Synopsys SmartStart Library Helps Start Your Optical Design

Are you designing an optical system with more than just a source and detector? If you answered yes, then chances are you could use the data in the Synopsys SmartStart Library.

What is the SmartStart Library, you ask? Great question! The SmartStart Library is an extensive collection of optical data for commercially available glasses, plastics, and surface treatments that can be licensed for use in LucidShape, LucidShape CAA V5 Based, or LightTools. Datasets in the library provide a complete picture of how light behaves in the volume of a glass or plastic optic or how light interacts with a surface treatment.

For many optical designers, a typical project might include these steps:

1. Decide what materials and surface treatments you want to use in your system
2. Get samples or data from optical material, optical coating, or texture vendors
3. Have the samples measured or integrate the data into your optical design software

This is a time-consuming and tedious process. Alternatively, you could simply choose material data from our SmartStart Library. Read the following examples to learn how this can save you time and effort.

Amber Is Not Just for Dinosaur Movies

Color is an important consideration for many optical systems. For motor vehicle turn signals/direction indicators, which are commonly amber or yellow, the color of light transmitted into the far-field light distribution is strictly regulated. Plus, the lit and unlit appearance of the lamp generally impacts the how well the entire vehicle is perceived. You can get colored plastic samples from your favorite vendor, but what will the plastic (or your lamp) look like at a different thickness? Will you pass the Economic Commission for Europe (ECE) and U.S. Federal Motor Vehicle Safety Standards (FMVSS) color tests? The SmartStart Library can help.

In the SmartStart Library’s ever-growing library of colored plastics, we have more than a dozen yellow and amber tints from Covestro, Röhm, and SABIC. The following chart shows the chromaticity of the light of a 3000K blackbody radiator (think incandescent bulb) after passing through various thicknesses of two different amber plastics in the library plotted against the ECE Regulation 48 Amber color box.

The ECE Regulation 48 amber color box with the chromaticities of light transmitted through two amber plastics at various thicknesses

As you can see, the combination of plastic, source spectrum, and material thickness is critical to ensure that your turn signal is legal. For the plastic labeled “Amber A,” if you are working with a thin amount of plastic — less than about 1.75 mm — you run the risk of being beyond the green boundary of the color box. For “Amber B,” if the light travels through more than 4 mm of plastic, it will be too red. The SmartStart Library allows you to try various combinations of materials and sources and determine which are viable in your design.

“Diffuse” the Situation

Do you need to hide your sources, or just want a milky-smooth lit appearance in your design? Diffuse plastics are one tool you can employ to achieve either of these. With diffuse plastics, a scattering agent is added to the plastic and any light passing through the material is “homogenized.” Many plastic vendors offer diffuse plastics with varying concentrations of scattering agents, so you have options depending on the amount of scattering you need.

Choosing and modeling diffuse plastics is difficult. That’s one of the principal benefits of the SmartStart Library. We have a proprietary process for measuring diffuse plastics that results in a very accurate model that can be applied to any design in any shape. At the time of writing, the library contains nearly 100 diffuse plastics from vendors such as Covestro, MOCOM, Röhm, and SABIC in white, gray, black, and red plastic. As you can see from the renderings below, LightTools, LucidShape, and LucidShape CAA can all leverage these datasets to model the appearance of the plastic in any thickness and any shape.

Appearance renderings of two diffuse plastics from the SmartStart Library showing the effect of varying thickness and any tinting that occurs

Rough, Tough, and Hard to Bluff

Can’t use a diffuse plastic, but still need to smooth a light distribution? Maybe adding surface roughness to your design is right for you! In the SmartStart Library, we call this a mold texture since you are adding roughness (or texture) to the mold used to make your injection-molded part. In non-optical plastic parts, adding mold texture is quite common for appearance – would your dashboard be as nice if it didn’t have a leather grain molded into the plastic?

When working with optical designs, mold textures can still be used, but carefully. For example, you can apply mold textures to a reflector before metalizing. In this case, you can directly measure the bidirectional reflectance distribution function (BRDF) of the texture after metalization and use it in your model. The SmartStart Library contains nearly 100 reflective mold textures from vendors such as Mold-Tech and Tenibac that have been molded in black plastic and then aluminized by Vergason Technology Inc. with an in-chamber topcoat.

Want to texturize a refractive surface? That can be tricky. You need to be sure that the full bidirectional scatter distribution function (BSDF) is correct, independent of which way the light is traveling. You should also make sure that the refraction is correct for the type of plastic you are using. Again, the SmartStart Library has you covered, with 75 refractive mold texture datasets from Mold-Tech, Tenibac, and VDI 3400.

Don’t Stray from the Path

The previous examples described how to add additional scatter to your optical design. Now let’s consider how to reduce the amount of scattered or stray light in your system.

I enjoy looking at “ideal” optical designs in which everything is beautiful and works perfectly. Looking at a 2D lens diagram is like looking at a little slice of utopia. Light goes exactly where you want it to go, from left to right. Things become complicated when you modify the design to allow it to be built. Lenses get coated, baffles get designed — and stray light analysts find issues.

One mitigation technique for stray or scattered light is to absorb it. If the mechanics of your system are shiny — even when you block stray light with a baffle — it is likely that light will eventually end up somewhere you don’t want it. Enter the anodizers and ultra-black coating vendors like Acktar and Surrey NanoSystems. If you need light to disappear, the SmartStart Library can help. The library contains over a dozen of the darkest coatings you can find on the market today, as well as more common black anodized aluminum coatings. Apply any of these to a lens barrel or a telescope baffle and have confidence that your optical simulation will give you an accurate picture of how well stray light has been controlled in your system.

To Learn More

Read the Synopsys SmartStart Library datasheet to learn more about this feature and the latest updates.