Abstract
In this article, we report an integrated optical nanolens exhibiting a pseudo-graded index distribution in a guided configuration. This dielectric metalens relies on a permittivity distribution through dielectric strips of the core material, which is compatible with existing silicon photonic technology. We show in this paper that effective medium theory (EMT) inaccurately predicts the focal length of such devices, and we propose an efficient and accurate design approach based on 2D finite element method (FEM) mode calculations that are in good agreement with 3D FDTD simulations. The lens was fabricated on a 200 mm silicon on insulator pilot line, and fibre-to-fibre optical characterizations revealed an excellent transmission of 85% for TM polarization, in line with the simulated performance (90%). The proposed approach can be easily extended to width-variable strips, enabling the realization of all types of graded index devices, especially those derived from transformation optics.
Highlights
In this article, we report an integrated optical nanolens exhibiting a pseudo-graded index distribution in a guided configuration
We propose a more accurate approach based on finite element method (FEM) mode calculations to efficiently determine both the lens profile and focal length, taking into account technological constraints
We have shown that for such pseudo-graded index devices with realistic feature dimensions, second-order effective medium theory (EMT) can be inaccurate in generating the correct effective index profile
Summary
We report an integrated optical nanolens exhibiting a pseudo-graded index distribution in a guided configuration This dielectric metalens relies on a permittivity distribution through dielectric strips of the core material, which is compatible with existing silicon photonic technology. A diffractive medium composed of transparent subwavelength microstructures can emulate a continuously variable effective index profile[7] Such metasurfaces can benefit from thin subwavelength metallic resonators arranged in pseudo-arrays to obtain abrupt phase changes, drastically reducing the optical path necessary to shape light beams at the expense, of some metallic losses[9]. We propose a more accurate approach based on FEM mode calculations to efficiently determine both the lens profile and focal length, taking into account technological constraints We successfully compare this approach with 3D-FDTD, and we fabricate and characterize the resulting structure on a 200 mm Si platform. The proposed approach is applicable to any device exhibiting a continuously graded permittivity variation, such as most devices obtained from TO3
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