Designing free-form optics for multiple-source illumination using differentiable ray-tracing and neural networks

Designing free-form optics for multiple-source illumination using differentiable ray-tracing and neural networks

de Koning, Bart (TU Delft Electrical Engineering, Mathematics and Computer Science)

Möller, M. (mentor)
Heemink, A.W. (graduation committee)
Adam, A.J.L. (mentor)
Heemels, A.N.M. (graduation committee)

Delft University of Technology

Applied Mathematics | Computational Science and Engineering

2022-08-22

Differentiable ray-tracing is an exciting new development in computer graphics to approach all sorts of 3D scene design problems by obtaining gradients of renders produced by ray-tracing with respect to parameters that define the scene. These gradients can then be incorporated in a gradient-descent type optimization pipeline.

One such type of design problem is caustic design with free-form lenses. This is the process of obtaining the geometry of lenses in an optical system such that the light that passes through this system forms a desired illumination distribution on a target screen. A typical application of this is distributing the light from streetlights or car headlights in a pleasing and efficient way over the street.

The non-imaging optics literature offers many methods to design free-form lenses for caustic design, but differentiable ray-tracing is largely unknown in this field. Therefore this thesis proposes a method of optimizing free-form lenses for caustic design with differentiable ray-tracing.

The optimization pipeline starts with a multi-layer perceptron neural network which outputs parameters that define one free-form lens side in the form of a B-spline surface. A specially implemented ray-tracer then produces a caustic render by tracing through this lens from either a plane wave or a (grid of) point source(s). Back-propagation and optimization takes place using automatic differentiation in PyTorch and the Adam optimizer.

The results, which are verified with LightTools, show great promise for this technique, especially for the plane wave optimizations. The point source grid optimizations proved to be more challenging, but also here the optimization was able to achieve improvement. This shows that the proposed technique also has potential in positive etendue optimizations.

Optics
Differentiable ray-tracing
B-spline surfaces
Free-form lens
Neural networks
Caustic design

http://resolver.tudelft.nl/uuid:0c514716-f2db-455e-b75d-3cf9cfeed8bb

2023-08-22

Student theses

master thesis

© 2022 Bart de Koning