Tiny lasers acting together as one: Topological vertical cavity laser
arrays

Date:
September 24, 2021
Source:
University of Wu"rzburg
Summary:
An international research team uses topological platform to
demonstrate coherent array of vertical lasers.



FULL STORY ========================================================================== Israeli and German researchers have developed a way to force an array
of vertical cavity lasers to act together as a single laser -- a highly effective laser network the size of a grain of sand. The findings are
presented in a new joint research paper published online by the journal
Science on Friday, September 24.


==========================================================================
Cell phones, car sensors or data transmission in fiber optic networks are
all using so called Vertical-Cavity Surface-Emitting Lasers (VCSELs) - - semiconductor lasers that are firmly anchored in our everyday technology.

Though widely used, the VCSEL device has miniscule size of only a
few microns, which sets a stringent limit on the output power it can
generate. For years, scientists have sought to enhance the power emitted
by such devices through combining many tiny VCSELs and forcing them to
act as a single coherent laser, but had limited success. The current breakthrough uses a different scheme: it employs a unique geometrical arrangement of VCSELs on the chip that forces the flight to flow in a
specific path -- a photonic topological insulator platform.

From topological insulators to topological lasers Topological insulators
are revolutionary quantum materials that insulate on the inside but
conduct electricity on their surface -- without loss. Several years ago,
the Technion group led by Prof. Mordechai Segev has introduced these
innovative ideas into photonics, and demonstrated the first Photonic Topological Insulator, where light travels around the edges of a two- dimensional array of waveguides without being affected by defects or
disorder.

This opened a new field, now known as "Topological Photonics," where
hundreds of groups currently have active research. In 2018, the same
group also found a way to use the properties of photonic topological
insulators to force many micro-ring lasers to lock together and act as
a single laser. But that system still had a major bottleneck: the light
was circulating in the photonic chip confined to the same plane used for extracting the light out. That meant that the whole system was again
subject to a power limit, imposed by the device used to get the light
out, similar to having a single socket for a whole power plant. The
current breakthrough uses a different scheme: the lasers are forced to
lock within the planar chip, but the light is now emitted through the
surface of the chip from each tiny laser and can be easily collected.

Circumstances and participants This German-Israeli research project
originated primarily during the Corona pandemic. Without the enormous commitment of the researchers involved, this scientific milestone would
not have been possible. The research was conducted by PhD student Alex Dikopoltsev from the team of Distinguished Professor Mordechai Segev,
of the Physics Department and the Electrical & Computer Engineering
Department at the Technion -- Israel Institute of Technology, and
PhD student Tristan H. Harder from the team of Prof. Sebastian Klembt
and Prof.

Sven Ho"fling at the Chair of Applied Physics at the University of
Wu"rzburg, and the Cluster of Excellence ct.qmat -- Complexity and
Topology in Quantum Matter, in collaboration with researchers from Jena
and Oldenburg. The device fabrication took advantage of the excellent
clean room facilities at the University of Wu"rzburg.

The long road to new topological lasers "It is fascinating to see
how science evolves," said Prof. Segev of the Technion. "We went from fundamental physics concepts to foundational changes therein, and now
to real technology that is now being pursued by companies.

Back in 2015, when we started to work on topological insulator lasers,
nobody believed it's possible, because the topological concepts known
at that time were limited to systems that do not, in fact -- cannot --
have gain. But all lasers require gain. So topological insulator lasers
stood against everything known at that time. We were like a bunch of
lunatics searching for something that was considered impossible. And
now we have made a large step towards real technology that has many applications." The Israeli and German team utilized the concepts
of topological photonics with VCSELs that emit the light vertically,
while the topological process responsible for the mutual coherence and
locking of the VCSELs occurs in the plane of the chip. The end result is
a powerful but very compact and efficient laser, not limited by a number
of VCSEL emitters, and undisturbed by defects or altering temperatures.

"The topological principle of this laser can generally work for all
wavelengths and thus a range of materials," explains German project
leader Prof. Sebastian Klembt of the University of Wu"rzburg, working
on light-matter interaction and topological photonics within the ct.qmat Cluster of Excellence. "Exactly how many microlasers need to be arranged
and connected would always depend entirely on the application. We
can expand the size of the laser network to a very large size, and in
principle it will remain coherent also for large numbers. It is great
to see that topology, originally a branch of mathematics, has emerged
as a revolutionary new toolbox for controlling, steering and improving
laser properties." The groundbreaking research has demonstrated that
it is in fact theoretically and experimentally possible to combine
VCSELs to achieve a more robust and highly efficient laser. As such,
the results of the study pave the way towards applications of numerous
future technologies such as medical devices, communications, and a
variety of real-world applications.

========================================================================== Story Source: Materials provided by University_of_Wu"rzburg. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Alex Dikopoltsev, Tristan H. Harder, Eran Lustig, Oleg A. Egorov,
Johannes Beierlein, Adriana Wolf, Yaakov Lumer, Monika Emmerling,
Christian Schneider, Sven Ho"fling, Mordechai Segev, Sebastian
Klembt.

Topological insulator vertical-cavity laser array. Science, 2021;
373 (6562): 1514 DOI: 10.1126/science.abj2232 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210924104254.htm

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