Speaker: Lei Shi (Fudan University)
Time: 2025 July 2nd, 14：00 PM
Location: 1510, SIMIS
Zoom Meeting ID: 479 937 5280 (Passcode: SIMIS)
摘要：
Inverse problems in optics involve deducing the corresponding structure from a known spectral response. Traditional physical simulation algorithms primarily focus on predicting the physical response given known structural parameters, which is typically unique. However, inverse problems face significant challenges: establishing the mapping from spectra to structure is inherently difficult, and they generally suffer from non-unique solutions. This presentation will introduce inverse problems through two practical applications: metrology and inverse design.
The first part focuses on metrology, primarily discussing methods that employ neural networks (NNs) to construct the mapping from spectra to structure, along with their application in grating measurements. Subsequently, we constructed a backpropagation (BP) algorithm within physical simulation frameworks. This was applied to problems such as single-layer film thickness determination and detection of anomalous layers in multilayer films. Furthermore, the BP algorithm was implemented for grating measurements.
The second part focuses on inverse design, primarily discussing the use of the backpropagation algorithm for optimizing thin films, gratings, and photonic crystal slabs (PCS). For thin films, we employed a strategy of progressively inserting layers to continue the optimization. For gratings, we simultaneously optimized hundreds of parameters to discover new nanophotonic structures.
About the speaker:
Dr. Lei Shi is a Professor at the Department of Physics, Fudan University, appointed in December 2018. He received his B.Sc. from Nanjing University in 2005 and Ph.D. from Fudan University in 2010. Prior to his current position, he served as a Young Investigator at Fudan University from December 2013 to November 2018. His earlier research training included postdoctoral appointments at Aalto University, Finland (2013–2014) and at the Madrid Institute of Materials Science/Technical University of Valencia, Spain (2011–2012), following a short-term visiting scholarship at the Department of Physics, National University of Singapore in 2010. His research focus on optical field manipulation in photonic crystals, optical metrology for micro-nano fabrication processes, and optical inverse problems.
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