. 24/7 Space News .
TECH SPACE
A new trick for controlling emission direction in microlasers
by Staff Writers
St. Louis MO (SPX) Jun 22, 2016


An artist's view showing the control of the emission direction of lasing at exceptional points in a whispering gallery mode microlaser. The tori and the spheres represent the microtoroid resonators and the scatterers, respectively. With two scatterers with appropriate sizes and locations in the field of the resonator, light is emitted in only one direction. The lasing is bidirectional when there is one or no scatterer. Image courtesy B. Peng, F. Monifi, S. K. Ozdemir and L. Yang.

Researchers at Washington University in St. Louis have found a way to give photons, or light packets, their marching orders. The researchers have capitalized on the largesse of an energy state in an optical field to make photons in their lasing system travel in a consistent mode, either clockwise or counterclockwise.

Consistency in light propagation is important to get a reliably strong photonic signal and light pulse for all lasing systems and applications. Lasing alone is a multibillion-dollar industry with thousands of applications from communication to medicine to hair removal. Yet this consistency also behooves present and future optical sensing devices, be they aerosol detectors or cancer spotters.

Lan Yang, the Edwin H. and Florence G. Skinner Professor of Electrical and Systems Engineering, and Sahin K. Ozdemir, research associate professor, both in the School of Engineering and Applied Science, along with collaborators Stefan Rotter at Vienna University of Technology in Austria and Jan Wiersig at Otto-von-Guericke University in Germany, have exploited the benefits of a physical phenomenon called an exceptional point to force photons to go either clockwise or counterclockwise instead of both directions randomly.

Findings were published June 6 in an early edition of the Proceedings of the National Academy of Sciences.

An exceptional point arises in physical fields when two complex eigenvalues and their eigenvectors coalesce, or become the same. These are mathematical tools that describe a physical system. Think of the exceptional point as a complex bewitching environment where often unpredictable and counterintuitive phenomena occur.

For instance, in a 2014 paper in Science, Yang and Ozdemir described harnessing the exceptional point to add loss to a laser system to actually gain energy - to gain by losing, if you will. The exceptional point has contributed to a number of counterintuitive activities and results in recent physics studies with more certain to come.

Yang and Ozdemir induced the existence of an exceptional point in an optical field through insertion of two silica scatterers, or nanotips, which help to create the perfect storm that conjures up an exceptional point. Using nanopositioning systems, Bo Peng, then a doctoral student and one of the lead authors of the 2014 Science paper, tuned the distance between the scatterers and increased their relative size in the optical field to perturb the microresonator and beckon an exceptional point. Thus, they have a controllable system.

"One of the exciting things of this research is it presents an on-demand control of the laser," Yang said. "By changing the scatterer location, you can change the operating regime. This opens the possibilities for new functional devices based on lasers."

"This finding further enhances our capability to harness microlasers, not only by power boost with loss, as we achieved previously, but also by precisely controlling the lasing direction now," Peng said.

The microresonator they use is in a class called whispering gallery mode resonators (WGMRs) because they work similarly to the renowned whispering gallery in London's St. Paul's Cathedral, where a person on one side of the dome can hear a message spoken to the wall by a person on the other side. The WGMR device does a similar thing with light frequencies rather than sound.

Light is injected into and coupled out from the WGMR through tapered fiber waveguides on either side. Nanopositioners control the scatterers, which probe the chirality of the WGM. In the absence of the scatterers, when light is injected into the WGMR in the clockwise or counterclockwise directions: A resonance peak appears in the transmission and no signal can be obtained in the reflection.

"When the system is brought to an exceptional point by the help of the scatterers, this situation changes" Ozdemir said. "The reflection shows a pronounced resonance peak for only one of the injection directions. This asymmetric reflection is a distinguishing characteristic of chirality, an intrinsic property of a mode."

There can be multiple exceptional points in a physical system.

"Bringing the system to a different exceptional point results in the appearance of a reflection peak only for the other injection direction," Ozdemir said.

Added Yang: "Thus, we can control the chirality of a mode by going from one exceptional point of the system to another."

The team then established the link between asymmetric reflection at exceptional points and the intrinsic chirality of lasing modes. For this purpose, they used an erbium-doped WGM microresonator. Erbium serves as a kind of doping agent that encourages laser activity at a wavelength different than the light that is used to excite lasing.

