Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Quantum physics discovery may bring about changes in optical communications, scientists report

28.10.2005


Results from experiments conducted at the University of California, Santa Barbara may lead to profound changes in optical communications. The discovery is reported in the October 28th edition of the journal Science.

Physicist Mark Sherwin at UCSB explained that as information technology advances, scientists are intent on transmitting information much more quickly. "We are working toward sending information 100 times faster than it can be sent now," he said. His research group has spent five years on this project. The experiments were performed using the university’s room-sized, free-electron laser. The research was funded by the National Science Foundation.

"We took an existing semiconductor device that is essentially an electrically controlled shutter and we have tried to open and close the shutter at the rate of three trillion times a second," he explained. "We found that in addition to opening and closing the shutter we are making the shutter itself vibrate."



Those vibrations of the shutter may enable the shutter to be opened and closed with weak light beams rather than strong voltages, said Sherwin. In optical communications there are different channels of communications, so these light beams could correspond to different channels. "It would be a way of changing channels really fast," he added. "Right now it is a very slow process to change channels in optical communications."

Sherwin explained that electronics are much slower than optics and that one optical fiber could transmit information more than 1,000 times as fast as the information could be put on it by an electronic device like a computer.

"What we have here at UCSB is a special source of radiation, the free-electron laser, that can generate electromagnetic oscillations at the rate of a few trillion per second," said Sherwin. "We found that when you drive the modulator, or shutter, that fast it acts in a peculiar way. Rather than absorbing light near a single frequency, it can absorb light near a second frequency as well. This opens the possibility of a new type of cross modulation, where a beam of light at one of the absorption frequencies can turn on or off the light of the other."

Sherwin said that light has been used to send information rapidly over long distances for more than 3000 years. The ancient Greeks, for example, used large fires to flash signals from mountain top to mountain top, as described by Homer in the Iliad. In order to send information, light must be modulated--that is, one must be able to turn the light beam on and off. In World War II, ships communicated with one another in code using searchlights that sailors modulated manually with shutters. Modern modulators for light are controlled by electrical voltages, explained Sherwin.

The Science article, "Quantum Coherence in an Optical Modulator," was co-authored by S. G. Carter, who worked on the experiments at UCSB and then moved to the University of Colorado; V. Birkedal, from UCSB; C. S. Wang, from UCSB; L. A. Coldren, from UCSB; A. V. Maslov, from the Center for Nanotechnology at the NASA Ames Research Center; and, D. S. Citrin from the Georgia Institute of Technology and Georgia Tech Lorraine in Metz, France.

More about the science article:

"In an electro-absorption modulator, light near a particular frequency, the carrier frequency, can be blocked or transmitted by tuning a material oscillation in or out of resonance with the carrier frequency," said Sherwin. "A common electro-absorption modulator is made of a semiconductor quantum well, a thin layer of a semiconductor with a relatively small "band gap" (or a relatively large affinity for negatively charged electrons and positively charged holes) sandwiched between two layers with a larger band gap."

Sherwin explained that when light of the correct frequency is incident on a quantum well, it creates bound electron-hole pairs called excitons and is absorbed. An electric field applied perpendicular to the plane of the quantum well shifts the frequency of the excitonic absorption so that light resonant with the zero-field excitonic resonance is no longer absorbed. Quantum well electro-absorption modulators are currently used to modulate light at rates exceeding 10 billion bits per second.

In this article, the scientists report that a quantum well electro-absorption modulator has been strongly driven at frequencies exceeding one Terahertz (1 trillion cycles). This is more than 100 times faster than quantum well modulators are usually operated. At these extremely high frequencies, internal quantum-mechanical oscillations of the excitons themselves were excited. When the strong Terahertz drive was resonant with the excitonic oscillations, the absorption spectrum of weak light near the excitonic absorption of the quantum well was transformed from a single peak to a double peak, or doublet. This doublet is a signature that light with frequency near the excitonic absorption can no longer simply create an exciton in its lowest-energy state, but must create a quantum mechanical superposition of an exciton in its ground and excited states.

A potential application for optical communication is that two arbitrarily weak light beams separated by the frequency of the Terahertz drive could modulate one another. "Usually, such cross-modulation occurs only when light beams have power exceeding a certain threshold," said Sherwin.

On a separate note, Sherwin said, "In atomic gases, the doublet observed here has been the first step toward creating a system that could greatly slow or even stop the propagation of light. The ability to slow or stop light in a semiconductor would also enhance the toolbox for optical communications and computation. However, in order to achieve slowing or stopping of light, the mechanisms for energy dissipation in the quantum well modulator would have to be significantly reduced."

Gail Gallessich | EurekAlert!
Further information:
http://www.ia.ucsb.edu

More articles from Physics and Astronomy:

nachricht Witnessing turbulent motion in the atmosphere of a distant star
23.08.2017 | Max-Planck-Institut für Radioastronomie

nachricht Heating quantum matter: A novel view on topology
22.08.2017 | Université libre de Bruxelles

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

What the world's tiniest 'monster truck' reveals

23.08.2017 | Life Sciences

Treating arthritis with algae

23.08.2017 | Life Sciences

Witnessing turbulent motion in the atmosphere of a distant star

23.08.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>