will be created in the Simulation panel.

6. Meshing parameters can be accessed through the options (right click) on the ODX feature. Meshing quality affects the simulation performance and the quality of the produced results. It is recommended to set the following meshing values for optical imaging systems. Additional information about the meshing can be found in the “Important Speos Model Settings” section. Tip: You can export the meshing settings of the ODX component as a Speos "Preset" and set them as default to save time for future projects.

7. Go to the definition panel keep the "Axis system references default (the Image surface is located at the Global Coordinate Reference) and browse for the "Lens @hyperfocal.odx" file.
8. Click on "Compute" to launch the import. During computation, the geometries and sensors are created inside a component. The geometries name indicate the type of object (lens or stop) and the corresponding indices in OpticStudio. The parameters and associated geometries (solids or surfaces) of each object are "read-only" for validation purposes. Default dimensions are in mm and wavelengths are expressed in nm. The radius parameter is set to infinite by specifying its value as zero.
9. As a next step we can add the ODX feature to the two predefined simulations.
10. Verify that all 17 geometries (incl. Optical Design Exchange.1) are added to the simulations and check LXP is active for all sensors in both simulations.
11. Now save the project and run the following simulations on CPU:
    1. Detecting all critical sun positions – 10min on 20 cores
    2. SLA 20deg sun position LXP – 30min on 20 cores

[[NOTES:]]

Stray light analysis simulations are computationally heavy because they require a high number of traced rays. The quality of the results depends on the available hardware.
To continue with the next steps, you can download the project with pre-computed results from the shortcut "Stray_Light_Analysis_Simulation_Results" provided in the downloaded folder.

Then open the “Stray Light Analysis - Smartphone Camera.scdocx“ project (located in “\Speos\”).

Step 3b: Detection of all possible critical source positions and light leakage for the complete system

Duration: 20min

In the second step of the stray light analysis we will identify all critical source positions both inside and outside of the cameras field of view. In this example, a 180° intensity sensor is placed in front of the system to cover any critical source position within the hemisphere. A non-sequential Monte Carlo simulation is performed: rays are randomly emitted from the source and propagated into the optical scene. Any ray intersecting the sensor plane is considered. Each ray path is then attributed to a sequence, e.g. an ordered list of interactions on geometries or faces. All sequences are sorted by the energy that reaches the sensor. The sequences are separated as 'Layers' in the result, allowing for isolation. The simulation result will uncover any potential light leakage caused by improper design of the opto-mechanical or enclosure components. Speos Light Expert (LXP) is used to visualize these critical ray paths and their interactions within the system. In this step, we introduce a workflow to analyze the ray path sequences and object interactions leading to unwanted stray light, utilizing the Speos 'LXP' and 'Sequence Detection' features.

