Integrated photonic guided metalens based on a pseudo-graded index distribution

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.

Bayesian optimization and rigorous modelling of a highly efficient 3D metamaterial mode converter

“…As it can be seen from the shaded region, there are three global points similar to what we have found in Table 1 and the best FOM is obtained at L = 3700 nm. In order to render further physical insights on the results achieved from the optimization method, we provide an estimation of the widths of the strips using the graded index lens profile [14]. Following the same strategy presented in our former work for the TM case [14], the widths of the strips are roughly estimated by calculating the effective mode index for each strip, by considering a single strip placed in a periodic configuration, with period 250 nm.…”

“…In order to render further physical insights on the results achieved from the optimization method, we provide an estimation of the widths of the strips using the graded index lens profile [14]. Following the same strategy presented in our former work for the TM case [14], the widths of the strips are roughly estimated by calculating the effective mode index for each strip, by considering a single strip placed in a periodic configuration, with period 250 nm. Changing the width of this single strip and computing the corresponding effective mode index creates a library for effective mode indices as a function of the corresponding widths.…”

“…Changing the width of this single strip and computing the corresponding effective mode index creates a library for effective mode indices as a function of the corresponding widths. Afterwards, only strips that provide a graded index lens profile [14] will be chosen from the library. In Table 3, we present the values based on this approximated technique [14], which are similar to the best design obtained from our optimization approach (see the first row in Table 2).…”

“…Afterwards, only strips that provide a graded index lens profile [14] will be chosen from the library. In Table 3, we present the values based on this approximated technique [14], which are similar to the best design obtained from our optimization approach (see the first row in Table 2). Nevertheless, the graded index profile approach does not give any information about the optimal length along the propagation direction.…”

“…Consequently, they might be stuck in local minima/maxima rather than achieving the best design in the search parameter space. In this work, we concentrate on optimizing a silicon mode converter which has been identified as a critical component being realized in all the integrated photonic systems, while playing a fundamental role in wave division multiplexing and demultiplexer systems [12][13][14][15][16][17].…”