Posted in | Laser | Semiconductors

A Study on Topological Insulator Lasers

A team of researchers at the Technion and in the U.S. have created a new, very efficient and powerful semiconductor laser system: the topological insulator laser.

Dr. Miguel A. Bandres, Technion Distinguished Professor Mordechai Segev and Gal Harari (Image credit: Nitzan Zohar, Office of the Spokesperson, Technion)

The findings are reported through two new joint research papers, one describing theory and the other explaining the experiments, published online on February 2 by the renowned journal Science.

Topological insulators are one of the most advanced areas of physics in current times, providing new developments for the standard understanding of protected transport. These are unique materials that are insulators in their interior but that conduct a “super-current” on their surface. The current on their surface is not influenced by defects, disorder or sharp corners - it continues unidirectionally without being dispersed.

Some years ago, the same group from the Technion put forth these ideas in photonics and showcased a Photonic Topological Insulator, where light travels around the edges of a 2D array of waveguides without being impacted by disorder or defects.

Currently, the scientists have discovered a way to employ the properties of photonic topological insulators to construct a new type of laser, which exhibits a unique elementary behavior and significantly enhances the robustness and the performance of lasers arrays, opening the door for an enormous number of future applications.

This new laser system went against all common knowledge about topological insulators. In a nut shell, the unique robustness properties of topological insulators were believed to fail when the system contains gain, as all lasers must have. But we have shown that this special robustness survives in laser systems that have a special (“topological”) design, and is able to make the lasers much more efficient, more coherent, and at the same time immune to all kinds of fabrication imperfections, defects and the like. This seems to be an exciting avenue to make arrays of miniature lasers work together as one: a single highly coherent high power laser.

Professor Mordechai Segev

In their research, the team constructed a special array of micro ring resonators whose lasing mode displays topologically-protected transport – light propagates in one direction along the edges of the laser array, resistant to defects and disorder and unaltered by the shape of the edges. This in turn, as they experimentally showed, results in very efficient single-mode lasing that lasts high above the laser threshold. “It is a great pleasure to see fundamental research pans out to have such profound yet tangible applications” said Prof. Christodouldies from UCF.

The fabricated array used typical semiconductor materials, without the need for magnetic fields or unusual magneto-optic materials; hence it can be incorporated in semiconductor devices. “In recent years, we have found new tricks to manipulate light in an unprecedented way. Here, by using clever designs, we fooled photons to feel as if they are experiencing a magnetic field and they have spin,” said Prof. Khajavikhan, one of the team’s lead researchers.

The researchers showed that not only are topological insulator lasers theoretically possible and experimentally viable, but that combining these properties create very efficient lasers. As such, the study’s results pave the way towards a unique class of active topological photonic devices that may be combined with antennas, sensors and other photonic devices.

The studies were done by Technion Distinguished Professor Mordechai Segev and his team: Dr. Miguel A. Bandres and Gal Harari, in collaboration with Professors Demetrios N. Christodoulides and Mercedeh Khajavikhan and their students Steffen Wittek, Midya Parto and Jinhan Ren at CREOL, College of Optics and Photonics, University of Central Florida, along with scientists from the US and Singapore.

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