1. Click on the "Detecting all critical sun positions" simulation in the Speos simulation panel. The simulation results include a “Detecting all critical sun positions.Intensity.lpf” result which is the Intensity captured by the “Intensity” sensor from the camera system with the “Imager” defined as Lambertian source.
2. Double-click the “Detecting all critical sun positions.Intensity.lpf” result to open the intensity map including the information of the light paths in the Virtual Photometric Lab.
3. The intensity map answers two important questions:
   1. At what source angles does stray light reach significance?
   2. How critical are these angles in terms of intensity?
4. The "Light Expert" provides a visual understanding of the interactions between ray geometry within the system for a defined area on the intensity plot. We can categorize the plot into four distinctive areas. The measurement areas are color-coded for easier comprehension: Complete_Area (green), covering the entire object space in front of the camera; Area 1 (yellow), highlighting rays within the designated FOV (orange); Area 2 (blue), situated at the edge of the diagonal FOV; and Area 3 (purple), encompassing the source angles outside the FOV.
5. To observe the internal ray paths of the camera system, activate the cross-section by clicking on the "Section mode" icon in the top-left corner of the 3D view. Then, click on the "Plane" element in the structure view.
6. To display the rays for each area, click on the “Measures” icon and select the area of interest (row highlighted in blue). The ray paths will update in the 3D view. Tip: You can export the ray paths as line geometry by right-clicking on the “Detecting all critical sun positions.Intensity.lpf” file.
7. The "Radial_Line" measurement allows the display of intensity variation for all source angles along the sensor diagonal from 0deg-90deg. Click on the "2D view of section" icon.
8. In the bottom of the graph, select "Section" to align the maximum intensity value on the displayed values.
9. As shown in the graph, with increasing source angles, the intensity value decreases, and the stray light radiation entering the optical system also decreases. When the incident angle of the light source is greater than the FOV (40deg), the intensity drops by a factor of ~10, followed by a small spike between 42-44deg (Area2) and some lower radiation until 90deg (Area 3). This graph includes the intensity of the intended optical design path (signal) and the straylight paths (noise). The simulation result contains information about the 25 most energetic ray path sequences (the number can be set in the sensor definition). We can utilize the Virtual Lighting Controller to deactivate the contribution of the Signal (Sequence1) to display only the stray light sequences.
10. Open the Virtual Lighting Controller and uncheck Sequence 1. The 2D view is updated, and only the contribution of the stray light sequences is displayed. Out of all straylight sequences, we focus, in this example, on the four most energetic ones and identify their origin.
11. Step through the five most energetic sequences by changing the active "Layer" to better understand their contribution. "Sequence 1" represents the intended optical design path; all following are considered as noise. We can conclude that Seq.1, Seq.2, and Seq.4 contribute to Area 1, Seq. 3 to Area 2, and Seq.5 to Area 3.
12. The Sequence Detection tool will provide more details about each sequence. It helps to understand the interactions of each sequence with the elements hit by the rays as well as the order in which elements have been hit. The list of sequences provides information about the number of interactions (length, number of hits on the sensor, and the energy in % with respect to the overall integrated energy). In this simulation, rays are launched from the image sensor (interaction 1) through the lens system to the intensity sensor. In reality, light is propagated in the opposite direction, so we have to read the sequences from right to left.
13. Go to "Tools" -> "Sequence Detection" and analyze the ray path of sequences No 1,2,3,4,5. In this project, Sequence 1 represents the direct ray path interactions starting from the source object (1) through the lens's front and back faces (1 2 3 4 5 6 7 8 9 10 11 12 13 14 15) to the sensor.
14. To identify the critical face from which the sequences originate, we compare the optical paths and extract the element (face) (highlighted in yellow) where the second and following sequences (most energetic noise sequences) diverge from the first sequence.
15. In the list of interactions, click on element "55" to highlight the corresponding face geometry in the 3D view and analyze the ray path interactions. Repeat this step for all other critical faces highlighted above.

From the stray light analysis, based on the five most energetic sequences, the critical surfaces and their type of interaction could be identified for each area:

1. Complete Area: Unveils some light leakage due to a small air gap between the lens barrel and camera housing geometry.
2. Area 1 (In-field): Specular reflections on the back face of "Lens_1_1-2" and front face of "Lens_7-8".
3. Area 2 (Field Edge): Specular transmission on the front face of "Lens_11_12". Rays hitting the flat surface between the chip zone and mechanical diameter.
4. Area 3 (Out-of-field): Lambertian scattering on the Inner lens barrel face, at the physical aperture.

To reduce the level of stray light, you could apply an anti-reflection (AR) coating on the lens faces showing a specular reflection and a high-absorbing coating to reduce the amount of scatter on the most critical faces from the optomechanical components. To avoid light hitting the flat surface for lens 11-12, the inner radius of the spacer could be modified to block the rays hitting this area. The stray light reduction techniques will be applied in Step5.

Having the holistic understanding on the stray light behavior of the camera system and mastering the stray light analysis concepts and techniques, we can apply them to analyze the camera system for a specific sun source position within the camera FOV (20deg).

Step 4: Analyzing the stray light path sequences for one sun position and identifying the most critical faces causing scattering.

