June 04, 2019

Imaging, illumination, or laser design: OpticStudio is the only tool you need

Imaging, illumination, or laser design: OpticStudio is the only tool you need

Sequential ray tracing

If you’re designing any sort of optical equipment, such as camera lenses, microscopes, or telescopes, you’ll need a sequential ray tracing model. For anything that is expected to form an image, you’ll need to know exactly how the light will behave when going from the source to the image. Fortunately, this is a relatively straightforward (and therefore less time-consuming) calculation, because you only need to trace a few rays of light. It’s an efficient way to get an accurate model of your optical design.

Sequential ray tracing involves modeling how light rays come into the system from a target, strike a mirror, perhaps another mirror, then some lenses, and then the detector. Add or subtract a mirror or lens here and there, and that covers these examples: telescopes, microscopes, cell phone cameras, etc. Sequential mode is also useful for designing afocal systems, such as binoculars, a microscope/telescope used with an eyepiece, or a beam expander. In these examples, the system does not make an image as its final output; it instead magnifies or concentrates the input light.

For the most part, in imaging and afocal systems, light rays will interact with a specific optical element (mirror, lens surface, etc.) only once and then proceed to the next surface in the path. A light ray that deviates after hitting a surface such that it doesn’t hit the next is considered lost and is not tracked further. 

In real systems, though, the lost light goes somewhere and can contribute to things like lens flare such as you might frequently see in a J. J. Abrams movie. And although that’s cool in movies, it will compromise performance in some applications: lens flare is not so great if it lands on your actors’ faces during dramatic dialogue. 

Sequential ray tracing is a straightforward and robust way to create a manufacturable system. It is faster and less complex than non-sequential or physical optics propagation. In some cases, the lack of physical accuracy is not a problem, but if you’re building a high precision system, you want to make sure the end user doesn’t end up with scattered light compromising otherwise excellent system performance. 
 
Non-sequential ray tracing

For some applications, it is clear in advance that light rays will take a more complicated path than just A to B to C. For daytime sun and sky illumination for solar power applications, LED illumination in TV or monitor displays, or the backlight of your cell phone, the non-sequential nature is critical to operation, not just a nuisance factor. Even for simpler systems, it is often wise to run a non-sequential analysis to run a stray light analysis and prove that sequential mode is good enough and not hiding a critical issue. 

The key difference with non-sequential mode is that rays are no longer lost when they miss the “next” surface. In fact, there really is no next surface—any of the other surfaces could be struck next. This means that many more possible paths must be evaluated, and therefore the analysis is more computationally complex.

That’s also where the benefit of non-sequential ray tracing comes in. In OpticStudio, you can switch modes to take a closer look at stray light and, if necessary, devise a way to eliminate it so that it doesn’t end up scattered into the detector. In this way, OpticStudio’s non-sequential ray tracing is a cost-effective way to avoid expensive mistakes.

Ultimately, whether you’re working on a simple optical design or something more complex, OpticStudio offers everything you need. 

 

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