Capasso lab demonstrates highly unidirectional 'whispering gallery' microlasers

December 13, 2010

Cambridge, Mass., December 6, 2010 - Utilizing a century-old phenomenon discovered in St. Paul's Cathedral, London, applied scientists at Harvard University have demonstrated, for the first time, highly collimated unidirectional microlasers.

The result of a collaboration with researchers from Hamamatsu Photonics in Hamamatsu City, Japan, and the Institute of Theoretical Physics of the University of Magdeburg, Germany, the advance has a wide range of new applications in photonics such as sensing and communications.

Published online this week in the Proceedings of the National Academy of Sciences, the research team took advantage of a concept in physics referred to as "whispering gallery modes."

Over a century ago, British scientist Lord Rayleigh wondered how two people standing on opposite sides of the dome in St. Paul's Cathedral could hear each other by whispering into the circular wall. He discovered that the sound skirts along the smooth surface of the wall with negligible attenuation due to scattering or absorption.

The optical analog of whispers in a dome are light rays confined to the perimeter of tiny circular disks by multiple reflections from the boundary as they circle around. Because attenuation is minimal within the smooth disk, these resonators have already been used to make some of the world's lowest-threshold lasers. Circular disks, however, have posed certain challenges.

"One of the crucial unsolved problems of these microlasers for practical applications has been that their emission is non-directional and their optical power output is negligible," said team leader Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at Harvard's School of Engineering and Applied Sciences (SEAS).

"Light gets trapped by these whispering gallery modes with little chance to escape except by a faint isotropic emission. Strategies to suitably deform the disks to solve this problem have yielded disappointing results," Capasso added.

By shaping the microlaser as an ellipse with a wavelength-size notch carved out from its edge, Capasso's team found that the cycling whispering gallery modes scatter efficiently off the notch and emerge as nearly parallel beams from the microlaser.

The prototypes are quantum cascade lasers emitting an optical power of 5 milliwatts at a wavelength of 10 microns. The microlaser performance is insensitive to the details of the notch, making this device design very robust.

"Our calculations show that the notched elliptical microlaser should have even better performance at the shorter wavelengths near 1 micron, typical of laser diodes used in optical communications, where the attenuation of whispering gallery modes is negligible," said coauthor Jan Wiersig of the Institute of Theoretical Physics of the University of Magdeburg.

"The successful realization of these simple-structured and robust microlasers through standard wafer-based fabrication makes small-volume directional light sources possible for many important applications such as photonic integrated circuits with high-density chip-scale integration, optical communications, medical/biological sensors, and lab-on-a-chip," said coauthor Masamichi Yamanishi, Research Fellow of Central Research Laboratories at Hamamatsu.
The team's other authors are postdoc Nanfang Yu, research associates Laurent Diehl and Christian Pflügl, all at SEAS; Qi Jie Wang and Changling Yan, formerly postdocs at SEAS and now with the Technological University in Singapore, and the Changchun University of Science and Technology in Changchun, China, respectively; graduate student Julia Unterhinninghofen of the Institute of Theoretical Physics at the University of Magdeburg; and researchers Tadataka Edamura and Hirofumi Kan of Hamamatsu Photonics.

The research was partially supported by the Air Force Office of Scientific Research. The Harvard authors also acknowledge the support of two Harvard-based centers, the National Science Foundation Nanoscale Science and Engineering Center (NSEC) and the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Infrastructure Network (NNIN).

Harvard University

Related Photonics Articles from Brightsurf:

Tiny device enables new record in super-fast quantum light detection
Researchers from the University of Bristol's Quantum Engineering Technology Labs (QET Labs) and Université Côte d'Azur have made a new miniaturized light detector to measure quantum features of light in more detail than ever before.

Researching the chips of the future
The chips of the future will include photonics and electronics; they will have a bandwidth, speed and processing and computing abilities that are currently unthinkable.

Intelligent nanomaterials for photonics
2D materials - combined with optical fibres - can enable novel applications in the areas of sensors, non-linear optics, and quantum technologies.

Parylene photonics enable future optical biointerfaces
Carnegie Mellon University's Maysam Chamanzar and his team have invented an optical platform that will likely become the new standard in optical biointerfaces.

Photonics researchers report breakthrough in miniaturizing light-based chips
Electrical engineers at the University of Rochester have created the smallest electro-optical modulator yet, using a thin film of lithium niobate bonded on a silicon dioxide layer.

Recent advances in 2D, 3D and higher-order topological photonics
A research team from South Korea and the USA has provided a comprehensive review covering the recent progress in topological photonics, a recently emerging branch of photonics.

Topological photonics in fractal lattices
Photonic topological insulators are currently a subject of great interest because of the features: insulating bulk and topological edge states.

Novel "dual-resonant method" in 2D materials can spur advances in the field of photonics
Scientists at Daegu Gyeongbuk Institute of Science and Technology, Korea, have developed a new process that provides an ultrafast process of photon generation in two-dimensional materials.

A different slant of light
Giant clams manipulate light to assist their symbiotic partner.

Photonics: From custom-built to ready-made
An international collaboration team of University California, Santa Barbara (UCSB), California Institute of Technology (Caltech) and EPFL has developed an integrated technology that may revolutionize photonic systems.

Read More: Photonics News and Photonics Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to