Photonics Products: Lens-design Software: Optical design benefits from interconnected software
Before the rise of computers, lens design relied on the use of a large number of calculation-simplifying mathematical theorems, formulas, and techniques developed over time; beyond thin-lens theory, these included approaches such as the "four-ray method," the "matching principle," and many others.1 Even so, many of the optical systems designed before the availability of lens-design software were nothing short of amazing in their performance and elegance.
However, the use of computers has brought the advantages of great speed, sophisticated optimization algorithms, and the ability to straightforwardly take manufacturing tolerances into account. These allow even unskilled designers to produce acceptable results, and skilled designers to concentrate on improving field sizes, spectral bandwidths, and other essential optical-system qualities to levels unimaginable before the availability of imaging lens-design software.
Optical-design software also extends to the design and analysis of nonimaging optics such as illumination systems, as well as to stray-light analysis; these capabilities are often part of lens-design programs to varying degrees, and also exist as add-ons or standalone software.
Virtually all of these design programs can export the resulting lens and lens-mounting data to external computer-aided-design (CAD) software to ease the creation of engineering drawings. The chosen computer platform for all these types of optical-design packages is quite consistent: all software programs mentioned in this article run on Microsoft Windows.
Imaging-system design
An imaging lens-design program usually aims to optimize many parameters at once. Depending on the optical system, these can include spot size, encircled energy, Seidel and other aberrations, spectral bandwidth, physical size, acceptable range of glasses, acceptable tolerances, object-to-image distance, pupil position and size, diffractive surfaces, incoherent and coherent image properties, and many others.
The CODE V optical-design software produced by Synopsys (Mountain View, CA) includes a fast wavefront differential method for analyzing system sensitivity to tolerances. "For typical optical systems, it can be 100 to 1000 times faster than traditional tolerancing methods such as Monte Carlo," says David Hasenauer, CODE V product manager. "The speed of the algorithm has allowed us to incorporate the algorithm into the CODE V optimizer to allow users to directly optimize for as-built root-mean-square [RMS] wavefront-error performance. In a recent case study with a four-element, all-aspheric cell-phone camera lens, the field-averaged mean plus 2-sigma performance probability was improved by 11% relative to a system optimized without regard to tolerance sensitivity [see Fig. 1]. The improvement was even more significant [24%] when global optimization with the tolerance-desensitization-error function was used."
Rick Elento, sales and marketing manager at Radiant Zemax (Redmond, WA), notes that the company's OpticStudio has been improved in three key areas: user interface, data plotting/charting/visualization, and data caching. "The program's features have been organized by task and type so that users of any experience level can efficiently find what they need without reading through a dense manual," he says. "Windows can be docked into multiple workspaces or can be independently floating to easily make best use of all available monitors."
The Optics Software for Layout and Optimization (OSLO) lens-design program by Lambda Research (Littleton, MA) comes in three levels of capability; the feature set in each edition is a subset of the features found in the next higher edition. Michael Gauvin, VP of sales and marketing, notes that OSLO includes a high-speed macro language to aid problem-solving. OSLO is designed to work seamlessly with the company's illumination-system design software, TracePro.
Qioptiq (Fairport, NY) produces a software package that includes WinLens 3D lens-design and analysis software, Tolerancer, Glass Manager (a glass and optical materials database), and Material Editor (to create custom optical materials). Also included is a Concept Development utility for "back-of-the-envelope"-style functionality, which helps to establish key system parameters such as effective focal length, beam waist, divergence, and so on for a given task, notes Geoff Adams, a developer at Qioptiq.
The most common applications include the modeling of trains of Qioptiq optical components in R&D rigs and checking designs from colleagues or consultants, along with the custom design of multielement systems. The software excels at the analysis of ghost reflections, says Adams.
"Ghost reflections can show themselves in several, more or less, unhelpful ways: flare (veiling glare), unwanted ghost images, dysfunction in laser resonators, and even actual physical damage to an element," Adams explains. "In WinLens3D, we provide tools to check all paths automatically, indicate those that might be troublesome, and then allow the engineer to inspect any they wish in more detail, all without any need to setup any of the 'daughter' ghost-path systems."
Two software tools made by Breault Research Organization (BRO; Tucson, AZ)—the Advanced Systems Analysis Program (ASAP) and APEX—are both nonsequential ray-tracing programs, that is, they can model light distribution in an optical system regardless of the position of the optics, mechanical elements, and sources that are defined. As these elements can be defined in a very general way and in any order, ASAP and APEX are applicable to a wide variety of optical systems, says Robert Shroder, director of sales at BRO.
"ASAP was originally developed as a stray-light-analysis tool for ground- and space-based imaging systems, as opposed to a straightforward lens-design software," says Shroder, noting that its capabilities include simulation and glare analysis in automotive lighting, beam propagation and diffractive analysis in coherent systems, scattered light and fluorescence in tissue, human eye modeling, and general illumination.
