Currently, many nanophotonic structures are designed based on heuristic principles, for example the design of gratings based on wavevector matching, or the design of a nanoantenna to have a length equal to a half-wavelength. In contrast, automated iterative optimization-based approaches can yield complex nonintuitive structures that provide better performance than heuristically-designed structures. This is especially true for 3D photonic structures, whose behavior can be more dificult to conceptualize than that of 2D structures. The challenge is that multi-parameter optimization routines often require hundreds or thousands of iterations, but a typical full-wave nanophotonic simulation may take hours per iteration. One type of optimization approach that has been applied to nanophotonics is topology optimization (TO). While TO works well for top-down fabrication where structures are fabricated from continuous media, it is not as well-suited for bottom-up, or additive-type fabrication methods based on building blocks of non-negligible size. Here we present a design methodology based around iterative object placement optimization, where the iterative loops are rapidly computed using a coupled dipole approach. The coupled dipole approach cannot capture all of the same physics as full-wave simulation approaches, however it can provide approximate results much more rapidly. We compare the accuracy of the coupled dipole approach to finite-difference time domain simulations. Two application designs will also be presented: compact 3D waveguide couplers and superresolution imaging structures.
Euan McLeod and Weilin Liu, "Rapid nanophotonic structure design and optimization using a coupled dipole approach (Conference Presentation)," Proc. SPIE 10541, Photonic and Phononic Properties of Engineered Nanostructures VIII, 105411J (Presented at SPIE OPTO: February 01, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2290774.5751523659001.
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