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A FreeForm Optics Application of Entropic Optimal Transport

Giorgi Rukhaia 1
1 MOKAPLAN - Méthodes numériques pour le problème de Monge-Kantorovich et Applications en sciences sociales
CEREMADE - CEntre de REcherches en MAthématiques de la DEcision, Inria de Paris
Abstract : In this work, we address the “freeform optics” inverse problem of designing a reflector surface mapping a prescribed source distribution of light to a prescribed target far-field distribution, for the point light source and the extended light source. When the source is a point source, the light distribution has support only on the optics ray directions. In this setting, the inverse problem is well-posed for arbitrary source and target probability distributions. It can be recast as an optimal transport problem and is a classic example of an optimal transport problem with a non-euclidean displacement cost. We explore the use of entropic Optimal Transport and the associated Sinkhorn algorithm to solve it numerically. As the reflector modeling is based on the Kantorovich potentials, several questions arise. First, on the convergence of the discrete entropic approximation and here we follow the recent work of Berman and in particular the imposed discretization requirements therein. Secondly, the correction of the bias induced by the entropic Optimal Transport using the recent notion of Sinkhorn divergences is shown to be necessary to achieve satisfactory results. For the point source problem, we discuss the necessary mathematical and numerical tools needed to produce and analyze the obtained numerical results. We find that Sinkhorn algorithm may be adapted to the resolution of the point source to far-field reflector problem. We are not aware of any similar mathematical formulation in the extended source case: i.e. the source has an “étendue” with support in the product space: physical domain-ray directions. We propose to leverage the well-posed variational formulation of the point source problem to build a smooth parameterization of the reflector and the map modeling the reflection. Under this parametrization, we can construct a smooth cost function to optimize for the best solution in this class of reflectors. Both steps, the parameterization and the cost function, are related to entropic optimal transport distances. We also take advantage of recent progress in the optimization techniques and the efficient implementations of Sinkhorn algorithm to perform a numerical study.
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https://hal.archives-ouvertes.fr/tel-03447718
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Submitted on : Wednesday, November 24, 2021 - 6:22:52 PM
Last modification on : Saturday, January 22, 2022 - 3:24:21 AM

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Giorgi Rukhaia. A FreeForm Optics Application of Entropic Optimal Transport. Mathematics [math]. PSL Université Paris Dauphine; INRIA Paris, 2021. English. ⟨tel-03447718⟩

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