A Study on Function-Expansion-Based Topology Optimization without Gray Area for Optimal Design of Photonic Devices

Masato TOMIYASU  Keita MORIMOTO  Akito IGUCHI  Yasuhide TSUJI  

IEICE TRANSACTIONS on Electronics   Vol.E103-C    No.11    pp.560-566
Publication Date: 2020/11/01
Publicized: 2020/04/09
Online ISSN: 1745-1353
DOI: 10.1587/transele.2019ESP0005
Type of Manuscript: Special Section PAPER (Special Section on Recent Advances in Simulation Techniques and Their Applications for Electronics)
topology optimization,  function expansion method,  finite element method,  adjoint variable method,  

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In this paper, we reformulate a sensitivity analysis method for function-expansion-based topology optimization method without using gray area. In the conventional approach based on function expansion method, permittivity distribution contains gray materials, which are intermediate materials between core and cladding ones, so as to let the permittivity differentiable with respect to design variables. Since this approach using gray area dose not express material boundary exactly, it is not desirable to apply this approach to design problems of strongly guiding waveguide devices, especially for plasmonic waveguides. In this study, we present function-expansion-method-based topology optimization without gray area. In this approach, use of gray area can be avoided by replacing the area integral of the derivative of the matrix with the line integral taking into acount the rate of boundary deviation with respect to design variables. We verify the validity of our approach through applying it to design problems of a T-branching power splitter and a mode order converter.