Virtual Prototyping of Optical Systems: Leveraging ImSym and Optical Scattering Data

Before starting production of a new optical system, engineers must validate the system with accurate prototypes.

With the powerful optical design software tools available from Keysight, you can create virtual prototypes of complex models that analyze physical properties. These prototypes can vary from micro-optics to large complete systems.

Optical models for scientific and industrial applications require precise material measurements to achieve realistic simulations. This involves characterizing optical properties to predict light–material interactions accurately.

Techniques such as ray tracing, beam propagation, and Maxwell’s equation solvers model intricate light–matter interactions. These methods require significant computational resources, but provide highly detailed and accurate results. This level of precision is crucial for designing optical systems, developing new materials, and improving manufacturing processes.

As a result, virtual prototyping now plays a critical role in validating and refining new optical products before production.

The importance of BSDF measurements in virtual prototyping

Integrating bidirectional scattering distribution function (BSDF) measurements in virtual prototypes help engineers create reliable, high-quality optical products that meet technology demands. BSDF quantifies scattering behavior as a function of source incident angle and wavelength.

Engineers typically split this data two ways: reflected bidirectional reflectance distribution function (BRDF) and transmitted bidirectional transmittance distribution function (BTDF) components. By measuring reflection angles and BSDF values, you can accurately model surface roughness.

Figure 1. Link between the roughness of a material, the associated BRDF component, and visualization of the material.

Use BSDF data to:

• Innovate materials: Quantify properties to select optimal lenses, coatings, and diffusers, or explore new surface treatments for augmented reality.
• Optimize designs: Analyze how design changes affect light behavior to maximize system performance.
• Ensure quality: Incorporate data into automotive or aerospace models, and verify compliance with industry standards.
• Enhance rendering: Create lifelike visual experiences in virtual reality and computer graphics.

Keysight offers a variety of solutions to help you integrate BSDF measurements into virtual prototypes. With our optical scattering instruments or on-demand measurement services, you can quickly obtain precise data for any optical surface or material.

End-to-end virtual prototyping with ImSym

The ImSym – Imaging System Simulator provides an end-to-end, physically accurate virtual prototype. By modeling the entire imaging chain – including optics, sensor, and image processing pipeline – ImSym delivers an integrated view of performance that translates into production-ready designs.

Figure 2. ImSym simulation workflow

Engineers can incorporate BSDF measurements into ImSym simulations and visualize how light behaves when it interacts with surfaces and materials.

Using ImSym with BSDF data for machine vision design

In modern factories, cameras with machine vision technology inspect products and detect minute flaws and inconsistencies. Virtual prototyping helps engineers evaluate required camera speeds and troubleshoot unwanted stray light.

For this example, we’ll simulate a machine vision camera for printed circuit board (PCB) inspection using this ImSym workflow (pictured in Figure 3):

1. Define the scene object: Start with the PCB image file and add a light source, specifying the geometric and material properties of the PCB. This is crucial for accurate optical simulations.
2. Model the lens: Design complex assemblies, including aspheric lenses and freeform optics. Select specific focal length, aperture size, and lens materials to optimize performance.
3. Analyze stray light: Evaluate illumination conditions using models ranging from first-order approximations to detailed as-built mechanical housings.
4. Configure the detector: Define the sensor type (CCD, CMOS), its resolution, sensitivity, and other relevant characteristics to simulate how the optical system captures and processes light.
5. Simulate the image signal processing (ISP): Run the image signal process — which includes noise reduction, color correction, and image enhancement — to predict final image quality.
6. Generate the final image: Review the final image for quality and identify any potential issues. Make adjustments to achieve the desired system performance.

Figure 3. Diagram of ImSym simulation steps to reach the final detector image

Below, Figure 4 shows the initial ImSym simulation of the PCB. Notice some holes are circled in red, indicating they were successfully detected; however, those that weren’t detected remain without red circles. This is because the specular reflection of the PCB’s copper material overwhelmed the camera sensor, obscuring critical features.

Figure 4. Initial ImSym simulation result

One way to address this issue is by including an optical scattering measurement of the green PCB and copper in the ImSym simulation. This provides a more realistic view of the interaction between light and the PCB. The simulation can account for both specular and diffuse reflections, providing a comprehensive representation of how light behaves when it encounters the copper surface. This provides additional insights that you can use to adjust the detector and ISP model.

Using the Keysight Mini-Diff V2, we obtained the following measurement results for the copper:

• Diffusion: The reflection is not purely specular; there is also a diffusion around the peak. This indicates the reflective properties of the copper surface are more complex than anticipated.
• Scattering: The diffusion scatters light in various directions, which may obscure or blur details.

Figure 5. Left: BRDF perspective view of the copper for an incident angle of 20° and the 630nm wavelength; right: RGB view of the copper for an incident angle of 20°

Adding Mini-Diff V2 data to the ImSym model mitigates oversaturation and enhances the ability of the optical system to detect fine details. As a result, the inspection process is significantly more accurate, leading to better quality control and more reliable PCB manufacturing. The updated ImSym simulation is shown in Figure 6, with all PCB holes detected.

Figure 6. ImSym simulation after including BSDF data and adjusting detector and ISP model parameters

Understanding and accounting for the reflection’s specular and diffuse components are crucial for improving the detection algorithms and ensuring precise inspection.

Accelerating innovation in imaging design

ImSym allows engineers to model virtual prototypes of optical systems, providing early warnings of issues and enabling direct testing of image quality and signal processing. This proactive approach saves time and reduces costs.

By combining ImSym’s end-to-end modeling with precise BSDF measurements, engineers create high-fidelity virtual twins that closely mirror physical prototypes for reliable, production-ready results.

Ready to learn how ImSym and BSDF data can streamline your optical design? Contact us for a free trial or demo today.

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