Understanding that optical design tasks can be daunting, Michael Stevenson from Tucson, AZ-based Breault Research Organization offers some guidance on optical software programs that help engineers and designers turn their creative ideas into products.

The first thing that you need to know about all of these programs is that their core engines generally fit into one of three categories: sequential ray-tracing, non-sequential ray tracing, and finite-difference time-domain (FDTD) simulation. Here’s a brief summary of the features and applications unique to each category:

Sequential Ray-Tracing

Ray-tracing involves modeling the geometrical components of optical systems, defining the optical properties of these objects, approximating light sources with directional rays and then predicting real-world system behavior by propagating these rays through system models and by observing.

Sequential ray-tracing engines trace the rays created to approximate source characteristics in a sequential fashion — intersecting optical elements one at a time and in a pre-defined order.

Sequential ray-tracing software is most often used to design, optimize, and set tolerance systems of lenses — providing insight into the number of lens elements required in an optical system, their curvatures and ideal glass types. Cameras, endoscopes, microscopes and telescopes are examples of lens systems amenable to sequential ray-tracing analysis.

Non-Sequential Ray-Tracing

As the name suggests, non-sequential ray-tracing engines permit rays to encounter surfaces in any order and any number of times with automatic ray splitting. Allowing rays to scatter and interact with system components as they do in reality, this type of ray-tracing methodology can accurately predict the real-world behavior of optical systems. This approach to ray-tracing also lends itself to the Gaussian beam summation model for considering coherent effects in optical systems.

Non-sequential ray-tracing software is often used to model complex optical systems in which scattering, stray light characteristics, coherent effects, and polarization effects must be known and controlled. Examples include imaging systems, medical devices, and telecommunications systems.

FDTD Simulation

As optical systems shrink or otherwise need to include wavelength-scale structures, the Gaussian beam summation model breaks down, and conventional ray-tracing engines become increasingly less able to accurately predict the kind of behavior seen in micro- and nano-optical systems.

FDTD engines solve Maxwell’s equations to propagate electromagnetic fields through micro- and nano-scale structures. This enables the consideration of wave-optics phenomena, without approximation, in arbitrary materials having microscale system geometry.

FDTD codes are used for design and analysis of integrated optical devices, plasmonic devices, optical microcavities and scattering from wavelength-scale objects and structured surfaces.