Topology optimization of blazed gratings under conical incidence
arxiv(2024)
Abstract
A topology optimization method is presented and applied to a blazed
diffraction grating in reflection under conical incidence. This type of
gratings is meant to disperse the incident light on one particular diffraction
order and this property is fundamental in spectroscopy. Conventionally, a
blazed metallic grating is made of a sawtooth profile designed to work with the
+/-1st diffraction order in reflection. In this paper, we question this
intuitive triangular pattern and look for optimal opto-geometric
characteristics using topology optimization based on Finite Element modelling
of Maxwell's equations. In practical contexts, the grating geometry is
mono-periodic but it is enlightened by a 3D plane wave with a wavevector
outside of the plane of invariance. Consequently, this study deals with the
resolution of a direct and inverse problem using the Finite Element Method in
this intermediate state between 2D and 3D: the so-called conical incidence. A
multi-wavelength objective is used in order to obtain a broadband blazed
effect. Finally, several numerical experiments are detailed. The results show
that it is possible to reach a 98
diffraction order if the optimization is performed on a single wavelength, and
that the reflection integrated over the [400,1500]nm wavelength range can be
29
grating when using a multi-wavelength optimization criterion (from 52
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