Optical and Photonic Solutions Blog


How to Reduce Stray Light in Your Optical Design Project with Scattering Measurements

As technology evolves, optics also evolve to meet the demanding needs of product development. Optical design simulations must be as accurate as possible, which in turn requires accurate characterization of materials such as plastics, diffusers, displays, and other surfaces used in optical systems.

One of the most important tasks for an optical design team is to understand and reduce the impact of stray light on design performance. What is an effective way to do this? This is where light scattering measurements can be very effective.

Light scattering measurements help you virtually evaluate the impact of materials on your optical product performance prior to physical prototyping and fabrication. You can obtain insights into how materials interact with light sources by considering factors like surface topography, surface contamination, bulk index fluctuations, and bulk particles. You can also evaluate the impact of surface coatings in controlling stray light.

In this blog post, we’ll provide examples of using ultra-black coating measurements in optical system designs to suppress stray light.

What is an ultra-black coating and how can you measure it?

Acktar, a company that specializes in advanced coatings for light absorption and stray light control, has developed an ultra-black coating for opto-mechanical components. The purpose of Acktar’s Fractal Black surface coating is to absorb light, which makes it a viable solution for eliminating stray light in any optical simulation and project. It works in the visible range and in infrared wavelengths.

In the examples shown in this article, we compare stray light suppression provided by Acktar’s Fractal Black surface coating versus standard black surfaces. We measured the surfaces with the Synopsys REFLET 180 instrument and imported the measurement data into LightTools to perform stray light analysis.

Measurement usage examples and impact on stray light in a cooke triplet

The following figure shows an example of stray light illuminance on a Cooke triplet on a sensor, excluding the main path.

The bottom left image shows the stray light illuminance for a housing of standard black anodized aluminum. After reproducing the same simulation using Acktar Fractal Black coating measurements, stray light is reduced on the sensor by a factor of 20x, as shown in the bottom right image.

Example of Fractal black versus standard black paint
Stray light illuminance on a Cooke triplet on a sensor

Stray light analyses in an head-mounted display

The next example illustrates the use of the Acktar Fractal Black surface coating in a heads-up display (HUD) design. After comparing the stray light field of view coming from the housing with Fractal Black versus the housing with black anodization, we see a 30% reduction in stray light from the Fractal Black surface.

Using BSDF measurement data from the REFLET 180 instrument provided a fast, accurate way to simulate and compare the projected amount of stray light in the designs.

Fractal Black coating results
Fractal Black coating results
standard black paint results
Standard black paint results

How to learn more

To learn more about reducing stray light in your optical design project, contact us to request a demo or evaluation of our optical design and scattering measurement solutions.

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