Capacitive actuation and switching of add–drop
graphene-silicon micro-ring filters
TOMMASO CASSESE,
1
MARCO ANGELO GIAMBRA,
2
VITO SORIANELLO,
2
GABRIELE DE ANGELIS,
2
MICHELE MIDRIO,
3
MARIANNA PANTOUVAKI,
4
JORIS VAN CAMPENHOUT,
4
INGE ASSELBERGHS,
4
CEDRIC HUYGHEBAERT,
4
ANTONIO D’ERRICO,
5
AND MARCO ROMAGNOLI
2,
*
1
Scuola Superiore Sant’Anna-TeCIP Institute, via Moruzzi 1, 56124 Pisa, Italy
2
CNIT-Consorzio Nazionale Interuniversitario per le Telecomunicazioni, via Moruzzi 1, 56124 Pisa, Italy
3
CNIT-Consorzio Nazionale Interuniversitario per le Telecomunicazioni, Università degli Studi di Udine, 33100 Udine, Italy
4
Imec, Kapeldreef 75, 3001 Heverlee, Belgium
5
Ericsson Research, Via G. Moruzzi 1, 56124 Pisa, Italy
*Corresponding author: marco.romagnoli@cnit.it
Received 25 July 2017; revised 27 September 2017; accepted 27 September 2017; posted 28 September 2017 (Doc. ID 303062);
published 1 December 2017
We propose and experimentally demonstrate capacitive actuation of a graphene–silicon micro-ring add/drop
filter. The mechanism is based on a silicon–SiO
2
–graphene capacitor on top of the ring waveguide. We
show the capacitive actuation of the add/drop functionality by a voltage-driven change of the graphene optical
absorption. The proposed capacitive solution overcomes the need for continuous heating to keep tuned the
filter’s in/out resonance and therefore eliminates “in operation” energy consumption.
© 2017 Chinese Laser
Press
OCIS codes: (250.5300) Photonic integrated circuits; (230.0250) Optoelectronics; (130.3120) Integrated optics devices.
https://doi.org/10.1364/PRJ.5.000762
1. INTRODUCTION
Photonic switching is one of the fundamental topics of inte-
grated optics. Thanks to development in the field of silicon
photonics, reaching high miniaturization and low cost, silicon
and silicon nitride (Si
3
N
4
) optical add and drop multiplexers
(OADMs) based on micro-ring resonators (MRRs) currently
offer perspectives [1,2], in particular for access networks that
require large volumes [3]. The add/drop functionality of a
silicon photonic OADM can be switched by properly tuning or
detuning the MRR resonance with respect to the signal wave-
length. In particular, switching is achieved by exploiting the
thermo-optic effect by means of metallic or Si-based Joule heat-
ers integrated in close proximity of the MRR waveguide.
Although the thermo-optic effect is very efficient in silicon,
the thermo-optic actuation requires continuous power con-
sumption that can easily sum to some milliwatts [4]. In a com-
plex switching matrix with tens or more MRRs, this power
consumption can be detrimental. Moreover, this approach
may limit the wavelength channel density in wavelength-
division-multiplexing (WDM) systems. In fact, the thermo-
optic actuation implies that the MRR resonance must be tuned
to a wavelength in the center between two adjacent channels in
order to avoid crosstalk. Depending on the shape of the MRR
resonance, the detuned wavelength may set a limit to the
minimum grid separation. Switching could also be achieved
by using free-carrier effect modulators, either in depletion
p–n junctions or in injection p-i-n junctions, or in a semicon-
ductor–insulator–semiconductor capacitor (SISCAP) configu-
ration [5]. However, depletion p–n junctions and SISCAP
modulators allow for only resonance detuning, thus limiting
the channel density, whereas large variation of optical losses
can be obtained with carrier injection in p-i-n junctions, but
at the cost of large power consumption (of the order of
hundreds of milliwatts) due to forward bias current [6]. For
these reasons, alternative approaches are needed for add/drop
switching, e.g., suppressing the resonance rather than relying
on thermal tuning/detuning.
Graphene is a versatile 2D material with tunable optical
properties allowing large spectral bandwidth, high speed, small
footprint, and CMOS compatibility. Graphene has recently
raised interest for application in photonics integrated circuits
[7]. Graphene–on–Si modulators and photodiodes have already
been successfully demonstrated [8–11]. These devices exploit
the possibility of large tuning of the complex optical conduc-
tivity of graphene by electrical gating [12]. The in-plane com-
plex optical conductivity of graphene can be expressed as a
function of the Fermi level as [13]
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Vol. 5, No. 6 / December 2017 / Photonics Research
Research Article
2327-9125/17/060762-05 Journal © 2017 Chinese Laser Press