Over the past years, global data traffic has experienced a boom, with over 12.5 billion
connected devices all over the world.
The current world-wide deployment of the 5G telecommunications standard is triggering
the need for smaller devices with enhanced performances, such as higher speed, lower
power consumption and reduced cost as well as easier manufacturability.
In search for the appropriate technology, photonic devices emerged as the leading technology
for the evolution of such information and communication technologies, already surpassing
the capabilities of current microelectronics and CMOS technologies.
Optical communication systems rely on three basic components: modulators, waveguides and
photodetectors.
The modulation of light is key for photonic integrated circuits because it allows to transmit
multiple signals simultaneously over a single channel.
More specifically, electro-absorption (EA) modulators modulate the amplitude of the light
passing through the optical waveguide.
So far, silicon and graphene are winning the race since they are proving to be the most
scalable, cost-effective and CMOS compatible materials for optical modulation and detection.
Graphene-based modulators have already shown broadband optical bandwidth and temperature
stability, but in occasions, they have been incapable of showing both high-speed and high
modulation efficiencies simultaneously, due to the limited quality of graphene and a combination
between the graphene and the dielectric material.
Now, in a study published in the journal Nature Communications, researchers from ICFO - The
Institute of Photonic Sciences have reported on a novel EA modulator capable of showing
a 3-fold increase in static and dynamic modulation efficiency while maintaining the high-speed,
a value that surpasses those for previously reported graphene EA modulators.
To achieve this, the team of researchers developed a high-quality graphene-based electro-absorption
modulator by combining high-quality graphene and a high-k dielectric, also used in microelectronics.
The high quality of the graphene was achieved by integrating it with the 2d-material dielectric
hexagonal boron nitride (hBN).
Interestingly enough, the team was then able to add the high-k dielectric material sandwiched
in between two layers of boron nitride, which permitted operating with much smaller voltages,
and, at the same time, achieving symmetric and hysteresis-free operation due to the high quality
of the graphene.
By doing this, the dielectric combination was able to enhance the EA modulator capacitance
without compromising the robustness of the device against high voltages, preserve the
high mobility of charge carriers (increasing the modulation efficiency) while maintaining
low levels of doping.
The researchers say that Optoelectronics is one of the first where this 2D material overcomes
current state-of-the-art technologies, bringing an encouraging prospect for other commercial
applications.
In summary, the device was capable of outperforming previous modulators, operating at high-speeds
while, maintaining a very high modulation efficiency, low power consumption, achieving
a record breaking 39GHz bandwidth, with operations up to 40Gbps speed, and consequently overcoming
the fundamental limitations obtained so far with double layer graphene systems.
The compatibility of this device with silicon technology and microelectronics could facilitate
the scaling improvements that we face nowadays for the photonic industry as well as implement
this type of technology for a much greater range of functionalities in electronic and
optoelectronic applications.
Such results could definitely benefit applications for high-speed and low-latency optical networks
such as autonomous vehicles, remote surgery, IoT, to name a few.