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 Astronomers find unexpected, dust-obscured star formation in distant galaxy
24.03.2017 | University of Massachusetts at Amherst

nachricht Gravitational wave kicks monster black hole out of galactic core
24.03.2017 | NASA/Goddard Space Flight Center

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: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Northern oceans pumped CO2 into the atmosphere

27.03.2017 | Earth Sciences

Fingerprint' technique spots frog populations at risk from pollution

27.03.2017 | Life Sciences

Big data approach to predict protein structure

27.03.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>