Duration: 20min

In step 4, we simulate the stray light on the imager for a sun source at 20° within the camera's FOV and analyze the ray path sequences and object interactions leading to unwanted stray light, utilizing again the Speos "LXP" and "Sequence Detection" features. From the previous analysis, we know Fresnel reflections on the optical polished lens surfaces (causing lens flare or ghost spots) are the most dominant source of stray light for light sources within the camera's FOV and can be optimized beforehand in OpticStudio. In the following analysis, we will address stray light originating from optical interactions of light with the optomechanical components in the system causing scattering. We introduce an efficient way to identify the most critical optomechanical surfaces that contribute significantly to the noise level on the sensor and have a negative impact on the optical performance.

1. Click on the "SLA 20deg sun positions LXP" simulation in the Speos simulation panel. The simulation includes a “SLA 20deg sun position LXP.Imager Layer Seq.lpf” result which is the illuminance captured by the “Imager Layer Seq” sensor separated by 100 sequences.
2. Double-click the “SLA 20deg sun position LXP.Imager Layer Seq.lpf" result to open the irradiance map in the Virtual Photometric Lab.
3. The result was simulated with a colorimetric sensor and includes one measurement area for the complete sensor. By default, the layer separation the viewer is set to “All layers,” which means that no sequence filter is applied, and all sequences are displayed. Change the active layer to discover the ray path sequences from sequences 1 to 20. The sequences are ordered by energy hitting the sensor. As the energy is decreasing, adapt the scale level for higher sequences. Tip: In the definition panel of the light expert, increase the ray number displayed in the 3D view to 500.
4. From the first 20 sequences only sequences 14 and 17 including a scattering interaction caused by the face of the lens barrel before the aperture.
5. To speed up the identification of other sequences including scattering events, click on "Sequence Detection" from the Tools menu. Sequence 1 represents the direct ray path interactions starting from the sun source object (1) through the lenses' front and back faces (2-16) to the sensor. Out of all listed sequences, “Sequence 1” contains 93.51% of the energy detected by the sensor. The remaining energy (6.49%) can be seen as “image contamination”. One indicator of a ray scattering in the sequence is a high number of hits on the detector. Sorting the list of sequences by No. hits will ease the identification of these sequences and related faces with scattering interactions.
6. For a direct simulation, the sequence needs to be read from left to right. Go through the sequence's interactions and extract the element (face) with a scattering event. Note: A sequence can include multiple scattering interactions (for example, sequences 79 and 83). If we sort this list in respect to the energy, we can derive a ranking of the most critical faces from the opto-mechanics. Note that a solid (here lens barrel) can consist of many faces (indicated by a unique face ID at the end of the name). Tip: To find all sequences including an interaction with a certain face, the filter can be used. This is illustrated beneath for object 17. For advanced filter functions, a regular expression syntax can be used.
7. The following animation is showing the sequences which include at least one scattering event from one of the faces sorted by energy.
8. From these results, we can conclude that the inner faces of the lens barrel have a strong contribution to the noise level on the sensor. Another powerful method to gain an understanding of the critical illuminated faces of a specific geometry is to apply a 3D irradiance sensor on it and to evaluate the solar irradiance load.
9. Open the “SLA 20deg sun position LXP.3D Irradiance.xm3” result in the Virtual 3D Photometric Lab. Change the layer to “Reflection (Radiometric)” and set the legend maximum to 2W/m2. The area around the aperture and some faces on the inner parts show a strong reflection, confirming the location of the most critical areas.

Once the system is analyzed, the understanding of how different optical components contribute to stray light can be discussed with design and mechanical team.

Step 5: Minimize stray light within the system by implementing design and material modifications on the most critical surfaces identified in the preceding steps.

Duration: 15min

To reduce stray light and enhance image quality, various techniques and technologies are applied in camera design. While some correction methods can be applied during post-processing, minimizing stray light at the time of image capture is generally the most effective approach. Here are some common camera stray light reduction techniques:

• Anti-Reflective (AR) Coatings: Multilayer coatings on lens elements help minimize reflections and increase light transmission, reducing the chances of stray light entering the lens.
• Baffle design: Specially designed baffles and spacers within the lens or camera body can prevent stray light from bouncing around and entering the lens.
• Anti-Reflective Coating on the Optomechanics: Similar to lens coatings, optomechanical parts and sensors can be coated with anti-reflective materials to reduce internal reflections and minimize stray light impact.

