Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Tightly focused laser light generates nonlinear effects and rainbow of color

21.05.2004


Physicists at Lehigh University achieve supercontinuum generation in nonlinear fibers

Two physicists at Lehigh University have produced a rainbow of visible and invisible colors by focusing laser light in a specially designed optical fiber that confines light in a glass core whose diameter is 40 times smaller than that of a human hair.

Jean Toulouse, professor of physics, and Iavor Veltchev, research associate in Lehigh’s Center for Optical Technologies (COT), are among the few scientists in the world to achieve and study the phenomenon, which is called "supercontinuum generation in nonlinear fibers."



The phenomenon can be observed in a new class of optical fibers, called photonic crystal fibers. PCFs consist of a tiny solid glass core surrounded by a cladding, or casing, that contains air holes along the length of the fiber.

When Toulouse and Veltchev run a demonstration in their lab, incoming infrared (IR) light waves, which are invisible to the human eye, are converted to visible lightwaves. As the IR light propagates, or spreads, through a 1-meter-long fiber, the light appears, first orange, then yellow and finally green.

IR and UV light of varying wavelengths are also generated at both ends of the visible spectrum.

The visible lightwaves emerge from the fiber as white light, which contains all the colors of the spectrum. The colors are dispersed by the precisely spaced grooves of a diffraction grating, in the same way that water droplets create a rainbow.

Potential uses for supercontinuum generation in nonlinear fiber optics range from medical applications, including non-invasive imaging of live tissues, to all-optical networks, in which light waves, not electronics, perform switching, routing, amplifying and other functions.

Nonlinear optical effects are the main focus of the COT’s All-Optical Network research thrust, which Toulouse directs. Toulouse receives funding from the National Science Foundation.

Supercontinuum generation is not observed in conventional optical fibers, Toulouse says, because their optical intensity (the optical power per unit area) is too low. In the new fibers, the light is confined in a much smaller core and the optical intensity is much greater. This modifies the optical properties of the medium (the fiber), creating new, nonlinear optical effects.

Linear optical effects occur when the optical intensity of light is not great enough to alter the properties of the medium (especially the speed at which the light propagates) through which the light is passing.

Nonlinear effects occur when the light’s optical intensity alters the properties of the medium, which, in turn, affects the manner in which the light itself propagates. The increased intensity, says Veltchev, also causes a corresponding increase in the refraction, or bending, of the light wave by the medium.

Nonlinear effects cause different parts of a wave to move at different velocities and distort the light’s periodic sinusoidal pattern. These effects generate new wavelengths and result in what Toulouse calls an "avalanche effect" - as more wavelengths are generated, more distortion results, leading to yet more wavelengths.

"What we see in the nonlinear regime," says Toulouse, "is that if we send light in at one wavelength, we generate many other wavelengths" - thus achieving supercontinuum generation in nonlinear fiber optics.

The high optical intensity necessary for supercontinuum generation is achieved by the tight confinement of the incoming light wave in the extremely small core of the fiber, says Toulouse.

Toulouse and Veltchev begin their demonstration by using lenses to steer and focus the incident, or incoming, lightwaves with a wavelength (the distance between two adjacent crests of the wave) of approximately 800 nanometers (1 nm is one one-billionth of a meter). At 800 nm, the lightwaves fall within the infrared range and are not visible.

The incident lightwave, being powerful enough, creates nonlinear effects inside the glass fiber, generating new light waves with longer and shorter wavelengths (visible and multi-colored). This is caused by two factors. First, the light waves are confined to a solid glass core inside the optical fiber that measures only 2.5 microns in diameter. (A micron is one one-millionth of a meter; 2.5 microns is roughly one-fourtieth the thickness of a typical human hair.) By contrast, the core of a typical optical fiber, measures 10 microns in diameter. And a typical laser beam has a diameter of about 2 millimeters, almost 1,000 times greater than the diameter of the Lehigh researchers’ new optical fiber core.

The optical intensity (power transmitted per unit area) in the core of these new fibers, says Toulouse, is thus almost 1 million times greater than the intensity in the core of a typical laser, given that the area of a circle equals p times the radius squared.

The creation of nonlinear effects is also triggered by air holes in the cladding around the fiber core. The holes force the light to remain confined inside the narrow glass core, Toulouse says, because "light hates to be in air when it can be in a medium where it travels more slowly."

The tight confinement of light inside the new PCFs forces the waves to propagate coherently (with a well-defined initial-phase relationship), thus producing the full spectrum of visible colors.

The optical fiber used by Toulouse and Veltchev costs up to several thousand dollars per meter, and is manufactured by only five companies in the world, several of which have ties to the COT.

Toulouse has contacts with other researchers who have achieved supercontinuum generation in nonlinear fibers. In 2002, he spent six months studying the nonlinear effects of new types of optical fibers at the University of Bath in England, with the very people who invented PCFs in 1992.

Veltchev has a Ph.D. in physics from the Free University of Amsterdam (The Netherlands) and will soon join the Fox Chase Cancer Research Center near Philadelphia on a project utilizing laser radiation in cancer treatment.

Kurt Pfitzer | EurekAlert!
Further information:
http://www.lehigh.edu/

More articles from Physics and Astronomy:

nachricht Ultra-compact phase modulators based on graphene plasmons
27.06.2017 | ICFO-The Institute of Photonic Sciences

nachricht Smooth propagation of spin waves using gold
26.06.2017 | Toyohashi University of Technology

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: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Touch Displays WAY-AX and WAY-DX by WayCon

27.06.2017 | Power and Electrical Engineering

Drones that drive

27.06.2017 | Information Technology

Ultra-compact phase modulators based on graphene plasmons

27.06.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>