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An array of small lasers acting as a single light source

A joint team of researchers from the Technion and Germany has developed a coherent array of vertical lasers - a technology that was considered impossible until a few years ago

Israeli and German researchers have developed an array consisting of many small vertical lasers but acting as a single light source, all in the volume of a grain of sand. This breakthrough by Technion and Würzburg University researchers was recently published In a joint article in the prestigious journal Science.

Vixels (VCSELs) are tiny laser devices that play an essential role in a wide range of technological developments including cell phones, automotive sensors and fiber optic networks for data traffic. Their tiny dimensions, which are of course a huge advantage in these and other applications, place a limit on the light power emitted from them. In other words, they produce radiation that is very limited in intensity. For years, scientists have been trying to increase this power by connecting many tiny voxels and forcing them to act as a single coherent laser, but so far no significant success has been achieved. Hence the importance of the breakthrough published inScience: a coherent laser composed of many voxels. The key to this achievement lies in a unique geometric arrangement of the voxels on the photonic chip; This arrangement, which forces the light to move and flow in a specific path, is based on a platform of a topological photonic isolator.

From topological insulators to topological lasers

Topological insulators are revolutionary quantum materials characterized by the fact that on their surface they conduct electricity, moreover, they conduct it without energy loss, while inside they are insulators, that is, they do not conduct electricity at all. The research group of Research Prof. Mordechai (Moti) Segev from the Viterbi Faculties of Physics and Electrical and Computer Engineering at the Technion implemented these innovative ideas in the field of photonics already a few years ago when they introduced the first photonic topological insulator. In this system, the light moves around the edges of a two-dimensional array of waveguides, where this movement is not affected by the presence of defects or disorder. This research opened a new field of research known today as "topological photonics" and employs hundreds of research groups around the world. In 2018, Prof. Segev's research group developed A way to use the properties of photonic topological isolators to make many lasers lock together and act coherently as a single laser. But still, even in this system there was a power limit: the light emanating from the lasers was emitted within the plane of the photonic chip, which is also the same plane in which the light progressed between laser and laser. The in-plane emission of light limited the ability to efficiently extract the light from the laser array and created a bottleneck. This means that the device that puts the light out severely limits the output power, similar to a single electrical outlet used by an entire power station. The current breakthrough is based on a different method: the lasers are "locked" through the passage of photons between the lasers within the plane of the photonic chip, but the light is now emitted perpendicular to the chip, emanating from the surface, therefore allowing the total light beam to be easily collected.

This Israeli-German research project was launched during the Corona epidemic and therefore required a particularly great commitment from all the researchers involved. The research was conducted by PhD student Alex Dikopoltsev from Prof. Segev's research group, in collaboration with PhD student Eran Lustig and Dr. Kobi Lommer from the Technion, and by PhD student Tristan Harder from the research group of Prof. Sebastian Klambet and Prof. Sven Hofling from the University of Würzburg in Germany in collaboration with Researchers from Vienna and Oldenburg.

The long road to new topological lasers

"It's fascinating to see how science develops," he said Research Prof. Segev, holder of the Dr. Bob Shilman Chair and member of the Israel National Academy of Sciences. "From innovative principles in basic physics we moved to fundamental changes in topological physics and now we have created a real technology in which commercial companies are already showing interest. In 2015, when we started working on topologically isolated lasers, no one believed it was possible because the knowledge of topological physics at that time was limited to systems that do not contain man - and moreover - cannot contain man. But lasers are based on the man, so the idea of ​​topologically isolated lasers went against everything that was known at the time. We were like a bunch of "delusions" looking for something that was considered impossible. After a long road - we have now taken a big step towards a real technology that has many applications."

The research groups in Israel and Germany used the principles of topological photonics for an array of voxels that emit light vertically, perpendicular to the plane of the photonic chip, while the topological process responsible for the coherence that causes the voxels to act as a single laser occurs in the plane of the chip. The end result is a powerful but compact and very efficient laser that is not limited by the number of voxels and without being disturbed by defects or temperature changes.

"The topological principle of this laser can work in general on all wavelengths and therefore on a variety of materials," he explains Prof. Sebastian Klambet from the University of Würzburg. "The number of microlasers that can be connected in this way will always depend entirely on the application. We can expand the laser network to a very large network, and basically it will remain coherent even with a large number of lasers. It's great to see that topology, which is originally a branch of mathematics, has become a new and revolutionary toolbox for controlling, guiding and improving the properties of a laser."

The groundbreaking research demonstrated that it is theoretically and experimentally possible to combine vixels to obtain a highly efficient laser on a photonic chip. Therefore, the results of the research pave the way for the development of future technologies in many fields, including mobile phones, medical devices, communication and transportation.

The research was conducted at the Solid State Institute in collaboration with the Helen Diller Quantum Center and the Russell Berry Research Institute in Nanotechnology (RBNI) at the Technion.

to the article appearing in Science  click here

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