• Lens Hood Design: Blocks extraneous light from entering the lens, crucial for reducing lens flare.

It's worth noting that while these techniques can significantly reduce stray light, complete elimination may not always be possible. Combining multiple methods, described above can yield optimal results.

In this example, we apply AR coatings to the most critical lens faces determined in Step 3b to minimize the impact of Fresnel reflections. To reduce the noise peak at the edge of the FOV (Area 2), we block the light hitting the flat lens surface between the clear aperture and mechanical diameter of front face of "lens 11_12" by changing the inner radius of the spacer ring. The most critical optomechanical faces identified in Step 4 will receive a high-absorbing coating (R < 0.5%). In the end, we compare the signal-to-noise ratio (SNR), the noise level over the full sensor FOV, and the stray light for one sun position before and after the optimization.

1. Start Ansys Zemax OpticStudio24R1 and open the the "Lens @hyperfocal.zmx" project (located in "\ZOS\"). Save the file with a new name "Lens @hyperfocal_with_AR_coatings"
2. Apply an ideal high performing AR coating with a reflectivity of 0.5%=I.995 (Format: I.transmission) on the following five lens faces:
3. Generate a new (*.odx) file and import it to Speos as a second ODX component as described in the steps 3a (don't forget to check the meshing settings).
4. Copy and paste the simulation "Detecting all critical sun positions" rename it to "Detecting all critical sun positions optimized ". Do the same for simulation "SLA 20deg sun position LXP"
5. For both simulations replace the "Optical Design Exchange 1" component by "Optical Design Exchange 2" (double check you have 17 geometries in the simulation).
6. 
7. As a next step we need to modify the design of the spacer to block rays reaching the flat lens surface of lens. Hide all geometries except Spacer "Solid2" and Lens_11-12.
8. To block the rays hitting the flat les area, we need to modify the inner radius of the spacer. Follow the steps from the video. Tip: Press the "space bar" on the keyboard to enter the dimensions (-0.04mm).
9. Next add an high absorbing coating (R<0.5%) face optical property (FOP) on the most critical optomechanical faces identified in Step4. These faces are saved as "Named Selection" group under the name "Faces to be coated"
10. Apply an absorbing coating FOP on these faces, by adding them as a named selection group to the Absorbing coating definition. Using a FOP for these faces will overwrite the "black anodized" surface optical property (SOP).
11. Run both simulations:
12. Compare the noise levels on the intensity plot for both the unoptimized and optimized systems.

The stray light signal-to-noise ratio (SNR) is a measure used in various optical and imaging systems to quantify the quality of the signal relative to unwanted stray light.

The formula for the stray light SNR is often expressed as:

\[ \text{SNR} = \frac{\text{Signal}}{\text{Noise}} \]

1. Calculate the Signal-to-Noise Ratio (SNR) value using the energy information provided in the sequence detection viewer for both the unoptimized and optimized systems at the 20-degree sun position.
2. Calculate the SNR by using this formula: \[ \text{SNR} = \frac{\text{Signal}}{100 - \text{Signal}} \]
3. For the unoptimized optical system, we obtain an SNR_unoptimized of 14.41. After optimization, the SNR increases to 33.79, indicating a 55.7% reduction of stray light on the detector.

In summary, the workflow for stray light analysis for a cellphone camera system using Ansys Optics involves several steps. Beginning with the optical design and optimization of the lens system, the process considers main path performance metrics like MTF and PSF. Ghost optimization addresses the reduction of Fresnel reflections, followed by a system-level stray light analysis that includes the transfer of the optical system from Zemax to Speos and the consideration of opto-mechanical components. Detection of critical source positions assesses potential light leakage within and outside the Field of View (FOV). The workflow concludes with an analysis of the most energic stray light path sequences, identifying critical objects and implementing design modifications to minimize stray light within the system.

Taking the model further (Advanced Stray Light Techniques):

• Full FOV stray light visualization for the sun positions (0°-42°).

