Ultra-compact on-chip metaline-based 1.3/1.6 μm
wavelength demultiplexer
YULONG FAN,
1
XAVIER LE ROUX,
1
ANATOLE LUPU,
1
AND ANDRÉ DE LUSTRAC
1,2,
*
1
Centre de Nanosciences et de Nanotechnologies, CNRS, Université Paris-Sud, Université Paris-Saclay, C2N—Avenue de la Vauve, 91220
Palaiseau cedex, France
2
Université Paris Lumières, Univ Paris Nanterre, 92410 Ville d’Avray, France
*Corresponding author: andre.de-lustrac@c2n.upsaclay.fr
Received 15 October 2018; revised 15 January 2019; accepted 23 January 2019; posted 24 January 2019 (Doc. ID 348256);
published 28 February 2019
In this paper, we report an experimental demonstration of enabling technology exploiting resonant properties of
plasmonic nanoparticles, for the realization of wavelength-sensitive ultra-minituarized (4 μm × 4 μm) optical
metadevices. To this end, the examp le of a 1.3/1.6 μm wavelength demultiplexer is considered. Its technological
implementation is based on the integration of gold cut-wire-based metalines on the top of a silicon-on-insulator
waveguide. The plasmonic metalines modify locally the effective index of the Si waveg uide and thus allow for the
implementation of wavelength-dependent optical pathways. The 1.3/1.6 μm wavelength separation with extinc-
tion ratio between two demultiplexers’ channels reaching up to 20 dB is experimentally demonstrated. The con-
sidered approach, which can be readily adapted to different types of material planar lightwave circuit platforms
and nanoresonators, is suited for the implementation of a generic family of wavelength-sensitive guided-wave
optical metadevices.
© 2019 Chinese Laser Press
https://doi.org/10.1364/PRJ.7.000359
1. INTRODUCTION
The continuous improvement of fabrication technologies was
the main driving factor enabling miniaturization of electronic
circuit components to nanometer scale. Similar trends hold also
for optical circuits, with many efforts devoted to bridging the
gap between photonics and electronics. Because of their mass-
less natur e, photons are orders of magnitude less confined than
electrons. Even in the case of high-index materials, such as
silicon, implementation of optical functions exploiting interfer-
ence between co- or contra-propagating waves in nanostruc-
tured dielectric materials such as photonic crystals [1,2]or
similar [3] requires an interaction length of at least several
wavelengths.
The change in paradigm brought by the advent of metasur-
faces made it possible to control the phase and amplitude of
reflected or transmitted waves on a “skin depth” propagation
length on the order of λ/10 [4–8]. Based on this approach,
numbers of functionalities targeting flat optics applications
have been demonstrated [4–15]. Meanwhile, another possibil-
ity for the manipulation of optical flow by means of metasur-
faces is to use them in a guided-wave configuration [16–22].
The demonstration of a gradient effective index metalens based
on this concept was recently reported [23]. The technological
implementation is performed by means of a metasurface made
of a 2D array of gold cut wires (CWs) integrated on top of the
Si waveguide. The aim of the present work is to provide a fur-
ther impetus to this direction by introducing the concept of
wavelength-dependent optical pathways, distinctly different
from the wavelength-dependent angular beam steering effects
in photonic crystals [24,25] or bi-directional coupling using
plasmonic Fano nanoantennas [19]. To prove the feasibility
of the considered approach, we report the design, fabrication,
and experimental demonstration of an ultra-compact
(4 μm × 4 μm) demultiplexer (DMUX) operating in the wave-
length range 1.3/1.6 μm.
2. METALINES-BASED WAVELENGTH DMUX
OPERATION PRINCIPLE, DESIGN, AND
MODELING
The operation principle of the reported wavelength DMUX is
based on the wavelength-dependent local variation of the hy-
brid metal–dielectric waveguide effective inde x (n
eff
) induced
by plasmonic nanoresonators. Here, we use metalines made
of 1D arrays of gold CWs instead of 2D metasurfaces to modify
locally the index of a Si waveguide, creating thus the equivalent
of color-sensitive optical fibers into the Si layer. They can serve
as building blocks for numbers of guided-wave optical metade-
vices based on local variation of the effective index.
The schematic of the hybrid metal–dielectric DMUX oper-
ating in a guided-wave configuration is shown in Fig. 1(a).
Research Article
Vol. 7, No. 3 / March 2019 / Photonics Research 359
2327-9125/19/030359-04 Journal © 2019 Chinese Laser Press