The development of complex optical filters has seen significant growth in recent years, and manufacturing technologies now enable the creation of highly complex optical functions, both spectral and spatial. Among these are complex optical coatings, such as butcher blocks filters, linearly variable filters, and patterned filters. These filters play a key role in meeting optical needs for space applications, particularly for Earth observation systems. Specifically, for hyperspectral applications, these components are central to the overall performance of the mission.

However, their design and optimization face major challenges in terms of optical modeling, manufacturing, optical thin-film coating, as well as spectral and spatial characterization. It is therefore crucial to master all the different stages, from specification to evaluation, and to consider all the issues specific to each step. In particular, efforts will focus on distinguishing the effects of stray light in structured components to integrate them early in the instrument design process. Through simulation and characterization work, comparisons of different technological solutions for these filtering functions can be made. This thesis, which would be 100% funded by CNES, is part of a strategic roadmap dedicated to thin-film optical filters for hyperspectral imaging. Its aim is to cover a broad spectrum of activities, ranging from advanced optical modeling to integration in an optical system, including the use and optimization of high-precision test benches for the fine characterization of the performance of these complex optical filters.

The research will address several crucial technical aspects. First, the development of an optical simulation tool, along with advanced simulation of interference filter components, will take into account all physical phenomena related to the component’s architecture, particularly diffraction, scattering, and ghost images. Second, the spectral and spatial characterization of elementary components will be carried out, including the understanding, implementation, and optimization of test benches to measure the performance of filters at very high spectral and spatial resolutions. These activities will rely on specific metrological resources available in the laboratory, which will need to be optimized and supplemented to meet the high-performance characterization requirements demanded by hyperspectral missions. These characterizations will also include the study of scattering phenomena and stray light, which can degrade the performance of hyperspectral instruments. Spectral and spatial characterizations will further allow for evaluating the impact of cosmetic defects given the particularly stringent requirements on characterization quality. Comparative characterizations may also be performed at the Fresnel Institute laboratory, which has metrological capabilities complementary to those developed by CNES. Third, the comparison of different filtering technologies in an instrumental configuration will be explored. This aspect may be approached experimentally by proposing a laboratory demonstration and validating the concepts by cross-referencing the results obtained with the expected optical performance modeling. The objective will be to identify critical instrumental parameters and propose optimizations for realistic application scenarios.

The Fresnel Institute, particularly the CONCEPT team and the RCMO team will play a central role in this thesis. The PhD candidate will benefit from their recognized expertise in the fields of optical coatings and characterization, enabling high-dynamic-range measurements of transmission coefficients, angular and spectral resolved scattering on complex optical coatings. Their contribution will focus on the development of high-dynamic-range characterization methods, precise measurement of scattering phenomena and stray light, as well as the provision of calibration samples for thin-film optical filters. With their advanced measurement system SALSA (Spectral and Angular Light Scattering characterization Apparatus), the Fresnel Institute will enable a deeper exploration of these critical aspects in close collaboration with CNES teams.

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For more Information about the topics and the co-financial partner (found by the lab !); 

contact Directeur de thèse - julien.lumeau@fresnel.fr

Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online  before March 14th, 2025 Midnight Paris time !