• Simulate stray light on the camera imager and analyze the ray paths on multiple sensors for different sun positions (not covered in this article, more info can be found here ).

Full FOV stray light visualization for the sun positions (0°-42°)

When directly observing a bright source (here the sun) with the camera system, you will notice a bright spot (depicted as a purple spot) along with a wide variety of ghost images. These ghost images, which contribute to the degradation of optical performance, result from reflections and ray interactions between lenses and optomechanical components.

The project includes a parametrized sun source model based on a surface source. The parameters for rotation in XY plane, the FOV angles and steps can be modified in the "Groups" panel. Tip. You can effortlessly integrate sources into the simulation by simply selecting them in the 3D view.

To illustrate the importance of detailed testing with full FOV coverage, a stray light simulation is conducted from 0° to 42°, using field angle increments of 2°. Some stray light patterns and artifacts are only visible at specific sun positions. For this system, lens dispersion effects become apparent between 19° and 25°. Thanks to sensor layer separation by "Source" and the performance, scalability of Speos HPC, all sun positions can be simulated simultaneously.

Important Model Settings

Description of important objects and settings used in this model

General Info - Camera design specs.

• Based on 5 asphere lenses
• Molded lenses with optical resign (DX4900 & Okp-1)
• Window for IR cut between sensor and lens system (Bk7)
• Mechanical protection window outside the camera (sapphire glass)
• Optimal Field of view: 80° (full field corresponding to the sensor diagonal)
• Effective Focal length: 2mm
• Aperture: F#1.8
• Lens depth (from first lens to sensor): 5.3mm

Meshing

Meshing settings are critical for getting correct simulation results. They define the quality of geometries that will be simulated. A mesh gives better results but also requires longer simulation time. Rough mesh can lead to poor results, especially for precise optical components. Meshing in this project is set to be proportional to the body size and a fine local meshing is applied on all optical elements. Further details about mesh settings can be found in Meshing Properties .

Materials

To determine how rays interact with geometry in Speos, we need to define optical properties of the objects included in simulation.
In Speos and in the real world, there are two types of optical properties, Surface/Face Optical Properties (SOP/FOP) such as optical polished, rough, coating and Volume Optical Properties (VOP) such as air, glass, and so on.
The materials of this project are listed in the following table:

Different options are available to define optical properties files including user definition via optical property editors, Plugin for surface properties which is programmable by user, and optical library which contains a set of surface and material properties measured or defined by Ansys which can be downloaded in Add-On Packages on Ansys Customer Portal .

Sun Source

For an observer on the earth, the sun has an apparent angular diameter of about 0.5 deg.

More information can be found here.
The sun source in this project is setup as a circular surface source in a distance (D) of 151.26mm with a diameter (d) of 2.64 mm resulting in an angular diameter (δ) of 0.5 deg.

The sun source has a lambertian intensity distribution with a total angle (α) of 0.5° result in a beam diameter (a) of 1.32 mm which covers the complete entrance pupil.
The source spectrum can be selected from Library or using Blackbody to set the temperature of the source spectrum in Kelvins. In this example, we used Blackbody at 5780K.
The flux of the source is set to 0.44 lm, which results in an average irradiance value of 100000 lx on the imager plane.
The surface source is patterned in 5° steps from 0° to 15°. The patterned is parametrized and can be easily modified for more sun positions or other incident angles.
More information regarding surface and ambient sources can be found Surface Source (ansys.com) and Ambient Sources (ansys.com)

Additional Resources

Project data:

• Project (start data)
  • Stray Light Analysis - Smartphone Camera 24R1 -w/o results
• Project (end data)
  • Stray Light Analysis - Smartphone Camera 24R1 incl. simulation results

Relevant Speos Ansys Learning Hub courses

• Speos Getting Started
• Speos Workflow & Geometry Management
• Speos Camera Sensor (optional)
• Ansys Speos Stray Light Analysis

More information about smart phone lens design and stray light analysis in Ansys Zemax OpticStudio can be found in:

• Smartphone lens modules
• Introduction to stray light analysis - Part 1
• Introduction to stray light analysis - Part 2
• Introduction to stray light analysis - Part 3