APEX is an optical simulation add-in for the SolidWorks (Dassault Systèmes; San Diego, CA) 3D CAD environment and was conceived as an easy-to-use illumination design tool for the many nonoptical engineers engaged worldwide in consumer and industrial product designs involving some type of optics and light source (typically LEDs), says Shroder. "Several years into its development, it now shares many of ASAP's capabilities and is appropriate for many of the same applications," he adds.
Nonimaging and illumination design
Standalone nonimaging and imaging optical design software packages from the same company are usually made compatible with each other, aiding in the creation and analysis of optical systems that handle both tasks.
For example, LightTools software, produced by Synopsys, can swap files with Code V. LightTools is used to design illumination systems where the goal is to control the distribution of light rather than to form an image. It supports virtual prototyping, simulation, optimization, and photorealistic renderings of a wide range of illumination applications, says Hasenauer. Users can define detailed characteristics of a light source and trace millions of rays to optimize any desired illumination pattern on a receiver.
Common applications for LightTools (and other nonimaging optical-design software as well) include LED-based sources, general lighting, backlit displays, light pipes, refractive optics, projector systems, solar concentrators, and vehicle interior and exterior lighting.
The OpticStudio optical-design software by Radiant Zemax, mentioned earlier, is an example of an optical-design package that has illumination-system design capabilities built in. Elento of Radiant Zemax notes that to improve the speed of design, "OpticStudio performs smart data caching so that lengthy calculations are only recomputed when necessary. Calculated data is also saved with the lens file so that it doesn't need to be recomputed upon file open."
Pairing with its OSLO software, Lambda Research produces TracePro optomechanical software, which is used for the design, analysis, and optimization of both imaging and nonimaging optical and illumination systems. The software is applicable to all stages of the design process, from CAD layout through analysis and reporting, notes Gauvin of Lambda Research. TracePro uses virtual prototyping via a 3D CAD interface, interactive optimizers, fast ray tracing, and visualization and analysis tools to reduce development time.
TracePro's capabilities include baffle design for stray light suppression, aperture diffraction, and ghost image analysis. Other analysis capabilities include self-emission of infrared and longer-wavelength systems, simulation of polarization effects including birefringence, simulation of spectrometers and other multispectral systems, thermal effects and loading, narcissus effects, and diffraction gratings, says Gauvin.
Designing for photometric requirements
Photopia, a nonimaging optical design and analysis program produced by LTI Optics (Westminster, CO), is oriented toward applications in the architectural, industrial, signal, medical, aerospace, and automotive lighting industries where products need to meet specific photometric requirements. "We put a large emphasis on Photopia's source and material libraries, since many of our customers do not want to be burdened with defining detailed source and material properties for standard products on their own," says Mark Jongewaard, Photopia product manager and senior optical engineer at LTI Optics.
"We therefore create our own source models, based on the actual geometry, material, and luminous properties of the source as well as measure our own material BSDF (light-scattering) data so our customers can just pick what they are using from our library," explains Jongewaard. "We consider the accuracy of the analyses our responsibility, and since the accuracy is highly dependent upon the source and material properties, we don't put that responsibility on others. This is why we also don't rely on the use of 'ray sets,' often posted on lamp manufacturers' websites, to sufficiently represent light sources since they have several limitations that can lead to inaccurate results [see Fig. 2]."
Photopia comes with a light-source library that currently includes nearly 900 different lamps of all types; however, the library is now more than half LEDs, notes Jongewaard. The library models include the full 3D source geometry, with luminous properties and materials assigned to the various parts, and full spectral data representing the color changes over emission angle as well as over the emission area.
"Photopia also includes reflector and lens-design tools that have been developed from our own optical design consulting experience," says Jongewaard. "Parametric Optical Design Tools (PODTs) create the optical shapes based on how the light needs to be controlled (over a desired range of angles, for example) and then allow the user to control how much light is directed to each part of the beam. These tools provide the user with much more insight into how and why the optical shapes are the way they are, which allows them to make the best decisions about what performance is possible within their constraints."
A note about the lens- and illumination-design software packages mentioned in this article: while learning one of these software applications from scratch may seem daunting, many software makers offer tutorials and courses; visit their websites to see what is available. Also, many of the screen captures produced by these software packages have such high resolution and fine detail that they fare badly when appearing in print.
REFERENCE
1 R. Kingslake, Lens Design Fundamentals (Academic Press, 1978).
For More Information
Companies mentioned in this article include:
Breault Research Organization
Tucson, AZ
www.breault.com
Dassault Systèmes
San Diego, CA
www.3ds.com
Lambda Research
Littleton, MA
www.lambdares.com
LTI Optics
Westminster, CO
www.ltioptics.com/home/index.html
Qioptiq
Fairpoint, NY
www.qioptiq.com
Radiant Zemax
Redmond, WA
www.radiantzemax.com/en
Synopsys
Mountain View, CA
www.synopsys.com/home.aspx
FOR A COMPLETE LISTING OF COMPANIES making lens design software, visit the Laser Focus World Buyers Guide (http://buyersguide.laserfocusworld.com/index.html).
John Wallace | Senior Technical Editor (1998-2022)
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.