New optical design library reduces error margin for freeform mirrors

A recently closed activity with TDE and Onera, France, has developed an open source optical design library capable of optimising freeform mirrors using ray-tracing.

The first of its kind library, called FORMIDABLE, will reduce the convergence difficulties often created due to the many degrees of freedom freeform mirrors bring to optical systems. Current commercial optical software are limited in their capacity to design freeform optical system as they do not optimise Non-Uniform Rational B-Spline (NURBS) surfaces efficiently.

The closed-source nature of commercial optical software makes them resistant to collaboration with external algorithms and thus limits stakeholders innovation capacity. Unlike previous librarys, FORMIDABLE can simulate and especially optimise NURBS surfaces. The key advantage of NURBS lies in their ability to locally describe an optical surface, thereby minimizing preconceived notions about the surface shape, aside from the surface sampling determined by the density of the NURBS representation.

It's main drawback is the significant increase in the degrees of freedom within the optical system, making the optimization of these surfaces a complex task with a conventional commercial optical design software. FORMIDABLE's implementation of differential ray-tracing capabilities allows faster convergence of systems described by many degrees of freedom and makes optimization with NURBS surfaces viable.

Now available on the ESA public repository, gitlabspace-codev.org, it needs a critical mass of users for wider adoption.