In the absence of an exceptional point, the emitted light from the erbium into the WGM resonator can go clockwise and counterclockwise simultaneously. This makes extraction of the laser light from WGM microlasers inefficient. At an exceptional point, the photons will move in a consistent way either in the clockwise or counterclockwise.

"We now have a control on the chirality of the whispering-gallery modes and hence the emission direction of lasing thanks to the exceptional points," Yang said. "Where we place the scatterers and how big we make them changes the operating regime, adding to the technique's versatility."

"We can tune the whispering-gallery-modes to have a bidirectional (both clockwise and counterclockwise directions) microlaser or a unidirectional laser with emission in the clockwise or counterclockwise direction. We can completely reverse the emission direction by transiting from one exceptional point of the system to another exceptional point," Ozdemir said.

The results provide WGMR systems new functions that will be useful for lasing, sensing, optomechanics and quantum electrodynamics.

"The findings of the team prove yet again that if engineered properly, exceptional points, and thus engineering of loss and scattering, provide new tricks for optical sciences to solve problems, which have hindered progress and limited the usefulness of devices," Yang said.

"This finding further enhances our capability to harness microlasers, not only by power boost with loss, as we achieved previously, but also by precise control of the lasing direction now," Peng said.

The researchers say their findings will help develop novel technologies for controlling light flow, pave the way to chiral photonics on chip and could affect scientific fields beyond optics. They have already set to show and use other counterintuitive features of non-Hermitian photonics at the exceptional points.

Research paper: Peng B, Ozdemir S, Liertzer M, Chen W, Kramer J, Yilmaz H, Wiersig J, Rotter S, Yang L. Chiral modes and directional lasing at exceptional points. PNAS, published online ahead of print June 6, 2016, DOI:10.1073/pnas.1603318113.


Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only


.


Related Links
Washington University in St. Louis
Space Technology News - Applications and Research






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Previous Report
TECH SPACE
First Light For ESO's VLT Four Laser Guide Star Facility
Munich, Germany (SPX) May 03, 2016
On 26 April 2016 ESO's Paranal Observatory in Chile hosted an event to mark the first light for the four powerful lasers that form a crucial part of the adaptive optics systems on ESO's Very Large Telescope. Attendees were treated to a spectacular display of cutting-edge laser technology against the majestic skies of Paranal. These are the most powerful laser guide stars ever used for astronomy ... read more


TECH SPACE
US may approve private venture moon mission: report

Fifty Years of Moon Dust

Airbus Defence and Space to guide lunar lander to the Moon

A new, water-logged history of the Moon

TECH SPACE
A little help from friends

CaSSIS Sends First Image of Mars

Rover Opportunity Wrapping up Study of Martian Valley

Delayed ExoMars mission gets 77-mln-euro boost

TECH SPACE
TED Talks aim for wider global reach

Disney brings its brand to Shanghai with new theme park

Tech, beauty intersect in Silicon Valley

Second Starliner Begins Assembly in Florida Factory

TECH SPACE
China to send Chang'e-4 to south pole of moon's far-side

Experts Fear Chinese Space Station Could Crash Into Earth

Bolivia to pay back loan to China for Tupac Katari satellite

China plans 5 new space science satellites

TECH SPACE
Three astronauts touch down after 6 months in space

Cygnus spacecraft begins next phase of OA-6 mission

Cygnus space capsule departs International Space Station

Russian, US Astronauts to Return From ISS on June 18

TECH SPACE
McCain Stands Down: Congress Reaches Compromise on Russian Rockets

Launch Vehicle Ascent Trajectories and Sequencing

MUOS-5 satellite encapsulated for launch

Airbus Safran Launchers confirms the maturity of the Ariane 6 launcher

TECH SPACE
Largest crowdsource astronomy network helps confirm discovery of 'Tatooine' planet

Largest, Widest Orbit "Tatooine" Bolsters Planet Formation Theories

Clouds, haze cause astronomers to overestimate size of exoplanets

New planet is largest discovered that orbits 2 suns

TECH SPACE
Oregon chemists build a new, stable open-shell molecule

Marrying superconductors, lasers, and Bose-Einstein condensates

Researchers open hairy new chapter in 3-D printing

Underlying connection found between diverse materials with extreme magnetoresistance









The content herein, unless otherwise known to be public domain, are Copyright 1995-2024 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us.