Global Optimization in reTORT, Try It, You’ll Like It
Global Optimization scares some designers. It often doesn’t play a key role in their workflow. We did not understand that until recently. But then, we ran a focus group on optimizers with a group of our Customers.
But why? These designers told us that some of the ray tracers they have used took hours or days to run Global Optimization. And then, they returned one hundred or more possible solutions. After that, the designer needed to sift through the solutions to find one or more they wanted to further refine.
That’s a huge time commitment. After all, your time is money. It can significantly stall progress on a lens design. But, that’s the way some ray tracers implement Global Optimization. reTORT is an exception to this rule. In fact, Global Optimization in reTORT is extremely useful and will speed up your workflow.
reTORT‘s global optimizer returns one optimum result within your design constraints. On average, for a typical complex lens, it does this within a few minutes.
How reTORT works
In reTORT, optimization wizards allow easy setup and running of global or local optimization. You can run a global or a local optimization from this one window.
Right at hand, you can easily change settings, goals and parameters.
reTORT employs evolutionary algorithms for its global optimizers. Specifically, they are based on a modified version of CMAES, or Covariance Matrix Adaptation Evolution Strategy. The E x H modifications to CMAES provide for speedy and accurate results.
CMAES is capable of optimizing a very large search space with many variables. CMAES can easily generate new candidate lens designs from scratch with minimal oversight.
But contrary to other prevailing logic, E x H found through its research that CMAES is much more efficient if you apply bounds. Now, do bounds mean over-constraint? Not at all. In fact, almost all designs have some over-riding design objectives that provide the basis for applying realistic bounds.
We hope to start bragging about our very useful status bar. You can see it below in an illustration of a global optimization. You see that 12,000 simulations were run and two can be seen taking from 65 to 85 milliseconds each.
The entire optimization took a total of 3.37 minutes.
Bounded versus Unbounded
Please remember, reTORT also offers a very efficient local optimizer based on the Damped Least-Squares (DLS) algorithm. DLS is run unbounded by default, in contrast to its global sister.
In our research, we found that bounded DLS algorithms tended to more easily fall into near optimums. In other words, they often take one of the first valleys they find. This is even though a better solution was available in the search space. It acted like one of our favorite little guys searching for an optimum below:
And so, reTORT’s DLS is unbounded based on our preferred workflow of first using bounded global optimization. Global optimization with CMAES is used to find a candidate design within mere minutes. Then, we use local optimization to test variations of that design and tune it even further. In that way, we can hone the design in less time. And with reTORT each iteration is faster than other tools.
But reTORT allows you to do the opposite or use one or the other. The choice is always yours. The combination of global and local optimizers allows a variety of workflows.
A Variety of Workflows
Workflow does vary among designers, no matter which ray tracing tool they are using. In our recent focus groups among designers with experience with other ray tracers, we found that workflow preferences varied:
- Some designers prefer always using Damped Least Squares (DLS)
- Others test various designs using DLS and then run global optimizers. This is the group that finds hundreds of possible optimum solutions in tools other than reTORT. The reTORT global optimizer returns only the best solution. They then rank them, usually by merit function or cost scores. And finally, they focus on three or four finalists to refine. Ultimately, they finalize their design.
- The third group runs a global optimizer to zero in on one optimum solution within their design parameters. Then, they use DLS to search the local space to refine that solution.
Workflow varies from designer to designer. So, by design, reTORT does not force the designer into one particular workflow. reTORT allows you to follow the workflow just right for you and your task at hand.
But There’s More
You can easily have global and local optimizers configured at the same time. But they don’t necessarily run at the same time. You can switch from one to the other as you prefer. You can see this in the Optimizer Settings image above. Both methods are enabled at the same time.
The reTORT wizards also give you immediate control over optimization settings, goals, and parameters. As you proceed with your design, your optimizer controls are right at hand for making quick tweaks.
You can also save multiple optimization configurations. The optimization wizard creates optimizations under the names “AutoCMAES” and “AutoDLS”. Save your optimizations by simply renaming them before running the wizard again. If you wish, come back later to revisit a prior configuration.
And the same power of our optimizers is equally available to you for including gradient index lenses and metasurfaces in your optical lens system design. You are able to use the full power of reTORT using the most powerful and advanced lens features available to any designer today.
The reTORT Ray Tracer is truly a unique state-of-the-art tool for today’s optical lens designer.
Get Your Copy of v2.1 of the reTORT Ray Tracer
Please visit the site to download v2.1 and update the version you are currently running.
For those who are not yet using our reTORT Ray Tracer, the same download link will provide you with a free two-week trial. Our license pricing and ordering list is the place to go to order. You will be committing to the most technologically advanced ray tracer available today.
About E x H, Inc.
E x H’s mission is to provide you with advanced optical system simulation tools. The result is tools that allow you to design optical systems that are smaller, lighter and faster. Watch our SWaP reduction use case tutorial for a taste of this.
Some of our solvers are licensed from Penn State University. PSU is one of the leading research institutions in the USA.
We have participated on multiple programs funded by DARPA that have allowed us to develop software on the leading edge of technology. Outside of the optical space, this same reTORT Ray Tracer was used to fast prototype the transformational optics that proved the concept for Isotropic Systems’ high throughput, multi-beam satellite terminals (https://www.isotropicsystems.com/).
On the business side, we have been backed by Gran Sasso Ventures, the same venture capitalists that funded collaboration software firm Compoze Software, now a part of Oracle [ORCL:NYSE], and multitouch technology inventor FingerWorks, the driver of touch screen technology and now a part of Apple [AAPL:NASDAQ]. E x H is at the forefront of transformation optics.
